Accelerated bonding as the basis for the serial production of electrical steel stacks

Despite all their advantages, previous Backlack systems had the disadvantage of a relatively slow and sluggish bonding reaction. backlack-v® + accelerator is a high-speed bonding varnish system for electric motors of all sizes and types, even enabling large-scale production. The backlack-v® varnish features a significantly reduced bonding temperature, and the combination of backlack-v® with a reaction accelerator reduces bonding times to a minimum.

backlack-v® with an accelerator is a system for all applications and motor sizes. The extremely fast reaction speed during the bonding process avoids any squeeze-out, even in the smallest motors. The achieved high speed also makes large-scale production possible.

What are the additional advantages presented by bonding with backlack-v® + accelerator?

backlack-v® + accelerator offers a number of advantages in addition to the well-known technological advantages of full-surface bonding with Backlack—including freedom of design, mechanical stability, retention of magnetic properties, higher thermal conductivity and improved acoustic behavior:

Minimum bonding times

The bonding process is activated within a very short time by targeting just the right temperature effect.

No squeezing out during bonding

Even for the smallest sizes: The special fusion viscosity and high reaction speed avoids any squeezing out in even the smallest components.

Low reaction temperature

backlack-v® reacts at lower temperatures, thus leading to shorter heating and cooling times.

Improved hydrothermal and thermal resistance

backlack-v® + accelerator leads to a significant increase in ageing resistance at high temperature and humidity levels.

Improved heat resistance

Significantly higher strength at high temperature levels when compared to standard bonding varnishes

Large-scale serial production

The entire production operation can be carried out in a closed system (punching and bonding in one process).

 Such an advantage can only be achieved through optimum material coating. The many years of experience gained by voestalpine 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.

Which layer thickness is the right one?

Layer thicknesses in the range of 3-5 μm per side meet the highest requirements with regard to adhesive strength, mechanical stability and acoustic behavior. However, even with a reduced layer thicknesses of 1 to 2 μm per side, a large part of the Backlack advantages are retained over conventional joining processes. These include, for example, improved acoustics achieved by a flat and damping intermediate layer and improved thermal conductivity through the reduction of hollow spaces. By filling the area between the laminations with Backlack, bonded stacks feature an excellent stacking factor comparable to conventionally coated material, e.g. C5 insulation. In addition, magnetic properties are improved by damage-free joining and freedom of design because joining points must not be taken into account.

A clear advantage is seen in the stack strength—despite a thin bonding layer with reduced bonding strength when compared to interlocked stacks—especially in thin electrical steel.


With backlack technology, the foundation has been laid for an electrical steel stack that meets the ever-increasing demands on the efficiency and performance of electric motors. In terms of stack productivity, the backlack-v® + accelerator now makes Backlack technology ready for large-scale serial applications, thus compensating for previous speed disadvantages when compared to conventional joining technologies. In an effort to provide the most optimized solution, it is worth critically questioning the layer thickness required to achieve the desired technological properties.