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Home / How to control viscosity in electric injection molding machine of medical products?

How to control viscosity in electric injection molding machine of medical products?

2024/08/12 By Topstar

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When manufacturing high-precision medical products, controlling the viscosity during injection molding can ensure the quality of the finished product. Medical products have very high standards for cleanliness and precision so that everyone will choose an electric injection molding machine as the core machine in the production process. In this article, we will share how Topstar’s electric injection molding machine can effectively control the viscosity of medical products during injection molding.

Viscosity in Injection Molding

The viscosity of a material determines how easily it flows through the mold cavity, which affects the overall quality and precision of the final product. Controlling viscosity can avoid defects such as incomplete filling, warping, or internal stress. Electric injection molding machines have the advantages of higher precision, higher energy efficiency, and better repeatability than hydraulic injection molding machines. They use electric drives to control injection speed, pressure, and temperature, which all affect the viscosity of the material during the molding process. By fine-tuning these parameters, manufacturers can ensure that the material flows smoothly and consistently, filling the mold cavity without defects.

The effect of temperature control of electric injection molding machine on viscosity

The temperature control of electric injection molding machines is one of the main factors affecting viscosity. The viscosity of polymer melt decreases as temperature increases, making it easier for the material to flow through the mold. If the temperature is too high, the polymer degrades, resulting in discoloration, surface defects, or impaired mechanical properties in medical products with strict transparency, clarity, and surface finish requirements. On the other hand, a too low temperature will increase the viscosity, making it difficult for the material to flow properly and resulting in incomplete filling or internal stress in the molded part.

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Injection speed and pressure of electric injection molding machine

Injection speed and pressure in injection molding are two key parameters that can directly affect the viscosity of the material during the molding process. It affects the shear rate of the polymer melt, which in turn affects the viscosity. At higher injection speeds, the shear rate increases, causing the material to exhibit shear-thinning behavior. That is, its viscosity decreases as the shear rate increases. However, an injection speed that is too high can cause problems such as flow marks, jetting, or overfilling, especially in precision medical parts, where accuracy is critical.

Pressure can stabilize the flow and ensure the mold cavity is filled without cavitation or voids. High pressure can help overcome the material’s resistance flowing into the mold, reducing the possibility of incomplete filling. If the pressure is too high, it over-compresses the material, resulting in problems such as overflow and dents in the final product.

Topstar’s electric injection molding machine uses an integrated injection unit, which has higher structural stability and rigidity and can more accurately control the injection speed. Regarding pressure, a linear guide rail is used to lower the damping, the pressure detection more sensitive, and the pressure can be controlled more accurately.

The role of screw design in controlling viscosity

The screw is responsible for melting, mixing and conveying polymer materials through the machine and is a key component that determines the flow characteristics and overall viscosity of the material. The screw is usually designed with multiple zones, each of which has a specific purpose in the material preparation process. The feed zone is where the polymer particles are introduced and begin to melt, the compression zone further melts and homogenizes the material, and the metering zone ensures that the melt is evenly mixed and ready for injection. The design of these zones, including their length, pitch and pitch depth, can significantly affect the viscosity of the material.

Topstar’s electric injection molding machine uses a special screw that can accurately control the screw speed and back pressure to achieve good plasticizing quality and high efficiency. It can reduce the plasticizing temperature and AA value, effectively improve product shrinkage and increase transparency.

The effect of the cooling system on viscosity control

Appropriate cooling in injection molding can avoid solidification of the material in the mold. It will not cause defects such as warping and shrinkage that damage the integrity of the medical product. Electric injection molding machines usually achieve cooling through mold cooling channels and external cooling systems. The cooling channel in the mold is to adjust the temperature of the mold and material during the cooling stage to ensure that the polymer solidifies at a controlled rate.

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The external cooling system mainly uses auxiliary equipment such as chillers to manage the mold temperature and hydraulic system in the electric injection molding machine. They can ensure that the machine runs at the optimal temperature, prevent overheating and maintain consistent viscosity control. The fully computerized thermostat accurately controls the water temperature at 5-35℃. Ensure the material reaches the correct viscosity when cooling, producing high-quality medical products.

Achieving optimal viscosity control

From temperature control and injection speed to the cooling system, each factor affects the material’s flow characteristics and the product’s quality. By leveraging electric injection molding machines’ precision and speed capabilities, manufacturers can fine-tune processing parameters to achieve the desired viscosity, producing plastic parts with the desired dimensional accuracy and surface finish.

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