There are variations to the extrusion process depending upon what type of extrusion is being performed. Here is a look at the different types of extrusion, and the differences from the basic process for each.
Sheet extrusion, also known as film extrusion, is used for making plastic sheeting and films, and it generally varies from the basic extrusion process in regards to the cooling process. Rather than using a water bath to cool the finished product, the sheets are cooled by being pulled through a series of three to four pinch rollers. In addition to cooling the product, the rollers are also used to determine the thickness of the final product.
BLOWN FILM EXTRUSION
Blown film extrusion is used for making products such as plastic shopping bags. The process is the same as the basic extrusion process up until the point of the resin going into the die. The die is an upright cylinder with a circular opening. The melted resin is pulled upwards from the die by a pair of nip rolls high above the die. Changing the speed of these nip rollers will change the thickness of the plastic film. Around the die sits an airflow based cooling ring, which cools the product as it travels upwards. Air is blown into the die, expanding the extruded product. This film can then be spooled or printed on, cut into shapes, or heat-sealed into other products.
Tubing extrusion is used to make products such as straws or medical tubing. The process is the same as the basic process up until the resin reaches the die. A pin (mandrel) is placed inside of the die. The melted resin is then pushed into the die, forming around the mandrel. This is how the hollow shape of the tubing are formed. Air pressure is used to gauge the thickness of the tubing.
These are just a few of the process used for plastic extrusion. The biggest advantage to all of these forms of the plastic extrusion process is that they give a wide range of geometric possibilities over other forms of plastic form production. The differences in shapes and sizes that can be produced is vast, with the only limitation being that the product must have a continuous profile.