Chapter 13 Rolling-contact Bearings Key Terms: rolling-contact bearing ball bearing roller bearing thrust bearing

radial load thrust load basic dynamic load rating basic static load rating equivalent load the rated life expected life

13.1 Types of Rolling-contact Bearings and the Representing Code 1. Construction width Materials: GCr15、GCr15SiMn 58~65HRC outer ring D inner ring Retainer d rolling element outer ring race

2. Parameters Contact angle Load angle Limiting speed Misalignment Capacity: allowable angular deviation 

3. Types of Rolling-contact Bearing According to loading direction: radial bearings thrust bearings angular contact bearings According to rolling element shapes: ball bearings roller bearings

4. Types Double-row angular contact bearings

Double-row tapered roller bearings 35

Double-row self-align ball bearings 1

Double-row self-align roller bearings 2

Self-align thrust bearings 2

Tapered roller bearings 3

Double-row deep groove bearings 4

Thrust bearings 5

Deep groove bearings 6

Angular contact bearings 7

Thrust roller bearings 8

Roller bearings N

Double-row roller bearings NN

Needle bearings NA

Four points contact bearings QJ

5. Numbers of Rolling-contact Bearings(GB/T272-93) Bearing Designation: 71206AC/P6/C2 pre-symbol basic number post number

First & second: inner diameter number d=065=30mm Basic Number First & second: inner diameter number 　　 　　　　　　　d=065=30mm Third: diameter number 　　　　　　　 1－extra-light series 2－light series 3－medium series 4－heavy series

Fourth: width number 　　　　　　　 0－narrow series (omitted ) 1－normal series 2－wide series Fifth: Type number 　see table 13.1　　　　

First: Internal configuration number Post Number First: Internal configuration number 70000： C：=150 AC：=250 B：=400 Fourth: Tolerance lever /P2：2 /P4：4 /P5：5 /P6：6 /P6x－6x /P0－0(omitted) -

sixth: free clearance number /C0: 0(omitted) /C3: 3 /C4: 4 /C5: 5 + Pre-symbol Partial symbol of the bearing, e.g. L, K, R, etc.

Example Explain the following bearing codes: 6308 ，7211C/P5 Solution 6308－ Tolerance 0, 0 Group Clearance For the diameter of 40mm, deep groove ball bearings, in the series, 7211C/P5 － The inside diameter is 55mm, the angle contact ball bearing, light series, angle of contact =150,5 level common difference, 0 group of windage

6. The Choices of the Bearing Types Load Limiting Speed Misalignment Capacity Mount and Dismount

13.2 The Forces and Failures 1. The loading analysis

Fig. 13.5 the force changing procedure

2. The Failure types of rolling-contact bearing 1) Pitting

2) Plastic deformation

3) wear

4) breakage

5) burning

3. Design Criterion 1）for revolution bearings: calculate the fatigue life 2）for static or low revolution speed bearings: calculate the static strength

13.3 The Selection of Rolling-contact Bearings 1. The fatigue life of rolling-contact bearings 1)Life The life is the working revolutions or hours before the pitting occurs on the bearing. 2) Rated life L10 , Lh The rated life is the life that 90% of the bearings would achieve successfully under a rated load.

Rated Life of Different Reliability

3) Basic dynamic load rating C The basic dynamic load rating is the load to which the bearings can be subjected while achieving a rated life of 106r. Cr or Ca 4) Basic static load rating C0 The basic static load rating is the load that the bearings can withstand without permanent deformation of any component. C0r or C0a

5) Load/life relationship P/kN L10 /(106r) 3 10 1 C =3, for ball bearings; =10/3, for roller bearings.

C——basic dynamic load rating P——equivalent load —— check formula Lh——the rated life C——basic dynamic load rating P——equivalent load n——rotational speed (rpm) ——3 or 10/3

C——basic dynamic load rating P——equivalent load —— design formula L'h——the expected life C——basic dynamic load rating P——equivalent load n——rotational speed (rpm) ——3 or 10/3

2. Equivalent load of bearings 1)Concept 2)Calculation For radial load only: P=fpR For thrust load only: P=fpA

For radial and thrust load: P= fp(xR+yA) P——equivalent load; R——applied radial load; A——applied thrust load; fp——load coefficient, table 13.4 x——radial factor, table 13.3 y——thrust factor, table 13.3

3. Determination of radial load R According to force equilibrium principle:

=3000N

4. Determination of thrust load A —for angular ball bearings and tapered roller bearings (1) Two mountings of angular contact bearings: Face to face Back to back

(2) According to equilibrium condition: S1 S2 Derived axial load S

(3) Calculation of applied thrust load for angular contact bearings

(4) Procedure 1) Draw directions of derived axial load and compute its magnitude; 2) According to direction of resultant axial forces on shaft, judge moving tendency of shaft, judge “loosen bearing” and “pressed bearing”; 3) The applied thrust load of “loosen bearing” is equal to its own derived axial load; 4) The applied thrust load of “pressed bearing” is equal to algebraic sum of other thrust loads (except for its own derived axial load ).

Example As shown below, R1=10000N, R2=5000N, FA=2000N, S=0.68R. Find: A1=? A2=? 1 2 Solution

—for deep groove ball bearings Determination of thrust load A —for deep groove ball bearings Regarding the gulley ball bearing, its axial loading A decided by the external influence on axis axial force FA, aims the bearing, its withstands axial force A is the external influence on axis axial force (A=FA), another bearing withstands the axial force is zero.

Procedure for Bearing Selection Determine the design life L'h Determine the equivalent load P=xR+yA Calculate the required basic dynamic load Select a bearing with C( > Creq’d) and a bore that closely matches the shaft diameter.

Procedure for Bearing Life Check Determine the basic dynamic load rating Determine the equivalent load P=xR+yA Calculate the expected life Check the bearing life

1.The angular contact bearings (7207C) are shown below, they are subjected to radial loads R1=1500N, R2=875N, the applied external thrust load FA=400N, the derived load S=eR. Compute the applied thrust loads A1, A2 .

2. The tapered roller bearings are shown below，the external applied load FA=1030N, FR=6000N, n=1000r/min, load coefficient fp=1, the basic dynamic load rating C=34000N， Find： 1) The equivalent dynamic loads P1, P2； 2) The rated life of bearings.

3. Two angular contact bearings 7207AC are mounted back to back on the shaft, the applied loads on the gears as know that is Ft=2200N, Fr=900N, Fa=400N, the reference diameter d=314mm, the rotational speed n=520rpm, medium shock, Find the rated life of bearings.

13.4 Mounting of Bearings 1. Tolerance and Fit The Basic Hole System interference fit Shaft tolerances: k6, m6, n6, etc. The Basic Shaft System clearance fit Hole tolerance: H7, J7, Js7, etc

“walks the inner loop” the scratch

Heat crack

Hot adhesion

“walks the addendum circle” the scratch

1, in forbids to rap the addendum circle directly with the iron hammer! 2, forbids through the rolling body transmission installment strength!

2. Dimensions The shoulder is lower than the inner loop altitude highly!

Dismount of bearings

3. Axial Retaining of bearings 1) inner race retaining (a) (b) (c) Retaining ring End cap Locknut

2) outer race retaining (a) (b) a) Retaining ring b) End cap

4. Mount Types 1) Two bearings retained in one direction

C=0.2~0.4mm

2) One bearing retained in two directions, one bearing float The inner loop is fixed, the addendum circle is not fixed!

At the same time inner loop, addendum circle fixed!

3) Two bearings float

13.5 Practical Considerations in Application of Bearings 1. Lubrication Function: 1.Provide a low-friction film; 2.Protect the bearing components from corrosion; 3.Carry heat away from the bearing unit; 4.Dispel contaminants and moisture from the bearing; Lubricant: grease and oil: table 13.5

2. Bears’ Preloading

3. Sealing 1) Contact sealing a) Felt circle seal

b) Lip Seal

2) Non-contact Sealing a) Groove seal b) Labyrinth seal

4. Modify Clearance 1) By shim Attention: The bevel gear must adjust the shafting the axial location. method: Between adjustment retainer cup end surface and bearing seat end surface filling piece thickness.

2) By screw

3) By locknut

5. Stiffness

Derived Axial Load S Direction:

Magnitude of Derived Axial Load Tapered Roller Bearing Angular Contact Ball Bearing 70000C(a=15°) 70000AC(a=25°) 70000B(a=40°) S=R/(2Y) S=eR S=0.68R S=1.14R

a) face to face

b) Back to back

Typical Shapes of a Roller

Radial Bearing : (a)、(b) =00 Thrust Bearing: (c) 、(d) =45~900 Angular Contact Bearing: (e)、(f) =0~450

Life Distribution Chart 1 90 Amount of no failure /%

Angular contact bearings 7

The end Thanks!