Power Transmission
should select a lubricant which offers the following performance benefits:
● High temperature performance and low oil release: Electric motor bearings, especially the outboard bearing, often operate at higher temperatures than other equipment. This is why high temperature performance and low oil release are so important to performance. Even a totally enclosed, fan cooled motor can run at a steady 95°C/200°F.
● Corrosion protection: Electric motors are ‘wet’ by exception but not by design, and by running at, often, high temperatures, water can evaporate more quickly leaving the bearings potentially exposed to corrosion. If the use of the motor is intermittent then a grease offering corrosion protection can be beneficial to protect against possible condensation when the bearing cools down in a humid atmosphere.
● Low temperature performance: A grease designed to operate at low temperatures can be beneficial during the start-up of electric motors which are exposed to winter conditions as the resistant torque can damage seals.
The base oil used in electric motor greases can be mineral or synthetic with the majority of mineral oils providing sufficient protection for most electric motor bearing applications. However, more advanced synthetic base oils may be needed where motors are exposed to extreme temperatures or where longer re-greasing intervals are desired.
The thickener in the synthetic oil acts as a carrier and prevents it from leaking out of the application. Some common thickeners include metallic soaps that can be composed of calcium, lithium, sodium, aluminium or barium, and complex metallic soaps such as lithium-complex.
A thickener increasingly employed to
protect electric motor bearings is polyurea and this is a key part of the make-up of Mobil Polyrex EM Series – a range of greases engineered specifically for use in electric motor bearings and able to withstand degradation under high temperatures and speed.
ExxonMobil’s proprietary polyurea thickener may provide outstanding ability to lubricate bearings at very high temperatures. The Mobil Polyrex EM range can operate at temperatures from as low as -20°C up to highs of 160°C. It also helps increase equipment protection, extend re-lubrication intervals and reduce maintenance costs.
Reducing downtime
One case that demonstrates the potential value of using an advanced grease such as Mobil Polyrex EM is from a steel manufacturer in Russia where the use of this high-performance grease significantly improved the service life of bearings.
The company used a 185kW blower electric motor for hot aluminising aggregate, reaching speeds of 2900- 4500 rpm. The combination of these speeds with working temperatures up to 120°C resulted in bearings beginning to fail after a short life span. On closer inspection by an ExxonMobil field engineer, a recommendation was made to use Mobil Polyrex EM. The previous grease used lasted only one and a half months before the bearing failed but Mobil Polyrex EM performed for nine months.
Using the right grease is not only important to ensure the smooth running of equipment but it can also have a positive effect on the wider business. ●
* This proof of performance is based on the experience of a single customer. Actual results can vary depending upon the type of equipment used and its maintenance, operating conditions and environment, and any prior lubricant used.
Umut Urkun is with EAME ExxonMobil Lubricants & Petroleum Specialties.
www.mobilindustrial.com
www.engineerlive.com 29
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