Gear tooth failures& lubrication

Basically, the performance of a pair of gears can be assessed by the measure of success achieved in providing a positive drive, while operating at the requisite speeds, transmitting the maximum designated power

Main points Performance parameters The failure forms of gear Failure reasons Lubrication of gears Lubrication methods

Main points Performance parameters The failure forms of gear Failure reasons Lubrication of gears Lubrication methods

Performance parameters strength - life and durability noise level - smoothness in operation efficiency - operating temperature size and weight of transmission cost of manufacture - materials,

machining, heat treatment and assembly running costs

Main points Performance parameters The failure forms of gear Failure reasons Lubrication of gears Lubrication methods

The failure gear one of two forms:

The failure gear one of two forms: A. complete fracture of the gear tooth; this

usually occurs at the root of the tooth

B. damage or destruction of the working surfaces of the gear tooth

Either of these forms of failure may be the result of one or a combination of any of the following factors:

Main points Performance parameters The failure forms of gear Failure reasons Lubrication of gears Lubrication methods

Failure reasons failure may be the result of one or a

combination of any of the following factors:

1. Initial stresses.2. Poor tooth design.3. Use of an incorrect material.4. A material defect.

Failure reasons5. Incorrect heat treatment for the selected

material.6. Poor mounting and casing design.7. Surface damage in final machining or

grinding operation.8. Excessive operating temperatures.

Main points Performance parameters The failure forms of gear Failure reasons Lubrication of gears Lubrication methods

Lubrication of gears Up to a few years ago the engineering

world in general paid little or no attention to the gearbox lubrication system during the initial design stages.

Thus when the internal running gear was finalized, lubrication became a major problem when the design of the gearbox casing commenced.

Lubricants used for: Lubricants used for:

Reduce friction coefficient between gears

Remove the dissipation heat

Protect bearings &gears against external pollutants

Main points Performance parameters The failure forms of gear Failure reasons Lubrication of gears Lubrication methods

Lubrication methods 1 ) Hand lubrication -where the lubricant

is applied from an oil can or similar type of container.

2 ) Drip-feed lubrication - where the lubricant is applied from an oil container by means of a wick or a restricted oil feed pipe.

Lubrication methods 3) Bath-type lubrication or, as it is more

commonly known, ‘splash lubrication’ where the gear teeth are used as paddles to circulate the lubricant.

4) Pressure lubrication - where the lubricant is circulated by one of the various types of oil pump through oil galleries or oil pipes to oil jets which are directed at the gear.