July/August 1994
Some see this aluminum can processing equipment as a solution to contamination problems, but others dismiss it as a high-priced product out of cost-range for most scrap processors.
By Si Wakesberg
Si Wakesberg is New York bureau chief of Scrap Processing and Recycling.
If there's one piece of equipment that has people in the aluminum can recycling business talking these days, it's the air knife, a product designed to remove heavy contaminants from used beverage cans (UBCs).
The talk should come as no surprise. After all, UBCs have become a vital segment of the aluminum market, with more and more types of consumers using more and more cans in their feedstock.
Along with this growth has come increasing consumer concern about contaminants in the UBC stream. Dirt, moisture, glass, rocks, plastic, paper, and the like in a load of UBCs are major bugaboos for consuming operations, which maintain that such contamination represents a major threat to the quality of their products.
Underscoring this concern is the fact that new aluminum cans are being made lighter, using lighter gauges of metal. According to a representative of Aluminum Co. of America (Alcoa) (Knoxville, Tenn.), producing this thinner sheet "further reduces already tight tolerances for imperfections in the raw materials that Alcoa and other producers buy," so UBCs used to make new can stock (its primary consuming market) must be that much cleaner than in the past.
As one industry official puts it: "It's obvious that buyers are looking for clean UBC material. Sheet mills certainly want the material better prepared. And any piece of equipment that promises to do a better job will be welcomed."
Just What Is It?
That's where the air knife comes in. Invented by Alcoa in 1990 for its own use at its can reclamation and sheet plants in Indiana and Tennessee, and now being built and distributed by Harris Waste Management Group Inc. (Peachtree City, Ga.), the air knife is an air classification system designed to reduce the amount of foreign material found in the UBC stream. Just how much reduction are we talking about? According to Harris, it's 97-percent efficient in removing heavy contaminants. As such, Alcoa says, "it represents a quantum leap" in the recycling industry's efforts to improve UBC quality.
True to the first half of its name, an air knife relies on a stream of air to eliminate contaminants in UBCs. It hardly resembles a knife, however. Instead, picture this: Loose, flat UBCs are conveyed across a vibrating feeder and "float" across a short gap, supported by a thin, invisible wall of continuously moving high pressure air. Non-aluminum objects (or cans containing water or foreign material) are too heavy to be carried across this gap and therefore drop out of the UBC stream, falling into a receiving trough for later examination (see the figure, page 97).
Alcoa also uses other equipment with its air knife, including a trommel screen to remove dirt and sand, a cyclone system to remove combustibles such as plastics and paper, and a magnetic head to remove steel.
A Savior Perhaps--If You Can Afford It
Air knife users generally praise the system. Don Johnson, senior vice president of Metal Resources Inc. (Loudon, Tenn.), for one, speaks glowingly of its accomplishments. "It's the greatest piece of equipment," he says enthusiastically. "Really amazing. We've had it for about a year and it seems to give us aluminum cans free of all kinds of contaminants--metallics, glass, dirt, and so forth. It's very effective."
"It works very well," agrees F. Robert Hubbard, plant manager for IMCO Recycling Inc. (Rockwood, Tenn.), which uses the system in handling a large volume of UBCS. "It certainly is a very effective piece of equipment."
In addition to this reported effectiveness, Alcoa points to another benefit of its use of air knives: For the first time, the company says, it can actually measure contamination levels in its incoming scrap and provide appropriate feedback to shippers.
David C. Rosenblum, secondary aluminum manager for MG Metals (Chicago), offers a similar take on this benefit. "The most important aspect of the air knife," he says, "is that it will yield a quantitative analysis of non-aluminum contaminants in shipments of UBCS." This, in turn, can translate to more companies being able to use UBCs not only more efficiently, but also in greater volume.
Good as it sounds, however, air knives appear to have some drawbacks. Foremost among them is not so much a problem with the equipment as the price. As Tom Stengel, senior director of marketing for Anheuser-Busch Recycling Corp. (St. Louis), puts it, the current cost of an air knife--reported to be between $50,000 and $100,000--“makes it prohibitive for the average collector." While air knife systems can definitely improve the quality of UBCs shipped, he says, "under present conditions, I think they're simply the last line of defense for consumers." Processors surveyed affirm that the air knife's cost "outprices" it for most of them.
Back on the other side of the issue, Johnson agrees that the price is high, but insists that for those companies that can afford it, an air knife is a very good investment. And Alcoa maintains that the equipment can save processors money by significantly decreasing the chances of downgrades or rejections and eliminating the manpower needed to manually remove contaminants on a traditional "picking line."
Of course, some processors counter that other existing technologies for cleaning UBCs--a mix of shredders, magnets, densifiers, and/or similar machinery--can yield nearly comparable results more cost-effectively.
Stephen Nedelman, vice president of nonferrous for Steiner-Liff Iron and Metal Co. (Nashville, Tenn.), for example, says that his firm has been buying and shipping UBCs for years, using trained personnel and less-expensive technology such as magnetic separation, a variety of hoppers and conveyors, and visual inspection. The result? "We've been able to remove contaminants to the satisfaction of our customers," he says.
A similar view is offered by Raymond Sloan, president of Sloan Metal Co. Inc. (Chicago), who notes that his company has devised a simple, inexpensive system to remove contaminants from the UBCs it ships to mills. In this process, cans are dumped onto a screen that slants toward a conveyor. Dirt, stones, plastics, and other heavy materials fall through the screen, he says, and clean cans flow onto the conveyor, where they're met with a magnetic separator.
Even some of those UBC processors who are willing to spend big bucks to keep their can shipments clean don't see the air knife as a necessary purchase. "From my point of view," says Tom Mele, president of Connecticut Metal Industries Inc. (Monroe, Conn.), "the eddy current separator does as good a job, if not better." Admitting that such separators can be costly, he reasons that scrap processors, when faced with a choice of expensive equipment, will have to make their own decision and "my preference currently is for the eddy current separator." The air knife seems to fit the needs of mill consumers, he adds, "but it has some flaws: It blows paper all over the place and it often doesn't remove the plastic bottle parts efficiently."
Then there are those processors who claim that cans coming into their plants are so free of contaminants that it takes little effort to prepare them for mill shipments. Marc Schupan, president of Schupan & Sons Inc. (Kalamazoo, Mich.), reports just such a welcome situation. "We find very little glass, dirt, or heavy metal in the material we process and ship," he says, attributing the virtual lack of contamination to his state's can-deposit system. As a result, the firm generally simply uses densifiers with magnetic heads to remove steel cans as preparation for final processing and shipment to consumers. "In Michigan," he concludes, "we find little need for air knives."
Growth in Sight?
Despite those who swear by the air knife, it's obvious that it's not for everyone. Currently, in fact, there are only nine air knives in operation, according to Harris. Nevertheless, UBC consumers generally foresee a growing trend in the use of some new technology to achieve a cleaner product, and the air knife has some ideal qualifications to fill that need.
Of course, there’s still the cost issue, but some suggest that a change in the mills' pricing structure could encourage more air knife use. Says one industry member: "Perhaps if consumers were to pay premiums for better-grade UBCS, as they have for shredded material, the larger dealers might show more interest in purchasing this equipment."
And there's always the possibility that the cost of the equipment could come down. In fact, an Alcoa representative indicates that he could imagine the production of a smaller-sized air knife at a more affordable cost. Scrap processors surveyed appear to agree that such a development would make them take a second look at an air knife.
As one aluminum industry expert puts it, "As we approach 2000, I can say with some assurance that effective technology, such as the air knife, if brought within reasonable cost limits, will certainly come into popular use." •
Some see this aluminum can processing equipment as a solution to contamination problems, but others dismiss it as a high-priced product out of cost-range for most scrap processors.