{"id":1933,"date":"2026-07-21T07:17:44","date_gmt":"2026-07-21T07:17:44","guid":{"rendered":"https:\/\/gearrack.top\/?p=1933"},"modified":"2026-07-21T07:17:44","modified_gmt":"2026-07-21T07:17:44","slug":"helical-gears-for-extruder-drives","status":"publish","type":"post","link":"https:\/\/gearrack.top\/fr\/helical-gears-for-extruder-drives\/","title":{"rendered":"Helical Gears for Extruder Drives"},"content":{"rendered":"
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GEAR APPLICATION GUIDE \u00b7 HELICAL GEAR \u00b7 H07<\/span><\/p>\n

Helical Gears for Extruder Drives:
\nSingle-Screw, Twin-Screw and Co-Rotating Extruder Gearbox Design<\/span><\/h1>\n

Extruder drive gearboxes present a unique set of design challenges \u2014 combining the continuous high-torque, low-speed output of a plastics or rubber processing screw with the need for precise speed control, compact installation, and thermal stability across years of uninterrupted production. The helical gears inside an extruder gearbox must handle sustained torques at the upper limit of their rated capacity for 6,000\u20138,000 hours per year, while the screw itself generates thrust loads, radial loads, and, in twin-screw applications, complex shaft interaction forces that must all be absorbed by the gearbox without affecting gear contact quality. This guide covers helical gear specification, material selection, and gearbox integration for single-screw, parallel twin-screw, and conical twin-screw extruder drive applications.<\/p>\n

18CrNiMo7-6 \u00b7 42CrMo4 \u00b7 M6\u2013M20 \u00b7 DIN 5\u20137<\/span>
\n6,000\u20138,000 h\/yr \u00b7 Torque Split \u00b7 Thrust Bearing<\/span>
\nSingle-Screw \u00b7 Twin-Screw \u00b7 Co-Rotating \u00b7 PVC<\/span><\/div>\n<\/div>\n<\/div>\n
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DUTY CYCLE<\/p>\n

6,000\u20138,000 h\/yr<\/p>\n

Extruder drive gearboxes are among the highest duty cycle gear applications in industry \u2014 plastics compounding and pipe\/profile extrusion lines run continuously with only brief planned shutdowns for screw cleaning and maintenance, placing helical gears at their thermal and fatigue limits for extended periods<\/p>\n<\/div>\n

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HELIX ANGLE<\/p>\n

15\u00b0 \u2013 30\u00b0<\/p>\n

Extruder gearbox helical gear helix angles. Single-screw extruder main reduction: 20\u00b0\u201325\u00b0. Twin-screw torque split gears: 15\u00b0\u201320\u00b0 (lower angle to manage axial load on the torque split shaft bearings). Ground helical gears in extruder gearboxes above 10 MW: 25\u00b0\u201330\u00b0<\/p>\n<\/div>\n

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MODULE RANGE<\/p>\n

M6 \u2013 M20<\/p>\n

Small single-screw extruder gearbox (screw diameter 30\u201360 mm): M6\u2013M8. Medium (screw 60\u2013120 mm): M8\u2013M12. Large industrial blown film and pipe extrusion line (screw 120\u2013250 mm): M12\u2013M16. Very large compounding extruder: M16\u2013M20<\/p>\n<\/div>\n

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QUALITY CLASS<\/p>\n

DIN 5 \u2013 7<\/p>\n

DIN 5\u20136 ground for twin-screw torque split gears and high-speed first-stage pinions. DIN 6\u20137 for single-screw main reduction gears. DIN 7 acceptable for final-stage large gears in low-speed extruder gearboxes where noise and TE are not specification drivers<\/p>\n<\/div>\n<\/div>\n

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Extruder Drive Gearbox Architecture and Helical Gear Roles<\/h2>\n

The extruder drive gearbox serves three simultaneous functions that no other single machine component performs: speed reduction from the electric motor (typically 750\u20131,500 RPM) to the screw shaft (10\u2013150 RPM depending on extruder size and process), torque multiplication from the motor rating to the process-required screw torque, and thrust load absorption \u2014 carrying the full axial thrust generated by the screw as it pushes melted polymer toward the die, which in a large pipe extrusion line can exceed 500 kN. The helical gears inside the gearbox handle the first two functions; the thrust bearing (typically a large tapered roller or spherical roller thrust bearing) handles the third, but the gearbox housing and gear arrangement must be designed to keep the thrust bearing loads from interfering with the helical gear mesh geometry.<\/p>\n

Korea Ever-Power’s helical gears for extruder drives<\/a> are manufactured in 18CrNiMo7-6 case carburized (for all first-stage and second-stage helical gears in extruder gearboxes where maximum contact fatigue resistance is required at the high rotational speeds of these stages) and 42CrMo4 through-hardened (for final-stage bull gears in large slow-speed extruder gearboxes above M16 where through-hardening provides adequate load capacity at reduced manufacturing complexity). All extruder gearbox helical gears from Korea Ever-Power are ground to DIN 5\u20137 quality class depending on the stage position and speed \u2014 first-stage pinions at 750\u20131,500 RPM are ground to DIN 5\u20136; final-stage gears at 30\u201380 RPM are ground to DIN 6\u20137 where noise is the specification driver, or hobbed to DIN 7 where it is not.<\/p>\n

\"ground<\/p>\n

The twin-screw extruder gearbox introduces a design requirement absent in single-screw applications: the torque split \u2014 dividing the motor torque equally between the two output shafts driving the two intermeshing screws. The torque split is achieved through a set of matched helical spur gears on an intermediate shaft (the \u201ctorque distribution shaft\u201d) that meshes simultaneously with gears on both output shafts. Equal torque split requires that both output shaft helical gears have identical tooth geometry and the torque distribution shaft gears are matched to within \u00b11% of theoretical torque split \u2014 verified by measuring the torque on each output shaft under load. Unequal torque split in a co-rotating twin-screw extruder causes one screw to run at higher torque than the other, potentially exceeding the screw shaft fatigue limit while the other screw runs underloaded \u2014 the imbalance is progressive as the overloaded screw gear wears faster, increasing the split imbalance. Korea Ever-Power torque distribution shaft helical gear sets are matched as complete sets to \u00b10.5% torque split at the specified load.<\/p>\n

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Korea Ever-Power 18CrNiMo7-6 case carburized and ground helical gear for extruder drive gearbox first-stage reduction \u2014 M8, 28 teeth, helix angle 22\u00b0 RH, HRC 60\u201362 tooth surface, effective case depth 0.8\u20131.2 mm, DIN 6 quality class. Profile crowning 8 \u03bcm to distribute load evenly across the tooth face under gearbox housing deflection at maximum screw torque. Lead crowning 6 \u03bcm to accommodate shaft misalignment from thrust bearing deflection during melt pressure peaks. Ground tooth surface Ra \u2264 0.4 \u03bcm for optimal EHL film formation at 1,200 RPM pinion speed in ISO VG 150 synthetic PAO gear oil. Used in first-stage reduction of 75\u2013132 kW single-screw extruder gearboxes for PE pipe, PVC profile, and rubber extrusion applications running at 6,000\u20137,500 hours per year.<\/figcaption><\/figure>\n<\/section>\n
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Extruder Type Application Specifications<\/h2>\n
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TYPE 01<\/p>\n

SINGLE-SCREW
\nEXTRUDER<\/p>\n<\/div>\n

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Helical gear specification:<\/strong> M6\u2013M16, 18CrNiMo7-6 carburized (first stage) and 42CrMo4 QT (final stage above M12), DIN 6, two or three helical gear stages, total ratio 8:1\u201325:1, wide face width b\/d\u2081 \u2265 0.8 for bending fatigue safety. Single-screw extruders for plastics (PE, PP, PVC, PS, ABS) and rubber (EPDM, NBR, silicone) processing are the most common extruder type \u2014 millions of units worldwide from 20 mm laboratory extruders to 200 mm production extruders for large-diameter pipe. The gearbox for a single-screw extruder is straightforward in concept: a two or three-stage helical gear reduction with a large tapered roller or cylindrical roller thrust bearing on the output shaft to absorb the screw thrust. The critical parameter for helical gear sizing in single-screw applications is the screw-specific torque \u2014 the torque per unit screw diameter cubed, which scales with the polymer melt viscosity and die pressure. Rigid PVC at high output rates is the most demanding single-screw extruder application, with screw-specific torques approaching 11 Nm\/cm\u00b3 \u2014 approximately double the screw-specific torque of a low-viscosity PE film extruder. Korea Ever-Power sizes single-screw extruder gearbox helical gears to the maximum screw torque at the maximum die pressure, not just the rated motor torque \u2014 because the motor can be overloaded by a blocked die, and the gear must survive this event.<\/p>\n<\/div>\n<\/div>\n

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TYPE 02<\/p>\n

PARALLEL
\nCO-ROTATING
\nTWIN-SCREW<\/p>\n<\/div>\n

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Helical gear specification:<\/strong> M6\u2013M14, 18CrNiMo7-6 carburized, DIN 5\u20136 ground (all stages), torque split shaft helical gear set matched to \u00b10.5% split, centre distance between output shafts constrained by screw barrel bore spacing. The parallel co-rotating twin-screw extruder (ZSK-type, widely used for plastics compounding, masterbatch, and reactive extrusion) uses two intermeshing screws rotating in the same direction at the same speed \u2014 the screws are designed to be self-wiping, with the flights of one screw cleaning the channel of the other. This means the two screw shafts must rotate at identical speed with a fixed angular phase relationship, which the gearbox torque split shaft maintains. Any backlash in the torque split shaft gear train causes the two screw shafts to lose their angular synchronisation momentarily during torque reversal (which occurs during startups and during processing instability events) \u2014 potentially causing the screw flights to contact instead of wiping. Twin-screw extruder torque split gears are therefore specified to DIN 5\u20136 with backlash below 0.03 mm to minimise angular phase error during these transients.<\/p>\n<\/div>\n<\/div>\n

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TYPE 03<\/p>\n

CONICAL
\nCOUNTER-ROTATING
\nTWIN-SCREW<\/p>\n<\/div>\n

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Helical gear specification:<\/strong> M6\u2013M14, 18CrNiMo7-6 or 42CrMo4, DIN 6\u20137, converging output shaft centre lines (the two output shafts are not parallel \u2014 they converge toward the die end at the included cone angle of the screws), special gearbox housing geometry to accommodate the shaft angle. Conical counter-rotating twin-screw extruders (Battenfeld-Krauss-Maffei, Cincinnatti Milacron type) are used almost exclusively for PVC pipe, profiles, and window frame extrusion, where the high melt pressure and compressive action of counter-rotating screws generates the dense, homogeneous melt structure that rigid PVC requires. The gearbox for a conical twin-screw extruder must accommodate the converging shaft geometry while still providing a clean helical gear torque split \u2014 the converging shafts are typically housed in separate conical shaft housings that bolt to the main gearbox body, allowing the shaft angle to be set at assembly without changing the helical gear geometry. Korea Ever-Power supplies conical twin-screw gearbox helical gear replacement sets for Battenfeld, Cincinnati, Theysohn, and other conical twin-screw extruder brands \u2014 contact with the extruder model and screw diameter for gear set identification.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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\"industrial
Korea Ever-Power industrial alloy steel helical gears for large extruder drive gearbox application \u2014 42CrMo4 through-hardened QT, HB 310\u2013350, M14, face width 140 mm, helix angle 20\u00b0 per side. These final-stage reduction gears for 200 kW+ rubber and plastics extruder drives are hobbed to DIN 7 quality class with profile modification (tip relief 12 \u03bcm) applied to reduce dynamic mesh force at 85 RPM output shaft speed. Paired with ISO VG 220 mineral gear oil at rated operating temperature 68\u00b0C \u2014 oil cooling is provided by the gearbox oil-to-water heat exchanger mounted on the side of the housing. Tooth flank contact pattern verified at full rated torque under blue marking \u2014 contact covers 70% of tooth face width centrally, confirming correct lead crowning for the housing deflection at rated load. Korea Ever-Power supplies these gears as replacement sets for large rubber calender and compounding extruder gearboxes including Farrel, HF Mixing Group, and Maplan designs.<\/figcaption><\/figure>\n<\/section>\n
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Thermal Management and Lubrication for Extruder Gearboxes<\/h2>\n

Extruder gearbox thermal management is a critical design requirement that distinguishes extruder gearbox helical gear specification from industrial gearbox specification. An extruder running at 90% of rated screw torque for 7,000 hours per year generates a sustained heat input from gear mesh losses, bearing losses, and oil churning losses that must be removed from the gearbox oil by an external cooling system \u2014 because the gearbox surface area is insufficient to reject this heat by natural convection alone at sustained full-load conditions. Overheated gear oil in an extruder gearbox degrades the base oil oxidation resistance rapidly (halving for every 10\u00b0C above 80\u00b0C), producing varnish deposits on gear tooth surfaces and bearing raceways that progressively reduce the EHL film parameter and accelerate micro-pitting.<\/p>\n

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EXTRUDER GEARBOX HELICAL GEAR \u2014 LUBRICATION AND THERMAL REFERENCE<\/p>\n

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OIL SELECTION<\/p>\n