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.
 Manufacturer
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.
 Most
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. 
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.
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