Bimetal Injection Screws and Barrels

Screw-barrel solutions designed to reinforce the working surface under high wear and corrosion conditions.

Main use: plastic injection molding machines.
Application conditions: high wear • high corrosion • thermoset • heavy recycled content.
Product scope: bimetal screw • bimetal barrel • complete set • complementary parts.

Key message: the bimetal structure aims to reinforce the working surface in contact with the raw material with special alloys more resistant to wear and corrosion, while preserving the mechanical strength of the supporting body.

Let's Evaluate the Right Bimetal Solution for Your Application

The Basic Logic of a Bimetal Structure

In bimetal screws and barrels, the main body and the working surface take on different roles. The base material provides the structural strength and toughness of the part, while the special alloy layer used in the zones in contact with the raw material helps increase surface resistance to wear, corrosion and process loads.

• Supporting body — structural strength, toughness and dimensional stability
• Alloy layer — a working surface reinforced against wear and/or corrosion
• Precision working surface — contributes to maintaining the screw-barrel clearance and plasticizing stability

When Should a Bimetal Solution Be Considered?

• If glass fiber, calcium carbonate (CaCO₃), talc and other mineral fillers cause rapid dimensional loss on the screw flights or inside the barrel
• If PVC, flame retardants or chemically aggressive additives cause surface deterioration and corrosion
• If heavy recycled content, foreign particles or a variable formulation structure increase wear
• If more demanding process conditions such as thermoset / BMC / DMC are involved
• If frequent screw-barrel replacement and unplanned downtime are affecting production continuity

Bimetal Application on the Screw and Barrel

Although the screw and barrel operate in the same plasticizing unit, their wear patterns differ. For this reason, alloy selection is made separately for the two parts, while the working clearance and surface compatibility are evaluated together.

Schematic cross-section of PTA hardfacing / bimetal alloy application on the screw (bimetallic alloy layer / screw stem)

On the screw, a hard alloy can be applied to the flights and the heavily worn working surfaces using PTA welding, hardfacing or other application-specific surface methods, depending on the design. The supporting body provides mechanical strength while the working surface is reinforced with a special alloy.

On the barrel, the inner surface in contact with the raw material can be reinforced with a bimetal alloy layer, a special inner layer, or a centrifugally cast liner, depending on the design. The goal is to slow dimensional loss on the inner diameter caused by wear and corrosion.

Important distinction: a bimetal PTA/hardfacing layer of around 3–5 mm on the screw is not the same application as very thin special surface coatings of around 3–5 µm. The final thickness and method should be verified according to the alloy selected, the zone and the production method.

Bimetal Surface Application Structures

The type of application is selected according to the location of wear, the formulation, temperature, corrosion risk and target service life.

• Screw flight hardfacing — to reinforce the flight areas where wear is most concentrated.
• Wider working-surface alloying — for applications where wear is not limited to the flight tip alone.
• Full-surface / special geometry application — a project-based solution for high wear or special process conditions.
• Barrel inner alloy layer — reinforcing the barrel inner diameter against wear and corrosion.
• Bimetal inner liner — designing the barrel body and the working surface with different material properties.

Solution Guide by Operating Condition

• Standard process (PE, PP, PS, ABS; low filler and low corrosion) — a nitrided screw-barrel can be sufficient for most applications.
• High wear (glass fiber, CaCO₃, talc, mineral filler, heavy recycled content) — bimetal / highly wear-resistant hard alloy surfaces.
• High corrosion (PVC, flame retardants, chemically aggressive additives) — a highly corrosion-resistant base material and suitable nickel/cobalt-based alloy systems.
• Wear + corrosion (formulations containing both filler and aggressive additives) — a special bimetal alloy selection based on the balance of wear and corrosion.
• Thermoset (phenolic, BMC, DMC) — a special surface / material solution based on geometry, temperature and material behavior.

Selection note: the formulation name alone is not sufficient. Filler type and ratio, additives, process temperature, cycle time, capacity and where existing wear occurs should all be evaluated together.

Benefits Provided by a Bimetal Structure

• Helps slow dimensional loss on the working surface.
• Can reduce surface deterioration caused by corrosion when the appropriate alloy is selected.
• Can contribute to maintaining the screw-barrel working clearance for a longer period.
• Can help reduce the need for frequent part replacement and unplanned maintenance.
• Allows the base material and the working surface to be optimized for different roles.

Technical Structure and Options

• Product scope — bimetal injection screw, barrel, complete set and complementary parts
• Reference screw diameter — Ø15–Ø360 mm; the final production range is verified on a project basis
• Reference L/D — 12–45; verified according to the machine and injection unit
• Base material options — 38CrMoAlA, 40Cr / 42CrMo, SKD61, DC53 and application-specific alternatives
• Screw surface application — PTA welding / hardfacing or application-specific alloy surface solutions
• Barrel inner surface — an alloyed inner layer or a centrifugally cast bimetal liner depending on the design
• Alloy systems — iron, nickel, cobalt and tungsten-carbide-based options
• Reference alloy hardness — HRC 55–65; the final value is confirmed according to the alloy and production method
• Screw bimetal layer — approximately 3–5 mm; verified on a project basis according to the application zone and production method
• Special thin coating option — approximately 3–5 µm for some surface applications; a different process from the bimetal PTA layer

Injection Machine Compatibility

Screw, barrel or complete set solutions can be evaluated for a wide range of injection machines, including Haitian, Yizumi, Fanuc, Toyo, Demag, Toshiba, Sumitomo, Engel and Arburg.

Compatibility note: final suitability is determined not by brand name but by machine model, injection unit, technical drawing and verified dimensions.

Complete Set and Complementary Parts

• Bimetal injection screw and barrel
• Screw tip, check ring and check ring seat
• Barrel head, flange and nozzle
• Heaters and connection parts
• Application-specific injection unit components

Information Needed for Technical Evaluation

• Machine brand, model and injection unit
• Screw diameter, L/D and existing screw-barrel dimensions
• Polymer processed, filler and additive types and ratios
• Process temperature, cycle time and capacity expectations
• Existing screw-barrel photos, technical drawing or sample
• Zone where wear/corrosion is seen and measurement values, if available
• Operating time of the existing part and the production problem experienced

Our approach: we do not select the alloy based on a generic product name alone. We evaluate the formulation processed, the wear marks on the existing part, the machine's operating conditions and the screw-barrel mating together. The goal is not simply to create a harder surface, but to establish the right balance of geometry, clearance, base material and alloy together.

Frequently Asked Questions

Is bimetal necessary for every injection application?

No. For unfilled, non-corrosive standard formulations, a nitrided solution can be sufficient. Bimetal should be chosen when wear or corrosion conditions technically require it.

Can only the screw or only the barrel be made bimetal?

Yes. Depending on the wear pattern, the parts can be manufactured with different surface solutions. However, the working clearance, hardness balance and condition of the mating surface must be checked together.

Are a 3–5 µm coating and a 3–5 mm bimetal layer the same thing?

No. A micron-level thin surface coating and a millimeter-level bimetal working layer created by PTA welding / hardfacing are different applications.

Are injection and extrusion bimetal screw-barrels the same?

The alloy and surface-strengthening approach can be similar; however, screw geometry, L/D and process operation are different. Extruder bimetal screw-barrels should be considered as a separate product group.

Share your machine information, raw material formulation and wear details of the existing part; let's determine the right bimetal screw-barrel solution for your application together.

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