Canadian Plastics

Cool to be Hot

"A place for everything and everything in its place"....

May 1, 2006   By Jim Anderton



“A place for everything and everything in its place”.

It’s age-old wisdom and for molders moving into truly high-volume commodity molding, the place for high-cavitation tools is in the biggest, best presses in the shop. That’s because high cavitation means big business, but the price of volume is low margins, making cost control more crucial than ever for a profitable job.

Specialty machines have evolved to speed cycle times and increase throughput. Getting rid of regrind with hot runner systems is an essential part of the equation. But just what defines ‘high cavitation’ is subject to debate.

“It depends on the product,” Paul Boettger, owner of Bolton, Ont.-based Technoject Machinery Corporation, said. “If you’re looking at bottle caps for beverage containers, it’s definitely high cavitation. They can run typically from 96 to 128 cavities. On the other hand, there are other products in automotive, for example, where 24 or 32 cavities would be considered high cavitation,” he added.

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Boettger noted that while triple-digit cavitation is normally seen only in the packaging or commodity products sector, the resins they run are familiar to most molders.

“The other issue with the packaging industry is that they tend to run reasonably easy to process materials like polypropylenes (PP), polyethylenes (PE) and styrenes. With these resins, they’re easier to run at high cavitation compared to more sensitive resins like nylons and acetals. When you go to very high cavitation, the larger manifold means that the polymer’s residence time goes up quite a bit. With commodity resins, you have a wider processing window,” he said.

“It used to be in Europe, instead of building a 64-cavity mold, they would build two 32-cavity molds and run two machines, or maybe four machines with 16 cavities. From an economic sense the larger operation makes sense, but it’s like putting all your eggs in one basket,” he added.

While Boettger makes a good case for decentralization of critical production to reduce the effects of downtime, today’s cost structure means the economies of scale possible from larger, often purpose-built presses have made big machines running big molds the only game in town for running parts like packaging closures.

Packaging is the big user of high cavitation molds. With high resin and energy prices, relentless downward price pressure and the need to improve product quality in often aseptic end-use parts, eliminating the gate vestige might be reason enough to invest in hot runner technology. Fortunately, it offers more.

HOT RUNNERS FOR HIGH CAVITATION

Hot runners exist to make molders money. But they also cost money, up front and in power, machine space, maintenance and depreciation. Determining if hot runners can work for a given application can be something more than the $64,000 question for a major production run. The question is, how much money can you really save?

“It’s a loaded question”, Dave Boxall, general manager for East Dundee, Ill.-based Ewikon Hot Runner Systems of America, Inc. said. “It depends on the size of the part, how much regrind you can use and the size of runners. There are a number of ways you can achieve savings with a hot runner.”

“If you’re running a commodity resin, it’s often possible to regrind and re-use every part of the runner. If you use that as your only guideline, the cost savings aren’t great. If you consider cycle time improvements and quality, running a relatively thin-walled part however, the runner may be the driving factor in cycle time. In terms of the cycle time, you can achieve the difference between the time it takes for the part to set up and the time for the part plus the runner. Depending on the size of the part, that can represent 25 per cent of the cycle time. That’s where we find that most customers generate cost savings,” he said.

“The other factor is material handling. With large cavitation molds, such as closures, coloured parts are often not as easy to regrind and feed back into the system. There are other benefits for some parts when they’re direct gated,” Boxall added.

HOT HALVES

Injection molding shops dealing with high cavitation molds face hot runner systems that require control of more parameters than other forms of commodity molding.

Tooling is generally large and complex, so managers used to pulling inserts from standard bases may find the uniqueness of each tool puts a premium on documentation and a solid mold history.

Moldmakers can help by eliminating one-off or under documented hot runner components and by using systems designed by specialists.

“Hot half” systems are one way to economically cope with more cavities without excessive iterative testing. Essentially a hot runner system in a box, the hot half allows moldmakers to design the cavity plate to accept an outsourced system and bolt it in.

“By buying a hot half, you eliminate the assembly step,” Ray Quinn, applications engineer for Mold-Masters Ltd. of Georgetown, Ont., said. “Often, people aren’t sure about water lines and wire channels, but with a hot half, they effectively need to put in only a nozzle bore detail in the cavity block and they’re done. When they get the finished product there are no issues,” he added.

Quinn noted that for cavitation into the 48, 64 or higher range, wiring is a significant factor in the system price, so simple scaling of the cost of smaller systems won’t necessarily define the true value. The other way to trim the cost is considering the hot runner “right from the get-go”, Quinn said. “If you start at a late stage, it’s not pretty.”

CONTROLING DOWNTIME

High cavitation means more resin flowing through more manifold. Keeping the mold packed shot after shot often requires sophisticated sequential valve gating techniques and closed-loop temperature controls.

High cavitation can also mean that downtime is a more serious profit killer than production distributed among several presses. Modern controls can quickly pinpoint a shorted or open heater, for example, but what about the controller itself?

“My perspective is that molders are looking at both the hot runner and the temperature controls,” Ken Kurtz, product manager, hot runner systems for Mississauga, Ont.-based D-M-E Co., said. “Modularity is a major asset. The benefits of modularity are in ease of replacement and ease of troubleshooting. If you suspect that there is a problem with the controller, you can take the module out, swap it with a working module and debug more easily,” he added.

“You can usually eliminate one variable just by swapping the control module. It’s a simple test. There are more diagnostics in newer controllers, which definitely helps hot runner operators, but training is needed,” Kurtz said.

But there is no such thing as a one-size-fits-all hot runner solution. “I think it’s application-specific”, John Blundy, vice president, business development at Incoe Corp., in Troy, Mich., said. “When you think of simple hot runners as being thermally operated and the more complex ones as valve gates, the molding conditions direct the design; some applications require the added sophistication. That would include sequencing controls and more sophisticated temperature controls,” he added.

Blundy noted that a well designed system at both the manifold and controller can simplify the hardware and software’s task, adding reliability. “When you have good engineering and manufacturing technique up front, it’s possible to reduce the reliance on an anticipatory temperature control. Hot runner manufacturers all have our own ‘black art’,” he said.

How sophisticated can the controls get? Advanced systems can spot issues such as heater shorts or opens and burn off moisture on startup. Diagnostics and even on-press calibration is available and as controllers get smarter, the ability to log process data can generate substantial savings.

“Molders can easily create a report with this data and send it t
o their computer’s hard drive with a date and time stamp. This is invaluable to pinpoint any problems, and can save entire gaylords of parts from being thrown out due to doubt about their quality. This feature gives molders peace of mind, knowing whether their parts are OK or not,” Mike Brostedt, director of market development, at Sterling, Va.-based Gammaflux L.P., said.

Brostedt noted that with the ability to control multiple molds from a single point, keeping track of the tooling is no longer a trivial task. “There has been a push in the plastics industry for better access to operating data for multiple molds. This greatly improves plant organization and can dramatically reduce downtime in the molding operation,” he said.

Many injection molders have developed their own ‘black art’ in profitably making parts, but with proper technology and training, high-volume/low-margin molding can become a science instead of an art. Hot runners are a natural part of the high-volume picture; properly ‘spec’d’, built, documented and maintained systems can keep costs in their place — a very small place.

Resource List

D-M-E of Canada Ltd. (Mississauga, Ont.); www.dme.net; 800-387-6600

Ewikon Hot Runner Systems of America, Inc. (East Dundee, Ill.); www.ewikon.com;

800-980-4815

Gammaflux L.P. (Sterling, Va.); www.gammaflux.com; 703-471-5050

Control Solutions Inc. (Brampton, Ont.);

905-458-8382

HEITEC (Burgwald- Bottendorf, Germany); www.heitec.com.

J-Tech Hotrunner Inc. (Bolton, Ont.);

www.jtechhotrunner.com; 866-267-5832;

Technoject Machinery Corp. (Bolton, Ont.); www.technoject.com; 905-951-7144

Husky Injection Molding Systems Ltd. (Bolton, Ont); www.hotrunners.com; 905-951-5000

Incoe Corp. (Troy, Mich.); www.incoe.com ;

248-616-0220

Mold-Masters Limited. (Georgetown, Ont.); www.moldmasters.com ; 905-877-0185

Moldflow Corporation (Framingham, Mass.); www.moldflow.com; 508-358-5848

SWM & Associates (Kilbride, Ont.); 416-558-6526


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