September/October 2005
Medium-speed tire grinders go by different names, but they have a common purpose: to turn a single product into two clean commodities—ferrous wire and recovered rubber—and, in the process, increase the value of each.
By Robert L. Reid
Separating steel wire from scrap rubber in shredded tires is a great way for recyclers to satisfy two markets at once.
Clean rubber is in demand for use as playground surfacing, rubber mulch, and similar higher-end products, which represent the fastest-growing segments of the recycled rubber industry. At least one processor says he earns six times more for wire-free rubber shreds than he earns for tire-derived fuel in which the rubber chunks often contain wire.
Likewise, processors who cleanly separate tire wire can market that material to steel mills instead of sending their steel-and-rubber “waste” to a landfill. In this way, some tire processors have turned a disposal cost of $20 to $30 a ton into revenue of $100 to $200 a ton, notes one equipment manufacturer.
Thus, what begins as a single scrap product ends up as two separate, higher-value commodities—wire and rubber. It’s a typically American story of how to succeed in business and, like many such stories, this one involves an immigrant experience. Only, in this case, the immigrant was a new type of machinery.
Coming to America
The equipment that separates tire wire from tire rubber is essentially a medium-speed grinder of the sort that first came to America from Denmark’s Eldan Recycling A/S in the early 1990s, says Tom Wendt, sales manager for Wendt Corp. (Tonawanda, N.Y.), exclusive representative of Eldan machinery in North America. These machines were a variation on Eldan’s “rasper” grinding technology, which had been used since the 1970s primarily for nonferrous wire chopping.
Eldan knew that its raspers could also pull steel wire out of chunks of scrap rubber, but “at that time there really wasn’t a need for the machine,” Wendt says, because there wasn’t much of a market for the wire-free product. That changed in 1989 when Eldan manufactured a much more “robust” rasper with thicker housings, heavier serrated knives, a larger rotor, and an interior cutting chamber lined with replaceable wear plates, Wendt says. The new machine weighed four times more than a traditional rasper and, thus, was dubbed a Heavy Rasper.
North American tire processors installed about a half-dozen Heavy Raspers in the first half of the 1990s, says Wendt. Today, U.S. tire recyclers operate about 55 Heavy Raspers in three models. Eldan also recently introduced another variation—the Tire Rasper—that is a “complete reevaluation” of the technology, featuring higher capacity and easier maintenance, Wendt notes.
More for the Market
Though Denmark’s Eldan introduced the first medium-speed grinders to North America, at least two domestic manufacturers responded with similar equipment. Various European firms also make rasper-like machines.
Granutech-Saturn Systems Corp. (Grand Prairie, Texas) began offering a medium-speed grinder called the Grizzly in 1995, says Mike Hinsey, sales manager and director of international sales. The company already manufactured traditional high-speed granulators, but it felt that these machines couldn’t economically process tire shreds (which can contain as much as 15 percent wire). So Granutech designed a machine specifically for tire processors, with heavier construction and a straight-edge knife design to increase blade life and reduce maintenance costs, says Hinsey. About 50 Grizzlies are in operation worldwide, with the vast majority in North America. Though the firm currently offers one Grizzly model, both smaller and larger models are in the works.
The third major player in the U.S. market—tire shredder manufacturer Columbus McKinnon Corp. (Sarasota, Fla.)—began offering its CM Liberator in 2004. This entrant, available in three models, features an “armor-plated” rotor and rotor housing, plus a “flow-through” design to allow the machine to purge itself of fine pieces of bead and tread steel, notes Charles Astafan, general manager. Three Liberators are currently in operation—one domestically and two internationally—with another two machines recently sold, one domestically and the other internationally, Astafan says.
A System Is the Solution
Medium-speed grinders such as Raspers, Grizzlies, and Liberators aren’t designed to work alone. Instead, they sit roughly in the middle of a larger scrap tire processing system. The first stage of this system involves feeding whole tires into a shredder that reduces the tires to small chunks of rubber embedded with steel (and fiber if the tire was from a passenger car).
These chunks—which can range in size from one to 10 inches—are then fed into the medium-speed grinder at stage two, which further reduces the rubber in size and basically pulls the steel out of the rubber. The rubber pieces are now generally smaller than two inches, depending on the size of the screens used.
Subsequent stages use magnets and aspiration to sort the rubber from the steel. The rubber can then be sold for use as playground material or rubber mulch, or it can be processed in granulators into smaller and smaller pieces for markets such as molded products. The tire wire is collected and sold in loose or baled/briquetted form to ferrous scrap consumers. A portion of this steel wire might still contain rubber and so must either be reground or discarded.
Speed and Strength
Speed obviously is a key difference between medium-speed grinders and other machines used to shred whole tires and subsequently reduce the tire shreds. Situated at stage two in the tire reduction process, medium-speed grinders operate at a much faster rate than the shredders that chop up whole tires in stage one but considerably slower than the subsequent granulators.
Tire shredders, for instance, run at slow rotor speeds of roughly 25 to 30 rpm, notes Granutech’s Hinsey. Conversely, “a typical granulator would run somewhere in the range between 800 and 1,200 rpm,” says Columbus McKinnon’s Astafan. “These [medium-speed] machines are running between 80 and 300 rpm—so we’ve drastically slowed them down.” The slower speed, he explains, helps reduce friction and the resulting heat that can cause fires, especially when grinding passenger tires that contain cotton-like fiber.
Medium-speed grinders are also made heavier and stronger for greater “resilience against the toughness of the tire,” Astafan says. The Liberator, for example, includes larger bearings, a larger transmission, and a more powerful motor—200 to 400 hp compared with 100 to 200 hp in a typical granulator.
“The tire has been designed for over a hundred years not to come apart, not to be torn, ripped, or cut apart,” Astafan states. “But that’s exactly what we’re trying to do—we’re trying to destroy something that was designed to be indestructible.”
Other ways of making medium-speed grinders heavier and stronger include housings with four-inch-thick plates on Heavy Raspers rather than one- or two-inch-thick plates on regular raspers, notes Tom Wendt. Heavy Raspers also use thicker, heavier blades—60 mm or 90 mm rather than the 40 mm in regular raspers, he adds. Likewise, the rotors in a Grizzly weigh nine tons compared with about four tons in a heavy-duty granulator, Hinsey says.
On the Infeed
Since medium-speed grinders and the other equipment in a wire-removal system work at different speeds, they produce material at different volumes and, thus, should not be connected inline, manufacturers recommend.
A Wendt “Super Chopper,” for instance, can process eight to 16 tons of whole tires an hour, whereas the Heavy Raspers operate at two to eight tons an hour.
Likewise, Granutech has one customer who feeds material from a single shredder to two medium-speed Grizzlies to compensate for a similar disparity between stage one and stage two processing capacity, Hinsey notes.
Another reason not to run such equipment inline, says Charles Astafan, is that “if any individual piece of equipment goes down, then the whole line is down. So we’d like to see the components run as separate individual processes.”
Separate processes also help reduce the risk of fires. When tire shreds come out of the medium-speed grinder, “the material can be quite warm,” Astafan explains, adding that “it would make sense to feed it into a location to let it cool.”
In addition, this approach helps avoid cross-contamination. “Truck tires have almost no fiber, and they’re also all black and made of a different type of rubber,” says Astafan. “So people process truck tires separately from car tires. Also, some car tires have white walls, so if a customer wants all black material, it’s an issue.”
To optimize the separation of scrap rubber and tire wire, Tom Wendt stresses the importance of properly feeding material into a medium-speed grinder. “The more evenly and consistently you feed the machine, the better it performs—you don’t see major peaks in the amps and you don’t put stress on your chain and gearbox,” he explains. “You also see more production because you don’t have the peaks and the valleys. You’re running at a more regulated, more consistent flow.”
The best way to feed a Heavy Rasper, Wendt says, is with the tumbleback feeder that Wendt Corp. initially developed for auto shredder fluff and then adapted to tire recycling. This machine, which can be batch-fed by a front-end loader, meters the flow of tire shreds into the Heavy Rasper and then, through electronic feedback, speeds
up or slows down the feeder to ensure consistent operation.
Of the 55 Heavy Raspers in operation, roughly half use tumbleback feeders on the front end, he adds. Those customers report better Rasper performance than customers using belt conveyors, surge hoppers, or other methods to feed their medium-speed grinders.
Cutting Edges
Inside the cutting chamber itself, a series of knives attached to the spinning rotor fly closely past stationary or “bed” knives, ripping apart chunks of scrap rubber and tire wire. The largest Heavy Rasper, for instance, offers 25 rotor knives (with five triangular edges per knife) and 26 stationary knives, while the largest Columbus McKinnon Liberator features 48 “fly” or rotor knives and 19 “bed” knives.
Knife design is critical, though manufacturers disagree on which style works best. Eldan and Columbus McKinnon use a serrated knife, while Granutech and at least one major European manufacturer use a straight edge.
Columbus McKinnon’s Astafan compares the Liberator’s serrated knives to steak knives with a sawtooth-design. The jagged points “increase the linear inches of cut” on each blade, he says, and “promote better separation” because of the ripping and tearing effect they create.
Granutech’s Hinsey acknowledges that “those who use the serrated knife report that it makes a cleaner wire product.” But he can also point to customers who are “producing a clean wire product off the Grizzly” with its straight-edged blades. Moreover, straight-edged blades offer advantages in cost and useful life, Hinsey says. A straight-edged blade is essentially a rectangular piece of heat-treated tool steel that offers four cutting surfaces—when one edge dulls, the user simply has to flip the blade to its next edge. Plus, each edge on this heavy-duty tool can be resharpened twice and then repositioned in the cutting chamber for a tight fit.
“So, for a knife that costs perhaps $50, you can get 12 uses out of that knife,” Hinsey says.
While serrated knives can be sharpened, Astafan says, they do not offer the flippable multiple edges of straight-edged blades.
On the Inside
Screens are another key feature inside a medium-speed grinder’s cutting chamber. Recyclers select a screen size based on the product they want to make, with the smaller screen sizes producing a better separation of rubber, wire, and fiber. Heavy Raspers, for instance, offer screens with hole sizes from a half-inch to two inches.
Screens also give operators the versatility to collect over- and undersized pieces, which enables them to sell into multiple markets. This, in turn, allows operators to “derive the best price and gives their business more balance so it’s not so susceptible to market changes,” says Tom Wendt.
All three major manufacturers say they offer a two-piece modular screen, which allows users to rotate the screen from side to side and flip it from back to front. As Hinsey explains, screens wear primarily in the center of the machine in the direction of rotation.
Because the Grizzly uses two symmetrical screens, customers can flip them, moving the lesser-worn area on the outside toward the center. Then, after that side wears, customers can turn the screens again to the side with the least amount of wear.
Fire and Outflow
Because of the ever-present danger of fire during tire processing, medium-speed grinders use water in the cutting chamber along with heat-detection, spark-detection, and fire-suppression systems, especially around the exhaust ports of the machines, notes Columbus McKinnon’s Astafan.
Wendt Corp. even requires Heavy Rasper customers to buy a specific fire safety system. If they refuse to buy the system, they must sign a letter that says “they’re going to use some other method of fire detection and suppression of their own choice,” notes Tom Wendt.
Grinding tires also sends thin, sharp wire throughout the machinery. This was especially true early on, when operators initially put rubber-belt conveyors beneath medium-speed grinders to carry off the rubber and steel pieces. Operators quickly learned, however, that wire came off the grinder with enough velocity to “turn that belt into a porcupine in a short period of time,” says Hinsey.
That’s why all three major manufacturers recommend using a metal vibratory pan to catch the processed material, which then passes under magnets that pull the steel wire from the rubber stream. Granutech also recommends additional shielding on the magnet itself.
Maintenance Matters
Medium-speed grinders are high maintenance machines, manufacturers and operators report. Granutech, for one, recommends various maintenance actions on a daily, weekly, monthly, semiannual, and annual basis.
Daily service might involve checking housing bolts and performing housekeeping to combat the dust and fiber generated during processing—especially to reduce the risk of fire, says Hinsey. Weekly maintenance can include checking the condition of screens, liners, filters, and dust collectors, along with conducting a general walk-through of the system to be sure everything is working properly, with no accumulation of metal in the grinder, on the conveyors, or on the magnets, he notes. Monthly activities would typically involve a more detailed version of the weekly maintenance regime.
Charles Astafan recommends checking knife gaps daily and resharpening blades every 40 to 80 hours—quite a change from the knives on a typical granulator, which can run for hundreds of hours before being sharpened, he notes.
To combat these maintenance demands, manufacturers have been refining and redesigning their medium-speed grinders, often based on customer feedback. The switch from rubber to vibrating metal conveyors was an early customer-driven change. Other improvements include the armor-plating that Columbus McKinnon designed into the Liberator’s rotor and rotor housing, with the goals of reducing wear and increasing the machine’s uptime, says Astafan.
In particular, these replaceable wear liners eliminate the need to take the machine down and build up worn surfaces with welding.
Granutech changed the shape of the Grizzly’s rotor, switching to a scalloped design that improved the rotor’s fan effect to help move air and cool down the cutting chamber. The company also redesigned the knife housings to make it easier to adjust or rotate the blades, reducing the time to perform such maintenance from an hour to about 20 minutes, says Hinsey.
Eldan went even further, developing an entirely new machine to serve as its premier product for tire processing. Introduced in December 2004, the Tire Rasper is a “complete reevaluation of the machine with the goal of simplifying it, reducing its cost to operate, and reducing time to get back up and running after any sort of failure,” Tom Wendt says.
Changes include a simplified drive with fewer parts for reduced maintenance, a slightly higher rotor speed for greater capacity, and a redesigned static knife area that simplifies the cost to operate and reduces the time to do knife changes, says Wendt.
Costs and Opportunities
Medium-speed grinders tend to cost from $250,000 to $330,000 based largely on capacity, manufacturers report. Adding the front-end and downstream equipment to support the grinder—such as conveyors, feeders, magnets, aspirators, and balers for processing the clean wire—can make the total cost of the complete system $500,000 to $1 million, depending on how many bells and whistles the processor wants.
Choosing the right equipment can open up new markets or at least give the operator the option to pursue other markets, the manufacturers note. These market options cover the various sizes of ground rubber, the growing demand for clean tire wire, even the possibility of expanding into markets beyond scrap tires—such as electronics recycling. Medium-speed grinders “do a phenomenal job breaking e-scrap down into separable components,” states Granutech’s Hinsey.
That’s why it’s critical for processors to decide exactly which market or markets they want to supply. “If the processor doesn’t know where he’s going, no manufacturer can help him,” Hinsey concludes.
Robert L. Reid is managing editor of Scrap.
Medium-speed tire grinders go by different names, but they have a common purpose: to turn a single product into two clean commodities—ferrous wire and recovered rubber—and, in the process, increase the value of each.