September/October 2011
More specialization and more competition are trends in the low-speed, high-torque shredder market, as companies find a wider array of scrap materials they want to cut down to size.
By Jim Fowler
One manufacturer of low-speed, high-torque shredders shows off the power and versatility of its equipment—and has a little fun at the same time—by posting videos online of its “Shred of the Month.” The series has covered routine scrap materials such as electronics, tires, metal, plastic, paper, and wood, but more memorable are the unusual items: an upright piano, bowling balls and pins, a Dodge Daytona, and even boxes of Hostess Twinkies. The take-away message is that whatever you’ve got, these machines can shred it.
Indeed, recyclers are using low-speed, high-torque shredders for a wide variety of scrap processing. “In the past, we did simple [size] reduction applications, such as [with] pallets, to reduce the volume to make a more efficient landfill,” one manufacturer explains. “Those applications are still out there, but we don’t see as much of them anymore. Today there are more applications in recycling and recovery, including an ever-wider range of materials, such as e-scrap, alternative fuels, aluminum, carpeting, plastic fibers, and used beverage containers. We’re using the shredders to do higher volumes as well as [to] clean and separate the material for better recycling efficiency.” In other words, it’s not just the markets that have changed. The goals of shredding, in addition to size reduction, might be size uniformity or liberation of joined or mixed materials. This evolution in low-speed scrap shredding has led to changes in what equipment producers offer and increased competition to be the recycler’s shredder of choice. Notable trends include the following:
More want four. The growth of the e-scrap market is what manufacturers credit for the growing popularity of the four-shaft shredder over its single- or dual-shaft brethren. You can’t scrap electronics with a single-shaft shredder, asserts one company representative, “because they tear as opposed to cut the material. Since they work at high speed, you get a lot of potential sparking. And you don’t get size control.” Another company’s engineer points out that “four-shaft shredders are screen-integrated, so the product can’t exit the machine until it’s reached that [screen] opening’s desired size.” With electronics, “you want to break hard drives enough so you destroy the data and get material separation to achieve the best price for the product,” says a different company rep. “Separation and size control are two of the reasons four-shaft shredders are in such demand.”
Other companies disagree that four shafts are the only way to achieve those goals. One says its higher-speed, single-shaft machine can do the job just as well. “We’re running our single-shaft shredder at about 190 rpm as a pre-chopper,” a company representative says. “We don’t feel it’s necessary to run at 48 rpm for e-scrap. We’re running at the higher speed for production purposes, to get more material through the machine, and it’s processing e-scrap just fine. Our pre-shredder cuts the plastic, and we do have size control, with screens in both our pre-shredders and our granulators. … We do not ever tear [the product]—our blades are sharp, and we have blades on the rotor and fixed blades with a 3 mm gap” that cut the product. Another manufacturer points out that with the right set of cutting knives and classification system, its dual-shaft machines for tire shredding can produce the uniform tire-chip sizes that many markets demand.
Bigger is better. Buyers don’t just want more shafts, they want more power and capacity as well. “Four-shaft shredders have gotten huge, and they continue to get bigger and more powerful,” one manufacturer says. He attributes this demand to scrap industry consolidation. “Larger companies want more throughput and fewer, more versatile machines, so we have just gotten bigger and bigger.” Increased capacity and strength is not the only benefit of a larger machine, one manufacturer points out. “Making the machines more robust leads to more uptime,” he says. “Larger shafts and drives and bigger bearings allow the machines to perform at a very high level while still being online a greater percentage of the time.”
Another driver of the demand for big, powerful equipment, at least in Europe, is the growth of dedicated processing for large appliances. In the European Union, large appliances such as washers and dryers fall under the Waste Electrical and Electronic Equipment directive, points out one manufacturer. “The need to process these items intact, at high capacity, has driven the design for the larger, more robust four-shaft shredders.”
When processing tires, however, bigger is not necessarily better, says a company that specializes in that market. “When you overbuild these [shredders] and make the shafts too long, they bend or twist, which affects how the knives cut. That can reduce efficiency and break the equipment. We keep our boxes and shafts to a standard size so [the shafts] don’t warp or twist in the box, and you get a good, clean, consistent scissor cut. … We don’t think faster or bigger is better.”
Scrap-specific shredder designs. “Shredders have gotten away from being a general design for all applications,” with manufacturers instead creating specific designs for specific applications using the same basic shredder model as a base, one manufacturer says. At his company, he says, “we’ve developed specific cutting-chamber designs—the knives and the configuration of the knives—that optimize the shredder performance for particular applications. That’s done through the design and emerging technology [for] the cutting-chamber components and the drive components. … With e-scrap, paper, and metal we can do very well, but when you try to [design a machine to] do everything, it’s a compromise.”
These modifications have been largely customer-driven. As one design engineer puts it, “You have a client with a specific application that doesn’t fit with the old knowledge, so you work on developing a solution. ... We are dealing with more challenging applications than we were a decade ago, and the standard machine doesn’t fit as many applications as it did previously. We have to custom-tailor our standard machine to meet the customer’s needs.” Special knife designs and configurations for which one company has received requests include additional hooks, harder cutter treatments, designs that allow the processing of metals such as titanium, and those that can shred small items such as ammunition. Those applications would not have been common a decade ago, that company representative points out. Another manufacturer offers 300 different cutting system combinations for different applications. “As new applications come along, a good company is willing to try different things, such as the arrangement of cutters and the number of and shape of teeth to accommodate a different material,” says that company’s rep.
What makes all this customization and variation possible is new design technology, says one manufacturer. With computer-aided design, “you can try different things and do it a lot faster than you could in the old days,” he says. “You can do [finite-element analysis] to see how much stress is going to be put on a tooth. You take a design that you think is going to work a little better, run it through the FEA, and you learn, no, that won’t work, I’ve got a stress riser where I put this hook on the tooth.”
These manufacturers point out that one major market for their shredders, tire recycling, remains challenging in terms of equipment design. “Tires are an expensive component to recycle,” one shredder engineer says. “Tire manufacturers are trying to build tires so they last. That makes them much harder to shred and process down to crumb, [tire-derived fuel], or tire-derived aggregate. It’s very expensive to size-reduce a tire because there are a lot of abrasive components, dirt being one of them. It takes more power, and it’s hard on the knives.”
These manufacturers characterize the domestic tire market as “mature”—in other words, their sales of shredders to U.S. tire recyclers have been flat or down, though overseas markets are growing. The company that specializes in the tire market says that domestically its growth is in turnkey systems and advanced processing, such as granulation and wire removal, that creates cleaner material for more and better revenue streams.
Though potential new markets for low-speed, high-torque shredders might seem unlimited, one manufacturer is more cautious. “We’re always cognizant of what the shredders are not capable of doing and trying to make sure they don’t get into applications they’re not suited for, long term.” He gives the example of potential customers who want to use his company’s low-speed shredder as a car shredder. “You still want to stay within the niche the equipment is good at and try to not push it into areas it’s not good at. It might work in those areas for a short while, but long term it’s not a good solution.” (Even the company that has video of its machines shredding a car or two notes that it did so only to demonstrate the machine’s strength—the company does not recommend these shredders for processing automobiles.)
Real-time monitoring. Ever-improving computer technology also has aided low-speed-shredder users, who can now keep a closer eye on shredder operations. “Instead of just having an on/off switch and some [programmable logic controller] that tells you the machine ran into something that’s causing it to run light, you can look at a computer touch screen at the shredder that will show you that this shaft ran into something and there is high amperage on those two motors,” says a company engineer. “It tells you what’s actually happening with the machine in real time. It also monitors the oil level in the gear box and other parameters that previously required someone to do those checks manually.” Another company touts its tire shredders’ touch-screen systems, which can display any of 40 different languages. With them, users “can speed up and slow down conveyors and feeders to prevent overload, and they can manage water temperature to keep material at a certain heat level.” The user can monitor the shredder from elsewhere in the facility, not just on the plant floor, and the manufacturer can check diagnostics remotely.
No consensus on electric vs. hydraulic. One manufacturer believes the industry wants more direct, electric-drive shredders for their higher torque and reportedly better reliability. Though a direct, electric drive “simplifies installation and maintenance, it requires the processor to be more diligent with its feed systems,” he points out, “because electric drives can’t deal with an unshreddable or high-load condition as [well as a shredder] with a hydraulic drive. You either have to be more attentive to the feed side or have a greater degree of certainty that the feed material is not going to generate a high percentage of unshreddables.” Two vendors say they only use a hydraulic drive for their shredders if the customer insists on it.
But hydraulic drives have advantages, too, companies say. Hydraulics offer good speed control and packaging control, which means you can put the power pack where you want it, the shredder where you want it, and run the hydraulic lines between the two. Further, says one manufacturer, with hydraulic drives, “there is a certain amount of sponginess when the cutter runs up against something it can’t shred. Because there is internal leakage in the hydraulic motors, you’re going to get a little bit of give, so you won’t be getting a huge shock load.” The disadvantages of hydraulic drives, he adds, are that they’re less efficient and produce more heat.
One four-shaft shredder manufacturer believes that e-scrap processing requires a hydraulic drive. “Within the e-scrap stream, you may have large, solid masses of metals—smaller motors, transformers, heat sinks—which can be difficult in an electric-drive shredder. We’ve developed a line of hydraulic-drive quads because if you try to do that [material] with electric drives, you’re forced to put in an even heavier, more robust gear box. While hydraulic drives can handle these metals, electric drives can struggle with them.”
Another manufacturer points out that hydraulic drives “will always play a role, especially in mobile equipment, where there is no way to get [electric] power in. They also have a place where you experience high shock loads. You can put nitrogen-charged accumulators in the system that have a bladder that takes up shock so you don’t have that mechanical shock going back into the drive train.”
One company has designed a shredder with four motors that indirectly drive four shafts through a newly designed gear box that allows a great deal of flexibility in terms of the size and type of motors it can use— either one or two hydraulic or electric motors—making it very versatile, the manufacturer says.
Increased competition. With the growth in markets for low-speed, high-torque shredders has come more companies wanting a piece of the action. “The market has become a bit more crowded with low-priced shredders,” one manufacturer notes, “making it more difficult for buyers to make informed choices about what shredder or brand to buy.” He warns buyers about copycat products manufactured in Asia: “They look like a shredder you would buy from North America or Europe, but they’re not made nearly as well, and they sell basically on price. … Usually a processor buys one of them, but only one, because they don’t last.”
The competition isn’t just coming from Asia, however, says one North American manufacturer. “Some farmer who’s retired and has been fixing his equipment with baling wire and duct tape for years thinks he can make a shredder, and he does, and it hurts everybody.” He adds that “There are so many more players, and players that don’t know what they’re doing. I’m hoping the day will come when they’ll just go away, but they probably won’t.”
Despite this increased competition, these shredder manufacturers see a rosy future for these machines. “I think the future for low-speed, high-torque shredders is very good,” says one company rep. “There are people who will use these machines for functions we haven’t even thought of yet. It’s like the application finds the machine.”
Jim Fowler is retired publisher and editorial director of Scrap.
More specialization and more competition are trends in the low-speed, high-torque shredder market, as companies find a wider array of scrap materials they want to cut down to size.