A Look at Tree Chippers
A tree chipper, also known as a wood chipper, is a special piece
of equipment used to change wood and brush into wood chips. Most
tree chippers are portable and mounted on wheels so they can be
towed behind a truck. In the case of paper making, however, the
wood chipper is much larger and is generally a semi-permanent feature
at the paper mill.
The Makings of the Tree Chipper
Most tree chippers contain a hopper with a collar, a chipper mechanism,
and a bin for collecting the resulting chips. To start the process,
a tree limb or trunk is inserted into the hopper. The collar serves
to protect the person inserting the wood from getting cut by the
chipping blades. After the wood is passed through the blades and
chipped, the chips leave through a chute and go into a container
for easy transport to the digester. Typically, the chips are one
to two inches in size.
The Drum Tree Chipper
The first tree chippers, which are still made today, were drum-based.
The chipping mechanism in one of these tree chippers is in a large
steel drum and powered by a motor. Most of the time, a belt supplies
this power. The steel drum is located parallel to the hopper and
it spins toward the chute. At the same time, the drum draws new
materials in to be chipped. This type of tree chipper is sometimes
referred to as a chuck-and-duck chipper because materials
placed inside begin moving almost immediately after they come in
contact with the drum.
The drum-style chipper is not as commonly found in the paper making
industry as it once was because it is not as safe as newer designs.
The chances of the operator becoming snagged by the materials being
placed inside and consequently being fed into the machine are too
great. In addition, drum-style chippers are very loud and produces
inconsistently sized wood chips. Materials can also become easily
stuck in the drum.
The Disk Tree Chipper
The disk tree chipper is a newer design that utilizes a steel disk
containing mounted knives. The wheels inside the chipper draw the
material to the hopper and toward the disk. These wheels are hydraulically
powered and reversible in order to move materials that have become
damaged back out.
The disk inside the tree chipper is mounted at a perpendicular
angle in relation to the incoming material. As the material approaches,
the disk spins and the knives cut the material. The resulting chips
are thrown out the chute by flanges located on the drum. Although
this design is not as energy efficient as the drum-style tree chipper,
it produces more uniformly sized wood chips.
Large Wood Chippers
The wood chippers generally used by pulp and paper mills are larger
machines called whole tree chippers, or recyclers.
These tree chippers may use drums, disks, or both. They are capable
of chipping wood two to six feet in diameter. Even bigger tree chippers,
called grinders, are capable of chipping wood more than
eight feet in diameter by using special hardened hammers to tear
the wood up instead of cut it.
Knives for Chippers
Despite the variance in the type of tree chippers, the knives used
in them are all basically the same. The knives are generally anywhere
from four to six inches across and range from six to twelve inches
in length. They have a rectangular shape and can vary from one-half
to two inches in thickness. A high-grade steel is used to make chipper
Tree chippers are an important component in the paper making process.
Without them, the wood would not be broken down into smaller, uniform
pieces and, therefore, would not be able to be added to the digester
where they are softened and turned into pulp to be made into paper.