In the process of plastic processing, it is often necessary to exhaust. The sources of gas are as follows:
One is the air entrained between particles and the water adsorbed on the surface; Second, volatile substances remained in the raw materials. For example, many plastics are polymerized by solution method. After polymerization, the solution should be concentrated, granulated, and the monomer, catalyst and other volatile residues with incomplete solution and reaction should be removed. However, a very small amount will remain in the plastic particles; Third, some components will produce gas during processing, such as slight decomposition caused by long-time stay at high temperature or too strong screw shear.
The gas generated in the process of appeal processing must be eliminated, otherwise there will be internal or surface bubbles, dark surface and other defects in the manufactured particles or molded products, which may also affect the physical, mechanical and chemical properties of the products.
Therefore, exhaust is a very important part.
According to the process requirements, the exhaust port in the extruder barrel can be operated under atmospheric pressure or vacuum. The most typical mixing process includes two kinds of exhaust. The extruder can be equipped with multiple vacuum vents to remove a large amount of solvents or monomers, so as to keep the residual volatiles in the finished product at a low level.
For the co-rotating twin screw extruder, a variety of exhaust port designs have been developed to adapt to various applications and materials. These designs include exhaust port feeder, extended exhaust barrel, side exhaust port, etc.
Composition of vacuum system:
Exhaust chamber of extruder + manual ball valve + one-way valve (optional) + vacuum tank + ring vacuum pump (installed on the bottom plate)
Vacuum degree in operation is generally -0.06~-0.09mpa;
How to operate the vacuum exhaust of twin screw extruder?
- Firstly, open the upper cover of the condensate tank, add clean tap water to the middle of the upper window after cleaning, pad the sealing ring, install the filter plate and upper cover, and close the water valve.
- After the main machine enters the stable operation state, start the vacuum pump, open the inlet valve of the vacuum pump at the same time, observe the water volume at the outlet pipe end of the vacuum pump, and adjust to the appropriate working water volume.
- Open the exhaust chamber cover and observe the filling and plasticizing state of the materials in the screw groove from the exhaust outlet. If it is normal, slowly open any condensate inlet and outlet valve, cover the exhaust chamber and condensate tank, and the vacuum degree shall be displayed.
- If there is material emission at the exhaust port, it can be solved by adjusting the screw speed or vacuum degree of the host and feeder.
- When cleaning the materials emerging from the exhaust chamber, do not touch the cleaning tool against the rotating screw.