Gearbox Bearings Installation and Common Problems

Gearbox Bearings Installation and Common Problems


Gearbox Bearings Installation:

Gearbox bearings installation is as below,

1. Check bearing model, inspect surface, measure radial clearance, clean bearing with oil and heat bearing to 80~100℃. Then keep bearing at this temperature for 30 minutes.

2. Install the bearing (the model should face outwards) and knock the inner ring with a copper rod, close to the shaft shoulder, without clearance, and no looseness. After the bearing has cooled down, the bearing should be rotated flexibly by hand, and the cage should work normally and rotate smoothly without impact sound. When assembling, pay special attention to the assembly sequence of each part to avoid incorrect assembly or forgetting.

3. Temperature limit is as below,
Rotating machine rolling bearing: 80℃
Rotating machine sliding bearing: 65℃
Motor rolling bearing: 100℃
Motor sliding bearing: 80℃

Maintenance Steps of Gearbox and Bearings:

(1) Prepare the required lifting tools, disassemble the relevant oil and water pipes, and seal them in time.
(2) Remove the screws on the joint surface of the reducer and the end cover screws, take out the stabilizing pins, and place them properly after cleaning.
(3) Measure and record the clearance of each part before repair.
(4) Hang down the upper cover, lift out the gear, and put it in the designated place.
(5) Use kerosene to clean and inspect bearings and gears, and measure bearing clearances, and check the wear of gears and bearing cages.
(6) Release the oil in the box and clean it up.
(7) When replacing the bearing, use a special squeegee. When it is difficult to squeeze and unload, use 120℃ hot engine oil to pour the inner ring of the bearing for heating. It is strictly forbidden to heat by acetylene flame.
(8) Measure the dimensions of the journal and the inner ring of the new bearing, measure the clearance and record it.
(9) Install the bearing on the journal with oil heating, and install the elastic retaining ring at the same time.
(10) Retest the bearing clearance and record it.
(11) The internal cooling water of the reducer shall be subjected to a hydraulic test and the wear condition shall be checked.
(12) The hoisting gear is in place, and the large gear is turned to make the large and small gears mesh normally and the center is aligned.
(13) Hoist the upper cover of the reducer, measure the clearance at the top of the bearing, measure the axial clearance of each part, and adjust it appropriately.
(14) Coat the joint surface with sealant, put on the positioning pins, and tighten the flange screws on the joint surface.
(15) Assemble the end cover and adjust the cushion.
(16) Connect the oil and water pipes and valves.
(17) Gearbox alignment.

Common Problems and Failures of Reducer Bearings:

1. Why does the gearbox bearings should have thrust clearance and expansion clearance?
① Metal materials have the properties of thermal expansion and contraction. When the shaft works under different temperature conditions, the length and diameter of the shaft will also change. Therefore, in order to ensure that the thrust bearing forms a pressure oil film, a thrust gap must be left.
② In order to ensure that the shaft will not be hindered or restricted during the expansion process, there must be a gap.

2. How to measure the gap between the split bearing cap and the top of the bearing by the lead wire method?
① Place a lead wire on the joint surface of the bearing seat and the bearing cover near the bolt hole and along the arc length of the top of the bearing.
② Install the upper cover, and tighten the bolts diagonally evenly. Remove the bearing cover and measure the thickness of each lead wire with an outside micrometer.
③ The average thickness of the lead wire at the outer ring of the bearing is subtracted from the average thickness of the joint plane of the bearing seat. The difference is a positive value that is the gap, and a negative value is the tightening force.

3. What is the hazard if the bearing oil level is too low or too high?
① If the oil level is too high, the resistance of the oil ring will increase and it will slip or stop. The friction of oil molecules will increase the bearing temperature and increase the oil leakage at the gap and the friction power loss of the oil.
② If the oil level is too low, the ball or oil ring of the bearing will not be able to carry oil, resulting in the bearing not being lubricated and the temperature will increase, and the bearing will burn out.

4. What is the reason for the high temperature of rotating machinery bearings?
① Low oil level, oil shortage or no oil.
② The oil level is too high and the oil volume is too much.
③ The oil quality is unqualified or deteriorated (impurities in the oil).
④ The cooling water is insufficient or interrupted.
⑤ The oil ring does not carry oil or does not rotate.
⑥ The bearing is defective or damaged.
⑦ Equipment vibration.

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Gearbox is a kind of rotating equipment, and gearbox bearings (for example: 621 GXX, CPM2513) play a very important role when the equipment rotates.
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