Stanley MBF5 User Manual page 24

PRYING
This is the most common cause of tool failure. Even
when there is no surface damage, the stress from prying
can easily break a working steel. This kind of failure
generally results from any type of side pressure such
as an incorrect breaking angle or from using the tool to
reposition material. The tool should not be used as a
pivot point when repositioning the carrier. The power
generated by the carrier will far exceed the strength of
the tool.
Similar failures can also occur when the steel is used
with extreme down pressure and the steel repeatedly
slips off the work at an angle, or the material itself moves
from under the working steel.
As the next illustration shows, fatigue failures take many
forms, but they all exhibit similar features. Generally, the
broken surface is brittle and has a "lip" like that in the
bending failure, even though, in some cases, the lip has
been broken.
24 ► MBF5 User Manual
PROPER CARE OF TOOL BITS
CORROSION
Tools should be greased and stored out of the weather.
Corrosion will accelerate fatigue fractures.
MUSHROOMING
Driving the tool into hard material for a long period of
time generates intense heat, indicated by a blue tone just
above the point. This heat will soften the steel and cause
the point to fold over, or mushroom, the end of the bit.
Avoid hammering in one location for too long. If material
does not break after a short period (approximately 15 to
20 seconds), reposition the tool.
If the overheated steel is suddenly cooled by being
dipped in water, the metal will harden and become brittle.
The illustration shows some examples of failure caused
by temper changes.
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 grain. The result is
an inherent weakness in the tool shank and eventual
breakage.
The broken surface exhibits a shell pattern at the point of
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.
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.