USER REPORT: Injection core compression moulding process for thermosets

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  • Company: Winkelmann Powertrain Components, Germany
  • Process: injection core compression moulding process
  • Material: fiberglass reinforced phenolic resin
  • Application: belt pulleys

Equal or superior performance, but lighter in weight. This is a typical requirement in the automotive industry and a reason why innovative, extremely hard-wearing plastic parts are becoming increasingly important. Winkelmann Powertrain Components, a company based in Ahlen, Germany, recognized this trend at an early stage and has relied on thermoset materials for the production of belt pulleys.

Winkelmann’s belt pulley production originates from sheet metal cold forming. In 1992, the production of plastic parts was introduced. Phenolic resin reinforced with fiberglass and minerals was chosen as the material to be processed, and to be formed by a unique injection core compression moulding process (registered trade mark “WIN:DUR”) specially developed for this purpose. Battenfeld supplied the injection moulding machines. The first belt pulleys made of this thermoset were delivered to BMW.

During the injection core compression moulding process, phenolic novolac resin is injected into the mould at low pressure to prevent orientation of the fiberglass particles. Then the stamping core is shifted inside the mould in order to generate the necessary cavity pressure and final geometry of the part in the mould. The pressure is subsequently maintained until chemical cross-linking of the phenolic resin has taken place. The process allows the production of parts with high dimensional stability under thermal stress, a wear-resistant surface and very good homogeneity since the fiberglass is not oriented. In addition, the material features high media resistance against all known substances in the engine compartment and as the outer skin of the product consists exclusively of resin, a long service life is ensured as well.
Basically, it is also possible to manufacture belt pulleys from fiberglass-reinforced thermoplastics. However, thermoplastic materials with comparable performance characteristics are more expensive. And because of the more complex material composition, which is required to ensure the necessary thermal stability, thermoplastics are not competitive.

Fixed mould half with sprue bushing and base plate (Photo: Winkelmann Powertrain Components)

Fixed mould half with sprue bushing and base plate (Photo: Winkelmann Powertrain Components GmbH & Co. KG)

Winkelmann currently operates its thermoset production plant in Ahlen with 23 injection moulding machines with clamping forces ranging from 100 to 150 t, all coming from company Wittmann Battenfeld. The latest delivery included two machines of the HM series with 150 t clamping force, energy-efficient servo drives, robots for parts removal and insertion of metal rings and other options required for thermoset processing. And in order to ensure tension-free formed parts, an additional core compression cylinder has been mounted on the machine to condense the cavity, with the effect of applying additional force to the cavity by the hydraulic cylinder via the core during the injection process.

Thermoset toothed belt wheel for a camshaft drive with integrated setting device for adjustment of the camshaft (Photo: Winkelmann Powertrain Components GmbH & Co. KG)

Thermoset toothed belt wheel for a camshaft drive with integrated setting device for adjustment of the camshaft (Photo: Winkelmann Powertrain Components GmbH & Co. KG)

Today, Winkelmann has already injection core compression moulded some 50 million belt pulleys used in air-conditioning compressors, water pumps and power steering pumps. Mainly due to the enormous reduction in weight compared to metal, Winkelmann sees future fields of application in camshaft drive systems, crankshaft dampers and belt drive systems for power steering, which are currently still at the prototyping stage. Apart from that, the company is working on the further development of hybrid components made of steel, thermoset and elastomer, which could have a wide range of applications primarily in the area of damping. Here, the “decoupled” belt pulleys, whose designation is derived from their special design and function, offer the option of decoupling the belt drive and the aggregates connected with it from the rotational vibration of a combustion motor’s crankshaft drive.

Main picture: Dipl.-Ing. Axel Neukirchen, Thermoset Product Manager at Winkelmann, and Kai-Uwe Hilker, Wittmann Battenfeld salesman, in front of an HM 150 equipped for thermoset processing

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