Backlack—the joining technology for perfect lamination stacks!

The stator and rotor cores of electrical machinery are manufactured using thin sheets stacked together in order to minimize eddy current losses. The laminations are bonded in order to create a stable core. A general distinction is made between techniques integrated into the punching process (interlocking, full-face bonding or spot bonding) and those downstream from the punching process (welding, clamping, conventional bonding). The joining technique is selected depending on the application, electrical machine design and by taking economic aspects into consideration.

Material processing and the joining technique used contribute substantially to the behavior of our electrical steel inside an electric motor. Our most non-damaging and flexible process is full-face bonding of the laminations. Optimized performance and a high degree of efficiency are achieved for the following reasons:

Freedom of design: The Backlack self-bonding technology allows complete freedom of design and leads to ideal motor engineering because manufacturing aspects such as the positions for interlocking or weld seams do not have to be taken into account. This makes it possible to engineer a more efficient electric motor.

Mechanical stability and dimensional accuracy: Full-face adhesive bonding allows compliance with the narrowest tolerances and excellent shape stability because the laminations have no way of expanding. Tensions in the core can be caused when heat is introduced during the welding process, a problem that does not occur during the adhesive bonding process.

Maintenance of magnetic properties: Bonding is our most non-damaging joining technique. and has no impact on the magnetic properties of the electrical steel. In contrast, interlocking and welding can substantially damage the microstructure and thus impair the magnetic properties of the material.

Improved thermal conductivity: Lamination stacks with the narrowest manufacturing tolerances improve the dissipation of heat through improved transfer of heat between the laminations and the housing. This makes smaller cooling units possible, thus making them less expensive and lighter. These compact lamination stacks also exhibit excellent stacking behavior and a favorable insulating effect that results in electrical short-circuit protection.

Acoustic advantages: Our viscoelastic Backlack effectively dampens the vibrations in laminations. This effect is utilized in selected electric machines to minimize sound levels.

Such an advantage can only be achieved through optimum material coating. Our many years of experience gained by in the development and improvement of Backlack systems and the optimization of substrate coating processes has led to a high-quality product characterized by a high level of adhesive strength and excellent processability.

Full-face bonding — our most non-damaging technique in the production of stator and rotor cores. Fully processed and Backlack-coated electrical steel is used as the basis for adhesive-bonded electrical steel cores. After the laminations have been stamped, we connect thermally in a two-step adhesive-bonding process. The Backlack coating is softened in the first phase by increasing the temperature. The viscosity of the coating decreases dramatically, making it possible for the coating layers to diffuse and intermix. This phase determines the quality of the bond to a considerable degree. Complete melting results in high adhesive strength and a high level of resistance to a variety of different media.

Further increasing the temperature leads to the second phase in the bonding process, which is dominated by chemical cross-linking processes. The Backlack hardens, loses its thermoplastic properties and becomes a stable and highly cross-linked duroplast. The viscosity and adhesive strength between the laminations increase substantially during the second phase.

Conclusion: Whereas full-face bonding was used mainly for Backlack prototyping only a few years ago, the technique today is used in a wide variety of important applications. As the newest generation of joining techniques, full-face bonding and all of its benefits are especially suited to the high demands of and applications in the field of electric mobility. We provide full support for a perfect material combined with innovative Backlack coating systems.