A cover story: Valmet’s polyurethane roll covers lead the way in sizing and coating

Over the decades, Valmet has developed an unmatched film coater and sizer offering and process knowhow leading to market-leading roll cover innovations. Valmet’s advanced polyurethane roll covers deliver stable, high‑quality performance in both sizing and coating applications – with grooved or smooth rods, as well as coating blades.

Ongoing material development has made today’s polyurethane covers more durable than ever. Expanded thickness and hardness ranges allow operation in any sizer or coater, while newly engineered surface features address specialized needs in film sizing and coating.

Today, Valmet offers two polyurethane roll cover product families for sizing and coating. Valmet Sizer Roll Cover CF family provides excellent wear resistance, uniform film formation, and reliable operation. Valmet Coater Roll Cover CC enables an unmatched backing roll solution for blade coating.

A complete product family for every production need

The Valmet Sizer Roll Cover CF product family provides optimized cover options for graphical papers, specialty papers, containerboards and packaging grades. Mills benefit from long grinding intervals, robust mechanical strength, excellent wettability, and highly uniform film formation for trouble-free operation.

Valmet Sizer Roll Cover CF product family.  

Valmet Sizer Roll Cover CF

Valmet Sizer Roll Cover CF cover is a cost-efficient solution thanks to its long reliable runs with excellent wear and deformation resistance. Coating application is easy and high amounts of coating can be applied. It’s a versatile solution for switching between sizing and coating without need for roll changes.

A roll cover for both film coating and surface sizing, the extremely wear-resistant Valmet Sizer Roll Cover CF gives high-quality coating film formation for easy operation with both smooth and grooved rods.

Valmet Sizer Roll Cover CF‑M

Valmet Sizer Roll Cover CF-M provides excellent wear resistance, long running times and exceptional cover surface stability. It is designed for applications requiring a controlled matt surface. CF‑M is particularly well suited for swing machines alternating between starch sizing and pigment, barrier, or other special coatings.

Valmet Sizer Roll Cover CF-M is well suited for swing machines alternating between starch sizing, pigment, barrier, and other special coatings.

Valmet Sizer Roll Cover CF‑EC

Valmet Sizer Roll Cover CF-EC is designed for harsh sizing environments, especially in containerboard production, including high nip loads, elevated temperatures, and high machine speed. The updated cover structure maximizes durability and starch efficiency under these demanding conditions.

Blade coating: polyurethane outperforms rubber

Rubber covers have traditionally been used on blade coater backing rolls, but they are prone to scratching and grooving — especially at the cover edges where the blade contacts the surface directly. This leads to premature roll changes. Based on Valmet’s unique polyurethane technology, Valmet Coater Roll Cover CC offers superior wear resistance and a highly uniform surface profile. Mills using CC covers report significantly longer running periods and reduced regrinding frequency, particularly in the critical edge areas.

The uniform surface and superior wear resistance, especially in the edge areas, allows Valmet Coater Roll Cover CC to significantly extend the operating period and reduce the need for roll changes and regrinding.

When every detail counts

Valmet’s continuous R&D work ensures that the products meet all the requirements of board and papermakers around the world. Innovation is driven by in-house initiatives and close cooperation with customers.

For example, the Valmet Sizer Roll Cover CF family features a patented polyurethane solution which prevents scratching and enables the application of high coating grammages without compromising surface quality. The solution was developed to tackle the risk that film coating with smooth rods sometimes causes – that is pigment particles scratching the smooth cover surface, leading to defects such as orange peel.

Film sizing, on the other hand, requires a cover that can withstand continuous contact with a grooved rod without excessive wear or profile deformation. Chemical compatibility and thermal stability are equally important. Valmet’s CF, CF‑M, and CF‑EC covers incorporate all these requirements, ensuring stable profiles and long, trouble‑free operation.

Swing machines: one cover for both sizing and coating

Historically, swing machines have required separate covers for sizing and coating, resulting in frequent roll changes and increased downtime. Valmet Sizer Roll Cover CF and CF‑M have demonstrated that a single polyurethane cover can successfully handle both processes. Mills can now operate swing machines with one roll cover, reducing maintenance needs and improving overall efficiency.

Continuous development towards better performance

Valmet’s polyurethane roll covers combine advanced material engineering with deep process expertise to deliver unmatched performance in sizing and coating applications. Valmet’s sizer roll covers are known for their long running intervals, excellent wear and marking resistance, and highly uniform film formation across a wide range of paper and board grades. With continuous development, expanded hardness and thickness options, and specialized surface features, these covers meet the increasing demands of modern production environments – from high‑speed containerboard sizers to sensitive blade coater operations.

Valmet’s offering extends beyond roll covers: solutions such as iRoll Sizer, iRoll portable, and optimized crowning help mills improve runnability, reduce web flutter, prevent wrinkling, and achieve even more uniform paper surface treatment. Working together with Valmet experts ensures fast payback and measurable improvements in sizer performance.