Understanding Tool Failures Tool Analysis

• Working Environment• Areas of Tool Failure• Piston Impact Area• Blank firing • Fatigue • Seizures• Bending• Tool Tip• Brittle• Modifications• Manufacturing Defects• Extending Tool Life

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Working Environment

Mechanical SurfaceDamages

Impact loads (from piston)

Torsion

BendingPressure & Heat

Seizures

External Factors:- Temperature- Corrosion- Mechanical Surface Damage- Wear and Tear- Dirt

Axial Loads(Compression)

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Bushing area - Upper Top of Tool

Retainer pin area

Bushing area - Lower

Working area

Tip of Tool

DeformationChipped Edges

FatigueSeizuresExcessive bushing wear

FatigueSeizuresBlank firingWorn retainer pinsExcessive bushing wear Fatigue

SeizuresBendingExcessive bushing wear

FatigueBendingMechanical damages i.e. deep gouges

Tip breakage MushroomingWrong tool in application

Areas of Tool Failure

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Piston damage • Deformation is caused by:

- Improper impact energy - oil flow and pressure.- High working temperature (e.g. foundries)

• Chipping or corner loading is caused by:- Excessively worn bushings.

• Common failure of pirate tools• Tools with a deformed or chipped top edge will cause piston failure.

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Piston Impact Area

Blank Firing

Blank Firing occurs where tool is not properly preloaded. - Impact energy from piston is absorbed partially or fully by retaining pins. - Prevalent in most applications: Bridge work,quarrying, or trenching.Failure of tool in slot area is caused by: - Worn lower tool bushing. - Worn retaining pins - usually with chisel tool.

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Fatigue -1

Starting point

Beach marks

Common Failure

Fatigue failure starts on surface from stress concentration points :- Scratches or gouges on working length .- Seizures in bushing areas or retaining pin slots.

Fatigue cracks are recognized by “Beach mark” patterns. - Semi circular marks around failure point.

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Fatigue -2Working Area

Beach marks

Failure occurring on working area outside lower tool bushing.Heavy gouges or scratches on surface create stress concentration points, leading to fatigue failure.Unexpected breakage can be attributed to: - High frequency with low loads.

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SEIZURESMost Common Failure

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Over 50% of Fatigue Failures are seizures in lower tool bushing area.• Seizures occur as tool slides against bushings or retaining pins.• Seizures are caused by: - Wrong working angle. - Insufficient grease. - Wrong type of grease - Improper greasing interval. • Fatigue failure results from stress concentration once crack is formed.

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Bushing Bushing Bushing

Tool Tool Tool

Friction heating Welding Crack

Signature mark(High lip)

• Bending stresses exceed material strength.• Excessive bending is caused by: - Prying with tool. - Wrong working angle. • High lip formation occurs in or near lower tool bushing.

BENDING.1#1 Failure caused by Operators

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BENDING.2

• Bending occurring inside lower bushing caused by: - Operator lifting and prying on tool stuck in material. • High lip formation occurs on bearing surface of bushing.

Inside bushing

Combination ofPrying while Lifting up

#1 Failure caused by Operators

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Mushroom affect

TOOL TIP Mushrooming

Chipped Edge

Hammering in one spot too long. - No tool penetration. - Produces higher heat loads on tip.Wrong working method.To small hammer for application.

Chipping caused by: - Improper contact with material. - Wrong selection of tool for application. Causes faster wear on retainer pins and tool slot.

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MODIFICATIONSWelding on Tools

DO NOT weld on tools Welding produces cracks on tool surface leading to fatigue failure.

Resharpening Tools• Tools are thru hardened.• Resharpen : - By milling. - By turning on a lathe. - By Sawing at low temperatures (Max 150 C / 300 F)

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Model A B C D E F

H115 10 30 20 60 24 142

H120 18 30 20 60 24 172

H130 20 30 20 60 24 197

H140 20 30 20 60 24 225

H160 20 30 20 60 24 230

H180 20 30 20 60 24 257

Chisel Moil

A min

B

C

D

F

E

RESHARPENING

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Tools are ultrasonic-tested to prevent such failures.

Manufacturing Defects

Failure starts under the surface and radiates out because of:- Impurities in steel- Weak spot in material.

Inclusion

Anywhere

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Extending Tool LifeGreasingLowers Owning & Operating Cost by: - Extended Tool life. - Extended Bushing life.

Greasing Interval

• Every TWO hours of machine operation. - Extreme conditions more often.• 20 - 30 strokes from grease gun.• Optimum for hammers an Autolube system.

Grease TypeCAT Multipurpose Molybdenum grease (MPGM) - Molybdenum based grease. - Dropping point over 250 C / 480 F - Grade equal to an NGLI Number 0...2 - Water resistant.

Inadequate greasing

Using Correct Working Methods

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