Iron drawing. Four simple designs of metal fences and their installation. How to make a metal oven with your own hands: step by step

Any fence, after a while, becomes unusable or needs current, or maybe major repairs. But, as practice shows, a fence correctly installed from high-quality material will serve its owners much longer than those on which the owner decided to save.

For example, the service life of some metal fences can reach 60 years, however, with proper care. Here we will talk about simple, but durable structures.

Fencing base

Not a single fence can do without supporting elements, and the more stable they are installed, the more reliable the structure will be. Even a front garden fence will look more respectable if it is equipped with support posts, and the service life of such a fence is much longer.

Metal fences are often installed on supports made of the same material. Massive, monumental fences for a private house are installed on strip or column foundations, and less heavy structures for a summer house or a front garden around the house can be built without a fundamental foundation.

Pillars are fixed in several ways:

1. For driven supports, shallow holes are dug or drilled. Their diameter should be slightly larger than the diameter of the supports themselves. Then the supports are inserted into the holes and clogged. This procedure is best done together, so that one person holds the support in a strict vertical position. After filling the void, the pits are filled with rubble or covered with earth and carefully compacted.
2. Combined installation is carried out by drilling holes with a diameter twice the diameter of the pillars to half the depth of immersion. The support is inserted into the hole, hammered to the desired depth, secured with spacers. Hole voids are filled with concrete in several steps, each of which is accompanied by a rammer.
3. Zabutovka differs in that the bottom of the hole for the support is filled with construction debris (small stones or broken bricks), rubble. After installing the pillar, the hole is filled to the top with rubble, carefully compacted, and poured with concrete mixture from above.
4. Full concreting is carried out by digging holes for the pillars to the desired depth, installing and reinforcing the supports, and pouring the concrete mixture. To make the support more stable, the bottom of the pit is slightly expanded to the bottom, covered with sand or gravel by 10 cm, the support is installed, reinforced and poured with concrete.

The depth of the holes for the supporting elements depends on many factors, such as the complexity of the soil, the occurrence of groundwater, the unevenness of the terrain, and the severity of the fence spans, but from 80 cm to 1.5 m is considered optimal.

Simple metal fences of light weight do not require volumetric supports; for them, it is enough to purchase pipes with a diameter of 80 * 80 mm. It is better to purchase metal pipes manufactured in accordance with the requirements of GOST, so you can extend their service life. These products are made of high quality metal and treated with anti-corrosion agents.

The height of the pipe is calculated depending on the height of the fence plus the recessed part. Most often, pipes with a length of 3 - 3.5 m are used.

Cheap and high quality

Such a building material as chain-link mesh is one of the simplest for fencing areas of any shape, length and height. It has found its application for fencing summer cottages and a plot of a private house, in the form of a fence for a front garden and for fencing industrial areas. It is one of those metal materials that is easy to deform, in a good way.

For example, for a figured front garden, you will not find a material that is easier to install. Well, if it is necessary to protect the site of the house or cottage, then a properly installed high-quality chain-link mesh will last for more than a dozen years. And the most attractive thing is that you don’t need special skills to install metal mesh fences. It is enough to prepare drawings and calculate the amount of material.

And if we already talk about the service life, then the design created by the sectional method will be more reliable. To do this, you will need to make separately the required number of sections, and then mount them on pre-installed poles.

If there is a desire to get a more aesthetic view of the fence for a private house or cottage, then you can purchase ready-made sections with poles, manufactured in accordance with GOST. Industrial products are mainly covered with protective agents, which can significantly increase their service life.

Simple welded construction

More expensive designs include metal fences made of welded mesh. Due to the fact that in the manufacture of sections of such structures in production, the material is galvanized and coated with a polymer composition. For manufacturing, a high-quality metal bar is used that complies with GOST, which ensures a long service life for the fences.

For the installation of such structures, welding equipment is not required; you can get by with a screwdriver and self-tapping screws.

A metal fence in the form of a welded mesh is installed in several stages:

• the site is marked around the house or in front of the cottage;
• marking posts are installed along the edges;
• the rope is pulled at the intended height of the fence;
• 2.5 m is measured from the outermost pillar, and this is repeated the required number of times;
• in the marked places, supporting elements are installed by any of the above methods;
• if finished products manufactured in accordance with GOST are used to fence a summer house or house, then a diagram is attached to the design, with the sequence of mounting sections;
• everything else is assembled as a designer, adhering to the drawing.

The manufacturer provides connecting brackets with holes. They are fixed with a screwdriver on the supports, and sections of welded mesh are already attached to them. You can learn more about the installation of a simple design from the video.

Popular corrugated board

No less easy to install is a metal fence made of corrugated board. Its installation principle is practically the same as the two previous designs. To facilitate installation, the distance between the supporting elements must be made to the width of the profiled sheet.

If it is supposed to leave the posts open, then the distance from the end of the post is calculated, and if the supports need to be closed with a sheet, then the distance should be measured from the middle of the support.

For fences in the country or for the front garden, cheaper profiled sheet models are more often used, for example, only galvanized sheet. If it is necessary to protect the site of a private house, then it is better to use better products that meet the requirements of GOST. Such metal material has a longer service life and does not require annual maintenance.

In order not to be mistaken in the calculations of the material, and to purchase exactly as much as required, it is necessary to prepare drawings in advance, which will indicate all the dimensions of the fence elements.

Fence for a garden plot

Not every owner is ready to pay a tidy sum for metal fences in the garden plot, made by the manufacturer in accordance with GOST. In order to save money, many are trying to build protective structures from cheaper material.

If you have a welding machine at hand, then a simple fence made of fittings or a profile pipe will perfectly fit into the design of a garden plot, a private house or a summer house, it is important to prepare drawings. And its unattractive appearance can be decorated with climbing plants or painted. Many craftsmen even enclose the front garden with such a simple design.

We will assume that the pillars have already been installed, it remains only to fill the spans. To do this, you need to decide on the width of the spans and the height of the fence. It is better, of course, to draw up a diagram in order to correctly calculate the material.

The transverse logs are immediately welded to the posts. The bottom crossbar should be 20 cm from the ground, and the top one should be the same distance from the top of the support. Further, the places of welding of vertical elements are marked, according to the design drawing.

Such fences from a metal rod for a summer residence or from fittings for a front garden are installed in place. Pipe cutting is carried out in stages, for each span separately. This method allows the welding equipment heated during the welding of the parts of the first span to cool down. While the material is cut for the next filling, the device has time to cool down, and the work is carried out almost continuously.

For the front garden, as a rule, used material is used. It is not necessary to purchase rods or fittings of an expensive series manufactured in accordance with GOST and make drawings. Even a rusty rod can be thoroughly cleaned and used to fence small areas. And the shape and configuration of the fence depends on the imagination of the manufacturer.

Manufacture and installation of high-quality turnkey fences with and without PICS
Professional approach to the construction of combined concrete-metal fences

A metal detector or a metal detector is designed to detect objects that differ in their electrical and / or magnetic properties from the environment in which they are located. Simply put, it allows you to find metal in the ground. But not only metal, and not only in the ground. Metal detectors are used by inspection services, criminologists, the military, geologists, builders to search for profiles under the skin, fittings, reconciliation of underground utility plans, and people of many other specialties.

Do-it-yourself metal detectors are most often made by amateurs: treasure hunters, local historians, members of military historical associations. They, beginners, are primarily intended for this article; the devices described in it make it possible to find a coin with a Soviet penny at a depth of up to 20-30 cm or a piece of iron with a sewer manhole about 1-1.5 m below the surface. However, this home-made device can also be useful on the farm during repairs or at a construction site. Finally, having found a centner or two of an abandoned pipe or metal structures in the ground and handing over the find for scrap, you can get a decent amount. And there are definitely more such treasures in the Russian land than pirate chests with doubloons or boyar-robber egg-pods with efimki.

Note: if you are not well versed in electrical engineering with radio electronics, do not be afraid of diagrams, formulas and special terminology in the text. The very essence is stated simply, and at the end there will be a description of the device, which can be made in 5 minutes on the table, not knowing how to not only solder, but twist the wires. But it will allow you to "feel" the features of the search for metals, and if interest arises, knowledge and skills will come.

A little more attention compared to the rest will be given to the Pirate metal detector, see fig. This device is quite simple for beginners to repeat, but in terms of its quality indicators it is not inferior to many branded models priced up to $300-400. And most importantly, it showed excellent repeatability, i.e. full performance when manufactured according to descriptions and specifications. Circuitry and the principle of operation of the "Pirate" are quite modern; There are plenty of guides on how to set it up and how to use it.

Operating principle

The metal detector operates on the principle of electromagnetic induction. In general, the metal detector circuit consists of an electromagnetic oscillation transmitter, a transmitting coil, a receiving coil, a receiver, a useful signal extraction circuit (discriminator) and an indication device. Separate functional units are often combined in circuitry and design, for example, the receiver and transmitter can work on one coil, the receiving part immediately highlights the useful signal, etc.

The coil creates an electromagnetic field (EMF) of a certain structure in the medium. If an electrically conductive object is in the area of ​​\u200b\u200bits action, pos. And in the figure, eddy currents or Foucault currents are induced in it, which create its own EMF. As a result, the structure of the coil field is distorted, pos. B. If the object is not electrically conductive, but has ferromagnetic properties, then it distorts the original field due to shielding. In both cases, the receiver captures the difference between the EMF and the original one and converts it into an acoustic and/or optical signal.

Note: in principle, for a metal detector it is not necessary that the object be electrically conductive, the ground is not. The main thing is that their electrical and / or magnetic properties are different.

Detector or scanner?

In commercial sources, expensive highly sensitive metal detectors, e.g. Terra-N are often called geoscanners. This is not true. Geoscanners operate on the principle of measuring the electrical conductivity of the soil in different directions at different depths, this procedure is called lateral logging. According to the logging data, the computer builds on the display a picture of everything in the earth, including geological layers of various properties.

Varieties

Common parameters

The principle of operation of a metal detector can be implemented in technically different ways, according to the purpose of the device. Metal detectors for beach gold digging and construction and repair searches may look similar in appearance, but differ significantly in design and technical data. To properly make a metal detector, you need to clearly understand what requirements it must meet for this type of work. Based on this, the following parameters of search metal detectors can be distinguished:

1. Penetration, or penetrating power - the maximum depth to which the EMF of the coil extends in the ground. Deeper, the device will not detect anything at any size and properties of the object.
2. The size and dimensions of the search area is an imaginary area in the ground in which the object will be found.
3. Sensitivity is the ability to detect more or less small objects.
4. Selectivity is the ability to respond more strongly to desirable findings. The sweet dream of beach miners is a detector that only beeps for precious metals.
5. Noise immunity - the ability not to respond to EMF of extraneous sources: radio stations, lightning discharges, power lines, electric vehicles and other sources of interference.
6. Mobility and efficiency are determined by power consumption (how many batteries are enough), the device's weight and dimensions, and the size of the search area (how much you can "probe" in 1 pass).
7. Discrimination, or resolution - gives the operator or control microcontroller the ability to judge the nature of the object found by the reaction of the device.

Discrimination, in turn, is a composite parameter, since there are 1, maximum 2 signals at the output of the metal detector, and there are more values ​​that determine the properties and location of the find. However, taking into account the change in the reaction of the device while approaching the object, 3 components are distinguished in it:

• Spatial - indicates the location of the object in the search area and the depth of its occurrence.
• Geometric - makes it possible to judge the shape and size of an object.
• Qualitative - allows you to make assumptions about the properties of the material of the object.

Operating frequency

All parameters of the metal detector are connected in a complex way and many relationships are mutually exclusive. For example, lowering the oscillator frequency makes it possible to achieve greater penetration and search area, but at the cost of increased power consumption, and worsens sensitivity and mobility due to an increase in coil size. In general, each parameter and their complexes are somehow tied to the frequency of the generator. So The initial classification of metal detectors is based on the operating frequency range:

1. Super-low-frequency (VLF) - up to the first hundreds of Hz. Absolutely non-amateur devices: power consumption from tens of watts, without computer processing, it is impossible to judge anything from a signal, vehicles are needed to move.
2. Low-frequency (LF) - from hundreds of Hz to several kHz. Simple circuitry and design, noise-resistant, but not very sensitive, poor discrimination. Penetration - up to 4-5 m with power consumption from 10 W (the so-called deep metal detectors) or up to 1-1.5 m when powered by batteries. They react most sharply to ferromagnetic materials (ferrous metal) or large masses of diamagnetic materials (concrete and stone building structures), therefore they are sometimes called magnetic detectors. They are not very sensitive to the properties of the soil.
3. Increased frequency (IF) - up to several tens of kHz. More difficult than bass, but the requirements for the coil are low. Penetration - up to 1-1.5 m, C grade noise immunity, good sensitivity, satisfactory discrimination. Can be universal when used in pulsed mode, see below. On flooded or mineralized soils (with fragments or particles of rock that shield EMF), they work poorly or do not smell anything at all.
4. High, or radio frequency (HF or RF) - typical metal detectors "for gold": excellent discrimination to a depth of 50-80 cm in dry non-conductive and non-magnetic soils (beach sand, etc.) Power consumption - as before. n. The rest is on the verge of "failure". The efficiency of the device largely depends on the design and quality of the coil(s).

Note: mobility of metal detectors according to paragraphs. 2-4 is good: from one set of salt cells ("batteries") AA and without overworking the operator, you can work up to 12 hours.

Pulse metal detectors stand apart. Their primary current flows into the coil in pulses. By setting the pulse repetition rate within the LF, and their duration, which determines the spectral composition of the signal corresponding to the IF-HF ranges, you can get a metal detector that combines the positive properties of LF, IF and HF or is tunable.

Search Method

There are at least 10 EMF search methods. But such as, say, the method of direct digitization of the response signal with computer processing is the lot of professional use.

A home-made metal detector is schematically built most of all in the following ways:

• Parametric.
• Receiving-transmitting.
• With phase accumulation.
• On the beat.

Without receiver

Parametric metal detectors in some way fall outside the definition of the principle of operation: they have neither a receiver nor a receiving coil. For detection, the direct influence of the object on the parameters of the generator coil is used - inductance and quality factor, and the structure of the EMF does not matter. Changing the parameters of the coil leads to a change in the frequency and amplitude of the generated oscillations, which is fixed in various ways: by measuring the frequency and amplitude, by changing the current consumption of the generator, by measuring the voltage in the PLL loop (phase locked loop, "pulling" it to a given value), etc.

Parametric metal detectors are simple, cheap and noise-resistant, but their use requires certain skills, because. the frequency "floats" under the influence of external conditions. Their sensitivity is weak; most of all are used as magnetic detectors.

With receiver and transmitter

The device of the transceiver metal detector is shown in fig. at the beginning, to an explanation of the principle of operation; the principle of operation is also described there. Such devices allow to achieve the best efficiency in their frequency range, but are complex in circuitry, require a particularly high-quality coil system. Transceiver metal detectors with a single coil are called induction. Their repeatability is better, because the problem of the correct arrangement of the coils relative to each other disappears, but the circuitry is more complicated - you need to highlight a weak secondary signal against the background of a strong primary.

Note: in pulsed transceiver metal detectors, the emission problem can also be eliminated. This is explained by the fact that as a secondary signal they “catch” the so-called. "tail" of the pulse re-radiated by the object. The primary pulse due to dispersion during reemission spreads, and part of the secondary pulse is in the gap between the primary ones, from where it can be easily distinguished.

Click to Click

Metal detectors with phase accumulation, or phase-sensitive, are either single-coil pulsed, or with 2 generators, each working on its own coil. In the first case, the fact is used that during re-emission pulses not only spread out, but are also delayed. In time, the phase shift increases; when it reaches a certain value, the discriminator is triggered and a click is heard in the headphones. As you get closer to the object, the clicks become more frequent and merge into a higher pitched sound. It is on this principle that Pirate is built.

In the second case, the search technique is the same, but 2 strictly symmetrical electrically and geometrically generators work, each on its own coil. At the same time, due to the interaction of their EMF, mutual synchronization occurs: the generators work in time. When the overall EMF is distorted, synchronization breaks begin, audible as the same clicks, and then a tone. Two-coil metal detectors with a synchronization breakdown are simpler than impulse ones, but less sensitive: their penetration is 1.5-2 times less. Discrimination in both cases is close to excellent.

Phase-sensitive metal detectors are the favorite tools of resort miners. Aces of the search adjust their devices so that exactly above the object the sound disappears again: the frequency of the clicks goes into the ultrasonic region. In this way, on a shell beach, it is possible to find gold earrings the size of a fingernail at a depth of up to 40 cm. However, on soil with small inhomogeneities, watered and mineralized, metal detectors with phase accumulation are inferior to others, except for parametric ones.

By squeak

Beats of 2 electrical signals - a signal with a frequency equal to the sum or difference of the main frequencies of the original signals or multiples of them - harmonics. So, for example, if signals with frequencies of 1 MHz and 1,000,500 Hz or 1.0005 MHz are applied to the inputs of a special device - a mixer, and headphones or a speaker are connected to the mixer output, then we will hear a pure tone of 500 Hz. And if the 2nd signal is 200 100 Hz or 200.1 kHz, the same thing will happen, because 200 100 x 5 = 1,000,500; we "caught" the 5th harmonic.

There are 2 generators in the beat detector: reference and working. The reference oscillatory circuit coil is small, protected from extraneous influences, or its frequency is stabilized by a quartz resonator (simply, quartz). The contour coil of the working (search) generator is a search coil, and its frequency depends on the presence of objects in the search area. Before searching, the working generator is tuned to zero beats, i.e. until the frequencies match. As a rule, they don’t achieve a complete zero sound, but tune it to a very low tone or wheezing, so it’s more convenient to search. By changing the tone of the beats, the presence, size, properties and location of the object are judged.

Note: most often, the frequency of the search generator is taken several times lower than the reference one and works on harmonics. This allows, firstly, to avoid the mutual influence of generators, which is harmful in this case; secondly, to tune the device more precisely, and thirdly, to search at the optimal frequency in this case.

In general, metal detectors based on harmonics are more complicated than impulse ones, but they work on any ground. Properly made and tuned, they are not inferior to impulse ones. This can be judged at least by the fact that beach gold diggers do not agree in any way on what is better: impulse or beat?

Coil and more

The most common misconception of novice radio amateurs is the absolutization of circuitry. Like, if the scheme is "cool", then everything will be tip-top. With regard to metal detectors, this is doubly untrue, because. their operational advantages strongly depend on the design and workmanship of the search coil. As a resort prospector put it: "The findability of a detector should pull the pocket, not the legs."

When developing a device, its circuit and coil parameters are adjusted to each other until an optimum is obtained. A certain scheme with a “foreign” coil, if it works, will not reach the declared parameters. Therefore, when choosing a prototype for repetition, see first of all the description of the coil. If it is incomplete or inaccurate, it is better to build another device.

About coil dimensions

A large (wide) coil radiates EMF more efficiently and “enlightens” the ground deeper. Its search area is wider, which allows you to reduce the "finding by feet". However, if there is a large unwanted object in the search area, its signal will be "hammered" by a weak one from the desired trifle. Therefore, it is advisable to take or make a metal detector designed to work with coils of different sizes.

Note: typical coil diameters are 20-90 mm for searching for rebar and profiles, 130-150 mm for beach gold and 200-600 mm for big iron.

Monoloop

The traditional type of metal detector coil is the so-called. thin coil or Mono Loop (single loop): a ring of many turns of enameled copper wire with a width and thickness of 15-20 times less than the average diameter of the ring. The advantages of a monoloop coil are the weak dependence of parameters on the type of soil, the search area narrowing downwards, which allows, by moving the detector, to more accurately determine the depth and location of the find, and structural simplicity. Disadvantages - low quality factor, which is why the tuning “floats” during the search, susceptibility to interference and a vague reaction to the object: working with a monoloop requires considerable experience in using this particular instance of the device. It is recommended for beginners to make homemade metal detectors with a monoloop in order to get a workable design without any problems and gain search experience with it.

Inductance

When choosing a circuit, in order to verify the authenticity of the author's promises, and even more so when designing or refining it yourself, you need to know the inductance of the coil and be able to calculate it. Even if you are making a metal detector from a purchased kit, you still need to check the inductance by measurements or by calculation, so as not to rack your brains later: why, everything seems to be in order, and not beeping.

Calculators for calculating the inductance of coils are available on the Internet, but a computer program cannot foresee all cases of practice. Therefore, in fig. given an old, decades-tested nomogram for calculating multilayer coils; a thin coil is a special case of a multilayer coil.

To calculate the search monoloop, the nomogram is used as follows:

• We take the value of the inductance L from the description of the device and the dimensions of the loop D, l and t from there or at our choice; typical values: L = 10 mH, D = 20 cm, l = t = 1 cm.
• According to the nomogram, we determine the number of turns w.
• We set the laying coefficient k = 0.5, by the dimensions l (coil height) and t (its width) we determine the cross-sectional area of ​​\u200b\u200bthe loop and find the area of ​​​​pure copper in it as S = klt.
• Dividing S by w, we get the cross section of the winding wire, and along it - the diameter of the wire d.
• If it turned out d = (0.5 ... 0.8) mm, everything is OK. Otherwise, we increase l and t at d>0.8 mm or decrease at d<0,5 мм.

Noise immunity

The monoloop "catches" interference well, because arranged in exactly the same way as a loop antenna. You can increase its noise immunity, firstly, by placing the winding in the so-called. Faraday shield: a metal tube, braid or foil winding with a break so that a short-circuited coil does not form, which will “eat” all the EMI of the coil, see fig. on right. If there is a dotted line near the designation of the search coil on the original diagram (see the diagrams below), this means that the coil of this device must be placed in the Faraday shield.

Also, the screen must be connected to the common wire of the circuit. There is a catch for beginners here: the grounding conductor must be connected to the screen strictly symmetrically to the section (see the same figure) and connected to the circuit also symmetrically with respect to the signal wires, otherwise the interference will still “penetrate” into the coil.

The screen also absorbs some of the search EMF, which reduces the sensitivity of the device. This effect is especially noticeable in pulsed metal detectors; their coils cannot be shielded at all. In this case, an increase in noise immunity can be achieved by balancing the winding. The bottom line is that for a remote source of EMF, the coil is a point object, and emf. interference in its halves will overwhelm each other. A symmetrical coil may also be needed in circuitry if the generator is a push-pull or inductive three-point.

However, in this case it is impossible to symmetricalize the coil with the usual bifilar method (see Fig.): when conducting and / or ferromagnetic objects are in the field of the bifilar coil, its symmetry is violated. That is, the noise immunity of the metal detector will disappear just when it is most needed. Therefore, the monoloop coil must be symmetrical by cross winding, see the same fig. Its symmetry is not broken under any circumstances, but winding a thin coil with a large number of turns in a cross way is hellish work, and then it is better to make a basket coil.

Basket

Basket coils have all the advantages of mono-loops to an even greater extent. In addition, basket coils are more stable, their quality factor is higher, and the fact that the coil is flat is a double plus: sensitivity and discrimination will increase. Basket coils are less susceptible to interference: harmful emfs. in crossing wires they cancel each other out. The only negative is that basket coils need a precisely made rigid and durable mandrel: the total tension force of many turns reaches large values.

Basket coils are structurally flat and voluminous, but electrically voluminous "basket" is equivalent to flat, i.e. creates the same EMF. The volumetric basket coil is even less sensitive to interference and, which is important for pulsed metal detectors, the pulse dispersion in it is minimal, i.e. easier to catch the variance caused by the object. The advantages of the original "Pirate" metal detector are largely due to the fact that its "native" coil is a voluminous basket (see Fig.), but its winding is complex and time-consuming.

It is better for a beginner to wind a flat basket on his own, see fig. below. For metal detectors "for gold" or, say, for the "butterfly" metal detector described below and a simple 2-coil transceiver, unusable computer disks will be a good mandrel. Their plating will not hurt: it is very thin and nickel. An indispensable condition: an odd, and nothing else, the number of slots. A nomogram is not required for calculating a flat basket; calculation is carried out in this way:

• They are set with a diameter D2 equal to the outer diameter of the mandrel minus 2-3 mm, and take D1 = 0.5D2, this is the optimal ratio for search coils.
• According to formula (2) in fig. calculate the number of turns.
• From the difference D2 - D1, taking into account the flat laying factor of 0.85, the diameter of the wire in insulation is calculated.

How not to and how to wind baskets

Some amateurs take it upon themselves to wind bulky baskets in the manner shown in fig. below: make a mandrel from insulated nails (pos. 1) or self-tapping screws, wind according to the scheme, pos. 2 (in this case, pos. 3, for the number of turns, a multiple of 8; every 8 turns the “pattern” is repeated), then foam, pos. 4, the mandrel is pulled out, and the excess foam is cut off. But it soon turns out that the stretched coils cut the foam and all the work went soft. That is, in order to wind securely, you need to glue pieces of durable plastic into the holes of the base, and only then wind it. And remember: an independent calculation of a volumetric basket coil without appropriate computer programs is impossible; the flat basket technique is not applicable in this case.

DD coils

DD in this case does not mean long-range, but a double or differential detector; in the original - DD (Double Detector). This is a coil of 2 identical halves (shoulders), folded with some intersection. With an accurate electrical and geometric balance of the DD arms, the search EMF is pulled into the intersection zone, on the right in Fig. on the left - a monoloop coil and its field. The slightest inhomogeneity of space in the search area causes an imbalance, and a sharp strong signal appears. The DD-coil allows an inexperienced searcher to detect a shallow, deep, well-conducting object when a rusty can lies next to it and above.

Coils DD are clearly oriented "on gold"; all metal detectors with the GOLD marking are equipped with them. However, on finely heterogeneous and / or conductive soils, they either fail completely, or often give false signals. The sensitivity of the DD coil is very high, but the discrimination is close to zero: the signal is either marginal or not at all. Therefore, metal detectors with DD coils are preferred by seekers who are only interested in "being in the pocket."

Note: more details about DD coils can be found later in the description of the corresponding metal detector. They wind their shoulders DD or in bulk, like a monoloop, on a special mandrel, see below, or with baskets.

How to attach a coil

Ready-made frames and mandrels for search coils are sold in a wide range, but sellers are not shy about cheating. Therefore, many amateurs make the base of the plywood coil, on the left in the figure:

Multiple designs

Parametric

The simplest metal detector for searching for fittings, wiring, profiles and communications in walls and ceilings can be assembled according to fig. The ancient transistor MP40 changes without any change to KT361 or its analogues; to use pnp transistors, you need to reverse the polarity of the battery.

This metal detector is a parametric type magnetic detector operating at low frequencies. The tone of the sound in the headphones can be changed by selecting the capacitance C1. Under the influence of the object, the tone drops, unlike all other types, so initially you need to achieve a “mosquito squeak”, and not wheezing or grumbling. The device distinguishes wiring under current from “empty”, a hum of 50 Hz is superimposed on the tone.

The circuit is a pulse generator with inductive feedback and frequency stabilization by an LC circuit. Loop coil - an output transformer from an old transistor receiver or a low-power "Bazaar-Chinese" low-voltage power transformer. A transformer from an unusable power source of a Polish antenna is very well suited, in its own case, by cutting off the mains plug, you can assemble the entire device, then it is better to power it from a 3 V lithium tablet battery. Winding II in fig. – primary or network; I - secondary or step-down at 12 V. That's right, the generator works with transistor saturation, which provides negligible power consumption and a wide range of pulses, making it easier to find.

To turn the transformer into a sensor, its magnetic circuit must be opened: remove the frame with the windings, remove the straight jumpers of the core - the yoke - and fold the W-shaped plates in one direction, as on the right in the figure, then put the windings back on. With serviceable parts, the device starts working immediately; if not, you need to swap the ends of any of the windings.

The parametric scheme is more complicated - in fig. on right. L with capacitors C4, C5 and C6 is tuned to 5, 12.5 and 50 kHz, and quartz passes the 10th, 4th harmonics and fundamental tone to the amplitude meter, respectively. The scheme is more for an amateur to get drunk on the table: there is a lot of fuss with the setting, but there is no "flair", as they say. Provided as an example only.

transceiver

Much more sensitive is a transceiver metal detector with a DD coil, which can be easily made at home, see fig. Left - transmitter; on the right is the receiver. It also describes the properties of different types of DD.

This metal detector is LF; search frequency is about 2 kHz. Depth of detection: Soviet penny - 9 cm, canning tin - 25 cm, sewer hatch - 0.6 m. The parameters are "triple", but you can master the technique of working with DD before moving on to more complex structures.

The coils contain 80 turns of 0.6-0.8 mm PE wire, wound in bulk on a mandrel 12 mm thick, the drawing of which is shown in fig. left. In general, the device is not critical to the parameters of the coils, they would be exactly the same and arranged strictly symmetrically. In general, a good and cheap simulator for those who want to master any search technique, incl. "for gold". Although the sensitivity of this metal detector is not high, but the discrimination is very good despite the use of DD.

To set up the device, first, instead of the L1 transmitter, turn on the headphones and make sure that the generator is working by the tone. Then L1 of the receiver is short-circuited and, by selecting R1 and R3, a voltage is set on the collectors VT1 and VT2, respectively, equal to about half the supply voltage. Next, R5 set the collector current VT3 within 5..8 mA, open L1 of the receiver and that's it, you can search.

With phase accumulation

The designs in this section show all the advantages of the phase accumulation method. The first metal detector mainly for construction purposes will be very inexpensive, because. its most labor-intensive parts are made ... of cardboard, see fig.:

The device does not require adjustment; integrated timer 555 - an analogue of the domestic IC (integrated circuit) K1006VI1. All signal transformations take place in it; search method - impulse. The only condition is that the speaker needs a piezoelectric (crystalline), a regular speaker or headphones will overload the IC and it will soon fail.

Coil inductance - about 10 mH; operating frequency - within 100-200 kHz. With a mandrel thickness of 4 mm (1 layer of cardboard), a coil with a diameter of 90 mm contains 250 turns of PE 0.25 wire, and a 70 mm coil contains 290 turns.

Metal detector "Butterfly", see fig. on the right, in terms of its parameters it is already close to professional devices: the Soviet penny is found at a depth of 15-22 cm, depending on the soil; sewer manhole - at a depth of up to 1 m. Acts on disruption of synchronization; diagram, board and type of installation - in fig. below. Please note, there are 2 separate coils with a diameter of 120-150 mm, not DD! They must not overlap! Both speakers are piezoelectric, as in the previous. case. Capacitors - thermostable, mica or high-frequency ceramic.

The properties of the "Butterfly" will improve, and it will be easier to set it up if, firstly, wind the coils with flat baskets; the inductance is determined by the given operating frequency (up to 200 kHz) and the capacitances of the loop capacitors (10,000 pF each in the diagram). Wire diameter - from 0.1 to 1 mm, the larger the better. The tap in each coil is made from a third of the turns, counting from the cold (lower according to the diagram) end. Secondly, if individual transistors are replaced with a 2-transistor assembly for K159NT1 dif-amplifier circuits or its analogues; a pair of transistors grown on a single chip has exactly the same parameters, which is important for circuits with a synchronization failure.

To establish the "Butterfly" you need to accurately adjust the inductance of the coils. The author of the design recommends moving apart and shifting the turns or adjusting the coils with ferrite, but from the point of view of electromagnetic and geometric symmetry, it would be better to connect trimmer capacitors of 100-150 pF in parallel with 10,000 pF capacitances and twist them when tuning in different directions.

The actual adjustment is not difficult: the newly assembled device beeps. We alternately bring an aluminum saucepan or a beer can to the coils. To one - the squeak becomes higher and louder; to the other - lower and quieter or completely silent. Here we add a little capacity of the trimmer, and remove it in the opposite shoulder. For 3-4 cycles, you can achieve complete silence in the speakers - the device is ready to search.

More about Pirate

Let's return to the famous "Pirate"; it is a pulse transceiver with phase accumulation. The scheme (see fig.) is very transparent and can be considered a classic for this case.

The transmitter consists of a master oscillator (MG) on the same 555th timer and a powerful key on T1 and T2. On the left - a variant of the ZG without an IC; it will have to set the pulse repetition rate of 120-150 Hz R1 and the pulse duration of 130-150 μs R2 on the oscilloscope. Coil L - common. The limiter on diodes D1 and D2 for a current of 0.5 A saves the QP1 receiver amplifier from overload. The discriminator is assembled on QP2; together they make up the dual operational amplifier K157UD2. Actually, the "tails" of the reradiated pulses are accumulated in the capacitance C5; when the “reservoir is full”, a pulse jumps at the output of QP2, which is amplified by T3 and gives a click in the dynamics. Resistor R13 regulates the filling rate of the "reservoir" and, consequently, the sensitivity of the device. More about "Pirate" can be found in the video:

Video: Pirate metal detector

and about the features of its settings - from the following video:

Video: setting the threshold of the Pirate metal detector

On the beat

Those who wish to experience all the delights of the process of searching on beats with replaceable coils can assemble a metal detector according to the scheme in fig. Its peculiarity, firstly, is efficiency: the entire circuit is assembled on CMOS logic and, in the absence of an object, consumes very little current. Secondly, the device works on harmonics. The reference oscillator on DD2.1-DD2.3 is stabilized by ZQ1 quartz at 1 MHz, and the search oscillator on DD1.1-DD1.3 operates at a frequency of about 200 kHz. When setting up the device before searching, the desired harmonic is “caught” by the VD1 varicap. The mixing of the working and reference signals occurs in DD1.4. Thirdly, this metal detector is suitable for work with replaceable coils.

It is better to replace the ICs of the 176th series with the same 561st ones, the current consumption will decrease, and the sensitivity of the device will increase. It is simply impossible to replace the old Soviet high-resistance headphones TON-1 (preferably TON-2) with low-resistance ones from the player: they will overload DD1.4. You need to either put an amplifier like a "pirate" one (C7, R16, R17, T3 and a speaker on the "Pirate" circuit), or use a piezo speaker.

This metal detector does not require settings after assembly. Coils are monoloops. Their data on a mandrel 10 mm thick:

• Diameter 25 mm - 150 turns of PEV-1 0.1 mm.
• Diameter 75 mm - 80 turns of PEV-1 0.2 mm.
• Diameter 200 mm - 50 turns of PEV-1 0.3 mm.

It doesn't get easier

Now let's fulfill the promise given at the beginning: we will tell you how to make, without knowing anything about radio engineering, the metal detector that you are looking for. The metal detector is “easier than simple” assembled from a radio receiver, a calculator, a cardboard or plastic box with a hinged lid, and pieces of double-sided tape.

The metal detector "from the radio" is pulsed, however, to detect objects, it is not dispersion and not delay with phase accumulation that are used, but the rotation of the EMF magnetic vector during re-emission. On the forums, they write different things about this device, from “super” to “sucks”, “wiring” and words that are not customary to use in writing. So, in order to get, if not “super”, but at least a fully functional device, its components - the receiver and the calculator - must meet certain requirements.

Calculator we need the tiniest and cheapest, "alternative". They make them in offshore cellars. They have no idea about the standards for electromagnetic compatibility of household appliances, and if they heard about something like that, then they wanted to spit from the bottom of their hearts. Therefore, local products are quite powerful sources of impulse radio interference; they are given by the clock generator of the calculator. In this case, its strobe pulses on the air are used to probe the space.

Receiver you also need a cheap one, from similar manufacturers, without any means of increasing noise immunity. It must have an AM band and, absolutely necessary, a magnetic antenna. Since receivers with short wave (HF, SW) reception on a magnetic antenna are rarely sold and are expensive, you will have to limit yourself to medium waves (MW, MW), but this will make tuning easier.

1. We unfold the box with a lid into a book.
2. We stick strips of adhesive tape on the back sides of the calculator and the radio and fix both devices in the box, see fig. on right. The receiver - preferably in the lid, so that there is access to the controls.
3. We turn on the receiver, we are looking for a section free from radio stations and as clean as possible from radio noise by setting it to maximum volume at the top of the AM band (bands). For MW this will be around 200 m or 1500 kHz (1.5 MHz).
4. We turn on the calculator: the receiver should buzz, wheeze, growl; in general, give a tone. We do not remove the volume!
5. If there is no tone, carefully and smoothly adjust until it appears; we caught some of the harmonics of the calculator's strobe generator.
6. We slowly fold the “book” until the tone weakens, becomes more musical, or disappears altogether. Most likely this will happen when the lid is rotated about 90 degrees. Thus, we have found a position in which the magnetic vector of primary impulses is oriented perpendicular to the axis of the ferrite rod of the magnetic antenna and it does not receive them.
7. We fix the cover in the found position with a foam insert and an elastic band or supports.

Note: depending on the design of the receiver, the reverse option is possible - to tune in to the harmonica, the receiver is placed on the included calculator, and then, laying out the “book”, the tone is softened or disappears. In this case, the receiver will catch the pulses reflected from the object.

And what's next? If there is an electrically conductive or ferromagnetic object near the opening of the "book", it will re-emit probing pulses, but their magnetic vector will turn. The magnetic antenna will “smell” them, the receiver will again give a tone. That is, we have already found something.

Something strange in the end

There are reports of another metal detector "for complete dummies" with a calculator, but instead of a radio, supposedly 2 computer disks, a CD and a DVD, are needed. Also - piezo headphones (precisely piezo, according to the authors) and a Krona battery. Frankly speaking, this creation looks like a techno-myth, like a memorable mercury antenna. But - what the hell is not joking. Here's a video for you:

try it, if you wish, maybe something will be found there, both in the subject and in the scientific and technical sense. Good luck!

as an application

There are hundreds, if not thousands, of schemes and designs of metal detectors. Therefore, in the appendix to the material, we also give a list of models, in addition to those mentioned in the test, which, as they say, are in circulation in the Russian Federation, are not overly expensive and are available for repetition or self-assembly:

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Metal furnaces have a number of undoubted advantages and equally significant disadvantages. The former include an order of magnitude smaller or more price, high efficiency, light weight, high strength and advanced technology for processing the source material - metal. To the second - lack of "breathing", limited service life, increased danger and short heat dissipation after the flood. These factors give some consequences, which should be considered in more detail before starting to analyze the actual metal furnaces.

Advantages

Metal is a much more malleable material than ceramics, but comparable in strength. Metal can be melted and poured, drilled, cut, bent, forged; after forming the part, it does not require mandatory additional energy costs for firing it. There are many known methods for the production and processing of metal, and their scientific and industrial base is huge. Therefore, when creating a metal furnace, it is possible to apply almost without restrictions a variety of theoretical and design tricks to improve its technical and operational parameters without a significant increase in price. If the marginal average per season CFL of brick ovens is about 70%, then for metal 85-90% is not a wonder.

Note: based on modern environmental conditions, it is necessary to strive to obtain a furnace efficiency of at least 70%

The specific, per unit cross-section, strength of bricks and ceramics in general decreases sharply with a decrease in the thickness of the part, while for metal, on the contrary, it increases. As a result, such important furnace indicators as weight and cost per unit of generated heat are 10-20 times or more lower for metal furnaces than for brick ones. A good new metal oven for heating 100 sq. m of living space can be purchased for $250-300, and used for $50.

In addition, the metal oven is a one-piece construction, it can be transported ready for use, tilted, pushed, hit, even dropped without being damaged. That is, the metal furnace is mobile. At the place of operation, it does not require a foundation, and its installation is reduced to the withdrawal of the chimney into the smoke channel of the building. After the need has passed, the stove can be removed and placed in storage until the next occasion.

The thermal conductivity of the metal is high, and the total heat capacity of the furnace from it is small due to its small mass. Therefore, the metal stove warms up quickly and heats the room just as quickly. The same factor gives high efficiency: in a brick kiln, up to 20% of the fuel energy flies into the pipe during heating, until internal heat transfer is established in the massive body of the kiln and it begins to accumulate heat.

Further, the metal product is physically more uniform than masonry and is not porous. The metal furnace does not dampen, is not afraid of long breaks in the furnace, does not require accelerating fires after downtime. The actual absence, due to the high thermal conductivity of the metal, of internal heat flows in the body of the furnace, causes the rapid burning of flue gases in it in a small volume of space, which facilitates the integration of a hob and water heaters into the furnace.

Finally, which is important for private owners, a metal factory furnace can be certified in advance for fire safety as a finished product. In this case, it is immeasurably easier to get permission from firefighters to use it, both in terms of nerves and money. There are models of metal furnaces of industrial production that do not require registration at the Ministry of Emergencies at all, if only the building had a gas duct separate from ventilation.

disadvantages

The main disadvantage of metal furnaces is the lack of "breathing". The brick oven, as it cools, absorbs moisture vapor, and when heated, it releases them into the air. Therefore, in a house with brick-stove heating, the relative humidity of the air itself is maintained within optimal health limits. A metal stove can be made to “breathe” a little by lining with brick, steatite (“soapstone”, soapstone), basalt or drywall, but the effect will be weaker, the strength of the stove will decrease, and its mobility will completely disappear.

Due to the low total heat capacity, the heat transfer of the furnace after heating does not exceed 2-3 hours. A metal furnace must either be heated all the time, or performed in the form. Both are a constant source of fire. When installing the stove in a residential area, this gives a round-the-clock danger of waste. In addition, a metal furnace can become red hot during operation, and this creates a fire and injury hazard. Therefore, the Ministry of Emergency Situations certifies home-made metal furnaces with great difficulty, and then only intended for installation in isolated non-residential premises.

The third significant drawback of metal furnaces is a short service life compared to brick ones. Chemically, metal is much less resistant than ceramics, and at high temperatures it reacts even more actively with substances that can damage it. The service life of a metal furnace with regular firing rarely exceeds 20 years; however, this pays off in reduced fuel costs and the ability to replace the stove without repairing the building.

About furnace metal

As you can see, it is the physical and chemical properties of the metal for the furnace for the furnace that largely determine its quality. Whether the stove will be purchased ready-made or made independently, the first attention should be paid to it.

Surrogates

In popular sources, you can find descriptions of stoves from ... aluminum milk cans. But for a more or less acceptable efficiency of the furnace, it is necessary to burn the flue gases. At the same time, a temperature of at least 400 degrees Celsius develops, and in furnaces that meet environmental requirements, at least 600. The melting point of aluminum is 660 Celsius; temperature tensile strength - 140 for structural aluminum and 160-210 for aluminum alloys. On this the question of aluminum furnaces can be considered closed.

plain steel

The temperature limit of strength and resistance of conventional structural steels is about 400 degrees during prolonged exposure; at 2 hours 600. Steel on the furnace comes with a thickness of 4 mm. But even in this case, it is impossible to talk about regular use: in frosty regions where an intensive firebox is needed, the stove can burn out before the end of winter. Some exceptions are long-burning furnaces, some of their designs make it possible to avoid prolonged heating of the furnace body above 600 degrees, and very hot parts in them are massive and replaceable. Such ovens are most often made by hand; some popular designs will be described below.

Heat resistant steels

Metal furnaces of industrial production are made of heat-resistant and heat-resistant steel. Modern special steels with a thickness of 1.5-3 mm make it possible to obtain a furnace service life of up to 20 years or more, its low weight, and the combination of heat capacity with thermal conductivity of furnace steels, with the correct design, guarantees high efficiency, up to 80%. Branded steel furnaces for sale are certified according to the requirements of the Ministry of Emergencies, for fire and injury safety they are quite suitable for the home. Their installation is most often possible simply on the floor and requires only a connection to the chimney. In most cases, they are equipped with a hob and a low-power hot water hot water register.

The design of such furnaces at first glance is available for repetition. But in order to do something like this yourself, even if you have the material, you need to master at least quite complex TIG / MIG welding technology and expensive equipment for it. Attempts to cook heat-resistant stainless steel in artisanal ways are meaningless: after remelting under an arc, the steel loses its qualities and the stove cracks at the seams faster than the tin stove burns out.

However, it is quite possible to make a furnace yourself using heat-resistant steels, and this will greatly increase its reliability and durability. We are talking about air distribution devices for long-burning stoves of the Slobozhanka type, see more details below. Expensive material will take a little, you can pick up and trim. And the connections in this case can be made on a mustache, rivets or in a fold.

Cast iron

Cast iron in a furnace is both metal and non-metal at the same time. From the metal in it remains a low cost and the ability to carefully, without dropping or hitting, move the stove. Cast iron has in common with brick not only brittleness, but also low thermal conductivity for metal, combined with good heat capacity. It is cast-iron stoves that can heat up to 3 hours after heating, but they also warm up for at least 40 minutes.

Cast iron on the furnace is 6-25 mm thick. It is impossible to thinner, the stove will be too fragile. But it’s also impossible to get thicker, the temperature coefficient of expansion (TC) of cast iron is quite metallic, and with a “brick” wall thickness, the furnace will crack during heating. Therefore, cast-iron stoves are heavy, you cannot put them directly on the floor, you need to disassemble its flooring to the screed and build it up to the floor level. And the "brick" qualities of a cast-iron stove appear only when heating small, up to 60 cubic meters. m, premises. In large ones, due to the low thermal conductivity of the walls, the efficiency of the furnace will be negligible.

Cast iron does not breathe like brick, but its chemical resistance approaches that of ceramics. Cast iron, like metal, is not afraid of interruptions in the furnace and air dampness. Therefore, it is advisable to use cast-iron stoves for heating utility rooms with delicate small animals: poultry houses, rabbitries, small greenhouses.

Cast iron, as you know, after casting in the factory, is not subject to handicraft machining. All that a do-it-yourselfer with a cast-iron stove can do is paint the purchased. Painting stoves, by the way, is also not an easy job, see below.

Schema and type selection

What is an oven?

Since we are talking about furnaces as such, let's decide what we are dealing with; in the classification of furnaces, there is more confusion than clarity. For example, a fiery channel furnace is considered a furnace with forced circulation of flue gases, and a bell-type furnace is considered a furnace with free circulation. But what freedom does it have for flue gases, if the vault of the cap prevents them from going up, and the same cap, absorbing their heat, makes them descend to the chimney located below in the most unnatural way? The only heating and cooking device with completely free circulation is a fire on the ground.

On the other hand, the definition of "forced" implies the presence of a pressurizer or a smoke exhauster, or both. Finally, the use of heat from the same source in the same device at different times is possible for different purposes. And the source of heat and its transmitter where it should be does not have to be fuel and flue gases.

Therefore, we will define a furnace as a device in which the heat flow from its compact source is directed to the heat energy receiver by technical means within one integral device without the use of separate heat transfer lines. Under this definition, a kitchen wood-burning stove, and a melting electric arc furnace, and a laboratory muffle, and a solar camping stove are suitable.

Domestic ovens

We are interested in household heating and cooking stoves. Let's look at them first in general, and then take into account the features of our material - metal. The main schemes for the construction of household stoves are shown in fig.

chamber

On the left pos. scheme of the oldest furnace as such - chamber. In it, flue gases from the furnace are transferred to the gas chamber, where they burn out, due to natural circulation. Also, in a natural way, outside air leaks to the burning fuel. In essence, this is a fire in a cave.

In modern industrial chamber furnaces, it is difficult even for a specialist to recognize their primitive ancestor, but with domestic ones it is easier, here the furnace with the afterburner is combined into one module - the crucible. For effective afterburning, the chamber must be vaulted. "Primitive" chamber furnaces, with some improvements, can be very effective. An example is surviving to this day.

Drier

On the middle pose. - channel oven. Flue gases, first burning down, and then gradually cooling down, pass through the channels between the partitions, giving off heat to the body of the furnace. Perhaps that is why the channel furnace is considered “forced”, the path of gases in it is physically organized. Until such a furnace inside warms up to at least 400 degrees, there is no afterburning at all, and then it stretches from the furnace to the chimney, and it is very difficult to achieve an efficiency of over 60% here.

Kolpakovaya

On the right is a bell-type furnace. The flue gases in it linger under the dome of the hood until they burn out, and then fall down along its walls, giving off the remaining heat. When kindling, it is necessary to warm up only a small section of the bell roof to start afterburning, so a bell-type furnace can provide an efficiency of over 70%

Applied to metal

The ratio of the thermal conductivity of a metal to its heat capacity is ten times higher than that of a brick. Therefore, metal is a lousy heat accumulator. Absorbing it, it quickly heats up to a high temperature, and then cools down just as quickly.

But if we accurately take into account the properties of the material, metal heating furnaces can also be made according to classical schemes, and higher parameters can be achieved from them, because. heat losses for heating the furnace during heating are minimal. And the high connectivity of the metal structure makes it possible to apply the principles of fuel combustion, for brick ovens, either completely unfeasible, or feasible with great difficulty. The main schemes of metal household furnaces are shown in fig.

chamber

Metal chamber furnace - on pos A. Do you recognize it? . Her ancestors, indoor stoves, appeared at the beginning of the 19th century, but were distinguished by their rare voracity; However, the fuel then cost pennies. The devastation after the revolution in Russia forced the "former specialists" to improve the potbelly stove, at the same time it got its name. The following has been improved:

• To adjust the power according to the weather, a grate with a blower and its door was built into the crucible.
• The chimney was made low, up to 2.5-3 m from the level of the grate.
• The diameter of the chimney was taken approximately 7-9 mm per 1 kW of thermal power, in terms of modern units of measurement.
• The initial section of the chimney, about 1-1.5 m, was made vertical and wrapped with thermal insulation.
• This was followed by a horizontal piece of the chimney - hogs - at least 2.5 m long, it was brought out into the window and increased by a vertical section that also provided traction, also 1-1.5 m.

The role of the arch of the crucible on the minimum firebox was played by the first vertical isolated section of the chimney - a gas economizer, in which flue gases burned out. At the maximum, the throughput of the chimney turned out to be less than the volume of gases generated in the furnace. At the same time, a vortex appeared in the crucible, providing the main afterburning, and the stove became self-regulating: the gases went into the pipe only after they had completely burned out. Heat transfer to the room is approximately 25% provided by the heated body of the furnace and 75% by convection from a red-hot hog. At the outlet of the chimney, the temperature of the gases is above 100 degrees, so condensation (see below) is excluded. Cleaning the chimney from soot is required no more than 1 time per year and is not difficult, since the chimney is collapsible. Furnace efficiency - up to 60% on dry wood or coal.

Drier

It is easy to adapt a potbelly stove to a channel scheme, but the resemblance to a brick channel stove remains only external. Firstly, due to the high thermal conductivity of the metal, there will be no sense from the developed labyrinth of gas ducts, so only one horizontal elbow remains from it. And its role is completely different: the partition separates the afterburning chamber from the furnace. The secondary air required for it enters either through the slots in the burner on the hob, or through a separate air throttle-regulator. The outlet to the chimney is horizontal. These improvements gave the following:

1. Efficiency due to afterburning concentrated in one place has increased to 70-80%
2. The volume-specific thermal power of the furnace increased by 2-3 times.
3. The stove is not critical to the amount of draft and, in general, to the parameters of the chimney, like an ordinary potbelly stove: draft has increased, combustion in the furnace will increase, but also rarefaction in the afterburner. More secondary air will pass into it and the gases will still burn out completely.
4. Since the main heat is generated in the afterburner, the furnace can operate in both flame and long burning modes.
5. Heat transfer through a thin metal partition from the furnace to the afterburner immediately ensures the flash point of unburned gases in it, so the furnace enters the mode almost instantly, which further increases its efficiency.
6. Separate adjustment of the air supply to the furnace and afterburner allows you to adjust the furnace for almost any type of solid fuel.
7. The power of the furnace can be adjusted not by the amount of fuel loading, but by the air supply. In a potbelly stove, the ability to adjust power with air is very limited, no more than 2-2.5 times.
8. The temperature of the hob, due to the uniformity of thermochemical processes in the afterburner, is kept within 250-300 degrees, which is quite suitable for cooking.
9. The high intensity of heat release in the furnace allows you to organize a quick and uniform heating of the room by convection.
10. At the outlet to the chimney, you can put a DHW heat exchanger without fear of deterioration in the parameters of the furnace and increased soot deposition.
11. On good wood fuel or coal, cleaning the chimney is required only once every 4-5 years.

Almost all modern heating and cooking household stoves of small (up to 12-15 kW) power are built exactly according to this scheme. When self-manufacturing from heat-resistant steel, you need to make an afterburner, in the form of a trough open on top (partition + side walls). At the same time, ordinary steel from 4 mm will go to the furnace body, and cast iron or steel from 8 mm will go to the hob. The plate must be made removable, especially steel, because. from heat and thermochemistry in the afterburner, it will last a year or two.

long burning

The use of an effective bell scheme in relation to metal made it necessary to abandon the flame: no metal bell can absorb, without overheating, as much heat as it emits. I had to switch the stoves to smoldering mode, which at the same time made it possible to bring the heat transfer time up to 60-72 hours from one load of firewood or up to 20-30 days (!) On coal. Further on, we will dwell on long-burning furnaces in more detail, and a simplified one, without an air supply system and technological hatches, is shown on:

• The fuel mass 1 smolders in a thin surface layer 2, and air is supplied here in one way or another.
• Pyrolysis, the thermal decomposition of solid fuel into combustible volatile components, plays a significant role in the smoldering process.
• The combustion of volatiles occurs in the space under the lid of the furnace ("hood") 3, up to 60% of heat is released here.
• If it is necessary to obtain an efficiency of the furnace of more than 70%, it is equipped with a gas jacket 4, here the flue gases burn out in the usual way. The air required for this is sucked in at the pass from the fuel chamber into the gas jacket.

Long-burning furnaces with a simple design can provide an efficiency of up to 80% or more, and the temperature in any of their places rarely exceeds 600 degrees. Therefore, home-made metal furnaces, except for, are mostly performed according to this scheme. Taking into account such a design, you need to consider the following:

1. Although long-burning stoves operate on any solid fuel from sawdust to coal, they will show the calculated (or verified on an experimental design) parameters only on the fuel for which they are designed. For example, KV on coal is heated like on wood, up to 3 days. A special coal-fired boiler, also of slow burning, on the same amount of coal - up to 20. And it is not capable of working on wood at all.
2. The products of complete combustion of fossil fuels are carbon dioxide and water, regardless of the degree of its watering; this process is akin to the formation of metabolic water in living organisms. Gases in the chimney of long-burning furnaces go very cold, because. The efficiency of the furnace is high, and the temperature in the furnace is low. Therefore, abundant condensate is formed in the chimney, which is very toxic, and the design of the chimney must contain its collector with the possibility of draining.
3. Long-burning stoves do not tolerate wet fuel; as you know, the wet does not smolder, no matter how much air is supplied to it.
4. It is impossible to add fuel to the furnace until the previous load is completely burned out, with one exception, see below. Opening the lid or loading hatch of an unburned furnace is deadly: pyrolysis gases are chemically aggressive and poisonous!

Note: directly above the smoldering zone, the furnace body is red-hot, but this does not prevent its manufacture from ordinary steel. As it burns out, the red-hot belt shifts down and the duration of exposure to the metal of the limiting temperature does not exceed the allowable 3 hours.

The furnace body can be made from any suitable round steel container, e.g. from a barrel. But it is already more difficult to surround it with an airtight gas jacket. In any case, such a stove heats mainly by radiation, which is not very good. The way out is to surround the furnace body, at a distance of 70-80 mm from it, with a hot water hot water register in the form of a coil or an annular tank. Convection will increase and there will be hot water in the shower and in the kitchen. It is only necessary to provide a storage tank with a capacity of approximately 10 l / kW, otherwise the system will boil.

Oil pyrolysis

Such an effective thermochemical process as pyrolysis could not help but receive independent development among do-it-yourselfers who were very willing to experiment. They, as a rule, form some reserves of waste heavy combustible liquids, for example. working off. So the metal pyrolysis was born,.

The oil burns in the tank, where primary air is supplied through the throttle - the power regulator (it is also the filling hole). Combustion is weak, it is only needed to evaporate the fuel. Its vapors rise into the pyrolysis column - a pipe with perforated walls; secondary air passes through the perforations. It enters the mixing zone in excess.

In the pyrolysis zone, the fuel vapor columns burn, but the heat from this is mostly spent on the decomposition of the fuel to light volatile components that burn in the combustion zone; Approximately 35% of useful heat is released here. The other 35%, from the heavy residues escaping pyrolysis, are released in the afterburner.

In the afterburner, there is an incomplete partition, horizontal or vertical, inside. Why is she? In the combustion zone of the column, due to an excess of oxygen, a high temperature, up to 1000 degrees, develops. In this case, endothermic oxides of nitrogen are formed. They are toxic and take a lot of fuel energy to form them.

At temperatures above 700 degrees, nitrogen oxides are stable and in the zone of oxygen afterburning of heavy radicals they will remain as they were. If they are allowed to cool quickly, they will skip the peak of the instability of their phase diagram and fly away into the chimney, taking away the efficiency of the furnace. In order for nitrogen oxides to decompose themselves, releasing the energy spent on them, they must be kept in a zone with a temperature of 450-600 degrees. It is she who is formed behind the partition before exiting the chimney. Why? There is a whirlwind.

Note: No one really measured the efficiency of furnaces during mining. Only the fuel consumption for heating a standard garage 4x7x2.2 m is known. It is 1.5-2.5 l / h.

Sometimes a garage potbelly stove is made with a round blower with a diameter along the outer diameter of the oil stove column and placed on high legs. A tank with a column is left from the oil pyrolysis furnace, and the column itself is made in the form of an arc with a horizontal outlet. Then, as mining accumulates, the potbelly stove is used as an afterburner in a pyrolysis furnace. The exit of the column is inserted into the blower, and the oil potbelly stove is ready. The mining is over - we heat again with firewood / coal.

Note: in principle, it is possible to refuel the furnace during mining, but it is dangerous. In general, these furnaces are an incendiary time bomb with a fuse set for an unknown period. Fire regulations prohibit their use in everyday life and they are not widely sold.

About shielding furnaces

A steel furnace in operation becomes very hot and warms to a large extent with thermal (infrared, IR) radiation. For residential premises, this is undesirable: it swells in the face, and the back freezes. They are preferably heated by convection. In addition, a hot stove can cause severe burns.

How to turn IR into a stream of warm air? Very simple: surround the oven from the sides with a metal sheet screen at a distance of 70-100 mm from the oven and with the same clearance from the floor.

You can meet statements: they say, an iron screen is useless, metal for IR is the same as glass. First, the metal begins to transmit electromagnetic radiation from x-rays and higher in frequency. Secondly, not like window glass, but like milky glass, partially and diffusely. And for IR, any metal is opaque, but diffusely reflects about half of them. In the IR photo, the metal sheet looks light gray.

Assume that an IR flux of unit power falls from the furnace onto the screen. 0.5 of it will be reflected back, and the remaining 0.5 will be radiated by the screen in both directions, back and out. In total, only a quarter will come out. This is a rough scheme, if the screen becomes very hot and its temperature approaches the furnace temperature, the proportion of external radiation increases; up to 1 at equal temperatures.

When calculating the screen, it must be coordinated with the heat capacity and viscosity of the air so that the heat between the screen and the furnace gives rise to intense convection, which cools the screen. With the dimensions indicated above, the external temperature of the screen will not exceed 70 degrees and the heat transfer by convection will be at least 85% of the heat output of the furnace.

Note: it is better to make the screen sliding in breadth, in the form of 2 L-shaped halves, and on separate legs. Then, by pushing / moving the sidewalls, you can adjust the gap between it and the furnace in accordance with the furnace mode.

It will be bad to shield the internal partition in the furnace, because. temperatures in the furnace and afterburner are close. But radiation upwards from the hob is not dangerous and does not suppress convection. It is simply impossible to shield from the front: there are doors and an approach to the furnace. It remains to decide what to do with the radiation down from the bottom of the furnace, there is nothing for him to heat the flammable floor in vain.

This problem is also solved without much difficulty: we deepen the ash pan down from the blower door and lay it out on a dry, without mortar, brick. You can fill it with brick battle or sand, but then when you excavate the ash, you will have to rake and throw away the backfill. If we bring all these methods into one, we get the shielding scheme shown in Fig. higher.

Shielding for a bath

Specific, per unit volume of the room, the power of bath stoves is 3-5 times higher than that of room stoves, and the walls of a normal bath are wooden, poorly conducting heat. Therefore, a quick heating of the bath can be provided only by convection, on the one hand. On the other hand, a metal sauna stove gives too hard heat for the same reason that it does not breathe. Based on this, we make a brick screen for the bath; enough laying in half a brick for. It is only necessary to lay out the first row at intervals to ensure convection, as shown in fig. on right.

Shielding for giving

The country house is also small, it is empty in winter and it is not necessary to heat it to the bath temperature. Therefore, a country stove can, in principle, be screened like a bathhouse. But it’s better not to be too lazy, install a hot water storage tank in the attic, and surround the stove for giving, like a screen, with its water heater, see fig. left. Water absorbs IR completely, and while people stretch their hands frozen in the garden to the stove, and then gobble up sandwiches, a kettle will boil on the hob, and enough water will accumulate in the tank for a shower.

Note: shielding the hearth of the oven from the inside with heat-intensive material gives an additional advantage here - you can put shoes under the oven to dry without fear that it will dry out and crack.

The development of the idea of ​​a screen-convector was the appearance of stoves-heaters. They are initially designed so that as much of the heat as possible is converted into the energy of the movement of the heated air flow. To do this, the convector is built into the furnace or a precisely calculated screen is made along with the body of the furnace.

The most famous model of this kind - or simply a buller (left and middle pos. in the figure). In the Russian Federation, bullers are produced under a license under the Breneran brand. Buller features are as follows:

• Buleryan - exceptionally long burning. The flame mode is an emergency for her, and all attempts to adapt bullers to any other type of fuel have so far been unsuccessful.
• Fuel-mode fastidiousness allowed air to be supplied to the furnace through one throttle. Air enters the afterburner partly mixed with flue gases, partly through a perforated partition between the furnace and the afterburner.
• A well-thought-out design and an optimal configuration of the entire furnace allow for power adjustment over a wide range, by 10-12 times.
• The firebox, rounded in section, and the convector built into it 2/3 deep from the tube batteries provide powerful convection (6 cubic meters / min per 1 kW of firebox power) without a significant deterioration in the efficiency of the stove.
• The temperature of the air leaving the batteries and the outer surface of the furnace does not exceed 70 degrees.
• When the power is reduced by the throttle, the temperature of the outgoing air drops faster than its flow, i.e. at lower power, the buller heats up just as quickly, but weaker.

The duration of heat transfer of buleryan with one full load of fuel is 8-12 hours. Serial bullers are produced for a power of 10-200 kW. The efficiency of the buller is about 60% By surrounding the stove with a screen, it can be increased to 66-67%, while the temperature of the outer surface of the screen will be about 55 degrees. The temperature inside the buller never exceeds 600 degrees, so it is quite possible to make it yourself from ordinary steel, but you can’t do it from the tip.

Buller's secret is in the exact internal balance of heat and air. To take away too little heat for convection - the stove will give little hot, overdried air. Take away a lot - the fuel will not burn out properly, a lot of ash, soot is formed, the efficiency of the furnace will drop. It is the same with air: the configuration and size ratio of all furnace parts provide automatic redistribution of air flows inside according to the combustion mode. But a step to the right, a step to the left - again ash, soot, gluttony and little heat.

Therefore, it is better not to try to calculate the buller yourself, guided by the initial information about heat engineering. It is possible to replicate a proven design, but with precise dimensions, instructions, and specifications. The length and configuration of the chimney is not critical, but a condensate collector is necessary in it, because. flue gas temperature is low.

Bullers are usually used for heating industrial premises that require uniform heating to a comfortable or process temperature: greenhouses, conservatories, nurseries of heat-loving animals. However, by installing a buller of suitable power in the basement, it is possible to provide air heating for a private house of almost any area: a large number of convector nozzles (from 7 to 23-25) allows you to organize a uniform distribution of heat throughout the rooms. The nozzles of the furnace batteries are simply mated with air ducts made of cheap thin-walled corrugation, and it is easier and cheaper to arrange an air duct system in the house than to mount pipes and water heating registers. In addition, there is no need for complex, expensive, energy-intensive and maintenance-intensive water boiler piping.

In Russia, a lot of similar designs budded from the buller; one of the most famous is the Professor Butakov line of stoves, right pos. in fig. The Butakovs are multi-fuel, their efficiency is higher than that of a buller, they have a hob, but here, in an article for home-made people, it is worth mentioning them only in passing: the construction of special steel is designed exclusively for industrial production. In addition, the Butakovs can heat only 1 room well: it is very difficult to connect air ducts to the outlet of their batteries.

About air heating

Air heating is optimal for individual houses with 1-2 floors. The number of storeys of the house is rapidly devouring its efficiency, so it went out of use even in cramped medieval cities, although rich estates in ancient times were heated with air.

Its widespread introduction into the private sector is actually hindered only by the lack of legalized norms, rules, recommendations and methods of engineering calculation. However, for do-it-yourselfers with a vein of an experimenter, this is a plus: since it is not prohibited, then it is possible, as long as the buller itself is certified. Do as you want and know how, without fear of sanctions: why punish if it is not in the law at all?

Slow homemade

If there are no parts in the potbelly stove and its relatives, the rough or careless manufacture of which would completely ruin the stove, then buller already gives an example that you need to be more careful with long-burning stoves. They have nodes, a small mistake in the execution of which will make the oven not only bad, but also dangerous. Therefore, we will dwell on slow-burning stoves in more detail; 2 popular and 1 promising designs are shown in fig.

Pos. A - the famous bubafonya, homemade based on the Latvian slate boiler Stropuva. It belongs to furnaces with a closed smoldering zone, therefore its efficiency is under 70%, and with a gas jacket over 75%. Air through the oppression-"pancake" is supplied to the center of the combustion zone. The increased efficiency is due to the fact that the pyrolysis gases burn out even under pressure, so it must be either made of special steel or thick, 8-12 mm. The second feature, as a result of closed combustion, is that bubafonya, in extreme cases, can be reloaded on the go. The stench shibanet, but you will not be poisoned.

The specific power of bubafoni is about 0.3 kW per 1 cubic meter. dm of fuel, which is not bad. But the fuel itself is sawdust, shavings, small combustible debris, and dry. On wood and coal, the efficiency drops sharply: the duration of heat transfer remains the same, 6-8, up to 12 hours. You can “feed” bubafonya with high-quality high-energy fuel if you are not too lazy and make a “pancake” with curved profiled blades. This will also increase the possibility of reloading: turning the oppression when lifting / lowering will not bring down the combustion and re-ignition of the furnace is not required.

At pos. B1-B3 no less popular open burning stove "Slobozhanka". Its design is elementary, it is not critical to the size and proportions, from the pot to the barrel. The furnace can operate on waste fuel, wood, coal, tropho briquettes. 3 circumstances prevent "Slobozhanka" from competing in bubafonei:

1. Additional loading on the go is impossible, removing the lid in an unburned furnace is deadly.
2. Due to open combustion, the specific thermal power is 2-3 times lower than in furnaces with a closed combustion zone.
3. An air distribution shaft made of ordinary steel with a thickness of 6 mm with regular intensive combustion burns out before the end of the heating season, and a body made of 3 mm steel lasts 2-3 years due to active chemical corrosion in the gas cushion.

It is possible to increase the durability and specific power of the Slobozhanka by making the fire body of special steel. Air distributors are made several directly in the walls of the housing (its development is at pos. B2). But then you have to surround the oven with an air jacket with partitions, and even make an annular blower, pos. B3. For a do-it-yourselfer, such a design is too complicated, and unprofitable in production. Therefore, "Slobozhanka" is produced only in small batches by small firms, and they are in some demand only in the southern regions as stoves for occasional heating of utility rooms.

Note: for furnaces with a gas jacket, the condensate collector will have to be buried in the floor, and the accumulated pump out, because. in furnaces with a gas jacket, the outlet to the chimney is lower.

At pos. B - scheme of the furnace, once produced by the Soviet military industry for heating the barracks of small remote garrisons. Possessed high specific power; a stove the size of a barrel heated a room of 150-160 sq. m. with a ceiling of 4 m. It is omnivorous, everything burned in it, from Suchansky anthracite to fresh household waste. Reloading - on the go without restrictions: a fungus on the air duct / air distributor did not allow a fresh portion of fuel to bury the smoldering zone, and completely burnt gases escaped through the mass of fuel. Only a perforated cone was made of heat-resistant steel, with a seam connection.

Now this furnace seems to be forgotten. The probable reason is the bulkiness and unaesthetic nature of the whole system. In addition to the furnace, its standard equipment included 3 sections of 2 m gas-air heat exchange registers, each in the form of a finned bundle of 5 two-inch thin-walled pipes. Attempts to replace them with a bourgeois chimney led to the fact that the hog heated up to orange, and the stove began to "spit" gas from under the lid.

Installation of a metal furnace

Before taking on any stove, you need to decide on the place of its installation. The first rule in this case, if the oven is convection, it can be placed anywhere. If the stove heats mainly by radiation, it must be placed away from the outer walls, otherwise the rising temperature gradient between the room and the street will lead to large heat losses and eat up a good share of the efficiency of the stove.

Next, we estimate the weight of the furnace per unit area of ​​its projection on the floor. If the weight load does not exceed 150 kg / sq. m, then everything is OK, the stove can be placed directly on the floor. If the load is within 150-400 kg/sq. m, the flooring will have to be dismantled and put the stove on the screed. Installation of metal furnaces, as a rule, does not require parsing the flooring and foundation. In utility rooms with earthen or any other floor without a screed, a reinforced concrete slab with a thickness of at least 7 cm must be placed under the stove. The removal of the slab beyond the contour of the projection of the stove is at least 0.6 m in all directions.

The stove must be at least 0.6 m away from concrete walls or covered with refractory plaster on vermiculite. At least 0.8 m from ordinary plastered walls without wallpaper. If any decorative wall decoration is combustible or can decompose when heated (paint , plastic, wallpaper), the stove must not be moved closer than 1.2 m to it. The use of stationary metal stoves for heating wooden buildings is allowed by fire safety rules in exceptional cases with special permission.

Now, if the stove is a factory one and a chimney is provided in the house, it remains to put heat and fire insulation (see below), connect the stove to the chimney and, without making the slightest fire, call the fire inspector for examination. As a rule, it is limited to small remarks, and after payment of state fees, permission to operate the furnace is issued. The whole procedure will cost about $150 and about a month of time.

If there is no chimney, it must be made and legalized by firefighters and SES separately, before installing the stove. In the case of a branded purchased stove, this is easier: the specifications for a good stove must also be accompanied by specifications for the chimney. Having fulfilled it according to the requirements, you can safely go to the firefighters: after examination and payment of what follows to the treasury, the necessary papers will be issued. Things are worse with the “left” chimney; an approved project is needed for its construction. They will consult free of charge where to order it and what should be in it at the local branch of the VNII PO (VNII Fire Protection Ministry of Emergencies). The bad thing here is that there are branches or departments of VNII PO only in fairly large cities (from 150 thousand approximately), and they do not provide online consultations.

And it turns out really badly if the stove is completely homemade: in order to legalize it, it will first have to be certified in the same VNII PO. Moreover, with long-burning furnaces, any on liquid fuel and gas, you can not go there: they are certified only by the factory ones. There is no law on punishment for home-made stoves, so they won’t be fined for the “left” one. But, if the property is insured, then the mere presence of such a stove, even if it is cold lying far away in the closet, makes the case not insured. And if some “suddenly something” caused damage to the neighbors, it is better to immediately pay off amicably, there will be nothing to cover in court.

Finally, if all these vicissitudes are passed, we put insulation: at least 4 mm of asbestos or basalt cardboard, and on it a sheet of iron with a thickness of 1.5 mm. Removal of insulation from the furnace contour at least 50 mm on the sides and rear and at least 300 mm in front of the furnace. If the furnace is shielded, the offset is calculated from the contour of the shield. Now to the firefighters, as already mentioned, and, after the elimination of the shortcomings indicated by the inspector and the issuance of a permit, you can drown.

Sample drawings

Generally speaking, it is easier to buy a room potbelly stove and a buller. Therefore, for example, we give drawings of 2 popular designs: a small bath potbelly stove, 40-50 cubic meters. m of premises, with a water heater, and a garage furnace for testing. For a potbelly stove, a steel or aluminum storage water tank from 100 liters without thermal insulation is needed, and for an oil stove - a chimney from 4.5 m in height with a condensate collector. The material both there and there is ordinary 4 mm steel.

Video: an example of self-made metal sauna stove

About fireplace stoves

For a fireplace stove, aesthetics are more important than heat engineering. With regard to metal, it is best to buy a ready-made fireplace insert, and apply creativity in design terms. On sale there are special fireplace cassettes, or fireplace cassettes, see fig. on right. They differ from a conventional firebox with a built-in smoke box and an afterburner. The fireplace cassette is more expensive than a simple firebox, but it pays off with simplified requirements for the chimney, and the fins on the afterburner allow you to arrange air heating of the room. You can embed a fireplace cassette anywhere, its outer surface heats up no higher than 70 degrees. Registration in the Ministry of Emergency Situations is not required.

How to paint the oven?

Bare metal looks bad even in a garage or barn and is more prone to corrosion than painted metal. But ordinary paint for the oven will not work, it holds no more than 140-160 degrees. So, how to paint a metal stove?

Silicone and organosilicate enamels are suitable for painting hot surfaces. Who knows that silicon in Latin is silicium, do not be surprised. In organosilicon compounds, hydrogen atoms (and not carbon, as is often incorrectly thought) are partially or completely replaced by silicon. And in organosilicates, the silicon-containing filler is mixed with an organic binder, which evaporates upon drying.

Organosilicon enamels are heat-resistant up to 800 degrees Celsius for 5-12 hours, but are more expensive than organosilicate ones, about 180 rubles / kg versus 150. The heat resistance of organosilicates is 250-350 degrees. Taking into account the fact that the consumption per unit area of ​​organosilicon is higher, and it is heavier, the cost of the finished coating is about twice as high. According to the UP-1 device, organosilicates are also approximately twice as strong as organosilicons for chipping.

Based on this, actually it is better to paint the oven with organosilicon, and its screen with organosilicates. In terms of chemical resistance, they are equivalent. The quality and price of foreign and domestic manufacturers differ little. Of the domestic ones, Certa and KO-828 have proven themselves well; from foreign ones - Norwegian Jotun.

How to paint

Heat-resistant enamels for metal are applied only on a clean, fat-free surface from a spray gun in a warm, dry room. Do not paint with a brush or roller. Apply necessarily in 2 layers; the second after the complete drying of the previous one. According to the specifications on enamels, they can also be applied in sea fog at sub-zero temperatures, but only in an electrostatic field using special equipment. Up to the 3rd degree (without a noticeable tack), the enamels dry out in 20 minutes - 3 hours, but for full readiness to keep the heat, the product must be kept for at least 7 days. It is unacceptable to speed up drying with a hair dryer or a stove, the coating will peel off.

Where to begin?

So which stove is better to make first? No doubt - to room potbelly stove with afterburner and hob. If electricity suddenly disappears, gas or coal runs out, and there will be no delivery, she will always help out. At home, it does not take up much space in the pantry, but in the country it can be stationary. Then, as needed, the same potbelly stove without much difficulty will acquire improvements.

As for seemingly simple long-burning furnaces, they are highly efficient precisely because their heat engineering and thermochemistry are very complex. It should be taken for a long-heating stove only after gaining experience.

Conclusion: where metal is good

In everyday life, metal stoves are used more as alternative emergency sources of heat. The second extensive area of ​​​​their application is the periodic heating of utility and utility rooms, incl. country houses. For continuous heating of industrial premises, heaters are optimal.

In residential premises, the role of metal stoves is mainly decorative, as ready-made purchased fireplace stoves. As stationary heating stoves for heating houses, they are poorly suited for safety requirements.

In the monatomic state under normal conditions, only noble gases are found. The remaining elements do not exist in the form of an individual, as they have the ability to interact with each other or with other atoms. In this case, more complex particles are formed.

In contact with

A set of atoms can form the following particles:

• molecules;
• molecular ions;
• free radicals.

Types of chemical interaction

The interaction between atoms is called a chemical bond. The basis is electrostatic forces (forces of interaction of electric charges) that act between atoms, the carriers of these forces are the nucleus of an atom and electrons.

The electrons located at the external energy level play the main role in the formation of chemical bonds between atoms. They are the most remote from the core, and, consequently, are associated with it the least firmly. They are called valence electrons.

Particles interact with each other in various ways, which leads to the formation of molecules (and substances) of different structures. There are the following types of chemical bonds:

• ionic;
• covalent;
• van der Waals;
• metal.

Speaking about different types of chemical interaction between atoms, it is worth remembering that all types are equally based on the electrostatic interaction of particles.

metal chemical bond

As can be seen from the position of metals in the table of chemical elements, they, for the most part, have a small number of valence electrons. The electrons are bound to their nuclei rather weakly and are easily detached from them. As a result, positively charged metal ions and free electrons are formed.

These electrons, freely moving in the crystal lattice, are called "electron gas".

The figure schematically shows the structure of a metal substance.

That is, in the volume of a metal, atoms constantly turn into ions (they are called atom-ions), and vice versa, ions constantly receive electrons from the “electron gas”.

The mechanism of formation of a metallic bond can be written as a formula:

atom M 0 - ne ↔ ion M n+

Thus, metals are positive ions, which are located in the crystal lattice in certain positions, and electrons, which can move freely enough between atom-ions.

The crystalline grid represents the "skeleton", the core of matter, and electrons move between its nodes. The forms of crystal lattices of metals can be different, for example:

• the volume-centric cubic lattice is characteristic of alkali metals;
• face-centric cubic lattice have, for example, zinc, aluminum, copper, and other transition elements;
• the hexagonal shape is typical for alkaline earth elements (an exception is barium);
• tetragonal structure - in indium;
• rhombohedral - in mercury.

An example of a metal crystal lattice is shown in the picture below..

Differences from other types

A metallic bond differs from a covalent bond in strength. The energy of metallic bonds is less than covalent ones by 3–4 times and less ionic bond energy.

In the case of a metallic bond, one cannot speak of directionality, the covalent bond is strictly directed in space.

Such a characteristic as saturation is also not typical for the interaction between metal atoms. While covalent bonds are saturable, that is, the number of atoms with which an interaction can occur is strictly limited by the number of valence electrons.

Communication diagram and examples

The process occurring in the metal can be written using the formula:

K - e<->K+

Al-3e<->Al 3+

Na-e<->Na+

Zn - 2e<->Zn2+

Fe-3e<->Fe3+

If we describe in more detail the metallic bond, how this type of bond is formed, it is necessary to consider the structure of the external energy levels of the element.

An example is sodium. The only valence 3s electron present at the outer level can freely move along the free orbitals of the third energy level. When sodium atoms approach each other, the orbitals overlap. Now all electrons can move between atom-ions within all interlocked orbitals.

Zinc has 2 valence electrons as many as 15 free orbitals in the fourth energy level. When atoms interact, these free orbitals will overlap, as if socializing the electrons that move along them.

Chromium atoms have 6 valence electrons and all of them will participate in the formation of an electron gas and bind atom ions.

A special type of interaction, which is characteristic of metal atoms, determines a number of properties that unite them and distinguish metals from other substances. Examples of such properties are high melting points, high boiling points, malleability, ability to reflect light, high electrical and thermal conductivity.

The high melting and boiling points are explained by the fact that the metal cations are strongly bound by the electron gas. At the same time, a regularity is traced that the bond strength increases with an increase in the number of valence electrons. For example, rubidium and potassium are low-melting substances (melting points of 39 and 63 degrees Celsius, respectively), compared to, for example, chromium (1615 degrees Celsius).

The uniformity of the distribution of valence electrons in a crystal explains, for example, such a property of metals as plasticity - the displacement of ions and atoms in any direction without destroying the interaction between them.

The free movement of electrons in atomic orbitals also explains the electrical conductivity of metals. Electron gas when applying a difference potentials goes from chaotic motion to directed motion.

In industry, not pure metals are often used, but their mixtures, called alloys. In an alloy, the properties of one component usually successfully complement the properties of another.

The metallic type of interaction is characteristic of both pure metals and their mixtures - alloys in solid and liquid states. However, if the metal is transferred to a gaseous state, then the bond between its atoms will be covalent. The metal in the form of a vapor consists of individual molecules (one- or two-atomic).

A self-made metal door makes it possible to save a lot of money. Making a door is not so difficult for those who know how and love to do everything with their own hands. In order to start work on the manufacture of the structure, it is necessary to complete a drawing of a metal door. It is necessary for the exact observance of the technological process of manufacturing the product, namely the dimensional features and the location of the rotary and locking devices. Metal doors are designed not only to protect against the penetration of those who like to "profit" from other people's property, but they are also a guarantee of a peaceful sleep and relaxation in the apartment.

The reliable door well isolates the room from noise, keeps heat and a cosiness. Those who really care about their family and home should choose an iron door. For example, wooden doors do not have such a burglary protection system as metal ones. In addition, the tree has the property of deformation under the influence of moisture. Also, do not forget about the aesthetic appearance. The door leaf is the beginning of the interior of any room.

Iron door drawing

The first, most important stage is the implementation of a sketch of the product, according to which the drawing will be made. In order for the drawing to be correct, it is necessary to make measurements, taking into account an additional distance of 2 cm from the wall to the future door. This distance is necessary so that the canvas closes and opens without additional effort. Let cracks form better - they can be easily eliminated with mounting foam.

The drawing of the iron door includes a canvas diagram. This door element consists of a metal frame with stiffeners, door locks, sheathing in the form of metal sheets, internal thermal insulation materials and hinges. The frame drawing contains a diagram of the steel frame and the procedure for attaching the door leaf to the frame.

There are some features of the assembly drawing of a metal door: it is necessary to determine the direction of the stiffeners in the structure. They can be arranged horizontally, vertically, or even intersect (like a grid). The drawing defines the number of steel sheets in the door structure. The diagram should also include the number of loops and their location. Most often put two loops.

You can also make sliding doors with your own hands. When making a drawing for sliding metal structures, it should be borne in mind that there are no hinges in such doors, since the canvases move along guides. It is also possible the use of several canvases in the design.

Making a door with your own hands

An iron door with your own hands can be quite within the power of everyone. Of course, its manufacture is a very laborious process, but with the necessary knowledge and skills, you can make a good quality structure in a short period of time. There are both simple and more complex designs. The model range of entrance metal doors was replenished with sliding doors. This is a real revolution, because before the entrance sliding doors simply did not exist.

This design is the first metal entrance door that slides along the opening, and has the same technical characteristics as traditional entrance doors, and also has a beautiful appearance. But since such entrance structures are rarely found in construction, the topic of how to make sliding doors with your own hands can be left and settled on the traditional version by the method of opening. These are hinged iron doors.

Structural scheme of a metal door

Before proceeding with the manufacture of a metal door, it is necessary to prepare a doorway, dismantle the old door structure, and thoroughly clean the walls. Next, you need to take measurements and draw a drawing of the future iron system. It is necessary to prepare materials and tools that will be needed during work. Required tools:

• drill;
• welding machine;
• measuring tool;
• screwdriver or a set of screwdrivers;
• Bulgarian;
• a table or goats for collecting a door structure;
• clamps;
• building level.

Necessary materials:

• door hinges;
• anchor bolts;
• profile pipe 5x2.5 cm, 9 running meters (6 running meters per door frame and 3 running meters for stiffeners);
• mounting foam;
• paint for metal;
• door fittings (locks, handles, etc.);
• steel sheet 1.5-2 cm thick (2x1 m);
• metal corner 3.2x3.2 m (6 running meters for the door frame).

Scheme of the device of a metal door

Do-it-yourself metal doors, work order.

1. Assembly of the door frame. According to the dimensions taken, cut the profile pipe, taking into account the gaps between the profile and the wall, approximately 1.5-2 cm. Cut the ends of the profile pipe at an angle of 45 °. Fold the cut material to the workplace. After leveling, lay out in the form of a box, then fasten with clamps. Start welding from diagonal cuts, while constantly monitoring the correct geometry of the entire structure. Seams after welding should be sanded. Weld steel strips to the box, with their help the box is attached in the doorway. Drill holes in them.
2. Door leaf manufacturing. Take measurements on the inner walls of the completed box, subtract the gap of about 7-10 cm on each side and get the actual dimensions of the canvas frame. Using a grinder, prepare the material for the frame in the same way. Saw off the bearing corners to the specified size and lay them in the inner cavity of the future door leaf. After the correct arrangement of the elements, level and weld the frame. You should get a frame for the door leaf. Next to the profile structure, fix the steel sheet. It should protrude from the frame by about 10 mm on each side. Do not make a continuous seam, this can lead to deformation of the sheet. After the steel sheet and door frame are fixed and welded, lay the stiffeners inside, weld with a grip after 5-7 cm. Determine and mark the places for the peephole, lock, handle and hinges, then drill and clean.
3. Installing loops. This etam is an important and therefore rather complicated process. Canopies should be located strictly along one axis. The lower elements of the hinges (with balls) are welded to the box, and the upper ones to the skin.
4. Grinding of all welding places, priming and painting of the product. Install the peephole and lock into the prepared cutouts. If necessary, sheathe the door leaf with selected materials.

The metal structure is ready. It is not easy to make such a product. It takes a little perseverance and skill, and the result will exceed all expectations.