1. Plastic Extrusion Definition
Plastic extrusion is a widely used manufacturing process in the modern industry, and it is can be understood as a method of processing plastics from raw materials into industrial products. Specifically, the raw material is pushed and/or pulled through the mold, and then cooled and shaped into a long object with a constant cross-section.
A significant feature is that extrusion should be continuous (producing indefinitely long product) or semi-continuous (repeatedly producing many shorter pieces) such as pipes, tubes, etc. If it is not a continuous long product, it needs to be produced by other machines such as pipe fittings, it needs injection molding machines to produce.
2. What Kind Of Plastic Raw Materials Can Be Extruded Into Products
The plastic extrusion process is suitable for all polymer materials. Almost all thermoplastics can be extruded. The opposite of thermoplastic is thermosetting plastics and can also be extruded, but only a few thermosetting plastics such as phenolic plastics.
What is thermoplastic?
Thermoplastic also named thermosoftening plastic, is a plastic polymer material that is pliable and moldable under certain temperature conditions, plastics can be softened or melted into any shape, and the shape will not change after cooling; this state can be repeated many times and always has plasticity, and this repetition is only a physical change, and this plastic is called thermoplastic plastic. Most plastics used in daily life fall into this category.
Including polyethylene (PE), polypropylene(PP), polyvinyl chloride(PVC), polystyrene(PS), polyoxymethylene(POM), polycarbonate(PC), polyamide(Nylon), acrylic plastics(PMMA), other polyolefins, and their copolymers, polysulfone, polyphenylene ether.
What are thermosetting plastics?
Thermosetting Plastic, also called thermoset, is a polymer that solidifies after heating is insoluble and non-melting. The biggest difference between thermosets and thermoplastics is the crosslinking process.
The “thermoset” materials that can be extruded are usually cross-linkable thermoplastic materials (or mixtures). Such materials have a relatively large molecular weight and have a certain melt or bulk strength under processing temperature conditions. After the extruder die head can still maintain the shape, and then complete the vulcanization/crosslinking in the subsequent sections. There are many such extrusion vulcanized products, such as rubber sealing strips, hoses, and cross-linked polyethylene cable sheaths.
3. What Kind of Products Need to Use the Extrusion Process?
Plastic extruded products include pipes, plates, rods, sheets, films, monofilaments, cable coatings, various profiled materials, and composites of plastics and other materials.
There are so many possibilities for forming shapes. The flat nozzle extrudes films, foils, and plates. The nozzles with larger openings can form solid rods, tubes, or flat airfoils. The extrusion molding process can also produce irregular shapes, such as angular pieces (such as L or T shapes), and complex structures such as plastic door and window profiles.
4. Extrusion Process
In the extrusion process, mainly refers to the extrusion of a screw to force the polymer material melted by heat to pass through the die of the die under pressure. A molding method for forming a continuous profile with a constant cross-section. The extrusion molding process mainly includes the processes of feeding, melting and plasticizing, extrusion molding, shaping, and cooling.
The extrusion process can be divided into two stages:
- The first stage is to plasticize the solid plastic (that is, turn it into a viscous fluid) and pass it through a special-shaped die under pressure to become a continuous cross-section similar to the shape of the die.
This process requires that the plastic fragments or pellets are dried in a hopper, and the polymer resin is heated to a molten state when it is fed to the extrusion screw. Then, the material is conveyed forward by the screw and passed through the die. The die molds the heated material into the desired shape.
- The second stage is to use an appropriate method to make the extruded continuum lose its plastic state and become solid to obtain the desired product.
After passing through the die, the heated material is transformed into a continuous polymer product by blowing air or cooling in a water tank.
5. What Kind Of Machinery is Needed to Complete the Extrusion Production Process
The screw extruder is the machinery needed to complete the extrusion process, and there are downstream auxiliary machines to complete the production of products.
Plastic extruders are basically classified according to the number of screws, twin-screw extruders, single-screw extruders, and rare multi-screw extruders and screw-less extruders.
Generally speaking, it is based on the products you need to produce, the form of raw materials, and the output and other requirements to determine which screw-type machine to use.
This article mainly describes the definition of the plastic extrusion process, as well as the applicable raw materials and what kind of products need to be produced by an extruder.
It can give a brief understanding of the industrial production process of extrusion, and the specific introduction of the extruder machine will be described in detail in addition.