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mod 6 > 6.8 bearings > Flashcards

6.8 bearings Flashcards

1
Q

What are bearings?

A

They constrain relative motion to desired motion

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2
Q

What are bearings designed to do?

A

Produce minimum friction whilst having maximum wear resistance

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3
Q

What are gears used in conjunction with?

A

Shafts and bearings to transmit power

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4
Q

What two groups can bearings be split into?

A

Plain bearings
Rolling element bearings

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5
Q

What are plain bearings?

A

They have no moving parts and comprise of a plain cylinder or flat washer surface with a softer material than the shaft they support

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6
Q

What are rolling bearings?

A

Assembly comprising of hardened and enclosed rolling components which roll in inner and outer casings

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7
Q

What are the inner and outer casings called?

A

Races

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8
Q

What are the sub categories of rolling and plain bearings?

A

Roller and Ball bearings

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9
Q

What characteristics must a bearing consist of?

A

Strong material (to ensure minimum friction and maximum wear resistance

Parts must be held together with tight tolerances (to provide efficiency and quietness)

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10
Q

What forces are the bearings subject to?

A

Axial thrust loads
Radial/journal loads

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11
Q

What are axial loads?

A

Acting along the supported shaft

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12
Q

What are radial loads

A

Acting at right angles to the eg vertically

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13
Q

Can a bearings have a combination of both loads?

A

Yes

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14
Q

What materials are suitable for bearings?

A

Lead
Copper
Iron
Synthetics
Dry powdered materials

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15
Q

What good properties do materials suitable for bearings have?

A

Sliding properties and emergancy properties

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16
Q

What do bearings require to reach a long service life?

A

Lubrucation

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17
Q

What are synthetic materials lubricated with?

A

Water

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18
Q

What else does this water act as?

A

A coolest as they get hot

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19
Q

What can happen if the lubricant is missing?

A

The journal can cut into the bearing

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20
Q

What problems do machines with sliding bearings face?

How can they be avoided?

A

Insufficient oil in the bearings

Using grease pumps and pre pumping machine before use

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21
Q

When is grease only used in sliding bearings? (Plain bearings)

A

Strongly stressed bearings with a large bearing play. Slow moving and swinging shafts and axels

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22
Q

What are plain bearings also known as?

A

Sleeve or sliding bearings

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23
Q

What are anti friction bearings also known as?

A

Rolling or roller elemenent bearings

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24
Q

What is a plain bearing designed to take?

A

Radial loads which act at right angles to the shaft

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25
Q

When are plain bearings used?

A

When the loads are light and continuous

26
Q

In order to work, what do plain bearings need?

A

A gap between the stationary part and the rotating part

27
Q

What are pivot or axial bearings?

A

They act longitudunially

28
Q

What are solid sleeves suitable for?

A

Radial loads only

29
Q

What are slot sleeves used for?

A

To compensate wear

30
Q

What are split sleeves used for?

A

Large diameter shafts

31
Q

What is great about anti friction bearings?

A

They eliminate any friction

32
Q

What are four advantages of antifriction bearings?

A

they have low starting resistance
They are cooler
They can carry heavy loads
Are good for oscillating or vibrations

33
Q

What does an anti friction bearing consist of?

A

A inner and outer race way, the rolling element and a rolling element cage

34
Q

When are roller bearings used instead of ball bearings?

A

When the stresses are too severe

35
Q

What are ball bearings best at?

A

High rotational speeds

36
Q

What are the major components of a standard ball bearing?

A

nner and outer raceways, a rolling element (balls) and retainer.

37
Q

What can aid installation in ball bearings?

A

Chamfered ends

38
Q

What can protect the lubricant and bearing?

A

Shield and seals

39
Q

What helps the races become self aligning?

A

The races can be machined internally or externally

40
Q

when are ball bearings used?

A

Where a narrow bearing is required

41
Q

What are ball bearings not good at?

A

Oscillating loads because of their size

42
Q

What is the most common use of a cylindrical bearing?

A

Non locating positions

One must float free, the other must be connected to the shaft

43
Q

One must float free, the other must be connected to the shaft

A

Thermal expansion

44
Q

Are the inner or outer races seperable or inseparable?

A

Seperable

45
Q

What helps cylindrical roller bearings bear radial bearings?

A

A line contact with the race

46
Q

What is the load capacity of roller bearings?

A

Low because the cage must align and retain the rollers

47
Q

What do needle roller bearings have that are beneficial?

A

A compact cross section

48
Q

What load capacity does a needle roller bearing have?

A

Radial. Only light axial loads

49
Q

What does spherical roller bearings allow for?

A

Angular displacement between shaft and housing

50
Q

What is the load like in spherical roller bearings?

A

They have high radial load capacity but the stress is not equally distributed

51
Q

What is bad about spherical roller bearings?

A

They skid because the rolling motion occurs at two contact points

52
Q

In spherical roller bearings , what feature must the cage have and why?

A

Must be robust to oppose any skewing effect which increases inertia

53
Q

What are spherical roller ball bearings best suited to?

A

Areas prone to misalignment, and where speed and deflection criteria are not extracting

54
Q

What is good about tapered roller bearings?

A

They can withstand radial and axial load
Longer service life
Less vulnerable in environments due to natural pumping

55
Q

What are air bearings?

A

They use pressurised air to provide zero friction load

56
Q

Why do air bearings avoid friction etc?

A

They don’t have contact

57
Q

How are air bearings fluid film created?

A

Through airflow through the bearing face and the bearing gap

58
Q

What are thrust bearings used for?

A

Combination of radial/thrust loads

59
Q

Ball, roller and needle bearings are designed for thrust loads only why?

A

They have the tracks of their races aligned to withstand it

60
Q

How are thrust bearings mounted?

A

Vertically

61
Q

If radial loading is expected, what must be placed next to the thrust bearing?

A

A normal bearing

62
Q

What are needle thrust bearings?

A

They have high load capacity

High radial load capacity when tapered

mod 6 (12 decks)

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