Some insights on injection molding

The property of friction between macromolecules when molten plastic flows is called the viscosity of plastic, and the coefficient of this viscosity is called viscosity, so the viscosity is a reflection of the fluidity of molten plastic. The larger the viscosity, the stronger the viscosity of the melt. The worse the fluidity, the more difficult the processing.

Comparing the fluidity of a plastic is not based on its viscosity value, but on its melt flow index (called MFI): The so-called MFI is the unit of time under a certain melting temperature under the action of the rated pressure of the melt (Typically 10 minutes) Melt weight through a standard die. Expressed in g / 10min, the viscosity of plastics is not static. The changes in the characteristics of plastics, the influence of external temperature, pressure and other conditions can all contribute to the changes in viscosity.

Effect of molecular weight

The larger the molecular weight, the narrower the molecular weight distribution, and the larger the reflected viscosity.

Effects of low molecular additives

Low-molecular additives can reduce the interaction between macromolecules. Therefore, the viscosity is reduced. Solvents or plasticizers are added in some plastic molding times to reduce viscosity and make it easy to mold.

Effect of temperature viscosity

Temperature has a great influence on the viscosity of most molten plastics. Generally, the higher the temperature, the lower the reflected viscosity, but the magnitude of the decrease in the melt viscosity of various plastics varies.

PE / PP plastics. Increasing the temperature has little effect on improving fluidity and reducing melt viscosity. If the temperature is too high, the consumption will increase, but it will pay more.

PMMA / PC / PA and other plastics, viscosity will decrease significantly with increasing temperature. PS ABS increasing temperature will also have greater benefits for reducing viscosity and molding.