7.11: Bearings Flashcards
What can bearings either be?
Sealed or shielded
What do tests for bearings involve?
Rotational checks for excessive backlash or free play, slow rotation indicates roughness due to damage, corrosion or wear
What are bearings cleaned with?
Preservative oil in a solvent bath and ultrasonic baths are used as a final cleaning method for stubborn particles or contaminants
What is grease used for?
Lubricating low rotational speeds but due to generating high temperatures at higher speeds, oil is used for higher speeds rotations
What are engine bearings lubricated by?
Oil spray
Oil splash
Oil mist
Drip feed
Controlled level oil bath
What is loss of lubricant prevented by?
Oil retaining devices
What are some oil retaining devices?
Labyrinth seals
Felt
Rubber washers
What are bearings packed with?
Antifreeze grease
What are wheel hub bearings and how should they be repacked?
Tapered roller bearings and they should be repacked with the correct grease, usually done by hand
What are basic types of lubricants for bearings?
Hydrodynamic
Hydrostatic
Boundary
Solid film
What is hydrodynamic lubrication?
The load carrying surfaces of the bearing are separated by a thick film of lubricant to reduce friction
What is hydrostatic lubrication?
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
What is solid film lubrication?
Paint like coatings of very fine particles
What is true brinelling?
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
What is false brinelling?
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
What are true brinelling solutions?
Isolation of bearings from shock, vibrations or high impact loads
What are false brinelling solutions?
Solved by using the correct amount of lubrication
What is burnishing?
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
What is burnishing solutions?
The prevention of movement, correction of fit and the correct lubrication
What is galling?
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
What is spalling?
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
What is electrical current damage in bearings?
Causes dark brown or greyish black fluting or craters in raceways and rollers, with balls having dark discolouration sometimes zigzag/localised burns
What type of currents do damage to bearings?
AC and DC
What type of bearings are more resistant to electric current damage?
Non-rotating bearings are more resistant to electric current damage than bearings in rotation
