Warpage in Reinforced PC: GF10 Versus GF20 and How to Control It

Where warpage comes from

Warpage is caused by non-uniform shrinkage. Unfilled PC shrinks about 0.5-0.7% reasonably evenly, but once glass fibre is added, flow-direction shrinkage is constrained by the fibres and falls to 0.1-0.2% while cross-flow stays around 0.5%. A shrinkage ratio above three to one guarantees that a thin flat panel will bow.

GF20 widens the gap further, and processing alone often leaves several hundred microns of flatness deviation.

What moulding can do

Raising mould temperature (90-110 °C for PC) reduces frozen-in orientation; higher hold pressure and longer hold time compensate for shrinkage; and lowering injection speed reduces orientation — each traded against filling difficulty.

Gate location usually matters more than process parameters. Multiple gates or fan gates reshape fibre orientation distribution and shift warpage into non-critical areas.

What the material spec can do

If warpage dominates and stiffness demands are moderate, GF10 is usually far easier to hold flat than GF20. Partial substitution of glass with mineral fillers such as talc or glass beads is another route — their flow and cross-flow shrinkage differ less, giving better isotropy.

Such changes cost some tensile strength, so they need to be discussed with the supplier at design stage.