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Guide to Electrically Insulating Bearings
Electrically insulated bearings play an important role in modern mechanical equipment. Insulated bearings can ensure that no current passes through them while meeting basic performance requirements such as load, speed, and life. It prevents corrosion or interference by current and ensures the smooth and safe operation of the generator or motor. This blog aims to introduce the basic concepts, types and advantages of insulated bearings, and analyze why electrically insulated bearings are so important.
The insulated bearing is a precision bearing with electrical insulation effect, which can block the passage of current and the bearing itself has insulating properties. Its insulation performance is usually guaranteed by using a special process to cover the outer ring or inner ring of the bearing with a layer of insulating material, or by using ceramics as rolling elements. The insulated bearing unit consists of inner and outer rings made of high-quality bearing steel, corresponding cages and ceramic or ceramic balls (or rollers).
Electrically insulated bearings use a special spraying process to spray a high-quality coating on the outer surface of the bearing. The coating has strong bonding force with the substrate and good insulation performance, which can avoid the electric corrosion of the bearings caused by induced current. Prevent current damage to grease, rolling elements and raceways, and increase the service life of bearings.
Applications of insulated bearings
Insulated bearings are used in special environments such as high temperature, high pressure, strong corrosion, etc., and can operate normally in these harsh environments. Insulated bearings use special materials and processes to give them better high temperature resistance, corrosion resistance and other properties. The electrical insulation properties of insulated bearings are evaluated through mechanical tests such as insulation resistance, shaft voltage and shaft current to determine whether they can withstand specified voltage values. For example, if the outer ring or inner ring of a bearing is coated with aluminum oxide, it can withstand DC voltages above 1000 VDC. Common types of electrically insulated bearings include: deep groove ball bearings, cylindrical roller bearings and angular contact ball bearings. Due to their good characteristics, they are widely used in various motor fields:
1. Insulated cylindrical roller bearings: wind turbines, hydroelectric generators, thermal generators and other power industry facilities, and also used in railway facilities such as diesel locomotive traction motors.
2. Insulated deep groove ball bearings: used in high-power variable frequency motors such as cranes, textile machines, printing machines, ironmaking, steelmaking, steel rolling, coking, etc.
3. Insulated spherical roller bearings: used in high-power and high-voltage motors of mining machines, coal preparation machines, coal washers, crushers, ball mills, grinders, sand mills and other equipment.
4. Insulated angular contact bearings: used in high-power explosion-proof motors for compressors, pumps and other equipment.
Grades of electrically insulating bearings
Electrically insulated bearings can effectively prevent current damage to bearings through high resistance and meet the insulation requirements for bearings in various power equipment. Insulated bearing grades are divided into:
1. Ordinary insulation: suitable for ordinary equipment and environments, with insulation resistance greater than 50MΩ.
2. High resistance insulation: suitable for equipment and environments with high requirements, such as moisture, high temperature, high voltage, etc., with insulation resistance greater than 500MΩ.
3. Ultra-high resistance insulation: suitable for special environments, such as chemical industry, nuclear power, etc., with insulation resistance greater than 1000MΩ.
Choosing bearings with appropriate insulation levels can improve the safety and stability of the equipment, reduce the failure rate, and extend the life of the equipment. It also helps protect staff safety.
Types of insulated bearings
Insulated bearings are used to prevent damage caused by current passing through the bearings. Some typical insulated bearing materials include ceramics, graphite, and the famous polytetrafluoroethylene (PTFE). There are two main types of insulated bearings: coated insulated bearings and ceramic insulated bearings.
Coated insulated bearings
Coated insulated bearings achieve their insulation effect by applying a 50μm-200μm thick insulating coating on the outer surface or internal components of the bearing. This coating is usually made of a high-resistance material, such as epoxy or polyimide, and effectively blocks the flow of electricity. Bearings made from this material generally cost less.
Ceramic insulated bearings
Ceramics are used in bearings because they are as hard as diamond, as wear-resistant as gold, and have outstanding insulation properties. Ceramic insulated bearings use ceramic materials (such as aluminum oxide or silicon nitride) instead of traditional metal rolling elements or bearing rings. Since ceramic is inherently non-conductive, this type of bearing provides a higher level of insulation. Bearings made of this material have higher resistance to wear and corrosion.
Other insulated bearings
According to actual needs, designers and engineers can also use other special materials to design insulated bearings. Graphite is widely used in the bearing field because of its extremely low friction and extremely high lubricity. PEEK is widely used because of its excellent corrosion resistance and super insulation. For example, in high temperature, high pressure or harsh environments, expensive but highly corrosion-resistant metals such as stainless steel or titanium can be chosen as the first choice.
No matter what the environment, the material selection of insulating bearings plays a key role in determining their performance and life. Designers and engineers must not only consider the purpose of the bearing, but also weigh environmental conditions and various material properties to select the best solution.
Advantages of electrically insulated bearings
Extended service life and reduced maintenance costs Insulated bearings extend the overall service life of a motor system because they mitigate electrical damage to motor components and prevent bearing failure. By reducing the number of repairs and maintenance workload, the use of insulated bearings also reduces maintenance costs and improves equipment reliability and operating efficiency.
Electrically insulating bearing brands
There are many well-known electrically insulating bearing brands in the world, such as SKF\NTN, etc.
SKF electrically insulated bearings
INSOCOAT electrically insulated bearings from SKF with coated outer rings are identified by the suffix VL0241. Recommended for medium size motors such as 6215, 6313 or larger. For applications using smaller bearings, SKF recommends hybrid deep groove ball bearings.
INSOCOAT bearings with coated inner rings from SK provide enhanced protection against current damage. The enhanced protection is due to the increased resistance due to the smaller surface area of the coating, which has the suffix VL2071. SKF recommends use with larger size motors (usually size 6226, 6324 or larger). INSOCOAT bearings with coated inner rings are suitable for applications in motors subject to high shaft voltages.
NTN electrically insulating coated bearings
NTN’s MEGAOHM™ series of insulated bearings are designed to resist electrical corrosion. These bearings are available in ceramic and resin versions and are suitable for a variety of applications. The bearing outer ring coating creates a barrier (capable of resisting a resistance of at least 100 Megohms at 500 VDC), preventing any stray current from passing through the bearing. MEGAOHM™ series bearings are used as OEM equipment in wind turbines, rail vehicle traction motors and variable speed motors in wastewater treatment facilities.
NTN ceramic hybrid bearings
For particularly difficult applications, NTN offers ceramic hybrid bearings. Using conventional steel inner and outer rings, silicon nitride rolling elements provide excellent electrical insulation while reducing rotating mass and improving heat dissipation.
Conclusion
Among all motors, than 80% of failures are caused by bearing failure. As a special kind of bearing, insulated bearings have excellent anti-electricity and insulation properties and are widely used in the power industry, petrochemical industry, non-ferrous metals, mining and other industries. Electrically insulated bearings have excellent reliability and ensure trouble-free operation of the motor. It is a very practical advanced technology to reduce equipment maintenance costs and improve equipment efficiency. As a leading manufacturer of electrically insulating bearings in China, Aubearing provides you with high-quality services. If you have any questions, please feel free to contact us.