How Shear Rate Influences Polymer Melt Performance > 자유게시판

The quality of a polymer melt is directly governed by the shear rate applied during processing. Shear rate refers to how rapidly layers of the polymer flow past one another, and it plays a pivotal role in determining the final properties of the molded or extruded product. At low shear rates, the polymer chains have sufficient time to relax and align slowly, which can lead to uneven flow and تولید کننده گرانول بازیافتی inadequate mixing. This often results in visible imperfections including sharkskin or melt fracture, particularly in high-viscosity resins.

As the shear rate rises, the polymer chains begin to follow the flow of the flow, which can boost the uniformity of the melt and reduce viscosity. This shear thinning behavior is advantageous in many processing applications because it facilitates enhanced flow through dies and molds eliminating the need for excessive pressure. However, if the shear rate becomes too high, the polymer chains can be overstretched or even broken down. This leads to chain scission, which compromises the mechanical properties of the final product.

Excessive shear can also induce frictional heating due to viscous dissipation, causing thermal degradation in thermally unstable resins. This can result in discoloration, unpleasant smells, or the release of volatile byproducts that undermine product integrity. In addition, high shear rates may cause non-uniform velocity profiles, leading to built-up tension that appear as warping or shape distortion after cooling.

To achieve superior melt performance, processors must strategically optimize the shear rate with the polymer’s flow characteristics, processing temperature, and machine configuration. Using the optimal screw geometry, zoned heating settings, and mold geometry helps ensure a stable and controlled shear rate throughout the process. Measuring and adjusting shear rate ensures that the polymer melt remains predictable, even, and intact, ultimately producing parts with uniform quality and flawless appearance.