Alb Mod Bearing Maint A Flashcards by Brandon Hatt

When using temperature as a clue to the condition of a bearing, you must be aware that temperature is the result of: (3)

Friction
Heat dissipation
Heat transferred from outside the housing

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Rapid oxidization of the lubricant occurs above this temperature:

55°C 131°F

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After the bearings have been running satisfactorily, and temperature then jumps, assuming there is adequate lubrication and no change in operating conditions, what could cause the change in temperature?

Rollers and raceways are deteriorating and causing more friction

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After bearings are freshly installed and lubricated, a temperature rise of ___° above normal is expected for a few hours.

15°C or 27°F

Note: if it continues to rise, this indicates faulty installation or the wrong bearing

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Unsealed bearing temperature is too high when it exceeds:

125°C (257°F)

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A sealed bearing temperature is too high when it exceeds:

80°C (176°F)

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The surface temperature of a housing is lower than the bearing temperature. To determine the bearing temperature, add:

20°C (36°F)

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The temperature of the inner ring is usually ___° higher than the rest of the bearing

10°C (18°F)

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____ is a periodic back and forth movement.

Vibration

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A deteriorating bearing can generate its own:

Vibration

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Amperage readings that are above normal indicate:

abnormal loads on the machine

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When you have an increased amperage reading on a machine, you should investigate further by checking: (3)

Vibration
Temperature
Lubrication

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If the bearings are the cause of an increase in amperage, it must indicate:

Bearings are in very bad condition

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A bearing should produce ___ noise to the unaided ear

very litte

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When listening to a bearing in good condition with a stethoscope, it should sound like:

Should have a soft purring sound

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When listening to a bearing in a bad condition with a stethoscope, it could sound like: (3)

Loud hollow noise,
High pitched scream
growling noise

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The causes of bearing failure may be grouped as: (4)

improper installation and handling
Improper maintenance
improper selection
fatigue

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When working near moving equipment, be cautious of parts that may not be covered by the guard and may not be obvious while rotating, such as: (3)

Keys
Setscrews
flingers

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Built in contamination is when:

Dirt is introduced to the machine either when it was built or when it was rebuilt

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It has been established that ____ is the biggest cause of premature bearing failure

contamination

Most abrasive compounds are smaller than 40 microns, invisible to the naked eye

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Always cover exposed bearings when:

you are not working on them

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Bearing rings have a very small cross section and depend on the:

Housing bore for support

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If the seating surfaces on the shaft and the housing bore are not true, the bearing:

distorts

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If the shaft and bore diameters are not to specification, the bearing won’t have the proper:

internal clearance

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Both distortion and incorrect diameters cause:

Early bearing failure

When checking a shaft for straightness, if it has more than ____" runout at the shaft center, seal seats or ends, it must be straightened or replaced

0.001"

If a housing bores seats have grooves or hollows from corrosion, the must be:

sleeved

If, when measuring for out of round or a taper, your seats are off by more than ___", it must be fixed or replaced.

0.0005"

When a bearing is heated above its stabilization temperature and cooled, it:

distorts

It is safest to assume a maximum of ____° when heating a bearing

120°C (248°F)

A bearing material that is dimensionally stabilized means:

The material has gone through a heating and cooling process

Although bearings can be stabilized to temperatures above 150°C, they cannot be run at that temperature because:

The bearing material is weakened at those temperatures

Brinelling is ____ and makes a bearing useless

impact denting

Brinelling can be caused by: (3)

- Hammer blows - dropping the bearing - shock loading on machine

False brinelling is caused by:

vibrations on a bearing that is not turning. Note: Allows film of lubricant to break and metal to metal contact. Wears bearing, causes depression under each rolling element

To prevent false brinelling:

Machine must be isolated from isolation and the shaft blocked to support it

Bearings should never be stored on a surface that is subject to:

prolonged vibration

The durability of an anti friction bearing depends on its:

accuracy

What are two practices relating to maintenance procedures that can lead to bearing failures? (2)

- Allowing contamination into housing | - incorrect lubrication

Contamination can be built in, or it can be: (2)

- Ingested during operation | - come from breakdown of lubricant

What are three of the contaminant entry points? (2)

- breather | - Faulty seals

Why should you filter new oil before putting it in a machine?

New oil does not meet cleanliness recommendations

Lubricants may be clean when they are installed, but they can generate their own contaminants as they break down. The breakdown is accelerated by: (3)

- Heat - Moisture - metal particles

Some of the contaminants produced by lubrication breakdown are: (3)

- acids - Sludge - Varnis

The oxidization rate of lubricants doubles ever ___° above ____°

Doubles every 10°C (18°F) above 55°C (130°F)

Inadequate lubrication means the lubrication is not doing it's job of:

Minimizing friction

Why could you have inadequate lubrication? (3)

- Wrong type of lubricant - Wrong amount of lubricant - Wrong type of lubrication system

What level should your oil be at in your bearing housing?

Only enough to wet contact surfaces, 1/3 to 1/2 up lowest roller

The normal recommended grease level for inside a housing is:

1/3 full

Most of the grease in a housing is used to:

prevent entry of water

When filling a housing with grease, there should always be room left to allow:

excess grease to escape

Vibrations can cause damage to machine parts, and can be caused by: (2)

- Imbalance | - Misaligned bearings or couplings

Imbalances account for __% of the causes of vibration

An added payback on the cost of balancing is a large savings in energy consumption, from 20% to ___%

Misalignment accounts for ___% of vibration problems

The two areas of misalignment in a machine are:

- Bearings | - Coupling

Besides causing vibration, misalignment causes a bearing to run at an angle to its normal running surface. This results in:

improper loading of the bearing surfaces and early failure

Coupling misalignment is caused by: (3)

- Faulty installation - poorly supported/anchored machine - thermal growth

Electric arcing in bearings refers to:

An electric arc jumping across the clearance inside the bearing and leaving a track on the surface.

What are the 3 common causes of electric arcing in bearings? (3)

- Welding - Residual magnetism in shaft - Static charges developed by dry gas

Static charges can be short circuited away from a bearing by installing:

a ground brush Note: in an axial direction as close as possible to the center of the roller

When checking a rotor for magnetism with a magnetometer, the rotor needs to be de-magnetized if the readings exceed:

3 gauss

Ceramic coatings are provided on the outside of plain bearings on large electric motors, these isolate the bearing from the:

induced current

Heat degrades a bearing in the following ways: (4)

- Bearing may be distorted if above its stabilization temperature - high temperatures lower a bearings load capacity - high temperatures reduce clearance - high temperatures change lubricant properties

At 200C a bearings load capacity is reduced by:

10%

at 250C a bearings load capacity is reduced by:

25%

at 300C a bearings load capacity is reduced by:

40%

The result of selecting a bearing with too small a clearance is:

Will run hot or seize

The result of selecting a bearing with too much clearance is:

The bearing is noisy and runs hot because the elements skid

What materials can be used to make a bearing cage? (3)

- Steel - Brass - Fiberglass-reinforced polyamide

Selection of the wrong cage material can lead to failure due to: (2)

- Corrosion of the cage | - Overheating at high speeds

A specialty stainless steel bearing is made for use in:

highly corrosive environments

A specialty vacuum remelted high temperature steel bearing is made for use in:

Jet aircraft, with temperatures up to 600C

A specialty plastic bearing is made for use in:

lightweight, low load, no heat appications

Selecting the wrong bearing type almost always leads to:

Early failure

____ is the failure or breaking up of any material that has been repeatedly deformed.

Fatigue

______ occurs as each rolling element enters the loaded zone and deforms itself and the raceway until it passes into the unloaded zone

Elastic deformation

Elastic deformation happens thousands of times per minute in a bearing. It eventually leads to developing micro cracks. This is known as:

Normal fatigue

Basic rating life of a bearing is based on fatigue tests. It is the number of millions of revolutions that 90% of bearings will take before ____ of a certain area is produced

spalling

____ fatigue results in failure before the rated bearing life

Abnormal fatigue

Bearing noise is most commonly monitored by ear, or with: (2)

- stethoscope | - screwdriver

If you hear an unusual sound from a bearing without the use of a stethoscope, it usually has to be replaced within:

Days or hours

Changes in ___ and ___ give much earlier warning of trouble than the hearing method

Temperature and vibration

When the machine is running, feel the machine bearing housings to sense:

temperature and vibration changes

When a machine is down, what checks can you do to the shaft in regards to bearing fit/condition?

- Turn by hand, look for roughness of movement - lift the shaft, look for radial looseness - push the shaft back and forth, look for axial looseness

During operation, the following areas should be checked for leaks: (3)

- Lubricant leaks at seals - Lubricant leaks at joints in housing - Discoloration of oil in sight glass. Sign oil is contaminated

___ is the most effective way to track the condition of a bearing while it is in operation

Vibration monitoring

____ measure vibration and are permanently mounted in a bearing housing.

Vibration probes

____ can collect, record and analyze vibrations in a single unit

Vibration analyzer

The use of vibration analysis equipment requires an understanding of: (2)

- Vibration theory | - The equipment

Oil analysis tells you about the condition of: (2)

- Oil | - Machine

By examining oil, you can learn a lot about the root cause of:

Bearing faiure

Darkened oil indicates:

oxidization

sludge and acids in oil indicates:

advanced oxidization

If oxidization of oil occurs early, it could be from:

excessive heat

On-site oil analysis involves checking for the following: (6)

- Dark oil - particles in oil - sludge - sour smell - thicker viscosity

An increase in bearing temperature is due to: (3)

- Transfer of heat from another source - reduced cooling affect - increase in friction

Increased friction due to something rubbing against a moving part can be caused by: (5)

- Too much, too little, or the wrong lube - Seal rubbing too hard - bearing failing - increase in load or speed - additional heat from outside source