A New Twist: Rotating Core Injection Process Improves Dimensional Stability

A molding process patented by Solvay has been shown to improve the strength of conical or cylindrical sections of complex parts by injecting the plastic onto a rotating core. In conventional injection molding, cylindrical sections are formed by flowing the melt around a stationary core. Solvay found that rotating the core during injection increases burst strength by more than two times in parts molded of semi-crystalline polymers reinforced with glass, minerals or both.

Solvay conjectures that the process produces a preferred orientation in the polymer as the molecular chains become arranged around the rotating core, rather than simply flowing along the path of injected plastic. Reinforcing fibres are also uniformly oriented by the process.

Solvay’s Jeff Peterson, a global market manager, says the process produces a part with improved dimensional stability during operation over a wide range of temperature and humidity conditions.

“What’s absolutely critical to an automotive throttle body, for example, is that it maintains both its dimensions and its roundness in operation,” says Peterson. “The dimensional design tolerance between the air-regulating valve and the bore is quite tight and ideally would not change with fluctuations in environmental conditions. So any process that improves the bore’s dimensional stability over the full range of operating conditions in turn improves engine performance.”

Speed and duration of core rotation during injection are critical parameters in optimizing strength of the finished part. Peterson expects the process to produce improvements not only in automotive parts but also in similar applications in other industries, for example plumbing fittings and thrust washers.

Solvay Advanced Polymers248-645-1012