Two gates and an overflow tab help fiber-reinforced resins defeat weld-line weakness

The study demonstrates a unique way to improve weld line quality for reinforced materials compounded with mineral fillers and fibers, according to Solvay. It is generally accepted that the strength of a reinforced polymer with a weld line is typically reduced by about 50% compared to a reinforced polymer with no weld line, due to an unfavorable orientation of the fillers at the weld line with respect to the load direction. An overflow tab, which is also known as spillover, relief tab, or overflow well, changes the fiber-orientation distribution.

Solvay modified a test specimen mold, creating an overflow tab, to quantify weld line quality. Three different types of test samples with a 4-mm thickness were made of reinforced grades of KetaSpirePEEK and AvaSpirePAEK. The overflow tab was positioned slightly off center from the weld line where the plastic flow ends, thereby creating an underflow in the molten layer that disturbs fiber orientation in the region, according to Solvay.

Impressive results
Flexural strength increased by more than 50% for all materials and jumped 160% specifically for KetaSpireKT-820 SL30 PEEK, a friction and wear grade, Solvay said. In all cases, the flexural strength of two-gate samples with tabs was only 15% to 20% less than one-gate samples with no weld line.

Solvay did add that the position and design of the overflow tab depend on the part design and must be carefully optimized. The company has successfully implemented overflow tabs in a variety of part designs using reinforced grades of KetaSpire PEEK and AvaSpire PAEK resins.