R3: Types of Lubrication (12-1)

Question 1

What are the 5 types of lubrication?

Answer 1

1. Hydrodynamic
2. Hydrostatic
3. Elastohydrodynamic
4. Boundary
5. Solid film

Question 2

What is hydrodynamic lubrication?

Answer 2

Load-carrying surfaces of the bearing are separated by a relatively thick film of lubricant to prevent metal-to-metal contact.

Question 3

What does hydrodynamic lubrication require at all times?

Answer 3

The existence of an adequate supply. Doesn’t necessarily need introduction of the lubricant under pressure.

Question 4

How is the film pressure in hydrodynamic lubrication created?

Answer 4

The film pressure is created by the moving surface itself pulling the lubricant into a wedge-shaped zone at a velocity sufficiently high to create the necessary pressure to separate surfaces against the bearing load.

Question 5

What is hydrostatic lubrication?

Answer 5

Hydrostatic lubrication is obtained by introducing the lubricant into the load-bearing area at a pressure high enough to separate the surfaces with a relatively thick film of lubricant.

Question 6

How is hydrodynamic lubrication different from hydrostatic lubrication?

Answer 6

Hydrostatic lubrication does not require motion motion of one surface relative to another.

Question 7

When should hydrostatic lubrication be considered?

Answer 7

When the bearings used have velocities that are small or zero, and,

Where the frictional resistance is to be an absolute minimum.

Question 8

What is elastohydrodynamic lubrication?

Answer 8

When a lubricant is introduced between surfaces that are in ROLLING contact.

eg. rolling of bearings, gear matings

Question 9

What factors can prevent the build-up of a full-film lubrication? (4)

Answer 9

1. Insufficient surface area
2. Drop in the velocity of the moving surface
3. Lessening in the quantity of lubricant delivered to a bearing
4. Increase in lubricant temperature –> decrease in viscosity

Question 10

What is boundary lubrication?

Answer 10

When even the highest asperities are separated by lubricant films only several MOLECULAR dimensions in thickness.

Question 11

What is the most important factor of a boundary lubricant?

Answer 11

Chemical composition.

Viscosity can also be important.

Question 12

What is solid-film lubrication?

Answer 12

Used when bearings must be operated at EXTREME TEMPERATURES.

Question 13

What is needed for solid-film lubrication? (2)

Answer 13

1. Low wear rates

2. Small frictional coefficients

Question 14

What is thick-film lubrication?

Answer 14

Hydrodynamic lubrication

Question 15

What is thin-film lubrication?

Answer 15

Boundary lubrication