How Shear Rate Influences Polymer Melt Performance > 자유게시판

The quality of a polymer melt is significantly determined by the shear rate applied during processing. Shear rate refers to the rate at which layers of the polymer flow past one another, and it plays a critical role in defining the final properties of the finished component. At low shear rates, the polymer chains have sufficient time to relax and align slowly, which can lead to irregular distribution and inadequate mixing. This often results in visible imperfections including sharkskin or melt fracture, notably in high-viscosity resins.

As the shear rate escalates, the polymer chains begin to follow the flow of the flow, which can boost the uniformity of the melt and reduce viscosity. This viscosity reduction under shear is desirable in many processing applications because it facilitates enhanced flow through dies and molds without requiring excessive pressure. However, if the shear rate becomes excessive, the polymer chains can be strained beyond capacity or even chemically compromised. This leads to decrease in average chain length, which diminishes the mechanical properties of the final product.

Excessive shear can also generate localized heat due to internal friction, causing heat-induced breakdown in heat-sensitive polymers. This can result in yellowing, تولید کننده گرانول بازیافتی 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 residual strain that result in warping or loss of tolerances after cooling.

To achieve optimal melt quality, processors must carefully balance the shear rate with the polymer’s rheological properties, melt temperature, and equipment design. Using the appropriate screw geometry, thermal gradients along the barrel, and exit configuration helps maintain a stable and controlled shear rate throughout the process. Monitoring and controlling shear rate ensures that the polymer melt remains uniform, consistent, and undamaged, ultimately producing parts with reliable strength and smooth texture.