News from plastics processing and recycling technical articles

In the automotive sector, Winkelmann has specialized in 4 product areas, namely transmission components, torsional vibration dampers, fuel distribution systems and pulleys and wheels.

News from plastics processing and recycling technical articles

All machines at Winkelmann are made by Wittmann Battenfeld All machines at Winkelmann are made by Wittmann Battenfeld

The manufacture of pulleys originated in the cold forming of sheet metal, a core competence of the Winkelmann company. The pulleys, originally molded from steel and later from aluminum, were supplemented in 1992 by the production of the parts from plastic. In this context, three landmark decisions were made: The material used should be glass- or mineral-fiber-reinforced phenolic resin; the material should be processed using the core embossing process adapted for this purpose and trademarked under the name WIN:DUR. And the injection molding machines to be used should come from the Battenfeld company.

The first pulleys made of thermoset went to BMW. In the meantime, Winkelmann has produced close to 50 million thermoset pulleys using the core stamping process for water pumps, hydraulic power steering pumps and for camshaft drives. Particularly in the latter case, Winkelmann sees the need for a new type of tool due to the weight of the core-. Cost reduction compared to metal parts a great potential for the future. In addition, the company is one of the few manufacturers that also offers hybrid discs made of thermoset in combination with other materials, such as metal, thermoplastic and elastomer.

Thermoset processing in core stamping technology as a recipe for success

News from plastics processing and recycling technical articles

Core stamping die: left, moving side with stamping core; right, fixed side with sprue bushing and base (Photo: Winkelmann Powertrain Components GmbH& Co. KG) Core embossing tool: on the left, moving side with embossing core, on the right, fixed side with sprue bushing and base (Photo: Winkelmann Powertrain Components GmbH& Co. KG)

In the core stamping process, novolac-based phenolic resin is introduced into the mold at low pressure to prevent alignment of the glass fibers. Then the stamping core is moved in the mold, creating the necessary cavity pressure in the mold and the final geometry of the component. The pressure is subsequently maintained until the later irreversible chemical crosslinking of the phenolic resin molecules has taken place. This is responsible for ensuring that the material later retains its shape under the influence of temperature.

Accordingly, the use of thermosets processed in the core stamping process for the manufacture of pulleys offers a number of advantages:

In addition to the already mentioned aspect of the reduction of weight and costs compared to metals, there is a high noise damping, a low-wear surface, a high dynamic load capacity even at extreme temperatures, a high homogeneity, since the glass fibers have no preferred direction, as well as a high media resistance against all known media in the engine compartment. Since the outer skin of the products is made of pure resin due to the process, a long belt life is also ensured.

In principle, it would also be possible to manufacture pulleys from thermoplastics that are also reinforced with glass fibers. However, thermoplastics comparable in performance are disproportionately expensive and thus not competitive due to the complex material composition necessary to ensure the required temperature resistance, and were thus never considered by Winkelmann.

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