We may classify failure of gears into four categories: 1 – Pitting, 2 – Wear, 3 – Plastic flow 4 – Breakage. The visual aspect of the various adversity and failure modes can differ between gears that have through hardened and those that have surface hardened teeth.

1. Gear Tooth
Failure

2. Gear Tooth Failure
Tooth
Breakage
Tooth Wear
Abrasion
Pitting
Scoring or
Seizure
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3. Abrasive wear
• Abrasive wear is the removal of material from a surface by a
harder material impinging on or moving along the surface under
load.
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4. Pitting
• Pitting or pitting corrosion on gears is a form
of wear and tear.
• It can be identified by darker patches or
shallow indentations on the toothed surfaces.
• These irregularities cause friction, resulting in
lots of heat being generated.
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5. Scoring
• Scoring refers to transfer of metal from one component to another
under sliding contact.
• This process is caused by lack of adequate lubrication under
extreme pressure.
• In gears, pitting occurs when continuous high-pressure forces act
on the surface of the gear teeth.
• Pitting, in turn, can cause scoring.
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6. Common Causes of Gear Failure
• Moderate wear:
• This type of where leaves contacts patterns that show the metal has been affected in the
addendum and the dedendum area.
• Issues with inadequate lubrication commonly cause it, but it may also be due to
contamination in the lubrication as well.
• Excessive wear:
• This is wear that has continued to be a problem until a significant amount of material has
been affected on the surfaces.
• You may see pitting on the surface with excessive wear, typically caused by not seeing the
first wear early enough, and it continues to progress.
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7. • Abrasive wear:
• In gears that are showing signs of abrasive wear, it may appear as radial scratch marks,
grooves or some other identifier that would show contact is a problem.
• One of the most common reasons why abrasive wear takes place is due to foreign bodies in
the lubrication.
• This issue could include metallic debris from the bearings or gear system, rust, sand or weld
spatter.
• It is common in new systems before the filter can clean the system.
• Corrosive Wear:
• Chemical action deteriorates the surface of the gear, such as through acid, additives or
moisture in the lubrication oil.
• As the oil breaks down, the chemicals that exist in the lubricant attack the surfaces.
• It tends to result in uniform, fine pitting on the two surfaces.
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8. • Pitting:
• A problem with pitting can be labeled as either initial, in which the surface is
experiencing small pits to destructive, in which the pits are larger in diameter.
• Initial pitting may be a problem with the gears not fitting together properly.
• Destructive pitting is typically an issue with surface overload.
• Breakage:
• It is possible for the entire tooth or a piece of the tooth to break away.
• It often leaves evidence of the focal point of the fatigue that led to the break,
which results from any number of issues, including high stress or excessive
tooth loads.
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9. • Frosting:
• This issue usually shows up in the dedendum area of the driving gear.
• The wear pattern gives a frosted appearance, which are many micro pits on the surface.
• Frosting is a common issue when the heat breaks down the lubrication film.
• Spalling:
• Although it is similar to severe pitting, the pits tend to be shallow and larger in
diameter.
• Additionally, the area that is showing spalling does not tend to be uniform.
• It is a common problem when high contact stress exists.
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10. Reference
• Machine Design by RS Khurmi and GK Gupta
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11. B.Varun
9787608011
bvarun.me@gmail.com
varun.me@srit.org
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