Rolling bearings for mechanical pumps

1. What are the reasons for the abnormal noise when the rolling bearing of the pump is running?

1) The rolling element or raceway is seriously peeled off and the surface is uneven.

2) Improper installation of bearing accessories, looseness or friction.

3) There are iron filings or dirt in the bearing.

4) Lack of lubricant.


2. What are the radial clearances of the rolling bearings of the pump?

1) Original clearance: the clearance in the free state before the bearing is installed.

2) Fitting clearance: the clearance after the bearing is installed on the shaft or in the hole, its size is determined by the amount of interference, and the fitting clearance is smaller than the original clearance.

3) Working clearance: Due to the structural characteristics of some bearings, the clearance can be determined by adjusting the mutual position of the bearing rings during assembly or use, such as radial thrust ball bearings.


3. What issues should be paid attention to when selecting rolling bearings for mechanical pumps?

1) The direction and nature of the load. 2) Alignment performance requirements. 3) Bearing speed. 4) Economy. 5) The accuracy is high or low.


4. How to choose the lubrication method for rolling bearing?

The normal operation of the bearing is related to lubrication. When the temperature of the conveyed medium is 80 degrees and the speed is below 2950r/min, it is lubricated with dry oil; when the temperature of the conveyed medium exceeds 80 degrees and the power is large, it is lubricated with thin oil.


5. How to check whether the rolling bearing is good or bad?

There should be no spots, dents, peeling or peeling on the surface of rolling elements and raceways. The rotation is flexible. After turning by hand, it should slow down and stop gradually. It should not stop suddenly or vibrate.

There should be a certain gap between the cage and the inner and outer rings, and the spacer can be pushed radially by hand to test. The clearance is suitable within the standard range and measured by the lead pressure method.


6. What should be paid attention to when disassembling and assembling rolling bearings?

1) The force application position must be correct. The principle is that the shaft cooperates with the inner ring and the outer shell with the outer ring to avoid force deformation or damage to the rolling elements and raceways.

2) The force should be applied symmetrically, and it should not be hit on one side only, causing the bearing to deflect and damage the journal.

3) Before disassembly and assembly, the shaft and bearing should be cleaned without rust and burrs.

7. What happens when there is too much oil in the bearing box?

If the bearing housing is filled with too much oil, the bearing has no space for heat dissipation, which will cause the bearing to heat up.


8. How to check the radial clearance of rolling bearings?

Use the lead pressing method and the feeler gauge method to measure. The translation of the radial clearance is not marked in the bearing code. The clearance of the bearing varies according to the size of its inner diameter. It is determined by looking up the table. In general, the radial clearance of the rolling bearing cannot be greater than 3/1000 of the inner diameter of the bearing, and the radial clearance of the centripetal short cylindrical sub-bearing cannot be greater than 2/1000 of the inner diameter of the bearing.


9. Why should the rolling bearing be preloaded?

When assembling radial thrust ball bearings or radial ball bearings, if a certain axial load is applied to the inner and outer rings of the bearing, then the inner and outer rings will undergo relative displacement, eliminating the gap between the inner and outer rings and the rolling elements. The initial elastic deformation is generated, and the preload can improve the rotation accuracy and life of the bearing and reduce the vibration of the shaft.


10. How to achieve rolling bearing preload?

1) Use the thickness difference between the inner and outer backing rings of the bearing to achieve preload.

2) The spring is used to achieve preload, and the spring acts on the outer ring of the bearing to realize the preload of the bearing.

3) Narrow the inner ring or outer ring used in pairs to achieve preload.

4) Adjust the axial position of the inner ring of the bearing tapered hole to achieve preload.


11. What is the substitution principle of rolling bearings?

1) The technical parameters such as the working capacity coefficient and the allowable static load of the bearing should be equal to or higher than the technical parameters of the original bearing as far as possible.

2) The allowable limit speed should be selected to be equal to or higher than the actual speed of the original bearing.

3) The accuracy grade of the substitute bearing should not be lower than that of the original bearing.

4) The size should be the same, and the matching size of the machine and the bearing cannot be changed arbitrarily because of the replacement of the bearing.

5) For bearings using the nesting method, the concentricity of the inner and outer cylindrical surfaces to be nested must be guaranteed, and the tolerance and fit should be selected correctly.


12. What kinds of fixing methods are there for rolling bearings?

1) Two-way fixation with unilateral force, 2) Single fixation with bilateral force, 3) Mixed fixation


13. On what basis is the bearing oil level determined?

For rolling bearings, the centerline of the lowest ball of the bearing is the normal oil level, the lower third of the ball is the low oil level, the upper two-thirds of the centerline of the ball is the high oil level, and the main shaft is lubricated by the oil throwing ring. In terms of installation, the oil ring is generally 1.5-2 times larger than the diameter of the main shaft to be lubricated.

The oil level in the oil chamber should be at a certain distance from the main shaft oil, which is generally 1/2 of the diameter of the main shaft or about 5mm below the bearing bush when the high oil level is removed.


14. Why is it not good if the bearing oil level is too high or too low?

1) The oil level of the bearing is too low so some parts of the bearing cannot be lubricated, so the bearing will wear and generate heat, which will cause the bearing to burn out.

2) If the oil level is too high, with the rotation of the main shaft, the rolling bearing and oil ring will easily leak oil from the shaft seal during the process of carrying oil; if the oil level is too high, the rotation of the oil ring will also be hindered, causing the bearing to heat up.


15. For bearings lubricated with grease, what are the requirements for oil filling?

1) For low-speed machines (speeds below 1500r/min), the filling oil volume is generally not more than two-thirds of the entire bearing chamber;

2) For machinery with a rotation speed above 1500r/min, the amount of oil filled should generally not be more than half of the entire bearing chamber.


16. What are the reasons for high bearing temperature?

1) The oil level is too low, and the amount of oil entering the bearing is reduced.

2) The oil quality is unqualified, water or impurities have entered, and the oil has been emulsified and deteriorated;

3) The oil ring does not rotate, and the oil supply to the bearing is interrupted.

4) Insufficient cooling water for bearings

5) Bearing damage

6) The tightening force exerted by the bearing gland on the bearing is too large, or too small, or the radial clearance is crushed to death, resulting in loss of flexibility.


17. What are the reasons for the overheating of the rolling bearing of the centrifugal pump?

1) The axial clearance of the rolling bearing is small

2) The installation direction is not correct

3) Dry wear or loose

4) The quality of lubricating oil is not good, the amount of oil is insufficient or the circulation is not good

5) The oil-throwing ring is deformed and cannot carry oil.


18. What is the standard for rejecting pump rolling bearings (radial ball bearings)?

1) The raceways of the inner and outer rings are peeled off, severely worn, or cracked.

2) The rolling element is out of round or the surface is peeled off and has cracks.

3) The cage is severely worn or deformed, and the rolling elements cannot be fixed.

4) There are noises or vibrations when turning, and there are braking phenomena and reverse reversal when stopping.

5) The fit clearance of the bearing exceeds the maximum value of the specified clearance.


19. The raceway surface of the inner ring and outer ring of the bearing or the rolling surface of the rolling body appear fish scale peeling phenomenon, what is the reason?

1) Excessive load, 2) Poor installation, 3) Intrusion of foreign matter, improper lubricant, 4) Improper bearing clearance, 5) Poor precision of shaft and bearing housing, uneven rigidity of bearing housing, large shaft deflection, 6) Rust, erosion points, abrasions, and indentations.


20. What are the performances of bearing alloys?

1) Low coefficient of friction reduces shaft wear;

2) High plasticity makes the shaft and bearing bush run well;

3) Good thermal conductivity;

4) Sufficient compressive strength and fatigue strength.


21. What are the reasons for the vibration of the rolling bearing?

1) Random vibration transmitted by rolling elements.

2) Random vibration due to improper installation and lubrication.

3) Vibration from outside the bearing.


22. What are the assembly requirements for rolling bearings?

1) The end face marked with the model number on the bearing should be installed in the visible part for easy replacement.

2) The radius of the arc at the shoulder of the journal or the housing hole should be smaller than the radius of the arc chamfering on the end face of the bearing to ensure that the bearing is close to the shaft shoulder and the shoulder of the housing hole after assembly.

3) The fixing device of the bearing must be intact and reliable, with a moderate degree of tightness and reliable loosening.

4) During the assembly process, keep it clean to prevent debris from entering the bearing;

5) After assembly, the bearing rotates flexibly without noise, and generally the temperature rise does not exceed 50 degrees.


23. What is the reason for the high-temperature rise of rolling bearings?

1) In the process of installation and operation, there is the intrusion of impurities or dirt.

2) Use of improper lubricant or insufficient lubricant.

3) Friction or lose of fit between sealing devices, thermal rings, bushings, etc. causes friction.

4) Improper installation, such as skewed inner and outer rings, non-concentric mounting holes, deformation of the raceway, and improper clearance adjustment.

5) Wrong type selection. When an unsuitable bearing is selected to replace it, it will generate heat due to overload or high speed.


24. How to install the radial ball bearing on the shaft, such as using the knocking method?

Use steel sleeves, copper sleeves, or copper rods to tap the bearing ring symmetrically and evenly into the designated position. It is forbidden to tap the outer ring of the bearing to avoid damage to the bearing. After installation, check that the outer ring of the rotating bearing should be flexible and free of obstructions Phenomenon.


25. What are the disassembly methods of commonly used rolling bearings?

Knocking method, pulling method, pushing method, and hot dismantling method.


26. What should be paid attention to when disassembling the rolling bearing (the bearing is on the shaft) by knocking or pulling out?

1) The knocking force should generally act on the inner ring of the bearing, and should not be knocked on the rolling elements and cages, and knocking on the outer ring of the bearing is not allowed.

2) When using the pull-out method, the inner ring of the bearing should be pulled, and the outer ring of the bearing should not be pulled only to avoid excessive loosening or damage to the bearing.


27. What are the main forms of rolling bearing damage?

1) fatigue pitting, 2) abrasion, 3) burn, 4) electric corrosion, 5) cage damage, 6) inner and outer ring fracture, 7) ball out of round, 8) raceway surface peeling.

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