Prototype machine with samples of void-free silicone insulators. components into the static mixer. The mixer itself can be under atmosphere or connected to a vacuum chamber or pressure compensation unit.”
“ It is essentially a process of preparation, dosing and mixing,” emphasizes Schedding.“ If this is done right, nothing can go wrong downstream during molding, such as air inclusions.” He also notes that Hübers has developed special technology involving pressure sensors under the pump to monitor for problems. Quality assurance can then more easily control and correct such issues.
To apply all these principles to production of LSR insulators, Hübers has built a prototype that engineers acknowledge is probably overdesigned but which nevertheless allows customers to see the machine in operation. Marketing Manager, Christian Averesch, says that this prototype allows full-scale run-offs under typical production conditions for the purposes of quality assessment of end products.
“ Our process allows full control over a constant pressure inside the mold regardless of whether the slightly pre-heated silicone material expands due to cross-linking.”
“ Based on our experience with resins,” says Schedding,“ we have developed a different production technology for silicone that is especially effective for applications where you need absolutely void-free insulators. Other injection machines fill up the mold and close it as it is being filled with the silicone.
They compensate for this by adding pressure or creating flashing through holding the pressure. Our concept is different since in our machine the molding operation reacts by retracting a plunger to add additional volume of space. All excess pressure then goes into this plunger and that means very little flash.” Averesch adds that this process ensures full control over a constant pressure inside the mold regardless of whether the slightly pre-heated silicone material expands due to cross-linking inside the mold cavity.
Another advantage of Hübers’ vacuum mixing technology, according to Schedding, is that virtually 100 percent of the LSR material inside each 1000-liter container is sucked out, unlike other methods where he claims from 4 to 5 percent remains unutilized. Concludes Schedding,“ basically, we have to convince customers to spend more on dosing equipment but less in tooling as a result of better process control. That’ s where we see our advantage.” �
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