Bearing Induction Heater Calibration

Induction heating is the safest and most effective method of heating and radially expanding bearings before their mounting (installation) onto the shafts. This method of inductive shrink-fitting ensures an even and controlled heating of the bearings, eliminating the risks of incorrect mounting and material instabilities. Unlike conventional heating bearings using blowtorches, hot plates, oil baths, and ovens, induction heating is safer, more environmentally friendly, and more controllable (adjusting the temperatures). Inductive heating also eliminates the risk of bearing lube contamination, often caused by oil bath heating techniques.

Working Principle:

Induction heaters work based on Faraday’s Law of alternating electric current and a magnetic field, similar to the working of a transformer with two coils – Primary and Secondary. For an induction bearing heater, the primary coil is the heater, and the secondary coil is the bearing. AC power is sent through an inductor (Primary coil – most commonly a copper coil for induction bearing heaters), and the bearing is placed within or around the inductor (crossbar or yoke). Once the heater is switched on, a high voltage, low AC (alternating current) passes through the numerous windings of the primary coil, inducing a low voltage, high current in the Bearing. When the Bearing is fixed within the inductor and enters the magnetic field, circulating eddy currents are generated within the Bearing. An eddy current is a localized electric current induced in a conductor by a varying magnetic field. When these electrical currents flow against the electrical resistance of Bearings, they generate precise and localized heat without any direct contact between Bearing and the heater.

These induction heaters can also be used on other applications such as gears, bushings, couplings, and other industrial metals to shrink-fit onto the shafts. Because of even expansion of the internal diameter of the Part (bearing, gears, etc.), Induction heating is the most effective method to mount parts onto shafts. The process ensures material stability and maintains tight shrink-fit tolerance levels.

Types of Bearing Induction Heaters:

Several types of Induction bearing heaters are available for industrial usage and are selected based on the size of bearings, application, and frequency of use. Common types of bearing induction heaters are:

Hand-held Bearing Induction Heaters:

These are heaters suitable for smaller-sized bearings and other metal parts, such as bearing housings, couplings, shaft keys, nuts, bolts, etc. Simple and one-handed operable heaters.

Portable Bearing Induction Heaters or Mobile Induction Heaters:

Suitable for bearings less than 100 Kg weight, they are commonly integrated with a temperature control digital display to adjust the intensity of heat and period of heating. These are portable heaters with a thermally insulated case for portability.

Benchtop models:

These are Roll-around induction heaters with swivel arms for movement and folding the heater panel. Benchtop models are workshop-operated induction heaters, suitable for Medium-sized bearings up to 300 kg, often integrated with more than one temperature sensor to control and adjust the heating.

Heavy-duty models:

Suitable for bearings up to 1500 Kg weight, these are fixed induction heaters for heavy industrial applications such as Ball mill and Rollers mill bearings. These models contain more than one induction coil and sensor and an adjustable temperature control unit.

Middle-frequency models:

Often considered the fastest induction heaters, these heaters can increase the temperature for bearings up to 100C in minutes. These are expensive inductive heaters used for applications where frequent shaft assembly failures are common (such as paper mills, steel industries, etc.).

Advantages of Inductive heating over Conventional heating methods:

1. Blow torch heating: This heating method lacks temperature control and increases the risk of overheating, resulting in material tension in the bearings. Whereas, Inductive heating adjusts the temperature by controlling the intensity of AC Current, resulting in even and zone-specific heating.

2. Hot Plate heating method: Similar to blow torch, this method too lacks temperature control, causes overheating and lubricant/grease leakages from the bearing, causing metal and ball race ruptures. Inductive heating ensures heating only on the inner diameter (shaft faced surface) and avoids lube leakages.

3. Oil Bath heating: Oil heating is an indirect heating technique and notably a slow process. This method is considered dangerous because heating oil is unfriendly to the environment and contains the risk of bearing grease and oil mixing (contamination). Inductive heating is a safe technique with no impact on the environment.

4. Oven heating technique: Radiation-based heating technique is often considered a slow and Energy-intensive process. This method is suitable only for miniature bearings and evenly heats all bearing components, resulting in material instabilities post-cooling, ultimately affecting the service life. On the other hand, Inductive heating is a simpler and more energy-efficient method.

Bearing Induction Heaters Calibration – Why is it essential:

1. Accuracy of Thermal Expansion: Temperature tolerance is strictly maintained for inductive heaters as overheating affects the metallurgical properties and dimensional stability of the bearing unit and permanently changes the absolute size. Most industrial Bearings are heated up to a maximum temperature of 120°C, and Precision bearings are capped at 70°C. A temperature differential of 65°C between the shaft and the bearing is optimal for a correct bearing mount and provides sufficient expansion to mount over shafts. Therefore, the thermal sensors of an induction heater should often be calibrated with a Standard pre-calibrated temperature gauge to achieve precision measurement.

2. Coil stability: Due to instabilities in the power supply, the primary coil of the heater can be damaged or lose precision response with temperature controls. Often seen in Portable or handheld bearing heaters, the coil health should be checked and maintained periodically.

3. Operational errors: Bearing induction heaters are designed to operate in industrial environments with an ambient temperature of 0°C to 50°C and are meant for indoor use. The supply voltage and current should meet the equipment specifications. Lack of training and skill can result in overheating or permanently damage the heater coils and bearings.

Cumulative defects in Bearing induction heaters often result in operational uncertainties leading to maintenance losses. About 16% of premature bearing failures are attributed to incorrect heating and mounting practices. Calibration avoids these errors, ensures induction heating accuracy. Following a regular and timely calibration schedule ensures the accuracy of thermal expansion and enhances the service life of bearings.

e2b calibration offers industry-leading ISO-certified induction heater calibration services. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to test and calibrate your Bearing induction heaters. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.