Bearings

Question 1

What are the advantages of anti friction bearings over other bearings

Answer 1

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

Question 2

Bearings can be classified into three main types

Answer 2

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

Question 3

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

Answer 3

Spotty, uneven wear, especially in sleeve bearings

Question 4

What is Critical speed

Answer 4

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.

Question 5

Bearing Fits and clearances

Answer 5

*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.

Question 6

Groove patterns in bearings

Answer 6

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.

Question 7

What are Bearing seals used for?

Answer 7

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

Question 8

Variations of the split bearing

Answer 8

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

Question 9

Split sleeve bearing

Answer 9

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

Question 10

What are Precision insert?

Answer 10

Keep vertical clearances like a connecting rod bearing.

Question 11

What are trimetal inserts?

Answer 11

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

Question 12

What is crush and spread?

Answer 12

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

Question 13

Conformability

Answer 13

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

Question 14

Embeddability

Answer 14

Ability of a bearing material to absorb dirt or other contaminants

Question 15

Advantages of Aluminum bronze alloys?

Answer 15

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

Question 16

Bearing replacement

Answer 16

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

Question 17

When regrooving a bearing what should its groove width be?

Answer 17

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

Question 18

Bearing idenification 10bcc02

Answer 18

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

Question 19

What is the cage in an anti friction ball bearing?

Answer 19

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

Question 20

Lubrication for anti friction ball bearings

Answer 20

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

Question 21

Tolerances for bearings

Answer 21

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.

Question 22

What are the factors that influence running accuracy of bearings?

Answer 22

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

Question 23

What is the major limitation of antifriction bearings?

Answer 23

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.

Question 24

How does fatigue failure start?

Answer 24

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)

Question 25

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

Answer 25

T

Question 26

What is a floating bearing?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

Describe staggered roller bearings.

Answer 29

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

Question 30

What are cylindrical roller bearing usually used for?

Answer 30

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

Question 31

Describe spherical roller bearings.

Answer 31

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

Question 32

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

Answer 32

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

Question 33

Loose needle bearings are also referred to as?

Answer 33

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

Question 34

Tapered roller thrust bearings is used in applications such as?

Answer 34

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

Question 35

The spherical roller bearing is also know as?

Answer 35

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

Question 36

Describe linear motion bearings.

Answer 36

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.

Question 37

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

Answer 37

T

Question 38

What are takeups when referring to mounted bearings?

Answer 38

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

Question 39

How do you properly measure a seal?

Answer 39

Seal width- overall thickness of the outer case | Seals outside diameter- the outermost measurement of the seal

Question 40

How do you select the correct seal for the application?

Answer 40

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)

Question 41

When are synthetic bearing seals used?

Answer 41

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.

Question 42

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

Answer 42

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.

Question 43

How to clean and maintain bearing lubricants?

Answer 43

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

Question 44

The hardness of a grease is expressed how?

Answer 44

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

Question 45

How much grease should be packed on the first use?

Answer 45

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

Question 46

Special notice for installing anti friction bearings!

Answer 46

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.

Question 47

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

Answer 47

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

Question 48

Bearing failure terminology

Answer 48

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.

Question 49

What are common reasons for bearing failure?

Answer 49

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