Unique Phenolic Molding Process Cuts Costs For Belts

One of the great things about molding is its technical diversity.

I came across a new twist today called the injection core compression molding process.

In this proprietary method developed by a German company called Winkelmann Powertrain Components,  phenolic novolac resin is injected into a mold at low pressure to prevent orientation of fiberglass. Next, a stamping core is shifted inside the mold to

Toothed belt pulley prototype made of thermoset for a camshaft drive.

Toothed belt pulley prototype made of thermoset for a camshaft drive.   (Winkelmann photo)

generate the cavity pressure and create the final geometry of the part. The pressure is maintained until chemical cross-linking of the phenolic resin occurs. The process creates dimensional stability under thermal stress in the final part, a belt pulley. Wittmann Battenfeld supplies the machines.

The company’s belt pulley production started with sheet metal cold forming. In 1992, the production of plastic parts was introduced in addition to the belt pulleys originally made of steel and later of aluminum. Use of plastic cuts costs and weight.

To date Winkelmann has molded some 50 million belt pulleys for water pumps, hydraulic power steering pumps and camshaft drives.

Other benefits of the Winkelman process include high sound absorption, a wear-resistant surface, excellent homogeneity since the fiberglass is not oriented, and resistance against all known substances in the engine compartment. The outer skin of the belt is resin rich.

It is also possible to mold belt pulleys from fiberglass-reinforced thermoplastics. However, thermoplastic materials with comparable performance attributes are more expensive because of the complex material composition required to ensure thermal stability.

Winkelmann currently operates its thermoset production plant in Ahlen, Germany with 23 injection molding machines with clamping forces ranging from 100 to 150 tons. Production started with the predecessor models of today’s W-B hydraulic HM series, the 3-platen machines from the CDC series with central clamping cylinders.

In order to ensure tension-free, perfectly 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.

Injection stamping mold. On the left: mobile mold half with compression core. On the right: fixed mold half with sprue bushing and base plate (Photo: Winkelmann Powertrain Components GmbH & Co. KG)

Injection stamping mold. (Photo: Winkelmann Powertrain Components GmbH & Co. KG)

About Doug Smock

Former Chief Editor at Plastics World and Senior Technical Editor Design News

Automotive, Compression, Europe, Phenolics , ,

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