Mechanical Force
Force per unit area acting parallel to the surface of a material or fluid represents the primary mechanical strain encountered by chemical pastes and yarns during high speed processing. In textile application, shear stress determines how effectively a finish or printing paste is distributed across the fiber surfaces. This force must be controlled to prevent fabric damage or uneven application.
Printing Pastes
Rotary screen printing machines force print pastes through fine mesh screens onto the fabric. The high shear stress experienced by the paste during this process reduces its viscosity, allowing it to pass through the screen easily. Once on the fabric, the stress is removed and the paste recovers its thickness.
Yarn Sizing
During warp sizing, yarn is pulled through a squeeze roller nip to remove excess sizing starch. The shear stress generated in the nip forces the starch into the yarn bundle, ensuring good adhesion and core strength. This mechanical action is necessary to prepare the warp yarn for the stresses of weaving.
Material Performance
Woven and knitted fabrics are subjected to multidirectional forces during garment wear and wash testing. If the shear stress exceeds the fabric strength, the yarns can shift or slip, leading to seam failure and garment distortion. This structural durability is verified using standard tongue tear and seam slippage tests.
