Stepfoils™
The Stepfoil™, when combined with proper vacuum control, has been shown to provide higher-quality sheets, higher productions speeds, reduced wet end breaks and faster grade change-over.
The unique pulse profile of the Stepfoil™ blade design gives the papermaker optimum flexibility in fourdrinier operation not duplicated in any other blade design. This blade design is available only through Kadant. Experience indicates that mills have been able to add more water to the headbox to lower consistency, thereby improving formation while still reaching their production goals. Water removal by the Stepfoil blade is controlled by the vacuum applied, blade spacing and step depth.
The diagram at the right shows the shape and typical pulse profile.
How It Works
Controlled Drainage
Vacuum application draws water through the fabric. The water contacting the step of the blade creates a hydrodynamic nip. Thereafter, drainage is induced mainly by the vacuum pulse created, and only secondarily by the applied vacuum.
The depth of the step initially determines the magnitude of the drainage pulse. Further control of the pulse is achieved by applied vacuum drawing down the fabric and effectively increasing the return angle of the fabric.
Controlled Turbulence
The span between the support points of the blades determines the ease with which the applied vacuum can deflect the fabric. The degree of turbulence achieved is determined by the extent of deflection and conformation of the fabric.
The conformation of the fabric can be adjusted by controlling the specific distance (X) from the nip to the following support point. A slight adjustment of applied vacuum will accomplish this without significantly affecting the drainage.
Advantages
- Combines benefits of the roll, foil and the vacuum foil - without the disadvantages. By proper design for the appropriate location on the table, suitable positive pulse levels can be achieved. This maximizes drainage from the headbox to the flatboxes, without setting the sheet.
- Complete operational flexibility, repeatability, drainage control.
- When combined with proper vacuum control, the Stepfoil™ has been shown to provide higher-quality sheets, higher production speeds, reduced wet end breaks and faster grade changeover. The system is also suitable for computer control.
- Lower white-water solids and reduced two-sidedness.