Wrinkled plumage areas are straightened, as a rule, manually using a special tool (metal, plastic, wooden hammers and various mandrels) and fixtures. Heated straightening is used for upsetting (contractions) highly stretched panel surfaces. To prevent sharp swelling and deterioration of the mechanical properties of the panel, it is heated to 600-650°C (cherry red). The diameter of the heated spot should be no more than 20-30 mm. The tightening of the surface is carried out as follows:
- metal is heated by gas welding from the periphery to the center of the defective area and heated places are upset by blows of a wooden mallet and hammer using a flat support or anvil;
- repeat the heating and upsetting operations until a flat 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 resin, regardless of the putty layer. At 20°C drying time 15-20 min. Therefore, 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. Elastic properties necessary for applying it to the metal surface of the panel, it 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 a new 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 sections 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 improve the plasticity of the resin and the impact strength of the cured epoxy), fillers (to reduce resin shrinkage and bring the coefficients of thermal expansion of resin and metal closer together).
Solders POSSu-18, -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 resistance welding and electric welding in a protective gas environment.