Novel Injection Unit’s Commercial Debut

Md Plastics is now offering for sale injection machines incorporating its novel Inject-EX injection-unit design with an inline screw and plunger. Inject-EX was previewed in prototype form at the last NPE in 2018. Now it is incorporated in servohydraulic machines from EdeX in Taiwan. The first Inject-EX model available is a 70-tonner with 2.2-oz. (64.23-cc) shot capacity. It’s also outfitted with the unique Temp-Sense melt sensor for melt-density verification. Md Plastics has one of these presses at its plant in Columbiana, Ohio.

As explained by Md Plastics president Mike Durina, “The Inject-EX plasticating unit is designed to address the deficiencies of the existing 70-year-old injection molding technology.” These include inconsistent shot size due to variable closing of the nonreturn valve and inconsistent plastication due to screw retraction, which causes incoming pellets to experience a constantly changing L/D. His design remedies the first flaw by virtue of spring-loaded shutoff valves (based on Md Plastics’ Mini-Shut design) between the screw and inline plunger and at the end of the plunger. The second flaw is avoided by having the screw/plunger unit and feed hopper reciprocate together. (For full details, see PT, December 2022).

Durina says, “Instantaneous mechanical shutoff of the plunger head isolates the melt pool from the screw melting chamber, which allows for discrete monitoring and control of the melt pool for improved shot control. Isolation between the melting chamber and melt pool also allow for more precise measurement of the shot volume for good/bad part discrimination using our Melt-Profiler melt-sensing technology.” He adds that this plasticating design makes the process more energy efficient, provides a first-in/first-out melt path, requires no melt decompression to seat the nonreturn valve, and thus avoids breakup of solids-bed compaction from melt decompression. Ultraprecise shot control, especially for small shots, is also claimed, in a simpler design with fewer parts than conventional two-stage units.

Durina says seven Inject-EX injection units have been operating for five years in the U.S. and Canada, providing confirmation of these claims. Versions of Inject-EX are available for conventional thermoplastics, LSR and recycling (with addition of a melt filter, degassing vent and starve feeder). In addition, a variant of the design can be used in large-area, pellet-fed 3D printing.