Longer life, improved performance – rethinking sizer roll covers

Sizer roll covers play a central role in the sizing process, directly influencing how evenly and efficiently starch or coating is applied to the paper or board surface. Their material composition, hardness, and surface characteristics define the nip conditions that determine film formation, penetration, and ultimately, the final product quality.

A well-matched cover supports stable runnability by minimizing vibration, preventing streaks, and maintaining uniform nip contact even at higher speeds. In contrast, worn or unsuitable covers can cause uneven application, increased breaks, and quality variability, turning the sizer into a potential bottleneck for the entire machine.

Today, our priority is to deliver sizer roll covers that are optimized for each customer’s process conditions and production targets. There are no one-size-fits-all solutions – the roll cover solution is always selected with care, and hardness, thickness, and surface roughness are all optimized for the specific application,” says Tatu Pitkänen, Global Technology Manager, Roll covers and Maintenance, Valmet.

It is our long experience and extensive global reference base that enables us to offer such a wide range of high-performing sizer roll covers. I’m looking forward to seeing how our new products support customers in achieving process improvements and cost savings with longer running intervals, greater operational stability or improved film quality,” Pitkänen continues.

Presenting the new sizer roll cover portfolio

Valmet’s updated sizer roll cover portfolio includes polyurethane, rubber, composite and hard coating​ covers for film sizer rolls, film coater rolls, hard and soft pond sizer rolls, gate sizer rolls, and hard nip sizer rolls. The latest product innovations reflect the major trends in papermaking today: higher efficiency, improved sustainability, and adaptability. Mills produce stronger, lighter grades at higher speeds while working with lower-quality raw materials and tighter cost margins.

As production efficiency demands increase, customers expect sizer roll covers to deliver longer running intervals even under harsh conditions, with reduced profile wear​, improved runnability, and stable cover surface roughness. Finding the right sizer roll cover for each application requires a deep understanding of the customer’s process – and an extensive product portfolio to choose from,” Pitkänen says.

Newest additions to Valmet’s sizer roll cover portfolio build on the proven characteristics of existing products while introducing new performance features. For example, the polyurethane cover known for its wear resistance and high-quality film formation, Valmet Sizer Roll Cover CF, now has two new siblings: Valmet Sizer Roll Cover CF-M and Valmet Sizer Roll Cover CF-EC.

Valmet Sizer Roll Cover CF product family is designed for optimal film quality in both coating and sizing.

CF-M is designed to maintain elevated, stable roughness over long running intervals. Its special filler technology creates a matte surface finish​, and the slightly textured surface keeps the film robust in film sizing and specialty coating applications. ​CF-EC is engineered for demanding sizing conditions in harsh environments, with a structure that is optimized for high nip loads and temperatures. Both offer premium performance at a reasonable cost​,” Pitkänen says.

Additionally, Valmet’s well-known rubber sizer covers Valmet Sizer Roll Cover SH and SH-W are being complemented with a new member, Valmet Sizer Roll Cover SH-EC. This new product secures long running intervals with uniform and reliable film transfer in containerboard film sizing especially when high amounts of sizing or sizing additive chemicals are used.

Valmet Sizer Roll Cover SH product family offers rubber covers optimized for long running intervals and robustness even in the toughest conditions.

Proven track record of excellent performance

Developing new products requires persistence and patience. Every new sizer roll cover undergoes a comprehensive series of laboratory tests before entering the market. In addition, Valmet always seeks real-world validation by running the covers in production at customer mills.

We have many long-term customer relationships, and it is very valuable for our product development to have the opportunity to trial new products in most demanding conditions. These trials are essential for demonstrating the excellent mechanical and chemical wear resistance of our covers, as well as their sizing and coating performance in real processes,” Pitkänen says.

All products now added to Valmet sizer roll cover portfolio have already proven their capabilities. For example, Valmet Sizer Roll Cover CF-M was tested on Zhejiang Huachuan’s PM8 in China with outstanding results. The CF-M delivered even and stable film formation with no missing starch or coating, whereas other roll covers had very limited running intervals due to these challenges. The sizer roll cover grinding interval increased from just three weeks to more than two months, resulting in significant savings in operating costs.

Lifecycle commitment to sizing and coating

In addition to offering world-class sizer roll covers, Valmet supports its customers with advanced technologies and expert services ranging from maintenance to process optimization. For example, roll covers can be paired with Valmet iRoll, an online profile measurement tool that provides real-time insights into the process, enabling higher production efficiency and improved product quality.

Valmet’s global roll workshop network ensures that skilled professionals are available to perform roll cover inspections and process audits, as well as application support and optimization – wherever the customer is located. With timely support, running times for rolls and equipment can be increased, runnability improved, and end-product quality enhanced.

Valmet’s experts are available around the world to perform roll cover inspections and process audits, as well as application support and optimization.

For customers interested in long-term partnerships with shared targets, we offer roll service agreements. These agreements provide easy access to world-class services tailored to the customer’s production goals and equipment lifecycle. Process improvement solutions around the roll covers, iRoll technology and on-site or remote support services can be built to find ways for performance optimization with best possible payback,” Pitkänen says.

Valmet’s renewed sizer roll cover portfolio brings together advanced materials, proven performance, and a strong lifecycle service offering. With tailored cover solutions, real‑time measurement tools, and global expert support, Valmet helps papermakers achieve longer running intervals, more stable operation, and consistently higher sizing and coating quality.

Written by Marianne Valta