Conical Twin Screw and Barrel

High-volume feeding, controlled compression and stable PVC extrusion.

MILON Endüstri determines the screw-barrel solution for conical twin-screw extruders by evaluating the existing machine's dimensions, screw standard, processed formulation and target capacity together. For new production or refurbishment projects, geometry, material and surface treatment are selected according to the application. For abrasive and highly filled formulations, nitrided and bimetal options are evaluated together.

Key message: A conical twin screw-barrel is used specifically for the controlled feeding and plasticizing of high-volume, multi-component formulations such as powder/PVC dry blend. The large inlet diameter supports feeding; the tapering geometry increases compression further along the process.

Let's Determine the Right Conical Screw-Barrel for Your Machine

What Is a Conical Twin Screw and Barrel?

A conical twin-screw system consists of two screws that start with a larger diameter on the feed side and taper toward the outlet, together with a twin-bore barrel matching this geometry. This structure eases the feeding of high-volume dry blends while providing controlled compression and plasticizing further along the process.

Conical twin screws are especially common in PVC and CPVC pipe/profile, PVC foam sheet and profile, WPC, SPC/LVT and other mineral-filled or multi-component formulations. Application suitability should be verified based on machine design and formulation.

Common Standard Sizes

Among the most commonly encountered sizes in the market are standards such as 51/105, 55/110, 65/132, 80/156 and 92/188. Various manufacturers also offer a wider series: 35/75, 40/84, 45/90, 45/97, 45/100, 50/105, 51/105, 55/110, 55/120, 58/125, 61/125, 65/120, 65/132, 68/147, 70/140, 80/143, 80/156, 80/174, 92/188, 95/191 and 105/216.

Sizing note: an expression such as "65/132" or "80/156" indicates the two characteristic diameters of the conical screw pair. However, this size alone does not guarantee machine compatibility; total screw length, gearbox connection, center geometry, shaft end, barrel bores and feed opening must all be checked.

Technical Dimensions and L/D Information

• Reference production diameter range — Ø25/50 – Ø185/340 mm (manufacturer capability range; not MILON's standard stock range)
• Common sizes — 51/105 • 55/110 • 65/132 • 80/156 • 92/188
• L/D ratio — varies for conical systems by manufacturer and machine design; some sources give an approximate range of 8:1–25:1
• Material — 38CrMoAlA and special alloys depending on the application
• Surface treatment — Nitriding • Bimetal • Hardfacing / special alloy
• Production type — OEM / custom size / reverse engineering according to the existing machine

L/D note: interpreting L/D from a single diameter is not as straightforward for conical screw systems as it is for single-screw systems. Therefore, during quotation and production, the manufacturer's L/D definition, effective working length and the machine's original technical drawing should all be verified together.

How Does It Work?

• Feed Zone — thanks to the large inlet diameter, PVC dry blend, mineral-filled or bulky formulations are drawn into the screw channels more easily.
• Compression / Pre-plasticizing — as the screw diameters and channel volume decrease toward the outlet, the material is compressed in a controlled way; plasticizing progresses through heat and mechanical shear.
• Mixing / Melting — the mating profiles of the two screws support homogeneous distribution of PVC, CaCO₃, pigment, stabilizer and other additives in the formulation.
• Metering / Pressurizing — the plasticized material is delivered to the die with more stable flow rate and pressure.

Conical twin screw and barrel — real production example

Which Applications Is It Used In?

• PVC pipe and fittings extrusion
• PVC window and door profiles
• CPVC pipe and profile applications
• PVC foam sheet, panel and profile
• WPC (Wood Plastic Composite) profile and board
• SPC / rigid core flooring formulations
• PVC compounding / pelletizing applications
• Refurbishment projects where the machine's original design is a conical twin screw

Key Difference Between Conical and Parallel Twin Screws

• Screw diameter — larger at the inlet and tapering toward the outlet in conical twin screws; the same diameter along the length in parallel twin screws
• Feed volume — conical twin screws have a high-volume advantage at the inlet; parallel twin screws have a fixed structure depending on geometry
• Barrel — conical twin screws have a tapered twin bore, parallel twin screws have a parallel twin bore
• Gearbox / center structure — conical twin screws have a design specific to the conical geometry, parallel twin screws have a parallel axis arrangement
• Interchangeability — the two systems are not a direct alternative to each other

The choice is not made based on raw material alone. The machine's original gearbox output, center geometry, torque transmission, screw length and barrel design are decisive.

Why Is Conical Geometry Used?

Conical geometry provides greater volume on the feed side, supporting the intake of PVC dry blends with low bulk density or high filler content. The tapering channel volume toward the outlet helps compression and plasticizing progress in a controlled way. For this reason, conical twin-screw systems are widely used in PVC profile, pipe and board lines.

Material and Surface Treatment Options

• Nitrided — for standard / low-to-medium abrasive PVC formulations; an economical and common solution using nitriding steels such as 38CrMoAlA
• Bimetallic Barrel — for CaCO₃, mineral filler, WPC and recycled formulations; an alloy layer can be applied to the barrel inner surface to increase wear and corrosion resistance
• Bimetal / Hardfacing Screw — for cases with high wear on the screw flights; hardfacing / alloy can be applied to the flights and contact zones to extend service life
• Special Alloy — for cases requiring high wear resistance, corrosion resistance or special processing; selected according to formulation, operating temperature and target service life

Bimetal Solution for Conical Twin Screw-Barrels

In conical twin screw-barrel systems, bimetal application is evaluated to support the service life of the working surfaces, especially in abrasive formulations such as CaCO₃, mineral filler, WPC or recycled material.

• Bimetallic Barrel — an alloy layer can be applied to the twin-bore working surfaces of the barrel to increase wear and corrosion resistance.
• Bimetal / Hardfacing Screw — hardfacing or a special alloy can be applied to the screw flights and critical contact zones to increase resistance to wear.

Evaluation as a set: for highly filled formulations, the wear condition of the screw pair and the barrel should be evaluated together rather than the screw or the barrel alone.

Correct selection: bimetal selection should not be made based solely on the logic of "harder material." The type and ratio of filler in the formulation, operating temperature, capacity target and existing wear pattern should be evaluated together.

Why Is Wear Critical?

• CaCO₃, talc, wood flour and other mineral/fiber fillers can accelerate wear.
• The two screws and the barrel operate together as a matched system; measuring only one part is not sufficient.
• Screw outer diameters, side surfaces, barrel bores and critical mating zones should be checked together.
• Wear can lead to backflow, capacity loss, high amperage, uneven plasticizing and surface quality problems.

Information Needed to Determine the Right Conical Screw-Barrel

• Machine brand, model and year of manufacture
• Current screw standard: e.g. 65/132, 80/156, 92/188
• Total screw length and, if available, L/D / effective working length
• Gearbox output, shaft end and connection details
• Center and mating geometry of the screw pair
• Barrel total length, twin-bore dimensions, flange and connection details
• Location of the feed opening, degassing/venting port and heater zones
• Raw material processed: PVC, CPVC, WPC, etc.
• CaCO₃, pigment, stabilizer, wood flour and recycled content ratios in the formulation
• Current and target production capacity
• Problem experienced: wear, low capacity, high amperage, unstable pressure or plasticizing
• Photos of the old screw-barrel, technical drawings and measurement report, if available

Critical note: having the same "65/132" or "80/156" designation alone is not sufficient for compatibility. Different machine manufacturers can have differences in total length, shaft end, gearbox connection, barrel flange and screw profile even at the same nominal size.

Frequently Asked Questions

Are 65/132, 80/156 and 92/188 standard sizes?

Yes, these are commonly encountered conical twin-screw sizes in the industry. However, the connection and total length may not be the same across every brand and model.

Can a 92/188 be fitted in place of an 80/156?

No. These belong to different machine and gearbox geometries; they are not a direct alternative to each other.

Is a conical screw or a parallel screw better?

There is no single "better" option. The machine's original design, formulation and capacity target are decisive.

Is bimetal always necessary?

No. It is advantageous for CaCO₃, WPC, high mineral filler or abrasive formulations; a nitrided solution may be sufficient for standard formulations.

Can it be manufactured without a technical drawing?

Detailed measurement and reverse engineering can be carried out based on the existing screw-barrel. Critical mating and connection dimensions must be reliably extracted.