Hollow moulding is to fix the tubular or billet materia […]
Hollow moulding is to fix the tubular or billet material which is still in the plasticized state by extrusion or injection into the moulding die, and immediately introduces compressed air to force the material to expand and stick to the wall surface of the mould cavity. After the mould is cooled and demoulded, the mould is obtained, that is, a processing method of the desired hollow product is obtained.
Suitable plastics for hollow moulding are high pressure polyethylene, low pressure polyethylene, hard polyvinyl chloride, soft polyvinyl chloride, polystyrene, polypropylene, polycarbonate, and the like. According to the different moulding methods of the parison, the hollow moulding is mainly divided into two types: extrusion blow moulding hollow moulding and injection blow moulding hollow moulding. The advantage of the extrusion blow moulding hollow moulding is that the structure of the extruder and the extrusion blow moulding mould is simple, and the disadvantage is that the wall thickness of the parison is inconsistent, and the wall thickness of the plastic product is likely to be uneven.
The advantage of the injection blow moulding hollow moulding is that the parison has a uniform wall thickness and no flash. Since the injection parison has a bottom surface, the bottom of the hollow product does not have a seam and a seam, and is not only beautiful but also high in degree. The disadvantage is that the moulding equipment and the mould used are expensive, so this moulding method is mostly used for mass production of small hollow products, and there is no extensive extrusion blow moulding method in use.