Abstract: The structural types and lubrication methods of motor sliding bearings are briefly introduced, providing a reference for motor users to better select bearings.

Keywords: sliding bearing; bearing structure; lubrication

1 Introduction
Bearings are important components of electric motors. During the operation of electric motors, faults in the bearing area caused by improper lubrication account for a large proportion of all motor faults. Therefore, bearing lubrication is extremely critical in motor design.

2 Structure of Sliding Bearings
Bearings are generally classified into sliding bearings and rolling bearings. The standard cylindrical sliding bearing is the most common and most frequently used type of sliding bearing, and its cross-section is shown in Figure 1.

Figure 1 Sectional View of a Standard Cylindrical Sliding Bearing

A sliding bearing generally consists of the bearing, oil ring, inner and outer oil seals of the C-shaped housing, inner air seal ring, vent (embedded in the oil guard or housing), and internal pressure transport pipes and reservoir (depending on the size and speed of the motor), as shown in Figure 2.

Figure 2 Structural Diagram of a Sliding Bearing

The bearing bracket fixes the housing to the motor frame. The housing may contain oil seals, which are separately bolted components. A sliding bearing generally has one or two oil seals. The oil seals obtain oil from the reservoir and distribute it onto the oil ring when the oil ring is mounted on the shaft.

3 Bearing Lubrication Methods
The lubrication of sliding bearings can be divided into oil-ring lubrication and forced lubrication. Oil-ring lubrication is generally used for cylindrical bearings. The oil ring rotates through contact with the shaft. The lower part of the oil ring is immersed in oil, travels along the surface of the shaft, and rotates to the top of the shaft. The depth of the oil ring in the oil is very critical. If the oil level is too low, the oil ring cannot pick up oil; if the oil ring is immersed too deeply, it will inhibit the normal rotation of the oil ring. Both of these conditions will result in an insufficient oil supply to the bearing. Forced lubrication is generally used when oil rings cannot be used or when additional bearing cooling is required. A forced lubrication system can deliver a specific volume of oil under a certain pressure. Orifices in the sliding bearing housing will restrict the oil flow to deliver the required volumetric flow rate. The oil is discharged at atmospheric pressure and returns to the forced lubrication system reservoir through drain pipes. Oil rings are also frequently used in forced lubrication systems, allowing the motor to coast safely to a stop by inertia in the event of a forced lubrication system failure.

Sliding bearings operate on the principle of hydrodynamic lubrication. When the shaft rotates, an oil wedge is formed between the shaft and the bearing. The design of sliding bearings should take into account the inherent viscosity of the oil. The selection of viscosity should consider factors such as oil film thickness, heat generation, and bearing performance. The minimum oil film thickness in the load-bearing section of the bearing should be 3 to 5 times the journal surface roughness. If the surface finish is smooth enough, the oil film can be very thin. However, a thinner oil film increases the probability of bearing failures, making the bearing more susceptible to damage. The oil film thickness for general sliding bearings ranges from 0.8 to 4 μm.

4 Conclusion
The actual selection of bearings is quite complex. Once the bearing type is selected, the lubrication method must be determined. Some aspects of bearings are difficult to quantify, making the actual selection process complicated. It is hoped that readers will be able to make sound choices after gaining a good understanding of the structure and lubrication of motor sliding bearings.

2026 October 3rd Week Marginal Product Recommendation

MG-090 Bronze Wrapped Bushings:
MG-090 bronze self-lubricating bearings use a kind of high density bronze alloy of special compositions as backing, the surface of alloy is rolled with diamond pattern of the oil indents or half ball oil indents, this kind of bearing has a higher density, a higher load capacity.

https://www.marginalbearings.com/bronze-wrapped-bushings/mg-090-bronze-wrapped-bushing.html