In blow molding, the compressed air has two functions. First, the molten tube is expanded by compressed air, and the shape of the cavity is formed.The second is the cooling effect on blowing products.According to the different temperature of plastic variety and billet, air pressure is different, generally controlled at 0.2-0.7MPA.For low viscosity, easily deformed plastic such as polyamide, fiber, etc.For viscosity and high modulus of plastic such as polycarbonate, polyethylene and other higher values.In addition, the air pressure is also related to the size of the product and the thickness of the billet.General large volume and thin wall products should use high pressure, while small volume and thick wall products use lower pressure.The most suitable is to be able to make the product in the shape after the shape, decorative pattern and so on show clear pressure.
Blowing in order to shorten the time for products to obtain a uniform thickness and good surface, inflatable speed (air volume flow per unit time) as far as possible big some, but also shoulds not be too large, otherwise it will bring bad influence for products, it is can cause a vacuum in the air inlet, make this part of the parison retraction, and when the parison swell in full, invagination can form diaphragm fragments;The second is that the mold part of the mold can be pulled by the extremely fast air, resulting in waste, which needs to increase the blowpipe diameter or properly reduce the inflation rate.
The blowing ratio
Generally, the ratio of the size of the product to the size of the billet is called the blowing ratio, i.e. the expansion ratio of the billet.When the size and weight of the type billet are certain, the larger the size of the product, the bigger the billet expansion ratio.According to the variety, nature, shape and size of the plastic and size of the shape, the size of blowing ratio is determined.It can be economical to increase the blowing ratio, but the thickness of the product wall is thinner, the strength and rigidity are reduced, and the molding is also difficult.Get more knowledge of blowing plastic!Please pay attention to "blow molding machine" WeChat public platform, WeChat search Kinggle_song) blowing ratio too small, increase the amount of plastic consumption, reduce the effective volume of products, lengthen the cooling time and increase the cost.As a result, it is usually two to four times more likely to be blown.
Mould mild cooling time.
In order to ensure the quality of the products, the temperature of the mould should be evenly distributed, and the products should be uniformly cooled during the cooling process, and the mold is generally kept at 20-50 degrees.The mold temperature is too low, it will reduce the extension of plastic, not easy to blow up, and make the product thicken in this part, and make the molding difficult, the contour and pattern of the products are not clear.The mold temperature is too high, the cooling time is prolonged, the production cycle is lengthened.At this time, if the cooling is not enough, it will also cause the product to deform, shrink, and the surface will be dull.The height of mold temperature depends on the variety of plastic. When the glass temperature of plastic is high, it can adopt higher mold temperature.On the contrary, the mold temperature should be reduced as far as possible.
In order to prevent the polymer from producing elastic response, the product deformation.Blow molding product cooling time is generally longer.Usually 1/3 to 2/3 of the molding cycle, depending on the shape of the plastic variety and the product.For example, polyethylene with low thermal conductivity requires longer cooling time than polypropylene with the same thickness.The cooling time is usually extended as the thickness of the product increases.Sometimes in order to shorten the production cycle, to speed up the cooling speed, except for mold cooling, molding products can also be internal cooling, internal access to products all kinds of cooling medium (such as liquid nitrogen, carbon dioxide, etc.) in direct cooling, yet there is a new heat pipe cooling technology.
Blow molding cycle includes extruded blank, intersecting blank, mold, blowing, cooling, air release, mold opening, extraction process and so on.The principle of this cycle selection is to shorten the product as long as possible.But usually because of the consistency and accuracy of the operation is poor, die poor cooling effect, can artificially lengthen cycle, which directly affect the efficiency and benefit, this is must pay attention to the problems in the industrial production.
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