Degassing, drying, conveying - vacuum technology is used in a variety of processes in the plastics industry.
During processing, thermoplastics are melted in an extruder and degassed in the extruder's screw section.
A vacuum is used to extract gaseous and vaporous components from the melt. All low-molecular substances are extracted to obtain optimal quality thermoplastic with a smoother surface, more strength, better insulating properties and a lower off gassing rate.
Calibrating table (profiling)
Plastic material that has been melted and degassed in the extruder is processed into continuous profiles on the calibrating table. Typically, these profiles are made into pipes or various technical profiles for windows, cable ducts, medical tubing, etc.
The plastic material is suctioned into a negative mold. For cooling and lubrication purposes, a film of water is generated between the inside of the mold and the continuous work piece and is steadily extracted by the vacuum pump.
For the production of EPS blocks and molded parts, pre-expanded polystyrene beads are first blown into a mold by a side-channel blower and then pressurized with steam. Finally, they are polymerized and "baked" into molded parts. To prevent deformations during this process - which can easily take up to 3 to 4 minutes for large blocks - the parts must be cooled. A vacuum applied to these parts ensures that they retain their shape and that the water evaporates in a flash. Heat produced by the evaporation process is drawn out of the workpiece, thereby speeding up cooling.
Before pellets are further processed in an extruder, a pneumatic conveyor (see below) transports them to a dryer through which warm air is circulated from a closed-circuit system. The air in the dryer absorbs moisture from the pellets, which is then evacuated to the outside by means of a hygroscopic agent. Periodically, the drying agent itself must have hot air blown through it in order to regenerate it.
Pneumatic conveying systems
At various stages in the production process, plastic pellets must be transported from one place to another (for example, from the silo to the dryer). This process can be automated and accelerated with a pneumatic conveying system. A pipeline is run from the starting point to the destination and connected to a vacuum pump or compressor.
The air in the pipeline is "loaded" with the material to be conveyed - comparable to a strong wind which, depending on its velocity, can stir up leaves or at hurricane strength, can even tear the roofs off houses. Depending on the bulk weight of the material and length of the pipeline, the system is designed so that the vacuum pump (vacuum conveying) or compressor (pressure conveying) generates enough air speed to pick up the material and convey it to its destination without depositing it in the pipeline.
Because pneumatically conveying plastic pellets results in a lot of dust, a filter system is also recommended.
Extraction and compression of vinyl chloride gas
During the production of PVC, liquid vinyl chloride is polymerized under pressure in the autoclave to form polymerized PVC. The gaseous monomers that are also produced are then pumped out, compressed and liquefied.