The deformed places of the panels are straightened, as a rule, manually using a special tool (metal, plastic, wooden hammers and various mandrels) and fixtures.
If necessary, straightening with heating is used for upsetting (contractions) strongly stretched surfaces of panels with the obligatory subsequent restoration of anticorrosive protection. 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 done as follows:
- with a carbon electrode of a semiautomatic welding machine or a gas burner, the metal is heated from the periphery to the center of the defective area and the 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 the desired 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. Drying time at 20°C 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 a temperature of 150-160°C. The surface to be filled must be thoroughly cleaned of rust, scale, old paint and other contaminants. The adhesion of thermoplastic 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 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 processed by 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 soldering method.