7.11: Bearings

Question 1

What can bearings either be?

Answer 1

Sealed or shielded

Question 2

What do tests for bearings involve?

Answer 2

Rotational checks for excessive backlash or free play, slow rotation indicates roughness due to damage, corrosion or wear

Question 3

What are bearings cleaned with?

Answer 3

Preservative oil in a solvent bath and ultrasonic baths are used as a final cleaning method for stubborn particles or contaminants

Question 4

What is grease used for?

Answer 4

Lubricating low rotational speeds but due to generating high temperatures at higher speeds, oil is used for higher speeds rotations

Question 5

What are engine bearings lubricated by?

Answer 5

Oil spray
Oil splash
Oil mist
Drip feed
Controlled level oil bath

Question 6

What is loss of lubricant prevented by?

Answer 6

Oil retaining devices

Question 7

What are some oil retaining devices?

Answer 7

Labyrinth seals
Felt
Rubber washers

Question 8

What are bearings packed with?

Answer 8

Antifreeze grease

Question 9

What are wheel hub bearings and how should they be repacked?

Answer 9

Tapered roller bearings and they should be repacked with the correct grease, usually done by hand

Question 10

What are basic types of lubricants for bearings?

Answer 10

Hydrodynamic
Hydrostatic
Boundary
Solid film

Question 11

What is hydrodynamic lubrication?

Answer 11

The load carrying surfaces of the bearing are separated by a thick film of lubricant to reduce friction

Question 12

What is hydrostatic lubrication?

Answer 12

Air and oil, where the air is forced into the bearing area at high pressure to separate surfaces. It does not need motion of one surface relative to another

Question 13

What is solid film lubrication?

Answer 13

Paint like coatings of very fine particles

Question 14

What is true brinelling?

Answer 14

Caused by excessive impact and appears as indentations in the bearing cup raceways and an increase in vibrations. It is an indication that the load on the bearing is greater than the elastic limit

Question 14

What is false brinelling?

Answer 14

Caused by vibrations of the bearing in a static state, causing lubricant to leave and wear to increase. It is identified by a corrosion pattern similar to brinelling

Question 14

What are true brinelling solutions?

Answer 14

Isolation of bearings from shock, vibrations or high impact loads

Question 14

What are false brinelling solutions?

Answer 14

Solved by using the correct amount of lubrication

Question 15

What is burnishing?

Answer 15

The smoothening of the original surface roughness in the bearing races, from being mechanically rolled over during normal running. It can be discoloured with no measurable wear. This is due to insufficient lubrication

Question 16

What is burnishing solutions?

Answer 16

The prevention of movement, correction of fit and the correct lubrication

Question 17

What is galling?

Answer 17

The rolling element of the bearing skids, which causes metal to be transferred from one surface to the other due to the welding or tearing action at the point of contact

Question 18

What is spalling?

Answer 18

The breakdown of the surfaces due to cyclic loading resulting in fatigue of the metal at certain points. It causes materials loss from the metal of the bearing racewy

Question 19

What is electrical current damage in bearings?

Answer 19

Causes dark brown or greyish black fluting or craters in raceways and rollers, with balls having dark discolouration sometimes zigzag/localised burns

Question 20

What type of currents do damage to bearings?

Answer 20

AC and DC

Question 21

What type of bearings are more resistant to electric current damage?

Answer 21

Non-rotating bearings are more resistant to electric current damage than bearings in rotation