Ceramic coated bearings prevent fan motor failures

Process plants typically have hundreds of electric motors in them carrying out a wide range of activities. Depending on the situation, many such motors can be affected by stray currents that leak through generators and associated equipment. When this happens the stray currents can damage the rolling elements and raceways of steel bearings and rapidly degrade the lubricant.

The result is unplanned down time along with increased costs related to bearing replacement and lost productivity. While attempts are sometimes made to alleviate the problem by insulating the housing or shaft, this can be an expensive and time-consuming task that may not yield optimum results.

This was the situation in a modern, integrated pulp and carton board mill in Europe that was losing productivity due to bearing problems in the pulp boiler flue gas recirculation fan motors. The 400 kW AC motors with frequency converters were running at 950 rpm with an operating temperature in excess of 100oC. The motors were equipped with standard bearings, which lasted only six months on average due to damage caused by stray electric currents.

To improve reliability and reduce fan maintenance and repair costs, Insocoat bearings from SKF were installed in the fan motors. The Insocoat bearing is a standard, all-steel bearing that is plasma sprayed with a ceramic coating. The coating is applied to the outside surface of the inner or outer ring, depending on the application, and sealed to protect against the conductive effects of water and moisture. As well as being environmentally friendly, the coating provides a consistent insulation layer that is virtually insensitive to high operating temperatures and chemicals.

Well suited to medium- and large-sized motors, the bearings have the same boundary dimensions as standard bearings so do not require special installation procedures or expensive modifications. The advantages over other methods used to prevent stray currents include:

• extended bearing service life,
• increased machine up time,
• reduced maintenance and repair costs,
• cost effective when compared to other insulating methods,
• drop-in replacement for easy installation,
• no degradation of the lubricant caused by current discharges,
• virtual elimination of bearing damage from stray electric currents

Since installing Insocoat bearings at the mill, there have been no failures. The mill has realised considerable savings in maintenance and repair costs, along with additional benefits in reduced down time and increased productivity, yielding a significant improvement to the bottom line.

An ROI summary based on the customer's estimates shows an impressive 4900% return on investment.

Previous costs:

• Cost of replacement bearings - $1000
• Cost of replacement bearings - $1000
• Cost of maintenance/repair - $6000
• Cost of down time - $43,000
• Total cost - $50,000

Insocoat costs:

• Insocoat bearings - $300
• Cost of maintenance/repair - $700
• Total cost - $1000

Other applications where Insocoat bearings have proved successful are AC and DC electric motors, generators, and machines connected to electric motors.