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 Gouging (Continued)
Alternatively, use the cutting flame to wash a rivet
Manual gouging is a rapid metal removal method.
head away. This leaves the rivet shank accessible to a
Speeds from 12-84 ipm (inches per minute) are
punch and washed plates undamaged and unmarked.
possible; 24 ipm across 1/4 in. plate will make a gouge
Merely punch the shank of the rivet out and the
3/8 in. wide. Gouging accuracy can be controlled to
diameter of the hole in the plate remains unchanged.
width and depth tolerances of about 1/16 in.,
The rivet washing process has wide application when
depending on the skill of the operator.
plates and rivet holes are to be reused.
Piercing and Washing
Cutting Manganese Steel
Piercing is used to cut holes in a workpiece. An
Very high quality cut surfaces can be produced when
important example is rivet piercing. Rivets and similar
MAPP gas is used to cut Hadfield's manganese (Mn)
fasteners can be removed entirely from a workpiece by
steel (approximately 13 percent manganese). With two
burning them out. It is possible to do this without
important exceptions, cutting manganese steel is
damaging the holes in the plates through which the
similar to cutting mild carbon steels. One, a preheat is
rivets pass.
required, and two, cutting oxygen pressure should be
kept as& as possible. Without a preheat, and with
Flame piercing is used when the rivet shank cannot be
too much oxygen pressure, a very rough, notched
removed because of poor alignment of the original
surface will result.
holes in the mating plates. After piercing, use the
oxygen stream to wash away the remaining rivet
CAUTION: The preheat should be applied only along
material. This method requires a high degree of skill
the line of cut since heating can destroy desirable
and great care must be exercised.
4-22
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