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What Are the Different Types of Injection Molding Equipment?

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  • Written By: G.W. Poulos
  • Edited By: Daniel Lindley
  • Last Modified Date: 24 October 2014
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    Conjecture Corporation
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Injection molding equipment, also called injection presses, injects molten plastics into a mold and then cools the plastic and extracts the freshly made parts. The equipment itself is often identified as belonging to one or more different types. Types of injection molding equipment include vertical and horizontal presses, injection cylinder and injection screw presses, hydraulic and electric presses, and other presses rated by the amount of pressure they can apply to molds. There are also hot and cold runner molding systems used with injection molding equipment.

Sometimes injection molding equipment is identified as horizontal or vertical. This identifies the way that the injection press holds the mold in the machine. For a given application, this may be a critical factor for a manufacturer. If the parts being produced are large, gravity may be needed to help extract the part from the machine. If the parts are small, they may need to be extracted horizontally onto a table or another device to further the manufacture of the parts.

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The way the molten plastic is injected into the mold can also identify the type of molding equipment. Some kinds use a cylinder that collects the molten plastic in a chamber, then drives a piston down on the chamber to create the pressure to inject the plastic into the mold. The other system involves a long, heated barrel that contains a screw. The plastic is fed into one end and driven down the barrel by the screw melting the plastic as it goes along. The pressure needed to inject the plastic into the mold is created not by a cylinder, but by pressure created by the screw.

Some injection molding equipment is identified by how the pressure needed to keep the different parts of the mold together is created. In hydraulic systems, a series of hydraulic cylinders moves the pieces of the mold and creates the pressure to hold them steady while the plastic is injected. In other types of injection molding equipment, the molds are moved and held together by a series of electric motors. Higher pressure mold systems tend to use hydraulic, and lower pressure systems tend to use electric; there is a wide area of overlap where either may be suitable for a given application, however.

The molds used in injection molding can be of two general types: hot runners or cold runners. Runners are the passages in the mold that the molten plastic travels to reach the various chambers that it needs to fill to create the part. If the molding equipment cools these runners, it is referred to as a cold runner system. If the runners are heated, the equipment is called a hot runner system.

When defining injection molding equipment by type in the plastics industry, the primary feature needed for a given application tends to determine how the machine is referred to. Those who use hot runner systems will often say they use a hot runner injection molding machine even though it's also horizontal and electric. Those who make large plastic parts may refer to their machines as vertical even though they also have hot runner and hydraulic systems. As there are many types of injection molding equipment, each piece of equipment is actually one of many different types and can be unique, depending on the combination of systems it possesses.

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