Lubrication Systems for Paper and Pulp Mills
A paper machine is a continuous process running at speeds of 400 to 1,800 metres per minute, 24 hours a day. It has hundreds of rotating rolls, each supported by bearings that must be lubricated reliably through extreme changes in environment: the wet end is cold and saturated with water, the dryer section runs at 150 degrees Celsius with steam, and the calender and reel operate at high nip pressures and variable speeds. No manual lubrication programme can cover all bearing positions at the correct intervals while the machine is running at production speed.
Centralized lubrication systems deliver grease automatically to each bearing position on a set schedule, regardless of what section of the machine the bearing is in. The lubrication system is one of the few systems on a paper machine that runs continuously in the background with no operator interaction required between servicing intervals.
Forming Section (Wire Section)
The forming section converts the headbox jet of dilute fibre suspension (typically 0.3% to 1% consistency) into a wet web on a moving wire or between two wires. The forming section rolls, suction rolls, table rolls, and wire drive rolls all have bearings that operate in continuous contact with process water and white water. Water washout of grease is the primary lubrication concern.
Wire Roll and Table Roll Bearings
Forming section roll bearings receive grease via a centralized grease system, delivered in small doses at short intervals (typically every 15 to 30 minutes). The short interval is critical: it maintains a continuous positive grease pressure at the bearing seal, which prevents process water from penetrating into the bearing housing. If the interval is too long, water enters the bearing between grease doses and the bearing fails from corrosion and loss of lubricant film.
Suction Roll Bearings
Suction rolls operate under high vacuum and carry significant loads from felt and wire tension. The bearings must be lubricated reliably in a very wet environment. High-vacuum suction rolls also create negative pressure at the bearing seal, which actively draws liquid into the housing if grease pressure is not maintained. Short lubrication intervals and water-resistant grease are essential.
Press Section
The press section removes water from the wet web by passing it through nip pressures of 80 to 200 kN/m between press rolls. Press rolls, felt rolls, and press frame rolls all have bearings carrying these high nip loads in a wet environment.
Press Roll Bearings
Press roll bearings are large spherical roller bearings or cylindrical roller bearings carrying full nip load. They operate in water and often in contact with the shower water used to keep press felts clean. Grease must resist water washout under these conditions, and the lubrication interval must be short enough to prevent any grease-free period at the bearing seal. A dual line lubrication system is typically used for press section rolls due to the number of points and the importance of reliable delivery to all positions simultaneously.
Felt Roll Bearings
Press felts are kept running by a series of felt guide rolls, felt tension rolls, and felt stretch rolls. These rolls have smaller bearings than press rolls but are more numerous and equally exposed to water. They are served by the same centralized system as the press rolls.
Dryer Section
The dryer section is the most thermally demanding section of the paper machine. Steam-heated dryer cylinders run at surface temperatures of 120 to 160 degrees Celsius. The dryer section enclosure is hot and humid. Bearings in this environment are subject to thermal breakdown of grease if the wrong specification is used, and to moisture condensation that accelerates corrosion if lubrication intervals are too long.
Dryer Cylinder Bearings
Each dryer cylinder is supported on two bearings (one fixed, one floating). A modern paper machine may have 40 to 80 dryer cylinders, giving 80 to 160 bearing positions in the dryer section alone. These are served by a centralized grease system using high-temperature grease, typically a lithium complex or aluminium complex NLGI Grade 2 grease rated for continuous service above 150 degrees Celsius. The pump station is located outside the dryer section enclosure, and high-pressure tubing is routed through the enclosure wall to each bearing position.
Dryer Section Gearboxes
The dryer cylinders are driven through a system of dryer gears (in older machines) or individual gearboxes (in newer designs). These gearboxes require forced oil lubrication via an oil circulating system that provides continuous filtration and temperature control. The heat load from the dryer section requires the OCS to include oil cooling, typically a water-cooled heat exchanger.
Calendar Section
The calendar stack uses heavy rolls to smooth and gloss the paper surface. Calendar roll bearings carry the full stack load (which may be 200 to 600 kN on a large machine) and operate under variable speed. These bearings use centralized grease, delivered at relatively longer intervals than wet end bearings because the calendar operates in a dry environment. The primary requirement is precise quantity control: too much grease in a calendar bearing housing can contaminate the paper if it reaches the roll surface.
Winder and Reel
The winder and reel convert the continuous paper web into rolls for shipping or converting. Reel spool bearings, rider roll bearings, and winder drum bearings all require lubrication. Winder positions change frequently as reels are completed and new reels started, so the lubrication system must handle moving lubrication points or provide sufficiently long intervals that the system cycles before a reel change interrupts normal lubrication.
Pulp Processing Equipment
Pulp mills (chemical or mechanical) have their own lubrication requirements separate from the paper machine. Digesters, refiners, pulp washers, and screening equipment all have bearings requiring regular lubrication. Refiner bearings are particularly demanding: high-consistency refiners operate under large axial and radial loads, in a wet, high-temperature environment. Progressive or dual line centralized systems serve refiner bearings with short intervals suited to the operating conditions.
System Architecture for Paper Machines
Most paper machines use a dual line lubrication system for all grease points, with the pump station located in the machine room basement or ground floor and distribution lines routed through the machine frame to each bearing. The dual line architecture is preferred because it can serve 200 to 500 points from a single pump station, handles the long line distances common in wide paper machines, and a single blocked dose feeder does not interrupt lubrication at any other point.
Separate oil circulating systems serve the main drive gearbox, dryer section gearboxes, and any other enclosed gear drives. These are independent systems with their own reservoirs, pumps, and filters, managed by the machine's control system alongside the centralized grease system.
SP Engineers in Paper and Pulp
SP Engineers has supplied lubrication systems for the paper industry covering complete paper machine installations, pulp mill equipment, and converting line machinery. Our systems include dual line pump stations, dose feeders, progressive distributor blocks, high-pressure tubing assemblies, and oil circulating systems, all manufactured at our Faridabad facility under ISO 9001:2015.
Frequently Asked Questions
Lubrication Systems for Paper Machines
Tell us your machine width, speed, and section (wet end, dryer, calendar) and we will specify the right system.
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