Paint preparation
To obtain a high-quality coating, the correct preparation of the paint is of great importance: the selection of color, bringing the paint to the working viscosity, filtering the paint. The synthetic paint ML-197 received the greatest application for VAZ cars. The paint is thoroughly mixed, bringing it to a homogeneous mass. For dilution, use the solvent P-197. The viscosity of paint and other paints and varnishes is determined by a VZ-4 viscometer at a temperature of 20°C. Carefully mixed paint is poured into a cylindrical vessel of a viscometer with a capacity of 100 ml3, passing at the bottom into a cone with a hole of 4 mm, which is preliminarily closed. The paint is allowed to settle in the cylinder to remove air bubbles. The resulting foam is removed with a glass rod and, having opened the hole, turn off the stopwatch. When the continuous stream of paint stops, the stopwatch is stopped. The flow time from the viscometer in seconds is the conventional viscosity. The viscosity of the paint should be 20-22 s. The diluted paint is filtered through a No. 14K mesh or gauze folded in 4 layers.
For mixing paints and varnishes in barrels or other containers, a special paint and varnish installation with a capacity of 23 l / min can be used, which allows you to mechanize the mixing and unloading of paints and varnishes.
Preparation of surfaces for painting
Strong stageability (adhesion) paintwork with a paintable surface can only be obtained after its thorough cleaning of dirt, rust, old paint and grease stains. In preparation, mechanical and chemical methods are used (grinding skins, washes, white spirit or BR-1 solvent gasoline). Machining is recommended after degreasing to prevent premature failure of the abrasive skins.
You can remove old paint, rust mechanically using a mechanized tool: grinders of the MSh-1, I-144, ShR-2 types, etc. Removal of the old complex coating is most effectively done by a chemical method. It is based on the dissolution, swelling of the coating, which turns into a loose state and can be easily removed mechanically.
The chemical method uses organic washes, which are a complex mixture of solvents with evaporative retardants and other additives.
Organic washes SP-6, SG1-7, SPS-1, AS-1, etc. are used. SPS-1 and AS-1 washes are non-flammable, SPS-1 is less toxic compared to other washes. Thus, the SP-7 wash is applied with a brush 2-3 times, depending on the thickness of the paintwork. The softening time of the wash is 30-40 minutes, after which the softened coating is removed with a spatula or brush. Then wipe the surface with white spirit to remove the remnants of the wash, rinse abundantly with water and dry the body. It must be remembered that the wash is not allowed to get on the chrome and rubber parts of the car.
After removing the old paintwork, wet grinding of the painted surfaces is carried out with sanding sheets 55C 4-P. With a small thickness of the coating that does not have mechanical damage, grind mechanically to the epoxy primer of the factory color.
With significant corrosion, as well as surfaces previously painted with nitro enamel, they are cleaned to metal. The body is washed again with water, blown with compressed air and dried. Degrease the painted surfaces with white spirit or BR-1 solvent gasoline and coat with sealing mastic «plastisol D-4A» welds and joints of replaced parts. Remove the remains of the mastic with a rag moistened with white spirit. Surfaces not to be painted are insulated with thick paper and adhesive tape. Then, degreased surfaces polished to metal are coated with GF-073 primer to obtain high adhesion to metal, good adhesion to overlying layers and reliable anti-corrosion properties. The primer is applied with a paint sprayer in a thin uniform layer. For better wetting of the surface to be painted and adhesion to the latter, the working viscosity of the soil should be 23-24 s.
Dilute the primer GF-073 with xylene or solvent. Low viscosity does not provide reliable protection against corrosion, high viscosity does not provide good adhesion to subsequent layers of coatings. Priming should be carried out as soon as possible after surface preparation. After 5 minutes of drying, EF-083 epoxy primer is applied with a second layer. Primer EF-083 is also applied to the surfaces of replaced body parts. Epoxy primer EF-083 provides more reliable adhesion to synthetic enamel. The second layer of EF-083 on the bottom of the body protects the surface from corrosion in cases of water ingress or damage to the anti-noise coating for a long time. Epoxy primer is used for all work, both for tinting and repainting the car body. The viscosity of the soil should be 23-25 s. EF-083 is diluted with xylene or RE-11V solvent. The soil dries at a temperature of 145-150X20 min. To reduce the drying temperature, a catalyst is added: NF-1 desiccant to 5-7% by weight of the soil. As a catalyst, dibutyl phosphate acid can be used up to 4% by weight of undiluted soil. The shelf life of the finished soil with a catalyst is no more than 7 hours.
After priming and cooling the body, wet sanding is carried out with 55C 4-P sandpaper, washed with water, blown with compressed air, and dried. If necessary, putty uneven places. The putty is applied in a thin layer: for lacquer putty no more than 0.3-0.5 mm, for others no more than 0.1 mm. It is not recommended to apply putty more than five layers. The thickened MS-00-6 putty is diluted with xylene to a viscosity suitable for application. After applying the putty, the body is dried at a temperature of 18–20°C for 30 minutes and the putty surfaces are again sanded with 55C 4-P sandpaper. Sanding is necessary to smooth out the roughness left after the putty, and to create a better adhesion between the coating layers. Sand the intermediate and final coats after each coat has dried. Wet sanding with waterproof sandpaper is recommended to avoid dust formation. Grinding is performed manually or with pneumatic grinding machines of types PPM-2, RD-1, MSH-2, OPM-7, etc. Then the body is washed, blown with compressed air and dried. Isolate the unpainted surfaces of the body with thick paper, adhesive tape and install it in the spray booth. Degrease the painted surfaces with white spirit. Open doors and hood.
Applying paintwork
After surface preparation, the first layers of paint are applied. The number of layers of paint depends on the material of the paint, its performance properties and the method of application. The first coat of paint reveals all the defects of the putty surface. Sometimes layers of paint are applied to a dry layer of soil (only slightly dried from solvents). This reduces the painting time and provides better interlayer adhesion. Paint is usually used from the same materials as the body was painted earlier. For painting VAZ cars, mainly synthetic melamine-alkyd hot-drying enamels ML-197, ML-152, ML-12 are used, which have good durability and high decorative effect. Two layers of enamel are applied with a paint sprayer (with intermediate drying 7-10 min) on the internal painted surfaces of the passenger compartment, engine compartment, luggage compartment, doorways, end surfaces of doors. Then three layers of enamel are applied to the outer surfaces of the body with intermediate drying for 7-10 minutes.
Methods for applying paintwork can be very different, to a greater extent depending on the availability of the necessary equipment. Pneumatic spray painting is carried out by compressed air flowing around the paint stream. A finely dispersed aerosol is created, which is applied in the form of a mist to the surface to be painted. In this case, there is a significant loss of paint. When painting, the sprayer must be perpendicular to the surface to be painted, otherwise the paint will lie unevenly. To reduce paint consumption, the paint sprayer should be at a distance of 250-300 mm. At a closer distance, the paint will churn and form smudges. The paint sprayer is moved at a speed of 0.2-0.3 m / s and the paint is applied in parallel stripes: from top to bottom and from bottom to top with an overlap of 40-50 mm.
Airless spray painting is carried out without supplying compressed air for spraying. Spraying is carried out under the influence of high pressure on paintwork materials, while it is possible to use compressed air to drive the pump. With airless spraying, paint consumption is reduced, more viscous materials can be used. The disadvantage is the need for high pressure equipment up to 25 MPa. The best quality of the coating is obtained by spraying paintwork materials heated to 60–100°C. Materials with airless spraying can have a viscosity of up to 100 s according to the VZ-4 viscometer. For airless spraying, URB installations can be used, «Visa-1», «Torch-2», «Luch-2» and etc.
Coloring can be done in a high voltage electric field. In this case, the paint is given one charge, and the painted surface is the opposite. Losses of paint will be the most insignificant.
Drying paintwork
Drying enamel is the longest process. To dry the enamel, a temperature of 130°C is required. But when painting the assembled car, high temperatures are unacceptable so as not to destroy the plastic and rubber parts of the seals and upholstery. Therefore, enamel drying is carried out at a lower temperature of 60–90°C by adding an acid curing catalyst. As a catalyst, up to 4-5% of a 10% solution of maleic anhydride in ethyl acetate or DGU-70 catalyst is added to the enamel. The working viscosity of ML-197 enamel at 20°C should be no more than 20 s. To working viscosity, the enamel is diluted with R-197 solvent.
Drying acceleration is affected by the heating temperature of the paint layer and air mobility, which accelerates the removal of solvent vapors. Heating source can be thermoelectric heaters (heating elements), installed in reflective reflectors, or incandescent mirror lamps.
When painting a car in special auto centers, one-pigment enamels ML-1195 or enamels with a metallic effect ML-1198 can be used.