During the operation of the car, it is necessary to check the condition of the anti-corrosion coating and, if necessary, additional protection, especially hidden cavities, by applying special anti-corrosion compounds, and the joints of parts by applying sealing mastics. For the introduction of anti-corrosion compounds into hidden cavities, the manufacturer provides technological holes or openings through which the tips of the guns can be passed. After the introduction of the composition, close the holes with rubber plugs. Particular attention during the operation of the car should be paid to the integrity of the protective coating on the bottom of the body, which is subject to the most intense external influences, and therefore corrosion.
The materials used for anti-corrosion treatment are listed in Table. 15:
- protective lubricant NGM-ML is used for processing hidden cavities. The hidden cavities of all new cars are treated with this material;
- autopreservative «Movil» used for processing hidden cavities during operation. It is allowed to apply autopreservative on surfaces previously covered with oils, as well as on a rusty surface. It is recommended to treat cavities every two years;
- protective film coating NG-216B is used to cover the components and parts of the car under the body for the period of transportation;
- plastisol D-11A is used to protect the bottom of the body from corrosion, abrasive wear and for soundproofing new cars. Coating thickness 1-1.5 mm;
- anti-noise bituminous mastic BPM-1 is used to protect the underbody from corrosion during vehicle operation. Mastic is applied with a thickness of 1-1.5 mm. It reduces noise well, but has insufficient anti-corrosion properties and cannot withstand salt solutions, abrasives and other substances for a long time;
- plastisol D-4A is used for sealing welds and joints of parts on the outer and inner surfaces of the body;
- non-drying mastic 51-G-7 is used for sealing body joints, corner joints and gaps.
Anti-corrosion compounds are applied evenly and should not contain pores. For their application in the hidden cavities of the body, a KRU-1 gun with a special elastic tubular plastic extension is used. The extension cord is connected to the air gun with a union nut at one end, and has a sawing nozzle at the other end, which creates a spray jet. Due to its elasticity, the extension ensures the penetration of the sawing nozzle into hard-to-reach places of the body.
Apply anti-corrosion compound to surfaces by air or airless spray. Air spraying requires compressed air at a pressure of 3-4 kgf/cm2, which is fed into the paint spray gun with a tank and then into the sawing nozzle. The best quality of the coating is achieved with airless spraying under pressure up to 160 kgf/cm2, which allows you to cut materials of considerable viscosity.
Preparation and anti-corrosion treatment of hidden cavities
Due to the need for sophisticated technological equipment to perform work and the requirement for high-quality work, it is recommended that processing be carried out at car service stations.
The procedure for performing operations for corrosion protection of hidden cavities is as follows:
- install the car on a lift, remove parts and upholstery that prevent access to hidden cavities;
- flush with water at a temperature of 40-50°C through technological and drainage holes hidden cavities (tab. 16), bottom of the body and rear wheel arches. It is necessary to flush hidden cavities until clean water flows out of the hole. In this case, the sliding windows of the doors must be raised;
- remove moisture that has entered the passenger compartment and trunk, blow out all hidden cavities and places where anti-corrosion compounds are applied with compressed air;
- drive the car into the anti-corrosion spray booth and place it on a lift. Spray the anti-corrosion compound in the places indicated in fig. 290-292;
- lower the car from the lift, clean the front surfaces of the body from dirt with a rag soaked in white spirit.
Restoration of anti-corrosion and anti-noise coating of the underbody and wheel arches
During the operation of the car, the coating on the bottom of the body is exposed to gravel, sand, salt, moisture, as a result of which the mastic and soil are damaged and erased. Bare metal corrodes.
At the car factory, 1-2 mm thick plastisol D-11A polyvinyl chloride compound was applied on the lower surface of the body base, wheel arches and spars for noise insulation and protection against corrosion and abrasive wear, over EP-083 epoxy primer.
In case of damage to the D-11A plastisol coating without disturbing the soil layer, clean the damaged areas from dirt, degrease and apply plastisol to a dry surface with an airless spray or brush. Dry the plastisol at 130°C for 30 minutes. Due to the significant complexity of heating the body coating to a high temperature and the need for complete disassembly of the car, it is allowed to restore the coating by applying BPM-1 anti-noise mastic, which can be dried in natural conditions.
Before restoring the coating, place the car on a lift, carefully inspect the bottom of the body and identify defects in the coating. Clean the bottom of the body from dirt, remove rust with a spatula, sandpaper or rust converter according to the instructions for use. Blow the bottom of the body with compressed air. Then place the car on a lift in the mastic chamber and remove the wheels. Close the brake drums and discs with protective covers, isolate the driveline, mufflers, cables and other places that cannot be treated with mastic with thick paper and adhesive tape. With a rag soaked in white spirit, degrease the places cleaned to the metal, apply primer GF-073 on them with a spray or brush and let dry for 5-10 minutes. Then apply by spray or by hand (brush or spatula) mastic BPM-1 on defective places with a layer 1-1.5 mm thick. The application of mastic to adjacent areas that do not have damage should be minimal. In the cold season, the mastic is kept in a warm room before use until the temperature rises below 20°C. If the mastic is contaminated, dilute it with xylene, adding no more than 3%.
If contaminated with mastic, clean the paintwork on the front panels with a rag soaked in white spirit. The mastic is dried at a temperature of 18–20°C for at least 24 hours. To speed up drying, hold the coating at 100–110°C for 30 minutes.