Apr 29, 2015
Valmet Calender Roll Cover CL, Valmet's new composite cover, provides extremely high wear and barring resistance in physically demanding or barring-ridden calender positions. It provides paper and board makers with extended running time, resulting in signicant cost savings for every ton produced and trouble-free papermaking.
Barring is often a problem with on-line calender rolls. With Valmet Calender Roll Cover CL, material development has now taken a leap forward in barring resistance, including increased wear resistance, increased deformation resistance, plus a special base layer reduces cover shape deformation and roll vibration. Valmet Calender Roll Cover CL running time exceeds that of other covers in barring-ridden roll positions, and its barring resistance has been demonstrated on both multi-nip and soft calenders.
At Stora Enso Kvarnsveden's PM 12 in Sweden, high quality SC paper is produced with a modern 5 + 5 TwinLine multi-nip calender. After already achieving running times of about 800 hours with Valmet Calender Roll Cover CJ-W, the new Valmet Calender Roll Cover CL has nearly doubled that time, at almost 1,600 hours.
The surface has remained very smooth throughout, even up to a Ra of 0.17 µm. Valmet Calender Roll Cover CL has managed this level of performance under harsh conditions: pressures of more than 400 kN/m and speeds of 1,130 m/min, while being doctored.
Anita Nordenström, Technician of the PM 12 TwinLine states: "With [Valmet Calender Roll Cover CL], we can run much longer without vibration." Longer running times have also given Maintenance Manager Håkan Kinnunen more flexibility in planning roll changes.
The new composite cover features high wear resistance, allowing for long regrinding intervals with predictable roll change times, less need for roll changes, and fewer regrindings. The latter lowers regrinding costs and extends cover lifetime. As a result, less wear in a cover translates into reduced maintenance costs and troublefree papermaking.
Valmet Calender Roll Cover CL extended running times are clear. A multinip calender at a North American SC paper mill achieved a running time in excess of 130 days at speeds of 1,170 m/min and a loading of 328 kN/m. This has been the longest run in this position without profile problems, according to the mill.
As calender covers are located in the physically most demanding positions in paper and board machines, they need to be durable. High-speed online calenders in particular pose a risk of cover failure, with web breaks causing very severe impacts on the cover. Valmet Calender Roll Cover CL sets a new standard in cover impact durability allowing for very high calender loads at a high nip frequency.
For more information on Valmet Calender Roll Cover CL or other Valmet roll covers, contact your Valmet representative.