Electric motors are the most important components of electrical equipment for industrial and domestic purposes, so the control of their technical condition is so important.

The need for repairs is determined by the rules of the PTE (Rules for the technical operation of electrical installations of consumers. Approved by order of the Ministry of Energy of Russia dated January 13, 2003 N6. As amended on September 13, 20018) and PTB (Safety regulations, POT RM-16-2001, Intersectoral rules for labor protection (safety rules) during the operation of electrical installations) and is carried out on the basis of the results of inspections. Timely diagnostics of the state of the electric motor prevents serious emergencies and the need for urgent and expensive repairs.

During the inspection, first of all, they pay attention to the condition of the bearings, they are mainly designed for continuous operation during the year 8-10 thousand hours, at standard loads.

Timely diagnostics and replacement of bearings will avoid more serious repairs.

Now about bearings, which are used for electric motors.

The basis for choosing a bearing is its durability.

- What affects the operation of the bearing in electric motors:

- Correct choice of bearing in terms of dimensions, clearances, lubrication (if open);

- Montage demontage;

- Lubrication and the frequency of its replacement;

- Mounting on equipment, shaft alignment accuracy, etc.

- Operating conditions - standard loads, weather protection, etc.

Which bearing to choose, more precisely which manufacturer? This primarily depends on the equipment in which it will work and the requirement for durability.

For electric motors, its durability is influenced by the method of transferring torque to the driven drive and the nature of the operation of the driven equipment. With different methods of torque transfer (gear, couplings, belt drive, etc.), different dynamic loads also arise. The nature of the operation of the driven equipment (smooth load, variable load, constant or intermittent jerks, etc.) also affects the life of the bearings.

Approximate requirements for the durability of bearings for electric motors:




For household appliances, hand tools, auxiliary equipment, assembly cranes, etc.

10000 h




Electric motors for machine tools and other industrial equipment

20000 h




Industrial electric motors for continuous operation

50000 h




Generators of power stations of water stations, etc.

100000 h




Traction motors for trolleybuses

0,6 х 10 *km




Traction engines for trams and public transport

1,5 х 10 * km




locomotives

1,5 х 10 * km




Table from the article "KINEX BEARINGS, SERVIS & CONSULTING"

According to the requirements of the bearing, its accuracy and quality is increased in accordance with the requirement for durability. The requirements for the quality of the lubricant and the frequency of its replacement are also increasing.


What type of bearings are used?

- Deep groove ball bearings - single row

- Execution of open type;

- Execution of closed type

- Suffixes in the designation - 2Z (ISO), prefixes in the designation - 80 (GOST) - metal washers on both sides, grease inside the bearing.

- Suffixes in the designation -2RS(ISO), prefixes in the designation -180(GOST) - rubberized metal washer with one or two lip seals with lubrication inside.

- With extended radial clearances suffixes - C3 and C4 (ISO), prefixes -7 and 8 (GOST)

- Accuracy class prefixes in designation - 6; 5; 4 according to GOST, prefixes - P6; P5; P4 according to ISO

- SKF current-proof suffixes VL0241 - protected inner ring.

VL2071 - protected outer ring.

- Single row angular contact ball bearings

Mainly with 40 degree and 25 degree contact angle

Example 7313 BECBM and 7208 ACDGA/P4A according to ISO. According to GOST 66 and 46 series, example 66414L, 46215L.

Accuracy class suffixes - P6; P5; P4 according to ISO, prefixes - 6,5,4 according to GOST
Separator brass suffixes in the designation - L and M, metal KM, polyamide E, suffixes - M; J; P according to ISO

- Single row roller bearings

- Structural designs

Suffixes in the designation N; N.U.; NJ; NUP according to ISO, and according to GOST -2, 32, 42, 52 series

- SKF current-proof suffixes VL0241 - protected inner ring.

VL2071 - protected outer ring.

- Double row spherical roller bearings

Mainly used for electric motors with heavy loads and low speed.

- Brass separators; metal; polyamide, according to GOST suffixes L and M, KM, E, suffixes according to ISO - ECM, ECJ, ECP.

An important condition for the operation of the bearing is competent installation according to the instructions.

Landing dimensions

It is especially worth paying attention to the seating dimensions if the bearing is not replaced for the first time: the shafts are restored, the seats in the housing are broken.

What to look out for

- The geometry of the shaft, measure the shaft at different points. The accuracy of cylindrical seating surfaces, bearing ends and shoulders of the shafts and housings mated with bearing rings must correspond to the accuracy of the bearings used.

For bearings of normal accuracy, the tolerances and dimensions of the cylindrical seating surfaces of the shafts must correspond to at least 6 ISO accuracy class, and the dimensions of the housing seating surfaces to 7 quality.

For bearings of higher accuracy, tolerances of higher qualifications are used, respectively.

Cylindrical tolerances, according to ISO 1101 - 1983, should be 1-2 degrees higher than the prescribed dimensional tolerances.

The perpendicularity tolerances of the bearing faces, according to ISO 1101-1983, must be at least one grade more accurate than the prescribed tolerances for the diameter of the adjacent cylindrical seating surface.

Internal clearance in the bearing.

Under the clearance in the bearing understand the amount of movement of one bearing ring relative to another in the radial (radial clearance) or axial (axial clearance) directions.

There are clearances in bearings before mounting (initial clearance) and after, which takes place under operating conditions (working clearance).

The clearance in the bearing prior to mounting is usually larger than the running clearance due to the influence of interference fit and thermal expansion of the bearing parts and mating parts.

As a rule, the working clearance in the bearing should be greater than zero, a small preload also does not affect the performance of ball bearings. However, for reliability reasons, preload should be avoided for bearings used for in-service repair of electric motors.

Radial fixation of bearings.

Bearing rings must not rotate in a load fit.

To prevent the rings from turning relative to mating parts, landings should be selected taking into account the magnitude of the load, the higher the load, the greater the fit interference should be.

If the bearing ring does not rotate and the load has a constant direction, or the ring and the load rotate in the same direction at the same speed, the rotating ring is installed with an interference fit. The other ring is in a loose fit.

If the load direction is not determined, or if there is significant vibration, then both rings should be installed with an interference fit. Rotating rings are installed with a fit according to the load, non-rotating rings with a looser fit.


Internal clearance in the bearing.

The reduction in internal clearance due to the fit interference may be so large that a bearing must be used.

Author: Vladimir Georgievich Ivanov