May 2006


Equipment Spotlight

Wood Grinders
by Mark Henricks

—View a list of manufacturers at the bottom of the page

Wood grinders today offer the recycling industry higher efficiency and capacity than ever, which is helping recyclers keep pace with growing demand from site development and forest management and the devastating 2005 hurricane season that created unprecedented amounts of building waste. No-burn laws and lower tolerance for green waste abound among municipalities, further increasing demand for faster, high-volume machines.

Sophisticated wood grinders are helping to expand the market for wood waste. Grinder technology has introduced machines that can handle more types of material, including asphalt shingles, produce a more uniform end product and blend colorants to produce colored mulch now popular with many landscapers.

Recyclers have a choice of either a tub grinder or horizontal grinder. Tub grinders were first on the scene, having gotten their start on farms more than 40 years ago where they were used to mulch hay. Today’s tub grinders can handle tougher and larger materials such as logs, stumps, even railroad ties. Horizontal grinders are relatively new to the market. They were introduced largely to answer safety concerns about tub grinders.

MorbarkManufacturer innovation makes tub grinders much safer than during their first days grinding wood, but a certain amount of risk still exists. “If you’re grinding with a tub grinder in a tight area, there’s always a chance of something being thrown off the top,” says Patrick Andres, Western United States regional manager for Morbark, Inc., in Winn, Minnesota. “A tub grinder can take a 200-lb. log and throw it 100 feet.” But still, he says, these powerful machines have their place. “They’re still one of the best machines out there in the landfill,” he says.

Horizontal machines, on the other hand, have their own advantages. These self-enclosed grinders with vertical feeders can handle a whole tree that would be difficult to feed into a tub grinder. And while tub grinders may have the unique power to take on a tree stump, most manufacturers don’t recommend it, even if it can be done, because items that large take a big toll on the machine. Splitting oversized materials beforehand instead helps extend the life of a grinder considerably.

VermeerMost manufacturers have made building a safer tub grinder a mission, resulting in some innovative improvements. Vermeer Manufacturing Company in Pella, Iowa, has a patented thrown object restraint device, a two-part system consisting of a tub cover and rotor deflector. The deflector directs debris into the tub cover, reducing the number of objects thrown and how far they can go.

More than safety is driving improvement in grinder technology. Progress in managing the inevitable chunk of ungrindable steel has also helped make wood grinders more reliable as well as durable. Manufacturers employ one of several approaches, including torque limiters and shear-pin-based systems.

Peterson Pacific Corp. in Eugene, Oregon, employs a combination on its latest machines, including shear pins, cushioned drive shaft mounts and an impact release system to detect and discharge pieces of metal and other contaminants through a hatch. The machine then automatically re-latches the hatch so grinding can continue. Peterson Pacific

Computer and electronic controls operate key functions on many modern grinders. Computerized controls monitor engine oil pressure, water temperature, clutch conditions, engine RPM, infeed rates and available horsepower so operators can make adjustments to adjust grinding conditions as necessary to maximize efficiency. One of the newest models from Morbark features a satellite system that lets users communicate with the company by phone hook-up from remote areas in the case of a malfunction. The phone contact provides technical support on-site or launches a rush order for replacement parts.

Better function control has helped manufacturers produce more material with the same amount of horsepower and fuel usage. “Operating costs are broken down to a per-hour cost,” says Dave Benton, marketing manager at Peterson. “But it’s also how much material you can produce in that hour. That’s the real cost standard.”

Higher functionality has its price. “The electronic engines have added performance features, but have some additional costs and complexity issues requiring field service staff to become more knowledgeable,” says Mark Byram, senior director of Vermeer’s environmental solutions business segment. Newer engines are also running at higher temperatures, Byram says, so they require more cooling capacity, which again raises power requirements.

Before buying, determine which type of machine, tub or horizontal, best fits the material to be ground, how much horsepower and production volume will be necessary, what type of jobsite the machine will be used in most and what ancillary equipment will be necessary to support that operation. For example, a tub grinder may be more productive with an excavator attached, but that means adding another piece of large equipment that will need to be transferred to and maintained at the work site.

Typical wood grinder prices range from $85,000 to $675,000. Horizontal units closely match the top price of the tub grinders, but start at higher price points, around $100,000. The machines range from 85 horsepower to as high as 1,600. The largest machines can handle volumes as up to 130 tons an hour, depending on the material being processed. Track-mounted machines are designed for on-site mobility. Trailer-mounted units make the machines easy to transport by road.

A few options exist to meet the needs of the small to mid-sized recycler with limited need for wood grinding. Burrows Enterprises, Inc., in Greeley, Colorado, manufactures a tub grinder for light industrial material, green waste, leaves and shredded wood. The company’s tub grinders generate around 200 horsepower and produce around 60 tons per hour of waste. Each of the company’s three recycling tub grinders starts around $17,800.

Shredders and brush chippers, also known as wood chippers, are sometimes considered an alternative to wood grinders. A shredder can handle more highly contaminated materials, particularly appliances, but the machine’s slicing action won’t produce wood waste in as great a volume as a wood grinder specifically designed for the job. Brush chippers offer horsepower similar to grinders, but have low tolerance for anything other than wood.

Company Name
Contact Person

Burrows Enterprises, Inc.

Royal Burrows 970-353-3769

CW Mill Equipment Co., Inc.

Tim Wenger 785-284-3454
Diamond Z Manufacturing Pat Crawford 800-949.2383
DuraTech Al Goehring 701-252-4601
Morbark, Inc. Patrick Andres 800-233-6065
Peterson Pacific Corp. Dave Benton 800-269-6520
Rotochopper, Inc. Monte Hight 608-452-3651
Vermeer Manufacturing Corp. Mike Byram 641-628-3141
West Salem Machinery Mark Lyman 800-722-3530


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