375At the beginning of knocking it, make your force slightly greater. In the finishing period of repair, make
your force softer and try your best to reduce the beating times. Make sure not to knock one point for too
many times to avoid extending on partial area of the metal plate, which may make the repair complex.
As to the concave with a comparatively big radian, a backing plate whose area should be comparatively
big can be put under the center of the concave. Directly push up the depressed plate by a propping-up
tool. Sometimes, the concave place can be heated to dark red to reduce the pushing force. A slight rise is
recommended when pushing up. (Figure 5-20)
Heat-shrinkable method:
After the concave area is pushed up, if the plate is greatly stretched and its area is too big to repair, the
heat-shrinkable method can be adopted.
Use oxygen-acetylene flame to heat to cherry red. The area of heating depends to its extension degree.
The heating area should be bigger (Diameter approx. 20-30mm), when it is seriously extended or the area
is big. If it is slightly extended or the area is small, the heating area should be smaller (Diameter approx.
10-15mm). Quickly knock the heated points with a wooden hammer while they are hot. A backing block
is recommended to push it up. After it cools down, use an iron hammer to gently knock for smoothness.
The shrinkage order is from the highest point gradually to the center and then to the edge. Heat and then
flatten the extended area repeatedly, till the plate is completely flat. If the protrusion is very high, first
compress the whole protrusion to its half. After it cools down, heat the former heating point to remove the
rest half of the protrusion.
When the method is applied, it must be specially noted that you'd better not use the heat-shrinkage
method to avoid side effects. Especially for thin plates, prevent them from being melted through hole..
When the outer plate is lightly crashed and the depressed area belongs to elastic deformation, you may
press its inside to recover to its former shape.
Some depressed area can be repair by prying which is a repair method without disassembling parts. YouIllustration 5-18 Panel Flattening (A)
A Concave Point B Protrusion Point C Knocking PointIllustration 5-19 Panel Flattening (B)
1 Hammer 2 Panel Parts 3 Backing BlockFigure 5-20 Heat and flatten the protrusion
1 heating point
