Stanley Black & Decker MBX138 Automobile Parts User Manual


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PROPER USE & CARE OF TOOL BITS
MAXFORCE BREAKER User Manual ◄ 19
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aw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 20. 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ring,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ring.
• Failures in this area are usually the result
ofprying,metal-to-metalcontactorcorro-
sion.Pryingfailuresoftenexhibitashell-
likeformationneartheedgeofthesteel
diameterwherethe breakbegan,anda
“tail” opposite that where the remaining
steelbentandtore.
• Failures in this area are usually the result
ofheatbuild-up,mushrooming,orimprop-
ercontactwiththework.
Figure21.DiagramofToolBitFailures
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