High-Temperature Resin Moulding Troubleshooting

Insufficient drying (silver streaks, voids, property loss)

Silver streaks and bubbles appear on the surface, with degraded properties and colour.

Sulfone and PEEK are hygroscopic; residual moisture causes hydrolysis and flashing off at high processing temperatures. This is the most common defect source in high-temperature resins.

Dry thoroughly immediately before processing (typically around 150°C for several hours for both sulfone and PEEK; a desiccant dryer is recommended). Material re-absorbs moisture if left standing, so maintain drying with a hopper dryer during production. Follow the grade TDS for exact temperature and time.

Short shot / poor flow (barrel temperature too low)

The cavity does not fill completely, or flow fronts are rough with pronounced weld lines.

High-temperature resins have high melt viscosity, and flow falls away sharply if barrel temperature is too low. Setting temperatures to commodity-resin norms causes short shots.

Apply a temperature profile intended for high-temperature resins (typically in the 340–400°C range for sulfone and PEEK, varying by grade). Raise nozzle and mould temperatures with it, and increase injection speed and pressure. Use the TDS recommended barrel temperatures.

Thermal degradation (black specks, burn odour)

Black specks and burn marks appear, with a distinct odour and reduced properties.

Excessive barrel temperature or long residence time causes thermal degradation. Frequent stoppages and small shot weights extend residence time.

Keep barrel temperature at or below the upper end of the recommended range and reduce residence time by matching shot weight to machine size. Purge or empty the barrel during extended stops, and clean thoroughly with a dedicated purging compound when changing materials.

Weak weld lines

A visible line forms where flow fronts meet, and strength is reduced at that location.

High-viscosity high-temperature resins fuse incompletely where flows meet, and low temperature makes it worse. Glass-fibre reinforced grades lose more strength because of fibre orientation.

Raise mould and barrel temperatures and injection speed to keep the meeting point hot. Move the weld line to a lower-stress area by changing gate position, and add an overflow (doubling as a gas vent) at the junction to expel the cooled flow front.

PEEK crystallinity variation (dimensional and property scatter)

Parts vary in dimensions, stiffness and chemical resistance despite identical settings.

PEEK is semi-crystalline and its crystallinity depends strongly on mould temperature. A cold mould freezes in an amorphous state, and later post-crystallization causes dimensional and property changes in service.

Hold the mould hot enough to complete crystallization during moulding (typically in the 170–200°C range, varying by grade). Keep mould temperature uniform and consistent, and anneal afterwards where crystallinity needs to be stabilised.

Warpage (reinforced grades)

Parts fail to stay flat, bowing or twisting out of shape.

In glass- and carbon-fibre reinforced grades, shrinkage differs by direction according to fibre orientation. Uneven cooling adds to it.

Design uniform wall thickness and optimise cooling circuits so mould temperature is even. Control fibre orientation through gate position, and allow adequate hold pressure and cooling time.

Sink marks and internal voids (thick sections)

The surface dimples over thick sections, or voids form internally.

High-temperature resins shrink appreciably on solidification, and hold pressure transmits poorly into thick sections, so internal shrinkage occurs.

Gate into the thickest section and allow sufficient hold pressure and time. Avoid abrupt thickness changes and keep ribs at or below half the nominal wall. Dry thoroughly so gas-related voids can be distinguished from shrinkage voids.

Colour shift and property loss after coloring

Colour changes during processing, or properties drop, once a high-temperature resin is coloured.

Ordinary masterbatches cannot withstand the processing temperature of high-temperature resins; pigments degrade or the carrier reduces properties.

Use a colour solution engineered for high-temperature resins (Avient Colorant Chromatics™). Sourcing resin and colour together as a pre-colored compound removes let-down variation and keeps colour and properties stable.