What are the molding methods of hollow blow molding equipment?
The production principle of hollow blow molding equipment and its molding method The so-called blow molding machine is also called hollow blow molding machine. The plastic is melted and quantitatively extruded in the screw extruder, then formed through the mouth film, then cooled by the air ring, and then blown into the mold. A rapid approach to plastic processing. The tubular plastic billet obtained by extrusion or injection molding of thermoplastic resin is placed in a split mold while hot (or heated to a softened state), and compressed air is passed into the billet immediately after the mold is closed, so that the plastic billet is blown and close to the inner wall of the mold, and various hollow products are obtained after cooling and demoulding.
The process of blow molding machine/began to be used to produce low density polyethylene vials during World War II. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, the technology of blow molding machines has been widely used. The volume of hollow containers can reach thousands of liters, and some production has been controlled by computers. The plastics suitable for blow molding are polyethylene, polyvinyl chloride, polypropylene, polyester, etc., and the resulting empty containers are widely used as industrial packaging containers.
The molding method of hollow blow molding is introduced:
Because of the difference in material, processing requirements, output and cost, different blow molding methods have different advantages in processing different products.
Blow molding of hollow products includes three primary methods:
1, extrusion blow molding: mainly used for the processing of unsupported billets;
2, injection blow molding: mainly used for the processing of the billet supported by the metal core;
3, stretch blow molding: including extrusion a stretch a blow molding, injection a stretch a blow molding two methods, can process biaxial orientation products, greatly reduce the production cost and improve product performance.
In addition, there are multi-layer blow molding, press blow molding, dip blow molding, foam blow molding, three-dimensional blow molding. But 75% of the blow molded products are extrusion blow molded, 24% are injection blow molded, and 1% are other blow molded; Of all blow molding products, 75% are bidirectional stretch products. The advantages of extrusion blow molding are high production efficiency, low equipment cost, wide selection of molds and machinery, the defect is that the scrap rate is high, the recycling of waste, the use of poor, the thickness of the product control, the dispersion of the material is limited, and it is necessary to repair the edge operation after forming. The advantage of injection blowing is that there is no waste in the processing process, the wall thickness of the product can be well controlled and the material can be scattered, the fine neck product has high molding accuracy, the product surface is smooth, and the small batch production can be economical. The defect is that the cost of molding equipment is high, and to a certain extent, it is only suitable for small blow molded products.
The process conditions of hollow blow molding require that the compressed air of the medium billet of the blow mold must be clean. Injection blow molding air pressure is 0.55 ~ 1MPa; Extrusion blow molding pressure is 0.2l ~ 0.62MPa, and tensile blow molding pressure is often required as high as 4MPa. In the plastic solidification, the low pressure makes the internal stress of the product low, the stress dispersion is more uniform, and the low stress can improve the tensile, impact, bending and other properties of the product.
