Injection Molding History
As a plastic injection molder we appreciate our trade and its origins. Here is brief look back through history to see how injection molding arrived with a bang.
In 1847 Jöns Jacob Berzelius produced the first condensation polymer, polyester, from glycerin (propanetriol) and tartaric acid. Berzelius is also credited with originating the chemical terms catalysis, polymer, isomer, and allotrope, although his original definitions differ dramatically from modern usage. He coined the term "polymer" in 1833 to describe organic compounds which shared identical empirical formulas but which differed in overall molecular weight, the larger of the compounds being described as "polymers" of the smallest.
The first man-made commercial plastic was invented in Britain in 1861 by Alexander Parkes. He publicly demonstrated it at the 1862 International Exhibition in London, calling the material "Parkesine". Derived from cellulose, Parkesine could be heated, molded, then retain its shape when cooled. It was, however, highly flammable, prone to cracking, and very expensive to product.
In 1868, American inventor John Wesley Hyatt developed a plastic material he named Celluloid, improving on Parkes' invention so that it could be processed into a finished form. Together with his brother Isaiah, Hyatt patented the first plastic injection molding machine in 1872. This machine was relatively simple compared to machines in use today: it worked like a large hypodermic needle, using a plunger to inject plastic through a heated cylinder into a mold. The industry progressed slowly over the years, producing small products such as collar stays, buttons, and combs.
The industry expanded rapidly in the 1940's because World War II created a huge demand for inexpensive, mass-produced products. In 1946, American inventor James Watson Hendry built the first screw injection machine, which allowed much more control over the speed and quality of the plastics injection. This machine also allowed material to be mixed before injection, so that coloured or recycled plastic could be added to virgin material and mixed thoroughly before being injected. Today screw injection machines account for the vast majority of all injection machines.
In the 1970s, Hendry went on to develop the first gas-assisted injection molding process, which permitted the production of complex, hollow articles that cooled quickly. This greatly improved design flexibility as well as the strength and finish of manufactured parts while reducing production time, cost, weight and waste.