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By Jim Montague, Executive Editor
What if you were the hero in the new Prince of Persia movie and had the magic dagger that could take you back in time just a minute or two so you could correct any problems? Well, besides being a fantasy warrior, you'd also make a heckuva plant engineer—assuming you had the right data to fix your problems and knew how to apply it. So, while it's too bad time travel isn't possible outside of Hollywood or other fictions, having lightning-fast access to more useful information can get you pretty danged close—especially in batch applications.
For instance, Plasticolors (www.plasticolors.com) in Ashtabula, Ohio, is a specialty color house that creates all kinds of colorant and chemical dispersions that plastics, coatings, inks and other producers use to help their manufacturing clients create an endless variety of products. Plasticolors uses high-speed-energy mineral mills to grind dry pigments, such as metal oxides and other dry chemicals, into resins to reduce particle size, and then adds dispersants to balance and stabilize the mixture. These are delivered in 1-lb. to 5000-lb. containers to its plastics customers and indirectly their clients, who make automotive parts, ladders, flooring, colored urethanes and other products.
Of course, the primary focus of all these coloring efforts is accuracy. So Plasticolors operates an extensive lab to match specified color requirements and maintain consistent product quality down the line. Because these processes weren't very high-volume historically, Plasticolors' staff usually did them manually over the years. However, that situation changed about five years ago, when one of Plasticolors largest customers requested larger shipments of colors in its smaller containers of just a few pounds each. These colors typically go to high-volume makers of fiberglass and epoxy-based flooring.
"There's a lot of pressure on us because we have to find and buy good raw materials in volume. Since the recent economic downturn and recession, our customers and their clients are stocking less on their shelves, working much more lean, but then also needing to make money as soon as they can," says Rick Georgia, Plasticolors' plant engineer.
Because of this heightened demand, Plasticolors decided to automate the machine it built and operates to fill its SoluPak pre-weighed tubs of liquid pigment (Figure 1). Georgia designed and built the pinch valve on the machine. He reports that it meters material out of a funnel and into the pre-weighed, 1-quart-size packages, and these need to maintain consistent weights of ±1% at minimum. "Operators used to manually open and shut the machine's valve all day by hand, but it was an ergonomic hazard because of the repetitive stress, and most operators could only get close to 1%," says Georgia. "We used to have one operator, who worked here for more than 20 years, and she alone could get to within 1% manually. But even she acknowledged that she couldn't do it consistently. Even so, we were able to meet our customers' needs for years, and yet we still wanted to get better. So when we read an article about P&G and Mettler-Toledo's (www.mt.com) Q.impact (Q.i) system, we thought it might work here too." Plasticolors was acquainted with Mettler-Toledo's lab scales because it used them for many years to handle intricate weighing of scaled-up batches.Michael McCormick, Plasticolors' coatings industry manager, adds that, "Our company has always made custom solutions, but Q.i enables our SoluPak packaging to meet the needs of our customers while exceeding their expectations. We have operators with a good feel for the process and a vast amount of experience who can target 1% accuracy, but the Q.i software lets any operator of any experience level run this filling operation. This means we don't have to rely on any one person, and it lets us be more consistent."
To better understand what makes predictive-adaptive material transfer control quicker and more accurate than traditional filling, weighing and reacting, it's first important to understand how the traditional way works. Typical material transfer in most batching applications uses some type of dribbler procedure that fully opens the valve and then begins to close and slow the flow before the target weight and final cutoff is reached. Some filling machines use a second, smaller valve to do this dribbling task. However, Georgia explains that the problem with dribbling is that it takes more time to achieve sufficient accuracy—about 12 to 15 seconds in most cases.
Dribblers also can't account for material added after the cutoff is reached and the order is given to shut off flow, but before the valve actually closes, and these amounts can add up to inaccuracy, poorer quality product and lost profit.
"Most filling machines just read from the scale, OK the cutoff and shut off the valve almost completely to dribble the rest of the fill. Or they choke off the main flow and then open another little internal valve to dribble the rest of the fill," says Georgia. This traditional, multi-speed method also means more lines, pumps and equipment than Q.i's single-speed control (Figure 2). Likewise, because they only seek to meet assigned weights, most filling devices can't account for changes in flow caused by changes in ambient temperature, humidity or other environmental shifts.Similarly, while most filling devices respond to signals from their load cells or other weighing sensors, they usually can't respond to changes in head pressure as the vessels they're filling from begin to empty out. Because of these limits, consistently performing precise fills—but also doing it fast—has been nearly impossible for many years. As a result, users often decide to err on the side of slightly overestimating and overfilling, which can add up to large losses in material and profit over time—not to mention risking poorer quality that may adversely affect subsequent processes.