What should be paid attention to in the design of extrusion dies for plastic products?
The design of plastic extrusion dies includes many aspects of design. At the same time, considering their impact on the processing and performance of plastic products, the guidelines for plastic extrusion design are listed below.
In the process of wall thickness change of plastic products, if the thickness change is too large, there may be problems in the process of balancing the flow field. The thickness of the rib should be 50% of the nominal wall thickness, and the radius should be carried out on this basis. design.
2. Radius of plastic fittings
Plastic parts use rounded corners instead of transitions for sharp changes, and the radius of the extruded part is 0.20mm.
Plastic products may have hollow sections in cross-section, extrusion dies may initially have a hollow cross-sectional shape, and compressed air may be used in the hollow cross-section to maintain that shape during cooling. Another method is to use a vacuum outside the extruder to help the hollow cross-section hold its shape.
The more hollow parts of injection molding parts, the more complex the design of the mold, and the more difficult the maintenance of the contour shape, unless there are design requirements, hollow parts should be avoided. Injected air blowing inwards during extrusion is a method of cooling the inner walls of the part, which requires air to circulate along the cutting line or punching direction.
4. Foam extrusion
Plastic products thermoplastic elastomer tpv can be foamed by chemical and mechanical methods. For chemical foaming, blowing agents can be used, achievable foam densities range from 0.97 (typical unfoamed tpv) to 0.70 specific gravity. Lower densities are subject to patent, blowing agents at 180°C to 190°C will degrade because most tpv bases are run at 195°C to 215°C.
For the mechanical method, water is the working medium, and here, the technology called "water foaming" is a patented technology. Specialized equipment is required to obtain a consistent foam structure and density, with densities reduced from 0.97 to 0.20. Densities in this range can be obtained by controlling processing techniques, the reduction in density affects mechanical properties and is therefore classified as a shape in application design.