The Principle of Plastic Extruder

A plastic extruder is a kind of industrial machinery and equipment widely used for processing pipes, rods, monofilaments, sheets, films, wire and cable coatings, profiles, etc.

The principle of the plastic extruder is to melt and plasticize solid plastic under the conditions of extruder heating and screw rotation and to form a continuous plastic product with the same cross-section and shape as the die head through A specific shape. The main materials used for manufacturing are carbon structural steel, alloy tools, etc. Some extrusion dies also embed wear-resistant materials such as a diamond in the parts that need to be wear-resistant. The extrusion process is usually only applicable to the production of thermoplastic products. It is structurally different from injection molds and compression molds.

There are three main different process principles for plastic extruders.

Foam extrusion: Thermoplastic elastomers TPV can be foamed by chemical and mechanical methods. For chemical foaming, a blowing agent such as bicarbonate of soda can be used. Achievable foam densities range from 0.97 specific gravity (typically unframed TPV) to 0.70. Lower densities are subject to patenting. Blowing agents degrade at 180°C to 190°C, as most TPV is based at 195 to 215°C.

Multi-layer extrusion: Co-extrusion is a technology that combines two materials into one component in one extrusion process. Two extruders are connected in series to provide a bottom die and co-extrude the corresponding polymer materials along the corresponding channels to obtain an extruded adhesive of both materials. Homogeneous materials such as TPV and polypropylene can be fused. Multi-layer extrusion is a good way to mix hard and soft materials. Typically, a high-durometer part, such as thermoplastic elastomer TPV, is often used as a support structure for the part, while a low-durometer material provides flexibility. This is common in sealing applications where the sealing area is soft, and the softer material can be crushed to obtain a good seal. Using the stiffer thermoplastic elastomer TPV as a rigid material instead of polypropylene when balancing the flow field is simpler.

Welded joints: Heat welding is a common material joining extruded gels made from TPV. Heat is introduced to the joint surface, which melts, then the surfaces are bonded together, and slight pressure is applied to ensure no gas enters the interface. After cooling, the joint is almost as strong as the part itself. Another method of joining extruded parts is to use a gluing system.

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