The surface contraction is carried out as follows: the metal is heated from the periphery to the center of the defective area with a carbon electrode of a semi-automatic welding machine or gas welding, and the heated metal is upset by blows of a wooden mallet and hammer, using a flat support or anvil, the heating and upsetting operations are repeated until the required panel surface is obtained.
Irregularities in the panels can be smoothed out with polyester fillers, thermoplastics, cold curing epoxy putties and soldering.
Polyester putties form reliable bonds with panels that have been stripped down to metal. They are two-component materials: an unsaturated polyester resin and a hardener, which is a catalyst for the rapid curing of the mixture, regardless of the thickness of the putty layer. At 20°C drying time 15-20 min. In general, the duration of applying the putty is reduced and there is no need to apply it in several layers.
The thermoplastic is available in powder form. The elastic properties necessary for applying it to the metal surface of the panel acquires at 150-160°C. The surface to be filled must be thoroughly cleaned of rust, scale, old paint and other contaminants. For better adhesion, it is recommended to create roughness on the surface with an abrasive tool. To apply thermoplastic, the area to be leveled is heated to 170–180°C and the first thin layer of powder is applied, which is rolled down with a metal roller. Then a second layer is applied and so on until the roughness is filled. Each layer is rolled to obtain a monolithic layer of plastic mass. After hardening, the layer is cleaned and leveled with a grinding wheel.
Corroded areas of body panels can be repaired with cold curing epoxy putties, which have high adhesion, sufficient strength and are easily applied to damaged areas. The composition of mastics includes hardeners, plasticizers (to increase the plasticity of the resin and the impact strength of the cured composition), fillers (to reduce resin shrinkage and bring the coefficients of thermal expansion of resin and metal closer together).
Solders such as POSSu-18 or -20 are used to level areas previously filled with solder, to build up the edges of parts and to eliminate gaps. To prevent corrosion, it is better to use an acid-free soldering method.
In case of significant damage, the panels are replaced with new ones using electric welding in a protective gas environment.