Heat Expansion Method
Most applications require a tight interference fit on the shaft. Mounting is simplified by heating the bearing to expand it sufficiently to slide easily onto the shaft. Two methods of heating are commonly used:
The first is accomplished by heating the bearing in a tank of oil that has a high flash point.
• The oil temperature should not be allowed to exceed 121˚ C (250˚ F). A temperature of 93˚ C (200˚ F) is sufficient for most applications.
• The bearing should be heated for 20 or 30 minutes, or until it is expanded sufficiently to slide onto the shaft easily.
• The induction heating method is used for mounting small bearings in production line assembly.
• Induction heating is rapid. Care must be taken to prevent bearing temperature from exceeding 93˚ C (200˚ F).
• Trial runs with the unit and bearing are usually necessary to obtain proper timing.
• Thermal crayons melted at predetermined temperatures can be used to check the bearing temperature.
• While the bearing is hot, it should be positioned squarely against the shoulder.
• Lockwashers and Locknuts or clamping plates are then installed to hold the bearing against the shoulder of the shaft.
• As the bearing cools, the Locknut or clamping plate should be tightened.
• In cases of outer ring rotation, where the outer ring is a tight fit in the housing, the housing member can be expanded by heating.
• The bearing should not be in direct contact with the heat source.
• The usual arrangement is to have a screen several inches from the bottom of the tank. Small support blocks separate the bearing from the screen.
• It is important to keep the bearing away from any localized high-heat source that may raise its temperature excessively, resulting in race hardness reduction.
Flame-type burners are commonly used. An automatic device for temperature control is desirable.
• If safety regulations prevent the use of an open heated oil bath, a mixture of 15 percent soluble-oil water may be used. This mixture may be heated to a maximum of 93˚ C (200˚ F) without being flammable.
• With this method, oil tank must be checked regularly to make sure that the mixture of oil and water is well mixed after water evaporates. The oil bath leaves a thin film of oil on the bearing surface that will temporarily prevent rust, but should be lubricated as soon as possible after installation. And make sure the soluble oil in the bearing is drained completely.
Heart bar pressure method
• The alternate method of mounting, generally used only on smaller sizes, is to press the bearing onto the shaft or into the housing. This can be done by using an arbor press and a mounting tube.
• The tube can be made from soft steel with an inside diameter slightly larger than the shaft.
• The O.D. of the tube should not exceed the maximum shoulder height given in the table of dimensions.
• The tube should be faced square at both ends. It should be thoroughly clean inside and out and long enough to clear the end of the shaft after the bearing is mounted.
• If the outer ring is being pressed into housing, the O.D. of the mounting tube should be slightly smaller than the housing bore. The I.D. should not be less than the suggested housing backing diameter in the table of dimensions.
• Coat the shaft with a light machine oil to reduce the force needed for a press fit.
• Carefully place the bearing on the shaft, making sure it is square with the shaft axis.
• Apply steady pressure from the arbor ram to drive the bearing fi rmly against the shoulder.
• Never attempt a press fit on a shaft by applying pressure to the outer ring or a press fit in a housing by applying pressure to the inner ring.
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