Canadian Plastics

Restoring the Vigor to Veteran Machines

If we accept that you can't afford a new injection molding machine this year, the important question becomes: What can you do with your existing machines to improve productivity, efficiency or capabil...

September 1, 2003   By Cindy Macdonald, associate editor



If we accept that you can’t afford a new injection molding machine this year, the important question becomes: What can you do with your existing machines to improve productivity, efficiency or capabilities?

There are a number of components that can be retrofit or added-on to existing machinery to boost performance. Depending on the age and condition of your machine, you could upgrade the controls or the feed screw, or even add a second injection unit to boost versatility.

Here are a few suggestions picked up at NPE.

Replace the controls

Price tag: US$40,000

“Over the last few years, people have been looking for cost-effective alternatives to buying a new injection machine,” explains Steve Schroeder, president of EPCO, a machinery services company. Schroeder says EPCO’s controls retrofit business has grown about 10 to 15% in recent years.

“We have done retrofits on 10- to 15-year-old machines, and brought them up to today’s standards for maintaining part parameters,” he adds.

“Machines manufactured in the late 1980s and 1990s all have suitable hydraulics for process control and linear positioning, so what we’re really doing is just upgrading an outdated controller.”

Best of all, many control upgrades can be done at the customer’s plant.

EPCO offers control systems based on Barber-Colman, Siemens or Allan-Bradley/Rockwell Automation. The ControlLogix offered by EPCO in conjunction with A-B/Rockwell uses high-speed closed-loop hydraulic valve controllers to monitor and control valve outputs, pressures and positions within the hydraulic circuit. Loop closure time is one millisecond or less.

Three new controls based on Siemens’ Simatic S7-300 “are being well-received in the field,” says Sam DeBartolo, EPCO’s national sales manager. “These packages offer lots of capabilities not typically found in this price range, and they’re extremely easy to operate.”

The Siject IM16-170, the open-loop controller of this new trio, is a low-cost solution for small- to medium-size injection molding machines. This system controls all timing, counting and machine sequencing, as well as clamp, eject and injection control. It provides diagnostic messages and stores mold recipes.

Replace the screw and barrel

Price tag: US$17,000

Xaloy is offering a retrofit kit that promises better part quality and lower part costs for conventional reciprocating screw machines. “The Xaloy ICU is an intensive-care system for melt preparation and delivery,” explains Hartmut Jahnke, the company’s vice-president for technology. “It overcomes the inherent limitations of reciprocating screw machine designs in melt temperature control and mixing, shot-size accuracy, machine wear, cycle time and other areas.”

The ICU uses an extruder with a fixed (non-reciprocating) screw, a separate ram to inject the material into the mold and an injection control unit that works like a shut-off nozzle to control flow and injection sequencing. Packing and hold pressure are generated by the control unit’s hydraulic system.

In a retrofit installation, the existing screw is bypassed, but the existing machine’s hydraulic injection cylinder is used to power the injection ram, which is fitted to the machine’s injection barrel. The existing screw drive assembly can be used for the ICU extruder. Or, a new electric screw drive motor can be used to gain energy savings.

The cost of an equipment package for a typical machine with a shot capacity of 400 g (14 oz.) ranges from US$17,000 to US$22,000.

In situations in which screw recovery is the limiting factor on cycle time, the new system can further enhance mold cycling because the screw can operate during all phases of the cycle except the injection fill phase.

The system eliminates the reciprocating screw’s non-return valve at its tip and its associated problems of wear and accuracy. According to Jahnke, the ICU’s injection control system can maintain shot weight accuracy better than +/- 0.1% versus +/-0.3% for a conventional injection machine.

Step up to multi-component molding

Price tag: US$80,000 to US$130,000

If you are hesitant to purchase a dedicated multi-component machine, you can have the flexibility to do occasional multi-component work by purchasing a plug-and-play type of injection unit. Van Dorn Demag, for example, offers independent Multi-plug injection units to retrofit on existing Van Dorn machines in seven sizes. They can be mounted in the horizontal L position or the vertical V position.

Van Dorn Demag’s machine-side units include a height- and lateral-adjustable injection unit; self-contained hydraulics including a pump unit; individual unit control; and a pre-configured electrical signal interface to the injection molding machine. With sufficient preparation, the system can be connected to an existing machine within one or two days. Similarly, it can be moved around to other machines in the plant when needed.

New screw, new tricks

Price tag: not disclosed

Another option for two-component molding is the Twinshot process marketed by Spirex, which allows a conventional injection molding machine with a single barrel and screw to inject two materials in one operation, with one totally enclosing the other.

Twinshot gives molders the capability to encapsulate low-cost material, providing up to a 30% savings on material cost, or to encapsulate foamed material to reduce sink and warp, and improve strength-to-weight ratio.

The TwinShot system can be retrofit to almost any standard, cold sprue injection-molding machine with at least 20:1 L/D available. The retrofit comes standard with screw, barrel, non-return valve, nozzle, nozzle tip, force feeder, barrel heaters and heater covers. Installation is similar to a standard screw/barrel changeover. Twinshot can easily revert to single-material mode by simply supplying the same material to all feeder hoppers.


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