In-depth technical articles on paper machine roll manufacturing, surface coatings, reconditioning and maintenance — from our engineers to yours.
A modern paper machine is a highly engineered system in which rolls play a central role in every process stage — from initial sheet formation to the final wound reel. Understanding the types, functions and demands placed on each roll is essential for maintenance planners, process engineers and procurement specialists responsible for roll supply and reconditioning.
The forming section is where the paper web is created from a dilute fibre suspension. Breast rolls support the forming fabric at the headbox discharge point and are exposed to aggressive chemistry and abrasive fillers. Forming rolls and wire guide rolls maintain fabric tension and alignment. Couch rolls — positioned at the end of the wire section — perform the first mechanical dewatering step, removing water by vacuum and pressure. All forming section rolls must resist corrosion, abrasion and the dynamic loads of high-speed operation.
The press section mechanically removes water from the web through a series of nip points. Pick-up suction rolls transfer the wet web from the wire to the press felt. Center press rolls and felt guide rolls form the main dewatering nips, capable of generating linear loads exceeding 500 kN/m on modern machines. Roll covers — rubber, polyurethane or hard coatings — are selected based on the required nip profile, felt life and sheet quality targets.
The dryer section is the largest section of the paper machine and the most energy-intensive. Dryer cylinders — heated internally by steam — evaporate the remaining water from the web through direct contact. They are large-diameter, thick-walled pressure vessels subject to thermal fatigue and condensate corrosion. VacRoll cylinders and dryer felt guide rolls support web transport between drying groups. Coatings on dryer cylinders must withstand high temperatures, steam condensate and the mechanical abrasion of the drying fabric.
The size press applies a starch or coating solution to both sides of the sheet. Rolls in this section face severe chemical attack from sizing agents and must maintain a precise surface finish — typically achieved by chrome or tungsten carbide coatings with mirror-quality grinding. Calender rolls compress and smooth the finished sheet to meet paper thickness, gloss and density specifications. Calender rolls may use thermal oil heating and carry rubber or polyurethane covers for soft-nip calendering.
The reel section winds the finished paper web onto a core at full machine speed. Reel drums and spool rolls must be dynamically balanced to high precision to avoid vibration at winding speeds that can exceed 2,800 m/min on modern machines. Any imbalance translates directly into web breaks and reel quality defects.
EKOSYS supplies and reconditions rolls for every section of the paper machine — up to 15,000 mm length, 5,500 mm diameter and 100 tonnes weight. Dynamic balancing is performed to ISO 1940 standards at speeds up to 2,800 m/min.
The manufacture of a precision paper machine roll is a multi-stage process that demands tight dimensional tolerances, metallurgical control and rigorous quality inspection. A single roll may take several weeks to produce — and any deviation from specification can have significant consequences for machine performance and paper quality.
Roll shells are produced from a range of materials depending on section requirements. Grey cast iron is the traditional material for dryer cylinders, offering good thermal conductivity and machinability. Ductile (nodular) cast iron provides higher tensile strength for press section rolls. Carbon and low-alloy steel is used for forming and press rolls requiring high nip loads. Duplex stainless steel is specified for suction roll shells, where resistance to chloride corrosion and high fatigue strength are essential.
Roll production begins with casting or forging of the shell blank. Casting is preferred for large dryer cylinders; forging is used for solid rolls and shafts requiring higher material integrity. After heat treatment to relieve residual stresses, the blank is rough-machined to approximate dimensions.
Finish machining — turning, grinding and boring — brings the roll to final dimensional specification. Journal diameter tolerances are typically held to ±0.01 mm. Shell surface finish is critical: the roughness (Ra) must match the coating or cover to be applied. Grinding is performed on CNC roll grinding machines capable of processing rolls up to 15 metres in length.
Every roll must be dynamically balanced before delivery. Residual imbalance causes vibration at operating speed, leading to nip barring, web breaks and bearing damage. Balancing is performed in accordance with ISO 1940-1. Paper machine rolls are typically balanced to Grade G2.5 or G6.3 depending on operating speed. EKOSYS balances rolls at peripheral speeds up to 2,800 m/min.
Quality inspection includes:
All measurement data is recorded and supplied with the roll as part of the delivery documentation.
Rubber roll covers have been used in the paper industry for over a century, and despite competition from polyurethane and hard coatings, they remain the dominant cover material in the press section. The correct selection of compound, hardness and geometry is critical to achieving the target nip profile and dewatering performance.
Several rubber compounds are used in paper machine press rolls, each with specific properties:
Rubber hardness — measured in Shore A or Shore D — has a direct effect on nip width and pressure distribution. Softer covers (45–65 Shore A) create wider, lower-pressure nips suitable for tissue and specialty grades. Harder covers (75–90 Shore A) deliver narrow, high-pressure nips for efficient dewatering at high speeds.
Roll crown — the slight convex profile across the roll length — compensates for deflection under nip load, ensuring uniform pressure distribution across the full web width. Crown is calculated based on roll span, applied load and shell stiffness.
Most press roll covers consist of multiple rubber layers bonded to the roll shell. A bonding layer ensures adhesion to the steel or cast iron shell. Base layers provide structural support and dampen vibration. The top layer defines the surface properties — finish, hardness and groove or blind-hole pattern.
Grooved and blind-drilled covers improve water removal by providing channels for water evacuation from the nip. Groove geometry — width, depth and pitch — is optimised for each machine position and paper grade.
Rubber covers are subject to mechanical wear, heat fatigue and chemical attack. Regular regrinding restores the surface finish and removes surface cracks or barring marks, extending cover life. Most rubber covers can be reground several times before replacement is required.
Polyurethane (PU) has emerged as a high-performance alternative to rubber in many paper machine roll applications. Its combination of excellent abrasion resistance, chemical stability and dimensional precision makes it the preferred cover for demanding positions where rubber would wear prematurely or deform under load.
Polyurethane covers are produced by casting or injection moulding of two-component PU systems. Polyether-based PU offers superior hydrolysis resistance — essential in wet press section environments. Polyester-based PU provides higher mechanical strength and is used in calender and guide roll applications.
Press section: PU is used on center press rolls, pick-up rolls and felt guide rolls where abrasion from fillers or mineral pigments would prematurely wear rubber covers. Grooved and blind-drilled PU covers provide efficient water removal with excellent durability.
Calender section: Soft-nip calender rolls use PU covers in the 60–85 Shore A range to produce smooth, high-gloss paper surfaces without excessive calendar loading. PU's dimensional stability ensures consistent nip width over long production runs.
Forming section guide rolls: In high-speed machines where forming fabric abrasion is an issue, PU outperforms rubber significantly in terms of cover life and consistency.
The primary limitation of polyurethane is temperature sensitivity. Most PU grades should not exceed 80–90°C in continuous service. For dryer section and size press applications requiring higher temperatures, ceramic or chrome coatings are preferred.
Tungsten carbide (WC) coatings represent the highest tier of wear protection available for paper machine rolls. Applied by High Velocity Oxy-Fuel (HVOF) thermal spray, WC coatings deliver hardness values exceeding 1,200 HV — several times harder than hard chrome — with outstanding resistance to both abrasive and erosive wear.
In the HVOF process, a fuel gas (typically propane, propylene or kerosene) is combusted with oxygen at high pressure. The resulting high-velocity gas stream accelerates powder particles to supersonic speeds before impact on the substrate. The kinetic energy of impact rather than high temperature drives particle bonding, resulting in:
Several WC-based coating compositions are used in the paper industry:
Dryer cylinders: WC coatings protect dryer cylinder shells from condensate corrosion and abrasion by the drying fabric. Coating thickness is typically 150–300 µm, ground to a defined roughness (Ra 0.2–0.6 µm) for optimal fabric contact.
Size press rolls: The abrasive nature of coated paper applications makes WC the preferred coating for size press rolls, where starch, pigments and mineral fillers cause rapid wear of softer surfaces.
Calender rolls: On hard-nip calenders, WC-coated rolls maintain dimensional stability and surface quality over long campaign lengths, reducing the frequency of roll changes and regrinding.
After HVOF spraying, WC coatings are precision-ground using diamond or CBN grinding wheels. Final surface finish (Ra 0.1–0.4 µm) is achieved by superfinishing. Coating thickness after grinding is typically 100–200 µm.
Hard chrome electroplating has been the standard surface treatment for size press and calender rolls in the paper industry for decades. Its ability to produce a precise, mirror-quality surface with high hardness and low friction coefficient continues to make it relevant despite growing environmental and regulatory pressures.
Hard chrome is deposited from a chromic acid (CrO₃) electrolyte bath at controlled current density and temperature. The process deposits pure chromium metal onto the roll surface through electrochemical reduction. Unlike decorative chrome, hard chrome plating uses high current densities to produce thick, dense deposits with maximum hardness.
Typical hard chrome deposits reach HV 850–1,000 (Rockwell 68–72 HRC) — significantly harder than stainless steel or case-hardened tool steels. Thickness is typically 50–300 µm depending on the application.
Size press rolls: Chrome provides the smooth, chemically resistant surface required for starch and coating application. Mirror-polished chrome minimises drag marks and ensures uniform coating weight.
Calender rolls: Hard-nip calender rolls rely on chrome's hardness and smoothness to impart gloss and smoothness to the paper surface without surface marking.
Hexavalent chromium (Cr⁶⁺) — the electrolyte used in hard chrome plating — is classified as a carcinogen and is subject to strict regulation under REACH (Europe) and similar frameworks globally. Environmental controls add significant cost to the process.
For new installations and where regulations permit no exceptions, HVOF tungsten carbide and high-velocity chrome carbide coatings are increasingly specified as alternatives, offering comparable or superior hardness without Cr⁶⁺ exposure.
The forming section of a paper machine is one of the most corrosively aggressive environments in industrial processing. Dilute fibre suspensions at low pH, abrasive mineral fillers, high-velocity fabric contact and continuous moisture exposure create conditions that rapidly degrade unprotected roll surfaces. Ceramic thermal spray coatings provide a robust and cost-effective solution for forming section roll protection.
Several ceramic materials are used as thermal spray coatings for paper machine rolls:
Plasma spray melts ceramic powder in a high-temperature plasma arc and accelerates molten particles toward the substrate. It produces moderate-density coatings (90–95%) suitable for most forming section applications.
HVOF ceramic spray achieves higher particle velocities, producing denser coatings (>97%) with lower porosity and higher bond strength. Preferred for the most demanding corrosive and abrasive conditions.
Thermal-sprayed ceramic coatings are inherently porous at the microscopic level. For forming section rolls exposed to corrosive chemistry, the coating pores must be sealed with an appropriate sealant — typically an epoxy, silicone or fluoropolymer resin applied by vacuum impregnation. Sealing prevents chemical penetration to the substrate and significantly extends coating service life.
Forming section rolls in acid-pH systems (sulfite, mechanical pulp) require maximum corrosion resistance — Cr₂O₃ with sealant is the preferred system. In neutral or mildly alkaline systems, Al₂O₃ or Al₂O₃-TiO₂ provide excellent performance at lower cost.
Nano-ceramic polymer composite coatings represent the most recent advance in paper machine roll surface technology. By combining nano-scale ceramic particles within a polymer matrix, these coatings deliver a unique combination of properties unavailable from any single coating material — hardness, flexibility, non-stick performance and thermal resistance within a single, thin coating system.
Nano-ceramic polymer coatings consist of ceramic nanoparticles (typically silicon carbide, alumina or zirconia in the 20–100 nm size range) uniformly dispersed in a polymer binder (fluoropolymer, silicone or epoxy-phenolic base). The nano-scale dispersion enables the ceramic particles to reinforce the polymer matrix at the molecular level, dramatically improving hardness and wear resistance without sacrificing the flexibility of the polymer binder.
The primary application of nano-ceramic polymer coatings is on dryer cylinders — particularly in tissue machines and specialty paper machines where sheet release and non-stick performance are critical. The coating replaces heavy chrome plating in many applications, eliminating hexavalent chromium from the process.
VacRoll cylinders benefit from nano-ceramic coatings that combine non-stick release with protection against the vacuum-induced condensate corrosion that is the primary cause of VacRoll shell degradation.
Nano-ceramic polymer coatings are applied by spray or roller coating, followed by oven curing at 180–220°C. The curing process crosslinks the polymer matrix and ensures full bonding of ceramic particles. Application can often be performed on-site by trained applicators, reducing downtime compared to workshop-based thermal spray processes.
Suction rolls are among the most technically complex and commercially critical components in the paper machine press section. A suction roll failure — whether shell fracture, bearing seizure or excessive leakage — can result in extended, costly downtime. Understanding suction roll design, shell materials and condition monitoring is essential for maintenance teams responsible for press section reliability.
The suction roll shell must withstand the combined demands of:
Duplex stainless steel (e.g., SAF 2304, 2205 or 2507) is the standard shell material for modern suction rolls. Its duplex microstructure (approximately equal austenite and ferrite phases) delivers the combination of high tensile strength (>620 MPa) and outstanding resistance to chloride stress corrosion cracking (SCC) that process water environments demand. Carbon steel shells — once common — are no longer specified for new builds due to their susceptibility to SCC.
The drilled holes in the suction roll shell allow vacuum to act on the drying felt and paper web. Hole geometry directly affects:
Holes are finish-deburred to prevent felt damage and stress concentration at the hole edge.
Suction roll condition should be monitored continuously to detect developing defects before catastrophic failure. Key monitoring methods include:
EKOSYS performs suction roll reconditioning including shell replacement from high-quality Duplex stainless steel, comprehensive inspection and integration of smart condition monitoring systems.
A structured roll reconditioning programme is one of the most cost-effective investments a paper mill can make. Rather than replacing worn rolls with new ones — at high capital cost and long lead times — systematic reconditioning restores rolls to OEM specification, often at 30–60% of new roll cost and with significantly shorter turnaround times.
A full reconditioning cycle typically includes the following stages:
Dynamic balancing is a critical final step before roll return to service. An unbalanced roll generates centrifugal forces at rotation frequency that excite machine vibration, causing:
Dynamic balancing is performed on precision balancing machines capable of measuring imbalance at two correction planes simultaneously. Correction is made by adding or removing material at designated correction planes — typically the roll ends — until residual imbalance is within the specified ISO 1940 tolerance.
EKOSYS performs dynamic balancing at peripheral speeds up to 2,800 m/min, covering the full range of modern high-speed paper machines. All balance test data is provided in the roll delivery documentation for traceability and future reference.
A roll reconditioned to full OEM specification performs identically to a new roll. With a typical reconditioning cost of 35–55% of new roll price and turnaround times of 4–8 weeks (versus 16–24 weeks for new), the economic case for reconditioning is compelling — particularly for large, expensive rolls such as dryer cylinders, suction rolls and calender rolls.
The paper machine is one of the most complex continuous manufacturing systems in existence. Over 200 years of development have produced a wide range of machine types, each optimised for a specific paper grade family, production speed and quality requirement. Understanding machine type is essential for roll and clothing selection, maintenance planning and process optimisation.
The Fourdrinier is the oldest and most widely used paper machine configuration, named after the Fourdrinier brothers who commercialised it in the early 19th century. A dilute fibre suspension (stock) is delivered from the headbox onto a continuous horizontal forming fabric (the wire), where water drains by gravity and vacuum through the fabric. The partially dewatered web then passes through the press section and dryer section.
Key characteristics: single forming fabric, bottom-wire drainage only, relatively slow drainage rate. Typical production speeds: 400–1,500 m/min for printing and writing papers. Fourdriniers remain the dominant machine type for uncoated woodfree, offset and specialty grades.
Twin-wire or gap former technology was developed to overcome the drainage limitations of the Fourdrinier at high speeds. The stock jet is delivered into a gap between two forming fabrics — an inner and outer wire — enabling simultaneous two-sided drainage. This produces more symmetric paper formation and allows significantly higher machine speeds.
Gap formers inject the jet directly into the gap between two converging fabrics. Hybrid formers use a short Fourdrinier section followed by a twin-wire forming zone. Modern gap formers run at 1,200–2,000 m/min for newsprint and woodfree grades. Two-sided drainage produces more uniform paper than single-wire forming, with better formation and filler distribution.
Tissue paper machines are specialised for the production of lightweight grades (15–35 gsm) at very high speeds. Several configurations exist:
All tissue machines feature a large-diameter Yankee cylinder (3.0–5.5 m diameter) — a steam-heated cast iron or fabricated steel pressure vessel — and an impingement hood for final drying and creping.
Paperboard and packaging grades (cartonboard, corrugating medium, kraftliner, fluting) require multi-ply construction to achieve the required grammage (150–500 gsm) and structural properties.
Board machines run at lower speeds than printing paper machines — typically 300–900 m/min — due to the higher grammage and longer drying requirements.
A wide range of specialty machines produce non-standard paper grades. Cylinder mould machines for banknote and security papers, inclined wire machines for filter papers and non-wovens, and highly modified Fourdriniers for technical and industrial papers. These machines typically run at lower speeds with highly controlled process conditions to achieve unique product properties.
Paper machine clothing — forming fabrics, press felts and dryer fabrics — is the collective term for the permeable textile components that carry the paper web through each section of the machine. Clothing selection has a direct impact on drainage performance, paper quality, machine efficiency and operating costs. Understanding the construction and function of each clothing type is essential for maintenance engineers and process specialists.
The forming fabric is a continuous woven textile belt that receives the stock jet from the headbox and transports the forming paper web while water drains through the fabric structure. Modern forming fabrics are woven from synthetic monofilament yarns (polyester, polyamide) in highly engineered weave patterns.
Single-layer fabrics — the simplest construction, with a single set of machine-direction (MD) and cross-direction (CD) yarns. Good drainage and open area. Used for lower-speed machines producing tissue and packaging grades. Typical mesh count: 40–60 yarns/cm.
Double-layer fabrics (SSB — single-layer binder) — two woven layers sharing some common yarns. The top (paper side) layer provides fine surface structure for good sheet formation; the bottom (machine side) layer provides durability and stability. The dominant fabric type for printing and writing paper machines.
Triple-layer fabrics — completely independent top and bottom layers joined by separate binder yarns. The top layer is optimised for formation and retention; the bottom layer for wear resistance. Preferred for high-speed, demanding applications where both paper quality and fabric life are critical. Typical service life: 50–120 million metres.
Position on machine: The forming fabric runs from the breast roll (at the headbox slice), across the forming table or forming rolls, over suction boxes and through the couch roll, returning underneath to the breast roll via guide rolls, tensioning rolls and cleaning showers.
Press felts are permeable textile belts that carry the wet paper web through the press section nips, receiving water expressed from the sheet and transporting it away from the nip. A press felt must simultaneously support the wet, fragile web, accept expressed water, release it on the return run, and withstand high nip pressures without compaction.
Construction: Modern press felts consist of a woven base fabric — providing dimensional stability and structural support — onto which batt fibres are needled in multiple layers. The batt provides the permeable, cushioning medium that contacts the paper web and absorbs expressed water.
Felt types by position:
Felt conditioners: Vacuum suction boxes, high-pressure cleaning showers and uhle boxes maintain felt permeability throughout the production run. Felt life ranges from 2–8 weeks depending on furnish, machine speed and press loading.
Dryer fabrics (also called dryer screens or dryer wires) carry the paper web in contact with dryer cylinders through the drying section. Unlike press felts, dryer fabrics are not designed to absorb water — they simply maintain web contact with the heated cylinder surface and control sheet transport between drying groups.
Construction: Woven from heat-resistant synthetic yarns (typically polyester with PEEK or other high-temperature yarns for hot sections). Open weave structure allows steam and evaporated water to pass through. Very stable dimensionally — must maintain precise length and width under thermal cycling.
Positions: Single-run or twin-run configurations. In single-tier drying, all cylinders are on one level with the fabric supporting the web on the underside. In two-tier (double-tier) drying, cylinders alternate between upper and lower rows, with separate top and bottom dryer fabrics. Single-tier is preferred on high-speed machines for web stability.
Paper machine design, roll specification and clothing selection are all heavily influenced by the grade being produced. Grammage (basis weight in g/m²), furnish composition and quality requirements determine machine speed, press loading, drying capacity and ultimately the roll coatings and covers specified. This guide provides a reference overview of major paper grades, typical grammage ranges and the machine speeds at which they are produced on modern equipment.
As a general rule, machine speed decreases as grammage increases — higher grammage requires longer drying time, limiting achievable speed for a given dryer section length. The relationship is not linear: improvements in press section dewatering (shoe presses, extended nip technology) can increase speed for a given grade by reducing the moisture content entering the dryer section.
Spreader rolls (also called bowed rolls or banana rolls) are passive or driven rolls with a curved (bowed) axis that spreads, smooths and tensions the paper web across its full width. They are used at multiple positions on the paper machine — forming section, press section, dryer section, calender and reel — wherever web wrinkling, edge curl or lateral tension imbalance must be corrected before the next process step.
Two independent design choices define a spreader roll: the surface construction (steel segments or polyurethane sleeve) and the bow configuration (fixed or adjustable). Each combination has distinct advantages, limitations and optimal applications.
A spreader roll works because its axis is bowed — curved in the machine cross-direction. As the web wraps around the curved surface, the bow creates a component of force directed toward the outer edges of the web. This outward force spreads the web laterally, removing wrinkles and ensuring even tension distribution across the sheet width. The spreading force depends on the bow angle, web wrap angle and web tension. Both surface construction types use this same fundamental principle; they differ in how the surface moves relative to the web.
The steel segment roll consists of a series of individual steel rings (segments) — typically 15–50 mm wide — mounted on the bowed shaft on anti-friction bearings. Each segment rotates independently about the bowed shaft axis, following the web as it passes.
| Advantages | Disadvantages |
|---|---|
| Excellent durability — steel segments withstand high web tensions and heavy grades | Segment edges can mark sensitive, thin or coated webs if segments are worn or misaligned |
| No temperature limitation — suitable for dryer section and high-temperature applications | Heavier construction — increased load on bearings and frames |
| Rebuildable — individual segments, bearings and seals can be replaced independently, reducing overhaul cost | Higher maintenance frequency — segment bearings require periodic lubrication and inspection |
| Wide speed range — suitable from slow board machines to high-speed tissue and newsprint machines | Noisier in operation — segment rotation at high speed generates audible noise |
| Proven, reliable technology — established for over 100 years in paper mills worldwide | Higher initial cost than equivalent PU sleeve rolls |
Best suited for: heavy paper grades, board machines, dryer section, high-tension press section positions, applications where temperature resistance is required.
The PU sleeve roll uses a continuous polyurethane tube (sleeve) that rotates freely over the fixed bowed shaft on a low-friction interface — typically supported by air film, oil film or rolling element bearings at the ends. The seamless sleeve eliminates segment edges entirely, providing smooth, uniform contact with the web.
| Advantages | Disadvantages |
|---|---|
| Smooth, seamless web contact — no segment edges; ideal for thin, coated or sensitive grades | Temperature limitation — most PU grades max 80–90°C; not suitable for dryer section without special compounds |
| Lighter weight — reduced loading on machine structure and drive components | Sleeve wear — PU sleeves require periodic replacement (typically every 1–3 years depending on duty) |
| Quieter operation — continuous sleeve eliminates the noise generated by rotating segments | Lower tension capacity — PU sleeve construction is less suitable for very high web tensions |
| Lower initial cost and simpler design than segmented steel rolls of equivalent size | Chemical resistance must be verified — sizing agents, solvents or bleaching chemicals can degrade certain PU compounds |
| Sleeve hardness can be selected (40–80 Shore A) to suit web sensitivity and required grip | Sleeve replacement requires roll removal from machine — planned downtime required |
Best suited for: tissue, coated papers, thin films, press section pick-up positions, calender entry, any position where surface marking must be avoided.
In a fixed bow roll, the shaft bow angle is set permanently at manufacture or installation. The bow cannot be changed without removing the roll from the machine and mechanically adjusting or replacing the shaft. Fixed bow rolls are simpler and less expensive but inflexible.
| Advantages | Disadvantages |
|---|---|
| Simple, robust construction — no adjustment mechanism to maintain or fail | Cannot adapt to grade changes — spreading force is fixed; over- or under-spreading if process conditions change |
| Lower cost — fewer components, simpler manufacturing | Bow adjustment requires machine stop and roll removal — significant downtime cost |
| Optimal for single-grade machines with stable process conditions and consistent web tension | Not suitable for multi-grade machines or where web tension varies significantly between production runs |
Adjustable bow rolls allow the bow angle to be changed while the roll is installed in the machine — either during a production stop or, in the most advanced designs, while the machine is running at full speed. The adjustment mechanism varies by manufacturer: eccentric shaft designs, hydraulic actuation, mechanical screw adjustment or pneumatic systems.
| Advantages | Disadvantages |
|---|---|
| Flexible — bow optimised for each grade, speed and web tension condition without stopping the machine (in best designs) | Higher cost — adjustment mechanism adds complexity and initial investment |
| Ideal for multi-grade machines — one roll serves all grades with optimised spreading performance | Additional maintenance — adjustment mechanism requires periodic inspection and lubrication |
| Rapid response to process disturbances — bow can be increased if wrinkles develop without stopping production | Risk of misadjustment — incorrect bow setting can over-spread the web, causing edge tears or lateral tension imbalance |
| Can compensate for wear — as web properties or tension patterns change over a campaign, bow can be fine-tuned | Adjustment range is limited (typically 0°–6°); very large bow adjustments may still require a roll change |
| Application | Recommended construction | Bow type |
|---|---|---|
| Tissue / thin coated grades | PU sleeve | Adjustable |
| Newsprint / printing papers, single grade | Steel segment or PU sleeve | Fixed |
| Multi-grade printing / packaging machines | Steel segment or PU sleeve | Adjustable |
| Dryer section (high temperature) | Steel segment | Fixed or adjustable |
| Board / heavy packaging grades | Steel segment | Fixed (stable grade) or adjustable |
| Calender / reel section (sensitive surface) | PU sleeve | Adjustable |
Source references: ANDRITZ Fabrics and Rolls product range (andritz.com). Finbow Spreader Rolls (finbow.com — manufacturer data, 2023).