16 Because
copper is an extremely good heat conductor, it cools the molten weld metal rapidly
and thus provides
weld metal support without being fused with the weld metal. Attempts have been
made to substitute
copper alloys, aluminum and aluminum alloys for pure copper, but the results
have been uniformly
unsatisfactory both in service per dollar expended and in the quality of weld
produced. The poor service
results from the fact that these substitutes have appreciably lower thermal conductivities
and fuse at lower
temperatures. Thus, they cannot withstand the high welding temperatures and deteriorate
rapidly in use,
even though some may have initially higher abrasion resistance.
It is essential that the copper backing
be held tightly against the bottom of the joint to prevent the weld metal
from flowing out between it and the
underside of the workpiece. FIG.
3 - Copper-Backed Joints
