All-electric injection-molding technology is taking hold in the packaging industry because it is usually more productive than hydraulic injection molding. And while the purchase price is comparable to hydraulic packaging injection machines, electric injection molding offers considerable energy savings.
As a result, whether it is closures, cups, or buckets, packaging molders are turning to electric-molding technology. That's especially true for a new breed of high-performance machines that were recently introduced, according to David Bernardi, marketing director for the Elektron Technologies unit of Ferromatik Milacron North America.
Bernardi says the new units, such as the company's Powerline 550 and 330-ton packaging machines, have tested faster than high-performance hydraulic machines. He cites a manufacturer of smokeless-tobacco cans as a case in point.
"A major tobacco-products company tested and purchased a Powerline, hoping to get more production from a 48-cavity stack mold that was already running 8 to 10-sec cycles, limited only by the cooling capacity of the mold," Bernardi explains. "It turned out the Powerline replaced three of his existing machines because of its quick start-up, faster cycle time, uptime, and repeatability." The customer also can change colors on the fly, he adds.
Another customer he cites ran sub-5 sec cycle times with a 32 X 32 stack mold for thin-wall polypropylene dairy closures. The part's wall thickness ranges from 0.010 to 0.040 in. Other benefits included a 60% energy savings and eliminating hydraulic oil, important in food applications. The customer also reduced spare-parts inventory because accumulator-based hydraulic machines tend to have more failure modes than do all-electric units. Milacron introduced the two all-electric Powerline machines at last summer's National Plastics Exposition, where the 550-ton unit demonstrated it could shave at least 6% from the cost of molding 5-gallon buckets. The machine offers precision shot repeatability, 60 to 70% energy reduction, and independent machine functions that allow preinjection and other standard capabilities.
Independent servodrives for each axis allow the Powerline to deliver precision motion control for injection, extrusion, clamp, and eject functions. Tighter injection control eliminates wasteful over-packing and allows the machine to operate close to the threshold of a short shot, without ever falling short, thus cutting resin and colorant use by 1 to 2%, says Bernardi.
Independent drives allow the machine to shave the cycle time by starting injection before the clamp builds full tonnage. "This shortens cycle time, allows faster and better mold filling and venting, and reduces stress in the part for better dimensional stability," adds Bernardi.
The two-stage injection unit for the bucket-molding system uses a servo-powered 120-mm extruder with output exceeding 600 lb/hr. The extruder fills an injection cylinder which delivers injection speeds to 521 mm/sec (equivalent to 37.75 in. 3 /sec) at maximum pressure of 27,500 psi.
Standard clamp dry cycle time for the 550 is less than 3 sec at half stroke. The direct-drive design is responsive yet quiet — the machine runs at about 70 dBA. With costs comparable to "industry standard" hydraulic packaging machines, equal or better performance, and a number of other advantages, packaging molders are increasingly turning to all-electrics, Bernardi asserts.
Information for this article provided by the Plastics Technologies Group of Milacron Inc., Batavia, Ohio.