A working roll in a printing or woodworking line loses its geometry long before its metal core wears out: it is the contact layer that wears, the web starts to drift and the nip pressure begins to wander. Buying a new roll for a surface worn by a few millimetres is expensive and slow. Polyurethane recoating restores precise geometry on the old core, and the cast layer withstands abrasion 2-5 times longer than rubber. Below I explain why polyurethane beats rubber and caprolon on rolls, how to choose the hardness, by what technology the layer is applied, and what is needed to order a restoration to your drawing.
Why recoating a roll with polyurethane beats replacing it
Recoating keeps the most expensive part of the unit, the metal core with bearing journals, and replaces only the worn working layer. That is why polyurethane roll restoration is almost always cheaper and faster than manufacturing a new roll, while the coating outperforms both rubber and metal in service life.
The worn polyurethane layer is stripped down to the metal, the core is checked for runout, the surface is prepared and a new layer is cast. The seating dimensions and geometry are preserved, so the roll returns to the line without regrinding the journals and without re-matching the adjacent units. An uncoated metal roll, by contrast, is reground to a smaller diameter or scrapped when it wears, and a rubber layer serves several times less than a polyurethane one.
Polyurethane also wins on environmental resistance. It tolerates contact with technical oils, hydraulic fluids and petroleum products, does not absorb moisture, does not corrode and does not grow mould. A working range from -60 to +100 C lets you install a recoated roll in both cold and heated zones, where rubber would harden or flow. That is precisely why one recoating cycle often outlasts several rubber-coating replacement cycles.
Roll coatings compared in numbers
Polyurethane surpasses rubber and caprolon in the combination of wear resistance, strength and elasticity, while bare metal loses to it in the ability to absorb impact and in corrosion resistance. Reference characteristics from standard tests are summarised below.
| Material | Abrasion (DIN 53516), mm3 | Working temperature, C | Hardness | Tensile strength, MPa | Oil resistance |
|---|---|---|---|---|---|
| Polyurethane (TIMOL) | 38-39 | -60…100 | 85A-95A | 39-87 | excellent |
| SBR rubber | 100-200 | -40…80 | 40A - 80A | 8-20 | low |
| NBR rubber | 80-150 | -30…100 | 40A - 90A | 10-25 | good |
| Natural rubber | 60-130 | -50…70 | 30A - 80A | 20-30 | low |
| Caprolon (PA6/66) | 30-90 | -40…100 | 75D - 85D | 60-85 | good |
The difference in abrasion determines service life. For polyurethane it is 38-39 mm3, for the most common SBR rubber 100-200 mm3, meaning the rubber layer wears several times faster under otherwise equal conditions. Natural rubber has higher rebound, but its abrasion of 60-130 mm3 and weak oil resistance make it unreliable in industrial rolls that contact lubricants. Caprolon is close to polyurethane in wear (30-90 mm3) and very strong (60-85 MPa), yet it is rigid, does not wrap around the web and is brittle on impact, so it suits bushings and guides rather than nip rolls.
Polyurethane remains the compromise that works: low abrasion, high strength of 39-87 MPa, and an elasticity that maintains even nip pressure along the whole roll barrel.
For rolls, the material behaviour under cyclic bending is separately important. Rubber and natural rubber gradually fatigue and crack along the edges of the working zone, while caprolon chips under repeated impacts because it is not resilient. Polyurethane, with its rebound elasticity of 34-61 percent, returns to shape after each load cycle and does not accumulate fatigue cracks as fast as rubber. That is why a polyurethane-recoated roll keeps stable contact geometry throughout its service life, not just in the first months after a coating change.
Roll recoating technology: preparation and casting
The quality of roll recoating is determined not by the polyurethane itself but by core preparation and adhesion. The cast layer holds for decades if the metal-polymer boundary is made correctly, and delaminates within months if the surface was prepared carelessly.
Work begins with stripping the old coating down to clean metal and inspecting the core: runout is checked, the surface is levelled, and sandblasting develops the micro-relief. Then an adhesive primer is applied that chemically bonds the steel or cast iron to the polyurethane. Next the polyurethane is poured into the mould by free casting and polymerised, after which the roll barrel is ground to size for the required cylindricity and seats. The layer hardness is set at the grade selection stage, from 50 Shore A for soft nip rolls to 70 Shore D for hard drive rolls.
On nip rolls, hard polyurethane is not always needed. A softer layer in the 60-80 Shore A range gives a wider contact patch and more even web pressure, and that matters more than maximum hardness where the roll does not transmit a large pulling force. Raise the hardness only for drive rolls with high specific pressure, otherwise you lose contact uniformity.
The layer thickness is chosen for the load and core diameter: too thin quickly reaches the metal, too thick overheats. Read more about the recoating service in the Services section.
Where polyurethane rolls work and how to maintain them
Polyurethane rolls sit in the nip, guide, conveying and drive units of woodworking, textile, metalworking, chemical, pulp and paper and printing lines. Their job is to guide and press the web, paper, veneer or fabric without slipping and without leaving marks on the material, since polyurethane leaves no imprints and does not attract debris.
Maintenance of a recoated roll is minimal: periodic cleaning of the surface from build-up and monitoring the integrity of the layer. Polyurethane does not corrode, does not rot and is not afraid of moisture, so the roll needs no protective coatings or special care. When the working layer reaches its wear limit, the roll is sent for recoating again, and the cycle repeats without loss of seating dimensions. Ready sizes and product types are listed in the catalogue.
The colour of the polyurethane layer does not affect quality, because the material itself is colourless and the pigment only adds a tint for marking or visual wear control. This is handy on lines where positions in a unit are told apart by different roll colours. What matters more: a recoated roll leaves no marks on the web and does not attract dust, so the finished material comes out cleaner and the unit keeps its presentable look longer without frequent cleaning.
How to order roll recoating for your production
For an accurate calculation the factory needs the roll drawing or the worn sample itself, together with the operating conditions: load, rotation speed, temperature, the type of material in contact with the roll, and the required hardness. From this data the process engineer selects the polyurethane grade, hardness and layer thickness, while production reproduces the geometry to the seats using free casting technology.
This format suits both a one-off restoration of a single roll and serial recoating of a set for a new line. To get a technical proposal for your task, contact the TIMOL factory through the Contacts page: send the drawing or sample and describe the operating regime, and the factory will calculate the restoration for your specific unit.