Views:1 Author:Site Editor Publish Time: 2021-04-08 Origin:Site
Plastic extrusion is to extrude molten plastic through a mold into a shape with a fixed cross-section. It is an effective method to produce a variety of shapes and is essential in industrial and household product applications. Since plastics are melted from a solid form and then liquefied, only thermoplastics can withstand extrusion. The characteristics of this plastic make it possible to recycle waste as well as post-consumer goods. We will find more about how products are manufactured by the pvc compound extruder.
The following knowledge points are listed below:
What is plastic extrusion
The manufacturing process of pvc extruder
When the polymer compound and additives enter the extruder continuously through the hopper in the form of granules, flakes, granules or powder, the plastic extrusion process begins. The screw gradually moves these materials along the barrel, in the process, generating enough heat to melt the plastic compound. The external heater helps to maintain the required temperature of the molten plastic as it moves inside the barrel.
When the molten plastic comes out of the barrel, it is forced through a mold, shaping it into the desired contour. The cooling part helps maintain the contour as the plastic solidifies and hardens.
In the plastic twin screw extrusion process, the thermoplastic raw material or resin is gravity fed into the cylinder of the pvc extruder from the hopper installed at the top. Additives such as colorants and UV inhibitors, whether in liquid or granular form, are often used and can be introduced into the resin that reaches below the hopper. This process has much in common with plastic injection molding, although the difference is that the process is usually continuous. Although injection molding can provide many continuous lengths of similar profiles, usually with reinforcement materials added, the finished product is pulled from the mold instead of extruding the fluid resin through the mold.
When the material enters the inlet near the rear of the barrel, it contacts the screw. The rotating screw pushes the plastic resin forward into the cylinder and heats it to the required melting temperature depending on the resin. In most processes, a heating zone controlled by three or more independent PID (Proportional-Integral-Derivative Controllers) is used to set a heating curve for the barrel, and the heating zone gradually rises from the back of the resin entering the front. The temperature of the barrel. This allows the plastic resin to gradually melt as it is pushed through the barrel and reduces the risk of overheating that can cause polymer degradation.
At the front of the barrel, the resin leaves the screw and passes through a reinforced screen to remove any contaminants. The crushing plate usually strengthens the screen because the pressure at this time may exceed 5000 psi (34 MPa).
The resin enters the mold of the pvc extruder after passing through the crushing plate. The mold is the contour or shape of the final product, and its design must make the molten plastic flow uniformly from the cylindrical contour to the contour shape of the product. At this stage, the uneven flow will generate unwanted stresses at certain points of the profile. These stresses can cause warpage during cooling. As long as it is a continuous outline, almost any imaginable shape can be created.
The product must now be cooled, which is usually achieved by pulling the extrudate in a water bath. Plastic is an excellent thermal insulation material, so it is difficult to cool down quickly. Compared with steel, the heat dissipation speed of plastic is 2000 times slower. In the pipe extrusion line, the sealed water bath utilizes a carefully controlled vacuum to prevent the newly formed pipe or pipe that is still in a molten state from collapsing. A set of cooling rolls are usually used in the sheet extrusion process to cool the sheet as it leaves the pvc extruder.
Sometimes, on the same production line, secondary processing may occur before the product has completed its operation. During the tape production process, the second pvc extruder melts the adhesive and applies it to the plastic sheet while the plastic sheet is still hot. Once the product has cooled down, it can be rolled up or cut into length for later use.
Plastic extruders are also widely used to prepare recycled plastic waste and/or raw materials, which are then washed, sorted and/or mixed into filaments suitable for mixing with resin pellets commonly used in the plastics industry.
So, after reading this article you may probably know how the products are made by the pvc granules making extruders.