One of the most common dilemmas in screw and barrel manufacturing is whether to choose a bimetal or a nitrided surface. Both methods aim to increase wear resistance, but their application methods and performance profiles differ.
What Is a Nitrided Screw-Barrel?
Nitriding is a process that forms a thin, hardened layer (typically 0.3–0.6 mm) on the steel surface through nitrogen diffusion. Surface hardness is high, but since the layer thickness is limited, this layer can thin and wear over time with raw materials containing abrasive fillers.
What Is a Bimetal Screw-Barrel?
In bimetal application, a special alloy layer is applied to the barrel inner surface or the screw flight backs using welding or centrifugal casting. This layer is much thicker than nitriding (typically 1.5–3 mm), and thanks to the hard carbides it contains (tungsten carbide, chromium carbide, etc.), it provides a much longer service life against abrasive and corrosive environments.
Wear Resistance Comparison
For raw materials containing abrasive fillers such as glass fiber, calcium carbonate and talc, bimetal coating has a noticeably longer service life compared to nitriding. Nitrided sets can be preferred as a more economical solution for unfilled or low-filled raw materials with low abrasiveness.
Cost and Return on Investment
The initial investment cost of a bimetal screw-barrel is higher than that of a nitrided one. However, for facilities processing abrasive raw materials, the longer service life and reduced downtime provided by a bimetal set generally make the total cost of ownership (TCO) more favorable.
Which Should Be Preferred in Which Situation?
- If abrasive additives such as glass fiber, mineral filler or flame retardants are used: bimetal
- For standard unfilled or low-filled PP, PE, PVC applications: nitrided can be a more economical option
- If high production continuity and low maintenance frequency are important: bimetal
- If initial investment cost is the priority and abrasiveness is low: nitrided
You can contact our technical team to determine the most suitable solution for the raw material you process and your production volume.
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