March/April 2002
No more shredding by guesswork. It’s time to get smart. here, Trevor Masters, shredding guru, reviews the state of modern shredding and tells what it takes to run an efficient, productive, and profitable shredder.
By Kent Kiser
Kent Kiser is editor and associate publisher of Scrap.
It’s a cold, bright January day in Harrisburg, Pa., and Trevor Masters is talking shredders. That’s no surprise. Masters has had shredders on his mind since 1975 when he began managing a shredder at a scrap plant near London.
Now, with 27 years of experience as a shredder manager—the last six as operations controller for the former Mayer Parry Recycling Ltd.—Masters qualifies as a bona fide shredder expert. You could say he knows shredders like Bill Gates knows computers.
Masters—now director of Smart Recycling Solutions Ltd., his own consulting firm—is visiting Harrisburg to help put the finishing touches on a new shredder at Consolidated Scrap Resources Inc. (CSR). This state-of-the-art system—made by Texas Shredder Inc. (San Antonio, Texas)—is a textbook example of a “smart” shredder, one that’s operated not by art but by the science of programmable logic control.
That, in a nutshell, is what Masters is all about—how to shred smart—and that’s why he’s talking shredders on a cold, bright January day in Harrisburg.
Getting It Right Up Front
What does it mean to shred smart?
First, you have to remember that the purpose of a shredder is to process the maximum tonnage in the time it’s operating to achieve the lowest cost per ton. Regrettably, few processors get the max from their shredder. “The main problem around the world,” Masters asserts, “is to buy a large shredder and then not maximize it.”
Smart shredding, then, is all about maximizing production while maintaining costs—but how do you achieve that? A large part of the answer lies at the beginning of the shredding operation in factors such as how the infeed scrap is prepared and how it’s loaded onto the conveyor. After all, these factors affect everything that comes afterward.
The Preparation Issue. Getting the most from your shredder starts with the proper preparation of incoming scrap, Master notes. A shredder can’t produce its best if you feed it a steady diet of loose, low-density scrap like white goods. “It’s nearly impossible to get high production on loose goods if they contain a lot of air,” Masters states. The solution is to flatten such airy material to make it denser.
Proper scrap preparation also includes checking for problem items such as gas tanks and unshreddables—any items that could slow production. These preparation steps “stage” the scrap for the infeed crane, which leads Masters to his second point:
Get Your ‘Craneage’ Right. It’s an unfortunate fact, he says, that most processors “under-crane” their shredding operations, expecting one crane to handle the two tasks of preparing and loading scrap. Ideally, one or more cranes would prepare and stage scrap while another crane or two would load the conveyor. As an example, Masters notes that he had four cranes preparing and loading scrap at a shredder he used to manage. “It’s impossible to get maximum output without adequate density and continuous feeding of the infeed scrap,” he says. Continuous feeding enables the shredder to achieve a steady production level. Plus, keeping the shredder full aids the “attrition” effect inside the shredding box—the process of shredded pieces hitting each other, becoming denser, and exiting the chamber, Masters explains.
Presentation Counts. Shredders also work best when they’re fed a well-presented bed of scrap, with no pieces in potentially problem-causing positions. “You need to be selective,” advises Masters. “This isn’t a matter of throwing on anything you find. If you do that, the material doesn’t work well when it gets to the shredder.” The goal is to load scrap onto the conveyor so it can go straight through the system. “That’s what the cranes need to do to enable the shredder to do what it’s supposed to do,” he says.
So much for the front-end rules of smart shredding. By following them, you’ll achieve higher, more consistent production and eliminate most problems at the shredder and beyond. As Masters notes, “If you’re consistent in the way you feed the shredder and consistent in filling the mill, everything will look after itself.”
The Sum of the Parts
Beyond these front-end rules, the success of any shredding operation depends on the system itself, of course—its features, layout, and so forth. In general, the better the parts, the better the sum of the parts.
CSR certainly spared little expense on its Texas Shredder system. “This shredder has most of the gadgets,” Masters says. “Most processors would die for this.” And Masters can’t resist showing off the system’s gadgets, so—despite the cold weather—he embarks on a show-and-tell tour of the shredder, pointing out various features that can make a bottom-line difference.
First, he offers a little background, noting that CSR’s shredding system was modeled after one designed by Gérard Lavoie and installed in 1999 at the Montréal headquarters facility of American Iron & Metal Co. Inc. Lavoie, who has been serving as director of the CSR shredder project, incorporated the best parts of the Montréal shredder in CSR’s system, plus some new features.
One such feature is the elevated infeed conveyor, where Masters begins his walking tour. The conveyor, he notes, is mounted on concrete supports that hold the conveyor several feet off the ground to prevent dirt from building up on it and impeding its movement.
There’s another unusual feature about halfway up the infeed conveyor—radiation detectors on both sides that take a “last look” at scrap before it reaches the shredder, Masters points out. If the detectors sense radiation, an alarm sounds in the control tower and the infeed conveyor stops automatically.
If the infeed scrap is radiation-free, it proceeds to the heart of the system—the shredding chamber, which has been opened for final tweaks. Inside is the centerpiece of the shredder—a disc rotor. This is no ordinary rotor. It’s a no-weld, virtually maintenance-free rotor, says Gérard Lavoie, who developed this rotor as a solution to the maintenance demands of spider rotors and other disc rotors. The rotor is made of high-quality, T-1-type steel discs that have been specially heat treated and rolled to resist wear, last longer, and shred more tonnage—400,000 tons or more—with minimal maintenance than other rotors, Lavoie claims. When the discs do wear down, they can be replaced—a cheaper option than buying a new rotor.
While the rotor is important, a shredder’s productivity relies heavily on the motor that powers the rotor. Masters has strong opinions about motors. In his view, “No one should use anything but a slip-ring motor. It’s a little more expensive, but it’s the easiest to work with and understand, plus it’s the most successful in actual shredding operations.”
Why is a slip-ring motor so good? Because, explains Masters, it can operate at constant speed—without power spikes—even as the demand load changes. Other motors tend to lose momentum and suck up energy when their demand load increases. A slip-ring motor, in contrast, senses the greater load and disengages, or slips, transferring its extra energy into a brine-filled tank (liquid rheostat) that dissipates the energy as radiated heat. The result is that the motor can turn at less than the rated speed without causing significant power spikes.
On the topic of motor speed, Masters notes that CSR’s shredder motor—a 4,000-hp Alstom unit—turns at about 450 rpms, which is relatively slow compared with other shredder motors. That’s a good thing, though, because slower rpms can translate into more consistent production at a lower energy level. As he explains, a motor and rotor turning at lower rpms draw scrap into the chamber better and have a lower wear part cost per ton than a motor and rotor turning at high rpms.
Before proceeding to the downstream part of CSR’s shredder, Masters notes two final innovations related to the shredding chamber: First, there are the vibration sensors at both ends of the rotor shaft and the motor shaft. These sensors monitor the vibration of the rotor and motor bearings, providing data that can warn of impending problems. Such monitoring is wise since the rotor and the motor are the two most expensive components in a shredding system.
Second, Masters points like a proud parent to the shredder’s Smart Water Injection System, which he developed with Jeremy Watson of The KA Wing Group. The water system begins at the infeed chute where jets on both sides spray incoming scrap to suppress dust.
The real water action, though, takes place inside the shredder. There, four to six jets—installed in the back vertical wall—squirt water into the chamber. The amount of water injected ranges from 5 to 11 gallons a minute based on the demand load on the motor—the higher the load, the greater the water flow, Master says. The injected water is turned into steam by the heat from the freshly shredded scrap and the air velocity from the scrap and swinging hammers. This steam removes the oxygen in the chamber and minimizes dust, reducing the potential for fires and explosions. If a fire does break out, the Smart system automatically fills the chamber with water to extinguish it.
By minimizing dust, the Smart water system not only minimizes the risk of fires and explosions, it also eliminates the need to have the dust-collection cyclone attached to the shredding box, as is common in dry shredding operations. Such cyclones are notorious sites for explosions because they provide a dry environment in which oxygen, fuel fumes, and dust can mix, Masters explains. Separating the cyclone from the shredding box and moving it farther downstream eliminates such concerns.
As Masters heads toward the shredder’s downstream system, he stops to note an unusual feature under the shredding chamber—the undermill vibrator (which catches the outgoing shredded scrap and feeds it onto the offtake conveyor) sits not on the customary steel springs but on solid rubber discs or “donuts,” as Masters calls them. These discs are better than springs at absorbing vibrations and aren’t damaged as easily, he says.
On to the downstream system, which begins with a single offtake conveyor that carries the shredded stream under two ferrous magnets installed in-series—one after the other. (Another option is to split the ferrous stream and run each line through a single ferrous magnet, Masters says, noting that each approach has its advantages.) The two magnets pull ferrous scrap from the stream and send it tumbling down a Z box, which removes any remaining unwanted material from the stream. A splitter chute then divides the ferrous scrap stream onto two conveyors to spread it out for the next step—sorting.
The two ferrous conveyors disappear into an enclosed sorting station that can accommodate four pickers (two on each belt, working from opposite sides). It’s their job to pull out any residue and nonferrous metals. Notably, the pickers can vary the speed of the conveyors to achieve maximum sorting, Masters points out. The clean ferrous scrap is then carried outdoors by the stacking conveyor and piled to await shipment.
As for the nonferrous residue stream, it flows under the two in-series ferrous magnets and passes under a magnetic ferrous recovery conveyor to extract any remaining ferrous scrap and ensure that no residual ferrous pieces enter the eddy-current system. On Lavoie’s recommendation, CSR installed its eddy-current system in-line, as an integral part of the shredder’s downstream system. While other shredder operators install their eddy currents off-line, Lavoie prefers the in-line approach because it eliminates the need to “double handle” the residue as is necessary with an off-line system. Lavoie’s in-line system, in fact, offers the best of both options: It can operate along with the rest of the shredder’s downstream system, or it can be idle thanks to a Lavoie-designed bypass door that can direct residue into a bay for future sorting.
When the nonferrous system is operating, residue feeds onto a bivi-TEC flexible screening device that divides the nonferrous into two streams of different sizes. The two streams are then carried on separate conveyors into the eddy-current building, which houses two separators from Huron Valley Steel Corp. that sort the metals from the nonmetallic materials.
Given the depressed state of the ferrous scrap market, such nonferrous recovery operations are more important than the ferrous side, Masters asserts. “Everybody’s shredding for the nonferrous—there’s a lot of money here,” he says, gesturing around the eddy-current building. “If you don’t do a good job on your nonferrous, you’re not going to make money.”
After the eddy currents have done their work, the remaining fluff is conveyed into a huge bay that’s enclosed on all sides except one. Lavoie came up with the idea for this bay to address several issues: For one, the bay would shield the fluff from the wind and prevent it from being blown into a nearby stream. Also, the bay would prevent the fluff from getting wet and heavy, saving additional per-ton costs to dispose of the material.
The Brains Behind the Brawn
You’d think that such a smart shredder would, by definition, have some kind of brain—and you’d be right.
Today, a shredder’s brain is a programmable logic controller (PLC) system, which is composed of a processor and input/output modules, explains Ken Lisenby of KDL Electrical Engineering (San Antonio), which designs automated machine controls for Texas Shredder and other manufacturers.
The PLC continuously monitors the shredder’s operations based on input data that’s sent from every part of the system. The PLC processes all of these inputs and determines which outputs should be turned on or off, Lisenby notes. In addition, if the PLC detects an alarm condition, it sends a descriptive error message to the operator’s screen.
Modern PLC systems are a vast improvement over previous shredder control systems, which relied on simple on/off relays, Lisenby says. It wasn’t unusual to have 50 to 100 relays in a system, and any change had to be done manually—a time-consuming and tedious practice. Old control systems were also bad at warning of potential problems and identifying the cause of problems when they did occur.
PLC systems, in contrast, can be changed easily and quickly via computer, Lisenby says. They also make it easy to know the status of any part of the system and to identify the source of problems. Among other benefits, he notes, PLCs can transmit information continually through a high-speed ethernet network to other computers—in the control room, the manager’s office, or elsewhere. PLCs can also interface with other information systems such as those attached to the motor or scale. Plus, PLC systems can be connected via phone modem to the developer (like Lisenby’s firm) for remote troubleshooting.
While a PLC system is great for controlling the logical functions of machinery, it’s not designed to store data or analyze it. Yet access to such data and the ability to analyze it is just what shredder operators need.
That’s where the Hawkeye shredder management system—another Masters creation—comes in. Drawing from his experience as a shredder manager, Masters designed the system to serve as a “yardstick” for measuring shredder performance. “The purpose,” he says, “is to give the operator better data to achieve maximum shredder operations.”
On his laptop, Masters calls up the program and begins to point out its features: The Microsoft-compatible system, he notes, has two “sides” to it—one for information-gathering and one for analysis. The analysis side wouldn’t be possible if not for Hawkeye’s ability to archive information. While other shredder management programs can indicate how a shredder is doing now, they don’t archive that operating information for future analysis, he claims.
When the Hawkeye program is started, a color bar at the top indicates the shredder’s current status—green if it’s running, red if it’s not running (with the reason and duration of the delay noted), or blue if it’s undergoing maintenance.
Before the operator can start the shredder, he must identify himself and note the material being shredded using the program’s touch-screen. No other data needs to be entered unless there’s a problem or delay.
Once the shredder is up and running, Hawkeye gives the operator real-time production data and provides information on important system variables such as the load demand on the motor, the temperature of the rotor and motor bearings, and more. All of this data and information is archived in Hawkeye’s memory for future reference.
If the system detects a problem or delay, a screen pops up with icons for the most-common shredder problems, such as blocked infeed rollers, gap in feed, unshreddable, and so on. The system won’t let the operator continue shredding until he selects one of these icons. When he does, another screen appears asking him to specify the problem area—infeed, hydraulic, mill, ferrous, nonferrous, sorting/waste, or miscellaneous. Touching one of these calls up a detailed list of problems in that area of the shredder, enabling the operator to quickly and precisely note the problem. Only by providing this information can the operator get the shredder working again.
While the Hawkeye system gives real-time data to the operator, it provides archival information for management. That’s the analysis side of the system, which enables shredder owners to scrutinize their operations in unprecedented ways, Masters states.
Hawkeye offers several analysis options, all of which are listed in an Outlook-type bar on the left side of the screen. The Current Status option, for instance, shows the shredder’s operations today, 30 seconds delayed. Here, management can review data on when the shredder ran, when it was delayed, who was operating it, what material was being processed, the shredder’s tons per net hour, tons per gross hour, ferrous tons produced today, nonferrous tons produced today, the number of unshreddables encountered, and on and on.
The other analysis options include Prior Performance, Plant Utilization, Plant Efficiency, and Material Performance. Within each area, users can “filter” the data in virtually any way and for any time period, creating customized reports to fit their needs. According to Masters, Hawkeye is “the only system that has a relational database, which means we can search it from a lot of directions.” If, for example, you want to know what was the most-frequent operating delay in the first six months of last year, no problem, he notes. Or you could see which operator had the highest productivity last month, or which material gave you the highest recovery, ad infinitum.
So, what do you do with all of this information? What’s the point?
Masters is more than happy to explain. “The goal of good shredding,” he notes, “is to achieve straight-line everything—straight-line production, straight-line costs, straight-line efficiency from day to day, week to week, month to month. When we graph it, we’re as straight a line as possible. We don’t have blips.” In essence, then, the Hawkeye system provides the information shredder operators need to measure their performance—and to see how close, or far, they are from the straight-line goal, Masters says.
The Final Key to Success
While there’s no denying that shredders have become more brainy and sophisticated, they can’t run themselves (yet). They still need people to prepare and load the scrap, maneuver the infeed rollers, pick through the processed streams, oversee the operation—and therein lies the final key to the success of any shredding operation: teamwork.
“Good shredder management really comes down to good teamwork,” Masters affirms.
Looking around at CSR’s shredder, he says, “This is a wonderful shredder plant. It’s one of the best you’ll come across in its layout, its logistics. But if it had a bad team, it couldn’t be a high-production shredder.” Having a great shredding system isn’t enough. “It’s like putting a Formula 1 car in the hands of a bad driver—he won’t get it to run fast,” Masters continues. “You need a good driver to go with the car and a good team of mechanics behind him.”
The point is this: Behind every productive, well-managed shredder are employees who work as a team and who are well-supported by their employer. “If you just want to buy one of these things and say, ‘It’s only a shredder, it’s going to make us pots of money, and we’ll never have to touch it again,’ that’s the wrong attitude,” Master says. “This is about building a good team and supporting it.”
It all starts with how a company takes care of its employees. In many shredding operations, employees work in less-than-ideal conditions. At CSR, in contrast, every shredder employee—from the crane operators to the pickers— works protected from the elements. The pickers on both the ferrous and nonferrous lines, for instance, have enclosed work stations, complete with heating and air-conditioning. All crew members also have access to the shredder building, which contains a lunchroom and bathroom on the first level, the shredder manager’s office and motor/PLC room on the second level, and a posh shredder control room on the third floor. Such amenities improve employee morale and make them feel “well-looked-after,” Masters says.
There’s more to building a good team than providing decent working conditions, of course. Other issues include wages, benefits, incentives, and a reasonable work schedule. These and other personnel issues must be addressed, Masters says, if you hope to have a dedicated, productive team—and, hence, a high-production shredder.
The prep work on CSR’s shredder is winding down, and the word among the shredder crew is that the system could process its first tons tomorrow. That moment will usher in a new era for CSR as a scrap company and represent one more step forward for the smart-shredding cause.
Masters, a foot soldier for this cause, is already looking ahead to future steps forward for the shredding niche. For one, he’d like to see broader use of an infrared imaging system that can look through steam at the shredding box and provide a clear picture of the material entering the chamber. For another, he hopes to create a maintenance module for Hawkeye. He’d also love to someday develop equipment that could detect unshreddables on the infeed conveyor and prevent them from entering the shredder.
G reat ideas all, and only time will tell if Masters can realize them. Regardless, he remains an optimist, a shredding dreamer. “The sky’s the limit with this—it can move on from here,” he says, looking out at the bright January sky. •
No more shredding by guesswork. It’s time to get smart. here, Trevor Masters, shredding guru, reviews the state of modern shredding and tells what it takes to run an efficient, productive, and profitable shredder.