EFFECT OF PRE-CROSS-LINKING ON MECHANICAL AND RHEOLOGICAL PROPERTIES OF SOLID SILICONE RUBBER AND ITS PROCESSABILITY IN EXTRUSION BLOW MOLDING

摘要

The blow molding process offers the possibility of reproducible, fully automatic and therefore cost-efficient mass production of complex hollow bodies. Due to the poor mechanical properties of uncured rubber, it has not yet been used for the manufacturing of elastomeric hollow parts. In this contribution, it is shown that with a defined pre-cross-linking of solid silicone rubber the blow molding of the material is possible. With pre-cross-linking the mechanical material properties can be adjusted precisely. This allows parison extrusion without strong drawdown. During the forming, it provides the necessary elasticity while maintaining the weldability and formability of the material. But pre-cross- linking also influences the materials rheological properties. Preliminary investigations showed pre-cross- linking has to take place in the blowing head bevor the material leaves the die. Therefore, changes in rheological material behavior are investigated and considered for the flow channel design. It is shown that the pre-cross-linking allows the blow molding of elastomeric hollow bodies with a surface stretch ratio of 3.6 to 1. However, pre- cross-linking can also lead to flow instabilities such as wall slippage and melt fracture.