The dented areas of the plumage are usually straightened manually using a special tool (metal, plastic, wooden hammers and various mandrels) and devices.
Heat straightening is used for upsetting (tightening) highly stretched panel surfaces. To prevent sudden swelling and deterioration of mechanical properties, the panels are heated to 600–650°C (cherry red color). The diameter of the heated spot should be no more than 20–30 mm.
Tighten the surface as follows:
- gas welding, from the periphery to the center of the defective area, heat the metal and with blows of a wooden mallet and hammer, press down the heated areas, using a flat support or anvil;
- repeat the heating and pressing operations until a smooth panel surface is obtained.
Unevenness in panels can be leveled using polyester putties, thermoplastics, cold-curing epoxy mastics and solder.
Polyester fillers form reliable connections with panels stripped to the metal. They are two-component materials: unsaturated polyester resin and a hardener, which is a catalyst for rapid hardening of the mixture regardless of the thickness of the filler layer. Drying time at 20°C is 15–20 minutes. Therefore, the time of application of the filler is reduced and there is no need to apply it in several layers.
Thermoplastic is produced in powder form. Thermoplastic acquires elastic properties necessary for its application to the metal surface of the panel at 150–160°C.
The surface to be filled must be thoroughly cleaned of rust, scale, old paint and other contaminants.
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For better adhesion, it is recommended to create roughness on the surface using 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 with a metal roller. Then the second layer is applied and so on, until the unevenness is filled. Each layer is rolled until a monolithic layer of plastic mass is obtained. After hardening, the layer is cleaned and leveled with a metal circle.
Corroded areas of body panels can be repaired with cold-curing epoxy mastics, which have high adhesion, sufficient strength and are easily applied to damaged areas. The mastics contain hardeners, plasticizers (to increase the plasticity of the resin and the impact strength of the cured epoxy composition), fillers (to reduce resin shrinkage and bring the thermal expansion coefficients of the resin and metal closer together).
Solders POSSu 18 or POSSu 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 method of applying solder.
In case of significant damage, the panels are replaced with new ones using contact welding and electric welding in a protective gas environment.