Category of plastic extruder
The plastic extruder needs to go through three stages in the extrusion molding of plastics, namely raw material plasticization, molding, and cooling. Plastic extruders are also divided into many different types, with screw extruders including single screw extruders, twin-screw extruders, multi screw extruders, etc; Extruders can be divided into continuous extrusion and discontinuous extrusion according to their functions. The output of the extruder is determined by the rotational speed of the screw. The screw speed can affect the output of plastic extruded by the extruder and also affect the plasticization effect.
Plastic extruders can be divided into single screw extruders, twin-screw extruders, and multi screw extruders based on the number of screws. At present, single screw extruders are widely used and suitable for extrusion processing of general materials. The twin-screw extruder has the advantages of less heat generated by friction, more uniform material shear, greater screw conveying capacity, stable extrusion volume, longer material retention in the barrel, and uniform mixing.
Single screw extruders play an important role in both plasticizing granulation machinery and molding processing machinery. In recent years, single screw extruders have made great progress in the industry.
The twin-screw extruder has good feeding characteristics and is suitable for powder processing. It also has better mixing, exhaust, reaction, and self-cleaning functions than the single screw extruder. Its advantage is demonstrated when processing plastics and blends with poor thermal stability. On the basis of twin-screw extruders, multi screw extruders such as Guanghua Plastic Extruder have been developed to facilitate the processing of blends with poor thermal stability.
- According to the number of screws, they are divided into single screw extruders, twin-screw extruders, and multi screw extruders;
- According to whether there is a screw in the extruder, it is divided into screw extruder and plunger extruder;
- According to the operating speed of the screw:
Ordinary extruder: speed below 100r/min;
High speed extruder: with a speed of 100-300r/min;
Ultra high speed extruder: with a speed of 300-1500r/min.
- According to the assembly structure classification of extruders, there are integral extruders and separate extruders;
- According to the spatial position of the screw in the extruder, it can be divided into horizontal extruder and vertical extruder;
- According to whether the extruder exhausts during the processing, it can be divided into exhaust extruders and non exhaust extruders.
Forming principle of plastic extruder machine
The extrusion method of a plastic extruder generally refers to melting plastic at a high temperature of around 200 degrees, and the melted plastic is then formed into the desired shape when passing through a mold. Extrusion molding requires a deep understanding of plastic properties and rich experience in mold design, and is a molding method with high technical requirements.
Extrusion molding is a method in which materials are continuously molded through a die in a flowing state by heating and pressing in an extruder, also known as “extrusion molding”. Compared with other molding methods, it has the advantages of high efficiency and low unit cost.
Extrusion method is mainly used for the molding of thermoplastic plastics, and can also be used for certain thermosetting plastics. The extruded products are continuous profiles, such as pipes, rods, wires, plates, films, wire and cable cladding, etc. In addition, it can also be used for plastic mixing, plasticizing granulation, coloring, blending, etc.
The extruded product can be called a “profile”, but due to its irregular cross-sectional shape, it is also known as a “profile”.
Working principle of plastic extruder
By applying pressure and shearing, solid plastic is transformed into a uniform and consistent melt, which is then sent to the next process. The production of melt involves processes such as mixing color masterbatch and other additives, blending resin, and re crushing. The finished melt must be uniform in concentration and temperature. The pressure must be large enough to extrude the viscous polymer.
The plastic extruder completes all the above processes through a barrel with a screw and a spiral channel. Plastic pellets enter the barrel through a hopper at one end and are then transported to the other end of the barrel through a screw. In order to have sufficient pressure, the depth of the threads on the screw decreases as the distance to the hopper increases. External heating and internal heat generated by friction between plastic and screws soften and melt the plastic. Different polymers and applications often have different design requirements for plastic extruders. Many options involve discharge ports, multiple feeding ports, special mixing devices along the screw, cooling and heating of the melt, or no external heat source (adiabatic plastic extruder), relative size changes in the gap between the screw and the barrel, and the number of screws. For example, compared to single screw plastic extruders, twin-screw plastic extruders can achieve more thorough mixing of the melt. Series extrusion is the melt extruded by the first plastic extruder, which is used as raw material to supply the second plastic extruder, and is usually used to produce extruded polyethylene foam.
The characteristic size L/D of a plastic extruder is the ratio of the length (L) of the screw to the diameter (D) of the screw. Plastic extruders usually consist of at least three sections: the first section, located near the feeding hopper, is the feeding section. Its function allows materials to enter the plastic extruder at a relatively stable rate. In general, to avoid blockage of the feeding channel, this part will maintain a relatively low temperature. The second part is the compression section, where the melt is formed and the pressure increases. The transition from the feeding section to the compression section can be sudden or gradual (gentle), with the last measuring section closely adjacent to the outlet of the plastic extruder. Its main function is to ensure that the material flowing out of the plastic extruder is uniform and consistent. To ensure the uniformity of composition and temperature in this section, the material should have sufficient residence time.
At the tail of the barrel, the plastic melt exits the plastic extruder through a head designed in an ideal shape, where the extruded melt flows through.
Another important part is the driving mechanism of the plastic extruder. It controls the rotation speed of the screw, which determines the output of the plastic extruder. The required power is determined by the viscosity (flow resistance) of the polymer. The viscosity of polymers depends on temperature and flow rate, and decreases with increasing temperature and shear force. Plastic extruders are equipped with filters that can block impurities in the filter. To avoid work stoppage, the filter screen should be able to be automatically replaced. This is particularly important when processing resins with impurities, such as recycled materials. The screw of the extruder is divided into feeding section, plasticizing section, and melting section. The temperature is based on the process parameters of the plastic particles, and the model is divided into 20, 36, 52, 65, 75, 95, 120, and 135 according to the screw diameter. There are many types of plastic particles that change their original state by the movement of the screw after heating, depending on the specific application. The capacity of the frequency converter is proportional to the diameter of the screw, and can be adjusted according to the different raw materials.
Zhangjiagang Carry Technology Co., Ltd. provides stable performance, high-quality and cost-effective plastic twin-screw/single-screw extruders and related PVC HDPE PP products extrusion production lines for customers to choose from, welcome to consult.