Industrial furnace applications come in various types and sizes; however, they all place similar demands on the bearings they use. Due to the high temperatures within a furnace application, shafts extending through the furnace will grow significantly in length. This heat will also travel up the shaft to the bearings, subjecting them to higher operating temperatures than normal.
Additionally, maintaining an adequate atmosphere within the furnace is critical for effective operation. In order for bearings to survive these temperatures while ensuring proper furnace operation, specific features must be designed into the bearing.
Most standard bearings have a maximum operating temperature of 225°F, but a furnace bearing must generally withstand temperatures up to 400°F.
Increasing the internal clearance of the bearings allows thermal expansion of the steel components and special high temperature greases are applied to the bearings. Steel rolling element fasteners and high temperature sealing materials are used.
To accommodate the significant shaft growth typical of this type of application, expansion bearings are equipped with cylindrical point set screws or special inverted pins in the bearing bore. These devices slide into a groove that has been machined into the shaft to allow expansion without allowing the bearing to rotate within the hole.
Furnace bearings also have special features to prevent internal furnace gases from escaping where the shaft exits the furnace. Typically, expandable bearings will have an extended cover to seal the bearing and shaft while allowing the shaft to grow. Fixed bearings have specially designed locking collars that seal around the shaft.
