R3: Boundary-lubricated Bearings (12-15)

Question 1

What is boundary lubrication?

Answer 1

When 2 surfaces that slide relative to each other have only a partial lubricant film in between.

Question 2

What is boundary lubrication also called?

Answer 2

Thin-film lubrication.

Question 3

In what type of bearings does boundary lubrication occur?

Answer 3

In hydrodynamically lubricated bearings.

Question 4

When does boundary lubrication occur in hydrodynamically lubricated bearings? (4)

Answer 4

When:

1. They are starting or stopping
2. Load increases
3. Supply of lubricant decreases
4. Operating changes occur

Question 5

How do oiliness agents reduce friction?

Answer 5

1. Because of their strong affinity for certain metallic surfaces
2. Because they form a soap film that binds itself to the metallic surfaces by a chemical
   reaction

Question 6

What are oiliness agents?

Answer 6

Fatty acids that greatly decrease the coefficient of friction for boundary-lubricated surfaces by binding themselves to to metallic surfaces with great strength.

Question 7

What are some examples of fatty acids?

Answer 7

1. stearic acid
2. palmitic acid
3. oleic acid

• they occur in animal or vegetable fats

Question 8

At what temperature do fatty acids break down?

Answer 8

250 degrees Fahrenheit

Question 9

How is the temperature limit of thin-films combated?

Answer 9

By mixing in extreme-pressure lubricants.

Question 10

What are the dangers of combining extreme-pressure and boundary lubricants?

Answer 10

Added possibility of excessive chemical corrosion of the sliding surfaces.

Question 11

What are the requirements for mixed-film lubrication? (2)

Answer 11

When a bearing operates under both

1. hydrodynamic lubrication
2. dry or thin-film lubrication

Question 12

Give an example of mixed-film lubrication. (6)

Answer 12

when a lubricant is supplied under

1. hand oiling/drop/mechanical feed
2. when viscosity is too low
3. when bearing speed is too low
4. when bearing is overloaded
5. when the clearance is too tight
6. improperly aligned journal and bearing

Question 13

What kind of lubrication is caused when:

viscosity is too low

Answer 13

mixed-film lubrication

Question 14

What kind of lubrication is caused when:

bearing speed is too low

Answer 14

mixed-film lubrication

Question 15

What kind of lubrication is caused when:

bearing is overloaded

Answer 15

mixed-film lubrication

Question 16

What kind of lubrication is caused when:

clearance is too tight

Answer 16

mixed-film lubrication

Question 17

What kind of lubrication is caused when:

journal and bearing are improperly aligned

Answer 17

mixed-film lubrication

Question 18

What kind of lubrication is this:

Relative motion between surfaces in contact in the presence of a lubricant

Answer 18

boundary lubrication

Question 19

What condition is present in hydrodynamic film bearings during
starting, stopping, overloading, or lubricant deficiency?

Answer 19

boundary lubrication

Question 20

In what situations is boundary lubrication used? (5)

Answer 20

When you have:

1. low journal speed
2. oscillating journal
3. padded slides
4. light loads
5. lifetime lubrication

Question 21

What are the characteristics of boundary-lubricated bearings? (3)

Answer 21

1. ability to tolerate expected wear without losing function
2. considerable friction
3. light loading.

Question 22

What are the limitations of boundary-lubricated bearings? (5)

Answer 22

1. lubricant temperature
2. speed
3. pressure
4. galling
5. cumulative wear

Question 23

What is w in this equation?

Answer 23

mbmnb