Drives for the pulp & paper industry: gearboxes, motors, brakes and couplings
Pulp & paper production runs on long continuous lines — paper machines (PM) 100–250 m long operate 24/7 with planned outages every 4–6 weeks — combining heavy low-speed drives for digesters and refiners with precision sectional control of the paper machine. The main sectional drive of a PM requires speed-holding accuracy better than 0.01 % between sections (otherwise the web tears), refiners with 1.5–7.5 MW motors run at peak load around the clock, and brakes on reels and slitter rewinders must stop rolls of up to 60 tonnes instantly without stretching the web.
Industry-typical tasks
- Main sectional drive of paper and board machines (PM/BM): forming, press, dryer and calender sections — 10–30 sections at 75–1,500 kW each with 0.01 % synchronization
- Drive for disc refiners and pulp refining mills — 1,500–7,500 kW, continuous S1 duty, heavy start under load
- Drives for continuous and batch digesters (Kamyr, Pandia) — low speeds, high torque, aggressive caustic environment
- Drives for corrugator lines — corrugating rolls, glue sections, reels and slitter rewinders — 75–355 kW per section
- Reels and slitter rewinders (winders, rewinders) — 30–250 kW with precision tension control and fast braking
- Cylinder dryer groups (Yankee) and flash dryers — continuous duty, +180 °C steam environment, high humidity
- Press section, drum screens, barking drums, chippers and chip conveyors — heavy starts, abrasive environment
- Multi-drive sectional control systems for the PM — common DC bus, 30+ VFDs per machine with coordinated torque and tension control
Gearboxes
Pulp & paper gearboxes fall into three classes. The first — main sectional drives of PMs and BMs: purpose-built multi-stage helical gearboxes with power split via torsion shafts, rated for 100,000+ hours of non-stop operation and a service factor of at least 2.0. The second — heavy-duty gearboxes for refiners and digesters with high reduction ratios. The third — industrial gear motors for chip conveyors, screens and roll machines. The hallmark of the industry is continuous S1 duty at 70–95 % humidity and ambient temperatures up to +60 °C in the dryer area, which calls for reinforced seals, synthetic oil and forced oil cooling.
Main drive for the forming and press section of the PM
Multi-stage helical gearboxes from the CGC ZSY/JSC series with a double-helical output pair transmit torque to the main rolls (couch roll, press roll). Double-helical gears cancel axial forces and run quietly at pitch-line speeds of 15–25 m/s — critical for continuous duty. They operate with electronic section synchronization via the HV inverter and precision encoders at 8,192 ppr.
- — Reduction ratio 8–40
- — Output torque 30–250 kN·m
- — Service factor ≥ 2.0 for S1 continuous duty
- — Forced circulating lubrication with an oil cooler
- — Angular positioning accuracy via an incremental encoder
Gearboxes for the dryer and calender section
The dryer section of a PM holds 30–80 steam cylinders 1.5–1.8 m in diameter, grouped into 4–8 sections. Each section has its own gearbox and motor with independent speed control — this compensates for web shrinkage as it dries. The environment is +180 °C steam, condensate and up to 95 % humidity. Heat-resistant Viton seals and high-VI synthetic VG 320 oil are required.
- — Heat-resistant seals (housing operating temperature up to +120 °C)
- — Synthetic polyglycol or PAO oil VG 220–320
- — IP56 with condensate protection
- — Ability for precise electronic synchronization between sections
Drives for disc refiners and refining mills
Two-stage helical or bevel-helical gearboxes transmit torque from a 1.5–7.5 MW HV motor to the refiner's main disc. A heavy start with the chamber full requires a service factor of at least 2.5 and frequently a Jiaohua YOX starting fluid coupling between the motor and the gearbox. The CGC HRC series is purpose-built for refiners and pulp refining mills.
- — Reduction ratio 4–12 (motor 1,000 rpm → disc 250–500 rpm)
- — Output torque up to 800 kN·m
- — Service factor ≥ 2.5 for heavy starts under load
- — Flange compatibility with a starting fluid coupling
- — Oil pump station with a fine filter
Drives for digesters and steaming vessels
Low-speed planetary or helical gearboxes with high reduction ratios drive rotating batch digesters and Kamyr continuous-cooking screws. Rotation speed is 0.5–4 rpm, continuous duty, with an aggressive cooking-liquor environment (NaOH, Na₂S, white liquor). Stainless or epoxy-coated housings and double seals with bearing-cavity protection are required.
- — Reduction ratio 200–800
- — Corrosion protection of the housing and shafts
- — Double seals with leakage drainage
- — Vibration and bearing temperature monitoring
- — Dual-drive capability on a single driven gear
Conveyor and auxiliary gear motors
K-series (bevel-helical) and F-series (parallel-shaft) for chip conveyors, finished-paper conveyors and feed screws. A heavy start with the chip bin full requires an SF of at least 1.8. Inclined chip conveyors mandate a backstop — Tianiu NJZ series — to prevent reverse running under load weight at stop.
- — K-series (bevel-helical) for heavy-duty chip conveyors
- — F-series (parallel-shaft) for screws and screens
- — Service factor ≥ 1.8
- — Backstop mounting option on inclined conveyors
- — Protection against dust and chip ingress (IP65)
High-power electric motors
Pulp & paper is one of the most electricity-intensive industries: refiners at a mid-size mill draw 30–60 MW, while a PM with its 10–30 sections adds another 10–25 MW. Main refiner motors are HV asynchronous machines at 6/10 kV, rated 1,500–7,500 kW. PM section motors are mostly low-voltage 400–690 V VFD-fed units rated 75–1,500 kW each, tied together in a multi-drive system on a common DC bus. Requirements: VFD compatibility (class H insulation), high starting torque for refiners, and precise torque/speed holding for PM sections.
HV motors for refiners and refining mills
Wolong YHTM/YKK asynchronous motors rated 1,500–7,500 kW at 6 or 10 kV. Continuous S1 duty; heavy start under load demands a starting torque of at least 1.8 of rated. Forced air-to-water cooling IC81W is used due to the high dissipation and compact layout. Frequently paired with a Jiaohua fluid coupling for soft starting.
- — Power rating 1,500–7,500 kW, voltage 6/10 kV
- — Starting torque ≥ 1.8 of rated
- — Forced IC81W cooling (air-to-water)
- — Insulated bearing on the non-coupling end
- — Pt100 RTDs in windings and bearings
PM section motors with VFD
Wolong YE3/YVF low-voltage asynchronous motors with independent forced ventilation, rated 75–1,500 kW. Operated via VFD in torque/speed control with ±0.01 % accuracy — critical for section synchronization as the web shrinks. Class H insulation and inverter-duty design (NEMA MG1 Part 31) are mandatory. An 8,192-ppr encoder is mounted on the free shaft end.
- — Class H insulation for inverter-duty operation
- — Independent forced ventilation (decoupled from motor speed)
- — Optical encoder, ≥ 8,192 ppr
- — Speed-holding accuracy ±0.01 %
- — IP55 minimum, protection from water mist of the forming section
Motors for the dryer section and calenders
The dryer-section environment is +60 °C steam at the machine frame and 70–95 % humidity. Dryer-section motors need reinforced sealing and anti-condensation winding heaters for downtime to prevent moisture build-up. The Wolong YBK3 (explosion-proof) series is used in zones with combustible dust or solvent vapors at specialty plants.
- — Anti-condensation winding heaters during downtime
- — IP56 with additional terminal box protection
- — Class H insulation with class F thermal margin
- — Vibration-resistant mounting (calender roll vibration)
Motors for auxiliary drives and pumps
Pulp stock pumps (medium- and high-consistency), forming-section vacuum pumps, recovery boiler ID fans, chemical mixers — these use standard Wolong YE3/YE4 asynchronous motors at IE3/IE4 efficiency. Continuous S1 duty, ratings 30–800 kW. Vacuum pumps require a reinforced bearing for the radial load from the pulley.
- — IE3 or IE4 efficiency class
- — Continuous S1 duty (24/7)
- — Reinforced bearings for belt drives (where applicable)
- — IP55 protection class against chemicals and splashes
Industrial brakes
In pulp & paper production, brake systems address four tasks. First — emergency stop of the PM on web break (a machine with a total mass of 800–2,500 tonnes is stopped within 5–10 seconds). Second — accurate stopping of reels and slitter rewinders (winders) for roll changes without stretching the web. Third — holding inclined chip conveyors and dryer sections at stop. Fourth — controlled braking of unwinders to maintain tension. On top of that, reels handle rolls up to 60 tonnes, and the kinetic energy at the moment of braking calls for brake torques up to 50 kN·m.
Brakes for reels and slitter rewinders
Huawu YPZ2/YWZ5 electrohydraulic disc brakes are mounted on the reel drum and operate in two modes: controlled braking (web tension control during winding) and emergency stop. On web break the brakes engage within 0.15–0.3 s, stopping the roll without surface slip. For 40–60 tonne rolls, certification and a calculated torque margin are mandatory.
- — Brake torque 5–50 kN·m with a 1.75 margin over calculated
- — Response time ≤ 0.3 s
- — Proportional control capability for controlled braking
- — IP55 protection class, heat resistance up to +80 °C
- — Pad wear monitoring (limit switch)
Emergency brakes for PMs and calenders
On web break or overload trip, the whole machine (or the affected section) must stop within 5–10 seconds to prevent wet stock from wrapping around the rolls. Jingu HSF / Huawu HW disc brakes with hydraulic clamping are mounted on the section's drive shaft. They are triggered from the machine PLC via the emergency-brake hydraulic station.
- — Hydraulic clamp with spring-applied engagement
- — Response time 0.15–0.3 s
- — Electronic position and pressure monitoring
- — Compatibility with the PM PLC system
- — UPS backup in case of power loss
Brakes for inclined chip conveyors
TKT/TKK shoe brakes with an electrohydraulic thruster hold the chip conveyor at stop and prevent involuntary reverse running under load weight. On long inclined conveyors they are used together with Tianiu NJZ backstops for redundant protection.
- — Electrohydraulic thruster Ed-50 to Ed-301
- — Combined operation with a backstop (redundant protection)
- — Manual brake release for service
- — Protection against chip dust (IP65)
Controlled brakes for unwinders
The unwinder at the head of the slitter line uses proportional brakes that maintain web tension at 50–500 N/m across a wide range of machine speeds. Disc brakes with proportional control via a servo valve or electromagnetic powder clutch-brakes are used. The Huawu YWZ series with proportional control suits the controlled-braking mode.
- — Proportional control via 4–20 mA or a servo valve
- — Characteristic linearity ±5 %
- — Thermal margin for continuous controlled-braking duty
- — Compatibility with the web tension control system
Couplings
Pulp & paper drives use four coupling types. Gear (drum) couplings on main drives of PMs and refiners — high torque with compensation for shaft misalignment after thermal expansion of the housings (relevant due to temperature differences between motor/gearbox/driven machine). Pin-and-bush flexible couplings on chip conveyors and stock pumps — pulsation damping. Hydrodynamic (fluid) couplings on refiners and chippers — soft start under load. Drum couplings with a brake wheel — for conveyors and drives with a brake. Couplings are sized to the rated torque with a 1.5–2.0 margin.
Gear couplings for main drives of PMs and refiners
Yongjing GIICL / Longxuan WGZ drum-type double-engagement gear couplings transmit torque up to 800 kN·m and compensate for radial, axial and angular shaft misalignment up to 1.5°. The crowned tooth shape allows operation under misalignment. Grease lubrication via a fitting with a 6-month service interval. The PM main drive requires G6.3 balancing at pitch-line speeds > 15 m/s.
- — Torque 50–800 kN·m
- — Angular misalignment compensation up to 1.5°
- — Crowned tooth profile for operation under misalignment
- — G6.3 balancing at pitch-line speeds > 15 m/s
- — Grease protection against wash-out by water
Fluid couplings for refiners and chippers
Jiaohua YOX/COX hydrodynamic couplings deliver smooth starting of refiners with the chamber full and of chippers with the bin full. Rated slip of 2–3 % protects the 1.5–7.5 MW motor from overload if the refiner disc jams. Versions with a fusible plug release oil on overheat and automatically trip the drive.
- — Rated slip 2–4 %
- — Fusible plug with a 145–160 °C set point
- — Oil fill 70–85 % of internal volume
- — Thermal margin for 4–6 starts per hour
- — Flange compatibility with HV motors
Pin-and-bush flexible couplings for stock pumps and conveyors
Jiaohua YOXp / Yongjing LX (LMC) series — pin couplings with elastic bushings for pulp stock pumps, chip conveyors and chemical mixers. They damp pulsations from high-consistency stock pumps and absorb small misalignments after thermal expansion. The service life of the elastic elements under pulp & paper conditions is at least 30,000 hours with proper alignment.
- — Torque 1–125 kN·m
- — Radial misalignment compensation 0.2–1.0 mm
- — Pulsation damping for pumps and screws
- — Elastic-element service life ≥ 30,000 h
- — Resistance to fiber and chip ingress (protective cover)
Drum coupling-with-brake-wheel for conveyor drives
The Longxuan WGZ series with an integral brake wheel combines a gear coupling and a brake drum in a single housing. Used on inclined chip and finished-product conveyors — saves space in tight layouts and simplifies service. The brake wheel is sized for TKT/TKK shoe brakes with an electrohydraulic thruster.
- — Combined gear coupling and brake wheel
- — Torque 5–125 kN·m
- — Brake wheel diameter sized for standard TKT/TKK brakes
- — G6.3 balancing for speeds > 1,000 rpm
Applications gallery
Our solutions for this industry
SDS portfolio brands that cover typical applications in this industry.
- CGCheavy-duty gearboxes for PM/BM main drives (ZSY, JSC), refiner gearboxes (HRC) and digesters — strong expertise in the pulp & paper industry
- WOLONGYHTM/YKK HV refiner motors 1,500–7,500 kW; LV YE3/YVF for PM sections 75–1,500 kW with VFD; general-purpose units for auxiliary drives
- BONENGindustrial K, F, HB gear motors for chip conveyors, finished-product conveyors, feed screws and auxiliary drives
- HUAWUbrake systems for reels, slitter rewinders and controlled braking of unwinders (YPZ2, YWZ5) — strong expertise in roll machines
- JINGUHSF disc brakes and emergency brakes for critical stops of PMs and calenders
- YONGJINGGIICL drum-type gear couplings for main drives of PMs and refiners — high torque with misalignment compensation after thermal expansion
- LONGXUANWGZ drum couplings with an integral brake wheel for conveyor drives, LX flexible pin couplings for stock pumps
- JIAOHUAYOX/COX hydrodynamic fluid couplings for refiners and chippers — soft starting under load
- TIANIUNJZ backstops for inclined chip conveyors and PM dryer sections
- INVTmulti-drive systems on a common DC bus for PM sectional control — 30+ VFDs per machine with coordinated torque control
- INOVANCEVFDs and servo drives for PM sections, corrugator lines and slitter rewinders — speed-holding accuracy ±0.01 %
- DEODFL/DFLA plate heat exchangers for the oil cooling system of PM gearboxes — high heat losses due to continuous S1 duty
Image credits: HEIMATWELTEN Zwönitz - Technisches Museum Papiermühle Niederzwönitz & Marco Kubitz (CC BY 4.0) · Wikimedia Commons (Public domain) · Marcel Antonisse / Anefo (CC0) · Work With Sounds (CC BY-SA 4.0) · Streetsoda (CC0)