July/August 2013
By tinkering with metal alloys and part designs, makers of automobile shredder wear parts are working to keep up with changes in shredder design, power, and feedstock and produce parts that balance price and longevity.
By Theodore Fischer
Manufacturer hyperbole notwithstanding, today’s automobile shredders really are better than ever. They’re bigger, faster, more efficient and reliable, and significantly easier to maintain. The current generation of shredders consumes less energy to produce cleaner, higher-density scrap and almost effortlessly process every type of metal that comes its way.
Of course, original equipment can’t last forever. Hammers, grates, rotors, and similar wear parts eventually will wear out, and shredder operators will need to replace them. Shredder wear part suppliers say they have adjusted to the evolving demands of their customers. “Shredder [operators] have a lot of choices to meet their changing needs these days,” says one wear parts manufacturer. “The focus has changed from [maximizing] volume to maximizing nonferrous recovery and cost control, and there are many tools available to the shredding team that knows how to deploy them.”
Beneficial wear-part innovations include specialized heat treatments, improved metallurgy, weight-efficient designs, and improved geometries. “We’re finding operators willing to experiment, measure, and benchmark improvements to … adjust their shredder setup to optimize operating conditions,” he adds. “That was not so widespread years ago.”
Another wear parts manufacturer says it has adapted its products to the larger and more powerful shredders that have emerged on the market. “As the size and horsepower of the shredders increased, the design of the wear parts stayed pretty much the same,” he says. “We had to make our wear parts stronger to handle the larger machines.”
Hammer Headings
The wear parts shredder operators most frequently replace are the bell-shaped hammers that do the shredders’ heavy lifting. “The application of hammers against scrap is the most aggressive application of a wear part known to man,” says one wear parts manufacturer. “Crushing, mining—compared to any of those other applications, the shredder is the most aggressive. So what you want is a material that is extremely tough but at the same time ductile.”
Shredder hammers traditionally are made of some type of manganese steel, an alloy patented in England in 1883 by Robert Hadfield. Manganese steel must contain between 11 and 15 percent manganese and 0.8 to 1.25 percent carbon, a mixture that manufacturers tweak according to their proprietary formulas. Resistant to abrasion, manganese steel hammers can handle scrap that’s three times their own hardness with no increase in the brittleness typically associated with hardened steels.
Some replacement hammer suppliers remain loyal to their original manganese formulations. “While there are ways to make the material a little bit cheaper, by removing alloying elements, you do run risks of reducing the ultimate wear life and toughness,” says one hammer manufacturer. “We tend to stay with the reliable chemistry because we know it pays dividends. The perceived economy [of less expensive blends] does not bear out.”
The principal alternative to hammers made of manganese alloys are those made of differentially hardened low-alloy steels, which are gaining a particularly strong following in Europe. As one company describes it, traditional manganese alloy hammers that are not work-hardened have the same hardness throughout. During use, however, they become “significantly harder” on the outside, which enhances their abrasion resistance, while retaining a ductile core, which improves their impact resistance. With differentially hardened low-alloy steel hammers, the impact surface is nearly twice as hard as the pinhole area, and harder than other hammers, which makes them an alternative in applications that have more abrasion and less impact. Which hammer works best for a given shredder operation depends on many abrasion-vs.-impact factors, which is why one vendor recommends a “test-and-try” approach.
Uniformly hardened manganese hammers tend to cost less, requiring only a single-step heat-treating process—one quench—while the four-step heat-treating process for differentially hardened alloy hammers significantly raises their price. Whether these hammers are worth the extra price depends on who you talk to.
“In certain applications it might be worth it … but the majority of our customers do not use them,” says one vendor. “If you’re not worried about unshreddables and you don’t have a lot of tough scrap, I can see taking a risk on differentially hardened alloy hammers or mixing them with [traditional] manganese hammers. But if you’re constantly having problems with unshreddables, you don’t control your mix, or your cars are not ripped apart—as they are in Europe, where they disassemble the cars and take out motor blocks so [the cars are] relatively clean—you should stick with manganese.”
Another supplier, who also offers both, swears by the differentially hardened alloys. “The initial cost to get the alloy hammer is more expensive when you buy a container or a truckload of them,” he says. “But in the end, the net total cost for the shred that’s going out the door and into the gondola or truck to be hauled away is less,” he says, because the hammers process more tonnage overall—“and the people who buy them are happy.”
Yet another supplier insists that differentially hardened alloy hammers are better equipped to handle what today’s operators are putting into their shredders. “As time has gone on, the mix has changed,” he says. “In a lot of the shredders there’s a lot more loose goods, loose material, loose whatever, and the alloy hammers are wearing better. The manganese hammer doesn’t have that impact and doesn’t shred as well.”
In a quest for a material that’s both harder and more wear-resistant, one manufacturer has been tinkering with the chemistry of the manganese and the differentially hardened alloys. “We have modified our chemistry to make, not exactly a mixture between the two, but actually an improvement [in] the manganese based on what we have seen as the benefits of the alloy,” he says. “The cost went a little bit higher because we’re starting to put some other elements in the casting that make it a little more expensive. But it prolongs the life way more than the actual cost of the casting itself, so it’s worth it.”
Grate Expectations
For the grates that filter metal out of shredders, wear parts manufacturers have adapted their output to satisfy shredder operators who are processing materials unheard of even 10 years ago.
One solution is to laminate two sets of grates together, called double-beam grates. “This gives us a lot more strength to handle what [shredder operators] are trying to do with these grates,” says one wear parts manufacturer. “That was a good solution for the larger machines, and we’re finding that it’s working in all the models, all the way down to the smaller ones—just giving that part more strength and longer life.” Along with their added strength, the double-beams are more rigid to better reduce flexing and bowing, which can occur when shredders run at lower revolutions per minute, significantly shortening the grates’ wear life. Some double-beam designs feature staggered grate openings that situate one grate beneath each hammer track to increase throughput.
An additional design innovation is a discharge grate with round openings that provide up to 35 percent more discharge area than typical rectangular grate designs, the manufacturer says, and they remain uniform throughout the grates’ wear life. The company offers circular grate openings in heavy-duty double grates and single grates.
Another manufacturer, as part of an ongoing effort to modify castings to reduce shredder maintenance, has bolstered the support plates that hold the bottom grates in place. “After a certain time, you have to rebuild the support plates because they start to wear out,” he says. “So we added a rib behind the bottom grate to make it stiffer and not require support in the middle, only at the end. Once you eliminate those pieces of the housing, you don’t have to do that maintenance work anymore; you lower your cost per ton and have less downtime.”
Rotor Derby
The rotor that turns the hammers is the Big Kahuna of shredder wear parts, by far the largest and costliest item to replace. The most common style is the disc rotor, which is generally considered the easiest to operate, requires the least maintenance, and can process a wide variety of mixed scrap. Enclosed barrel rotors, which protect rotor discs from scrap, are best suited for lighter scrap such as automobiles and white goods. Four-arm spider rotors, which usually have full helmet caps and fully capped end discs, excel in processing autos, aluminum, and light scrap, and they generally have the highest life expectancy, up to 500,000 tons.
What seems to be influencing customers’ choice of rotor most during these relatively hard times is the purchase price. “Buyers are going for the price of the rotor more than what it costs in the long run,” says one supplier. “Our company provides long-lasting rotors, and we’ve had pretty good success, but it comes with a price. Not everyone can see that, at the end of the day, it’s going to be better.” This company fortifies its replacement rotors with Faraday steels.
One shredder manufacturer recently began designing and manufacturing disc- and spider-style rotors for its and competitors’ shredders featuring high-grade materials such as tie rods that it says feature 30 percent greater mechanical properties than others on the market.
Maintenance First
Maintenance, which goes hand in hand with workplace safety, has been another preoccupation of shredder wear part providers. “Shredder guys today don’t want to have downtime; they’re looking at their total uptime,” says one parts producer. “They want to be running 95 percent of the time, and if they have a quality problem with a grate or a hammer or an anvil, it’s not easy to change parts, so total uptime is becoming more and more important.”
Consequently, wear part producers now focus on making parts easier to install, easier to remove, and longer lasting. “Our goal is to get the maintenance crew out of there, not only for cost reasons—these guys cost you so much per hour, plus downtime—but safety also,” says one wear parts provider. “We put in design features that make the parts pull out easier. That’s one side of it. The other side is that if you can make it last twice as long, you reduce your maintenance time—and the probability of injury—by half.”
Nevertheless, buyers have to carefully weigh the potential benefits of lower-maintenance parts against their higher prices. “I’ve been using a particular hammer for years, and it all comes down to how many tons I can process per set of hammers—it’s a definable cost,” says one shredder operator. “When someone comes to us and says they’ve got the best hammer in the world, we’ll try it because we’re always looking for betterment. But then it comes down to the old cost-benefit-ratio analysis of my cost per ton for whether brand X hammer is in fact better than what I have been using. The analysis has to prove if the vendor really has a better mousetrap.”
The Price Is All Right
Shredder wear parts cost more these days, but usually not a lot more. One vendor says his prices tend to track the prices for raw materials, which have remained relatively stable since the giant run-up before the recession.
Another manufacturer believes buyers today are less concerned with purchase price than with lifetime cost. “Today, after all the cycles we’ve been through, people are really watching the total net cost,” he says. “Some said they did this five, 10 years ago, but I think a lot more people are watching it a lot more closely today.”
Though European-made wear parts are for the most part priced out of the U.S. market, many, if not most, U.S.-based suppliers have their parts made less expensively in China, Brazil, and elsewhere, “which isn’t necessarily bad,” says one wear parts buyer.
In fact, one producer calls itself a “dying breed” because it still makes wear parts in a U.S. foundry—and consequently has to charge more than the competition. “We’re not playing by the same rules: While our costs seem to be going up, forcing us to raise prices, a lot of countries can come in a lot cheaper,” he says. “So we have to compete in other ways, by specially designing each part so it’s most effective for the shredder. The customer has to see the results, see the cost-effectiveness of our parts.”
Part-ing Shots
When do you need to replace shredder wear parts? A rule of thumb is that you need new hammers when they have worn down to less than half of their original weight. If only one hammer has to go, you should probably replace the opposite hammer anyway, to keep them in balance. Replace rotors when they crack or show obvious signs of wear, or when a catastrophic breakdown occurs upon encountering an unshreddable. Keep an eye out for cracks and erosion of bottom grates, which usually wear out sooner than top grates.
Finding the perfect shredder wear parts is no walk in the park, these vendors and shredder operators say. “If it was straightforward and there was an absolute formula for doing this, there would be only one style of hammer, one alloy chemistry,” says one shredder operator. “But it’s a moving target, and everybody has differing opinions.”
Much of the decision depends on your particular shredding activity. If you principally shred sheet iron, for example, one type of hammer will work better than another. Those who do wet shredding will benefit from different equipment than those who do damp shredding.
Though one size does not fit all, one tactic does. “Before you move to someone else’s wear parts, get a set of whatever it is and do a true analysis,” advises a seasoned shredder operator. “Install them, run them, see what kind of performance you get. If you don’t get good performance, don’t go back to that vendor; if you get poor performance, go and ask for some of your money back.”
This operator also believes advanced preparation is essential wear-parts strategy. With these parts, “you’re dealing with long-lead-time-type items, and the amount of spares you have in stock will determine what your success is in the industry,” he says. “In the last five years, there’s been a rush to the shredder industry. There are a lot of unsophisticated people operating a lot of relatively new equipment. The question is whether they’re willing to spend the money to be prepared for certain types of failures.”
And one wear parts producer passes along some advice he received from Ted Lipman, a former chairman of ISRI’s Shredder Committee: “Make sure you go to your [wear part] supplier and ask for stuff because they can make changes,” he says. “It’s important for us to hear your feedback on what’s working and what your parts need to be to make them work. Ask us for stuff. We can do a lot for you.”
Theodore Fischer is a writer based in Silver Spring, Md.
By tinkering with metal alloys and part designs, makers of automobile shredder wear parts are working to keep up with changes in shredder design, power, and feedstock and produce parts that balance price and longevity.