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A Wood Chipper
is a machine used for reducing wood (generally tree limbs or
trunks) into smaller parts, such as wood chips or sawdust. They
are often portable, being mounted on wheels on frames suitable
for towing behind a truck or van. Power is generally provided by
an internal combustion engine from 3 to 1,000 horsepower.
Tree chippers are typically made of a hopper with a collar, the
chipper mechanism itself, and an optional collection bin for the
chips. A tree limb is inserted into the hopper (the collar
serving as a partial safety mechanism to keep human body parts
away from the chipping blades) and started into the chipping
mechanism. The chips exit through a chute and can be directed
into a truck-mounted container or onto the ground. Typical
output is chips on the order of one to two inches across in
size. The resulting wood chips have various uses such as being
spread as a ground cover or being fed into a digester during
papermaking.
Woodchippers rely on energy stored in a heavy flywheel to do
their work. The chipping blades are mounted on the face of the
flywheel, and the flywheel is accelerated by an electric motor
or internal combustion engine. As large branches are consumed by
the machine, the inertia of the flywheel causes it to gradually
slow down; when the branch is consumed, the engine causes it to
speed up again. This is what produces the rising and falling
siren-like howl of these machines.
Large woodchippers frequently are equipped with grooved rollers
in the throat of their feed funnels. Once a branch has been
gripped by the rollers, the operator lets go of it and the
rollers transport the branch to the chipping blades at a steady
rate.
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