Plastic Extruder Tips 1: The Common Pelletizing Extruder Classification

The Common Extruder Classification

Posted by Andy

1.Single Screw Extruder

The single screw extruder is the most common extruder, widely used in plastic pipe extrusion, plastic sheet extrusion, plastic profile extrusion, blow molding machine, injection molding machine, and plastic recycling pelletizing field. Here we just discuss its recycling usage.

The single screw extruder normally just use for single plastic waste recycling & pelletizing, like PP/PE/PC/ABS etc. waste. It is simple in design and cheap in price. It adopts involute gear drive, which has the characteristics of low energy consumption, low noise, stable operation, large bearing capacity and long life. But due to its material transport by the screw friction, it’s hard work with powderpaste material, glass fiber and the inorganic filler, and several different materials compounding extrusion. And if the waste is dirty, the die-head of the extruder will always work at high pressure, the melt material will be easy to flow back and come out from the degassing port. And the degassing port of single screw extruder is also not stronger then twin screw extruder. If the waste material has too much dirt and moisture, we have to use the double stage design extruder.

The waste soft plastic film, shopping bag, woven bag etc. using, compactor with double stage single screw extruder line

Waste hard plastic flake, chips etc. using, double stage single screw extruder line

2. Co-rotating Parallel Twin Screw Extruder

As you see from the words, the most important difference between single screw extruder and twin screw extruder is the screw number inside the barrel. Co-rotating twin screw extruder has two tight meshing screws. And due to its modular design of the screw and barrel, it can be easily repaired and adjust the screw combination to achieve the different compounding purpose. But the single screw extruder just has no or only a little different mixing ability. The twin screw extruder has the characteristics of high torque, high rotational speed, and low energy consumption, so it has a unique advantage in the processing of high viscosity, heatsensitive materials. The complex flow spectra of the materials in twin-screw extruder show the advantages of the single screw extruder in a macroscopic way, for example, full mixing, heat transfer good, melting capacity, strong exhaust capacity and material temperature control good.

Examples of common applications:

  1. Glass fiber reinforced, flame retardant material granulation (PA6, PA66, PET, PBT, PP, PC enhanced flame retardant, etc.)
  2. High filling material granulation (PE, PP filled CaCO3, TiO2, Tale etc. )
  3. Heat-sensitive materials granulation (PVC, XLPE cable materials etc.)
  4. Color masterbatch (PP, PE, PS, ABS, PC etc. black/white/yellow/red/green/blue color masterbatch)
  5. Antistatic masterbatch, Alloy, coloring, low filled blending granulation
  6. Cable material granulation (sheath materials, insulating materials etc.)

3.Conical Twin Screw Extruder

Conical twin-screw two screw in the barrel of each other meshing, different rotation, a screw the top of the screw and another screw root has a reasonable gap.
Due to the different rotation, a screw on the material spiral forward road by another screw blocked, the material can only be driven by the thread, through the various parts of the gap axis. When the material through the two screw between the radial clearance, as if, through the roll gap between the two rollers, the agitation and shearing are very strong, thus, the plasticizing uniformity, especially suitable for the processing of PVC plastic.
The compression ratio of conical twin-screw is not only formed from deep and shallow, but also by the diameter of the screw rod from big to small, so the compression ratio is quite large, so the material is more fully and evenly molded in the barrel, which guarantees the quality of the products. Under this premise, can increase the rotational speed, thus enhances the extrusion quantity.
Any problems you meet, please feel free to contact us:
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