Chapter 8 Gear damage
Table 1 shows causes for gear damage and its countermeasures.
Table 1. Causes of gear damage and its countermeasure
Technical Know How - Design for gear strength extracted from JSME (Japan Society of Mechanical Engineers), and others.
Damage1 Breakage

2 Wear3 Plastic
deformation

4 Fatigue offlank5 Thermaldamage

Details of damage

Condition of flank

Causea. Overload
breakageFound crystallization on surface of break- Overload. Poor tooth contact. Mis- Find the cause of overload. Compreage flank similar to surface of cast iron.
usage.
hend usage conditions.

b. Fatigue breakage

Flank breakage has discoloration but Error in actual load calculation. Unsuit- Improve gear data for Tooth thickness.
less damage than overload breakage.
able shape of Dedendum.
Exchange material and heat treatment.

c. S hearing
breakageFound large plastic deformation at Overload. Defective and unsuitable ma- Practice warm up and test run. Exbreakage surface.
terial.
change material and heat treatment.

d. Impact breakage

Found crystallization on the surface ofOscillation of bearings from impulse Improve axis and bearing stability tobreakage flank similar to surface of castload.
ease impulse load.
iron.

a. Abrasive wear

Found small scratches or grooves at Metallic dust from worn gear and bear- Purify lubricating oil. Exchange material
sliding direction of flank.
ing.
and heat treatmentb. Scratching

Found rough scratches at sliding direcLarger particles than ‘a’ and waste obtion. Scratches are larger and deeper
Countermeasure is the same as 'a'.
jects.
than Abrasive wear.

c. Corrosive wear

Found rough pockmarks at flank.

d. Fretting

Found surface damaged with rust and Relative reciprocation motion from min- Decrease oscillation. Improve surface
oxidation by chemical change.
ute oscillation at surface of contact.
hardening.

e. Burning

Found discoloration and loss of hardInferior lubricating oil. Overload. Exces- Exchange type of lubricating oil. Imness due to high temperature fromsive speed. Increased temperature.
prove method of lubrication.
excessive wear.

f. Normal wear

This wear is within expectation of gear’
As expected and unavoidable.
s lifespan.

g. Moderate wear

Found flank with over excessive mark Unsuitable lubricating oil. Oxidation of Countermeasure is the same as 'a'. Praccannot engage normally.
flank. Water contamination.
tice warm up and test run.

a. Rippling

Found marks of corrugation or scale on Extreme sliding load. Deterioration of Improve gear strength and usage condicontact area at flank.
material or lubricating oil.
tion. Use extreme additive oil.

b. Rolling

Use shock absorber for design of driverFound polish mark at flank and curled Heavy load. Insufficient robustness, orside. Improve material and heat treatTooth tip.
hardness of material.
ment.

c. Peeling

Commonly, interpreted as rolling.

d. Plastic flow

Same as above and usually found in soft Same as above. Insufficient robustness Improve strength of material. Practicematerials.
or hardness of material.
warm up and test run.

e. Collapsing tooth

All teeth collapsed.

a. Pitting

Found small pockmarks just under pitch
Metal fatigue from repeated stress.
line.

b. Spalling

Detached large pieces of metal frag- Metal fatigue under surface from re- Same as above. Practice warm up andments from flank.
peated stress.
test run. Use extreme active oil.

c. Case crushFound extensive range of hardness layer Same as above. Extreme residual stress Same as above. Improve flank and coredetached from flank.
of core.
hardness. Design radiator for gear.

a. Scoring

Found many scratches and fusion marks Extreme load. Metal contact from lack of Emphasize on warm up and test run.
at sliding direction of flank.
oil film.
Exchange the lubricating oil.

b. Sand burning

Found extreme cohesion and fusion at Same as above. Inferior lubricating oil Same as above. Re-examine heat treatfinal form of scoring.
and accuracy. Increased temperature.
ment. Improve gear accuracy.

Exchange type of lubricating oil. ImUnsuitable lubricating oil. Oxidation ofprove countermeasures for moistureflank. Water contamination.
and waterproof.

Commonly, interpreted as rolling.

106

Same as above. Practice warm up andtest run. Improve assembly accuracy.

Same as above. Dedendum stress ex- Same as above. Re-calculate conditions
ceeds elastic limit.
of load and gear data.

Found large scratches, exfoliation anda. Damage and wear
falling apart at area of Tooth tip and Inferiors design. Insufficient backlash.
from interference
Dedendum.
6 Others

SolutionImprove gear strength, material andheat treatment.

Provide proper backlash to gears. Improve gear accuracy.

b. Damage andwear from waste
objectFound several detached tooth in various Waste objects from inside and outside Improve assembly method. Remove
conditions.
of equipment.
waste objects. Seal for dust proof.

c. Rust andcorrosion

Found rust and corrosion on flank.

Chemical changes of lubricating oil, Add anti-corrosion agent to lubricating
intrusion of impurities and water.
oil. Prevent intrusion of water and acids.