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6.8 bearings Flashcards

(62 cards)

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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
When are plain bearings used?
When the loads are light and continuous
26
In order to work, what do plain bearings need?
A gap between the stationary part and the rotating part
27
What are pivot or axial bearings?
They act longitudunially
28
What are solid sleeves suitable for?
Radial loads only
29
What are slot sleeves used for?
To compensate wear
30
What are split sleeves used for?
Large diameter shafts
31
What is great about anti friction bearings?
They eliminate any friction
32
What are four advantages of antifriction bearings?
they have low starting resistance They are cooler They can carry heavy loads Are good for oscillating or vibrations
33
What does an anti friction bearing consist of?
A inner and outer race way, the rolling element and a rolling element cage
34
When are roller bearings used instead of ball bearings?
When the stresses are too severe
35
What are ball bearings best at?
High rotational speeds
36
What are the major components of a standard ball bearing?
nner and outer raceways, a rolling element (balls) and retainer.
37
What can aid installation in ball bearings?
Chamfered ends
38
What can protect the lubricant and bearing?
Shield and seals
39
What helps the races become self aligning?
The races can be machined internally or externally
40
when are ball bearings used?
Where a narrow bearing is required
41
What are ball bearings not good at?
Oscillating loads because of their size
42
What is the most common use of a cylindrical bearing?
Non locating positions One must float free, the other must be connected to the shaft
43
One must float free, the other must be connected to the shaft
Thermal expansion
44
Are the inner or outer races seperable or inseparable?
Seperable
45
What helps cylindrical roller bearings bear radial bearings?
A line contact with the race
46
What is the load capacity of roller bearings?
Low because the cage must align and retain the rollers
47
What do needle roller bearings have that are beneficial?
A compact cross section
48
What load capacity does a needle roller bearing have?
Radial. Only light axial loads
49
What does spherical roller bearings allow for?
Angular displacement between shaft and housing
50
What is the load like in spherical roller bearings?
They have high radial load capacity but the stress is not equally distributed
51
What is bad about spherical roller bearings?
They skid because the rolling motion occurs at two contact points
52
In spherical roller bearings , what feature must the cage have and why?
Must be robust to oppose any skewing effect which increases inertia
53
What are spherical roller ball bearings best suited to?
Areas prone to misalignment, and where speed and deflection criteria are not extracting
54
What is good about tapered roller bearings?
They can withstand radial and axial load Longer service life Less vulnerable in environments due to natural pumping
55
What are air bearings?
They use pressurised air to provide zero friction load
56
Why do air bearings avoid friction etc?
They don't have contact
57
How are air bearings fluid film created?
Through airflow through the bearing face and the bearing gap
58
What are thrust bearings used for?
Combination of radial/thrust loads
59
Ball, roller and needle bearings are designed for thrust loads only why?
They have the tracks of their races aligned to withstand it
60
How are thrust bearings mounted?
Vertically
61
If radial loading is expected, what must be placed next to the thrust bearing?
A normal bearing
62
What are needle thrust bearings?
They have high load capacity High radial load capacity when tapered

mod 6 (12 decks)

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