Shear Rate’s Critical Role in Polymer Melt Integrity > 자유게시판

The quality of a polymer melt is heavily influenced 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 essential role in determining the final properties of the finished component. At low shear rates, the polymer chains have adequate duration to relax and align slowly, which can lead to uneven flow and poor homogeneity. This often results in surface defects such as sharkskin or melt fracture, particularly in high molecular weight polymers.

As the shear rate increases, the polymer chains begin to align in the direction of the flow, which can boost the uniformity of the melt and lower viscosity. This non-Newtonian response is beneficial 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 mechanically damaged or even broken down. This leads to molecular weight reduction, which weakens the mechanical properties of the final product.

Excessive shear can also produce concentrated thermal energy due to internal friction, causing thermal degradation in temperature-vulnerable materials. This can result in color changes, unpleasant smells, or the generation of volatile byproducts that damage product integrity. In addition, high shear rates may cause asymmetric flow distribution, leading to residual strain that appear as warping or dimensional instability after cooling.

To achieve superior melt performance, processors must strategically optimize the shear rate with the polymer’s viscoelastic behavior, processing temperature, and machine configuration. Using the optimal screw geometry, تولید کننده گرانول بازیافتی thermal gradients along the barrel, and mold geometry helps sustain a uniform and balanced shear rate throughout the process. Monitoring and controlling shear rate ensures that the polymer melt remains predictable, even, and intact, ultimately producing parts with reliable strength and smooth texture.