Reinforced PA6 Processing Essentials: From Compounding to Injection Moulding

Compounding: where to add fibre and how to keep it long

Twin-screw compounding of glass-reinforced nylon normally uses side feeding: once the nylon melts in the feed section, glass enters downstream, cutting residence time under shear and improving fibre length retention.

In screw design, kneading blocks provide dispersive rather than distributive mixing; too many of them shear fibres excessively. Experienced compounders balance the configuration so fibre disperses evenly without losing strength to over-cutting.

Moulding: moisture comes first

PA6 is strongly hygroscopic, absorbing around 3% at equilibrium under standard conditions. Undried material hydrolyses rapidly above 250 °C, cutting molecular weight and raising melt flow abnormally — the easiest sign to misread, since higher flow means degradation, not easier moulding.

Dry at 80-90 °C for 4-6 hours to below 0.1% moisture, ideally below 0.05% for reinforced nylon, using a dehumidifying dryer with dew point under -20 °C.

Tool and process parameters

Mould temperature of 70-90 °C balances crystallinity against cycle time; higher mould temperature raises crystallinity and therefore strength and heat resistance, at the cost of longer cooling.

Barrel at 250-275 °C and never above 290 °C to avoid degradation. Medium to high injection speed reduces fibre show at the surface; back pressure should stay moderate to limit shear heating.