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Successful with a new production concept – PFISTERER Kontaktsysteme

Application report

PFISTERER Kontaktsysteme in Winterbach, manufacturers of CONNEX plug systems for medium and high voltage in the electrical industry, in cooperation with Klöckner DESMA have implemented a new procedure for the market-driven production of insulating parts made from LSR silicone.

Since the 60s, the common production technology for silicone insulating parts has been the RTV procedure (RTV = room temperature vulcanized silicone rubber). With this procedure, two components are mixed by means of a metering and mixing system. The RTV was then casted directly from the metering system into the moulds. The casted moulds are basically made of simple, wrought aluminium parts. Although a few production improvements could be made throughout the years, there were still considerable disadvantages of the RTV system:

  • Elaborate manual and therefore personnel-intensive and expensive tasks
  • A variety of production steps that must be worked through subsequently
  • Long throughput times for the vividly growing manufacturing lot volumes
  • Lack of availability of numerous variants and this causing
  • A planning production with high stock numbers and respective capital tie-up

In 2001, PFISTERER decided to introduce a new production technology for the MV-CONNEX insulating parts. They selected a semiautomated LSR-injection moulding process. Klöckner DESMA was chosen as their partner in this venture. The new production should fulfil the following requirements.

  • Covering the increased variety of variants
  • High flexibility in order to manufacture large but also small lot sizes economically
  • Independent manufacture of deflectors, SPAG and the actual insulating parts on one machine only
  • Largely rework-free parts
  • Number of moulds reduced to a minimum

The insulation and controlled termination parts of the MV-CONNEX are manufactured out of addition-cross-linked silicone rubber.
MV-CONNEX family

The demands of this project were by no means ideal

The enormous variety of possible variants of deflectors and the hardly predictable required volumes called for a special solution. The different inner and outer diameters required different inserts. Ideally, it should be possible to produce using a constantly changing composition. Four identical parts were always supposed to be injected. The challenge was the flawless venting of the large-volume parts. Due to the better feeding of the inserts and the position of possible injection gates, the filling had to take place from the top. The non-rigid inserts should not be moved or come into contact with the second injection stage.

After determining the mould concept, the production system was projected:

  • Injection moulding machine D 968.250 ZO/T V, with 2,500 kN clamping force and two injection units
  • Temperated transfer pot for deflectors and SPAG
  • Injection moulds for deflectors and SPAG matching the ITM pot
  • Injection moulds for insulating part

Test series, system optimisation and initial sample production

In order to achieve more safety for the processing of LSR silicone using the ITM procedure, a trial mould was built. The system optimisation and sample part production was performed at the technical facility at Klöckner DESMA Elastomertechnik. This site presented ideal circumstances due to its vicinity to the DESMA-owned mould development centre and their experience in producing products of this type.

The results from these tests were completely confirmed with the series moulds. Even in case of completely different feeding, the production of items of impeccable quality was possible. When measuring the finished parts, there were some deviations. Here, inserts were reworked or newly manufactured. Following these corrections, parts could be manufactured within the required tolerance ranges. No problems were found during the subsequent installation tests, so that the remaining inserts of the different variants could be produced.

After that, the machine was brought to the production site and installed followed by a training of the operating and maintenance personnel. The start of the series production was attended by DESMA service personnel.

"The one who has the best delivery conditions will get the business"

In order to meet risen customer requirements, the complete confectioning of the MV-CONNEX plugs was gradually modified. In the meantime, five DESMA injection moulding machines have been put into service. The production takes place in three-shift operation and only stands still on weekends and holidays. All quantities have increased throughout the years. Besides a noticeable increase in process safety and a significant reduction of manufacturing costs, today, the quick availability of the insulating variants is of crucial importance.

Looking back, we can note that the described modification of the entire production, especially based on the joint cooperation of the two companies involved, has led to great success.

Dr. Eckhard Wendt, Production Manager Winterbach, Pfisterer Kontaktsysteme GmbH &Co. KG
Volker Krell, Manager - Development and Design, Klöckner DESMA Elastomertechnik