William H. Willert
Egan Machinery Co
Inducted 1973
William H. Willert (1920 – 2000) invented the reciprocating-screw injection molding plasticating unit in 1952 (patented in 1956), which combined the plasticating screw concept with the injection ram concept by using the plasticating screw as a ram. The invention of advanced injection molding technology made the injection of thermoplastics and thermosets more economical and practical and improved molded product quality.
Before Willert’s invention, injection molding machines used plungers to force the plastic into the mold. They could run only small shot sizes, up to about 24 ounces. The reciprocating screw opened up a world of larger part molding and thinner wall parts. It facilitated the molding of new materials, including nylon and polycarbonate. Willert’s reciprocating screw was an enormous improvement over previous injection molding techniques and operated as follows:
First, a large amount of plastic can be quickly melted and mixed with a screw that rotates to feed the plastic granules and melt forward. The rotating action of the screw improved the rate at which plastic could be melted relative to plunger machines which relied primarily on conduction. The shot builds up and pushes the screw back as it rotates (i.e., it reciprocates within the heated barrel). The screw eventually stops turning when it reaches a pre-set limit and then acts as a plunger to push the melt forward into the mold. After pressurizing the melt, the screw begins to rotate and generate the “shot” for the next molding cycle.
The reciprocating screw also was adapted for the blow molding process and facilitated the blow molding of vinyl compounds. According to the injection molding expert and fellow Plastics Hall of Fame member Irv Rubin, approximately 98 percent of injection molding machines used the reciprocating screw at the time of Willert’s death.
Willert was born in Michigan and graduated from Dundee High School during the Great Depression. In 1942, he earned a degree in chemical engineering from Michigan State University. The Willert family later established a scholarship at Michigan State for graduates of Dundee High. During the Second World War, Willert worked at Firestone Tire & Rubber Company as a development engineer in extrusion. From 1952 to 1978, he worked at Egan Machinery Co. in Somerville, N.J., advancing to vice president and eventually serving on the board.
It was at Egan that he developed his revolutionary reciprocating-screw design. Subsequently, he began his own screw-design company, W.H. Willert Inc., in North Plainfield, N.J. Reed-Prentice was the first molding machine company to manufacture reciprocating screw injection molding presses in the early 1950s. By the early 1960s, technology became the preferred method of plasticization for injection molding machines.
In 1977, Willert received the Society of Plastics Engineers (SPE) International Award, the organization’s highest honor. Willert served on the board of directors of the Society of the Plastics Industry (now PLASTICS) and was a member of the Plastics Pioneers Association for 32 years. His wife Eleanor Willert once said, “Her husband enjoyed pastimes such as hunting and fishing, but inventing things was his passion. He was so work-oriented,” she said. “Everything was working to him, and he enjoyed that so much. Inventing was so important to him.”