Bi-metallic Alloy Screw And Barrel for Extruder

A bi-metallic screw and barrel is an industrial component featuring a dual-layer metal composite structure. The base material primarily consists of SKD61 alloy steel, though other materials such as SACM645 and 38CrMoAlA are also utilized. The surface layer is bonded to the substrate using metallurgical bonding techniques, incorporating self-fluxing alloy materials—such as tungsten carbide (WC/Co), nickel-based alloys (Ni+B/Cr), and cobalt-based alloys (Co+Ni/Cr)—with alloy compositions that include 88WC/12Co. This product is manufactured using processes such as centrifugal casting, bi-metallic sintering, and PTA spray forming; additional processing steps include heat treatment, bi-metallic alloy spraying, and hardfacing.

The surface alloy layer of the bi-metallic screw and barrel achieves a hardness of HRC 60–65°, offering a service life 3 to 5 times longer than that of standard nitrided screws. It features a surface roughness of Ra 0.4 and a straightness tolerance of 0.015 mm. Primarily utilized in equipment such as injection molding machines, extruders, and thermoset molding machines, these screws are specifically designed to process highly abrasive and corrosive special engineering plastics—including glass fiber-reinforced plastics, PPA, PO, PPS, LCP, PC, ABS, and PA. They are particularly well-suited for processing materials containing over 40% glass fiber content, as well as halogen-free materials. Furthermore, the bi-metallic screw effectively eliminates the issue of chrome-plating detachment commonly associated with chrome-plated screws.

Dual- alloy screw and barrel are manufactured using materials such as 88WC/12Co, CrC/25NiCr, and XaloY108. Subjected to a comprehensive through-hardening treatment, these screws are suitable for processing a wide range of materials, including plastics reinforced with glass fibers, as well as specialized engineering plastics such as PPA, PO, PPS, LCP, ABS, flame-retardant compounds, phenolic molding compounds, magnetic powders, PC, and hard calcium carbonate fillers. Dual-alloy screws are categorized into various types based on their alloy composition, including tungsten carbide, chromium-tungsten carbide, and nickel-chromium-tungsten carbide variants.

These screw and barrel feature a progressive, variable-depth screw geometry with uniform pitch. The feeding section is designed with deep flights to maximize conveying efficiency; the compression section facilitates the melting and plasticization of the material; and the metering (homogenizing) section utilizes shallow flights to ensure melt uniformity. Furthermore, the feed throat area undergoes a specialized treatment involving the application of a nickel-based alloy reinforcement layer, effectively mitigating localized wear issues typically caused by the processing of highly filled materials. These screws are utilized in a variety of manufacturing applications, including injection molding machinery, extrusion machinery, and phenolic molding machinery.

The base material selected is SKD61 hot-work tool steel, which, following quenching and tempering treatment, exhibits high strength and thermal stability. Furthermore, depending on specific application requirements, alternative base materials such as 38CrMoALA or SACM645 may also be utilized. The surface treatment process employs the following combination of technologies:

Nickel-based Alloy Powder Spray Welding: Utilizing an oxy-acetylene flame to melt and spray a Ni+B/Cr alloy powder, thereby forming a metallurgically bonded layer with a thickness of 0.5–3 mm.

Tungsten Carbide Centrifugal Casting: Achieving a uniform distribution of WC/Co alloy under high-speed rotational conditions, resulting in a 400% enhancement in wear resistance.

Cobalt-based Alloy Hardfacing: Specifically tailored for the processing of highly acidic plastics, this technique employs multi-layer hardfacing with Co+Ni/Cr alloys to provide corrosion protection.

Other critical processing techniques include heat treatment, bi-metallic alloy spraying, hardfacing, and centrifugal casting.

The composition of the surface alloy layer includes formulations such as 88WC/12Co and CrC/25NiCr.

Key technical parameters include: Alloy Hardness: HRC 60°–68°; Surface Roughness: Ra 0.4; Screw Straightness: 0.015 mm; Processing Diameter Range: Ø20 mm – Ø250 mm; and Effective Length: up to 4000 mm – 8000 mm.

Wear Resistance: The 88WC/12Co surface layer is capable of withstanding the processing of plastics with a glass fiber content exceeding 40%.

Corrosion Resistance: The Ni-based alloy layer effectively resists corrosion caused by the acidic decomposition products of materials such as PPS.

Thermal Stability: Maintains structural integrity at operating temperatures ranging from 300°C to 420°C, making it suitable for high-temperature plastics such as LCP.

Maintenance Costs: Offers a service life 3 to 5 times longer than that of standard screws.