How Does A Plastic Extruder Work?

Pressure and shearing are used to convert solid plastic into a uniform melt, and the melt is sent to the next process. The production of melt involves the process of mixing additives such as color masterbatch, blending resin, and repulverizing. The finished melt must be uniform in concentration and temperature. The pressure must be strong enough to squeeze out the sticky polymer.
The plastic extruder completes all the above processes through a barrel with a screw and spiral path. The plastic pellets enter the barrel through the hopper at one end of the barrel, and are then transported to the other end of the barrel through the screw. In order to have sufficient pressure, the depth of the threads on the screw decreases as the distance from the hopper increases. External heating and internal heat due to friction between the plastic and the screw cause the plastic to soften and melt. Different polymers and different applications often have different design requirements for plastic extruders. Many options involve discharge openings, multiple feed openings, special mixing devices along the screw, cooling and heating of the melt, or no external heat source (insulated plastic extruders), relatively variable gap between screw and barrel size, and the number of screws, etc. For example, a twin-screw plastic extruder can mix the melt more fully than a single-screw plastic extruder. In tandem extrusion, the melt extruded from the first plastic extruder is used as raw material to feed the second plastic extruder, usually used to produce extruded polyethylene foam.
The characteristic dimensions of a D L plastic extruder are the diameter of the screw (D) and the ratio of the screw length (L) to the diameter D L/D (D). A plastic extruder usually consists of at least three sections. First Section, near L/D) The hopper is the feeding section. Its function allows the material to enter the plastic extruder at a relatively smooth rate. Under normal circumstances, in order to avoid clogging of the feeding channel, this part will be kept at 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). The last partial metering section is close to the exit of the plastic extruder. Its main function is to ensure that the material flowing out of the plastic extruder is uniform. In order to ensure the uniformity of composition and temperature, the material should have sufficient residence time.
At the end of the barrel, the plastic melt leaves the plastic extruder through a die head designed to the ideal shape through which the extruded melt flow passes.
Another important part is the drive mechanism of the plastic extruder. It controls the rotation speed of the screw, which determines the output of the plastic extruder. The power required is determined by the viscosity (resistance to flow) of the polymer. The viscosity of polymers depends on temperature and flow rate, decreasing as temperature and shear force increase. Plastic extruders are equipped with filters that can block impurities on the filters. To avoid downtime, the filter should be automatically replaceable. This is particularly important when processing resins with impurities, such as regrind. 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. The model is divided into 20, 36, 52, 65, 75, 95, 120, and 135 according to the screw diameter. After the plastic particles are heated, the original state is changed by the movement of the screw. There are many types, 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.