For large-sized motor bearings, the “hot fitting” process is a common assembly method. This process involves heating the bearing—leveraging the principle of thermal expansion and contraction in metals—to achieve an interference fit between the bearing and the shaft, thereby preventing mechanical damage to the mating surfaces.
There are various options for heating bearings, including oven heating, oil bath heating, induction cooker heating, and specialized bearing heaters. These different methods vary in terms of heating uniformity, heating speed, and the potential for contaminating the bearing. In actual manufacturing practice, specialized bearing heaters are widely utilized due to their convenience and controllability, making them the preferred tool for most motor manufacturers.
The operating principle of a bearing heater is based on electromagnetic induction: when a metal object is placed within an alternating magnetic field, it generates eddy currents, causing it to heat up. When a relatively thick metal object is subjected to an alternating magnetic field, electromagnetic induction induces electric currents; these currents flow in a spiral pattern within the metal, and the resulting heat is absorbed by the metal itself, leading to a rapid rise in temperature.
In the context of a bearing heater, the bearing essentially acts as a short-circuited, single-turn secondary coil; under a relatively low AC voltage, it carries a high current, thereby generating a significant amount of heat. However, because this heating method relies on inducing electric currents, there is a potential risk that the bearing may become magnetized. A magnetized bearing is prone to attracting metal debris during the installation process, which poses a potential operational risk. To prevent residual magnetism from adversely affecting the bearing’s normal operation, most bearing heaters are equipped with an automatic demagnetization function that activates automatically once the heating cycle is complete.
During the heating process, the temperature must be strictly controlled to prevent bearing failure. Motor technical specifications typically stipulate the maximum permissible temperature for bearings; this requirement serves primarily to preserve the performance of the lubricant, and—more importantly—to safeguard the structural integrity of the bearing material itself. When disassembling a failed motor, it is occasionally observed that the motor shaft itself exhibits residual magnetism. This phenomenon serves as a direct indication that a magnetization issue may have occurred either during the motor’s normal operation or during the failure event, a matter that warrants further in-depth analysis.
Post time: Apr-30-2026