伸胀区
点状加热
伸胀区
边缘呈波浪状
加热位置
三角形加热
（3）Cooling-contracting way: When the flame is taken away, proper cooling ways should be
chosen according to the stretched degrees of the metal panels. Different cooling ways bring about
different contracting effects.
① Natural cooling-contracting, or cooling in the air naturally, which is suitable for smaller
areas of deformities.
② Water cooling, or covering the heated area with wet cotton cloth to make it cool suddenly.
The contraction of metal plate cooled in this way is larger than that of the naturally cooled one, but
it may make the steel panel fragile.
③ Natural cooling and hammering, usually operated with a hand hammer and a underlay iron.
During the operation, beat around the heated area quickly to increase the compressing stress and the
contraction till that area is smoothed. The wooden hammer is preferred and do not use too strong a
force, or the metal panel may get re-stretched.
4.3. Restoration of Cutting & Patching
When any part of the metal door panel is eroded or damaged beyond repair, it should be
removed and replaced with a new piece by welding. The repairing methods include patching
repair and cutting.
Steps for cutting repair are as follows:
（1） Check the damaged part and determine the repairing area.
（2） Make a paper model according to the determined area.
（
3
）
Draw lines on the metal plates and cut material according to the paper model, and leave
proper processing allowance.
（4） Select proper processing and shaping methods so that the patch matches well with the
Stretched area
Spot heating
Waved edge
Stretched area Heated spots
Triangle heating
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