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May 27, 2002

8 Min Read
Maximizing profits, productivity in packaging

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In the packaging market, the only thing thinner than part walls are profit margins. Higher-precision parts in ever-faster cycles are a must, and idle time on a 96-cavity stack mold that runs 24/7 in 10-second cycles and spits out nearly 600 parts a minute will eradicate whatever slim profits were hoped for. Molders race to get parts out the door, and in the mad dash, many requisite steps in the molding process become casualties of the compressed cycle. For some shops, regular tool maintenance is often the first chore scratched from the to-do list.

Making a Pit Stop
Nadeem Amin, a product manager in Husky's Index Systems unit, equates the reluctance in packaging to suffer downtime for tool maintenance to an auto race. "It's sort of like the Indy 500," Amin says. "You're driving around, and you can make pit stops and do your tire changes, or you can just continue to drive around the track. The consequence is the performance of your vehicle."

Once employed in Husky's mold refurbishment and conversion business, Amin has seen many molds with a lot of miles and very few checkups. He says the key to getting the most out of a packaging mold is to strike a balance between mold operation and maintenance.

"There's a trade-off between doing too much maintenance and just enough maintenance to produce your product," Amin explains. "If you do too much maintenance, then you limit the actual production plan that you have for your equipment, although you maintain a good-quality tool that will last longer." In the short term, however, Amin says reduced maintenance can boost production, but the consequences of choosing regular checkups or virtually none are obvious for the life of the tool.

"We have some customers that just run their tools and do very little maintenance," Amin says. He adds that tools given minimal maintenance will not provide molders with as much use as those with a regimented maintenance program. Packaging molders interested in a long and fruitful mold life should watch several key areas.

Problem Spots
Amin says a regular maintenance program (see sidebar, below) will do a lot to extend a tool's life, but in his experience, many molders make mistakes in processing that accelerate tool aging, especially with overclamping.

"Tonnage plays a very key factor in the life of equipment," Amin says. "If you're running a tool with too high a tonnage then it's not going to last as long. Typically you should be running a mold with the minimum tonnage required."

Chuck Massie has seen his fair share of packaging molds. His company, Cavaform International LLC, does extensive work in caps and closures and builds molds, creates cavity inserts, and designs hot runner systems for medical, packaging, and writing implement applications.

Massie says hot runner molds are the norm in packaging, and they pose many unique problems. Massey recommends frequent pin checks to verify that all gate sizes are within spec. Even small corrections should be performed so the tips are matched and balanced. He says multitip nozzles need to be matched and balanced with the same diameter and length for balanced filling. Nozzle seals are another key area.

"You can have everything pretty well balanced mechanically, but you might have either seal damage or some mismatch on the nozzle seals, so you get leakage," Massie says. "Now you've got a pressure imbalance, plus over time you're going to pump material back up into the space between the probes and the manifold, which causes a whole other set of problems. Ultimately, you'll get up into the wires, and then you've got a major tear down, rebuild, and rewiring."

Massie says another neglected area is the quality of water used to cool the molds. The super-fast cycles in packaging require a large amount of water for cooling, and Massie says this can often lead to unexpected problems.

"You've got to make sure you've got clean, neutral-acidity water so you don't corrode or gunk up your waterline," Massie explains. "That can cause you some major imbalance problems. Often we get a mold returned for repairs and the outside looks good, but the waterlines and the flow channels around the cavity are so clogged that you've restricted the cooling capability of the mold."

Have a Gameplan
Everyone involved says the key is to be proactive. Do preventive maintenance; don't wait for parting line damage from flash, or worse.

"You need to set a time period—60, 90 days," Massie says. "I can't think of any reason why someone couldn't pull a mold down at least every six months and completely strip it down and check everything, clean it up, and put it back together."

John Thirlwell, vp of marketing and sales for Caco Pacific Corp., agrees, saying successful molders mark their calendars.

"They schedule their maintenance fairly strictly so that they don't wait for something to go wrong," Thirlwell says. "They schedule it so they can take the mold out on a predetermined time table."

Amin thinks many molders have the right intentions but feel management pressure to keep the mold running.

"One of the biggest problems when it comes to tool maintenance is that the guys at the corporate level are screaming and shouting for production," Amin says, "but it comes at the sacrifice of doing maintenance. The guys on the floor recognize that their equipment needs maintenance, but they're being forced to run the tools to maximize the production that the guys in corporate are looking for. The trade-off is tool life."

Tool maintenance top-10 list

Husky Injection Molding Systems Ltd. (Bolton, ON) and its Index Systems unit have worked extensively with PET preform technology and tooling since 1978. They currently offer mold refurbishing and conversion programs to extend tool life and rework existing molds for new functions. Husky tapped this expertise to provide IMM with the following 10 general tips for packaging mold maintenance.

1. Safety. Husky says maintenance programs begin with safety. Protective clothing and eyewear are musts around mold gates, the nozzle, and feedthroat. Lockout and tagout procedures on power sources are recommended, and for electrical problems that preclude lockout, use a sign or other means to notify operators.

2. Mold mounts. Many machines, especially in packaging applications, run at rates that loosen mounting bolts and clamps. Check tightness regularly. Screws and mold-mounting flanges must be inspected for wear and replaced as necessary. Husky also says to make sure everything is level. Off-level presses can create uneven, accelerated wear.

3. Cleanliness. Shutoff faces, tapers, vents, and parting lines can accumulate material that necessitates cleaning. Use appropriate cleaners with soft, nonabrasive pads, or a dry ice cleaning system. For heavy contamination, disassembly may be necessary.

4. Lubrication. A smooth-running press starts with good lubrication. After cleaning slides, wear plates, and cams, relubricate them and remember FDA regulations where appropriate. Stack taper locks present a unique problem since lubrication provides enhanced performance but can also lead to dust accumulation. Clean these areas regularly to prevent grease contamination; if your plant air quality is poor, consider foregoing lubrication on the taper locks altogether.

5. Clean vents. Clean vents and grooves are a necessity, and measuring vents to ensure proper length is also a good idea. Vents adjacent to shutoff areas hob over time, reducing vent depth. Regrind vents as needed and operate vent circuits manually to test internal blowoff vents.

6. Ejector functions. If working behind the ejector plate, block it to prevent any inadvertent movements that could cause injury. Check rods for straightness, length, and tightness.

7. Inserts. Disassemble mold inserts to check for hobbing and wear and make sure sealing surfaces and cooling channels are clean. Check cores and cavities to make sure all temperatures are equal during molding.

8. Mold bases. Remove cooling or fitting pipes to check for deposits and corrosion. Also check pH levels and microbiological contamination that can corrode iron and block heat exchangers. Treatment of the plant's water system may be necessary.

9. Stack molds. The complexity of stack molds makes them very sensitive to alignment issues and uneven wear. Contact your machine supplier to make sure the platen parallelism is within spec. If clamping force is uneven, isolated incidences of flash are likely.

10. Hot runners. Remove cavity plates to check nozzle tips, and then remove the plastic insulating bubble to inspect the tip for ovality or cracking. Check the nozzle tip height and clean the gate detail around sealoff areas. Scheduled replacement of piston seals is recommended on valve-gated systems. Clean plate and bushing contact surfaces. Reassembly for some designs must be done at room temperature to avoid sealing surface damage. Finally, referencing electrical schematics, check for electrical shorts or open circuits with an ohmmeter.



Contact information

Husky Injection Molding Systems Ltd.
Bolton, ON
Paul Thomson
(905) 951-5000
www.husky.ca

Cavaform International LLC
St. Petersburg, FL
Chuck Massie
(727) 384-3676
www.cavaform.com

Caco Pacific Corp.
Covina, CA
John Thirlwell
(626) 331-3361
www.cacopacific.com

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