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Wood Plastic Material Production Process

Wood plastic composite material refers to the low-value or waste biomass material as the main material, the use of polymer interface chemistry and the characteristics of plastic filling modification, mixing a certain proportion of plastic base material, and processing it after professional processing. A new type of material that can be recycled and processed. The biggest characteristic of wood plastic material is that it has multiple advantages of two different basic materials, natural wood and synthetic plastic. It has five characteristics:

  • Recycling of materials
  • The product can be plasticized
  • Application of environmental protection
  • Cost economy
  • Recycling

Wood plastic composite material production equipment is a new type of equipment that provides production for this material and is launched through independent integration and innovation.So what is the wood plastic material production process? Let us take a look.

Wood plastic material production equipment

The manufacturing of wood plastic composite materials mainly includes extrusion molding, hot press molding, injection molding and other processes, but the extrusion molding process is currently widely used and the most mature technology. According to the requirements of the production process, the equipment required for the entire production line is mainly composed of the following parts:

1. Biomass material preparation equipment This equipment is mainly composed of a wood chipper and a wood mill to form a mixing unit, which is mainly used for the preparation of biomass materials in wood plastic composite materials. The unit is required to crush all kinds of wood and agricultural residues, and produce biomass powder materials of different particle sizes according to the requirements of product manufacturing.

2. High-speed mixing unit This unit is composed of a high-speed hot mixer and a cold mixer. The hot mixed materials enter automatically, and the cold mixed materials are cooled and mixed to remove residual gas. It is mainly used for mixing, drying, batching, coloring and devolatilization of various resins and biomass powder materials.

3. Granulation equipment The main function of the granulation equipment is to make the wood plastic two-phase material realize the pre-plasticization process, which can realize the uniform mixing of the biomass powder material and the plastic under the melting condition, and is a wood plastic composite product. Pre-treatment for production. Due to the poor fluidity of wood plastic melt, the design of wood plastic material pelletizer and plastic pelletizer is not exactly the same. For different plastics, the design of the pelletizer is also different. The wood plastic composite pelletizer usually used for polyolefin plastics uses a parallel twin-screw extruder. The granulator used for polyvinyl chloride usually uses a conical twin-screw extruder. This is because polyvinyl chloride is a heat-sensitive resin, and the conical twin-screw extruder has strong shearing force and the length of the screw It is shorter than the parallel twin-screw extruder, which reduces the residence time of the material in the barrel. The outer diameter of the screw has a conical design from large to small, so the compression ratio is quite large, and the material can be plasticized more fully and uniformly in the barrel.

4. Extruder In the wood plastic composite manufacturing process of extrusion molding, the extruder is the key equipment to realize wood plastic composite manufacturing. Its performance not only has a great impact on the physical and mechanical properties of the material, but also has a great impact on the output per unit time, which affects the unit energy consumption and production cost. The extrusion models usually used in the production of wood plastic composite materials are mainly single-screw extruders and conical twin-screw extruders. The main function of the extruder is to complete the further plasticization of the material, provide a melt with uniform temperature and uniform composition, and carry out stable and controllable conveying, so as to realize the production.

Single screw extruder is mainly composed of three parts: extrusion system, transmission system and heating and cooling system. The extrusion system is mainly composed of a screw and a barrel; the transmission system group is composed of a motor, a speed regulation and a transmission device; the heating and cooling system is mainly composed of a heater and a refrigeration device. These systems can be designed with integrated modules to realize automatic control. Due to the high viscosity of the wood plastic composite melt, the screw is required to have strong material mixing, plasticizing and conveying capabilities, so a specially designed special screw design is required to meet the needs of production.

The main differences between twin-screw extruder and single-screw extruder are as follows:

  •  The twin-screw extruder is composed of two screws that mesh closely with each other;
  • The material conveying of the twin-screw extruder is forward displacement conveying, and the degree of displacement depends on the proximity of one screw to the corresponding groove of the other screw.
  • The material in the closely meshed counter-rotating screw can obtain the greatest positive displacement;
  • The material conveying speed distribution in a twin-screw extruder is much more complicated than that in a single-screw extruder. The twin-screw extruders used in the manufacture of wood plastic composite materials are mainly divided into two categories: parallel and conical twin-screw. Compared with single screw extruder. The twin-screw extruder has the following characteristics in the molding and processing of wood plastic materials:

    The material conveying efficiency of a single screw depends on the friction performance of the solid material and the viscosity of the melt. In the twin-screw extruder, the conveying of materials is carried out by the principle of positive displacement, and no pressure reflux is generated. Therefore, the material is easier to add than a single screw extruder.

    Because the length of the screw of the twin-screw extruder is short, the residence time of the material in the twin-screw extruder is short, which can avoid the occurrence of thermal degradation of wood fibers and reduce power consumption.

    The materials are sheared and mixed longitudinally and transversely, and have excellent homogenization and plasticization effects.

    It has excellent exhaust and self-cleaning functions.

    The flow rate of the twin-screw extruder is not sensitive to the die pressure, and it is more effective to extrude products with large sizes and areas. The flow rate of a single-screw extruder is more sensitive to die pressure.

    5. Forming mold

    The mold is an important part for cooling and forming the wood plastic melt to obtain extruded products. Because wood plastic composite materials usually have a high content of wood powder, the melt fluidity is poor and it is not easy to cool. Therefore, conventional molds and shaping equipment can no longer meet the needs of production. In addition to ensuring the smooth transition of the runner design and reasonable flow distribution, the design of the mold for the production of wood plastic composite materials also needs to streamline the inlet area of the die, which can increase the critical shear rate of the melt by 10 times Or more, thereby reducing melt fracture. In addition, the critical value of the wood plastic composite melt will increase with the increase in the aspect ratio of the die and the extrusion temperature, and has a greater relationship with the mold material. Therefore, the material used in the mold is required to have a higher heat capacity.

    The characteristics of special production equipment for wood plastic materials

    Although the extrusion processing methods and main equipment of wood plastic materials are similar to plastics on the surface, as an emerging industry with marginal, multi-faceted, and specialized characteristics, its equipment, technology and processes involve chemical engineering, fine chemicals, and precision. Machinery, hydraulic transmission, vacuum technology, heat conduction, fluid mechanics, sensor technology, electronic automatic control, computer programming and physical chemistry and other majors and disciplines, its production equipment is unique. After years of development and application, practice has proved that as a new type of material with independent characteristics, wood plastic materials are far more difficult to process than ordinary plastic products, and production equipment is becoming more and more specialized and specialized. The key technology for the production of wood plastic materials is to ensure that the wood powder has high fluidity and plasticization under the premise of high filling content, so as to promote the plastic melt to be fully combined with the wood powder to achieve the purpose of joint compounding. The product has high physical and mechanical properties and good use performance. Finally, products with excellent functions and high added value can be manufactured at a lower cost. Compared with processing plastics, wood plastic material production equipment has many new characteristics and requirements. In the production process of wood plastic composite materials, there are a large amount of wood or other biomass materials in the materials, which hinder the transfer of heat, so that the plasticization performance of the melt is reduced, the fluidity is deteriorated, and the extrusion resistance is increased. The torque of the screw increases, and the wood is easily decomposed at high temperature, which causes the quality of the product to decrease. Therefore, it requires the use of special processes in screw design to meet the requirements of good material plasticization performance and material conveying function at lower temperatures. In addition, due to the existence of a large amount of wood powder, it will increase the abrasion of the barrel and screw in the equipment. Therefore, the steel used in the equipment used for the production of wood plastic composite materials cannot follow the steel used in traditional plastic machinery. Due to the small specific gravity and large filling volume of wood materials, the volume of the feeding area is larger and longer than that of conventional models; if the volume of wood powder is large, the molten resin has strong rigidity, and a high back pressure resistant gearbox is required; the screw driving force is strong, so it should be used The screw with fast compression and melting and short metering section ensures short residence time of wood flour and so on. At the same time, the degree of fiber orientation of wood plastic composites during processing has a greater impact on product performance, so it is necessary to rationally design the flow channel structure to obtain appropriate fiber orientation to meet the performance requirements of the product. In terms of mold design, the melt fluidity of wood plastic composites is poor, and the melt self-repairing ability is poor, which can easily cause melt fracture.

    Therefore, it is required that the inner cavity has a higher smoothness or special materials are used for processing in the mold design.

    In addition, under the same strength requirements, wood plastic composites have a larger thickness than pure plastics, and they are mostly special-shaped materials with complex structures, which makes it more difficult to cool. Generally, water cooling is used, but for larger cross-sectional areas or complex structures Products also need to use special cooling devices and methods.

    The above is wood plastic material production process.I hope that wood plastic products can develop better and better and be accepted by more people.

    Seven Trust

    Seven Trust, Author

    China's leading wood-plastic manufacturer and supplier. Design inspiration and products - to provide customers with perfect outdoor landscape solutions.

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