Geometric Attribute
Geometric attribute defines the physical difference in material characteristics when measured along different axes. Within the paper web, fiber orientation anisotropy describes the ratio of fibers aligned in the machine direction compared to the cross direction. This alignment results from the hydraulic forces and drainage speeds present at the headbox of a paper machine.
The degree of bias influences every subsequent mechanical test performed on the finished sheet.
Production Variable
Production variable is determined by the jet to wire speed ratio which dictates how many fibers settle in a specific path. High fiber orientation anisotropy creates a sheet with great tensile strength in the machine direction but lower resistance to tearing or splitting across its width. Operators adjust the slice geometry or the wire speed to achieve a specific balance for the end application.
The turbulence in the headbox and the speed of the forming fabric act as the primary controls for this structural layout. When the jet speed matches the wire speed exactly, the alignment becomes more random, whereas a large difference forces the fibers into a parallel arrangement.
Performance Impact
Performance impact is observed when misalignment of the main axis causes secondary issues such as diagonal curl or twist during moisture cycles. In high speed printing, fiber orientation anisotropy dictates how the web responds to tension and heat. Stable sheets require a controlled ratio to prevent dimensional distortion in the final product.
