Variable fiber injection differs from SRIM by injecting the glass reinforcement - rope or "rovings" - at lengths up to 10 cm (4 in) directly into the PU liquid stream as it is poured into an open mold. According to Huntsman, SRIM technology uses a glass mat or preform that needs to be manually placed in the mold before PU injection. The new technique results in the glass fibers being more accurately distributed across the entire mold cross-section, producing a finished component with mechanical properties equal to a similar SRIM part, but with a lower mass, reduced wall thickness, and less glass scrap.

By using a robotically controlled, integrated cut, mix, and spray head, the company believes fiber injection can achieve rapid mold injection and shorter cycle times than SRIM. A major challenge with the new process has been to achieve a finished product with consistent mechanical properties that allow for fully automated production. This has led to the development of new PU technology that has sufficient "cream" time to allow the robot head to distribute the PU and glass mixture over the surface of the tool and then move clear before mold closure. Huntsman worked with Cannon Technos and Krauss Maffei on the new system. It is currently undergoing evaluation in Europe and North America.

Stuart Birch

AEI September 2000
For more information, circle 218 & 219