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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