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# Selection of bearing clearance

2020-05-04

I. clearance selection principle:

1. It is advisable to adopt a large clearance group in cases where the temperature difference between the inner and outer rings is large, the friction torque needs to be reduced, the deep groove ball bearing needs to bear a large axial load or the centering performance needs to be improved.

2. When the rotation accuracy is high or the axial displacement is strictly limited, it is advisable to use a small clearance group.

Ii. Factors related to clearance:

1. Coordination of bearing inner ring and shaft.

2. Coordination of bearing outer ring and housing hole.

3. The influence of temperature.

Note: the reduction of radial clearance is related to the actual effective interference of the matching parts, the size of the matching shaft diameter, and the wall thickness of the shell hole.

1, the actual effective interference (inner circle) should be: △dy = 2/3△d -- G* △d

Nominal interference, G* is the compaction size of interference fit.

2, the actual effective interference (outer ring) should be: △Dy = 2/3△D -- G* △D

Nominal interference, G* is the compaction size of interference fit.

3. The heat generated will cause the internal temperature of the bearing to rise, and then cause the expansion of the shaft, bearing housing and bearing parts.Clearance can be increased or decreased, depending on the material of the shaft and housing, and the temperature shaving between the bearing and the bearing support.

Iii. Calculation formula of clearance:

(1) influence of cooperation

1, bearing inner ring and steel solid shaft: △j = △dy * d/h

2, bearing inner ring and steel hollow shaft: △j = △dy * F(d)

F(d) = d/h * [(d/d1) 2-1]/[(d/d1)2 - (d/h)2]

3, bearing ring and steel body shell: △A = △Dy * H/D

4. Bearing outer ring and steel thin-wall enclosure: △A = △Dy * F (D)

F(D) = H/D * [(F/D) 2-1]/[(F/D)2 - (H/D)2]

5. Bearing outer ring and gray cast iron housing: △A = △Dy * [F(D) -- 0.15]

6, bearing outer ring and light metal shell: △A = △Dy * [F(D) -- 0.25]

Note:

△j -- expansion of the inner raceway rim diameter (um).

Delta dy - effective journal interference (um).

D -- nominal bearing diameter (mm).

H -- rim diameter of inner raceway (mm).

B -- bearing width (mm).

D1 -- hollow shaft diameter (mm).

△A -- the amount of shrinkage (mm) of the outer ring raceway baffle diameter.

Delta Dy -- actual effective interference (um) in housing hole diameter.

H -- rim diameter of outer ring raceway (mm).

D -- nominal diameter (mm) of bearing outer ring and housing hole.

F -- outer diameter of bearing housing housing (mm).

(2) the influence of temperature

Delta T = Г b * [De * (T0 - Ta) - di * (Ti, Ta)]

Including Г b for linear expansion coefficient of bearing steel is 11.7 * 10-6 mm/mm / 0 c

De is raceway diameter of bearing outer ring, di is raceway diameter of bearing inner ring.

Ta is the ambient temperature.

T0 is bearing outer ring temperature, Ti bearing inner ring temperature.

Iv. Relationship between axial clearance and radial clearance:

Ua = [4(fe + fi - 1) * Dw * Ur - Ur2] 1/2

Because radial clearance Ur is small, so Ur2 is small, ignore it.

Therefore, Ua = 2 * [(fe + fi - 1) * Dw * Ur] 1/2

Where fe is the curvature coefficient of the outer ring groove, fi is the curvature coefficient of the inner ring groove, and Dw is the diameter of the steel ball.

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