Alb Mod Bearing Maint A Flashcards
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
Rapid oxidization of the lubricant occurs above this temperature:
55°C 131°F
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
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
Unsealed bearing temperature is too high when it exceeds:
125°C (257°F)
A sealed bearing temperature is too high when it exceeds:
80°C (176°F)
The surface temperature of a housing is lower than the bearing temperature. To determine the bearing temperature, add:
20°C (36°F)
The temperature of the inner ring is usually ___° higher than the rest of the bearing
10°C (18°F)
____ is a periodic back and forth movement.
Vibration
A deteriorating bearing can generate its own:
Vibration
Amperage readings that are above normal indicate:
abnormal loads on the machine
When you have an increased amperage reading on a machine, you should investigate further by checking: (3)
- Vibration
- Temperature
- Lubrication
If the bearings are the cause of an increase in amperage, it must indicate:
Bearings are in very bad condition
A bearing should produce ___ noise to the unaided ear
very litte
When listening to a bearing in good condition with a stethoscope, it should sound like:
Should have a soft purring sound
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
The causes of bearing failure may be grouped as: (4)
- improper installation and handling
- Improper maintenance
- improper selection
- fatigue
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
Built in contamination is when:
Dirt is introduced to the machine either when it was built or when it was rebuilt
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
Always cover exposed bearings when:
you are not working on them
Bearing rings have a very small cross section and depend on the:
Housing bore for support
If the seating surfaces on the shaft and the housing bore are not true, the bearing:
distorts
If the shaft and bore diameters are not to specification, the bearing won’t have the proper:
internal clearance
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
50
An added payback on the cost of balancing is a large savings in energy consumption, from 20% to ___%
50
Misalignment accounts for ___% of vibration problems
40
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
