Actually film is finished by blown production with auxiliary extruder . Can be classified as extrusion, and sometimes also could finished by the blow molding.
While blowing by molding, the original material passed the extrusion machine and annular orifice into cylindrical for extrusion, quantitative of compressed air in the membrane tube drum again , the transverse blown; after cooling of the membrane tube is import traction roll, stacked in a double fold films, with constant speed into crimping device, is film semi-finished products. Blow molding process in accordance with the film into the direction of blowing, blowing and blowing. PVC film blowing and blowing method under the above.
In addition, the film after a blow, after re heating, in the viscoelastic state for the two blow, after cooling, can be obtained with a certain shrinkage of the heat shrink film.
Blowing method commonly used:
1, flat blowing on the up blow, suitable for high viscosity of plastics, such as PVC, PS, PE, etc.
2, flat blowing extrusion down blow, suitable for small viscosity of plastic, such as PA, PP, but does not apply to the production of thin film.
3, flat extrusion on same level, suitable for small size of the film, high viscosity, such as PE, PVC, etc..