Deformed areas of panels are usually straightened manually using a special tool (metal, plastic, wooden hammers and various mandrels) and devices.
If necessary, straightening with heating is used for upsetting (tightening) highly stretched panel surfaces with mandatory subsequent restoration of anti-corrosion protection. 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.
The surface tightening is performed as follows:
- using a carbon electrode of a semiautomatic welding machine or a gas torch, heat the metal from the periphery to the center of the defective area and, using blows from a wooden mallet and hammer, settle the heated areas using a flat support or anvil;
- repeat the heating and settling operations until the required panel surface is obtained.
Unevenness on panels can be leveled using polyester putties, thermoplastics, cold-curing epoxy mastics and solder.
Polyester putties form reliable connections with panels cleaned to the metal. They are two-component materials: unsaturated polyester resin and a hardener, which is a catalyst for rapid hardening of the mixture. Drying time at a temperature of 20°C is 15-20 minutes. In general, the time of application of the putty is reduced and there is no need to apply it in several layers.
Thermoplastic is available in powder form; elastic properties required for application to the metal surface of the panel are acquired at a temperature of 150-160°C. The surface to be filled must be thoroughly cleaned of rust, scale, old paint and other contaminants. Thermoplastic adhesion is better to a rough metal surface. Before applying the thermoplastic, the area to be leveled is heated to 170-180°C and the first 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 processed using conventional methods.
Solders such as POSSu 18-2 and POSSu 25-2 are used to level areas previously filled with solder, build up the edges of parts and eliminate gaps.
To prevent corrosion, it is better to use an acid-free method of applying solder.