The analysis and solution of the deformation defects of blow molding products are as follows: The greater the degree of deformation of the blow molded product , the proportional decrease in its appearance satisfaction and performance, and the serious deterioration of the product. The deformation of the blow molded product is not only unfavorable to the quality of the product, but also disadvantageous to the production and production cost of the blow molded product. The thermophysical properties of the plastic material and the conditions and parameters of the blow molding process have varying degrees of influence on the deformation of the blow molded article.
Effect of thermophysical properties of materials on deformation
(1) The use of a plastic having a low melting point and good fluidity, because of its small shrinkage rate, rapid cooling, and low deformation, can improve product quality and yield.
(2) The use of cyanide pigments in the blow molding plastic processing formulation will affect the crystallinity of the polyethylene and cause deformation of the product;
(3) The primary color blow molded products produced by the raw materials without adding any pigment are not easily deformed, and the quality and yield of the products can be improved;
Product wall thickness difference and cooling effect on deformation
(1) The structural design of the blow molded product directly affects the wall thickness difference and cooling of the product. The wall thickness difference is large, resulting in a large difference in cooling rate and deformation. When the transition of the product structure changes suddenly, the wall thickness is small, and conversely, the wall thickness is large. Therefore, the transition part of the blow molding product structure needs a smooth transition, and there are sharp corners and sharp edges. If the wall thickness differs greatly due to the special structure of the product, the cooling should be strengthened at the thick wall, and the cooling circuit of the mold should be set according to the cooling requirements;
(2) The greater the difference in wall thickness between the longitudinal wall thickness position of the blow molded product and the radial wall thickness position, the more easily deformed. The position of the mold line of the blow molded container article is more severe than the adjacent position, which is that the thicker region cools much more slowly than the surrounding region. The difference in cooling rate causes the contraction to be different and deformed. This defect is best solved by servo longitudinal wall thickness control and servo radial wall thickness control at the same time, but the equipment cost is high. It is also possible to replace the radial wall thickness control by trimming the nose die, but the effect is not good. For small and medium-sized blow molded containers of flat shape and square shape, the wall thickness difference of the blow molded product can be reduced by a method in which the size of the die and the core mold is slightly larger, so as to achieve the shrinkage balance, thereby solving the deformation defect.
The effect of premature mouth sealing on deformation
The product that has just been produced has not been sufficiently cooled. If the mouth is covered sufficiently early, the product will be deformed due to the difference in internal and external cooling rates and atmospheric pressure.
Effect of molding process on deformation
(1) The barrel temperature, head temperature and mold temperature of the extruder should not be too high, and the high temperature will cause the blow molding products to cool slowly and easily deform;
(2) insufficient molding cooling time, resulting in uneven cooling and deformation of the blow molded product after the mold is discharged;
(3) Finely adjust the servo wall thickness curve according to the shape of the product to make the wall thickness of the product as uniform as possible;
(4) Using a chiller to supply water to the mold for circulating cooling to improve the cooling effect;
(5) Improper adjustment of the mold opening stroke parameters will cause the product to be deformed when the mold is opened.
Effect of poor mold release on deformation
(1) Insufficient draft angle of the concave position of the blow molding container may cause tensile deformation during mold opening;
(2) If the mouth of the blow molding container is poorly cooled or the mouth is too long, it will cause deformation when the mold is opened;
(3) The blasting effect of the two sides of the blow molding machine mold is different, which will cause the product to be attached to the mold with good sand blasting when the mold is opened.
(4) The influence of uneven force on the deformation of the ejector device; when producing blow molded board products, it is generally necessary to design an ejector device on the mold. Uneven force on the ejector will deform the product. When designing the ejector unit, it should be balanced with the mold release resistance, and it is better to combine it with air pressure or hydraulic pressure.
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