July/August 2008
From shredding larger, heavier materials to extracting value from the tiniest piece of wire, shredder manufacturers are finding new ways to make their systems more productive, efficient, and safe.
By Theodore Fischer
An infeed conveyor, hammermill, and downstream separation system—the basic components of a shredder have existed since Sam Proler of Proler Steel Corp. (Houston) patented the "Prolerizer," what many consider the first scrap shredder, in 1960. But much has changed in nearly 50 years, too. Shredding systems have become faster, more powerful, more durable, and more technologically advanced in a variety of ways, Shredder manufacturers have had to keep improving their products to keep up with the volume of business and the fast-paced rate of change in the scrap industry. Today, "everything's more sophisticated," says Skip Anthony, vice president of sales and service for American Pulverizer Co. (St. Louis, Mo.). "Scrapyards today are no longer just scrapyards. They're producing a product. They're manufacturing outlets," producing clean, uniform streams of shredded materials.
Recent changes in shredder design are more evolutionary than revolutionary, with manufacturers responding to customer demand by constantly making incremental improvements to nearly every aspect of their machines—the way they shred scrap, the automatic controls that regulate the process, how they use energy, and how they assess their own performance. Here's a look at some of the most recent shredder system innovations.
Infeed Innovations
Shredder improvements begin at the beginning, with the infeed system. William Hayes, "semi-retired" plant manager of Camden Iron & Metal (Camden, N.J.), cites hydraulically driven double-feed rolls as the biggest improvement to shredders in his long career. "A lot of machines didn't have infeed conveyors [originally], but today almost everybody buys [them] because you're feeding materials too quickly to try to feed a chute," Hayes says.
Riverside Engineering (San Antonio) has replaced its standard 36/36 feed rolls at the shredder mouth with 36/60 feed rolls. (The numbers indicate the diameter in inches of the bottom and top roll.) The larger and heavier upper roll reduces the height of the input material more aggressively and consistently, the company says. "Historically, we had put those 36/60 feed rolls on only our megashredders," says Riverside's president, Randy Brace. "But we have started to install them on smaller machines, which benefit even more from the improved feed than the big machines."
A double-feed roller devised by the Harris Waste Management Group (Peachtree City, Ga.) uses a three-tube design that's more durable and easier to maintain, the company says. "It's basically a plate design with three tubes to resist torsion when the material is not distributed evenly under the rollers." says Javier Herrera, vice president of business development and technology. [Where are the three tubes?] A quick-release feature also allows operators to remove the complete roller without disassembling the shredder components.
A more responsive feed roll system is one of the most important advances in shredders at Wendt Corp. (Tonawanda, N.Y.), says Tom Wendt Jr., executive vice president. "The faster the feed rolls react, both in terms of up and down and rotational speed, the more quickly they can feed the mouth of the shredder," Wendt says. The shredder control system automatically adjusts the pressure of the hydraulic system, he says. "We're offering technology to drive the machine and [programmable logic controllers] with certain parameters, rather than an actual person pulling and pushing on a joystick."
Inside the Box
The shredder box, and what goes on within it, also has seen substantial improvements. Metso Minerals Industries (San Antonio) recently introduced a line of "hybrid" Texas Shredders that the company's Jim Schwartz characterizes as a "cross between the Texas Shredder traditional design and the Metso USA design." These wider shredders with heavier hammers (for greater strike force) are the only North American-built machines that will be able to accept disc, spider, or barrel rotors, Schwartz says.
Barrel rotors, now common in Europe, are starting to make inroads into the U.S. shredder market, Wendt says. The design of these rotors puts the bulk of their weight on the perimeter, which can give them more force with less energy. "Imagine a rotor turning at 400 [or] 500 rpm," he explains. "The heavier the rotor and the more weight on the perimeter of the rotor, the higher the inertia. A barrel rotor has all its weight located on its perimeter, giving it more inertia and allowing shredders to be more productive without consuming [more] horsepower."
Other shredder box design changes reflect customer demand for machines to process larger, heavier scrap, including thicker sections and heavier angles, channels, and I-beams that scrapyards customarily sent to shears, not shredders. Riverside Engineering has made the mouths of its machines larger, for example, to accommodate bigger pieces of scrap, and it has made its castings lighter, stronger, and more durable, Brace says. "We've been building shredders with heavier plate and more weld in areas that take the most significant impact," he explains.
Bigger isn't always better, though. American Pulverizer has designed a smaller heavy-duty 60x85 shredding system driven by a 2,000- to 2,500-hp motor that can produce between 4,000 and 6,000 tons per minute of shredded and separated scrap materials "at a lower investment cost than the larger shredders," Anthony says, which can be a good investment for a small to midsized scrap operation.
Wendt offers a variety of hammer designs to match shredder box geometry, rotor type, bottom grate hole pattern, and feed stock. "The hammer itself isn't a one-design-fits-all," Wendt says. "You have to match the hammer profile, its shape and thickness, to the scrap [the facility is] processing and the kind of horsepower [the shredder] has." The right hammer, rotor, and grate can make the difference between a machine that requires 45 kWh to process a ton of scrap to one that uses only 30 kWh per ton, he says.
The trend in motors, some manufacturers say, is a switch from alternating current to direct current. "We have seen increased interest in DC drive packages on shredders," says American Pulverizer's Anthony. "DCs seem to have a better control capability for in-rushes and peaks and surges, which makes them more efficient."
Manufacturers are also making improvements to water-injection systems, which create steam inside the box that can provide a variety of benefits. The water "effectively inerts the inside of the shredder chamber, displacing the volatile gases inside the shredder," says Riverside Engineering's Brace. His company's water-injection system reduces emissions and dust, minimizes explosions and fires, controls the dampness of the product, and monitors daily water usage, he says.
Unfortunately, damp shredding can interfere with the operations of a shredder's bag house, he adds, creating a need for new or better ways to control emissions. "Shredders processing automobiles might have a little residual oil, and we spray water to keep dust down and reduce explosions. Unfortunately, bag houses don't like moist, oily air," he says, nor are they something you want nearby when flammable material in a shredder explodes or catches fire, as happens on occasion.
American Pulverizer has been installing more closed-loop air cleaning systems, which eliminate the need for additional conveyors and a Z box. "By being closed-loop, you don't have to vent into the atmosphere and you don't have permit issues," Anthony points out.
Downstream Developments
One unusual turn in the history of shredding is that what was once a byproduct of the shredding process now can be its most valuable product. Though the original goal of a shredder was to liberate uniform, clean pieces of steel, downstream separation systems now capture more and smaller pieces of nonferrous metals and separate them into specific elements and alloys, allowing scrapyards to capture more of their value.
"Most of the gains come from the fines, including the little pieces of wire you [used to] see mixed up in the shredder residue," says Metso's Schwartz. "Previously, people were throwing away these fines. Now they are paying more money for the nonferrous systems than the ferrous line. They're doing it and they're making money."
Wendt outlines the evolution of shredder downstream systems: "It used to be magnets; then it was magnets and eddy current [separators]; then five or six years ago it became magnets, eddy currents, and ISS-type [sensor-sorting] equipment," he says. "Now it's evolving to trying to get those little bits and pieces of fine metal. Our customers are spending millions and millions and millions of dollars on additional equipment for mining that extra percent or quarter percent of nonferrous metal that gets into the [residue] from the shredder." Insulated-wire recovery is the hottest topic in the industry, Wendt says, and looming on the horizon is the recovery of plastics.
Downstream improvements also include larger magnets, more magnets, and more picking belts to keep up with higher-throughput machines. "On the higher-horsepower plants, it's common to have four picking belts running parallel, even dual-magnet systems so you can have four drum magnets all running parallel," Brace says.
Several manufacturers have added downstream recovery devices that remove "pokers," long pieces that somehow survive the shredding process and can wreak havoc with conveyors and other downstream equipment. "Recently we have designed automatic poker rejecters which remove the longer pokers from the stream before they get into the magnet and pick areas, to eliminate the jamming and tearing of belts," American Pulverizer's Anthony says. "They also eliminate the need for a person to handle the pokers." Its system places an adjustable splitter at transfer points between conveyors or processes; shredded materials go right through the system, while oversized materials fall into ground-level bins.
Automatic Pilots
Manufacturers boast they have made substantial strides in automating the systems that operate and regulate shredder processes and, at the same time, capturing valuable performance information.
Riverside Engineering's PLCs "take the control out of the operator's hands and automate it so that you're getting the same production at the beginning of the day as you do at the end of the day," Brace says. "Production rates, the number of unshreddables, and downtime are all tracked, and it's all matched to the shredder and crane operators," he says. "We're giving management valuable real-time information on how the machine's performing that hour, that day, that week."
Management can use this information to determine average production rates, number of explosions, and other performance-related data that some yards are using as the basis for employee bonuses. "In the yard we put it in initially, there's a lot of internal competitiveness, all the way up to the ownership, where everybody's really trying to outdo the other," Brace says. "We've given them the system tools to objectively evaluate how they're doing." Riverside also has begun to electronically track wear parts so that operators can understand the consumption rates not just of hammers but of all the various parts of the machine.
American Pulverizer's automatic control system is a "co-pilot-type arrangement," Anthony says. "Our software and processes allow the machines to set the pace, which increases production and maintains a consistency of the density and quality of the scrap produced."
Metso's Jim Schwartz sees the trend going in the opposite direction, though. He says that like so many of today's electronic gadgets, electronic shredder controls have in some ways become too darned complicated. Though they're effective, he says, they've also become "headaches—[and] everybody in the shredder business says this." Metso is working to make ESCs as "robust" as the rest of the shredding plant—"to maintain the functionality with the benefits of fewer problems."
One Texas Shredder improvement helps control energy use in response to jurisdictions that impose monthly peak demand charges. For the last 20 years, Schwartz says, shredders have had manual systems in which a series of lights indicates how much electricity shredders are using during a 15-minute period. "If the red light came on, the operator would just stop shredding for a minute or two to make sure he didn't go over the limit," he says. "Now we put in autopilot; it's programmed for maximum performance, but if it sees you're on track to bust the limit for [a 15-minute period], it'll slow down maybe to 90 percent. You're not necessarily going to use any less energy, but you're going to pay less for any energy you use" by not exceeding the limit.
Maintenance and Safety Improvements
Manufacturers also have found a variety of ways to reduce the need, cost, and difficulty of maintenance. In some cases, they have convinced customers of the value of greater up-front spending to reduce maintenance in the future. "Companies are willing to spend more money on larger, heavier wear parts that need to be changed less frequently," Wendt says. "That's in response to the shrinking population of qualified millwrights and maintenance people—a huge problem in our industry."
American Pulverizer uses new alloys for its parts that wear more predictably, the company says. "We also try to convince customers to prepare and inspect their scrap" to keep problematic materials from entering and damaging the system, Anthony says.
To make its products' maintenance safer and easier, Riverside Engineering has redesigned the process for changing shredder castings. "In our machines the heavier, difficult-to-replace parts are now removed with the shredder closed, from the outside," Brace says. "They're dropped in from the top and held in place with large pins, no longer requiring people to be working with these heavy castings overhead." In a similar vein, Harris Waste has made feed roller maintenance safer by installing hydraulic locks that workers can position from remote locations, "so there's no exposure for the operator," Herrera says.
Wendt sees shredder operation getting safer by using more video cameras coupled with high-quality visible light and infrared systems to move the operator farther from the equipment. "Shredder control pulpits are traditionally located just above the feed chute, in a potentially dangerous location," Wendt says. "There's been movement to eliminate those pulpits through the use of automatic controls and cameras, just like a security guard would have. We have nine or 10 cameras strategically positioned to give you a feel for what's going on, and you sit in a control room and operate the shredder rather than [sit] up in the air" above the feed chute.
Will Cold Be Hot?
What will be the next big revolution in shredder design? "The only thing I can see—and this has been written about for over 25 years—is cryogenic shredding," Schwartz says. "The people who have experimented with it have used liquid nitrogen, at around negative 200 degrees F, to freeze the metal so that it's very brittle and takes maybe one-fifth or one-tenth of the energy" as traditional shredding, he says, "but it's expensive as hell. It worked beautifully," but it's not economically feasible, he says.
Even if that's on the far horizon, manufacturers expect incremental changes will allow shredders to produce more and cleaner shred using less energy and producing fewer emissions. "There are many advancements in technology that provide more efficient shredding and better metals recovery," Wendt says. "It's an exciting time to be in this business—and our customers are really benefiting from it." •
Theodore Fischer is a writer based in Silver Spring, Md.
From shredding larger, heavier materials to extracting value from the tiniest piece of wire, shredder manufacturers are finding new ways to make their systems more productive, efficient, and safe.