Nitrided vs Bimetallic Screw Barrel: How to Choose

Materials15 Oct 2026·6 min read

A nitrided barrel is a steel barrel with a hardened skin. A bimetallic barrel is a steel barrel with a cast alloy bore. The first is cheaper, the second lasts far longer on abrasive material - and the crossover point is your resin.

What nitriding gives you

Gas nitriding diffuses nitrogen into the surface of 38CrMoAlA steel, producing a case hardness of HV 900–1100 to a depth of roughly 0.45–0.7 mm. It is hard, low friction and inexpensive. For unfilled PE, PP, PS, ABS and virgin PVC it is usually the correct choice and anything more is money spent for nothing.

What a bimetallic bore gives you

Instead of a diffusion layer a few tenths of a millimetre thick, the bore is centrifugally cast with a 2–5 mm alloy layer that is metallurgically bonded to the steel body. There is no plating to peel and no interface to flake. On glass-filled material the service life is typically three to five times that of nitrided steel.

Decide by resin, not by price

• Unfilled PE, PP, PS, ABS → nitrided is right
• Glass-fibre reinforced PA, PBT, PP at 15–30% → bimetallic pays for itself
• Mineral-filled, flame-retardant or halogen-free compounds → bimetallic
• Recycled material with unknown fillers → bimetallic, 3–5 mm layer
• PVC with high CaCO3 loading → bimetallic, especially on conical twin bores

The cost question

Compare cost per ton produced, not purchase price. A bimetallic barrel that costs 60% more and lasts four times as long is cheaper - the bigger real saving is the production you did not lose to output drift, rising melt temperature and an unplanned shutdown.

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