Recycling: New crushers punch above weight class
By David GodkinConstruction Materials Demolition Equipment Roads
Great hands, but can’t move his feet. Big and slow. And that jaw? Nothin’ but glass.
That last word is about the worst thing you can say about a professional boxer. But strength, mobility and durability are just as important in the demolition and recycling business. Just how tough are the crushers being pitched to demolition and recycling contractors out there? In this issue we find out.
When you’re considered an industry heavyweight, you have to be able to take on all comers, i.e. rock, iron, steel—anything that gets in your way. At 14,350 kg and an hourly throughput of up to 450 mtph the Nordberg C106 jaw crusher isn’t Metso’s biggest primary crusher: Central Canadian distribution manager Steve Craig says that distinction goes “to our C200 with a production rate of 1,100 metric tons an hour.” But together the C106 and LT106 mobile unit, he says “remain one of our hardest-working, most competitive machines.”
Metso’s other boast: the C106 aboard the LT106 mobile unit not only takes apart the hardest materials, its modular structure enables it to adapt to several configurations. “It’s the same crusher that would go on a stationary unit, but it’s been modified in terms of overall height,” says Craig, “and that’s important. When you go to a portable application, you need to make sure it can travel down the road legally.”
A jaw crusher is only as good as its ability to take repeated blows, of course. Craig says what keeps the C series jaw from breaking is the Nordberg’s bolted construction, “which has allowed us to get higher internal forces to crush material inside the chamber.” The only way the jaw frame’s high-torqued bolts can come loose “is with a torque gun.” The welding points on a welded frame, by comparison, are subject to stress and fatigue and become your weak points, according to Craig.
Sandvik’s Stationary Crushing & Screening Business line manager Stephen Dobler begs to differ. Sandvik boasts a single-toggle jaw crusher consisting of two side plates of rolled steel, plus hollow castings at the end of the front frame, to provide a very high rigidity/weight ratio. However, unlike the Nordberg jaw, Sandvik’s CJ series jaw crusher relies on a uniform welded construction—“equally strong in all directions and ensuring excellent durability against shock loads.” And that’s important, Dobler explains, because loading and unloading a jaw crusher while it’s crushing has a “bending” effect on the machine.
“Welding is an advantage, in that the frame remains rigid while crushing compared to a bolt design that can come loose where the part starts moving and cracks propagate at the bolt-hole location. Welding provides a much stronger design.”
Not that a bolted design isn’t strong, Dobler hastens to add. It just isn’t as strong or as durable as a welded frame. “This is a piece of equipment you want to install and keep for 20 or 25 years before you replace it.”
In fact, Dobler maintains that designing a single-toggle jaw crusher requires all the attention to detail that design engineers apply to a jet engine. That includes finite-element analysis to determine stress “at every location within the machine and how the components are integrated into the box to make it stronger and lighter. It’s pretty high-tech.”
Product manager Ron Kriess says that management at KPI-JCI and Astec Mobile Screens couldn’t be happier with their latest product launch—the track-mounted FT2650 jaw crusher. This is a 14,528 kg machine with a 256 mtph capacity. One highlight is a grizzly finger pre-screener designed in step decks “one underneath the other,” says Kriess. This is to allow the screen to adapt the crushing unit to multiple configurations, “to make them adaptable to the situation that you’re in.” Were there any bumps along the way in the design phase? Sure, says Kriess.
“Putting a screen under a grizzly module was always a problem, because the screen was just a wire mesh and would always end up plugging up.” By converting it to a high stroke/low speed pre-screener, the grizzly fingers, or tines, vibrate at a different rate than the pan, making it much less likely to plug from the excess -20-mm dirt that contractors are anxious to be rid of during recycling.
The other feature of KPI’s jaw crushers is a reduction in the number of processing attachments required to feed the crusher. “The wider the crusher,” says Kriess, “the less you have to do on the front end.” Kriess estimate the average jaw crusher width to be 42 to 44 in. The FT2650’s feed opening is 26 by 55 in., with production rates through the plant of up to 500 tons per hour. According to company literature, increased stroke provides up to 25 per cent more capacity, more compression, more relief and faster throughput.
But it’s claims about the importance of increased width which sparked debate among other crusher manufacturers. “Width is one thing, says Voghel Inc.’s general manager Jean-Sébastien Voghel. But a block of stone from a quarry normally has a cubic shape, so if you have a 55-in. width but only have 25 in. of depth it’s useless.”
A wider jaw works well in some applications like demolition where you’re “trying to put ‘slabbier’ stuff into the crusher,” agrees Steve Craig. But don’t focus on width at the expense of depth. “Slabbier material is going to vary widely in size distribution, so that it forms a bridge as it goes towards the crusher. You don’t want things to bridge or plug up your crusher’s feed opening.”
“A lot of our competitors’ jaws will have a very wide opening but a very shallow chamber,” Dobler adds. “The advantage our much-deeper chamber has is that we can actually have the same opening at the top and bottom, but the angle of the plate is much more vertical.”
Dobler is talking about the Sandvik deep crushing symmetrical chamber. A much more vertical nip angle allows you to get a firmer grip on the material and pull it up, which in turn eliminates bridging of material at the opening. There’s another consideration, too, Dobler says.
“The wider your jaw is, the more tonnes per hour you’ll be able to push through it. But the wider the jaw, the more horsepower you’ll need to do the same amount of work.”
Professional boxing is about defense, not just offense. The same is true when you’re designing a crushing machine. Lighter-division mobile impact crushers like Rubble Master’s compact RM 100 really require protection, says Voghel. “A wear plate at the top of the moving jaw is positioned at an angle and leads the material into the chamber,” says Voghel, but it also protects the machine. Meantime, a deflector plate at the bottom of the crushing chamber protects the discharge conveyor from falling crushed materials.
Sandvik’s CJ series has a deflector plate protecting the moving jaw, too. But at five in., the plate is “extremely thick compared to anyone else in the market,” Dobler says. That extra thick plate means the back wall of the rock box taking materials off the conveyor “can be located higher up and further back, which gives you a larger actual opening.” Because some other OEMs’ jaw crushers are “extremely thin, if non-existent,” he says they require a stationary cross-wall on the back on the rock box to protect the top of the moving jaw, he says.
Problem: this reduces effective feed opening. Material cannot be crushed until it has dropped deep into the crushing chamber. In other words, your effective feed opening is less than a nominal feed opening.
ABOVE ALL, KEEP YOUR FEET MOVING…
“Our RM crushers as a whole are an innovation,” says Voghel. Instead of building very large rock crushers and reducing the design to crush asphalt and concrete, Rubble Master went in the opposite direction—it designed the RM 50 to about the size of a small container bin to crush about 20 tonnes of concrete per hour, he estimates. This unit was soon joined by larger versions to crush larger and larger amounts of concrete.
“The crushing chamber is unique in the way it’s designed, too. It’s only got one crushing wall, so that makes more room inside the chamber to accelerate the material and provide a greater impact when the material is being hit by the rotor,” says Voghel.
Steve Craig is clear about what makes his product popular. The C series jaw crusher aboard the LT106 mobile unit provides a single move on a track-mounted unit. “You don’t have to disassemble the track unit, like taking heaters off, to make it go down the road legally.” Three different speeds—walking, loading and offloading from trailers—enable you to move efficiently on and off inclined demolition sites, for example.
Like Metso’s LT106, KPI’s FT2650 travels down the road at a low-height profile with its under-crusher conveyors, Kriess says. It has “three different positions to go under the jaw, so that it can travel at a tucked up height and be easily lowered into position.” In addition, disassembled feeders “sometimes require support equipment to put back on, and aligning that support equipment also takes time and money.”
That’s something that is a little easier in Canada than the U.S., with 52 regulatory agencies to worry about. But wherever you are, at the end of the day, Kriess concludes, “it’s all about getting your equipment into the site, getting the work done and getting out of there as quickly as possible.”
David Godkin is a B.C.-based freelance writer and editor. Send comments to firstname.lastname@example.org
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