CHASE GIBSON AND MARK SISSONS
The press section’s main function is the mechanical dewatering of the paper web. The press configuration also determines surface properties such as smoothness and two-sidedness. The goal in the press section is to achieve the greatest possible dewatering, since mechanical pressing is much more economical than drying by heat.
In addition, higher dry content contributes to higher web strength; this reduces the risk of web breaks during transfer to the dryer section and during the entire operation. The paper web enters the press section with a dry content of 15-22 percent and leaves the section with a dry content of 40-55 percent.
The requirements for press sleeves are different not just for every paper grade, but also for individual machines. With this in mind, Voith offers QualiFlex, a product portfolio designed to fit general grade specific requirements, with several possibilities for further individual customization. For every paper grade, mills can choose between different products in the QualiFlex family.
The company’s premium shoe press sleeve is the QualiFlex QRun, which reacts stable to compressions. The result: fewer failures of shoe press sleeves. The product’s improved elasticity guarantees high durability and thus reduces cracks and their propagation. These two properties ensure longer and reproducible running times.
The following two case studies illustrate these properties in different applications.
CASE STUDY 1:
BOARD MILL NETS SAVINGS
A leading US provider of packaging solutions was experiencing costly problems running its board and packaging machine, including short shoe press sleeve life and other inconclusive failures. The company asked Voith to assess the problems and recommend a solution that would improve production in the current run conditions.
After visiting the plant to investigate the machine while in full production, Voith experts recommended the QualiFlex QRun press sleeve to extend sleeve run-life and improve press performance in a demanding environment.
QualiFlex QRun shoe press sleeves are made from an innovative polyurethane which offers improved elasticity, strength, and stability, leading to fewer sheet breaks, reduced groove collapse through the nip, and improved dewatering. Voith is one of only a few suppliers able to manufacture press sleeves large enough for the diameter demanded by this particular machine. With support from Voith, the new sleeve was installed successfully.
Results: With the new QualiFlex QRun sleeve installed, the company noted improved performance immediately. Over nine days, the machine ran with no sheet breaks, an improvement over previous suppliers.
The mill collected data showing that QRun performed better than the previous sleeves under comparable conditions. The QRun’s initial run life was 186 days—a dramatic improvement over the previous supplier’s average of 87 days for its last 20 sleeves. As a result, the mill realized US$240,000 annual savings by using two fewer sleeves per year. Seeing such stark improvement in overall runnability, the company made Voith its main sleeve supplier.
Key performance indicators:
• Previous yearly sleeve cost: US$480,000
• Yearly cost of QRun sleeves: US$240,000
• Total annual savings: $240,000
Commented the packaging solutions plant’s operations manager: “The paper machine is running as well or better than I can ever recall in my five years working for the company.”
CASE STUDY 2:
MILL COMES BACK TO
HIGH OPERATION CAPACITY
A second leading US provider of packaging solutions recently changed from Voith QualiFlex QRun shoe press sleeves to alternate sleeves provided by another company. As a result, the board and packaging machine was tested in a competitive trial, and the machine was running significantly slower on the competitor’s sleeves.
The company asked Voith to assess the performance of those sleeves and recommend a solution that would improve machine speed and overall production. After reviewing the performance data of the competitor’s poor-performing sleeves—and noting their issues with swelling and a 25 percent loss of the operating void volume—Voith experts recommended a return to the QualiFlex QRun shoe press sleeve.
The design characteristics made possible by the QualiFlex QRun’s innovative polyurethane construction meant that, at this facility, the sleeve could operate with its void volume under load through its entire run life. This is because the polyurethane construction is more dimensionally stable.
Results: With the new QualiFlex QRun sleeve installed, the company noted a return to its previous operating speed and capabilities. With QRun sleeves on, average run life went up to 180 days, where the previous sleeve only managed 115 days on average. The previous sleeve saw a 25 percent loss of void volume, while further testing showed only a 5 percent loss for QRun under similar conditions. The improved speed and performance from QualiFlex QRun secured an order from the mill for two additional sleeves.
“Returning to QRun after the run with the other company’s sleeves made all the difference in the performance level of our paper machine. We are extremely pleased by the obvious quality of QRun,” said a mill spokesperson.
BENEFITS OF POLYURETHANE
Press sleeves in packaging and board machines are subject to severe compression and harsh exposure to chemicals. QualiFlex QRun polyurethane press sleeves can meet these challenges. The polyurethane avoids sleeve failures by remaining stable in response to compression. With its improved elasticity, the QRun polyurethane sleeve is more flexible and more resistant to cracking; as a result, the sleeve’s run life is longer and more reliable. Other benefits include:
• Tailor-made surface designs for optimum void volume over the life of the sleeve
• Product stability during compressions
• Excellent wear resistance
• Optimal, constant dewatering performance
• Highly dry content after the press
• Numerous surface designs for exact adaptation to mill needs
Voith Paper is part of the Voith Group. As a full-line supplier to the paper industry, it provides a large range of technologies, services, components, and products on the market and offers paper manufacturers solutions from one single source.
Chase Gibson is technical sales specialist, Voith Paper North America and Mark Sissons is senior technical sales specialist, QualiFlex, Voith Paper North America. Learn more at voith.com.