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Bearings heating

In applications that require a tight fit of the inner ring on the shaft, it can be easier to install the bearings if it is first heated to expand slightly.

For applications that require a tight fit of the outer ring in a housing, it may also be possible to heat the housing to expand it, allowing the bearing to install more easily. Small bearings can be heated using several methods. They can be heated in a pan or metal container filled with oil (Fig. 6). A screen or platform should be used to keep the bearing from resting on the bottom of the pan where heat is applied.

 fig_07_induction_20heater.jpg

A heat lamp can also be used to heat rings, and the temperature regulated by adjusting the distance from the light to the ring.

The fastest method of safely heating bearings is an induction heater (Fig. 7). Induction heaters work very quickly. Take care to avoid heating the bearing to temperatures higher than 120ºC (250ºF).

For larger bearings, you may need to use an oil bath to heat the bearing (Fig. 8). Maximum temperature of the oil bath should not exceed 120ºC (250ºF). The bearing should be positioned in the center of the tank, and allowed to heat long enough to fully expand. Do not allow the bearing to come in direct contact with the heat source.

fig_08_oil_bath.jpg

warning_05.jpg

 

Keep the bearings away from any localized high-heat source that may raise the bearing temperature too high, resulting in race hardness reduction.

When heating bearings, be sure that they have enough time to fully heat. Bearings typically require 20 to 30 minutes of soak time per inch of inner-ring cross section to fully heat in an oil tank.

While the bearing is still warm, remove it from the heater or tank and place it on the shaft. Slide the bearing up the shaft until it squarely contacts the shaft shoulder. Then install the locknut/ washer or clamping plate to prevent the bearing from backing off the shoulder while cooling. As the bearing cools, the locknut or clamping plate should be tightened.

Thermal growth of components can be calculated using the formula:

Thermal_growth.jpg


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