Blow molding is a fully automatic process in which the hollow body is made of plastic. There are two different ways of https://www.ipqcco.com/wiki/blow-molding blow molding. In the first method, the hose (parison) is extruded into the die space between two half dies. The second method uses injection molding, known as preform, which is heated and blown into the mold space. Most PET beverage bottles are made in this way.

Blow molding hose
The extrusion hose is lowered from the nozzle between the half dies. The mold is closed and compressed air is blown into the hose. The hose is formed and cooled completely according to the mold wall. The mold is opened and the finished product is taken out of the mold. In general, blow molding uses special varieties developed for the process, and the viscosity is relatively high. Common formable plastics include PE, PP, PVC, pet, PA and some thermoplastic elastomers. Multi layer extrusion can be used for hose extrusion, such as giving the product better barrier performance. The hose can also be extruded from different raw materials (such as hard and soft raw materials) in stages, so that it can be made into rigid pipe with integrated soft beam and flexible beam.

Blow molding and bottle blank
The injection molded preform is heated by an infrared heater.
The preform is placed in a closed mold.
The preform is stretched to the bottom of the die with a rod with a ball at the end.

The compressed air is blown into the preform and formed according to the mold wall. The mold is opened and the cooled workpiece is taken out of the mold.

Advantages (+) and disadvantages (-) of this method
+It can produce large parts
+Can produce complex parts
+Thin wall parts can be produced
+Possible raw material mix
-Not all plastics can be blown
-Mould price is high, the machine needs large series
-The surface quality of the workpiece is relatively poor
-The dimensional tolerance of parts is moderate

extrusion
Extrusion methods can be used to produce essentially endless products from many thermoplastics. The main difference between plastics for extrusion and injection molding is that there is no release agent. The raw material must also have a relatively high melt viscosity in order to maintain the shape of the extruded profile as it comes out of the mold before cooling. The most commonly used plastics in extrusion are PE, PP, PVC, PA, PC and some thermoplastic elastomers.

Advantages (+) and disadvantages (-) of this method
+Various "endless" pipes and profiles can be made from many different raw materials
+Nozzles are relatively cheap
+Can produce multi-layer profiles
+It can produce wide plates
+Manufacturing thin wall products (e.g. films)
+ can make foam interior trim.
+Metal wires (cables and wires) can be coated
+Manufacture of corrugated profiles
+Possible precise dimensional tolerance (0.01 mm)
+Good surface quality
-The production line takes up a lot of space
-Recycling of multi layer profiles

Blowing film
The method is based on extrusion, in which a hose through a tubular nozzle is stretched into a film by blowing compressed air. After the film is cooled, it is pressed into a pile by a roller. In the final stage, you can choose whether to print on the film, then roll it up, slice it, or weld it and cut it into, for example, plastic bags. In order to prevent the melted film hose from sticking to the nozzle, it is kept outside the nozzle through a small air gap. The thickness of the film can be adjusted by adjusting the air gap of the blowing nozzle. The width of the film is regulated by the diameter of the bubble (atmospheric pressure) and the orientation of the film (biaxial) by the speed of the winding roller. This method deals with a large amount of plastics.

Advantages (+) and disadvantages (-) of this method
+Automatic batch production mode, used to produce plastic bags, household films and other low-cost disposable products
+It can be made into very thin films
+A variety of raw food approved

-Limited quantity of raw materials (high viscosity materials)
-High investment threshold and high production space for film blowing line