Hot Shrinking. - od165370047

the metal locks the molecules in a new position.

They will resist any

subsequent force which tries to change their arrangement.

Metal has some

elasticity; that is, metal can be bent or twisted without permanent

disarrangement of the molecules.

When the force thus applied is removed,

the elasticity of the metal will cause it to resume the shape that it had

when the molecules of the metal were locked together in the dies. The body

repairman must avoid destroying this natural tendency of the metal to return

to its original shape. This is not always possible in collisions where the

normally smooth surface is badly creased.

Creases represent a portion of

the metal that has been distorted beyond its elastic limit and in which the

molecules have been displaced.

They are no longer locked together in the

same arrangement that was given to them in the forming die.

(2) Hot Shrinking.

(a) Hot shrinking is a simple process, but it requires careful timing

and proper tools. Tools required are those which are used for many other

operations in body work; i.e., a welding torch that is equipped with the

same size tip as used for welding the thickness of sheet metal being worked

on; a body hammer or mallet; shrinking dolly; a container of water, and a

sponge or rag.

(b) Arrange the tools so they are within easy reach. It is necessary

to change quickly from one tool to another when performing shrinking work.

(c) Locate the highest point in the stretched section of the panel

with which you are working. Light the torch and heat a spot the size of a

nickel in the center of the high spot (A) (figure 30 on the following page)

to a bright red. Use a circular motion when heating the spot, being careful

not to burn through the metal. As soon as the spot is bright red, place the

shrinking dolly under the spot and strike it several sharp blows with a

hammer or mallet (B).

(d) After driving

the center down, hold the dolly block loosely

against the underside of

the panel and exactly centered under the hotspot.

The hammer blow must hit

the spot accurately and with sufficient force to

push the metal down while

it

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