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2nd 2020 > Bearings > Flashcards

Bearings Flashcards

1
Q

What are the advantages of anti friction bearings over other bearings

A

*Less power demand because of the low starting friction.
Requires less maintenance and lubrication
Higher speed of operation

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2
Q

Bearings can be classified into three main types

A

Journal bearing- supports radial load on rotating shaft like a pulley bearing
*Thrust bearing- supports axial load on a rotating shaft and prevent axial or lateral motion.
Guide or slipper bearings- used to guide and support slidding components

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3
Q

Bending stress on shafts are from radial loads and can be recognized how?

A

Spotty, uneven wear, especially in sleeve bearings

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4
Q

What is Critical speed

A

When a shafts speed (rpm) synchronizes with the shafts vibration frequency. A violent vibration occurs and should be avoided at all costs. A shaft with a much high frequency should be used than what the shaft will see under normal load.

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5
Q

Bearing Fits and clearances

A

*Running and sliding fits allow freedom of movement while also allowing for proper clearances for lubrication.
Locational fits are for parts that normally don’t move but can easily be disassembled and replaced.
*Force fits are special interference fit used to maintain bore pressures.

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6
Q

Groove patterns in bearings

A

2 basic kinds- axial and circumferential. Axial groove allows oil flow lengthwise in the bearing. Circumferential groove allows lubricant to flow around the journal. Also acts as a collecting ring.

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7
Q

What are Bearing seals used for?

A

Help prevent dirt and other contaminants from getting into the bearing.

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8
Q

Variations of the split bearing

A

Half bearing- fit around the shaft and are used for downward loads ( crane)
Multipart bearing- usually comprised of 4 parts that fit around the journal

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9
Q

Split sleeve bearing

A

Made by lining steel , cast iron, or bronze shells with babbitt (very low friction metal)

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10
Q

What are Precision insert?

A

Keep vertical clearances like a connecting rod bearing.

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11
Q

What are trimetal inserts?

A

Thin steel backing
Middle layer a dissimilar metal
Inner layer is the antifriction bearing material

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12
Q

What is crush and spread?

A

Crush is the extra amount of lining material that makes each insert half slightly larger than a half circle.
Spread is the slight increase in diameter of the insert

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13
Q

Conformability

A

Desirable property of a bearing that allows the bearing to adjust to misalignment without failing

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14
Q

Embeddability

A

Ability of a bearing material to absorb dirt or other contaminants

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15
Q

Advantages of Aluminum bronze alloys?

A 
Good shock and wear resistance 
Keeps it strength at high temps.
Over 500+ degrees
used for heavy duty low speed operation applications
Bad: 
Poor score resistance 
Embedability 
Conformability
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16
Q

Bearing replacement

A

High speed equipment bearings should be changed at twice the amount of the original clearance

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17
Q

When regrooving a bearing what should its groove width be?

A

Should be approximately twice its depth and the depth should not be more than one-third of the wall thickness of the bearing.

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18
Q

Bearing idenification 10bcc02

A

10 is 10mm diameter
Be is standard single room ball bearing
02 being width of 2mm

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19
Q

What is the cage in an anti friction ball bearing?

A

The cage carries the ball assembly, bears none of the load, and is subject to very little wear.

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20
Q

Lubrication for anti friction ball bearings

A

They require less lubrication
Grease is used in low speed conditions
Oil is used in high speed operations because it dissipates heat better.

21
Q

Tolerances for bearings

A

ABEC rating- for ball bearings ABEC 1, 5, 7 ,9. The lower number represents a tighter tolerance.
BREC rating- for roller bearings RBEC 1, 5
* special bearings are used when the tolerance is tighter than ABEC 1 and RBEC 1.

22
Q

What are the factors that influence running accuracy of bearings?

A

Radial runout- allowable out of roundness of both the inner and outer rings
Side runout with bore- measured against the side of the inner ring
Groove runout-
Axial runout

23
Q

What is the major limitation of antifriction bearings?

A

Their lack of resistance to fatigue. Because the load is centered on such small contact areas of the rolling elements, the metal will eventually fail.

24
Q

How does fatigue failure start?

A

It starts as flaking ( when the bearing begins to fail from repeated stress. The failure starts as a crack and from there deteriorates to spalling ( chipping away or breaking away of material)

25
Q

Proper mounting and control of shaft deflection are vital to reliable bearing performance. except for inadequate or improper lubrication, misalignment and excessive runout are among common causes of bearing failure

A

T

26
Q

What is a floating bearing?

A

A floating bearing can be used where a little axial movement is ok and is accouted for. It prevents cracking or overloading of bearings.* fixed bearing also carries axial loads

27
Q

Whats the maximum runout for squareness of shaft end faces and shoulders?

A

.0001 full indicator reading per inch in diameter is usually specified.

28
Q

Describe double row angular contact bearings. (Double row ball bearing)

A

Resist radial loads
Thrust loads
And combined loads from all directions.

29
Q

Describe staggered roller bearings.

A

Many rows of short rollers arranged in a staggered pattern which permits the load to be distributed over many contact points.

30
Q

What are cylindrical roller bearing usually used for?

A

For heavy radial loads and to operate at higher speed than other roller bearings.

31
Q

Describe spherical roller bearings.

A

Angular contact bearings. Designed to support high radial or combined axial and radial loads.

32
Q

What are the four main parts of a tapered roller bearing (wheel bearing)

A

Cup- the outer ring of the bearing
Cone-corresponds to the inner ring
Tapered rollers
Cage

33
Q

Loose needle bearings are also referred to as?

A

Raceless or careless bearing. Very compact and high radial load capacity.

34
Q

Tapered roller thrust bearings is used in applications such as?

A

In crane hooks where they experience high thrust loads and heavy shock.

35
Q

The spherical roller bearing is also know as?

A

A self aligning bearing. Because of the shape of the rollers they automatically adjust to misalignment without any loss of its capabilities.

36
Q

Describe linear motion bearings.

A

Include plain and antifriction bearings on horizontal and vertical motions. Also known as way or shaft bearings. Ex. Ladder ( toolbox drawer slides) recirculating ball or roller, recirculating roller chain bearings.

37
Q

Another variation of the linear motion bearing is the open ball bushing. Its opening supports a shaft member along the length of the shaft similar to a track

A

T

38
Q

What are takeups when referring to mounted bearings?

A

Allow sideways movement of the bearing and shaft within a frame to permit adjustment of the shaft center distances of belts, conveyors, and chain drives. Can be manual (screw adjustment), automatic (spring) and hydraulic

39
Q

How do you properly measure a seal?

A

Seal width- overall thickness of the outer case

Seals outside diameter- the outermost measurement of the seal

40
Q

How do you select the correct seal for the application?

A

Type of fluid to be sealed
Condition and material of shaft
Temperature the seal will be exposed to
Speed of shaft surface (feet per minute)

41
Q

When are synthetic bearing seals used?

A

Used in higher speed applications, they high retention of the internal fluid. When used the shaft must be ground or polished to a very fine finish for the seal to operate properly and to last as it should.

42
Q

What should be used with a bearing seal when a large amount of lubricant works against the seal?

A

A spring closure ring is usually used to force the seal against the shaft. The fluid pressure also assists the spring in maintaing a seal.

43
Q

How to clean and maintain bearing lubricants?

A

Frequent cleaning of the oil sums in continuous systems is necessary
If its pressurized, the oil can be filtered/strained before reuse.
The sump is should be flushed with a solvent to remove carbon deposits. At that time inspect for metal particles or other indications that wear is occurring in the bearing.0]p

44
Q

The hardness of a grease is expressed how?

A

Number scale from 000 to 6 established by national lubricating grease Institute.

45
Q

How much grease should be packed on the first use?

A

From 1/3 to 1/2 full. Any more and it will cause leakage, churning, and excessive heating

46
Q

Special notice for installing anti friction bearings!

A

Misalignment may not be noticeable for a period if time because of their ability to accept slight misalignment. Even though they appear to be fine their life will be shortened considerably.

47
Q

Some of the noises to listen for after the bearing is running are?

A

High pitched whine from interference or over load
Medium to low pitched from bearing misalignment
rattles from poor fits or loose bearings
Rumbling sound from poor finish on shafts or housing

48
Q

Bearing failure terminology

A

Spalling- flexing of the metal beneath the bearing surface, small grains of surface flake away, damage increases till failure.
Scoring or scraping- caused by loose fits and improper lubrication or dirt in the bearing
Fretting-slight movement between bearing and housing will cause outer ring to crack or split.
Brinelling- flow of metal because if excessive pressure, appears as series of small indentations on each ball and in the races.

49
Q

What are common reasons for bearing failure?

A 
Improper load
Misalignment
Improper installation
Chemical breakdown of metal ( oxidation)
Improper lubrication is by far the most common

2nd 2020 (10 decks)

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