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3/6/2019 | 1 MINUTE READ

Rethinking Two-Stage Injection for Better Parts at Lower Cost

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Screw and plunger are mounted inline, and both move forward together for injection.

Even 64 years after the introduction of the reciprocating screw, it’s evidently not too late to come up with a new, and possibly better, concept for the plasticating and injection section of an injection molding machine. At the Molding 2019 Conference, March 19-21 in Indianapolis, you’ll learn about a new approach to two-stage injection. In the Tuesday afternoon session on Medical, Packaging & Precision Molding, Michael Durina of Md Plastics will present the latest version of a cure for the limitations of conventional reciprocating-screw injection.

Those limitations are commonly understood to include the potential for inconsistent shot size imparted by the nonreturn valve, and the fact that screw retraction during plastication means that every pellet (more or less) entering the screw experiences a different plasticating length. The conventional cure is a two-stage injection unit with a fixed plasticating screw and a plunger injection unit.

Durina proposes what he says is a simpler, less expensive solution: A non-reciprocating screw to do the melting, in line with a plunger for injection, and the two of them move together on a reciprocating carriage to inject the shot. Also unusual is the fact that the melt from the screw is channeled through the center of the plunger until it reaches the front end where the shot is accumulated. Learn more about this Inject-EX system, said to be suitable for both thermoplastics and LSR, at Molding 2019.

(Read about Md Plastics Inject-EX unit here.)

Register now for Molding 2019 here.