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Millwright Block 2 (harmonized) NS > Plain/friction Bearings > Flashcards

Plain/friction Bearings Flashcards

1
Q

What does plain bearings rely on to prevent the journal and bearing from contacting each other and reduce friction?

A

Film of oil

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2
Q

What is a plain bearing typically made up of? (2)

A

Journal
Bushing/shell

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3
Q

What is unique about plain bearings?

A

No rolling elements

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4
Q

What are the two main types of loads plain bearings support?

A

Radial
Axial

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5
Q

What load does journal bearing a typically support?

A

Radial load

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6
Q

What load does thrust bearings typically support?

A

Axial loads

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7
Q

What is the function of plain bearings? (2)

A

To hold the journal in the required location
Support the intended load

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8
Q

What is the journal?

A

The part of the shaft in contact with the bearing

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9
Q

What is the function of the journal?

A

Used to support a radial load on a shaft

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10
Q

What is another name for a shaft collar?

A

Thrust collar

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11
Q

What is a shaft collar used in conjunction with?

A

Thrust bearing

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12
Q

If the axial forces are to be controlled in two directions how is the assembly designed with the use of shaft collars?

A

1 collar located between 2 thrust bearings.

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13
Q

If the axial forces are to be controlled in one direction how is the assembly designed with the use of shaft collars?

A

The collar is located against one thrust bearing

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14
Q

What is the term bearing or journal bearing used to describe?

A

The bushing or shell that fits around the outside of the journal

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15
Q

Why is clearance between a journal and bearing required? (2)

A

Lubrication
Prevent binding

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16
Q

When is a thrust bearing used to locate a shaft?

A

When axial load is present

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17
Q

When axial load is present what type of friction bearing is commonly used

A

Thrust bearing

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18
Q

Why is a thrust bearing used when axial load is present?

A

Locate a shaft in a specific axial position without interfering with the shafts rotation

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19
Q

Where is a thrust bearings location on a shaft?

A

Near the component requiring accurate axial location control
(Typically the coupling)

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20
Q

How many thrust bearings are required on a shaft?

A

Only one per direction of axial thrust

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21
Q

What are the two components that make up a linear bearing?

A

Guide/rail
Bushing/carriage

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22
Q

What is the guide in terms of linear bearings?

A

The fixed part of the machine that has a smooth uniform shape that the carriage slides along

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23
Q

What is the carriage in terms of linear bearings?

A

The component that sits on or around the guide and slides along it’s length

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24
Q

What are journals commonly made from?

A

The same material as the shaft

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25
Q

What material are bearings made from?

A

Softer material than the shaft

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26
Q

Why are bearings made from softer material than the shaft?

A

They are the sacrificial components

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27
Q

What are the considerations made when choosing a material for friction bearings? (9)

A

Compressive strength
Fatigue resistance
High embeddability
Deformability (conformability)
Wettability
Thermal conductivity
Corrosion resistance
Bondability
Compatibility

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28
Q

What does compressive strength refer to in terms of friction bearing material? (2)

A

Strong enough to support the shaft load at maximum operating
Not so great that the west resistance is inadequate

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29
Q

When wear resistance is high what becomes lower?

A

Compressive strength

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30
Q

When compressive strength becomes higher what becomes lower? (2)

A

Wear resistance
Embeddability

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31
Q

What does fatigue resistance refer to in terms of friction bearing material?

A

The resistance to cracking and flaking by loads the increase and decrease in rapid cycles

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32
Q

How is fatigue resistance in a friction bearing increased?

A

Keeping liner material as thin as possible to allow the backing to handle the stresses

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33
Q

What does embeddability refer to in terms of friction bearing material?

A

How well a material handles contaminants without failing

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34
Q

When embeddability becomes higher what becomes lower?

A

Compressive strength

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35
Q

What does deformability refer to in terms of bearing material?

A

Allows a material to yield to a misalignment or imperfection in the shaft (such as change in diameter)

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36
Q

What does wettability refer to in term of friction bearings?

A

The ability to retain a film of lubricant

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37
Q

What does thermal conductivity refer to in terms of friction bearings? (2)

A

Allows rapid transfer of heat due to fluid friction
prevents local hot spots

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38
Q

What does corrosion resistance refer to in terms of friction bearings?

A

Resist corrosion from the acids in the oxidized oil

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39
Q

What does bondability refer to in terms of friction bearings?

A

Bearing material to form a good metallurgical bond to the backing material

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40
Q

What does compatibility refer to in terms of friction bearings?

A

Materials must not seize or weld to the journal under rubbing conditions

41
Q

What is another name for Babbitt

A

White metal alloy

42
Q

What can Babbitt alloys be composed of?

A

Tin
Lead
Copper
Antimony
Bronze

43
Q

What does lead provide to Babbitt?

A

Bearing properties

44
Q

What does bronze or copper provide to Babbitt?

A

Strength

45
Q

What are the 8 advantages to Babbitt?

A

Compressive strength
Embeddability
Conformability
Wettibility
Thermal conductivity
Corrosion resistance
Bondability
Low cost

46
Q

What is the limitation of Babbitt?

A

Low fatigue resistance

47
Q

Where is Teflon used in friction bearings? (2)

A

Light duty bushings
Or
Bronze matrix for strength

48
Q

What are the 3 advantages to Teflon?

A

Self lubrication
Chemically inert
Useful with soft journals

49
Q

What does chemically inert mean?

A

Withstand chemical attack

50
Q

What are the 3 disadvantages to Teflon?

A

Limited by temperature
Emits poisonous gas when burned
Absorbs water

51
Q

What does aluminum provide in an aluminum/tin alloy?

A

Strength

52
Q

What does tin provide in an aluminum/tin alloy?

A

Bearing material

53
Q

What was the aluminum/silcone alloy created for?

A

Extra strength

54
Q

What are the 6 advantages to aluminum/tin or aluminum/silcone alloys?

A

More embeddable than copper/lead or lead/bronze
More corrosion resistant than copper/lead or lead/bronze
Less expensive than copper or bronze
Softer than copper or bronze alloys
Higher load rating than Babbitt
Bond able to steel

55
Q

What are the disadvantages to aluminum/tin or aluminum/silcone alloys? (2)

A

Less embeddability and conformability than Babbitt

56
Q

What bearing component is located on a machine shaft and supports a radial load?

A

Collar

57
Q

What material property ensures that the journal and bearing do not weld together?

A

Compatibility

58
Q

What bearing material has the best load rating?

A

Aluminum/tin

59
Q

What determines the type of bearing design? (4)

A

Load
Machine speed
Installation requirements
Cost

60
Q

Where are plain bearings typically used?

A

To support high loads due to their large surface areas

61
Q

What are the 3 most common radial load types?

A

Stationary
Oscillating
Reciprocating

62
Q

What degree does a oscillating load move?

A

Shifts through an arc less than 180 degrees

63
Q

Where is the lubricant film on a stationary radial load?

A

One area of the bearing

64
Q

How many directions is the load on a stationary radial load?

A

Typically 1

65
Q

In terms of the bearing, where is the load supporting film on a oscillating load?

A

The film must move along the loaded area

66
Q

What is the difference between the fluid film between a stationary load and an oscillating load?

A

The fluid is much thinner but stronger on the oscillating load

67
Q

How does an oscillating load affect the bearing clearance?

A

Clearances are much smaller

68
Q

Why is the cleanliness of the oil more critical in bearings with an oscillating load?

A

The film is thinner

69
Q

In terms of bearings what degree does the load shift in a reciprocating load?

A

The load shifts 180 degrees from one side of the bearing to another

70
Q

What are the two configurations journal bearings can come in?

A

Split bearing
Bushing

71
Q

What features does a thin shell split bushing have? (4)

A

Flexible
Thin overly on steel backing
Must be seated in a strong housing with an accurate bore

72
Q

What’s the characteristics of a split bushing?

A

Light weight
With stands high loads

73
Q

What is a bushing?

A

A type of plain bearing that has not been split

74
Q

What are bushing typically designed to handle?

A

Radial or axial loads

75
Q

How can you tell if a bushing can support axial loads by its self?

A

It will be flanged

76
Q

What does a wrapped bushing consist of?

A

Thin steel shell lined with a soft bearing material

77
Q

What are the advantages of a wrapped bushing? (2)

A

High fatigue strength
Available in pre finished sizes

78
Q

Where should pre finished bushings be used? (2)

A

Only in light loaded
Non crucial applications

79
Q

What are solid bushings?

A

Bushings bored out of a solid piece of bearing material

80
Q

What are the advantages to solid bushings? (3)

A

Can be bored to non standard size
Easily made
Can accommodate deep lubricant grooves

81
Q

What is important to do after installing solid bushings?

A

Ream to their correct size

82
Q

What is the limitations of solid bushings?

A

Not as much fatigue strength of wrapped bushings

83
Q

What are floating bushings?

A

Bushings that consist of an outer bushing with a loosely fitted inner bushing

84
Q

Where can floating bushings be used? (2)

A

Lightly loaded / High speeds
Or
Heavily loaded / low speeds

85
Q

How can you help stabilize a floating bushing?

A

Film of oil between their inner and outer bushings

86
Q

What are water lubricated bushings?

A

Bushings made on non metallic material that are slippery when wet

87
Q

What materials can be used for water lubricated bushings? (3)

A

Rubber
Nylon
PTFE

88
Q

What type of loads are water lubricated bushings suited for?

A

Only very light

89
Q

What are pre lubricated bushings?

A

Either made of porous material soaked in lubricant or have a lining with pockets filled with lubricants

90
Q

How are porous bronze bushings charged?

A

Soaking in oil at 90 degrees Celsius for half an hour

91
Q

How much oil can porous bronze hold up to?

A

Max 30% of its volume

92
Q

What is the limitations of pre lubricated bushings? (3)

A

Poor heat distribution
Not good for high temps
Only good for light loads

93
Q

What are dry lubricated bushings?

A

Bushings made of a slippery material

94
Q

What are the features of dry lubricated bushings? (3)

A

Can run dry
Solid or lined
Available in a broad range of materials for different needs

95
Q

What are the limitations of dry lubricated bushings?

A

Not good for high speeds or heavy loads

96
Q

What are hydrodynamic bearings?

A

A widely used plain bearing, Designed to develop full film lubrication when a journal is at operating speeds

97
Q

What are the characteristics of a hydrodynamic bearing? (3)

A

Both split or bushing
Oil inlet
Supports full film

98
Q

How do you check the contact area of a plain bearing?

A

Look for the polished rub area

Millwright Block 2 (harmonized) NS (17 decks)

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