Thermoplastic WPC Material Manufacturing Process
The processing method of the WPC extrusion process is basically the same on the surface as that of plastics. At present, the equipment which can be used for extrusion of wood-plastic composite materials mainly includes twin screw extruder and single screw extruder. The single – screw extruder is usually used for conveying and plasticizing materials. However, the traditional single-screw extruder is greatly restricted in the extrusion of wood-plastic composite materials, so the special design needs to be carried out on the screw so that it has a strong capacity of raw material transportation and mixed plasticization, so as to achieve the mixed refining pellet technology of materials before extrusion.
The twin screw extruder can be divided into parallel twin screw extruder and cone twin screw extruder. Parallel twin – screw extruder can directly process wood powder or plant fibre. Conical twin screw extruder with than “mixing” type equipment, its conical screw feeding period of larger diameter, can be compressed to material continuously, can shorten the retention period of material in the barrel, and the metering section diameter is small, small shear of molten material, this for processing thermoplastic wood-plastic materials is a big advantage, so-called “profile” of low speed, low energy consumption equipment.
In addition, the extruder head and the cooling and shaping system are also important parts related to the quality of extruded products. Because of the particularity of wood plastic composite and wood powder of high filling amount, make difference in liquidity and not easy to cooling and conventional mould and finalize the design equipment have been unable to meet the needs of the product, which makes the design of the head in addition to the design to ensure the smooth transition and reasonable flow rate distribution, also need to head to build pressure ability and the temperature control precision is the key consideration, and reasonable decorate head heating-cooling device, the cooling speed, high precision, achieve the goal of guarantee product quality and production.
Moulds are essential to the manufacture of wood-plastic products, regardless of the processing method. Based on the thermal sensitivity of wood-plastic composite materials, the wood-plastic mould generally adopts a larger structure size to increase the thermal capacity, thus enhancing the temperature stability of the whole machine head. The size along the extrusion direction is smaller to shorten the residence time of materials in the machine head. In addition to reasonable shape and accurate parameters of the mould, the surface treatment of the mould is also very important, especially in the extrusion process.
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