module 7 - 7.11 - bearings

What type of things are tested for in bearings ?

Smoothness, free play axially and radially

How can bearings be cleaned ?

They can be simply cleaned in solvents baths, to get rid of old grease, oil etc

They can also be cleaned in ultrasonic baths

What are some important rules to remember in lubircation of bearings ?

It’s bad to overpack with lubricants, it can cause overheating, fod ingression,

Make sure to have clean lubrication equipment

What lubricant is better for low speeds compared to high speeds

Greases are better for low speeds, and oils are better for high speeds

What beneficial things do lubricants do for bearings ?

Reduce overheating

Reduce friction

Prevents fod ingression

Reduces corrosion

What are the 4 main lubrications in bearings?

Hydrodynamic

Hydrostatic

Boundary

Solid film

What is hydrodynamic lubricantion ?

This is where a thick layer of lubricant is applied between the load surfaces in a bearing

What is hydrostatic lubrication ?

Hydrostatic lubrication is where high pressure air separates the layers for lubrication, doesn’t require movement like hydrodynamic

What is boundary lubrication ?

Boundary lubrication is where the layer of lubrication is only a few molecules thick, and the lubricant stickiness matters,

What is solid film lubricant?

Where the layer is sprayed, dunked or painted on and waited to cure, it then provides a layer that improves water resistance, and improves lifespan

What is true brinelling ?

This is where indentations are made on the raceways from excessive loads, poor lube etc.

What is false brinelling ?

This is where marks may be made, but not true indentation hence flat brinelling

What is burnishing ?

This is where surface flattening occurs, and creates areas of splits and cracks, caused by excessive loading and poor lubrication

Overheating in lubircation causes ?

It causes discolouration of parts, due to over running speeds, and poor lubrication caused by the oil purging out of the bearing at high temps

What is galling in bearings ?

This is where skidding occurs on moving elements of the bearings, causing metal transfer and a welding effect

What is spalling ?

This is areas of localised breakdown of the surfaces

What is wear in bearings ?

Occurs especially during FOD ingression, where it removes areas of material, so creates dimensional imbalances

What is corrosion in bearings ?

It is where water, acids etc are ingressed and react with the bearing to produce rust, or erode material et

What is electrical current damage in bearings ?

This is where electrical current passes though a bearing either ac or dc, and for long periods of time at low current, or a short period at high current for example lightning, it produces evidence at sites of contact in the bearing.

How is lubricant loss stopped?

Seals like rubber washers, labyrinth seals

What causes false brinelling ?

Vibrations and lubrication, not excessive loading like true brinelling