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11/14/2011
1
Spindle bearings and SpindleSpindle bearings and SpindleChapter-04
Spindle and bearingSpindle and bearing
Spindle is subjected to torsion and bending
stress as well as column action
Load is static and dynamic
Spindle mounted to the bearing should also be
strong
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Requirements of spindleRequirements of spindle
Static and dynamic rigidity
Small overall size to reduce cost
Simple assembly and disassembly
Natural frequency of spindle should be away from
working range
Temperature change should have little effect
Requirements of antifriction bearingRequirements of antifriction bearing
Should take both axial and radial load
Minimum play under working load
Should take load uniformly
Self alignment capacity
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Types of antifriction ball bearingTypes of antifriction ball bearing
Deep groove
Filling slot
Angular contact
Double row
Magneto
Self aligning
Thrust ball bearing
Deep grooveDeep grooveBall BearingBall Bearing
Filling SlotFilling SlotBall BearingBall Bearing
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Angular contact ball bearingAngular contact ball bearing
Magneto bearingMagneto bearing
Thrust ballThrust ball bearingbearing
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Self Aligning ball bearingSelf Aligning ball bearing
Types of antifriction roller bearingTypes of antifriction roller bearing
Cylindrical
Needle bearing
Self aligning
Taper roller bearing
Thrust roller bearing
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Cylindrical roller Cylindrical roller bearingbearing
NeedleNeedle bearingbearing
Self AligningSelf AligningRoller bearingRoller bearing
Taper RollerTaper RollerBearingBearing
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Thrust Roller BearingThrust Roller Bearing
Properties of main spindle assemblyProperties of main spindle assembly
Deflection of spindle depends on◦ Spindle stiffness
◦ Rigidity of the bearing
◦ Rigidity of the structure
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Deflection of spindleDeflection of spindle
Deflection of a spindle nose is high at initial loading and reduces with increasing load
So the bearing is preloaded upto F compensate the initial deformation
Deflection of spindleDeflection of spindle
Load distribution among rolling member
become more uniform
Large number of roller support the load
Deformation is reduced
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PreloadingPreloading
Preloading is the methodology by which we remove the internal clearance in the bearing by applying a permanent thrust load to it. In other terms we can say that we push the bearing to such an extent that it has to move only in the groove (raceway) and cannot move axially in either direction.
Why preloading is necessaryWhy preloading is necessary To eliminate the radial and axial play in the bearing which
would be inherently present even after a bearing is mounted radially on a shaft.
To eliminate all the unnecessary clearances, which induces a rigidity to the bearings and thus to the system the bearing supports.
To control the rotational accuracy of the bearing by reducing the clearances.
When a clearance is present, there is every chance for the rolling element to stop rotating and just skid on the raceway. Preloading the bearings thus helps in preventing the skidding of the balls on the raceway of the bearing.
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How to preload a BearingHow to preload a Bearing
Relative axial displacement of inner and outer races by small amount
Methods of preloadingMethods of preloading
Grinding off the inner face
Inserting spacing rings
But at high RPM this initial Preload is weakened
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Methods of preloadingMethods of preloading
Spring preloading
Spring preloadingSpring preloading
Advantages◦ It tends to provide a constant preload from
the spring
◦ They tend to act as an automatic mechanism, which account for the wear in the bearings
◦ It has the capability to accommodate minor misalignments
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Methods of preloadingMethods of preloading
Thread preloading
Thread preloadingThread preloading
Advantage◦ Can be tightened to preload the bearing◦ If the preload reduces due to wear the
threaded member can always be tightened to take care of the preload◦ The only precaution to be taken in this aspect
is that the loosening of the threaded member should be prevented after tightening
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Deflection of a spindleDeflection of a spindle
The spindle represent a beam/shaft with◦ Supported length L acted upon force p2◦ cantilever length C acted upon force p1
Deflection of a spindleDeflection of a spindle
◦ Deflection y1 is due to bending force p1 and p2◦ Deflection y2 is due to compliance of spindle
support
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Optimum spacing between bearingOptimum spacing between bearing
l
c
Optimum spacing between bearingOptimum spacing between bearing
The optimum value of is between 3 and 5
depends on the ratio
depends on the factor
opt B
A
K
K
B
B
K Stiffness of front bearing
K Stiffness of rear bearing
opt . CB
C l
IKF
K I
B
C
C
K Stiffness of cantilever
I Avg MOI of spindle over cantilever
I Avg MOI of spindle over sup ported length
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Effect of Preloading on deflection Effect of Preloading on deflection
Effect of Preloading on deflection Effect of Preloading on deflection
Play of front bearing due to preload(µm)
Deflection of spindle nose due to bending(µm)
Deflection of spindle nose due to deformation of front bearing(µm)
Total deflection of spindle nose(µm)
15(clearance) 14 16 30
-5(Interference) 13 6 19
-15(Interference) 11 5 16
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Effect of Preloading on deflection Effect of Preloading on deflection
Example questionsExample questions What are the functions of m/c tool spindle
and bearing Description and function of different types
of bearing Why preload is necessary and how to
preload What do you understand by dynamic rigidity
of m/c tool Method to determine optimum spacing of
bearing. Method to determine optimum preload
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That’s all for today
You can download slide from the following address:
http://teacher.buet.ac.bd/aamamun/academic.html