Understanding Insulated Bearings

Bearings are important core components in mechanical equipment. Their main function is to support mechanical rotating bodies, reduce the friction coefficient during their movement, and ensure their rotation accuracy. Their performance directly affects the quality, performance and reliability of major equipment and main machines, and they are often hailed as the "heart" components of mechanical equipment.

my country's bearing industry has developed rapidly. The variety of bearings has increased from a few to many, the product quality and technical level have increased from low to high, and the scale of the industry has grown from small to large. A professional production system with a basically complete range of products and a relatively reasonable production layout has been formed.

Editor: Do you know what materials bearings are made of?

Reader: As far as I can remember, most of them are made of steel and are shiny, right?

Editor: That's right. Bearings are generally made of high carbon steel GCr15, which is commonly known as bearing steel. In addition, there are carburized bearing steel, stainless bearing steel, high temperature resistant bearing steel, medium carbon impact resistant bearing steel, and now the latest bearing material is ceramic.

Reader: How can steel bearings be insulated?

Editor: Let me tell you about the insulated bearings developed by the Institute of Composite Manufacturing and Intelligent Identification of the Tianjin Institute of Advanced Equipment, Tsinghua University, to solve your confusion.

Insulated bearings use a special spraying process to spray high-quality coatings on the outer surface of the bearings. The coatings have strong bonding with the substrate and good insulation properties. They can avoid the electro-corrosion of the bearings caused by induced currents, prevent damage to the grease, rolling elements and raceways caused by currents, and increase the service life of the bearings.
There are two measures to prevent electrical corrosion of bearings. One is to install a grounding device (shunt) on the motor shaft to prevent the current from passing through the bearing; the other is to make the bearing an insulator. From the perspective of reliability, the main way to solve the problem of electrical corrosion of traction motor bearings is to insulate bearings. Compared with other insulation methods, such as shaft or housing insulation, it is more cost-effective and reliable. The overall dimensions and basic technical characteristics of insulated bearings are the same as those of non-insulated bearings, so they are 100% interchangeable. It is suitable for motors, generators, and especially variable frequency motors.

How to make bearings an insulator?
Tsinghua researchers selected two different materials and used a plasma spraying process to make the bearing an insulator.
Method 1: Use insulating materials such as oxides and resins to spray bearing parts to make them insulating bearings.
Method 2: Using nitride insulating ceramics to make insulating bearings.

Oxide insulated bearings

Nitride Insulated Bearings

Advantages of insulated bearings manufactured by plasma spraying:
1. Good bonding strength The high-speed performance of plasma spraying ensures that the bonding strength of the bearing surface is greater than 30MPa, thus ensuring that the coating is durable.
2. Small thermal impact at work Due to the use of special process parameters, the molten particles are quickly cooled and solidified when sprayed on the surface of the ring, which can keep the bearing surface at around 100°C, eliminating the deformation effect of high temperature on the bearing.
3. Professional sealing technology After spraying, professional follow-up sealing technology is used, which can penetrate about 20% of the thickness of the spray layer.
① Prevent the abrasive particles falling from the grinding wheel during coating grinding from contaminating the pores in the coating;
② Ensure the insulation performance of the coating;
③ Improve the corrosion resistance of the coating;
④Seal the pores to prevent oxidation;
⑤ Ensure the air tightness of the coating.

The application of insulation method is generally determined according to the power supply status of the motor. For large high-voltage motors or motors powered by variable-frequency power supplies, the high-frequency components contained in the power supply will cause an increase in the motor shaft current. In addition, for some special working conditions, such as electric vehicles, rail locomotive traction motors, wind turbines, etc., corresponding insulation solutions must be adopted.
With the rapid development of science and technology, the application fields of insulated bearings are becoming more and more extensive, mainly including the following fields: power industry, railway industry, machinery and metallurgical industry, mining machinery industry, petrochemical industry, etc.