Paper and Pulp Mill Bearing Lubrication

Paper and Pulp Mill Bearing Lubrication

Modern paper machines represent some of the most demanding operating environments in all of heavy industry. A single paper machine can stretch over 100 metres in length, incorporate hundreds of rolling-element bearings, and run continuously at speeds exceeding 2,000 metres per minute. The bearings that support forming rolls, press rolls, dryer cylinders and calender stacks must endure a combination of extreme moisture, elevated temperatures, heavy dynamic loads and chemical exposure that would destroy standard industrial greases within hours. Selecting the correct lubricant for each machine section is not a matter of marginal efficiency gains — it is fundamental to achieving the uptime and bearing service life that keep a paper mill commercially viable.

At KOEED, as an authorised distributor of KLUBER Lubrication products, we work directly with maintenance teams across the pulp and paper sector. This guide draws on that field experience to explain the distinct lubrication requirements of paper machine wet-end and dry-end sections, outline the performance characteristics of three proven KLUBER greases, and cover the role of centralised lubrication systems in maintaining consistent bearing protection. Every recommendation is based on documented product specifications and real-world application data, not marketing generalities.

Lubrication Challenges Across the Paper Machine

Wet-End: Water, Load and Chemical Attack

The wet end — encompassing the headbox, forming section (fourdrinier or twin-wire) and press section — subjects bearings to near-constant water exposure. Stock at the headbox is approximately 99% water by weight. Forming rolls, suction couch rolls, wire return rolls and felt rolls all operate in an environment saturated with process water, pulp slurry and felt-conditioning chemicals. This water is not merely a lubricant contaminant; it is a hydrodynamic force capable of physically washing grease out of bearing housings. Water ingress also promotes hydrogen embrittlement and corrosion pitting on bearing raceways, particularly on the non-driven side where seals may be less robust.

Compounding the moisture challenge, wet-end bearings carry heavy loads. Press rolls in modern machines generate nip pressures exceeding 1,000 kN/m, transferring these forces directly into spherical roller bearing arrangements. The combination of high load and water contamination creates ideal conditions for fretting corrosion, false brinelling during standby periods and accelerated surface-initiated fatigue. A wet-end grease must therefore deliver three things simultaneously: exceptional water resistance (low washout, low emulsification), reliable extreme-pressure (EP) performance under boundary lubrication conditions, and robust corrosion inhibition.

Dry-End: Heat, Oxidation and Structural Stability

The dryer section presents the inverse problem. Here, the challenge is heat. Multi-cylinder dryer banks and Yankee cylinders operate with steam pressures that produce bearing housing temperatures in the 120 to 160 degree Celsius range, with short-term excursions above 180 degrees Celsius during sheet breaks or start-up transients. At these temperatures, the base oil in a conventional grease oxidises rapidly, forming varnish and sludge that can starve the bearing of fresh lubricant. The thickener structure can soften or collapse, causing the grease to slump away from the rolling elements. Oil separation (bleeding) accelerates, and any remaining grease may harden to a coke-like residue that blocks relubrication paths.

Dryer bearings are also subject to a condition known as "heat soak" — after a machine stop, the bearing housing temperature continues to rise as residual steam heat transfers from the cylinder journals into the stationary bearing. A grease that performs adequately at running temperature may fail entirely under these static soak conditions. Lubricant selection for dryer bearings therefore demands a thickener system with inherent thermal stability (such as polyurea), a base oil with high oxidation resistance (typically a blend of mineral and synthetic hydrocarbons), and sufficient structural integrity to remain in place during both dynamic and static high-temperature phases.

Recommended KLUBER Products for Paper Mill Applications

STABURAGS NBU 8 EP — Wet-End Workhorse

STABURAGS NBU 8 EP is a barium-complex soap grease based on mineral oil, formulated with extreme-pressure additives. It is one of the most widely referenced greases for paper machine wet-end bearings, and with good reason. Its defining characteristic is outstanding resistance to water washout and water emulsification — the dense barium-complex thickener structure sheds water rather than absorbing it. In the standard SKF-ROF water-resistance test at 120 degrees Celsius, STABURAGS NBU 8 EP demonstrates a continuous operating life exceeding 4,000 hours under direct water exposure, making it suitable for forming section breast rolls, wire return rolls, suction couch rolls and press section felt rolls where water deluge is continuous.

The product carries an NLGI Grade 2 consistency, with a worked penetration of 265 to 295 (0.1 mm) and a base oil viscosity of approximately 97 to 150 mm squared per second at 40 degrees Celsius. Its service temperature range spans minus 20 degrees Celsius to plus 140 degrees Celsius, with short-term capability to 180 degrees Celsius. The EP additive package provides protection under the shock and vibratory loading typical of wet-end roll bearings, while dedicated corrosion inhibitors guard against the rust that would otherwise develop on bearing surfaces during machine stops. The product is pumpable in centralised lubrication systems and is compatible with progressive divider block configurations commonly installed on paper machines. Shelf life in unopened original packaging is 36 months.

PETAMO GHY 133 N — High-Temperature Dryer Bearing Protection

PETAMO GHY 133 N is a polyurea-thickened grease built on a blend of mineral oil and synthetic hydrocarbon (PAO) base stocks. Polyurea is the thickener of choice for high-temperature rolling-element bearing applications because it does not rely on a metallic soap structure that can soften or melt at elevated temperatures. Instead, polyurea forms an organic gel network that remains mechanically stable up to and beyond 250 degrees Celsius — well above the grease's nominal upper service temperature of 160 degrees Celsius continuous, with excursions to 200 degrees Celsius.

The PAO component in the base oil blend contributes notably high oxidation stability compared to a purely mineral-oil formulation. This translates directly to longer grease life at temperature: in the FAG FE9 rolling bearing test at 160 degrees Celsius, PETAMO GHY 133 N achieves a minimum F50 life of 100 hours, which is indicative of a grease capable of extended relubrication intervals in the field. Base oil viscosity is approximately 165 mm squared per second at 40 degrees Celsius and 18 mm squared per second at 100 degrees Celsius, providing adequate film thickness in spherical roller bearings operating at typical dryer section speeds. The speed factor (n times dm) is rated at approximately 500,000 mm per minute, covering the rotational speeds encountered in multi-cylinder dryer and Yankee cylinder bearing arrangements. The grease also offers effective water resistance, and its compatibility with glycol-based coolants makes it suitable for ancillary equipment such as water-ring vacuum pump bearings and heat-recovery fan bearings. PETAMO GHY 133 N is available in 400 g cartridges, 1 kg cans, 25 kg pails and 180 kg drums, and has a 24-month shelf life in sealed original containers.

Kluberlub BE 41-1501 — Extreme Load and Slow-Speed Protection

Kluberlub BE 41-1501 addresses a different category of paper mill bearing: slow-speed, heavily loaded applications where conventional EP greases cannot maintain a sufficient lubricating film. This includes calender stack roll bearings, breaker stack bearings, press roll end bearings operating at low rotational speeds under extreme nip forces, and certain refiner and pulper bearings in the stock preparation area. The product is formulated with an ISO VG 1500 highly viscous mineral base oil — approximately ten times the viscosity of the base oil in STABURAGS NBU 8 EP — thickened with a special lithium soap and reinforced with both molybdenum disulphide (MoS2) and graphite solid lubricants.

The solid lubricant combination is key to the product's performance in the boundary and mixed-film lubrication regimes that prevail at low speeds and high loads. MoS2 provides a low-shear lamellar structure that plates onto bearing surfaces under pressure, reducing friction when the hydrodynamic oil film collapses. Graphite contributes additional sliding-layer protection and is effective even in the presence of moisture. The NLGI Grade 1 consistency (worked penetration 310 to 340 at 0.1 mm) ensures the grease flows adequately within the bearing even at low temperatures, with a flow pressure below 1,400 mbar at minus 10 degrees Celsius. The upper service temperature is 150 degrees Celsius, and the speed factor is approximately 100,000 mm per minute — reflecting the product's design intent for slow-speed, high-load duty. In the FAG FE8 tapered roller bearing test at 80 kilonewtons axial load and 80 degrees Celsius, Kluberlub BE 41-1501 limits cage wear to less than or equal to 100 mg and rolling element wear to less than or equal to 30 mg over 500 hours. The grease is approved under FAG grease category LG12 (low-speed, very high loads and shock) and carries Flender and David Brown approvals for gear applications. In paper mills, it is particularly suited to plain and rolling-element bearings in calender stacks and press sections where nip loads and vibration preclude the use of lighter-viscosity greases.

Recommended Practices for Paper Mill Grease Management

Centralised Lubrication Systems

Manual grease application — even with a well-trained crew — introduces variability. Some bearings receive too much grease (leading to churning, heat build-up and seal damage), others too little. In a paper machine with 150 or more grease points, manual lubrication also creates a scheduling conflict: bearings need grease while the machine runs, but safety protocols often restrict greasing access to scheduled shutdowns. Centralised automatic lubrication systems resolve both problems. Dual-line systems with progressive divider blocks — such as the SKF Maxilube configuration used successfully in paper mills across North Africa — deliver metered, consistent grease volumes to every bearing point at programmable intervals, without interrupting production. Documented results from these installations include reductions in grease consumption of 44 to 50 percent compared with manual lubrication, alongside measurable extension of mean bearing service life.

A dual-line system operates with two main supply lines pressurised alternately. When Line 1 is pressurised, each metering device dispenses its set volume; when Line 2 is pressurised, the devices reset ready for the next cycle. This architecture supports hundreds of lubrication points from a single pumping station and provides positive feedback via cycle-indicator pins or proximity sensors at each divider, allowing the control system to confirm that every point has received its dose. For paper machines, stainless-steel (AISI 316) divider blocks and fittings are strongly recommended to resist corrosion from the humid mill atmosphere and occasional wash-down events.

Grease Compatibility and Changeover Discipline

Mixing greases with incompatible thickener types is one of the most common causes of lubrication-related bearing failure in paper mills. Barium-complex greases (such as STABURAGS NBU 8 EP) should never be mixed with sodium-soap greases. Polyurea greases (such as PETAMO GHY 133 N) are generally incompatible with most metallic-soap greases, particularly lithium and calcium types. When converting a bearing to a new grease family, the old grease must be purged completely during a scheduled machine stop: the housing should be opened, cleaned and repacked, and supply lines should be flushed with the new product before reconnection. Consolidating the number of different greases used on a machine reduces both the risk of mixing errors and the complexity of procurement and storage.

Relubrication Quantity and Frequency

The appropriate relubrication interval and quantity for each bearing position depends on bearing bore diameter, rotational speed, operating temperature and environmental contamination severity. As a general guideline for paper machine spherical roller bearings, the relubrication quantity can be estimated using the formula G equals 0.005 times D times B, where G is the grease quantity in grams, D is the bearing outside diameter in millimetres and B is the bearing width in millimetres. Relubrication frequency should shorten as operating temperature increases — a useful rule of thumb is that grease life halves for every 15 degrees Celsius rise above 70 degrees Celsius. For dryer bearings operating at 150 degrees Celsius, this means relubrication may be needed three to four times more frequently than for a wet-end bearing running at 60 degrees Celsius. Centralised systems enable this differentiated scheduling without burdening maintenance personnel.

Key Takeaways

• Match the grease to the machine section: Water-resistant barium-complex greases for the wet end; thermally stable polyurea greases for the dryer section; heavy-duty solid-lubricant greases for slow-speed, high-load calender and press positions.
• Do not mix incompatible thickener types. Purging and flushing are mandatory when changing grease families.
• Centralised automatic lubrication systems eliminate manual-application variability, reduce grease consumption and measurably extend bearing life in paper machine service.
• Relubrication intervals must account for operating temperature. Grease life shortens rapidly above 70 degrees Celsius — dryer bearings require significantly more frequent replenishment than wet-end positions.

KOEED Support

Selecting the right lubricant for each position on a paper machine requires balancing water resistance, load capacity, temperature tolerance and system compatibility. At KOEED, we provide technical consultation to help maintenance teams identify the appropriate KLUBER product for their specific operating conditions. We can support lubricant consolidation reviews, compatibility assessments for centralised system changeovers, and on-site trials with documentation of bearing condition before and after conversion. For technical inquiries, product selection guidance or to arrange a lubrication audit, contact Moritta@KOEED.COM.