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What is a Plastic Injection Machine?

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  • Written By: Cassie L. Damewood
  • Edited By: C. Wilborn
  • Last Modified Date: 25 August 2016
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A plastic injection machine is used to shape liquid plastic into solids. The liquid plastic, made of various resins depending on the desired product, is used to create a wide variety of objects and parts. The machines used to produce the plastics vary in size from very tiny to extremely large, depending on the desired end product.

Part of the plastic injection machine's popularity is based on its simple, inexpensive construction and ease of use. It has only a small number of major parts. These include the hopper, the barrel, the heater, a plunger needle, a casing unit, and an ejection device. The sizes and types of each of these parts varies depending on the materials being molded.

After the dimensions and shape of the desired product are determined, the appropriate plastic injection machine is chosen. It may have to be specially built if the product is an odd size or shape. The raw materials are emptied into the hopper. If dyes or tints are being used, they are added at this point.

The materials are pulled into the barrel through gravity and become liquid as heat is applied. When this process is completed, the liquid is forced into the mold through a ram injection system or reciprocating screw. The ram injection system is preferred when at least 1/5 of the hopper material is needed in the mold; the reciprocating screw is favored for lesser amounts, as it provides greater control.

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While the liquid cools in the mold and becomes solid, the mold is held steady by mechanical or hydraulic force. This phase determines what the end product will look like. Different resins shrink at different rates, and mold designs take these fluctuations into consideration to guarantee the desired results.

Plastic injection machines are highly reliable in their performance. If performance problems do arise, they are normally simply and quickly resolved. Reducing the heating temperature in the hopper can usually quickly remedy singed or burned products. Making adjustments to the mold's thickness or heat can resolve warping issues. Regulating temperature, pressure levels, or moisture content can correct surface inconsistencies.

The introduction of the plastic injection machine in 1872 transformed the plastics industry. The plastic injection industry produces around 32% by weight of the earth's plastics and has annual revenues in the billions of US Dollars. The industry is credited with making millions of sturdy, inexpensive manufacturing parts, machine components, and consumer goods every year.

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Cageybird
Post 2

@Reminiscence- I also worked with a plastic injection molding machine, but thankfully it worked perfectly while I was employed at that factory. Other employees told me some stories about some big messes, but those machines were much older and a lot less reliable than the ones used these days.

My company made all sorts of molded plastic products, like the bottoms of cigarette lighters and the nozzles on ice cream machines. The work itself was pretty boring, but at least it was steady. Sometimes I'd be assigned to a different plastic injection mold machine and I'd have to do things like trim off excess flashing or break pieces off a frame.

Reminiscence
Post 1

When I worked with a plastic injection molding machine, the biggest problem I faced was a total blockage in the mold. All of that heated plastic would continue to flow, but it wasn't going into the mold at all. I'd have to hit the emergency shut-off button, then find a maintenance worker who could make the repairs. Even if this only took a few minutes, there would be a huge blob of hot plastic flowing onto the machine's parts.

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