55 Wagon Progress

[MP&C]

To help explain, let's look at the cross-section of a quarter. Where this is a lower crown panel, and the heat often wreaks more havoc on the center of the panel, in many cases it will shrink, lose some of the crown, (become more flat), and possibly start to oil can as the metal loses its shape. In the picture below, the red arc would represent a vertical weld through the original shape, and the blue shows what occurs as the weld and HAZ shrinks; the arc loses some of its length, becoming a smaller arc or more towards a straight line. This in effect pulls the adjoining metal into a valley. Many people will misread all this "panel movement" as a stretch, but it is indeed shrunk.



To correct this, the hammer and dolly principles as explained above are used to keep the shrinking effects in check.