Radically new PET preform machine injects and cools at the same time.

The new "Index" PET preform injection molding machine from Husky Injection Molding Systems, Bolton, Ont., has a truly revolutionary new design that incorporates a rotating turret on the machine's moving platen. With each 90 [degrees] rotation, the servo-driven turret moves a fresh set of cores into place for injection while the just-molded preforms cool. The two-platen clamping arrangement employs a new locking mechanism on the stationary side (see photo, p. 20).

Currently available in a 250-ton, 48-cavity configuration, the machine not only promises huge strides in output but also improvements in preform quality and the possibility of adding secondary operations - even stretch-blowing - in the machine.

PRODUCTIVITY LEAPS

The system's unique ability to cool and inject simultaneously adds up to 50% more output/cavity, says Dr. Michael Koch, v.p. of technology for Husky. He reports that the Index Machine can mold a 4-mm-thick, 47.5-g preform in less than 15 sec, compared with 22.5 sec for the same preform on a conventional 96-cavity machine.

In other words, a 48-cavity "Index" system can achieve the same output as a standard 72-cavity system - without eating up as much floor space. Even with the added capital costs for the turret and multiple core sets, the Index machine will be very cost competitive with a 72-cavity system, says Koch.

Despite its productivity advantages, the Index machine won't solve everyone's production problems. "For thicker pre-forms, we expect the system to be better than any other system on the market in terms of output per capital invested," Koch says. "For thinner preforms, the cycle-time benefit won't justify the added capital cost." It's too soon to tell for certain where the cut-off point will be, but Koch believes it will be in the mid 3-mm range, leaving plenty of opportunities in carbonated soft-drink, hot-fill, and refillable containers.

OTHER POSSIBILITIES

The two-platen arrangement and open design of the machine also create opportunities for all sort of platen-mounted secondary operations and handling options. To take one example, Husky has already built a fan-based cooling station on the top of the turret (see photo), and there is room for another such station on the back.

According to Koch, other possibilities include the addition of a decorating station and even a bottle-blowing station on the back of the machine.

As for preform handling, a conveyor at the back of the machine carries away the preforms, which are ejected straight downward from the bottom of the machine, eliminating the need for robotics. And since robotics can represent more than 10% of a pre-form system's total cost, this simple handling option can help throw the economic balance in favor of the Index Machine.

LOWER AA LEVELS

As if the productivity gains weren't enough, preform property tests conducted by Husky show that the Index machine will offer some quality improvements too. According to Koch, headspace tests have indicated acetaldehyde (AA) levels of 1.8 micrograms/liter for the Index Machine pre-forms, as opposed to the more typical 2-3 micrograms/liter. "And that wasn't even on a mineral-water material grade," says Koch. "With a mineral-water grade we anticipate 20-30% further reductions." Koch believes that the AA improvements result from the "continuous flushing" of the injection unit, which has no time to sit idle with a full barrel of hot material.

Koch also points to two other quality-enhancing factors from the shorter mold cycles made possible by the Index Machine: One, the Index preforms show no gate crystallinity because they don't sit on a hot valve stem after molding. Two, the preforms seem to have less molded-in stresses because they aren't subject to overpacking during the cooling phase.

Finally, the system has allowed Husky to build a 48-cavity system around a smaller machine. Normally a 48-cavity mold would run on a 300- or 350-ton machine, says Koch. Husky now has the clamp force down to 250 tons for start-up purposes, although normal production on the Index Machine needs only about 130 tons.

Future plans for the machine include extentions to both 72-cavity and 96-cavity systems as well as a smaller 24-cavity set-up for short-run applications and overseas markets.

Moduline G Machine in Two-Stage Version

Husky has also come out with a two-stage, accumulator version of its Moduline G Series, which was first introduced last year (see PT, Sept. '96, p. 24). The new Moduline two-stage shares many features with its reciprocating-screw cousin. Among them are modular construction, GE Fanuc controls, enclosed water-cooled motors, and advanced hydraulics. The two-stage version adds a new slanted barrel-head design that optimizes flow, according to Michael Koch, Husky v.p. of technology. Machine sizes range from 180 to 825 tons.