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The influence of electric corrosion on insulated bearings

by:JNSN     2021-12-21
Whenever current flows through insulated rolling bearings for motors, it may threaten the reliability of your equipment. Electrical corrosion can damage and degrade bearings in traction motors, motors, and generators, leading to costly shutdowns and unplanned maintenance. With its latest generation of insulated bearings, performance standards have been raised. Even in the most challenging environments, INSOCOAT bearings can improve the reliability of equipment in electrical applications and increase equipment uptime. The influence of electric corrosion In recent years, the demand for insulated bearings in motors has increased. Higher motor speeds and wider use of variable frequency drives mean that adequate insulation is required if damage caused by current is to be avoided. Regardless of the environment, this insulating property must remain stable; this is a specific problem faced by bearings when they are stored and handled in a humid environment. Electric corrosion damages the bearing in the following three ways: 1. High current corrosion. When the current flows from one bearing ring through the rolling elements to another bearing ring and passes through the bearing, it will produce an effect similar to arc welding. A higher current density is formed on the surface. This heats the material to a tempering or even melting temperature, and produces a discoloration zone (different sizes of the discoloration zone) at the tempering, secondary quenching or melting of the material, and pits are also formed at the melting point of the material. Current leakage corrosion current continues to flow through the working bearing in the form of an arc, even if it is a low-density current, the raceway surface will be affected by high temperature and corrode, because thousands of micro-pits (mainly distributed in the Rolling contact surface). These pits are very close to each other and have a small diameter compared to corrosion caused by high currents. Over time, grooves (shrinkage) will appear on the raceways of the rings and rollers, which is a secondary effect. The degree of damage depends on several factors: bearing type, bearing size, electrical mechanism, bearing load, speed and lubricant. In addition to the damage to the bearing steel surface, the performance of the lubricant near the damaged area may also degrade, eventually leading to poor lubrication and surface damage and peeling. The local high temperature caused by the electric current can cause the additives in the lubricant to be scorched or burned, resulting in faster consumption of the additives. If grease is used for lubrication, the grease will become black and hard. This rapid destruction greatly shortens the life of the grease and bearings. Why should we care about humidity? In countries such as India and China, humid working environments pose another challenge for insulated bearings. When the bearing is exposed to a humid environment (for example, during storage), moisture can penetrate the insulating material, thereby reducing the electrical insulation effect and shortening the service life of the bearing itself. The groove on the raceway is usually secondary damage caused by destructive current passing through the bearing. Micro-pits caused by high-frequency current leakage and corrosion. Comparison of balls with (left) and without (right) micro-pits. Cylindrical roller bearing outer ring with cage, rollers and grease: current leakage causes the grease on the cage beam to scorch (blacken) .
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