Bringing balance to the mold

When IMM first wrote about a mechanism that rotates the melt inside a runner to prevent flow imbalance in eight-plus-cavity tools, the technology was still in its infancy ("Mold Imbalance Goes With the Flow—Literally," April 1998 IMM, pp. 85-88). Today, Beaumont Runner Technologies (BRT, Erie, PA) and John Beaumont, president and inventor of the MeltFlipper (as it has been renamed), have close to 700 licensees in nearly 1000 cold runner applications. 

For those who missed the article three years ago (or if you misplaced your copy), here's the issue molders face: High-temperature, low-viscosity material resulting from shear thinning and heating flows along the outside perimeter of the primary runner, while cooler, high-viscosity material remains inside. When the flow hits the first runner branch, the hotter, more fluid material stays close to the inside wall of the secondary runner, while more viscous material flows around it and adheres to the opposite runner wall (Figure 1). The result is that the inside cavities fill faster with the less viscous material, while the outer cavities get shortchanged by the slower, cooler material. 

Beaumont's solution redirects the flow with a level change at the runner branch, rotating the orientation of the less viscous material (Figure 2). It turns the flow from being hotter on the left and cooler on the right, for example, to hotter on the bottom and cooler on top. This reorientation evenly splits the two different flow levels in the next runner sequence, resulting in even cavity fill. Branches between secondary and tertiary runners have diminishing elevation changes, notes Beaumont. 

To see how the application of this technology has fared in the field, IMM spoke with three MeltFlipper users whose names may sound familiar: Lear, Nypro, and Delphi. 

Filling Thin Walls 
Automotive supplier Lear Corp. (Southfield, MI) ran into runner balancing problems in a door panel retainer for General Motors. The cube-shaped nylon 6 part, about 2.5 by 1.5 inches, contained a feature with a very thin wall—approximately .5 mm, according to Ed Jamison, tool engineering manager for Lear Electrical & Electronics Div. (LEED). "This area has very tightly controlled tolerances of ±.002 inch," he says, "and the cavity imbalance range of 15 to 30 percent caused a great deal of difficulty in trying to produce accurate parts, cavity to cavity." 

Jamison had read about Beaumont's research in a trade magazine and followed its progress as it got more press. Then, about a year ago, when Lear's six eight-cavity tools running the door panel retainer showed classic signs of imbalance during testing, the company decided to give the MeltFlipper a shot. 

"We manufactured and installed one insert, ran the analysis, and ended up using inserts in the other five molds," says Jamison. "It turned out for all these tools that the vast majority of the imbalance was attributable to the runner and very little of it was attributable to the cavities." Every tool reached less than 10 percent imbalance, and two or three had less than 5 percent—closer to the LEED's specifications for new molds. 

Although the project was shelved, Jamison has four more licenses remaining on the set of 10 Lear purchased, since the license stays with the tool. "This is part of our regimen now," he explains. "We have included this technology on our mold concepts, where applicable." 

Watching the Burn 
About the same time that Lear was implementing the MeltFlipper, operators at Nypro Asheville (Asheville, NC) were watching a 32-cavity tool spit out medical IV drip chambers with long black and brown streaks. Technicians had just switched the clear, flexible PVC application for customer Alaris from a 16-cavity to a 32-cavity mold, and were suddenly confronted with burning in internal cavities (Figure 3) and significant imbalance between inner and outer cavities. 

Nypro went back to using the 16-cavity tool while it debugged the other, but Jason Hutchison, now a project engineer at Nypro Oregon (Corvallis, OR), says the staff had to work quickly. "We were delivering parts at 32-cavity pricing and running a 16-cavity tool," explains the former Nypro Asheville corporate management trainee. "That's why it was such a drive to try everything and try it fast." 

Trying everything involved opening the .250-by-.200-inch trapezoid runners to .290-inch full round; heavily venting the cavity to solve the outgassing problem associated with PVC; smoothing out contours between gates, runner systems, and the nozzle tip; cleaning out the runners; and machining the MeltFlipper directly into the tool, for speed. Because almost all corrections were implemented at once, says Hutchison, he's not certain how many of the other problems the MeltFlipper solved, although he's sure it balanced the cavities. 

"There was one iteration before we put the MeltFlipper in where we had streaking from the barrel and from shear," Hutchison recalls. "It was dark coming out of the nozzle, and it got darker as the shear continued to degrade the material." 

As a student at Penn State, Hutchison had friends researching Beaumont's technology, so his insider status helped when the burning part presented itself. "When the product came out, I knew this looked like a perfect application for [the MeltFlipper]," he says. Needing to convince more players than his old friend Jason, Beaumont jumped into the project and allowed Nypro to implement the technology without any paperwork. 

"[BRT] gave us the approval and the idea before we ever got a PO to them," Hutchison notes. "Beaumont's response was, 'Go ahead, we know you're in a time restraint. Put it in and see if it works.'" 

After the MeltFlipper was installed, the shear-induced staining and degradation disappeared, but burned material in the machine continued to produce black streaks directly out of the nozzle. 

"I remember looking at those parts and watching the burn run all the way through the runner system," continues Hutchison. "It would get heavier and heavier, and then when it went through the MeltFlipper the plastic did exactly what [Beaumont] said it was going to do—it transferred to the internal." After removing the degraded material in the machine, the parts ran to visual specifications (see runner comparison, Figure 4). These results came within two weeks of the first sign of trouble. 

True Believer 
While Nypro hasn't yet found any other tools in need of rotated melt, Delphi Automotive Systems, Packard Electric Div. in Warren, OH has installed the technology on more than 100 molds over the last three years. Eric Tomalski, senior mold design/analysis engineer, says Beaumont pitched the package to Delphi and convinced the electronic systems unit to try it. 

"It seemed like a good way to go—better than the way we'd been balancing molds in the past [changing runner sizes], so we picked a new mold to try it on," Tomalski relates. The eight-cavity mold, which produced nylon 6/6 seven-way connectors, exhibited a typical flow imbalance of 18 percent. After a couple of iterations with a MeltFlipper insert, the shear-induced imbalance dropped to 2 percent. Some cavities still had about 10 percent imbalance, Tomalski adds, but that indicated to him that the problem was in the steel. After some small dimensional differences were corrected, the total imbalance was brought down. 

The reason Tomalski prefers flipping the melt to adjusting runner sizes is the advantage achieved in material uniformity, he says. "When you change a runner branch size, your material still has a different viscosity between cavities," he explains. "This is much more consistent." 

At Delphi Packard Electric's just-built plant in Cortland, OH, every tool with eight or more cavities is evaluated for possible use of the MeltFlipper, in keeping with the facility's commitment to run with no blocked cavities. "Initially we used the technology just to meet our balance requirement, but we do recognize that there are quality improvements, uptime improvements, and a reduced need to block cavities," states Tomalski. 

When asked about the use of moldfilling software to identify runner imbalance, Delphi's Tomalski admits that current basic analysis packages geared toward molding do not predict that effect. Beaumont agrees, and although BRT has its own software, called RunnerFlow 3D, he envisions a joint development effort in the future with larger analysis software companies. 

Licensing fees range from $2600 for a single mold to less than $400/mold for 1000 molds or more. Beaumont has a money-back guarantee of sorts in place, but to date, no one's taken him up on the offer.