Basics of Crushing, Grinding, and Chipping

May 1, 2009

A smaller machine can be a smart choice when it comes to a crusher for onsite demolition debris. Today’s smaller crushers make it cost-effective to move into a demolition site, crush the concrete and asphalt, and either reuse the material onsite or haul it away. Onsite crushing saves trucking costs, tipping fees at the landfill, and labor expenses.

“Smaller crushers are more versatile and profitable, especially for demolition contractors,” says Nikolaus Hottenroth, business development manager for Rubble Master Systems Inc., a crusher manufacturer that makes compact machines. “We see a tendency toward smaller machines. I realized it at Conexpo 2008 when people came to our booth and asked for smaller crushers.”

As evidence of that trend, Rubble Master’s sales have doubled every year over the past three years. In 2008, sales of crushers reached in the area of 40 units, he says. “It’s mainly because of the economics of onsite crushing,” notes Hottenroth. “Onsite crushing eliminates a lot of trucking, which saves fuel, labor and insurance.”

At Telsmith Inc., another crusher manufacturer, marketing manager Jim Schreiner says there’s been an evolution toward smaller machines. Within the last 10 years, he says, the industry started building smaller track-mounted units—mostly jaw crushers. “More recently, in the past five years, they put impact crushers on tracks as well,” says Schreiner. (Jaw crushers use compression to crush rock or concrete. Impact crushers, or [ITALIC]impactors[ITALIC], either hit material with a hammer or throw it against a hard surface.)

“Demolition material is a different animal from natural stone,” says Schreiner. “If you use a portable crusher, you need an excavator with an attachment to munch it up. You need to prepare the material before you put it in the plant.”

Schreiner says an impact crusher will make a higher percentage of material 2.5 inches or smaller than will a jaw crusher. But an impact crusher will carry a higher maintenance cost. With a jaw crusher, just the opposite is true—larger end product, lower maintenance costs.

The type of crusher most often used by recycling contractors is the horizontal-shaft impact crusher, Schreiner says. A rotor with blow bars spins and strikes the material to break it. The material gets hit several times before it falls out the bottom.

Maintenance Required
The biggest issue on a crusher operator’s learning curve is maintenance, says Schreiner. For an impactor, it might be necessary to flip the wearing steel over every week or every month, depending on the material you’re running. But for a jaw crusher, depending on your material, you may go for six months to a year before you touch a wearing part.

What about the choice between tires or tracks under your crusher? Tire-and-chassis (portable) plants must be blocked up, so they take longer to set up than a track-mounted unit. With a track-mounted unit, you drive it off the trailer and it’s ready to work. A tracked machine is more popular for moving around the job site, and a portable plant is better for stationary applications once you’re onsite. But if you move often from site to site, a tire-mounted machine is probably the best choice.

Most portable plants rely on a separate power source, so that needs to be hauled on another trailer, says Schreiner. Tracked plants usually have a self-contained power source.

At Rubble Master, Hottenroth offers the following criteria for choosing an onsite crusher:

  • The crusher’s end product should have a high resale value and should be recyclable.
  • The crusher should be easy to transport and set up.
  • The crusher should offer ease of maintenance.
  • The production rate should be good.
  • Existing loading equipment should have appropriate capacity

Rubble Master’s crushers process concrete, asphalt, brick, and natural stone. The company offers three models of crushers with production capacities ranging from 60 tons per hour up to 250 tons per hour. All three units are impact crushers that can produce material down to three-quarters of an inch or smaller. Hottenroth says his crushers are very fuel efficient, burning from 3 to 5 gallons per hour. Wearing parts cost 30 cents per ton or less of material produced. By the end of 2009, Rubble Master will have nine dealers in North America.

Tubs Versus Horizontal Grinders
For land-clearing projects, two types of grinders—tub and horizontal—are commonly used. “Tub grinders generally perform better with heavy, large-diameter material such as stumps and root balls,” says Chris Nichols, environmental sales manager for Vermeer Corp. “But if processing longer raw material is the consistent application, a horizontal grinder may be the best choice.” Vermeer makes both types.

For some materials, Nichols says, a tub grinder is perceived to have a higher production rate, but the horizontal models may have the advantage when it comes to the longer, bushier material found in land-clearing applications. “That is mainly because the tub depth is limited, and when processing the longer material, long branches may be difficult to feed. Horizontal grinders have the long feed table and conveyor to guide material into the grinder, avoiding the sometimes tedious task of material placement and manipulation,” Nichols says.

C.W. Mill Equipment Co. Inc. manufactures the HogZilla lines of tub and horizontal grinders. “If I could only have one of them, I’d rather have the tub,” says Tim Wenger, president and sales manager at C.W. Mill. “That’s because if you clear 100 acres of land, the tub grinder should be able to grind everything on the property without having to haul anything away for processing.”

For a tub grinder, though, feed material needs to be processed down to at least 12 feet in length. Eight feet would be better, Wenger says. A horizontal grinder can accept 100-foot-long trees, but it is limited on diameter. “Generally they log out the bigger wood and push the rest of it into a pile for processing,” says Wenger.

Tracks Versus Towable?
Tub and horizontal grinders come mounted on tires as portable units, or with tracks. Track-mounted machines must be loaded onto a trailer for transport. “If the grinder will be used in applications where there will be muddy and uneven job sites that will not accept a rubber-tired machine, the track-mounted unit would likely be preferred,” says Michael Stanton, an assistant regional manager for Morbark Inc., which manufactures tubs and horizontal grinders alike.

“But if the machine will be moved frequently from job site to job site—or will be used predominately in a mulch application where the material is brought in by truck—a rubber-tired machine would probably be preferred, because the machine is easier to transport,” he says. The transportation of most track-mounted units requires special trailers, permits, and, sometimes, escorts.

With its tub spinning up on top of the machine, a tub grinder can throw out branches and debris from time to time. To prevent such debris from hurting anyone, some manufacturers offer systems of iron bars that guard the tub and stop thrown objects.

Jens Jensen, sales representative at Diamond Z Manufacturing, says that he sees a definite trend toward horizontal grinders and away from tubs. Diamond Z makes both types of machines. People like the ability to process over-length material, and the low feed height of a horizontal grinder,” says Jensen. “That’s where everybody is moving. They like the control aspect of the force-fed ability of a horizontal grinder.”

What edge does Diamond Z offer? “We have a fluid coupler that replaces the entire clutch assembly,” says Jensen. “The fluid coupler allows the mill to be engaged even when it is partially blocked by material—without damage to the grinder. It’s a softer engagement—it cuts down on the shock loads to the grinder.”

Self-Loader or No?
Many grinders have self-loading units that permit an operator to pick up feed material with a grapple and load the machine. Other grinders rely on a separate excavator to feed material into the tub or conveyor.

“We’re not big fans of putting loaders on grinders,” says Wenger of C.W. Mill. “A 10,000-pound loader simply will not do the work of a 40,000-pound excavator. But if a person is doing grinding for municipalities, let’s say, and someone else can push the material to you, then a loader is okay.” C.W. Mill offers loaders on all but the largest of it grinders.

Morbark offers the self-contained loader option on its 11-foot and larger tub grinders, with the exception of the Model 1600. If space for support equipment is limited, a self-contained loader is a benefit, says Stanton. That way the operator can pick material from a pile stationed next to the grinder.

A no-loader machine would be utilized on a job site where there is only one support piece of equipment and one operator. The operator can run the support machine from its cab and control the grinder with a wireless remote control, Stanton points out.

A grapple loader on your tub grinder provides better visibility of the tub, Vermeer notes. The loader cab provides better visibility of the tub cavity, so the operator can load the tub more

Maintenance Is Important
The keys to maintaining a wood grinder are consistent checks and replacement, when needed, of such wear items as hammers, inserts, rakers, screens, and anvils. Other maintenance imperatives include proper clutch adjustment and tub drive-chain tension on tub grinders. Proper drive belts and in-feed chain tension for horizontal grinders must be maintained to meet optimum production rates and eliminate downtime, says Stanton.

Recognizing that maintenance often gets neglected, Vermeer introduced the patented duplex drum system for tub and horizontal grinders. This feature offers the operator the ability to change out any individual hammer within minutes without removing other hammers. Vermeer claims that this feature makes its drum maintenance more efficient than competing models.

Bandit Industries Inc. offers horizontal grinders powered by engines ranging from 180 horsepower up to 1,200 horsepower. “We use Caterpillar and Cummins engines and a few John Deere engines,” says marketing manager Jason Morey. “Our grinders will process everything up to 46-inch logs.”

Unlike those of most traditional grinders, the cutter mills inside Bandit’s line of Beast grinders cut material apart rather than hammer it. The difference is best explained by comparing the action of an axe to a sledgehammer. “Which would you prefer to use to cut down a tree?” asks Morey.

“We offer a variety of teeth, depending on the application,” says Morey. “We have teeth specifically designed for grinding roofing shingles, teeth for grinding trees and brush, and teeth for pallets.”

Brush Chippers in Two Styles
Brush chippers are available in drum-style and disc-style models. Drum chippers are used for a wide variety of applications where large volume wood reduction is needed. Drum chippers excel in brush applications and cut like a shear as opposed to the scissor action of a disc-style chipper, says Jason Showers, commercial sales manager for Morbark.

The advantages of a drum chipper are those of reduced dead space between the drum and feed rollers, larger-diameter feed rollers to ease material climbing, reduced material side slashing, ease of maintenance, and increased wear component life, says Showers.

A disc-style chipper cuts like a pair of scissors and excels in whole-log applications, Showers says. Because of disc inertia, it is often argued that a disc chipper uses less fuel and requires less horsepower to chip a given quantity of wood. Traditionally, disc chippers have smaller feed rollers, sometimes making it difficult to navigate large brush clusters. Choosing between a disc-style and a drum-style chipper has a lot to do with personal preference and opinion. When someone is shopping for new equipment, Showers says, most of the time it comes down to what the person is comfortable with and what they have used in the past.

Bandit Industries makes disc- and drum-style units. “We’ve seen a definite trend to drum chippers,” says Morey. The reason: drum-style chippers have larger throat openings and are generally lighter in weight compared to a disc-style chipper. In addition to a full line of brush chippers, Bandit offers a line of whole-tree chippers that can accept trees with diameters ranging from 18 to 36 inches.

The whole-tree chippers are offered on tracks or as tow-behind models. Tracks allow an operator to take the chipper directly into the woods—the machine is loaded by a grapple boom—while tow-behind chippers are for stationary applications.

Morbark manufactures a complete line of tow-behind chippers with capacities ranging from 6 to 20 inches. The company makes a complete line of whole-tree chippers in disc-style and drum-style models with capacities up to 30-inches.

So whether you’re looking to crush concrete, grind up logs, or chip brush, there’s a machine just waiting for you. Once you’ve done some research, the decision becomes much easier.

Wood Grinding Prospers in Mississippi
“We’ve had a great year in 2008,” says Scott Hannon, owner of Triangle Maintenance Service LLC in Columbus, MS. Hannon’s company grinds and recycles on the order of 60,000 tons of wood waste per year from three sources: industrial development sites; a company-owned post-consumer recycling center; and wood waste brought to a landfill in Columbus.

Much of Triangle’s prosperity in 2008 stemmed from grinding timber cleared for a new Toyota manufacturing plant in Blue Springs, MS. The main plant itself will cover a 1,000-acre site that was largely wooded. Plus, Triangle ground and recycled the timber from several hundred additional acres that will be developed in connection with the Toyota plant.

Triangle’s workhorse wood recyclers are three Vermeer grinders—a TG9000 tub grinder, a TG7000 tub grinder, and an HG 6000 horizontal grinder. All three grinders are mounted on chassis and tires.

At the peak of work on the Toyota site, Triangle employed the two big tub grinders and six or seven Komatsu PC 200 excavators. Selected excavators were fitted with shears to cut the timber down to a maximum 12-foot length, while other excavators had rake-and-thumb attachments to load the big tub grinders. Most of the 4-inch minus wood material produced from the Toyota site was sold to Weyerhaeuser for use as boiler fuel in a paper-manufacturing plant.

What were the keys to success on the Toyota project? “Production,” Hannon answers—“Putting as much material through those tubs as fast as we possibly could. That’s the big trick. We can average between 150 and 200 tons per hour out of the tub grinders. It depends on the nature of the wood. If you’re running hardwood, your production will be on the low end. But if you run pine, that’s softer, and you can get closer to 400 tons per hour.

“Sizing the material is key. We use shears to size the trees down to 12-foot lengths or less. As for diameter, it’s a 12-foot tub. If you can get it into the tub, the machine will grind it up.”

The HG6000 horizontal grinder keeps busy most of the time at Triangle’s post-consumer recycling center. Commercial tree trimming contractors bring woodwaste, and other sources bring pallets, land-clearing waste, and consumer yardwaste. The center also processes paper, cardboard, plastics, and aluminum and steel cans for recycling.

Triangle Maintenance Service has two divisions. The environmental division handles wastewood recycling, the recycling center, and a rolloff container business. The construction division builds slipformed curb and gutter, exterior concrete pavements, sidewalks, and building foundations. As well, the construction division erects construction signage and finish signage for roadway projects.