Drives for the rubber & plastics industry: gearboxes, motors, brakes and couplings
Plastics and rubber processing is a distinct class of duties for drive equipment. An extruder screw transfers not only torque to the gearbox but also an axial force of up to 1,500 kN — equivalent to mounting a multi-ton press onto the output shaft. A calender rolls rubber compound between four rolls simultaneously, and any drive runout pushes the sheet thickness out of tolerance. An injection molding machine accelerates the injection screw from zero to full speed in 0.3 seconds and decelerates just as abruptly — a duty cycle that destroys ordinary couplings within months. That is why narrowly specialized product lines dominate this sector: extruder gearboxes with axial thrust bearings, IMM hydraulic power units with pressure-holding accuracy of ±1%, and fluid couplings for heavy-duty starting of pelletizers and Banbury mixers.
Industry-typical tasks
- Main drive for single-screw extruders producing PE/PP pipe, film, cable insulation and profiles — 22–630 kW, axial screw load up to 800 kN
- Main drive for twin-screw plastics compounding extruders and PVC pipe lines — 75–2,200 kW, torque split across two parallel shafts, axial load up to 1,500 kN per screw
- Hydraulic power units for thermoplastic injection molding machines, 30–450 kW — injection, pressure holding, mold clamping, hot-runner system drive
- Drives for 4-roll calenders at rubber goods plants, 75–300 kW — synchronous rotation of four rolls with runout tolerance ≤ 0.02 mm
- Drives for tire vulcanizers (curing presses) — hydraulic mold-half clamping, bladder drive, steam valves
- Main drive for Banbury mixers (internal mixers) for rubber compounds — 250–2,200 kW, heavy starting under load via fluid coupling
- Plastics pelletizers and polymer film recycling lines — geared motors with anti-jam protection, scrap and trim crushers
- Roll blenders and two-roll mills at rubber plants — low rotational speed, peak-torque damping via flexible couplings
Extruder and calender gearboxes
The key difference between an extruder gearbox and any industrial gearbox is the integrated axial thrust bearing that absorbs the reaction force from the screw (the melt pushes the screw back toward the motor). On a single-screw extruder this load is 200–800 kN; on a twin-screw machine it reaches up to 1,500 kN per shaft, exceeding the axial capacity of any general-purpose gearbox by 5–10 times. The market is therefore dominated by narrowly specialized lines: CGC ZLYJ extruder gearbox with axial thrust block — the classic choice for single-screw extruders, with the thrust block built around a stack of disc springs or tapered-roller thrust bearings; CGC SZ — for twin-screw machines, with a torque-splitting block and parallel output shafts. Rubber-plant calenders use a different category — heavy-duty gearboxes with double-helical (herringbone) gearing and low-speed planetary blocks, where synchronization of all four rolls is critical.
Single-screw extruder gearboxes (CGC ZLYJ series)
A specialized gearbox series developed specifically for single-screw plastics extruders. Construction: a two- or three-stage parallel-shaft gearbox plus an integrated axial thrust block on the output shaft on the screw side. The thrust block is built either around a disc-spring stack (for light duty up to 400 kN) or around tapered-roller thrust bearings (up to 800 kN). Forced circulation lubrication with an oil cooler is mandatory, since heat from bearings and gears in S1 duty cannot dissipate by convection alone. The CGC ZLYJ 112–450 range covers 22 to 630 kW and addresses 90% of pipe, film, cable-insulation and profile extrusion duties.
- — Integrated axial thrust bearing rated at 200–800 kN
- — Gear ratio 8–20 (matched to screw speed of 60–120 rpm)
- — Forced circulation lubrication with oil cooler
- — Service factor ≥ 1.5 for continuous S1 duty
- — Pt100 monitoring of oil and bearing temperatures
Twin-screw extruder gearboxes (CGC SZ series)
Twin-screw compounding extruders and PVC pipe lines require a different gearbox type — one that splits torque from the input shaft to two parallel output shafts rotating either co-rotating or counter-rotating. Center-to-center distance between the shafts is only 30–80 mm, so the gear train runs through intermediate idler shafts. Each output shaft has its own axial thrust block rated up to 1,500 kN. The CGC SZ series covers 75–2,200 kW and is the standard solution on BAUSANO, KraussMaffei and most Chinese extruder OEM lines. For counter-rotating PVC pipe lines, accurate angular timing of the screws relative to each other is critical — set during gearbox assembly and verified via phase marks.
- — Torque split across two parallel output shafts
- — Axial thrust block of 800–1,500 kN on each output shaft
- — Accurate angular timing of screws (inter-screw clearance ≤ 0.1 mm)
- — Forced lubrication with 10 µm filtration and oil cooler
- — Service factor ≥ 1.8, real-time vibration and temperature monitoring
Gearboxes for 4-roll calenders
Calenders at rubber goods plants use four massive rolls of 400–800 mm diameter that synchronously roll rubber compound into a sheet 0.3–6 mm thick with a thickness tolerance of ±0.02 mm. Each roll has its own motor-gearbox unit (the older group-drive scheme — one motor through a gear distribution box — has long been displaced by individual VFD drives). Heavy parallel-shaft gearboxes with a double-helical output stage are used — the CGC ZSY series. Double-helical gears cancel axial forces and run quieter than spur gears at peripheral speeds of 8–15 m/s. Between the gearbox and the roll runs a universal-joint spindle that compensates roll displacement caused by thermal expansion.
- — Gear ratio 16–63
- — Double-helical or helical output stage
- — 75–300 kW per roll
- — Service factor ≥ 2.0 (variable load on the roll)
- — Compatibility with universal-joint spindle (flange for the cardan joint)
Drives for Banbury mixers and roll blenders
A Banbury internal mixer is a two-rotor mixer with massive blades that knead rubber compound under ram pressure. Start-up takes place under full load (compound mass 50–620 kg), with peak torque 2.5 times nominal. The solution: motor + Jiaohua fluid coupling + heavy parallel-shaft gearbox. The fluid coupling provides soft starting and protects the motor from peak overloads when hard inclusions enter the compound. Two-roll mills (open mills) use classic CGC ZSY gearboxes or planetary blocks with a high reduction ratio and friction-based speed control of the rolls (one roll runs 10–20% slower than the other, generating shear stress in the rubber).
- — Service factor ≥ 2.5 for Banbury mixers, ≥ 1.8 for two-roll mills
- — 250–2,200 kW (Banbury), 75–250 kW (two-roll mills)
- — Compatibility with Jiaohua YOX/YOTX fluid couplings
- — Forced lubrication with heat exchanger
- — Reinforced bearings to absorb radial load from the rolls
Geared motors for profile and cooling conveyors
Downstream of the extruder or IMM, the finished profile travels through the calibration table, cooling bath and haul-off. Industrial Boneng K (helical-bevel) and F (parallel-shaft) geared motors handle these duties — 0.55–22 kW, IP55, heavy starting at 30–60 starts per hour under light load. On caterpillar haul-offs, accurate speed holding matters — encoder feedback combined with VFD control is used.
- — K-series or F-series geared motors 0.55–22 kW
- — Protection class IP55, IP65 for wet zones
- — Speed control via VFD with feedback
- — Service factor not less than 1.5 for frequent starts
- — Encoder option for haul-off units
Electric motors
The main drive of an extruder or calender is either a DC motor (on legacy lines) or an induction motor with a VFD (on modern installations). Twin-screw compounding extruders and Banbury mixers reach 2,200 kW at 6 kV, where high-voltage machines are unavoidable. A defining feature of extrusion and calendering is S1 duty with a wide speed range of 1:10–1:20, which requires motors with forced ventilation (rotor heat must be removed independently of the shaft-mounted fan speed).
Main drive for single-screw extruders
General-purpose Wolong YE3/YE4 induction motors, 22–630 kW, 380 V or 660 V, fed by a VFD. For speed control of 1:10 and wider, forced ventilation by a separate fan is required (the FV variant). Insulation class F with a thermal reserve to class B ensures longevity under 24/7 duty.
- — 22–630 kW, 380/660 V
- — VFD-rated (NEMA MG1 Part 31, insulation F+)
- — Forced ventilation IC416 (separate fan)
- — Encoder with resolution of at least 1024 ppr
- — Protection class IP55
Main drive for twin-screw extruders and Banbury mixers
High-voltage Wolong WD3000 / YHTM induction motors, 500–2,500 kW, 6 or 10 kV. Twin-screw compounding lines with 5–20 t/h throughput typically use 800–1,600 kW machines. Large-capacity Banbury mixers (270–620 kg) call for 1,200–2,200 kW. IC81W forced cooling (water-air) is mandatory, since duty is continuous and rotor heat must be removed efficiently.
- — 500–2,500 kW, 6/10 kV
- — IC81W forced cooling (water-air heat exchanger)
- — MV-VFD compatibility (insulation class F+, dV/dt-rated)
- — Insulated NDE bearing (protection against shaft currents)
- — Pt100 monitoring of windings and bearings
Motors for IMM hydraulic power units
A thermoplastic injection molding machine is essentially a hydraulic press with an injection unit. The main pump drive motor on the hydraulic power unit runs at variable load: high pressure during injection and pressure holding, low load during mold cooling. Wolong YE3 induction motors of 30–450 kW are used, with the option of VFD operation for energy savings (the servo-pump variant cuts energy consumption by 30–50% compared with a fixed-displacement pump). A hydraulic servo drive combines a motor with a built-in encoder and an axial-piston pump that responds to a control signal.
- — 30–450 kW, 380 V
- — VFD-rated for servo-pump operation
- — Built-in encoder (for servo-pump HPUs)
- — Protection class IP55, insulation class F
- — Thermal reserve for S6 duty (60% cyclic duration factor)
Motors for calenders and roll blenders
Calenders with individual drive per roll use 75–300 kW induction motors fed by VFDs. The defining requirement is high speed-holding accuracy (±0.1%) and tight synchronization between rolls. Wolong motors with 4096-ppr encoders combined with vector-control VFDs are used. Banbury mixer motors of 1,200–2,200 kW run at 6 kV through a fluid coupling, so VFD operation is generally not required — the fluid coupling handles starting, and speed control is not needed.
- — 75–300 kW for calenders (via vector-control VFD)
- — 1,200–2,200 kW for Banbury (6 kV, DOL start through fluid coupling)
- — Encoder with resolution of at least 4096 ppr (calenders)
- — Speed-holding accuracy ±0.1% (calenders)
- — Thermal reserve for S4 duty under frequent starts
Hydraulics and pressure control systems
In the rubber & plastics industry, the role of traditional industrial brakes is smaller than in metallurgy or mining. What is critical here is a different system — hydraulics. A thermoplastic IMM is a hydraulic press with injection-pressure holding accuracy of ±1%; a tire vulcanizer is a hydraulic clamping mechanism rated at 2,500–6,000 kN; a tire curing press uses steam at 15–25 bar inside the bladder. Selection of hydraulic components — pumps, valves, power units and heat exchangers — defines the throughput of the entire line and the dimensional stability of the finished product. This is the territory where Donly, Huade and Hengli cover 80% of the industry's needs.
Hydraulic power units for thermoplastic IMMs
A complete Donly hydraulic power unit for an IMM comprises a 200–2,000 L oil tank, an axial-piston pump (or a servo-pump with a Wolong motor), a stack of Huade proportional valves for injection and pressure holding, a DEO heat exchanger for heat rejection, and 10 µm filtration. Injection-pressure holding accuracy of ±1% is achieved by a closed-loop controller with a pressure transducer and a Huade 4WRZ-series proportional valve. A separate subsystem drives the hot-runner manifold, maintaining melt temperature in the runners within ±2 °C.
- — 200–2,000 L oil tank with 10 µm filtration
- — Axial-piston pump or servo-pump
- — Huade 4WRZ/4WRPH proportional valves
- — Water-cooled DEO heat exchanger (30–80 kW heat rejection)
- — Injection-pressure holding accuracy of ±1%
Hydraulics for tire vulcanizers
A tire curing press is a press with hydraulic clamping of the mold halves (2,500–6,000 kN), a pneumo-hydraulic bladder drive and a steam supply at 15–25 bar inside the bladder to heat the green tire. Huade hydraulic valves and Hengli pumps provide smooth clamping and force holding during curing (15–25 minutes per cycle). Multi-press vulcanizer lines (8–24 presses) share a common Donly hydraulic power unit with a pressure manifold and volume compensators.
- — Clamping force of 2,500–6,000 kN
- — Huade DBE/DBET-series valves for pressure control
- — Hengli variable-displacement axial-piston pump
- — Clamping-force holding accuracy of ±2%
- — Compatibility with 15–25 bar steam supply
Cooling systems for extruders and molds
Melt leaving the extruder is at 180–280 °C, and for calibration of pipe or film it must be cooled rapidly to 60–80 °C. This is the duty of large DEO DFL/DFLA plate heat exchangers with heat-rejection capacity of 50–500 kW. On IMMs, the mold cooling system provides uniform heat removal through channels in the mold halves — mold-temperature holding accuracy of ±1 °C directly affects the dimensional stability of the molded part. Mold temperature controllers with DEO plate heat exchangers and circulation pumps are used.
- — Heat-rejection capacity of 50–500 kW
- — Plate heat exchangers in AISI 304/316 stainless steel
- — Mold-temperature holding accuracy of ±1 °C
- — Circulation pumps for water or ethylene glycol
- — Dual-circuit system: mold cooling and oil cooling
Hydraulic components for IMMs and presses
INI Hydraulic supplies hydraulic components for IMMs and presses: axial-piston pumps with pressure and flow control, injection and clamping cylinders, and directional valves. Large compounding and polymer-scrap recycling lines use complete Donly hydraulic power units controlled by Inovance PLCs. The hot-runner drive is a separate compact hydraulic block with proportional pressure control.
- — Axial-piston pumps of 30–500 cm³/rev
- — Hydraulic cylinders with shock-load protection
- — Inovance PLC control with pressure feedback
- — Compatibility with Huade proportional valves
- — Dual filtration 10 µm + 25 µm for extended service life
Couplings
Three types of couplings are used in rubber and plastics lines. Gear couplings — on the main drives of extruders, between motor and gearbox, transmitting 50–500 kN·m and accommodating shaft misalignment after thermal warm-up. Fluid couplings — for heavy starting of Banbury mixers and pelletizers under load, providing soft start and overload protection for the motor. Flexible pin-type couplings — on calenders and roll blenders for vibration damping and small misalignment between gearbox and roll. Universal-joint spindles — between calender gearbox and roll, compensating axial roll displacement under thermal expansion.
Gear couplings for the main extruder drive
Between the Wolong motor and the CGC ZLYJ or CGC SZ gearbox, a Yongjing GIICL drum-type gear coupling (or equivalent) is fitted. It transmits 50–500 kN·m and accommodates radial, axial and angular shaft misalignment. The crowned tooth profile allows angular misalignment of up to 1°. Grease lubrication via a grease nipple, with a 6-month service interval. Large compounding lines with 1,500–2,500 kW motors use upsized couplings balanced to grade G6.3.
- — Torque rating 50–500 kN·m
- — Angular misalignment up to 1°
- — Compatibility with the extruder gearbox flange
- — G6.3 balancing at peripheral speeds > 15 m/s
- — Grease service interval of 6 months
Fluid couplings for Banbury mixers and pelletizers
The Jiaohua YOX/YOTX series provides oil-filled fluid couplings for soft starting of heavy machines under load. On 1,200–2,200 kW Banbury mixers, starting under a full charge (550–620 kg of rubber compound) without a fluid coupling would draw 6–8 times nominal current — unacceptable for the plant grid. The fluid coupling smoothly accelerates the rotor in 5–15 seconds and limits inrush to 1.5–2 times nominal. Polymer-scrap pelletizers use the same scheme — a YOX fluid coupling between motor and pelletizer gearbox protects the drivetrain from impacts when metal inclusions enter the feed.
- — Nominal slip 2–4%
- — Fusible plug 145–160 °C
- — Oil fill of 70–85% volume
- — Thermal reserve for 4–6 starts per hour
- — Compatibility with the 6 kV Wolong motor flange
Flexible pin-type couplings for calenders and two-roll mills
Between the CGC ZSY gearbox and the calender roll, a Longxuan LX or Yongjing LMC flexible pin-type coupling is installed. The elastomer elements damp torque pulsations during rolling of inhomogeneous rubber compound and absorb small misalignment. On two-roll mills, flexible couplings absorb peak loads when a hard inclusion enters the nip — saving the gearbox from impact tooth failure. Service life of the elastomer elements under calender vibration is no less than 30,000 hours.
- — Torque rating 5–125 kN·m
- — Radial misalignment 0.2–1.0 mm
- — NBR / polyurethane elastomer elements
- — Service life of at least 30,000 hours
- — Resistance to oils and rubber dust
Universal-joint spindles for calenders
Between the calender gearbox and the roll, a Yongjing SWP/SWC universal-joint spindle is installed. Its job is to compensate axial roll displacement under thermal expansion (a 600 mm-diameter roll heated from 20 to 80 °C elongates by 0.5 mm) and angular misalignment when the roll gap is adjusted. The universal-joint design accepts misalignment of up to 5–8° per joint. Forged-steel spiders run on rolling bearings; balancing is performed prior to installation per GOST 22061-76.
- — Torque rating 50–250 kN·m
- — Permissible joint misalignment up to 8°
- — Axial-displacement compensation 5–20 mm
- — Forged-steel spiders with rolling bearings
- — Balancing per GOST 22061-76 prior to installation
Applications gallery
Our solutions for this industry
SDS portfolio brands that cover typical applications in this industry.
- CGCspecialized extruder gearboxes — ZLYJ series for single-screw machines (22–630 kW, axial load up to 800 kN), SZ series for twin-screw machines (75–2,200 kW, up to 1,500 kN per shaft); heavy ZSY series for calenders and two-roll mills
- WOLONGhigh-voltage WD3000/YHTM motors for large extruders and Banbury mixers, 500–2,500 kW; general-purpose YE3/YE4 motors for IMM hydraulic power units and single-screw lines
- BONENGK- and F-series geared motors, 0.55–22 kW, for profile conveyors, haul-offs and auxiliary drives on calibration and cooling lines
- DONLYhydraulic power units for IMMs, 30–450 kW, with pressure-holding accuracy of ±1%; common HPUs for tire vulcanizer and compounding lines
- HUADE4WRZ/4WRPH proportional hydraulic valves for IMMs, DBE/DBET valves for tire vulcanizer hydraulics
- INIhydraulic components for IMMs and presses — axial-piston pumps, injection and clamping cylinders, directional valves
- HENGLIvariable-displacement axial-piston pumps for IMM hydraulic power units and tire vulcanizer lines
- YONGJINGGIICL drum-type gear couplings for main extruder drives, SWP/SWC universal-joint spindles for calenders
- LONGXUANLX flexible pin-type couplings for vibration damping on calenders and two-roll mills, WGZ gear couplings
- JIAOHUAYOX/YOTX fluid couplings for heavy-duty starting of Banbury mixers and pelletizers under load
- DEODFL/DFLA plate heat exchangers for extruder cooling systems (50–500 kW), IMM mold temperature control, and HPU oil cooling
- INOVANCEvector-control VFDs for calenders (speed-holding accuracy ±0.1%), PLCs for control of IMM hydraulic power units and compounding lines
Image credits: Snach812 (Public domain) · Bricetofly (CC0) · Naval Air Experimental Station; United States. Navy (Public domain) · Naval Air Experimental Station; United States. Navy (Public domain) · RICHI Machinery (CC BY-SA 4.0)