Bearings Flashcards
What are the two basic types of bearings?
Friction
Anti friction bearings
What is the Main difference between friction and anti friction bearings?
Friction bearings have sliding contact between the shaft and the bearing.
Anti friction bearings have rolling contact between the shaft and bearing.
What are the principle parts of the bearing housing?
Base
Base bolts
Cap
Cap bolts
What materials are used for housings?
Cast iron - light to medium loads
Cast steel - light to heavy loads
Fabricated - for special jobs
What are the factors when choosing bearing housing?
Load
Rotational speed
Direction of pull
Support design
What are the different types of friction bearings?
Solid - when speed and load are low
Split bearing - two bolt (light medium load) four bolt (medium to heavy loads)
Angle bearings - when bearing is mounted vertical or when the load is parallel or slight angle.
What considerations are taken when deciding a material for journal bearings?
Should be softer then the shaft material
Low coefficient of friction
Wear resistant
Good heat conductor and stable
Readily available
What are the different liner materials?
Babbitt - general use
Brass or bronze - higher speeds and heavier loads than Babbitt
Aluminum - common in hydraulic pumps
Sintered bronze - this is a porous bronze with built in oil supply
What are the non metallic liners?
Nylon
Polyurethane
Phenol laminate
What is an advantage of plastic bearing?
Inert to most mild acids and alkalis
What is the difference between expansion rates between plastic and metal liners?
Nylons thermal expansion is roughly 10 times that of steel
What is the melting temperature of Babbitt?
288 degrees C (550F)
What is the hardest babbitts?
Tin based (90% tin)
What are the three temperatures to consider when melting Babbitt?
Complete melting point - 275 to 285 Celsius
Pour point - 345 to 371 C
Complete solidification - 25 to 28 C below the melting point. (250)
What happens to Babbitt when it is over heated?
Material life is greatly reduced
When pouring Babbitt when must be removed first and why?
Water - if the melted babbitt hits the water it causes a very dangerous blow back.
What supplies are needed when pouring emergency Babbitt?
Fire extinguisher Oxyacetylene torch Putty Pliers Cake of Babbitt
Where do you cut the oil grooves?
Always in the unloaded section
What are shims made of?
Material that will not compress or not affected by oil.
What are some general rules for clearances?
Medium - loose: constant one direction load and rotation
Medium - tight: reversing rotation and fluctuating load
Tight: reciprocating action
Typically how is a shell held in place?
Pins, dowels, or screws
What is crush?
When the sleeve sits slightly above the housing it gets crushed to the right tolerance after cap is installed and torqued
What is an advantage to shell liners?
Worn liners may be changed by taking the weight of the shaft and rotating the shell out.
What is a bushing?
One piece liner made of any of the common bearing materials
What is the purpose of a kingsbury thrust bearing?
Designed to take heavy loads and high speeds
What is a guide bearing used for?
Positioning a device or guide for linear motion
When is a pivoted shoe bearing used?
Used for high peripheral loads and shaft stabilization
What are the three functions of the cage?
Prevent rolling elements from rubbing against each other
Push the rolling elements through the unloaded area
Guide the rolling elements with a minimum amount of friction
What are the parts of an anti-friction bearing
Inner ring Raceway Rolling elements Cage Outer ring Seal
What are some different types of round ball bearings?
Four point contact ball bearing
Self aligning
Thrust
Angular contact
Deep groove, single row
Deep groove, double row
What are some factors that affect bearing load?
Area of contact
Direction of load
Loaded zone
What is radial load?
When contact angle is 0• and the load Carries at 90•
What is axial load?
If the nominal contact is at 90• and the load is in line with the shaft axis
What is combination load?
If the nominal contact angle is between 0• and 90•
What are some features of a single row deep groove ball bearing (Conrad)?
General purpose
Mainly supports radial loads
Can support combination loads and moderate axial loads in both directions
Classes as radial load bearing
Tolerates very little angular misalignment
What is a feature of the double row ball bearing?
Higher radial load capacity with increasing the radial dimensions
1 bearing code
1 internal self aligning double row ball bearing
Used when alignment is impractical or impossible
Can support only small thrust loads
Speed rating is same as single row deep groove ball bearing
Available in tapered bore to be used with taper sleeve
External self aligning ball bearing?
What is the difference between internal and external self aligning bearings?
Intended to accommodate angular misalignment
External self aligning has a spherically ground outer ring that mounts in a spherical housing
Number 7 bearing code
Single Row angular contact bearing
Accommodates both radial and thrust loads
Higher load ratings then deep groove
Can move inner and outer rings to adjust internal clearance
Number 0 bearing code
Double row angular contact bearing
Takes heavy radial and axial loads in both directions
Speed rating is lower then deep groove or single row angular back bearings
Cannot tolerate and misalignment
Bearing code QJ
Four point angular contact bearing
Used for only combination of axial loads
Can handle reversing thrust loads in either direction
Can be manufactured with larger number of balls increasing its load capacity
Often used as a thrust bearing with a radial clearance in housing
Ball thrust bearings?
Bearing code number ?
Pure thrust load only
Cannot tolerate angular misalignment
Speed limit is only half the limit for radial load bearings
Slow speed
Bearing code number 5
4 types of roller bearings?
Cylindrical
Needle
Tapered
Spherical
Bearing code number N
Cylindrical roller bearing
Can only support pure radial load
Great radial load capacity
Can handle small misalignment
3 types of needle bearing?
No cage or inner cage
Drawn steel cup and no inner ring
Machined inner and outer rings
Parts of a single row taper roller bearings?
Inner ring (cone)
Outer ring (cup)
Tapered rollers
Features of single row tapered bearing?
Bearing code number 3
Can carry very heavy combined radial and thrust loads in one direction
Can be used in pairs to accommodate reversing loads
Tolerate little misalignment
Most commonly used tapered roller bearing
Features of double row tapered roller bearing?
Designed for heavy applications
Can be used as floating assembly in a housing
Bearing code # 2
Spherical tapered roller bearing
Barrel shaped rollers provide wide load carrying contact area
This shape provides combined thrust and radial load capacity in both directions
Compact aligning roller bearings(carb)?
Compact aligning roller bearing (CARB)
Can accommodate some misalignment
Same dynamic load rating as spherical roller bearings
Can allow more axial displacement than any other bearings (up to 20 percent of its width
Not recommended for thrust loads
What does the c represent?
Amount of internal clearance.
C1 smallest amount of clearance
C5 largest amount of clearance
C2or c3 standard amount of clearance
What does the K mean
Taper bore
K12 means taper ratio of 1:12
K30 means taper ratio 1:30
When using heat to mount a bearing what is recommended temperature? What is the dangerous temperature?
80 degrees C
Over 120 degrees C will cause permanent deformity
What are methods for heating the bearing for installation?
Induction heater
Heating cabinet
Oil bath
Heat ring
Max temp for heating sealed bearings?
80 degrees C
What size feeler gauge is used to determine there is no gap between bearing and shoulder?
.001”
What is internal clearance?
The total amount of clearance between the rolling elements and the raceway when one ring is pushed far away from the other ring as possible.
What is axial internal clearance?
The clearance between the rolling elements and the raceway when one ring is moved away from the other in a axial direction.
What is residual clearance?
The internal clearance (radial or axial) After the bearing has been mounted.
What is the running clearance?
The internal clearance in a bearing when it is running at its operating temperature
What are the 3 classes of preload?
1: lighter then normal preload
2: normal preload
3: heavier than normal preload
How is preload set?
By using spacers of shims to push one ring axially against the rolling elements
1 self aligning ball bearing
Great for misalignment
Often used on the coupling end of overhung fan shafts
Can support small axial load
2 spherical ball bearing
Intended to accommodate angular Mis alignment
3 taper roller bearings single row
Carry heavy combined radial and thrust loads in one direction
Can use in pairs to accommodate reverse loads
4 double row taper bearings
Heavy applications
Can be used as floating assembly in housing
5 thrust ball bearing
Pure thrust only
Speed limit only half the limit for radial load bearing
Intended for slow speeds
6 single row deep groove ball bearing
General use
Mainly supports radial loads
Can support combination loads and moderate axial loads in both directions
Tolerates very little angular misalignment
7 single row angular contact bearing?
Accommodate radial and thrust loads
Can order different contact angles to change axial loads
Can be used as one or in pairs
N single row cylindrical roller bearing
Support only radial load only
Can prevent axial movement in one direction
NA needle roller bearings
Series code 0
Extra light
Series code 1
Extra light thrust
Series code 2
Light
Series code 3
Medium
Series code 4
Heavy
Series code 8
Extra thin section
Series code 9?
Very thin section.
What are the bearing clearance codes?
C 1-5
C 1 smallest amount of clearance
C-5 most amount of clearance
Normal clearance lies between c2 and c3 it is the clearance in standard bearings and has no designation.
What are the shield codes for bearings?
Z single side metal shield ZZ both side metal shield RS single rubber seal 2RS both side rubber seal V single non contact seal VV double non contact seal NR snap ring and groove M brass cage
What are the last digit codes in bearing number?
00 = 10mm 01 = 12mm 02 = 15mm 03 = 17mm O4= (x5) = 20mm 05= (x5) = 25mm 06 = (x5) = 30mm And so on
Bearing sounds through a stethoscope should have a soft purring sound.
- loud hollow noise means?
- high pitched scream or whine?
- growling noise?
-To much internal clearance
- clearance to small
- surfaces of the rollers and raceways are deteriorating
Brinelling is impact denting and cause by:
When installing bearings
- hammer blows
- dropping the bearing on hard surfaces
- Shock loading on the machine from any source
False brinelling is round depressions worn into the raceways by a rolling member. What causes false brinelling?
- bearing is not turning and vibration is present
- the vibration causes the film lubricant between the rolling elements and the raceway to break, allowing metal to metal contact.
- rolling elements vibrate against raceways
How can false brinelling be eliminated?
Do not store bearings in areas subject to prolonged vibration.
Lubricant can generate its own contaminants as it breaks down (acids, sludges, and varnish. What are some measure to reduce this contamination?
- keep temperature of the bearing housing below 55 degrees C(130F)
- establish an oil change interval
- circulate oil through filter
- use oil mist system
- use oil that resist oxidation
Grease level inside a housing should be ________ full
1/3
Even total fill grease should only be filled to _______%
80
Two main causes of vibration are:
Imbalance - accounts for half the causes of vibration.
Misalignment -
Arc tracks in bearings look like?
Pencil lines on the raceways at each rolling element
If you have to remove your hand immediately from a bearing the temperature is about ______ degrees C
60
What are the things to check within the bearing housing when the temperature is running hotter than normal ?
- to much or to little lubricant
- a seal could be rubbing to hard
- bearing is failing
- there is an increase load
- there is additional heat from an outside source
Darkens oil indicates?
Oxidation and means oil should be changed
Sludge and acids in oils indicate?
Advanced oxidation and oil change intervals should be shorter
Sand in the oil indicates?
Paint chips in the oil indicate
Sand is coming out of the casting
Paint on the inside of housing is incompatible with oil.
Hydrostatic lubrication uses pressure instead of velocity to force fluid into the loaded area. What are some advantages?
Plain bearings
- no wear at start up
- low friction and therefore low power consumption at start up
- can dampen out vibrations
- cool operation
- best solution for slow speed, heavily loaded bearings, where low friction and accurate shaft positions are important.
Hybrid lubrication is?
A combination hydrodynamic (velocity) and hydrostatic (pressure) to lubricate bearings.
Advantages of hybrid lubrication?
- can support large, unbalanced loads at high speeds.
- it had the highest load rating of any bearing
- provides accurate shaft positioning when the load is unsteady.
- it provides full film lubrication at any speed or when journal is at rest
Oil mist systems use compressed air at ______ to _______ psi to atomize the oil and spray it on the bearing?
10 to 50
What does a sour smell from the bearing lubricant indicate?
Acid build up from oxidation in the lubricant or from external contamination
Why is it important to inspect bearing while it is running?
Noise, vibration and leaks are more easily detected
When is it best to re-lubricate bearings?
When machine is not running
Bearing is running to hot you would check and correct?
Oil level - to low add, to high drain
Check for external heat source
Check for soft foot
Check for rubbing seals
Check for coupling alignment
Check vibration levels
If a floating bearing is heating up you should check it has sufficient axial space in the housing to move. This is obtained by?
Removing the fixing ring
Or
Adding shims to the end cover
Unsealed bearings can be heated to a max temp of 120 Degrees C (248 F) but a sealed bearing can heated to _______ degrees C?
80 (175)
Cold mounting bearing should only be done with bearing bores up to ______ inches ?
1 1/2
When is preload applied to a bearing and why?
When the operating load is to light to make the rolling element roll properly. It ensures that the rolling elements have enough traction to roll and track properly.
Preload is also applied to reduce radial deflection of the shaft and make a stiffer assembly
When using coolant to remove a bearing is it important to not apply to the part you are apply force to. How come?
Parts become extremely brittle when chilled with dry ice or nitrogen
Why should you never pull on the outer ring of a self aligning ball bearing?
It can explode under tension
When using a punch to remove a bearing it is important NOT use brass, how come?
It work hardens when struck and a piece will break off
Rubbing seals are capable of?
Downfalls of a rubbing seal are?
Retaining oil and not just grease
Provide a positive seal against moisture and fine contaminants
Limited operating speed due to heat caused by friction
Non rubbing seals have no contact with with sealing surface, what are the advantages and disadvantages of non rubbing seals?
- There is no rubbing friction
- there is no wear as long as no contact is made
- they are not easily damaged by solid contaminants
- there are no speed limits
- they can operate at high temperatures
- pressing grease into gaps can increase sealing efficiency
Cannot retain oil
Radial labyrinth seal
Can only handle limited axial and radial movement
Axial labyrinth seal allows for what type of movement?
Axial movement will not affect sealing gaps
Combination labyrinth seal
Provides better sealing
Sealing washer set
Cheapest labyrinth seal and Efficiency can be increased by added more sets
What can extend the use of the labyrinth to oil lubricated bearings?
Flinger ring
If pillow blocks are mounted at 55 to 120 degrees ________ should be installed to stop pillow block from
Getting pulled out of alignment.
Blocks
When there is axial force on a pillow block the the radial capacity is reduced to ________%
65
Three types of loads on pillow blocks
Vertical
Horizontal
Axial
Load capacity can be reduced on horizontally split pillow blocks anywhere from 1/3 to 2/3’a it’s radial capacity if pulled at a ______ degree angle
55 degrees
Rule of thumb for grease fill in a pillow block is about ____ to _____ unless it is a total full application and can be filled to 80-90%
1/3 to 2/3 full
Grease fitting on pillow blocks for re greasing need to be mounted on which side of the housing? Nut side or no nut side
No nut side
Nut will tear the grease fibres
If only one big retaining ring is used on a pillow which side is it installed on and why?
On the retaining but side. So that the grease from the fitting has no restrictions into the bearings
How come set screw locking style bearing reduce the speed rating of the bearing?
Because it pushes the shaft slightly off centre causing more vibration
Strongest type of plain bearing pillow block?
Gib joint
