55/110 Conical Twin Screw Barrel

Executive Summary

• Configuration: 55/110 conical twin screw barrel; precisely designed for the high-efficiency and energy-saving extrusion of rigid PVC, UPVC, CPVC, and wood-plastic composites (WPC). It creates a natural and gradual compression profile along the barrel hole using two intermeshing and counter-rotating screws that taper from 110 mm diameter at the feed end to 55 mm diameter at the melt exit.
• Material and Process: Screws and barrel made from high-grade nitriding alloy steel (such as 38CrMoAlA / SACM645) or premium bimetallic alloys undergo rigorous heat treatment. Standard processes include gas and ion nitriding (0.5–0.8 mm hardening depth with 950–1020 HV hardness) along with wear-resistant bimetallic PTA welding or hard chrome plating.
• Performance: This conical geometry provides exceptional melt pressure, homogeneous plasticization, and superior shear control at low to medium screw speeds. This configuration offers higher production capacity (typically 120–200 kg/hour depending on formulation) while tightly maintaining thermal stability in heat-sensitive compounds.
• Operational Advantages: Key operational advantages include extended wear life in high-filled PVC blends (CaCO₃/TiO₂), low energy consumption, and a homogeneous self-wiping motion that prevents material stagnation and thermal degradation.

Design and Materials

The 55/110 barrel system consists of two conical screws that rotate in opposite directions and intermesh, placed inside a matching double-hole cylinder. The taper from 110 mm at the feed section to 55 mm at the dosing section ensures homogeneous pressure progression and stable compression.

• Base Structure: Manufactured from high-integrity 38CrMoAlA (JIS SACM645 / DIN 1.8509) or 42CrMo structural alloy steel, providing core toughness under heavy torque loads, high tensile strength, and impact fatigue resistance.
• Heat Treatment and Nitriding: After precise rough machining and stress relief, components are water quenched, tempered, and subjected to deep gas or ion nitriding for over 72–120 hours. This process creates a hardened diffusion layer with a surface hardness of 950–1050 HV (~58–62 HRC) at a depth of 0.5–0.8 mm.
• Bimetallic and Special Coatings: For processing abrasive compounds (high calcium carbonate fillers) or corrosive polymers (CPVC/fluoropolymers), a bimetallic alloy liner (2.0–3.5 mm thickness, 58–65 HRC) is cast into the barrel hole and welded to the screw flights.
• Precision Machining and Tolerances: Machined on multi-axis CNC screw milling centers with tight linearity tolerances (≤0.015 mm/m) and extremely smooth surface roughness (Ra ≤0.4 µm on screw flights; Ra ≤0.2 µm on barrel holes).

📊 Technical Specifications Table

Technical Advantages

• High Output and Homogeneous Plasticization: The conical reduction (110 mm → 55 mm) maximizes the input capacity in the feed zone while efficiently generating high extrusion pressure at the head section, providing higher output per kilowatt compared to parallel twin screw designs.
• Self-Cleaning and Residue Prevention: The intermeshing flight geometry continuously cleans opposing surfaces, minimizing burning or degradation during long production runs by eliminating resin dead spots.
• Optimized Thermal Efficiency: The conical design minimizes the need for external electric heating as it produces consistent mechanical cutting heat. Multi-zone cast aluminum or ceramic heater resistances paired with integrated cooling jackets offer precise temperature control across all zones.
• Extended Wear Resistance: The synergy of nitrided base steel with tungsten/nickel bimetallic layers ensures reliable operation in high-filled formulations for thousands of hours without losing critical clearances.
• Custom Screw Profiles: Screw geometries (flight pitch, channel depth, decompression zones, and gas vent/vacuum sections) can be customized for specific applications such as high-filled PVC pipe extrusion or precision foam profile production.

Applications and Industries

• PVC Pipe Extrusion: Ideal for producing rigid PVC (UPVC) pipes with high mineral filler content, pressure pipes, agricultural irrigation pipes, and drainage systems.
• Window and Door Profiles: Extrusion of multi-chamber UPVC window profiles, sills, and architectural moldings requiring tight dimensional stability and high surface gloss.
• Wood-Plastic Composites (WPC): Production of WPC flooring (decking), wall cladding, and decorative trims with high wood fiber and polymer mix ratios.
• PVC Ceiling and Wall Panels: Continuous extrusion of hollow PVC ceiling panels, decorative marble sheets, and foam profiles.
• Cable Jacketing and Compound Production: Continuous pellet cutting, masterbatch compounding, and PVC wire/cable insulation jacketing.

Installation and Compatibility Notes

• Drive Alignment: Ensure complete mechanical alignment with extruder reducer output shafts. Verify coupling tolerances and axial bearing alignment before bolting.
• Clearance Verification: Before initial startup, manually rotate the screw set at ambient temperature to ensure zero metal-to-metal contact and homogeneous thread clearance.
• Heating and Sensor Calibration: Calibrate all zone thermocouples and check heater resistance contacts. Preheat the barrel assembly to processing temperature for at least 60–90 minutes to ensure homogeneous thermal expansion before feeding resin.
• Gas Vent Adjustment: If a gas vent/vacuum port is present, ensure that moisture traps and vacuum pump locks are functioning properly to prevent gas outlet flow blockage.
• Standard Mounting: Barrels have standard flange models compatible with standard conical twin screw extruders (e.g., SJSZ-55/110 models) (DIN/ANSI or custom OEM specifications).

Maintenance and Service Life

• Clearance Monitoring: Periodically check the radial clearance between the screw flight outer diameter and the barrel hole. The standard operating clearance is ~0.08–0.15 mm; renewal or barrel liner replacement is recommended when wear exceeds 0.35 mm.
• Cleaning (Purge) Procedure: Thoroughly clean the extruder with cleaning compounds or thermal stabilizer mixtures immediately before shutdown to prevent abrasive hydrochloric acid (HCl) gas release from PVC residues.
• Expected Lifespan: Standard nitrided barrels provide 15,000–25,000 operating hours; premium bimetallic barrels operating in abrasive mixtures typically reach 35,000–50,000+ operating hours with proper maintenance.

Safety and Quality Standards

• Manufacturing Standards: Manufactured in accordance with ISO 9001:2015 quality management and international metallurgy standards (ASTM, DIN, JIS).
• Material Certification: Delivered with complete raw material factory test reports (MTR), ultrasonic defect detection certificates, and heat treatment hardness charts.
• Operational Safety: Ensure that all thermal insulation guards, emergency stop cables, and barrel pressure relief mechanisms are checked and active during production.