Equipment Focus: Preshredders

Sep 21, 2017, 19:59 PM
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September/October 2017


Sending end-of-life automobiles and other materials through a preshredder prior to a hammermill shredder used to be a foreign practice. Now U.S. recyclers are starting to appreciate the efficiencies and cost savings preshredders can provide.


BY Katie Pyzyk


PreshreddersIf shredder energy surges are driving up your electricity costs, if shredding baled material is placing heavier burdens on your smaller hammermill, or if the explosions or unshreddables in the hammermill are creating safety concerns, down time, and expensive repairs, the solution might be a preshredder.

In North America, using preshredders with hammermill shredders is almost unheard of, though they originally were developed in the United States in the late 1960s, according to one longtime industry participant. Yet low-speed, high-torque preshredders have been prevalent in overseas shredder yards for some time, especially in Japan and Europe. Now the equipment is generating more interest in North America. Why was there a delay? “In America, the idea [for preshredding] did not catch on at [first] because we were in the middle of developing larger and stronger shredders,” says the chairman of an El Paso, Texas–based equipment supplier. But now, he says, “interest is definitely increasing strongly in America and also in China.” Other equipment dealers observe the same trend. “We’re starting to see preshredders introduced into these markets, and we’re starting to get a lot more inquiries on the possibility [that they can] go in front of smaller automobile shredding systems,” says the vice president of sales and services for a St. Louis–based equipment manufacturer.

One reason for preshredders’ popularity is that they can help manage power costs. In countries without plentiful, consistent, or reasonably priced electricity, scrap processors have found preshredders can reduce the peak electrical demand and electricity costs of using a hammermill, manufacturers say. “It gives an overall line of protection from surges from a power standpoint as well as a material flow standpoint,” the St. Louis company vice president says. The CEO of a German equipment manufacturer concurs. “You have less power peaks,” he says, “and you have roughly 15 to 20 percent less power consumption in the main [hammermill] shredder” when a preshredder processes material first.

The United States has bountiful and inexpensive electricity compared with Europe, so U.S. customers “have a different philosophy: more horsepower versus less power consumption. We’re more [focused on using] brute force in the U.S. versus Europe,” says the general manager of North American sales for a San Antonio–based equipment manufacturer. Even so, “I do think there’s a future for [preshredders] here, and I think that market will continue to grow,” the St. Louis company representative says. Despite historically favoring large shredding equipment with high horsepower, U.S. auto recyclers are more recently recognizing the benefits of scaled-down machinery, and preshredders can help them make that transition. “In the last 10 years or so, there’s been a big push for smaller modular shredders … such as 60-inch-diameter hammer swings,” one of the San Antonio company’s reps says. Smaller shredders do not possess exactly the same processing abilities as larger models, so trying to handle the same type and size of feedstock can take its toll. That’s where preshredders come in. “Smaller shredders typically … can process car bodies in only limited quantities, so the addition of a preshredder allows for much more flexibility in what types of feed material these yards can acquire and shred,” another representative of that company says. “I think [a preshredder] is an ideal fit for that.”

Besides, “horsepower costs money,” the St. Louis–based rep says. A preshredder can “reduce the amount of horsepower required to shred, which, of course, should reduce the cost of shredding by not having to oversize the motor on the [hammermill] machine in order to get production.”


Dealing With Denser Infeeds Efficiently

In addition to the trend toward smaller shredders, equipment dealers note a shift in the types of materials scrap recyclers are processing. Baled material has become the norm, they say. “Before, you could collect scrap in a radius of 100 miles or less, so you didn’t have to bale that scrap. But now you have a lack of scrap, and you have to increase your radius to collect scrap, [so] you have to bale the material [because] that’s best for transporting,” says a representative for an Italian company’s German and French subsidiary.

Baled material might be more economical to transport, but it’s tough on all sizes of shredders, especially smaller ones. “A car is not a big problem for a shredder. A flattened car is OK. But the big problem is when you have cars baled,” the Italian company’s rep says. Sending dense materials such as bales through a hammermill shredder can cut production in half, says a shredding equipment consultant. “Electricity costs go up [and] production goes down,” he says. “A preshredder is better for bales.” The preshredder’s mechanics make it an ideal option for breaking down challenging stock, these companies say. For example, a New Hampshire–based manufacturer’s preshredder “runs at 20 to 30 rpm typically. It has a lot of torque,” the company’s regional sales manager says. “It can [work] its way through really tough material without bogging down.” Plus, the operator can alter each shaft’s speed and direction to assist with processing tough materials, he says.

Difficulty shredding dense material is exactly what prompted Crow Wing Recycling in Brainerd, Minn., to become one of the first U.S. recyclers to invest in a preshredder for a hammermill shredder. “We run a smaller shredder, 72 by 104, and we struggle to run baled material and larger vehicles,” says Grant VanWyngeeren, the company’s vice president. “We were looking at installing a larger shredder but came to the conclusion that the preshredder would give us similar capabilities as a bigger shredder but with a smaller investment.”

Preshredders increase operational efficiency by increasing throughput and reducing processing costs. A preshredder’s slow speeds and tearing action break down dense and potentially dangerous materials more easily and safely than a hammermill’s intense pounding motion, resulting in output that “can best be thought of as partially chewed food,” one of the San Antonio company’s reps says. Preshredders’ liberation and size-reduction capabilities ensure the material “goes into the secondary system easier, with less impact, with less electrical consumption, and with better wear life and protection of the [hammermill] machine,” the St. Louis company’s rep summarizes.

The result is more consistent flow, which increases efficiency. Measures vary depending on each scrapyard’s operations, but “in general, you have 25 to 30 percent higher production at the main shredder when using a preshredder,” the German manufacturer’s rep says.


Reducing Maintenance and Increasing Safety

A preshredder significantly reduces a hammermill shredder’s workload and, therefore, the wear. “The material will be less hard on [hammermill] internal wear parts and castings. It should reduce wear-parts costs, such as hammers and grates,” one of the San Antonio manufacturer’s reps says. In fact, a preshredder can reduce a hammermill shredder’s wear-parts consumption by up to 30 percent, according to the Italian manufacturer’s representative.

Because of a preshredder’s slow speeds and low-impact operation, its own wear parts—such as the rebuildable shaft teeth—have long lives. “It’s not like a [hammermill] shredder [where] you have to turn the hammers, and after 6,000 to 8,000 tons you have to throw away the hammers,” the CEO of the German equipment manufacturer says. “You have a much longer lifetime of all wear parts, so you have much lower costs.”

Numerous equipment dealers note the simplicity of maintaining a preshredder. “They don’t need detailed attention every day,” other than regular cleaning, says the St. Louis–based manufacturer’s rep. That said, one of the San Antonio company’s reps points out that “you have to keep up with the quality of your hydraulic fluids, with seals, and those type of typical hydraulic system things.”

If unshreddable materials find their way into a preshredder, the machine deals with them better than a hammermill could, manufacturers say. The preshredder’s hydraulic shafts automatically reverse the material flow when they contact unshreddables and reject any items that can’t go through after two or three attempts. This feature makes preshredders safer, they say.

A preshredder can eliminate a hammermill’s initial impact on potentially dangerous items, such as gas tanks, which increases safety by reducing explosions and fires. Equipment dealers say that’s a major selling point. “More [scrap recyclers] are coming under pressure about explosions,” the shredding equipment consultant says. Part of that is for scrapyard employees’ safety and part is because “there are more and more people moving near scrapyards around the country,” so explosions and fires at scrapyards raise concerns about the community’s safety, he says. In fact, some places, such as the United Kingdom, require a preshredder in order to get a permit to operate a shredder, according to the president of the El Paso firm. Mitigating the explosion risk with a preshredder also reduces expenses from downtime, repairs, and extinguishing fires.

Preshredders also can alleviate other undesirable conditions associated with hammermills, manufacturers say. “Preshredders … don’t typically produce lots of noise, dust, vibrations, or projectiles like higher-speed machinery can,” says the director of sales and marketing for an Oregon-based shredder manufacturer.


Purchasing Considerations

Some manufacturers offer all-in-one preshredder and hammermill shredder systems, but North American scrap recyclers more commonly purchase an independent preshredder they can add to the front of an existing line. The most popular preshredder design, manufacturers report, has hydraulic, counter-rotating twin shafts revolving at different speeds. Several dealers also offer three- or four-shaft models. “The four-shaft has a couple advantages over a two-shaft,” says the New Hampshire–based company rep. “You can run it with or without a screen. If you run it with a screen, you get to control the particle size, which you don’t get with a two-shaft.”

Preshredder operation typically requires only one person, who feeds it material, often with a grapple or bucket loader because most preshredders for hammermill shredder lines are top-loading models. Most preshredders are rated 350 to 1,000 hp; in comparison, hammermills tend to list horsepower in the thousands. Production varies from roughly 25 to 110 tons an hour, depending on the size of the preshredder and the items processed. The output produced would vary in size depending on such factors as rotor speed and distance between ripping teeth, these sources say, but “what matters is the density” and getting the material under about 40 pounds per cubic foot, the shredding equipment consultant says.

Material leaving a preshredder can enter a hammermill shredder either inline, with a conveyor that goes directly to the existing main shredder, or offline. Some scrap recyclers prefer the latter, using the preshredder as a standalone machine and stockpiling the processed material before sending it to the hammermill shredder. A stacking conveyor that catches the preshredder’s output can accommodate both inline and offline options.

Because the concept of using a preshredder with a hammermill shredder still hasn’t permeated North American markets, even some manufacturers and dealers of heavy-duty slow-speed, high-torque shredders that might suit that role question whether it’s a sound investment. “We have machines that could do that job, but generally this approach is not justifiable if a company is already planning to use a large hammermill for further processing,” such as one that boasts several thousand horsepower, the Oregon-based manufacturer’s rep says. “That would change significantly, though, if you start talking about a smaller hammermill. … The savings might be real … and enough to justify the use of a preshredder.” 

Preshredder prices vary greatly based on machine features such as size, the number of shafts, and horsepower, but they generally fall into the range of $500,000 to $1.5 million. The shredding equipment consultant believes some preshredders could cost $2 million or more, but he points out “they are cheap to run” at about $2 to $4 a ton. Dealers consider preshredders a tougher sell than other scrap processing equipment because the machines don’t produce a unique output and must be used in conjunction with an existing shredding line. But the dealers insist they can deliver a solid return on investment by reducing expenses from electricity and wear parts and by increasing production efficiency. “The additional fixed costs are more than compensated [for] by lower costs in the main shredder, higher productivity, and higher metal recovery,” the Germany-based representative says. “If the benefits offset the cost, it makes sense for nearly any [shredder operator] to reflect in detail on the installation of a preshredder.”


Get the Right Preshredder for Your Scrap Supply

Not all low-speed, high-torque shredders perform optimally when processing autos or other dense material, so recyclers should research the best machine for their business, one of the San Antonio company’s reps says. “If you do get the wrong preshredder, it can cost you a lot of money in downtime,” he says. Keep in mind that preshredders are powerful, but some can’t take on all materials. “They’re not fond of heavy steel castings, transmissions, cam shafts, and engine blocks,” the New Hampshire–based manufacturer’s rep says. “Aluminum castings you can do, [but] heavy steel rods and transmission gears and that sort of thing, it won’t shred.” Wires are another item to avoid whenever possible because they might wrap around the shafts of a two-shaft preshredder. Further, “you don’t want to put in big I-beams or lots of long, stringy rebar because even in a low-speed, high-torque preshredder, they still can wrap. It’s rotating, so anything long can wrap around the shafts,” one of the San Antonio manufacturer’s reps says.

The hammermill shredder size and likely feedstock seem to determine the economic value of adding this equipment. “There is now a positive economic gain available for preshredding a wide variety of types of scrap, but especially bales and complete automobiles,” the Texas-based equipment supplier says. Crow Wing Recycling’s research supports that assertion. “We believe that by preshredding bales and cars we will achieve better uptime, therefore more production, better wear life from our castings, and far fewer explosions,” VanWyngeeren says.

Other shredder yards might soon follow Crow Wing Recycling’s example. Product inquiries from within the United States have preshredder manufacturers and dealers encouraged about the industry outlook and future installations. “I think that’s one thing you’re going to see in the next couple years: people looking hard at preshredders to make their operation more efficient and to go after feedstock they would not consider previously,” one of the San Antonio company’s reps says.


Katie Pyzyk is a contributing writer for Scrap.


Sending end-of-life automobiles and other materials through a preshredder prior to a hammermill shredder used to be a foreign practice. Now U.S. recyclers are starting to appreciate the efficiencies and cost savings preshredders can provide.

  • 2017
  • Sep_Oct

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