For a small range of local bumps I and depressions, single shallow bumps and depressions can be repaired by knocking method, so that the metal deformation can be restored to its original state.
Second, the repair method of prying open the roof
Lever the top of the depression with leveling knife (or spoon plate) and pointed tools (such as various picks) to gradually restore the depression to its original state.
Three, stretch repair method
Pulling out the depression with a puller is also one of the commonly used methods. The pulling-out device comprises a sucker, a cylinder and a special puller.
There is a suction cup at the end of the pneumatic concave puller to generate vacuum, and the force exerted by the inertia hammer pulls the metal concave back to its original shape. Screw the screw at one end of the pull rod puller into the pre-drilled hole in the concave part, and repeatedly pull it in the direction of holding the handle with one hand to eliminate the concave part, and then block the through hole with filler.
In order to avoid the inconvenience caused by drilling, it is also possible to spot weld the recessed part with a pin instead of screwing in a screw, and then cut off the welding spot with a tool after pulling out, thus maintaining the integrity of the metal surface.
Fourth, the thermal shrinkage method
When the midpoint of the metal plate depression is rapidly and locally heated, the steel plate expands around the heating point during the heating process, resulting in compressive stress around it. When the temperature continues to rise, local steel plates turn red and soft, which reduces the pressure in the central area and makes the surrounding steel plates recover deformation. The red-hot area is compressed and thickened, and the surrounding steel plates can be freely deformed and stretched to restore their shape.
For local hot spots, you can suddenly spray water or apply wet cloth, so that the heated parts suddenly cool down, and the steel plate immediately shrinks, and the central part produces tensile load at the periphery, so that the periphery is strongly stretched toward the center, offsetting the compressive load generated during deformation and restoring the original shape.
Five, pleating method
The pleating method is a method to deal with tensile deformation. Instead of shrinking the metal by heating, it uses a hammer and anvil to make some folds at the tensile deformation. During the operation, the anvil was dislocated, and the parts were wrinkled when it was knocked with the beak hammer of the crane. The pleats will be slightly lower than other parts. After filling, use a file or sandpaper to grind this part flush with other parts.