When hatchets and handsaws
ruled the day, dealing with wood waste often meant backbreaking
labor. It took armies of men to cut it up. Bonfires were the
primary means of disposal.
Thankfully, times have changed. Today, wood
grinders handle a wide variety of wood and organic waste,
making wood recycling, forestry, tree care and cleanup operations
much easier than ever before. And with dozens of purpose-built,
excellent machines on the market, choosing the right grinder
for you may be the toughest part of the job.
Before you race off and buy a grinder though,
there are plenty of things to consider. Becky Smith, Communications
Manager for Peterson Pacific Corp. in Eugene, Oregon points
out, “Wood grinders are a significant investment for
most customers, so it pays to be informed. Potential buyers
should have a thorough understanding of their needs and know
exactly what the machine will be used for. They should also
collect and sort through information from various manufacturers
before moving ahead with their purchase decision,” she
Wood grinders were
developed to assist in land clearing and logging operations,
reducing unsightly wood debris and other organic waste to
manageable volumes. However, more recent refinements are enabling
grinders to produce mulch, ground cover and other saleable
products. In general terms, they can be divided into two distinct
categories – tub grinders; and horizontal feed recyclers.
We’ll look at tub grinders first.
Tub grinders originated in agriculture,
producing livestock feed and related products for use on the
farm. Over the years, their ability to reduce large volumes
of bulky materials eventually drew interest from the recycling
community. In the 1980s, tub grinders began showing up at
landfills across the country.
On the jobsite, raw materials are usually
gathered by crane and placed in a large, rotating hopper or
tub, where gravity delivers them to the hammermill. Inside
the hammermill, rows of heavy, rotating hammers equipped with
replaceable cutting tips break the material down and force
it through changeable grates or screens. An auger system then
delivers finished material to a discharge conveyor that moves
it safely away from the grinder.
According to Dan Brandon, Marketing Manager
for Winn, Michigan based Morbark, Inc., manufacturers of a
complete line of wood recycling, forestry and sawmill equipment,
“Tub grinders are versatile units and well suited for
the heavy stuff. Large stumps, tree roots and other items
are easily consumed and reduced.” They also tend to
be large, with impressive productivity to match. “Some
models can weigh up to 50 tons and process more than 500 cubic
yards of throughput per hour,” said Brandon.
Tub grinders are good choices where a wide
variety of material is processed and when high productivity
is important. Due to size and space requirements of the design,
they can normally be found in more controlled environments
such as mill yards and municipal landfills or transfer stations.
But wood grinders are becoming increasingly
more visible along roadways, in subdivisions and in places
where tub grinders just can’t access as well. “Those
are horizontal feed recyclers,” said Becky Smith, of
Peterson. Horizontal feed recyclers are similar to tub grinders
in that both use hammermills. The difference is in the feed
method. In place of a large, rotating tub, horizontal feed
recyclers use an infeed conveyor to move raw material through
an upturning rotor in the grinding chamber where fragmentation
occurs. Next, the material is sized by grates or screens.
Material that does not fall through the grate area is ground
by the rotor until the right size of finished product is achieved.
Finally, high value end products move along a discharge conveyor.
“It’s a positive feed system,”
said Smith. “The primary advantage is increased safety
with high productivity - equal to or exceeding tub grinders,”
she added. Due to a smaller footprint, horizontal feed recyclers
are often deployed where safety and limited working space
Like with any capital equipment, good maintenance
is essential to protect the investment and guarantee the most
favorable outcomes. “The most important maintenance
consideration involves hammer tips,” commented Dan Brandon,
of Morbark. “The tips are usually tungsten carbide.
They’re very hard and hold a sharp edge, provided the
inbound material is kept clean. Hammer tips should be inspected
on a regular schedule and replaced as often and quickly as
needed. Otherwise, hammers and other parts will wear, and
the quality of material produced will decline,” he said.
Other maintenance items include lubrication,
filters and general mechanical systems. Radiators should be
kept clean, belts and chains must be adjusted and all facets
of the grinder should be inspected on a regular basis, following
the manufacturer’s service recommendations.
it doesn’t end there. After-sale support can play an
important role in choosing the right wood grinder as well.
“Depending on how the equipment is used, maintenance
costs and the availability of parts may help determine which
machine is the best choice for a buyer,” notes Michael
Weible, Marketing Manager for Diamond Z Manufacturing, Inc.
of Caldwell, Idaho. “If a grinder isn’t maintained
well, replacement parts and downtime can become the most costly
part of owning the machine,” he added. “It’s
important to have a local dealer that knows the product and
keeps a good supply of parts on hand if needed.”
Grinders have become an essential tool for
wood recycling and the future looks bright. Recent trends
include a movement toward larger, more powerful engines, better
emissions controls for the environment and advancements in
power transmission systems. And with more and more markets
being developed for recycled wood products, these trends will