PROPER USE & CARE OF TOOL BITS
TOOL FAILURE COVERED UNDER WARRANTY
INTERNAL MATERIAL FLAW
This failure occurs when a foreign material is rolled into the steel during the manufacturing process, causing an imperfection in the internal material flaw grain. The re- sult is an inherent weakness in the tool shank and even- tual breakage.
The fatigue failure is started by the defects within the tool bit. The broken surface exhibits a shell pattern around the starting point of failure, like that in the fatigue failure. The other parts of the broken surface are brittle.
This is the only kind of tool bit failure that is always covered under warranty.
Figure 25. Internal Material Flaw
As a rule, working steel failures can be diagnosed by looking at the break itself, and at the place on the steel where the break occurred. Discoloration, like “rainbow” effects or blue bands, is the result of extreme heat.
Look for surface cracks, galling, or gouge marks. Breaks that start as surface damage have a “sea shell” pattern, with the damaged spot at the center. A large “sea shell” indicates a slow growing break; a small one indicates one compounded by side stress.
Stress failures start small, and spread into the center of the steel. In a stress failure, the coarser the grain, the greater the stress was, and the more rapid was the failure.
•Failures in this area are usually the result of blank firing, worn bushing(s), worn re- tainer pin(s) or the lack of lubrication.
•Failures in this area are usually the result of worn retainer pin(s) or blank firing.
•Failures in this area are usually the result of prying,
•Failures in this area are usually the result of heat
Figure 26. Diagram of Tool Bit Failures
22 ► MB656 User Manual
