How to straighten iron at home. Metal bending and straightening technologies. The main methods of straightening metal

Flame straightening of metal

Editing is a technological operation, during which local plastic deformations modify initial form sheet, blank or product. Yes, supplied metallurgical industry hot-rolled sheet steel may have waviness (curvature of sheets in the longitudinal direction) and warping up to 12 mm per 1 m. Distortions in the shape and supplied profiled steel are allowed. The manufacture of welded structures inevitably leads to their deformations and warping.

To cut precision blanks by mechanical means, oxygen or plasma cutting, it is necessary to have sheets from which they are cut, the most correct flat shape. Therefore, before cutting, the most deformed sheets must be corrected. For sheets of limited thickness, this is carried out by straightening in multi-roll rolls or cold presses or by heating the straightened metal. In this case, straightening by bending is carried out without shock (in rolls, clamps), or shock (with strikers, hammers, sledgehammers). However, mechanized dressing methods are limited in their use by the thickness of flat elements up to 100 mm.

With regard to structures of complex shape, these methods are generally inapplicable and for them straightening by local heating is used, in particular gas-flame straightening, which has received significant development in recent years.

The physical essence of flame straightening consists in changing the linear dimensions and shape as a result of the occurrence of localized plastic deformations caused by local heating of the metal, the free deformations of which are limited by the surrounding, rather rigid areas of the cold metal. So, for example, if in the central part of the sheet (see Fig. 128, a) there is a local bay with a center in zone A, then to align the sheet, you must either stretch all the peripheral zones (which can only be done manually for thin metal metalwork straightening - the creation of plastic deformations of the metal at the edges with hammer blows), or to tighten, reduce the linear dimensions of the metal in the region of the bay. This is achieved by local heating of the coil, for example with a flame, so that the surrounding cold metal would induce compressive stresses above the yield strength in the heated metal. Then, after cooling, deformations of size reduction will appear, and the bay will shrink or completely disappear, aligning with the rest of the sheet surface. Naturally, from the side of the flame, the heating zone will be larger (Fig. 128, b), and, consequently, the final contractions will also be large. Therefore, heating must be carried out from the side of the bulge of the bay.

Since the absolute value of the deformation depends on both the heating temperature and the heating zone, these values ​​must be selected (approximately by calculation, preliminary experiments and accumulated experience) to implement various occasions edits. In this case, of course, with flame heating important characteristic is the intensity of heating. In some cases, when the rigidity of the unheated part of the sheet (structure) is small (for example, the heating zone is large in relation to the entire sheet) and cannot cause the necessary plastic deformations of the heated zone compression during its heating, an artificial increase in the rigidity of the corrected element is used: for example, in case fig. 128, a - tacking along the contour (along individual edges) of hard squares, tees or channels. After the end of editing, these temporary stiffnesses are removed (tacks are cut or cut down, clamps are removed).

Local heating can also straighten elements of a different shape. So, for example, to straighten a square (Fig. 128, c), it must be heated in zone A with a heating spot schematically, in the form of a triangle, a trapezoid (shaded in Fig. 128, c). With sufficient rigidity of the heated system, large plastic deformations of compression (reduction of linear dimensions) of a widely heated edge (in Fig. 128, in the bottom) will lead to its greater shortening and, accordingly, straightening of the bend. Therefore, it is necessary to correctly choose not only the temperature and size of the heating zone, but also its shape, and sometimes, when editing several places, the sequence of heating and cooling. various sites sheet, design.

Heating for dressing can be carried out not only in spots, but also with a linear or wave-like movement of the heating source along the corrected product, causing the corresponding elongated rectilinear or tortuous heating zones (Fig. 128, d). When moving the heating zone, the linear contractions across and along such a zone are not the same. Transverse contractions are usually larger than longitudinal ones. So, if a relatively thin sheet of steel (dimensions 1 m X 1 m) is heated with a strip about 80 mm wide for the entire thickness, then the transverse contraction will be about 0.7-0.75 mm, and the longitudinal contraction will be only -0.15 mm. The value of longitudinal and transverse deformations also depends on the ratio of the overall dimensions of the sheet L / B (Fig. 128, d). The larger the L/B ratio, i.e., the narrower the sheet being heated, the relatively larger the longitudinal deformation. Therefore, for editing flat long elements, it is more expedient to use transverse deformations, and for products such as shafts, bars - longitudinal ones.

The location of the heating strip not along the axis of symmetry leads not only to a reduction in size, but also to a general bending of the straightened element, the value of which also depends on the rigidity of the workpiece (part).

When straightening thick sheets and thick-walled elements, in some cases it is necessary to take into account the possibility of changing the dimensions not only in the main plane, but also the appearance of deformations from the plane caused by uneven heating of them over the thickness, in accordance with Fig. 128b.

Flame straightening can be used not only for steels, but also for sheets and non-ferrous metal products.

At flame straightening both an acetylene-oxygen flame and a flame of various acetylene substitutes can be used. However, in some cases, it is necessary to take into account the possible degree of decrease in the heating intensity, leading to an increase in the heating spot (zone), and, consequently, to a change in the ratio of the heating zone and the rigidity of the surrounding cold metal.

Any additional input of heat into the product and the presence of additional local plastic deformations lead to an increase in the zones of high internal stresses, in particular stretching, reaching the yield point, i.e., to a general increase in the stress of the structure. Under certain conditions, and especially with a small margin of plasticity of the metal structures, this can lead to the appearance of cracks in them even during the manufacturing process or during operating conditions, causing sometimes a small but additional deformation. To prevent such damage or reduce performance characteristics structures that have a large overall tension (from welding, additional straightening), they must be subjected to a general heat treatment to relieve internal stresses.

In connection with the above, technological process the manufacture of welded structures must be built so that they are obtained as close as possible to the required shape and size, to limit their subsequent editing.

Local flame heat treatment

In many cases, in the manufacture of welded structures and in the processing of metal, it is advisable to use local heat treatment using local heating by highly efficient heat sources. Local flame heating is used in the following technological types of processing:

1) surface hardening of parts;

2) local annealing, normalization, tempering to improve the structure and properties of the metal (in particular, welded joints) and the possibility of subsequent machining;

3) local tempering, heating to relieve and redistribute internal stresses, in particular in welded structures;

4) surface cleaning of sheets and structures assembled for welding.

Surface hardening with a gas flame, as having the greatest industrial application and requiring special equipment and apparatus, will be considered in more detail in Chap. XIX.

Local annealing (normalization) or tempering to improve the structure and properties is mainly used for welded joints of alloyed steels and non-ferrous metals. Since in these cases only the weld metal and near-weld sections of the heat-affected zone require improvement, it is possible to apply not a general heat treatment of the entire product, but only a local one, in the area of ​​welded joints. Enhanced heat treatment mode (temperature, holding time, cooling rate) for various metals(as well as the purposes of processing) is different.

Although local heat treatment (even with the use of induction, in particular high frequency heating) is less perfect than general heat treatment, in some cases it provides the possibility of obtaining the desired results with minimal capital costs and using simple apparatus.

In gas-flame local heat treatment, heating to a designated temperature in a given zone is carried out by the flame of conventional burners (and sometimes cutters) using acetylene or its substitutes. Heating is usually carried out by a dispersed flame, which is achieved by choosing the power and moving the mouthpiece far from the heated surface in order to avoid its overheating and, moreover, melting. The heating temperature is estimated at the same time by thermocouples, at lower values ​​by thermal pencils, and with a fairly wide range of heat treatment temperatures (for example, for heat treatment insensitive to temperature low carbon steels) according to the color of heat, assessed visually.

The duration of exposure and the regulation of the cooling rate are limited by the expedient load of the welder. In some cases, slowing down the cooling rate is achieved by additional simple devices that limit heat loss to the surrounding space (use of asbestos blankets, room small parts in devices with dry, sometimes heated sand, etc.).

Local flame heat treatment, in order to facilitate subsequent machining, is used to temper the edges of workpieces hardened during oxygen cutting and less often for local machining (for example, drilling, milling) of hardened parts. As a rule, the requirements for the heating regime in these cases are less stringent than in the previous one and are easily mastered by a qualified operator.

Local tempering for relieving internal stresses is effective only for relatively simple welded joints, for example, the type of pipeline joint, branch pipe welding, etc. The mode of such heat treatment for steel structures is usually set by temperature (usually in the range of 600-680 ° C), exposure time and heating zone width. The methods for performing such processing and adjusting its mode in this case are similar to performing structure improvement processing, but Maximum temperature heating, as a rule, is less, and the holding time is achieved by means that delay cooling.

The redistribution of internal residual stresses in welded structures, mainly in butt welds, can also be achieved by the so-called thermoplastic treatment. At the same time, for the redistribution of stresses, strips with a width of about 80 mm are heated up to about 250 ° C by special multi-flame burners with linear arrangement flame nozzles simultaneously on both sides of the seam at a distance of 100-150 mm from it. As the burners move, the heated strips are filled with water for rapid cooling and non-spreading of heat over a large width. Water is supplied through special channels in the burner, behind the flame nozzles. In this mode, residual plastic deformations appear in the heated zones of the metal, stretching the weld and removing the existing residual tensile stresses in the weld metal and the near-weld zone. However, at the same time, residual stresses arise in the base metal, in the heating and cooling zone parallel to the seams, which are equal, as a rule, to the yield strength and spread over a larger zone than after welding. Due to the fact that such a redistribution of residual stresses, reducing them in the weld, creates approximately the same values ​​in the two zones of the base metal, it is advisable only when mechanical properties weld metal and heat-affected zone is lower than the properties of the metal being welded. At the current state of welding, when in most cases the necessary strength and reliability of the seams are provided, which differs little from the metal of the structure, the method of thermoplastic stress redistribution is almost never used at present.

Flame heating is also used to clean surfaces (to a lesser extent, gaps in structures assembled for welding) from oxides and rust. At the same time, due to a sufficiently concentrated heat input into surface layer heated oxides break off (bounce off) the colder metal and are blown away mechanical action flame. To some extent, with a flame of normal regulation, the reduction of oxides also occurs. For such cleaning of metal, either conventional burners are used (cleaning gaps, areas arriving at the place where the seam will be applied), or fire "mops" - multi-flame burners with long handles and rollers that provide required distance from the flame to the surface of the sheet to be cleaned.

Administration Overall rating of the article: Published: 2012.06.04

Sheet metal dressing performed to give the workpieces the correct geometric shape without bulges, bumps, kinks and dents. Curvature can be corrected manually or on straightening machines, presses. Automatic straightening is more productive and efficient, especially in mass production. Manual dressing sheet is used in repair shops, when performing small or single orders.

The site presents enterprises that carry out both automatic editing and manual editing.

Features of straightening sheet metal

The dressing operation is based on the property of metals to deform under pressure. It can be applied to blanks made of metals with good plastic properties, otherwise the metal will be destroyed during processing. The dressing operation is carried out with a thermal effect on the metal - hot way, or without it - a cold way.

Sheet metal dressing done manually with a hammer or wooden mallet and an anvil or steel/cast iron plate. This is a laborious operation, which has its own characteristics. So, the surface of a sheet of metal should lie on the anvil or plate over the entire area. Irregularities must first be noted with a pencil. Hammer blows are applied in the direction from the edge of the sheet to the bulge in order to avoid greater elongation. As you approach the bumps, the impacts should be more frequent, but less strong. Manual editing is also performed special keys, on the correct plate with pins and squares.

Sheet metal dressing on the straightening machines, rollers and presses. Small and medium workpieces are dressed on roller machines with different numbers of rollers. Sheets are rolled through rollers staggered at the top and bottom. Large-sized sheets are corrected on horizontal stretching machines, where metal fibers are aligned due to stretching.

Metal dressing

Editing is used in cases where it is necessary to eliminate the distortion of the shape of the workpiece - waviness, warping, dents, curvature, bulging, etc. The metal can be edited both in cold and heated form. Heated metal is easier to edit, which is also true for other types of its plastic deformation, for example, bending.

At home, dressing should be done on an anvil or a massive plate of steel or cast iron. The working surface of the stove must be flat and clean. To reduce the impact noise, the hob should be placed on a wooden table, which can also be used to level the hob so that it is in a horizontal position.

For editing, you need a special locksmith tool. You can’t produce it with any hammer that is at hand, the metal can not only not straighten out, but also get even bigger defects. The hammer must be made of soft material- lead, copper, wood or rubber. In addition, you can not rule the metal with hammers with a square head: it will leave traces in the form of nicks on the surface. The hammer head should be round and polished.

In addition to hammers, wooden and metal trowels and supports are used. They are used for straightening thin sheet and strip metal. For dressing hardened parts with shaped surfaces, there are correct headstocks.

It’s probably not worth reminding that metal straightening (straightening) must be done in work gloves, regardless of whether hard work or not, whether the workpiece is large or small, and whether it is severely warped.

To check the curvature of the workpiece, you need to lay it on a smooth plate with that surface, which, after straightening, should be a plane. The gap between the plate and the workpiece will indicate the degree of curvature that needs to be eliminated. Curved places should be marked with chalk - it is much easier to strike with a hammer than when focusing only on the curvature noticeable to the eye.

Editing of strip metal bent in a plane, is the simplest operation. The curved workpiece must be positioned so that it has two points of contact with the anvil. Hits with a hammer or sledgehammer should be applied to the most convex places and reduce the force of blows as the bulges become smaller. Do not strike only on one side of the workpiece - the metal may bend into reverse side. To prevent this from happening, the workpiece must be turned over from time to time. For the same reason, you should not strike several blows in a row in the same place.

If there are several bulges, you must first straighten the edges of the workpiece, and then its middle.

Editing of round metal. This kind of work is basically similar to straightening strip metal. To do this, mark uneven places with chalk and place the workpiece with the bulge up, apply blows to the convex part from the edges of the bend to the middle of the bulge. When the main curvature is corrected, the force of impacts must be reduced and periodically rotated metal rod around its axis to prevent curvature in the opposite direction.

metal rods square section must be done in the same order.

Editing of metal twisted in a spiral, produced by the spinning method. In order to straighten the curvature, you need to clamp one end of the twisted metal into a large vise on the bench table, the other into hand vise. Having untwisted the metal to the extent that can be controlled by eye, you need to continue editing on a smooth, verified plate conventional method, controlling the curvature through the light.

Sheet metal dressing

The complexity of straightening sheet metal depends on what type of defect the sheet has - waviness of the edge, or a bulge, or a dent in the middle of the sheet, or both at the same time (Fig. 15).

Rice. 15. Techniques for straightening sheet metal: a - with a deformed middle of the sheet; b - with deformed edges of the sheet; c - using a wooden trowel; d - using a metal trowel.

When editing the bulge, it is necessary to strike, starting from the edge of the sheet towards the bulge (Fig. 15 a, b).

The most common mistake is that the heaviest blows are applied to the place where the bulge is greatest, and as a result, small dents appear on the bulge area, which further complicates the uneven surface. In addition, the metal in such cases experiences a very strong tensile strain. You need to do just the opposite: the blows should become weaker, but more often, as the edit approaches the center of the bulge. The sheet of metal must be constantly rotated in a horizontal plane so that the blows are evenly distributed over its entire surface.

If the sheet has more than one convex section, but several, you must first reduce all the convexities into one. To do this, strike with a hammer in the intervals between them. The metal between the bulges is stretched, and they are combined into one. Then you have to keep editing. in the usual way. If the middle of the sheet is even, and the edges are distorted by waves, then the sequence of blows during editing should be the opposite: they should be applied starting from the middle, moving towards the curved edges (Fig. 15, b). When the metal in the middle of the sheet is stretched, the waves at its edges will disappear.

Very thin sheets cannot be corrected even with mallets made of soft material: they will not only leave dents, but can also tear thin metal.

In this case, ironing bars made of metal or wood are used for editing, with which the sheet is smoothed on both sides, periodically turning it. The quality of editing can be controlled using a metal ruler.

Anyone who has taken on the straightening of a steel sheet knows that this is a rather difficult job: while straightening one bend, others appear on the sheet. However, this can be avoided and thus significantly facilitate the work. Steel sheet it is necessary to lay for editing not on a smooth plate, as is usually done, but on a lining plate with many small blunt tubercles evenly spaced on its surface. In this case, the quality of work should increase, and the labor intensity should decrease. Metal under the blows of a rubber hammer will, as it were, look for its own place. At the same time, barely noticeable waves are formed on the sheet; during puttying and painting, they will begin to fill up and contribute to the fact that the putty and paint will adhere to the metal very firmly. Irregularities after coating the metal are completely invisible. The only difficulty is how to make the required lining plate. It is really difficult to make it at home: tubercles are usually obtained by cutting through on a smooth plate big number mutually intersecting and closely spaced grooves. You can do this on a planer or milling machine, so if there is such an opportunity, it is better to use it.

Edit hardened metal(straightening)

Soft dressing hammers are unsuitable for straightening hardened metal (straightening). A special hammer with a hardened metal head or with a rounded narrow side is required. You can make a straightening hammer yourself. To do this, it is necessary to make a slot in the narrow head of the hammer and tightly press into it a plate of hard alloy VK6 or VK8, sharpened under a radius of 0.1–0.2 mm.

Hardened metal is corrected by the reverse method: strikes must be applied not to the convex, but to the concave section of the workpiece: it will begin to straighten due to the fact that the metal on the concave side will stretch (Fig. 16).

Rice. 16. Editing of hardened metal (straightening): a - strips; b, c - squares.

Straightening is more convenient to produce not on flat plate, but on a special straightening headstock, which has a convex surface, moving the workpiece up and down along it.

An unsolvable task for an inexperienced locksmith is to edit a flat square, in which the angle has changed and has become more or less than 90 °. Such squares are no longer suitable for checking right angles, and, as a rule, they are thrown away. Meanwhile, the hardened metal square can be straightened. If the right angle has decreased and is less than 90 °, then hammer blows must be applied along the plane of the square at the top inner corner. If the angle has increased and exceeds 90°, strikes should be applied at the top of the outer corner.

After the metal is straightened, you can proceed to its further processing.