July/August 1992
Today's more durable, more versatile shredders are designed to meet both the processing demands of scrap recyclers and the quality needs of consumers.
By Kent Kiser
Kent Kiser is associate editor of Scrap Processing and Recycling.
Shredding technology has come a long way since the Proler family built the first shredder in the 1950s. In fact, in just the past decade, equipment manufacturers have thickened, strengthened, and/or enlarged almost every shredder component—all in the name of helping these workhorses of the scrap industry last longer, process more and heavier materials, and produce a higher-quality product.
"American manufacturers, in particular, have tried to beef up the traditional shredder, making larger diameter rotor shafts and using larger bearings, larger discs for the rotors, and thicker liner plates and base plates," says Gunn Phillips, sales director of Lindemann Recycling Equipment Inc. (New York City). The result is today's state of the shredding art: super-heavy duty machines designed to benefit shredder operators as well as their scrap consumers.
Modern shredding boxes—where all the action takes place—now feature walls and liners from 4 to 6 inches thick, while older models had walls and liners only 1 to 3 inches thick, notes Jim Schwartz, vice president of engineering for Texas Shredder Inc. (San Antonio). In addition, Nick Andrusyshyn, vice president of operations of Schnitzer Steel Products Co. (Oakland, Calif.), points out that his firm's new shredder is more solid than its previous machine thanks to its welded, rather than bolted, construction.
Super heavy-duty—or SHD —shredders have evolved, in part, out of the scrap recycler's need to process a wider range of materials. "The shredder population is getting out of sync with the available auto hulks, so more and more machines are having to shred material that hasn't normally been shredded," explains Phillips.
Scott Newell, chairman of Newell Industries Inc. (San Antonio), agrees, observing that "most processors complain that they don't have enough auto bodies and white goods to run in their shredders. With an SHD shredder, processors can add 20 to 40 percent heavier scrap to their mix." Several recyclers confirm this point, noting that their new shredders enable them to run more unprepared No. 2 and light No. 1 material, up to 1/2-inch thick. This versatility of infeed has opened up new scrap sources for some processors or expanded their options for handling their current scrap stream.
Today's SHD shredders are also essentially "an insurance package for the user," Phillips says. Increased shredder durability can translate to less damage to the machine and, thus, less downtime, reduced maintenance, and increased efficiency, he explains.
Shredder operators back up that assertion: "The trend toward reduced maintenance and much longer life of wear components has enhanced operations, in that we're able to run more time," says Keith Elkins, plant manager of LMC Recyclers (Redwood City, Calif.). And at Schnitzer Steel, says Andrusyshyn, "the new shredder is more efficient in that we don't have to worry about rebuilding it all the time."
Shredding More for Less
Beyond durability, SHD shredders are more productive than their predecessors, manufacturers say, thanks, in large part, to their more powerful motors and the use of hydraulic double-feed rolls, which regulate the quantity of scrap that enters the shredder. Double-feed rolls—now the industry standard—speed up the intake for smaller, unprepared scrap and slow it down for larger items such as auto hulks. This "intelligent" feeding reportedly enables the shredder to perform at capacity and results in a higher continuous production rate. "Better infeed systems can improve the efficiency of a shredding plant 20 to 40 percent," Newell asserts.
The effect of SHD shredders on production capabilities can perhaps best be seen in numbers: In 1980, the estimated 200 shredders in North America processed approximately 10 million tons of scrap. A decade later, when the number of machines was essentially the same—but more were of the SHD variety—North American shredders produced approximately 15 million tons, a 50-percent increase.
Some recyclers have also augmented the productivity of their shredders by using preshredders, which are particularly suited to boosting the capacity of smaller shredders, Newell says. In fact, preshredders have been especially popular in Japan for the past 15 to 20 years because their shredders are usually small, Schwartz observes. In addition, Japanese recyclers are said to shred a lot of bundles and need preshredders to break them up before processing.
In North America , on the other hand, only one or two scrap recyclers use preshredders. "If you can afford a larger shredder, there's no reason to have a preshredder," Schwartz asserts. Preshredders essentially duplicate the shredding process and can add about $3 to $5 per ton to the finished product, notes E. Paul Noring, vice president of sales and marketing for Universal Engineering Corp. (Cedar Rapids, Iowa).
In addition to maximizing production, shredder operators are always seeking ways to reduce operating costs, a combination of goals met by the latest shredding technology, manufacturers say. For example, Newell notes, SHD shredders consume about the same amount of energy per ton as older shredders, but are more profitable since they can process more material and require less labor to sort out unshreddable materials.
To increase shredder productivity while also reducing costs, some U.S. shredder manufacturers are pursuing the European practice of slowing the revolutions per minute of the shredder rotor, which increases the rotor's torque, notes Dennis Schreck, district manager for Universal Engineering. Such slow-speed shredding, Schwartz claims, allows operators "to achieve more production with the same amount of horsepower and extend the life of hammers, grates, and liners." When shredding heavier material, however, slowing the rotor speed may be detrimental, he points out. "The whole trick is not to go too slow," Schwartz says. "At some point, you're just not going to cut the scrap."
Perhaps the newest wrinkle in scrap shredding, however, is the use of direct-current motors that can operate at varied speeds to process different grades of scrap, Schwartz says. This practice is gaining popularity thanks to improved solid-state electronics that can efficiently convert alternating current to direct current.
At present, two small U.S. shredding firms use direct-current motors, Schwartz says, but several larger firms are reportedly interested in the practice. "Processors are definitely becoming more energy-conscious," says Chris Griesedieck, president of American Pulverizer Co. (St. Louis), who notes that some shredder operators are also considering using diesel motors to reduce their energy costs. Diesel motors make sense for shredder operators that either don't have access to sufficient electricity to power traditional shredder motors, or firms that face high minimum charges on electrical usage, Schwartz says.
The Quality Connection
In addition to addressing the concerns of shredder operators, SHD shredders have evolved to meet the quality demands of shredded scrap consumers. "There's always pressure to up the quality and get the nonferrous out," Elkins says. "Consumers want shredded scrap that's cleaner and cleaner." Quality concerns are even more pronounced for recyclers that export because "overseas consumers are extremely quality conscious," Andrusyshyn says.
While the quality of shredded scrap is determined in large part by the downstream separation system (see "Separation Technologies [FILL IN CORRECT HEAD]," beginning on page XXX), the shredder itself also affects the material grade. By enabling processors to run heavier, more valuable scrap, SHD machines naturally produce a higher-quality end product, manufacturers claim. Newell also observes, "There's less entrapped copper when you run heavy scrap through an SHD shredder, and the scrap is, generally speaking, more dense." In addition, Elkins notes, "shredding with this type of machine is very uniform, and that allows for better separation."
Shredder manufacturers and operators alike assert that steel mills—particularly minimills—are increasingly preferring shredded scrap over other scrap packages, such as bundles. "Shredded scrap has become the darling of the steel industry," says one Midwest processor. Phillips explains this trend by saying, "The beauty of the shredded product is that it's identifiable, it has a known range of contaminants. Shredded scrap's uniformity of size and quality lets it meet the demands of the consumer."
Is Bigger Better?
New shredder installations are centered mostly in Europe and the Far East —particularly South Korea , Taiwan , and Singapore —while North American operations primarily constitute a replacement market. In any case, manufacturers note, the market has expanded for both small and large shredders. Scrap recyclers that can't afford a large shredder or don't have the necessary feedstock to keep it running are buying smaller machines, such as the 60/80-size models, while steel mills and larger processing firms are purchasing the 98/104 models. (The first number represents the hammer swing in inches; the second number is the width of the shredding box in inches.)
The largest shredder on the market is reportedly Newell's megashredder, which features a 120-inch hammer swing, a 6,000-horsepower motor, and a processing capacity of 300 tons per hour. One megashredder is in operation at Chaparral Steel Co. (Midlothian, Texas), and two others are under construction for Hiuka America Corp. (San Pedro,Calif.) and A.F.L. Falck (Milan, Italy). Years ago, even more powerful 10,000-horsepower shredders were manufactured, but they were "white elephants" and have since been retired, Schwartz says.
Shredders in the 6,000-horsepower range represent "the top 5 percent of the market," Phillips asserts, and are practical in limited circumstances, such as when a steel mill processes its own scrap, when a scrap processing firm is contracted to produce large tonnages for a consumer, and when a large scrap company has sufficient material to feed the machine. In the United States , where shredders proliferate, the competitive supply of scrap makes megashredders unfeasible in most instances. "I don't see the need for extremely large shredders," Elkins says. "The 98/104 and comparable shredders seem to be a good size—a lot of times, in fact, they're a bit overkill—but they have the capacity to catch you up when you're behind or run extended hours."
The Future of Shredding
Despite the advances in shredder technology, there still exists what Phillips calls "the basic design problem with the shredder—there's a limit to the physical size of a piece it can digest without damage." This limitation, which is mitigated somewhat by the use of larger reject doors on newer machines, still requires recyclers to presort their scrap to ensure that unshreddable items don't enter and damage the shredder.
Lindemann, however, manufactures a shredder called the Kondirator, which "eliminates the fear of unshreddable pieces damaging the machine," Phillips claims. While most hammermill-type shredders rotate downward, he explains, the Kondirator rotates upward, pulling the scrap into the machine and shredding it against a hydraulically controlled anvil located above the hammers. Since the scrap is never forced into a confined area, unshreddable items can be simply carried over the top of the rotor and kicked out the back of the shredding box, preventing damage to the shredder, Phillips says.
Shredder manufacturers have considered other solutions to the problem of unshreddables, including the cryogenic freezing and processing of scrap. First tested more than 20 years ago in Belgium , this technique proved to be "effective but not cost-effective," Noring says, mainly due to the high cost of liquid nitrogen. The process also reportedly didn't lend itself to continuous feeding or handling odd pieces of scrap.
While most manufacturers have dismissed cryogenic shredding as a pipe dream, Schwartz says this dark horse could become a "big thing" if the costs could be reduced. He suggests one possible scenario: Steel mills use oxygen to make steel, producing nitrogen gas as a byproduct. A scrap recycler could install a shredder on-site at a steel mill, convert the nitrogen gas to liquid nitrogen, then freeze the scrap, process it, and feed it directly into the furnace. "You could take a steel plate four inches thick, freeze it, shred it, and it would shatter like glass," Schwartz observes. Not only would the shredder be able to handle heavier scrap, but wear parts would last longer, he says.
A more immediate and pressing concern for shredder operators is "getting rid of fluff," Schwartz notes. While many firms are trying to develop treatment and recycling processes to handle the material, automakers around the world could mitigate—even eliminate—the problem through auto dismantling and recycling programs. By removing all recyclable nonmetallic components from spent cars, many believe automakers and dismantlers could bring about a day when virtually no fluff is left over after shredding.
Looking to the future, shredder operators and manufacturers agree that the SHD trend will continue, driven by the need to shred a greater variety of scrap. "I don't see any technological breakthrough that's going to make the SHD generation of shredding plants obsolete," Newell says. "I think we're in a very mature business where there'll be gradual improvements." Griesedieck adds, "Ideally there would be a machine that could shred everything. Processors would like to have the machine be able to shred diverse items and only have to change the grates to make different scrap grades to sell to different end users."
While no one can chart the precise course of shredder developments, two goals seem likely to guide manufacturers: Create shredders that are more efficient—and, thus, more profitable—for operators and that produce a better product for consumers.
The Nonferrous Niche
Ferrous shredders aren't the only machines on the block.
Nonferrous shredders, which process aluminum almost exclusively, also represent "a big and growing market," Scott Newell says. Currently, there are approximately 40 to 50 aluminum shredders in North America , operated by scrap recyclers, secondary aluminum smelters, and primary producers. The machines are used primarily to process all-aluminum used beverage cans (UBCs) as well as mixed grades of aluminum, including sheet, plate, castings, extrusions, siding, window frames, lawn chairs, tube, turnings, and stampings.
Aluminum shredders are gaining popularity due, in part, to their ability to remove contaminants from aluminum scrap. Systems can feature both standard magnets to extract ferrous materials and eddy current magnets to separate the aluminum from rubber, paper, plastic, and other extraneous elements. In addition, aluminum smelters are said to prefer shredded aluminum because it's reportedly easier to handle, melts faster, and—in the case of UBCs—allows for better delacquering and drying.
Aluminum shredders come in two basic types: high-speed, hammermill-type machines that process material using one rotor equipped with swing hammers or rotating rings, and slow-speed shredders with two rotors that draw scrap down between them and process it using shear-type blades. High-speed shredders are generally larger and more powerful, ranging in size from 36- to 96-inch diameter rotor swings and 200- to 3,000-horsepower motors, notes Dennis Schreck, with the average being a 60- to 80-inch swing and 1,000- to 3,000-horsepower motor. "A high-speed aluminum shredder is basically the same machine as a ferrous shredder," Newell points out, "except with a different configuration on the hammers and grates."
Slow-speed shredders, on the other hand, have infeed chamber openings ranging from 40 by 25 inches to 120 by 64 inches, with motors from 50 to 500 horsepower. High-speed shredders may be able to process more, heavier, and a wider variety of aluminum scrap than the more-specialized slow-speed machines, but the latter is compact, produces no fines, and can reverse itself if it confronts unshreddable material, which reduces damage, manufacturers claim. Slow-speed, high-torque shredders also operate on less horsepower, require no heavy foundation, and eliminate the vibration, dust, and explosion concerns of many high-speed aluminum shredders, says Chris Griesedieck. "Unless the high-speed shredders are reconfigured to produce less fines, aluminum shredders will move into other means of processing to get more recovery," asserts Tom Garnier, president of SSI Shredding Systems (Wilsonville, Ore.), which specializes in slow-speed shredders.
Slow-speed systems, however, reportedly have trouble producing scrap of a uniform size, which can cause problems for some consumers. "Our challenge in the slow-speed field," Garnier says, "is to develop a machine that gives aluminum consumers on-line reliability and the kind of particle size they demand." —K.K.
Today's more durable, more versatile shredders are designed to meet both the processing demands of scrap recyclers and the quality needs of consumers.