Extrusion is a shape forming manufacturing process that involves forcing material into a die to make other shapes with that matetial. It’s like play dough. Imagine having play dough and pushing it through one of those tools with all the holes. You end up with play dough spaghetti. This is an example of extrusion. You can achieve a lot of different stock sizes and lengths by extruding. Like play dough.
The actual process involves a lot of math and hard work and a lot of set up. You start off with the material. Metal is typically used when doing extrusion. Then that material is pushed through another piece of stronger metal with a shape cut out of it where the material is forced out, creating that shape.
Extrusion blow molding is perhaps the simplest type of blow molding. A hot tube of plastic material is dropped from an extruder and captured in a water cooled mold. Once the molds are closed, air is injected through the top or the neck of the container; just as if one were blowing up a balloon. When the hot plastic material is blown up and touches the walls of the mold the material “freezes” and the container now maintains its rigid shape.
Extrusion blow molding allows for a wide variety of container shapes, sizes and neck openings, as well as the production of handleware. Extrusion blown containers can also have their gram weights adjusted through an extremely wide range, whereas injection blown containers usually have a set gram weight which cannot be changed unless a whole new set of blow stems are built. Extrusion blow molds are generally much less expensive than injection blow molds and can be produced in a much shorter period of time.