Induction heaters for mounting Motor Bearings


In the maintenance of electric motors periodic inspection of Insulation levels, vibration levels temperature rise and motor noise are generally considered a good practice.

When the noise or vibration levels increase significantly it is an indication that the bearing could need lubrication or a complete replacement. Bearings could be mounted using mechanical methods like pressing but this method poses a significant risk of damage to the bearings. This is why heat is used to expand the bearings so that it could easily slide into the shaft and grip the shaft firmly as it cools.

The procedure for using a bearing heater is pretty simple and generic. The appropriate yoke close to the inner diameter of the bearing to be heated is selected. This is important for effective and even heating. Then the bearing is placed in the yoke or over the coil. After this, the required temperature is chosen and the heater is switched on then the temperature starts to rise.

How induction heaters work

The first time I saw an induction heater in action I was marveled at their seemingly magical ability to generate heat and I know that its the same for someone out there.

The induction heating principle works only on metals and it works on Faradays Law of induction.
Faraday’s Law of Induction - Simply put, when electric current flows through a conductor it generates a magnetic field around it inversely when a conductor is put in a changing magnetic field an electric current is generated in the conductor.

 When electrical current flows through a conductor, it produces a magnetic field around the conductor. By alternating the direction of the current, the magnet field direction alternates. A typical induction heater has an electronic oscillator that passes a high-frequency AC current through the coil of the heater.  If conductive material like a motor bearing is placed within the alternating magnetic field the bearing would heat up.

This heating occurs because localized electrical currents called eddy currents are induced within the bearing by the rapidly alternating magnetic field. The metal(bearing) has a certain amount of electrical resistance and the circulating eddy currents flow against the electrical resistance of the bearing causing the bearing to heat up. Another contributing factor to heating is hysteresis. This occurs due to the resistance of the material to the changing magnetic field.

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