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Injection molding has continued to grow since the late 19th century. Capable of producing small items such as combs, it is also used to create parts for airplanes and medical supplies. It is hard to imagine the world without the products it produces. The process was patented by John Wesley Hyatt and his brother Isaiah in 1872. Today, injection molding is used to produce about 30 percent of all plastic products. The process is relatively simple, but expensive. Thus it is usually only used to mass produce items.
Clamp the mold shut. This will hold the mold in place while the mold is filled with melted plastic. It will also keep the mold still while the plastic cools.
Inject the melted plastic into the mold. The plastic starts out as polymer resin pellets which are poured into a large open-bottomed hopper. A motor turns the auger, feeding the pellets into the cylinder where they are melted and turned into molten plastic, then pushed into the mold. The auger injects the melted plastic into the mold at a pressure between 10,000-30,000 pounds per square inch. The auger then holds the plastic, forcing more plastic in to fill the mold completely. This guarantees that the final product will not contain any gaps. A gate closes keeping the plastic inside the mold while it cools. Molds are usually either water or air cooled.
Drill small holes into the mold, if it is cooled by water or another liquid. The cooling period accounts for about 85 percent of the molding process. The temperature of the water is usually between 33 and 60 degrees Fahrenheit. Water below freezing can be used. However, glycol, or a similar additive, needs to be used to keep the water from freezing. The major disadvantage to using water to cool the mold is the buildup of condensation.
Loosen the clamp and open the mold. Remove the plastic part that was just created. Then clean the part, removing any excess plastic.