Requirements for the production process conditions of blow molded hollow products:
1 parison wall thickness. The thinnest wall thickness of the parison should be controlled at about 2 mm. The wall thickness is too small, and the strength of the product is difficult to ensure. If the wall thickness is too large, the shape of the parison and the shape of the inflation cavity are difficult. It is generally required that the ratio of the maximum to the minimum of the wall thickness of the parison shall not be greater than 2:1.
2 core rods. The diameter of the mandrel should be smaller than the minimum diameter of the finished product after inflation, in order to facilitate the removal of the mandrel after the blow molding product is formed.
3 inflation ratio. It refers to the ratio of the cross-sectional dimension of the product after inflation molding to the cross-sectional dimension of the parison. It is generally required to be controlled within 3.5:1, and the shrinkage of the molded product after inflation is about 0.5%. The ideal inflation ratio is 2 to 3.
4 length to diameter ratio of the parison. Refers to the ratio of the total length L of the parison to the diameter d of the neck of the container, which should be 1:d<10:1
The mold for blow molding hollow molded products for blow molding hollow product molding can be divided into a mold for injection molding of parison and a mold for inflation molding.
Blow molding products process parameters selection:
1 parison molding process parameters. The process parameters of several commonly used plastic injection molding parisons are shown in Table 1, which can be used as reference for production work.
Table is the process parameters of common plastic injection molding parison
Plastic name hot runner temperature / ° C melt injection temperature / ° C injection pressure / MPa mold temperature / ° C
Polystyrene 185～195140～24060～11040～70
Polyethylene 160～170150～18060～10040～80
Polypropylene 200～280240～28055～10040～80
Polyvinyl chloride 180～190170～19080～13035～70
Thermoplastic polyester 250～280250～280-100～105
2 parison inflation temperature. For the hot billet, the inflation temperature is based on its own heat, and the second is provided by the mold heating. The molded article can be inflated when the heating temperature inside and outside the parison and the respective portions tend to be uniform. For cold billets, the parison should be heated to a temperature suitable for inflation and then inflated. It is necessary to pay attention to the uniform heating temperature of each part of the parison, and the temperature difference is not easy to be too large. This is more difficult to control.
3 parison inflation air pressure. The compression of the parison requires compressed air. The pressure of this compressed air depends on the properties of the raw materials for the product and the temperature of the parison. Generally, the pressure of the compressed air is controlled to be 0.2 to 0.7 MPa. The viscosity of the raw material is low, and the air pressure is low; the viscosity of the raw material is high, and the air pressure is high. When the wall thickness of the product is low, take a low air pressure; when the wall of the product is thin, take a higher air pressure. It can also be judged from the appearance quality of the product. If the appearance surface pattern and the text of the product can be made clear, the air pressure of the inflated parison is more suitable for production. The rate of inflation of the inflated article should be determined by the quality of the shaped article, and should be taken as large as possible, which is advantageous for shortening the production cycle of the inflated article.
4 molding hollow product mold temperature. The mold temperature control of the molded hollow product is also determined by the properties of the raw materials for the product, and is generally controlled at 20 to 50 °C. The mold temperature is low, the blown billet is difficult, and the appearance quality of the product is not too good. At this time, it is improved by increasing the inflation rate and the inflation air pressure; the mold temperature is high, and the product is cooled after inflation. The time is prolonged, the product is more difficult to demold, and the production cycle is increased. In order to speed up the cooling rate of the inflated product, the mold temperature control is mostly regulated by circulating cooling water, and the water temperature is controlled between 5 and 15 °C. The mold is required to be made of an aluminum alloy material having good thermal conductivity.
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