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Backlack, also known as bonding varnish, refers to the process of stacking the laminations by re-bonding the adhesive varnish applied to the surface of the lamination through temperature changes. Backlack is an almost non-damage technique of motor stator and rotor production. Since there is no need to design slots for welding or cleating on the iron core, the motor designer has more freedom in designing the motor, and the eddy current losses of the iron core will be minimized.

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Since the vibration and noise of the iron core are smaller, and the magnetic performance is stronger, backlack is suitable for producing stator and rotor cores for special motors with high performance requirements, such as the drive motors of EV. Some stator and rotor cores of wind turbine also produced by backlack technique.

In the production process, the silicon steel with special coatings are processed into laminations and then stacked together in a special tooling, and then heated for a period of time under pressure. The final step is the natural cooling of the iron core.

backlack rotor core block

The cost of the backlack process is relatively high, and it is not suitable for the production of large-sized motor cores. Besides, if the actual area of the punch is too small, it cannot be produced by backlack.


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