Operation, maintenance and troubleshooting of electric motor bearings

Care for wear

For proper engine operation, its bearings must be kept clean.

To prevent dust and dirt from entering them, the bearing caps are tightly closed. The drain holes and the cover at the end of the motor shaft are also tightly closed, otherwise the oil will leak out of the bearings and splash or get into the motor windings. The oil used to lubricate the bearings must be acid or resin free.

Avoid foaming in the bearings when the engine is running. Foaming can be eliminated by adding fresh oil, and if that doesn't work, you should change the oil completely. Before adding oil to the bearings, inspection holes are opened that serve as oil indicators. These holes are usually closed with threaded plugs. The oil level is considered normal when it appears at the inspection hole. Some bearings have sight glasses instead of a plug.

For normal operation of bearings with ring lubrication, at least two changes are required, even if the bearings do not heat up, check the rotation of the rings and the cleanliness of the oil (presence of mechanical impurities, sediments, etc.). If the rings rotate slowly or not at all, then the bearing lubrication has deteriorated, will be very hot and may melt. The oil in the bearings gets dirty over time and becomes thick, therefore, depending on the operating conditions, every 3 — 4 months, but at least once every six months, it is completely replaced, even if the bearings have normal heating.

When the bearings are operated under severe conditions (high dustiness in the room, high ambient temperatures, poor oil quality, etc.), the oil change time is shortened. Oil is usually added to bearings with ring lubrication after 200 - 300 hours of continuous operation. If topping up is done while the engine is running, do so as slowly as possible.

Before changing the grease, the bearings are washed with kerosene, blown with air, washed with the oil of the brand that is used for these bearings, and then filled with fresh oil.

Inspection of rolling bearings (ball and roller) same as behind bearings.

Before starting the electric motor for the first time, check the presence of grease in the bearings. The amount of grease should be no more than 2/3 of the volume of the chamber. If the bearings work normally and do not heat up, then the inspection and replacement of grease is carried out at subsequent repairs, as well as if necessary, depending on the condition of the lubricant.

Before changing the lubricant, the bearing with the caps removed is washed with clean gasoline with the addition of 6-8 volume% of transformer or spindle oil.The bearing is flushed from the end. In this case, the gasoline carries the dissolved lubricant with it. Flushing is carried out by slightly rotating the rotor and continues until clean gasoline flows out, after which the bearing must be dried with compressed air.

The process of filling grease is simple, you need to fill it with clean hands and a clean tool (wooden or metal spatulas). When packing, all the ring grooves in the parts of the bearing assembly facing the bearing are filled with grease with one third in their lower part. The space between the balls with the balls is filled with grease all around.

After assembling the bearing assemblies, check the ease of rotation of the rotor by hand, and then turn on the engine and run it for 15 minutes without load. If the bearings are in good condition, listen for a steady hum (buzzing of balls) without knocking or knocking.

The suitability of an oil for various engines under certain operating conditions is primarily determined by its viscosity. Oil viscosity in degrees is a number that indicates how many times longer it takes for a liquid to flow out relative to the same volume of water. Oil viscosity is conditionally determined in degrees according to Engler, usually at 50 ° C, because with an increase in oil temperature to 50 ° C, the viscosity decreases sharply, and after 50 ° C - more slowly.

In electric motors up to 100 kW with journal bearings, a spindle oil with a viscosity of 3.0-3.5 degrees according to Engler can be used.For bearings with forced lubrication circulation, turbine oils are used: for high-speed engines with a rotation speed of 1000 rpm and more, turbine oil «L» (light) and for engines with a rotation speed of 250 — 1000 rpm — «UT » weighted turbine.

Malfunctions in the bearings of electric motors and ways to eliminate them. Overheating of bearings

In ring-lubricated machines, excessive heating of the bearings can be caused by insufficient oil supply due to slow rotation or complete stoppage of the lubrication rings. Thickening of the oil can cause the lubrication rings to stop. Insufficient oil supply can also be the result of pinched oil rings, incorrect shape or low oil level in the bearings.

To eliminate the indicated malfunction, it is necessary to change the thick oil with a new one, check the oil level according to the oil indicator, replace the light rings with heavier ones and straighten the damaged ones or also replace them with new ones.

On machines with forced lubrication, bearings can overheat as a result of a clogged oil pipe or oil filter and contaminated oil in the bearings. This defect is eliminated by flushing the entire oil system, cleaning the oil chambers, changing the oil and sealing the bearings.

Bearings can overheat due to misalignment of the engine with the production mechanism, and also due to the small clearance between the neck and bushing. The substrate is considered well installed if the load traces are distributed evenly along the entire length of the lower lining along an arc of 25-30 °.

The heating of the bearings is also affected by the inadequacy of the used oil quality, poor filling of the sleeves, bending of the motor shaft or its studs, the presence of axial pressure on the bearings. The latter occurs due to axial displacement of the rotor or insufficient clearances between the ends of the bearing shells and the shaft fillets, which prevents its free thermal expansion.

Sprays and leakage of bearing oil lubricated with a ring

The cause of this malfunction is the overflow of the bearings with oil, which splashes from them and spreads along the shaft. To avoid this, it is necessary to pour oil into the bearings with the machine stopped to the line of the oil indicator, since the lubricating rings absorb part of the oil during rotation, and its level in the oil indicator decreases slightly.

If there is no control line on the pressure gauge, oil is poured into the bearings to the level at which the lubricating rings are submerged by 1/4 -1/5 of their diameters. Due to the viscosity of the oil, the level in the bearing is not established immediately, so the oil must be added gradually.

In the case of insufficient sealing of the bearings, large gaps at the ends of the sleeves, as well as with small dimensions of the drainage holes at the bottom of the sleeves, oil can enter the engine along the shaft. To eliminate this possibility, the bearings are additionally sealed with a 2 mm thick brass washer that is tightly attached to the shaft. Secure the washer with screws. Another type of sealing is with a steel washer 1 — 2 mm, with a distance between the washer and the shaft 0.5 mm. Between the washer steel and the bearing, a felt washer without a gap is installed, which is attached to the bearing with screws.

Oil or oil mist entering the machine

Oil or oil vapor from the bearings is drawn into the interior of the machine as a result of the action of the fan or other rotating parts of the machine. Most often, oil suction occurs in closed machines with end shields, since the bearings are partially located inside the machine body. In this case, when the fan is working, a vacuum is created in the bearing area, which contributes to oil suction.

To eliminate this phenomenon, it is necessary to eliminate defects in the bearings, as well as additionally seal the bearings and joints between the stator and parts of the shields.

Malfunctions of rolling bearings

One of the main disadvantages of rolling bearings is excessive heating. Overheating of the bearings can occur as a result of improper assembly, tight fit of the outer ring of the bearing in the end shield, and also due to the lack of axial travel in one of the bearings, which is necessary to compensate for thermal expansion of the shaft during operation of the machine. With this malfunction, the rotor easily rotates in a cold bearing, and sticks in a heated one.

To establish a normal axial clearance, it is necessary to grind the flange of the bearing cover or install seals between its cover and the housing. To reduce tight fit of the ring, the bearing seat is widened.

Sometimes an unusual noise appears in the bearings, accompanied by an increase in temperature. This can be the result of poor motor alignment, dirty bearings, heavy wear on individual parts (balls, rollers) and a loose inner race of the shaft bearing.

If the bearings contain more grease than it should, or its brand does not correspond to the ambient temperature and the seals are insufficient, then the grease will separate from the bearings during engine operation.