What are the requirements for the production process conditions of blow molded hollow products?

Core tips: ① parison wall thickness. The thin wall thickness of the parison should be controlled at about 2mm, and the wall thickness is too small to ensure the strength of the product; The wall thickness is too large, so it is difficult to preheat the parison and shape the blow molding cavity. It is generally required that the ratio of large to small value of parison wall thickness shall not be greater than 2:1. ② Mandrel. The diameter of the core rod shall be smaller than the small diameter of the finished product after blowing, so as to facilitate the removal of the core rod after the blow molded product is formed. ③ Expansion ratio. It refers to the ratio of the cross-sectional dimension of the product and the cross-sectional dimension of the parison after blowing. It is generally required to be controlled within 3.5:1, and the shrinkage rate of the product after blowing is about 0.5.

① Parison wall thickness. The Zui thin-wall thickness of the parison should be controlled at about 2mm, and the wall thickness is too small to ensure the strength of the product; The wall thickness is too large, so it is difficult to preheat the parison and shape the blow molding cavity. It is generally required that the ratio of Zui large value to Zui small value of parison wall thickness shall not be greater than 2:1.

② Mandrel. The diameter of the core rod shall be smaller than the Zui small diameter of the blown product, so as to facilitate the removal of the core rod after the blow molded product is formed.

③ Expansion ratio. It refers to the ratio of the cross-sectional dimension of the product and the cross-sectional dimension of the parison after the expansion molding, which is generally required to be controlled within 3.5:1, and the shrinkage rate of the molded product after the expansion molding is about 0.5%. The ideal blowing ratio is 2 to 3.

④ Length diameter ratio of parison. It refers to the ratio of the total length L of the parison to the diameter D of the container neck, which shall be 1: d < 10:1

Blow molding mold for hollow products blow molding mold for hollow products can be divided into parison injection molding mold and blow molding mold.

Selection of process parameters for blow molded products

① Process parameters of parison forming. The process parameters of several commonly used plastic injection molding parisons are shown in Table 1, which can be used for reference in production.

The table shows the process parameters of commonly used plastic injection molding parisons

Plastic name: hot runner temperature / ℃ melt injection temperature / ℃ injection pressure / MPA mold temperature / ℃

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 blowing temperature. For the hot billet, the blowing temperature is provided by its own heat and the mold heat. When the heating temperature of the inside and outside of the parison and each part tends to be the same, the product can be blow molded. For cold billets, the parison shall be heated to a temperature suitable for the blowing requirements before blowing. Pay attention to the uniform heating temperature of all parts of the parison, and the temperature difference is not easy to be too large. This is difficult to control.

③ Air pressure for parison expansion. Compressed air is required for parison expansion, and the pressure of this compressed air depends on the performance of raw materials for products and parison temperature. Generally, the pressure of compressed air is controlled at 0.2-0.7mpa. The viscosity of raw materials is low, and the air pressure is low; The viscosity of raw materials is high, and the air pressure is high. When the product wall thickness is low, the air pressure shall be taken; When the product wall is thin, the air pressure shall be higher. It can also be judged from the appearance quality of the product. If the appearance surface pattern and text of the product can be made clear, the air pressure of the blown parison is more suitable for production. The inflation rate of inflated products shall be determined according to the quality of the molded products, and shall be as large as possible, which is beneficial to shorten the production cycle of inflated products.

④ Mold temperature for forming hollow products. The mold temperature control for forming hollow products is also determined by the properties of raw materials for products, and is generally controlled at 20-50 ℃. The mold temperature is low, it is difficult to blow the parison, and the appearance quality of the product is not ideal. At this time, it is necessary to increase the inflation rate and the inflation air pressure to improve; The mold temperature is too high, the cooling time of the product after blowing is prolonged, and the demoulding of the product is more difficult, which will also increase the production cycle. In order to speed up the cooling speed of the blown products, the mold temperature is controlled by circulating cooling water, and the water temperature is controlled between 5 and 15 ℃. The mold is required to be made of aluminum alloy material with good thermal conductivity.