Curl Control for Paperboard Grades
The Steam-Foil® is the only system proven to control curl in paperboard even in the heaviest grades.
Features/Benefits
- No Spitting or Dripping
- Effective on any board thickness
- Simple to install and operate
- Adjustable steam application for varying board width
- Eliminates curl and checking-related rejects
- Convert rolls all the way to the core
- Eliminates static electricity
- Increases productivity while reducing cost
- Typically pays for itself in less than nine months
What is Curl?
Curl can be defined as the tendency for a flat piece of paperboard to distort in a cylindrical shape. Curl can occur in the cross-machine direction (CD) or the machine-direction (MD). Cross-machine direction curl is caused by uneven drying of the paperboard. Machine-direction, or "roll-set" curl, occurs when paperboard that's been wound onto a core starts to take the shape or the set of the roll. Machine-direction curl is more problematic closer to the core due to the tighter bend of the product in this area. Additionally, the problem is more severe on heavier grades and usually worsens over time.
The Need for a Solution
In paperboard production, the largest single source of product waste and converting difficulties is curl, specifically roll-set curl. Curl is responsible for jam-ups, off-spec production, and loss of unconverted product. Traditional attempts at solving this problem utilize mechanical decurl bars or homemade steam showers. Traditional steam showers are ineffective and provide more problems than benefits (e.g. dripping, spitting and streaking). Mechanical decurl bars provide limited decurling capabilities, and often over stress the paperboard causing checking or surface disruptions along with delamination on multiple grades. When curl becomes too extreme and causes butt roll, the roll is usually scrapped costing the paper-board producer material and lost production time.
The Steam-foil Solution
Technological developments in nozzle and actuator design have led to the development of the Steam-Foil. Through its unique construction, the Steam-Foil System can selectively and precisely control the amount of steam it applies across the width of board, providing both cross-machine direction and machine-direction curl control. At the heart of the system is the Coanda nozzle which applies steam counter and parallel to the web in the gap created between the board and the Steam-Foil. This steam flow pattern enhances the uniformity and efficiency of heat transfer by maximizing the time of steam engagement and minimizing entrained air traveling with the web. Cross-machine direction curl control is made possible by individual steam-flow control nozzles which can be located as close as 3 inches from one another across the web. This spacing also allows for selective control of the steam. The outer surfaces of the Steam-Foil are heated to prevent moisture from collecting and dripping onto the web. This design feature allows the actuator to be mounted in any orientation, including above the web.
Solving the Problem
The objective of curl control is to reset the fibers of the paperboard to a flat position while preserving both the structural integrity and surface qualities of the paperboard. The Steam-Foil® steam shower applies an efficient and uniform layer of steam to the paperboard, imparting both heat and moisture. The heat and moisture soften the fibers and loosen the fiber-to-fiber bond, allowing the product to reshape to a flat condition. Subsequent mechanical decurling is made more efficient and can be performed without fear of destroying the performance or quality features of the paperboard.
