Triple-win situation for liquid silicone rubber
07.02.2022 | Petra Rehmet

"If you can think of it, you can do it", is the slogan of Bernd Krebs, founder of Toolcraft. Since 1989, widely disparate areas have developed in which the company is active. Among them are metal cutting, additive manufacturing, and robotics as well as injection molding and moldmaking. The team uses the wide variety of available methods to present solutions – occasionally unusual ones – to customers. Toolcraft has often adopted new technologies from scratch, so introducing silicone certainly does not faze them.

SKZ, in turn, is number one in education, research, testing and certification in the plastics field. In addition to SKZ's many other industry-relevant events, the renowned industry conference on silicone elastomers takes place every two years. To date, however, SKZ had not had an LSR processing machine on its own premises. The topic was increasingly under discussion as a result of increasing electromobility with its high underhood temperatures and the increasing importance of elastomers in medical technology.

Valuable support was also provided by Nexus, a company that brought its experience in metering technology to the table. Because all parties involved are based in Bavaria, it is even possible to obtain state-specific subsidies for research projects.

As a result, SKZ can help its fellow network member, Toolcraft, with targeted analyses when implementing the new technology – while at the same time acquiring the expertise to provide customers with well-founded advice to spearhead innovative developments. The launch took place at a two-day training session held by the Plastics Technology department at the University of Kassel. "Our colleagues there are outstanding and being able to interact with them is extremely valuable to us," says Bastian. Schwalme adds, "Once we have mastered the process itself, we will be able to collaborate with others – just as we did with thermoplastics. This collaboration will include everything from basic research to practical aspects on the shop floor."      

One of the reasons Toolcraft gave the nod to KraussMaffei as machine partner was the people involved. "From the beginning, you made us feel welcome and that we were being taken seriously. And the expert support from Cordula Wieland is priceless."

The APC plus machine function will help to give the products a high weight consistency. It uses the melt viscosity and stored material parameters to regulate the changeover point freshly from shot to shot. For silicones, this is important insofar as the batch fluctuations are much more dramatic than for conventional thermoplastics.

However, the latter has very low viscosity, which makes moldmaking extremely difficult.  At a water-like consistency, the molds have to be perfectly sealed. Usually, a vacuum is even applied. The temperature control is the reverse of that used for thermoplastic processing to prevent premature wetting. While the plasticizing unit as well as the cold runner are cooled, the cavity is brought to a temperature of approximately 190 °C.

To date, most mold production for LSR has been in the hands of highly specialized providers centered regionally in Austria. However, because these providers are increasingly manufacturing silicone parts themselves and, furthermore, the prices for molds and cold runners are relatively high, more and more companies are looking for alternatives.

Toolcraft is also going to build its own tooling, drawing on its in-house experience with precision molds. Currently, about 50 percent of what Scheuerlein's team produces is for its own use, with the other half going to customers. Of course, plans call for offering LSR molds to external customers in the future.

 One such "hack" is the recommendation to purchase a chest freezer. Particularly in the experimentation phase – where a few weeks might pass between steps – freezing the unit in the meantime saves a good deal of work.

The top team from SKZ and Toolcraft will pave its way forward with support from KraussMaffei. We will follow up in two years.