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Q&A: Process

Injection molding is a method of obtaining a molded article by Injecting the heated and melted material into a mold, cooling and solidifying it. It is suitable for mass production of complicated shape products, making it a great field of molding processing.

In this process, resin is first melted in Extruder. The molten resin is forced out into the air in a shape like a tube. A certain amount of inflating air is then introduced into the molten tube. The molten tube is inflated into a bubble as balloon. This bubble is cooled by cooling air fed through a ring and it is taken off continuously to become solid so that it can make desired products shape.


Blown film bubble can be as large as 3 meters or more in diameter! That is enough to cover your entire car.  They are used as agricultural films for Green houses, mulches etc. (chapter1 P16)

A short hollow tube ( parison) is first extruded. In a hot state, the tube is sealed at one end and then blown up like a balloon by forcing air into it from the other end until it sticks firmly to the inner wall of the cold mold to create the product. Finally, it is solidified by cooling. This method is suitable for hollow products such as bottles, drums and jerry cans. Automotive fuel tanks are also produced by Extrusion blow molding.


PET bottles are produced by stretch blow molding. Recently, the technology for stretch blow molding has made progress since 1974, and the use of PET for bottles has rapidly increased. PET bottles are clear and have good gas barrier properties. They are also lighter than glass bottles. So the bottles are widely used as containers, for example, for soft drinks such as soda water and mineral water, for cooking oil and similar food products, and for household detergents. There are two methods to stretch blow molding: injection method and extrusion method. In injection stretch blow molding, an intermediate product like a test tube, called ” a preform”, is injection-molded and then a preform is stretched and blow molded at a temperature higher than the glass transition temperature (69 ℃). In extrusion stretch blow molding, a preform is extrusion-molded, heated again and stretched and blow molded.   (CT2-2 P108, chapter9 P137)


You should consider all the conditions in which your product is used. Firstly estimate the maximum stress and strain upon usage and compare with the Yield strength and Yield strain of the material. You should also take safety factor into consideration. You should also consider other conditions such as temperature, indoor or outdoor, chemical substances in contact, leagal regulations, how the force is applied, and so on. For example, in case of repeated force, you should look at fatigue properties of the material. You can consult with HIPF technical staff for more information and support.