Effect of electrocorrosion on insulated bearings

2018-09-07 17:33:50

Whenever current passes through insulated rolling bearings for motors, it can pose a threat to the reliability of your equipment. Electrical corrosion can damage bearings in traction motors, motors and generators and degrade their performance, resulting in costly downtime and unplanned maintenance. With its latest generation of insulated bearings, SKF has improved performance standards. Even in the most challenging environments, INSOCOAT bearings increase the reliability of equipment in electrical applications and increase equipment uptime.

The impact of electrical corrosion In recent years, the demand for SKF insulated bearings has increased. Higher motor speeds and wider use of variable frequency drives mean that adequate insulation is required if current damage is to be avoided. This insulation property must remain stable regardless of the environment; this is a specific problem faced when the bearings are stored and handled in a humid environment. Electro-corrosion damages the bearing in three ways: 1. High-current corrosion When the current flows from one bearing ring through the rolling element to the other bearing ring and passes through the bearing, it produces an arc-like effect, with less contact. A higher current density is formed on the surface. This heats the material to a temperature that is tempered or even melted, producing a fading zone (different size of the fading zone) at the tempering, secondary quenching or melting of the material, and also forming pits at the melting of the material.

Current Leakage Corrosion current flows continuously through the working bearing in the form of an arc. Even at low-density currents, the raceway surface is affected by high temperatures and corrodes because thousands of micro-pits are formed on the surface (mainly distributed in Rolling contact surface). These pits are very close to each other and have a smaller diameter than corrosion caused by large currents. Over time, a groove (shrinkage), a secondary effect, will occur on the raceway of the ferrule and the roller. The degree of damage depends on several factors: bearing type, bearing size, electrical mechanics, bearing load, speed and lubricant. In addition to damage to the surface of the bearing steel, the performance of the lubricant near the damaged part may be degraded, resulting in poor lubrication and surface damage and flaking.

Localized high temperatures caused by current can cause the additives in the lubricant to be scorched or burned, resulting in faster consumption of the additive. If grease is lubricated, the grease will turn black and hard. This rapid damage greatly reduces the service life of grease and bearings. Why pay attention to humidity? In countries such as India and China, the wet working environment poses another challenge for insulated bearings. When the bearing is exposed to a humid environment (such as during storage), moisture can penetrate the insulating material, reducing electrical insulation and shortening the life of the bearing itself. The grooves on the raceway are typically secondary damage due to destructive current flow through the bearings. Micro-pits caused by high-frequency current leakage corrosion. Comparison of balls with (left) and without (right) micro-pits Cylindrical roller bearing with cage, roller and grease Outer ring: current leakage causes burnt on the cage beam (blackening) .