Gearbox bearing standard installation and common problems

bearing 6201

A speed reducer is a rotating device, and bearings play a crucial role in its rotation. Therefore, the installation and testing of bearings are extremely important when using a speed reducer. In practical applications, speed reducers are compatible with a variety of bearing types, including commonly used small bearings such as bearing 6201, 608zz, and 6301, as well as specialized bearings such as pulley bearings, pulley wheels with bearings, track roller bearings, and router bit bearings. Among brands, Koyo bearings are often chosen for their stable performance, while the SKF bearing price list can serve as a cost reference when purchasing. Common problems with speed reducer bearings during use are also a concern. Below, we share relevant standard installation guidelines and some common issues regarding speed reducer bearings, hoping to be helpful to everyone.

Gearbox bearing standard installation (new bearing installation standard)

1. New bearings should be checked for model number (e.g., for purchased bearings such as 6201-2RS, 608zz, and 6301-2RS, confirm the model number matches the design; if using Koyo or SKF bearings, verify the brand identification). Surface inspection and radial clearance measurement should meet requirements. After cleaning with kerosene, heat with machine oil to 80-100℃ and maintain this temperature for 30 minutes.

2. Install the bearing (model number should face outwards). Tap the inner ring with a copper rod to ensure it is tight against the shaft shoulder without gaps or looseness. If installing a pulley bearing or a pulley with a bearing, pay special attention to the coaxiality of the bearing and pulley; if installing a track roller bearing or milling cutter bearing, ensure accurate running trajectory after installation. After the bearing cools, rotate it by hand; it should rotate freely, and the bearing housing should function normally, rotating smoothly without impact noise. During assembly, pay close attention to the assembly sequence of each component to avoid incorrect installation or omission.

3. Temperature limits for rotating bearings: 80℃ for rolling bearings and 65℃ for sliding bearings. 100℃ for rolling bearings and 80℃ for sliding bearings in motors.

Maintenance procedures for speed reducers and bearings

1. Prepare necessary lifting tools, disassemble relevant oil and water pipes, and seal them promptly.

2. Remove the screws from the gearbox mating surface and end cover, remove the retaining pins, clean them, and store them properly.

3. Measure and record the clearances of each part before repair.

4. Lift off the top cover, remove the gears, and place them in the designated location.

5. Clean and inspect the bearings and gears with kerosene. If the bearings are small bearings such as Bearing 6201ZZ or 608zz, carefully check the ball wear. If they are Koyo or NSK bearings, refer to the standard wear threshold of the brand bearing to determine their condition, measure the bearing clearance, and check the wear of the gears and bearing cage.

6. Drain the oil from the gearbox and clean it.

7. When replacing bearings, if replacing a pulley bearing, a pulley with a bearing, or a track roller bearing, a special pry bar must be used. If removal is difficult, the bearing inner ring can be heated by pouring hot machine oil at 120℃. Heating with an acetylene flame is strictly prohibited. Due to the special structure of milling cutter bearings, extra care must be taken to protect the cutting edge and related components during disassembly.

8. Measure the journal and the inner ring dimensions of the new bearing (for example, for a newly replaced 6301RS bearing, the inner ring diameter must be accurately measured to ensure proper matching with the journal). Measure the clearance and record it.

9. Heat the bearing with machine oil and install it on the journal. If installing a pulley with a bearing, adjust the pulley position simultaneously and install the retaining ring.

10. Re-measure the bearing clearance and record it.

11. Perform a water pressure test on the internal cooling water drain of the reducer and check for wear.

12. Hoist the gear into position, rotate the large gear to ensure proper meshing of the large and small gears and proper center alignment.

13. Hoist the reducer cover and measure the bearing top clearance. If the bearing is a track roller bearing, pay special attention to the clearance on the side in contact with the track; if it is a milling cutter bearing, adjust it according to the milling accuracy requirements, measure the axial clearance of each part, and adjust it appropriately.

14. Apply sealant to the mating surfaces, insert the locating pins, and tighten the flange bolts on the mating surfaces.

15. Assemble the end covers and adjust the gaskets.

16. Connect the oil and water pipes and valves.

17. Adjust the gearbox.

Common problems and faults of gearbox bearings

Why do bearings need thrust clearance and expansion clearance?

a. Metallic materials exhibit thermal expansion and contraction. When a shaft operates under different temperature conditions, its length and diameter will change. Whether it's a small bearing like the 608zz bearing or a specialized bearing like pulley bearings, a thrust clearance is necessary to ensure the formation of a pressure oil film in the thrust bearing.

b. To prevent excessive stress during shaft expansion that could damage the bearing, expansion clearance is essential for all types of bearings, including those from Bearing Koyo, SKF, router bit bearings, and track roller bearings.

How to measure the clearance between the split bearing cap and the top of the bearing using the lead wire pressing method?

a. Place lead wires near the bolt holes and along the arc length of the bearing top on the mating surface between the bearing housing and the bearing cover. If the bearing is a deep groove ball bearing such as Bearing 6201RS or 6301RS, ensure the lead wire placement avoids the rolling element contact area.

b. Install the top cover and tighten the bolts evenly diagonally. Remove the bearing cover and use an outside micrometer to measure the thickness of each lead wire.

c. Subtract the average thickness of the bearing housing mating surface from the average thickness of the lead wires at the bearing outer ring. A positive difference indicates the clearance, while a negative difference indicates the tightening force.

What are the dangers of bearing oil levels that are too low or too high?

a. Excessive oil level increases the resistance of the oil ring, causing slippage or disengagement. Whether it's pulley wheels with bearings or track roller bearings, the friction between oil molecules raises the bearing temperature, increasing oil leakage at the clearances and loss of frictional power.

b. Insufficient oil level prevents the bearing balls or oil rings from carrying oil. Whether it's a small bearing like the 608zz bearing or a specialized bearing like a router bit bearing, the lack of lubrication will cause the temperature to rise, potentially leading to bearing burnout.

What causes high temperatures in rotating mechanical bearings?

a. Low oil level, insufficient oil, or no oil.

b. Oil level too high, excessive oil.

c. Inadequate or contaminated oil (contains impurities).

d. Insufficient or interrupted cooling water supply.

e. Oil ring is dry or not rotating.

f. Defective or damaged bearing (e.g., worn Koyo bearing balls, broken SKF bearing cage, or deformed inner ring of 6301RS bearing).

g. Equipment vibration.

Analysis of factors causing gearbox bearing failure

a. Wear caused by improper adjustment of the radial clearance between the reducer housing bearing chamber and the bearing outer ring. Whether it's small bearings like Bearing 6201RS or specialized bearings like pulley bearings, the fit between the bearing and the bearing chamber must be precise. The bearing outer ring and bearing cap have a clearance fit; too tight a fit will result in insufficient radial clearance due to thermal expansion during bearing rotation, while too loose a fit will reduce rotational accuracy and cause runout. Therefore, there is generally a radial clearance of 0.05-0.10mm between the bearing outer ring and the bearing cap. Simultaneously, to allow for free expansion of the shaft after heating, sufficient expansion clearance should be maintained between the bearing and the bearing chamber end cover on both the thrust and load sides of the bearing. The clearance value is related to the shaft length.

b. The fit between the bearing and the shaft. The inner ring of a bearing is tightly fitted to the shaft tail, such as in 608zz bearings and router bit bearings. If the interference fit is too small, the inner ring will rotate, causing friction with the shaft, resulting in vibration, overheating, and bearing damage. Wear on the bearing seat can render the shaft unusable. Conversely, if the interference fit is too large, the radial clearance of the bearing will be too small, causing the bearing to seize or be damaged. Therefore, the interference fit should be determined according to the drawing requirements or testing specifications. Generally, the tightness between the bearing and the shaft is 0.02-0.05 mm.

Common faults and troubleshooting methods of speed reducers and bearings

Gearbox overheating

a. The shaft or journal is bent or deformed. Solution: Replace.

b. The bearing is not installed correctly or the clearance is inappropriate (e.g., the 6301RS bearing is misaligned, or the clearance of the track roller bearing is not adjusted according to the operating conditions). Solution: Reinstall or adjust.

c. The bearing is worn or loose (e.g., the bearing ball is worn, or the outer ring of the pulley wheels with bearings is deformed). Solution: Replace.

d. The gear meshing clearance is too small. Solution: Adjust.

The gearbox is noisy

a. Shaft bending or deformation. Solution: Replace.

b. Gears severely worn. Solution: Replace.

c. Incorrect gear meshing. Solution: Adjust.

d. Damaged bearings (e.g., broken SKF bearing cage, cracked inner ring of Bearing 6201ZZ). Solution: Replace.

e. Improper bearing clearance (e.g., excessive clearance in milling cutter bearings, insufficient clearance in 608zz bearings). Solution: Adjust.

f. Insufficient lubricating oil in the bearing. Solution: Add lubricating oil to the appropriate amount.

g. Loose connections. Solution: Tighten.

Gearbox oil leak

a. Damaged gasket between the split surfaces of the housing. Solution: Replace the gasket.

b. Aging, deformation, or wear of the sealing ring. Solution: Replace.

c. Wear or deformation of the shaft surface at the sealing ring. Solution: Repair or replace.

d. Oil seal damage caused by excessively high lubricating oil temperature (e.g., oil seal aging due to prolonged high-temperature operation of the pulley bearing). Solution: Check for the cause of overheating and replace the oil seal.