Anyone who has ever been bandaged because of a sports injury knows how important an even and flat wrap is. The same applies to the core of a large transformer, which can weigh a few 100 t. The automated process is much faster, but also much more difficult than that done by hand. Kohls Maschinenbau GmbH installs them in their new vertical taping machines for optimal results gas springs from ACE shock absorbers.

The company Kohls has good 20 years of experience in the construction of special machines when it comes to transformers. Especially in the areas of laying technology for stacks and cores as well as for the bandaging of cores, the family-owned company from the town of Freigericht near Hanau was able to gradually expand its know-how.

Managing Director and Founder Rüdiger Kohls relies on the development of the first proposals using 3D software right through to assembly and commissioning for solutions from a single source. That is why the Hessian specialists in transformer construction place increased value on long-term connections among their suppliers.

Calculate, design and order gas cable and gas pressure springs

One of them is the ACE shock absorber GmbH. Due to positive experiences with the use of the machine elements from Langenfeld, the supplier from Langenfeld in the Rhineland was again set when developing a new vertical taping machine. As the Kohling taping machine presented here was the first of its kind, a benchmark for potential competitors was to be identified right from the start when selecting the required components.

Good pairing: brake system and industrial gas springs

300 t, a meter-high tower, consisting of thousands of thin sheets and sometimes a complicated oval or even rectangular shape: The bandaging of an industrial transformer, which can often have the dimensions of a bungalow, is an elaborate work in which everything has to fit. After all, the thin sheets of the transformer must not shift a millimeter when erected in the vertical. This is ensured by special tensioning straps, whose task it is to enable trouble-free travel to the taping machine.

The safe transport of the then fragile construction takes place on a hovercraft. After the arrival of the transformer components at the taping machine, this now wraps the core with a resin tape, which consists of glass fibers impregnated with special resin. The resulting layers gradually increase the voltage on the individual transformer legs, which is up to 250 daN per revolution. Such transformers usually operate in an oil bath. Thanks to the bandage by means of the special machine from the transformer works quieter at the end, has a greater efficiency and ensures a more reliable cooling, so that with appropriate design expensive material can be saved.

Ballpoint pen principle makes the gas spring lockable on both sides

One innovation on the new machine is the braking system, for which a patent has been applied. It generates the massive belt tension mentioned above and converts it via the hydraulic circuit braking energy around.

Industrial gas springs prevent voltage drop

But even with oval transformer legs, it is not excluded that even the technically experienced bandage experts from Hesse need help from outside. For then, if at some points of the oval a loss of tension occurs. And in the process, Steffen Bonn, ACE's technical consultant for this region, supported the company with suitable industrial gas springs.

The appeal of this order was to avoid the voltage drop in oval Transformer legs. In addition, the machine manufacturer wanted to provide its globally renowned customers with a solution that ensures low vibration and fast response. Because for bandaging turns a toothed ring on which the brake unit with a stroke of 150 mm is mounted to the transformer legs up and down.

The solution from ACE was industrial gas springs of the type GS19-150-EE-550N. These usually ensure safe opening and closing of hoods and lids by supporting the operator's manual strength. In this case, however, the industrial gas spring is responsible for ensuring that the belt tension is maintained, since interruptions caused by e.g. B. almost right-angled cross-sections, the stroke is still used as a reserve.

The functional principle of gas springs is identical to the standard case of opening and closing flaps for which they were originally designed. In this case too, hydraulic oil is used for end position damping in the extension direction. When the gas springs are acted upon, for example when a flap is closed, the nitrogen flows through the throttle opening in the piston.

The forces act against the weight of the flap and thus regulate its speed. When the flap is opened, the nitrogen flows back, thus supporting the operator's manual strength and enabling a defined extension speed. In addition, the oil filling ensures that it touches down gently when it is extended to the end position. The retraction and extension speed is in turn determined by the throttle opening.

The model used by Kohls has an extension force of 550 N, which is individually adjustable. Because the modern machine elements are equipped as standard with a valve and can thus generate the desired pressure. If necessary, ACE supplies a special nitrogen filling case, which the customer can customize on site. Also thanks to the good cooperation with ACE, Kohls was able to integrate the gas springs in an ideally protected manner into the compact design, so that the entire process of entangling a transformer core could be further optimized.