"Troubleshooting Hard-Surfacing Problems"
Part One, Introduction
The problems encountered in hard surfacing with spray-and fuse, self fluxing alloys fall under four major categories: spalling, lack-of-bond, porosity and cracking. All of them can be eliminated or controlled through the use of simple techniques described here, with the understanding that the key to trouble-shooting these problems is correct identification of the base metal.
Those who operate spray and fuse equipment are often unaware of, or are misinformed about the composition of the base metal they’re working on. However, they can easily learn the relatively simple procedures used to identify base metals, which are outlined is ASM’s “Metals Handbook, Eighth Edition Volume 11, Non-Destructive Inspection and Quality Control”. One such procedure is spark testing, although this method is effective in identifying only carbon and molybdenum with certainty. The grinder should have at least a 1/4 –hp motor and tests should be run at least at 5,000 rpm or faster. The grinding wheels should be 46 to 60 grit, hard-bonded aluminum oxide, 1-1/2-in (38 mm) diameter and 3/8-in (9.5 mm) wide.
continued, Part Two: Spalling
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