Dip painting at home. Dip coloring. Influence of the Geometric Characteristics of the Substrate Surface Quality on the Adhesion of Powder Coating Materials

Application paintwork materials dipping- a simple and productive method that can be successfully applied in both mechanized and non-mechanized production.

Method Essence consists in the fact that the products to be finished are immersed in a bath filled with a paint and varnish material, then removed from the bath and kept for a certain time over the bath or tray for the excess paint material to drain from the surface. The quality and thickness of the coating are determined by the properties of the surface, as well as chemical and structural mechanical characteristics of the applied material.

The condition for the application of this method is a simple, well streamlined shape of the product, without internal nests and cavities in which paints and varnishes could linger. This method can be used to finish molded products, legs of chairs, tables, cabinet products, handles of knives, tools, spinning rods, bent-glued elements of sofas, armchairs, parts of agricultural machines, wagons, cars, etc.

Application scheme liquid materials dipping method on the example of a flat plate is shown schematically in fig. 4.13. When immersed, the rate of immersion of the parts in the bath, however, should not be high, since when the part is quickly immersed, air is carried along, which forms bubbles on the coating of the part when it is removed from the bath.

When removing the product from the liquid at a constant speed v c not only the adsorbed liquid layer is carried away; due to adhesion and internal friction F movement will be transmitted to parallel layers of varnish

When dipped in drying liquids, such as paints and varnishes, the process is complicated by a continuous change in the viscosity of the applied layer, as a result of which its runoff slows down and then stops. Obviously, quick-drying paints and varnishes, under other conditions, form more uneven and thick coatings than slow-drying ones.

Application of paints and varnishes by dipping can be carried out in various options. In conditions where the volume of painting work is small, and the products to be painted have a small mass and dimensions, use baths in which products are immersed and removed manually.

Viscosity of fresh varnish should be 30 ... 40 s according to VZ-246, the viscosity of the varnish in the working bath during operation is 40 ... 70 s. The temperature of the varnish in the bath must be maintained by cooling 16.. .20°C.

Finishing wood products by dipping has the following advantages: it does not require complex equipment, as well as highly qualified personnel to maintain installations; possibility of full mechanization; simultaneous finishing of external and internal surfaces a large number various products; practically no loss of paintwork materials; the possibility of creating a coating with high quality indicators in one technological operation without refining; combination of priming and varnishing operations on the same equipment.

To disadvantages the method may include the possibility of finishing products of only a streamlined shape without internal cavities and ledges; uneven coating thickness; the need to create special conditions for increasing the viability of reaction systems; necessity large volumes working solutions of paints and varnishes; loss of solvents from the open bath mirror.

For a product of a simple shape without internal corners LKM can be applied by methods of jet pouring. Slow drying coatings (alkyd, melanin) are used. Primers, enamels, paints are used, varnishes are not used.

This method is used to finish building products(windows, doors).

Scheme of installation of jet pouring

I - entrance vestibule, II - dousing chamber, III - steam tunnel.

1 - overhead conveyor, 2 - product, 3 - air curtain, 4 - container with coatings,

5 - pump, 6 - pipeline for supplying coatings, 7 - stack for coatings.

In the pore tunnel, drying does not occur, but on the contrary, liquefaction of paintwork materials occurs, for a stack of excess paintwork materials.

It is used when finishing products of a streamlined shape: legs of chairs, cabinets, sideboards. Essence: the products are immersed in a container filled with paintwork materials, and then, after a short exposure, they are removed and kept in it until the excess paintwork material drains completely. The excess is collected in special containers after cleaning and dilution with a solvent to a working viscosity and is reused. The quality of the finish depends on: the speed of immersion and extraction of the part, the viscosity and temperature of the paintwork material, the dry residue of the paintwork material, the shape of the part.

The method under consideration has advantages: paintwork losses are reduced (since excesses are used after draining)

The number of applied layers is reduced (the use of paintwork materials with a large dry residue), the finishing process can be automated and mechanized.

The disadvantage is the difficulty in obtaining coatings of uniform thickness along the height of medium and large parts, especially with a length of over 300 mm.

Dipping and pouring are the simplest and longest used methods of staining. They allow you to apply various paints and varnishes and get enough coverage good quality using simple equipment. By dipping a product into a paint-and-lacquer material, or pouring it over the product, it is possible to paint over almost all parts of the surface, including those hidden from the human eye, which is not achieved using other methods.

Dipping and pouring are mainly used to obtain primer and single-layer coatings on products. of varying complexity small and medium sizes. They are used in many industries (automotive, instrument-making, agricultural engineering, etc.), because they allow you to mechanize and automate the painting process.

Disadvantages of the methods: uneven thickness of the coatings along the height of the products, the impossibility of painting products with pockets and internal cavities, relatively large losses of paints and varnishes, often reaching up to 20% or more. Many of these shortcomings, however, are eliminated if the object of dyeing is flat products ( wooden shields, metal sheets, roll material) laid horizontally. At the same time, the paint and varnish material is applied using varnish pouring (varnish coating) machines. It was during the painting of such products, especially panel furniture, that the method of pouring was used.

Reducing the loss of paints and coatings and coatings with different thicknesses while improving their decorative look achieved by exposure of freshly painted products in solvent vapors. This method, as a kind of pouring method, called jet pouring, has become widespread in the industry. Similarly, dip coatings can be improved. Other varieties of the dipping method are the dyeing of long products by pulling and coating small products in rotating drums.

Dipping and pouring in any version are of particular interest when applying water-borne paints and varnishes in connection with the possibility of organizing in-line fire-safe technological processes.

Fundamentals of ways. The principle of application by dipping and pouring is based on wetting the surface to be painted with a liquid paint and varnish material, holding it on it in a thin layer due to the adhesion and viscosity of the material. The quality and thickness of coatings during painting by dipping and pouring are determined by the properties of the surface, as well as the structural and mechanical characteristics of the applied material.

Consider the process of applying liquid paint by dipping a product into it, for example, a flat plate (Fig. 8.13). The initial act is the immersion of the product in a liquid material, i.e., the establishment of adhesive contact. Depending on the viscosity of the material and the nature of the surface, this process can take seconds or minutes. Simultaneously with the establishment of contact, the adsorption interaction of the liquid with the solid surface occurs.

Rice. 8.13. Scheme of the forces acting on the liquid when removing the product from it

Rice. 8.14. Velocity distribution in the liquid layer when the product is removed from it

When removing the product, for example, at a speed w0, not only the adsorbed liquid layer will be entrained; due to adhesion and internal friction F, the movement will be transmitted to parallel layers of the liquid, but with a speed wp. In addition to the force F, these layers will experience gravity P, causing the liquid material to sink (flow) at a speed wp. the total speed of movement of each elementary layer wx, located at a distance x from the surface of the products, i.e. will be equal to:

wх = wп - wр. (8.10)

Under the condition of laminar motion and the exclusion of gravity, the speed of individual layers changes uniformly as they move away from the product by a distance, and becomes zero. In this case, the dependence wп \u003d f (x) is straightforward (Fig. 8.14), and the velocity gradient dwn / dx \u003d const.

In real conditions, when gravity P acts, the nature of the dependence changes, the volume of liquid extracted by the product is always less (in Fig. 8.14 it is shown as a shaded area).

If we take the layer width as a unit, and the thickness as dx, then dV will be: dV = wx × dx, and the volume of the entire liquid entrained by such a product per unit time will be equal to:

V=wх×dx. (8.11)

After removing the product from the liquid, part of it drains, and if it is a non-volatile liquid, then regardless of the extraction rate, a layer remains on the surface, the thickness of which is determined by the viscosity, density and energy factors, the interaction of the liquid with the solid surface.

When dipped in paints and varnishes, the process is complicated by a continuous change in the viscosity of the layer applied to the products, as a result of which its runoff slows down, and then completely stops.

It is easy to see that the thickness and degree of unevenness of the film will be the greater, the higher the product removal rate (Fig. 8.15), the viscosity of the paintwork material and the rate of its increase at the time of draining. From low-viscosity materials (20 s according to VZ-4 and less), relatively thin coatings are formed with a small spread of thicknesses along the height of the product. The same effect is achieved at low speeds for removing products from the paintwork material - 0.1 m / min or less (Fig. 8.16). However, in practice, this leads to a decrease in the efficiency of dyeing: with a decrease in the viscosity of materials, the consumption of solvents increases and, in some cases, it becomes necessary to apply several layers of coating. Reducing the rate of extraction of products reduces the productivity of the installations.

Rice. 8.15. The dependence of the thickness of coatings from oil paint on the speed of removing products from the bath at different paint viscosities (according to VZ-4) at 20°С

Rice. 8.16. Change in the thickness of coatings from cellulose nitrate varnish along the length of the product at different rates of its extraction from the bath

When applying paints and varnishes by the method of dousing, the patterns inherent in dipping are preserved. The layer of liquid supplied per unit surface during pouring, in contrast to spraying, exceeds the limiting thickness at which the liquid can be retained on vertical surfaces due to adhesion forces and internal friction. Therefore, its excess necessarily drains, leaving a layer of uneven thickness on the substrate, and on its descending edge - drips in the form of drops. The running time is mainly determined by the viscosity of the coating material and the rate of evaporation of the solvents included in its composition and for different types varnishes and paints is 5-15min.

Evaporation of solvents can be slowed down or eliminated by exposing the coated product to an atmosphere containing relatively high concentrations of solvent vapors. As a result, the increase in viscosity and surface tension of the paintwork material slows down or stops and conditions are created for it to spread and remove excess from the surface (Fig. 8.17). By changing the viscosity of the starting material, the concentration of solvent vapors, the duration of exposure of painted products in it, it is possible to regulate the thickness of the resulting coatings over a wide range, while improving their uniformity (Fig. 8.18).

Rice. 8.17. scheme for leveling a layer of paint and varnish material when exposed to solvent vapors: 1 - coating profile during conventional dipping; 2 - coating profile during dipping with exposure to solvent vapors

Rice. 8.18. Thickness dependency alkyd coatings from the duration of exposure in solvent vapors at a viscosity of the paintwork material of 20 s according to VZ-4 and different vapor concentrations (a), solvent vapor concentrations of 18 g / m 3 and different viscosity of the paintwork material

As can be seen from fig. 8.18, the coating thickness decreases the more intensively, the higher the concentration of solvent vapors in the steam chamber. Naturally, lower viscosity materials form thinner coatings. Established by experience optimal time exposure of coatings in solvent vapors, which maintains sufficient thickness and at the same time ensures satisfactory uniformity of coatings along the height of products.

With a viscosity of paints and varnishes of 20-40 s according to VZ-4 and a solvent vapor concentration of 15-25 g/m3, this time is 8-14 minutes.

Application of paints and varnishes by dipping. Variants of staining by dipping are very diverse in terms of hardware and technological design.

Fig.8.19. Diagrams of installations for dyeing by dipping:

a - with manual immersion of products; b - with immersion of products on a pulsating conveyor using a lowering mechanism; in - with immersion of products on the conveyor continuous action;

1 - bath; 2 - pump; 3 - pocket; 4 - waste tray; 5 - product

In conditions small-scale production use stationary baths; products are immersed in them using lifts, hoists or manually (Fig. 8.19, a). To prevent the evaporation of solvents in environment such baths, as a rule, are equipped with an onboard suction. In mass production, products are fed into the bath by a batch or continuous conveyor (Fig. 8.19, b, c), while the bath (stationary or rising) is placed in a chamber equipped exhaust ventilation. The continuous bath has a waste tray for collecting the paint material flowing from the products and mixing pumps (in the case of pigmented formulations). Mixing of paints is carried out by their selection from the upper part of the bath or from a pocket and feeding through a pipe with holes into the lower part; material circulation rate 3-5 rpm. You can also mix the paint in the bath with the help of mixers or compressed air; the latter method is not common.

Dipping with exposure to solvent vapors is carried out in baths equipped with a steam tunnel. Depending on the dimensions of the products to be painted, the volume of the baths ranges from several liters to several tens. cubic meters. Particularly large bathtubs are used for staining welded structures, power transmission masts, floors of car bodies and cabins, panel products. Baths for dipping with a volume of 0.5 m3 or more are equipped with an emergency drain - a pipe and an underground tank for evacuating flammable paintwork material in case of emergency. The speed of continuous conveyors in dip painting is usually less than 2.5 m/min.

Using the dipping method, any storage-stable paints and varnishes can be applied: bituminous, glyphthalic, pentaphthalic, urea- and melamine-formaldehyde, epoxy, etc. When painting small products, cellulose nitrate varnishes and enamels are often used. More convenient for dipping are non-pigmented paints and varnishes.

Coloring of flat products by pouring. Pouring is a type of pouring method, in which the paintwork material is applied to flat (or slightly curved) horizontally laid products in a strictly metered amount. Dosing provides for the supply of the same amount of material per unit surface, precisely such that its runoff is excluded and at the same time good leveling (spreading) is achieved on horizontal surface. For this purpose, varnish or paint is applied to the surface in the form of a flat jet (veil) covering the entire width of the product. Such a curtain can be obtained by draining liquid through a horizontal threshold (dam), or a narrow slot in the wall or bottom of the vessel. If the curtain is evenly carried over the product at a certain speed or the product is passed through the curtain (which is technically more convenient), then the surface will be covered with a uniform layer of paint and varnish material. Varnishing and painting of many types of products is based on this principle: panel furniture, chipboard and fibreboard, cardboard, plywood, door panels, skis, bar materials, etc.

Distinctive features of the filling method - high productivity, low losses of paints and varnishes, the possibility of applying coatings of different thicknesses (up to 300 microns) in one layer - make it possible to attribute it to the most promising methods of painting.

For application in bulk, various varnish-filling machines are used. The principle of their work is clear from Fig.8.20.

Rice. 8.20. scheme of operation of the filling machine lacon: 1 - filling head; 2 - coated product; 3 - transporting devices; 4 - receiving tray; 5 - settling tank; 6 - pump; 7 - filter

The coating material is fed onto the product from the pouring head. The material that did not get on the product (the length of the curtain is usually greater than the width of the product) flows through the receiving tray into the settling tank, from where, freed from the bubbles of air entrained by it, it returns to the cycle again. The process is carried out continuously. The products to be painted are moved automatically by means of conveying devices. The most important part of lacquering machines is the pouring head. It determines the profile of the outflowing jet and the flow rate of the coating material. Filling heads with a bottom slot (the most common type), with a drain dam, with a drain dam and a screen have found application; optimal distance from the filling head to the product is 50-100 mm.

The regulation of the supply of paints to products in coating machines is carried out by changing the width of the gap, pressure or volume of the material entering the pouring head.

The thickness of the coatings can also be changed by changing the speed of movement of the devices transporting the product. When painting and varnishing furniture products, the LM-3 varnish filling machine is widely used. It has two pouring heads and allows you to paint both flat parts and edges of products up to 2.2 m wide. The speed of movement of products can be varied within 10-170 m/min.

Coating machines (LM-3, LM-140-1, LMK-1, etc.) are a very productive and economical type of painting equipment. With automated feeding and removal of products from the conveyor, the productivity of the painted surface can reach tens of thousands square meters in hour.

When applied by pouring, in principle there are no restrictions on the use of any liquid materials. Since the pouring method is used mainly for finishing wood products, application is mastered in the first place. furniture varnishes and cellulose nitrate (I) and polyester (II) enamels. The main technological parameters of their application are given below:

Working viscosity according to VZ-4, s 80 55-100

Product movement speed, m/min 60-90 50-80

Average consumption of materials, g/m2 120-200 400-500

Thickness of single-layer coatings, microns 25-40 200-300

Components polyester varnishes mixed immediately before application (in the case of machines with one head) or during application (in the case of machines with two filling heads). By pouring it is possible to apply single-layer and multi-layer, homogeneous and heterogeneous coatings. When applied, only one side of the product is painted - the top. If necessary, paint reverse side or ends (edges) of products, they are turned over and the process is repeated. The most common coating defect is gas filling. It occurs as a result of air entering the jet of paint or its microdispersion in contact with a fast-moving surface. The elimination of this and other defects is achieved by changing the parameters of the paintwork material (viscosity, surface tension) and the operating modes of the machines. During the filling process or during the subsequent transportation of products to the dryer, solvents or monomers evaporate. Therefore, in the designs of coating machines, local suction is provided, and the rooms where staining is carried out are equipped with general ventilation.

Dyeing of long products by pulling. It is convenient to paint long products with a constant cross-section along the length (pencils, skirting boards, cornices, wire, pieces of pipes of small diameter) by pulling them through a bath of paintwork material (Fig. 8.21).

Rice. 8.21. Scheme for coloring pencils by pulling:

1 - feed rolls; 2 - pencil; 3 - bath with paintwork material; 4 - restrictive washers; 5 - drying conveyor

In this case, excess material is removed by restrictive rings (rubber washers) blocking the entry and exit of products from the bath. The role of the bath can be a porous material (foam rubber, felt, fabric bag), tightly compressing the surface to be coated. Dosing of varnish or paint on a porous material is carried out through a tube or wick method. When pulling products through a porous material impregnated with varnish, the latter is deposited thin layer on the surface of the product. This method is carried out, in particular, the varnishing of wires at the enterprises of the electrical industry.

For varnishing and dyeing by pulling, both fast- and slow-drying paints and varnishes are used: cellulose nitrate, oil, alkyd, polyester, epoxy (single-pack), etc.

So, pencils are coated with nitrate cellulose varnishes and enamels with a relatively high viscosity and a dry residue content of 50-60%. The pencil pushed out at the bath enters the receiving (drying) conveyor.

To coat the wire, varnishes with low-volatile solvents (kerosene, white spirit, cresols, etc.) are mainly used; coatings are cured in convective or induction type dryers at high temperatures. The thickness of single-layer coatings during pulling is small 2-5 microns, therefore, it is envisaged to apply several layers - from 2 to 12.

The pulling method is productive, economical enough, allows mechanizing and automating the painting process, however, it has great limitations in terms of the shape of the coated products.

Application of paints and varnishes in drums. The simplest and most cost-effective for small mass-produced products (shoe clips, hooks, loops, buckles, bolts, nuts, tool handles, typewriter parts, etc.) is the dyeing method in drums. Mechanical drums are used. They provide draining of paint and varnish material and often drying of products during rotation. In the latter case, feed into the drum is provided warm air and removal of solvent vapors from it. Products are loaded into the drum usually by 1/2-2/3 of the volume. The paintwork material is poured in such a way as to completely wet the products. Drum rotation time 5-7 min, rotation frequency 75-120 rpm. If the coatings are dried outside the drum, then the products are unloaded onto the nets and, after the excess paint has run off, they are sent to the dryer.

There are designs of drums in which the coloring of products is carried out not by immersion in the paintwork material, but by spraying it. At the same time, in the case of thermosetting varnishes and paints, their multilayer application is possible with drying of each layer directly in the drum during its rotation. Instead of drums, centrifuges can be used. Products are loaded into a perforated basket of a centrifuge, lowered into a container with paint, and after removing from it, the centrifuge is rotated to remove excess paint and dry the products.

For application in drums and centrifuges, mainly quick-drying paints and varnishes are used - bituminous and cellulose nitrate varnishes and enamels, in each case they are selected empirically. The coatings have a low finish class (not higher than III), there are defects in the places where the products come into contact, streaks are possible.

The dip (dip) painting method is highly economical and ecological way painting, which is one of the most modern surface technologies. The main area in which this method finds application is the automotive industry (painting of car bodies and their parts).

This method is also widely used for painting home household appliances(refrigerators, washing machines, radiators, etc.), agricultural machinery, metal furniture, building structures etc.

Compliance with very stringent surface quality requirements can be achieved by using electrophoretic painting methods (mainly cataphoretic KTL method), which, due to the properties of the process and the properties of the resulting coating, currently have no comparative competition in certain industries.

KOVOFINIŠ offers a complete line of equipment for dip painting, both by dipping in classic or water-based paints and by electrophoresis (cataphoresis and anaphoresis). At the request of the customer, our company is ready to offer equipment for both intermittent action and through-flow (continuous).

Clock type lines are characterized by high flexibility of operation. It is advantageous to use them for small volume, frequently changing shape of products, as well as for products large sizes. Continuous lines are convenient to use when high productivity is required, mass production or large-scale production of similar parts.

Our company supplies this equipment on a turnkey basis, including equipment for pre-treatment, varnish (paint) firing, exhaust air purification, handling equipment and transportation systems, control systems, visualization of the technological process, as well as equipment for preparing water for processes and waste water treatment.

We supply:

• cataphoresis painting lines (KTL)
• anaphoresis color lines (ANL)
• dip and spray painting lines

The dip dyeing method is widely used in various industries industry. It is simple and productive. But due to the fact that the resulting coatings have low decorative properties and uneven in thickness, the method is used mainly for applying slow-drying primers (phenolic, glyphthalic, etc.) and for painting products that do not require high coatings. decorative requirements. The quality and thickness of the coatings depend on the viscosity of the applied material, temperature, solids content in the paint or primer, brought to the working viscosity, and other factors.

To obtain coatings that are relatively uniform in thickness, the working viscosity of glyphthalium materials is recommended on the order of 20 ... 25 s, and phenolic primers 16 ... 18 s according to the VZ-4 viscometer at 20 °C. The speed of removing parts from the bath should be low, with an increase in speed, the unevenness of the coatings in thickness increases. Immersion and removal of parts from the bath must be done smoothly. Immersed parts or products must be completely covered with paint and varnish material, accumulation of materials in the recesses (pockets) of the product when removing it from the bath is not allowed, and the formation of noticeable smudges on the painted surface is also not allowed.

Parts should be hung on fixtures with a minimum distance

nothing between them. This contributes to a more complete runoff of excess applied material. The duration of dripping at a temperature of 18 ... 25 °C is recommended to be at least 10 ... 12 minutes. The slow runoff helps to achieve more uniform coatings and prevents the formation of large build-ups and streaks. Parts after dipping should remain in the same position for the period of paint dripping and drying as when dipped.

As the bath is used, the viscosity of paints and varnishes increases, mainly due to the volatilization of solvents, therefore it is necessary to correct it periodically by adding appropriate solvents.

Installations for painting by dipping are simple.

If the volume of painting work is small and the details small size, then for priming the parts are immersed in the bath manually. After dipping, they are hung on hooks to drain excess paint material and dry. In such cases, the bath shown in Fig. 31. The body of the bath 1 is equipped with a hood 6 to remove solvent vapors evaporating from the surface of the bath. Mixing is carried out by a pump 3 driven by an electric motor 4 installed on the base 5. For painting, the parts are placed in mesh baskets, dipped into the bath, then placed on the mesh 2 to drain excess paint through the gutter 7 and return to the bath. Tap 8 serves to drain the paint.

In conditions of mass production, when products are supplied continuously, dip painting is carried out when products are fed by an overhead single-chain or double-chain conveyor.

Spatulas are used to apply putties in order to even out irregularities on the surface. Spatulas are thin elastic plates made of steel and various types of wood (beech, ash, birch) and reinforced plastic. Steel spatulas (Fig. 32, a) are made in the form of blades with wooden handle. The blade is somewhat beveled for ease of use. The most commonly used spatulas with a width working surface 30 ... 100 mm. Wooden spatulas (see Fig. 32, b) are made with a pointed and beveled blade 40 ... 200 mm wide. For putty-

Rice. 32. Spatulas

metal; b - wooden

APPLICATION OF PUTTY

Rice. 33. Working with a spatula

For surfaces with roundings, small rubber plates are used.

When working, the spatula must be held obliquely with the handle forward in the direction of travel (Fig. 33). With this position of the spatula, the putty is better distributed over the surface and the irregularities are more completely filled. Putty should be applied in strips, with each subsequent strip should capture the edge of the previous one with a thin layer of about 0.2 mm.