Woodchipper
Encyclopedia
A tree chipper or wood chipper is a machine used for reducing wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

 (generally tree limbs or trunks) into smaller parts, such as wood chips or sawdust
Sawdust
Sawdust is a by-product of cutting lumber with a saw, composed of fine particles of wood. It can present a hazard in manufacturing industries, especially in terms of its flammability....

. 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
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 from 3 hp to 1000 hp. There are also high power chipper models mounted on trucks and powered by a separate engine. These models usually have also a crane.

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 1 inches (2.5 cm) to 2 inches (5.1 cm) across in size. The resulting wood chips have various uses such as being spread as a ground cover or being fed into a digester
Digester
A digester is a huge vessel where chemical or biological reactions are carried out. These are used in different types of process industries.Digester may also refer to :* Digester-Processes where digesters are used:* Anaerobic digestion...

 during papermaking.

Most woodchippers rely on energy stored in a heavy flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

 to do their work (although some use drums). The chipping blades are mounted on the face of the flywheel, and the flywheel is accelerated by an electric motor or internal combustion engine.

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 rollers transport the branch to the chipping blades at a steady rate. These rollers are a safety feature and are generally reversible for situations where a branch gets caught on clothing
Clothing
Clothing refers to any covering for the human body that is worn. The wearing of clothing is exclusively a human characteristic and is a feature of nearly all human societies...

.

History

The woodchipper was invented by Peter Jensen (Maasbüll, Germany) in 1884, the "Marke Angeln" woodchipper soon became the core business of his company, which already produced and repaired communal- and woodworking-machinery.

High-Torque Roller

Shredders that make use of high-torque low-speed grinding rollers are growing in popularity for residential use.
These shredders are driven with an electric motor and are very quiet, dust free, and self feeding. Some of these
machines are equipped with an anti-jamming feature.

Drum

Among the first commercially available, and still in production today, drum chippers employ mechanisms consisting of a large steel drum powered by a motor, usually by means of a belt. The drum is mounted parallel to the hopper and spins towards the output chute. The drum also serves as the feed mechanism, drawing the material through as it chips it. It is colloquially known as a "chuck-and-duck" chipper, due to the immediate speed attained by material dropped into the drum.

Chippers of this type have many drawbacks and safety issues. If an operator becomes snagged on material being fed into the machine, injury or death is very likely. Chippers of this type are also very loud. The chips produced may be very large, and if thin material is inserted, it may be cut into slivers rather than chips, and since the drum is directly driven by the engine, materials that are too large or long may stall the engine while usually remaining firmly stuck in the drum.

Newer models have overcome many of these disadvantages with digitally controlled reversible hydraulic feed wheels and muffling systems. The reversible feed system allows the newer style drum chippers to handle larger diameter materials.
Modern drum-style chippers usually have a material capacity of 6 to 20 inches (15-50 cm).

Disk

A newer chipper design employs a steel disk with knives mounted upon it as the chipping mechanism. In this design, (usually) reversible hydraulically powered wheels draw the material from the hopper towards the disk, which is mounted perpendicularly to the incoming material. As the disk spins, the knives cut the material into chips. These are thrown out the chute by flanges on the drum. This design is not as energy-efficient as the drum-style design, but produces chips of more uniform shape and size. Most chippers currently used by commercial tree care companies, such as Asplundh, are disk-type.

Consumer-grade disk-style chippers usually have a material diameter capacity of 6 to 18 inches (15-46 cm). Industrial-grade chippers are available with discs as large as 160 inches in diameter, requiring 4000-5000 horsepower.

Other

Much larger machines for wood processing exist. "Whole tree chippers" and "Recyclers", which can typically handle material diameters of 2 feet (61 cm) to 6 feet (182.9 cm) may employ drums, disks, or a combination of both. The largest machines used in wood processing, often called "Tub Grinders", may handle a material diameter of 8 feet (243.8 cm) or greater, and use carbide tipped flail hammers to pulverize wood rather than cut it. These machines usually have 200 hp to 1000 hp. Some are so heavy that they require a semi-trailer truck
Semi-trailer truck
A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...

 to be tranported. Smaller models can be towed by a medium duty truck.

Blades

Although chippers vary greatly in size, type, and capacity, the blades processing the wood are similar in construction. They are rectangular in shape and are usually 4 inches (10.2 cm) to 1.5 inches (3.8 cm) across by 6 inches (15.2 cm) to 12 inches (30.5 cm) long. They vary in thickness from about 1.5 inches (3.8 cm) to 2 inches (5.1 cm). Chipper blades are made from high grade steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 and usually contain a minimum of 8% chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 for hardness.

Safety

Thirty-three people were killed in wood-chipper accidents between 1992 and 2005 in the US, according to a 2005 report by the Journal of the American Medical Association
American Medical Association
The American Medical Association , founded in 1847 and incorporated in 1897, is the largest association of medical doctors and medical students in the United States.-Scope and operations:...

. One of those accidents that had occurred in Yuma, Arizona on August 11, 2003 was featured on the TV show 1000 Ways to Die
1000 Ways to Die
1000 Ways to Die is a docufiction anthology television series that premiered on May 14, 2008 on Spike. The program recreates unusual supposed deaths and debunked urban legends and includes interviews with experts who describe the science behind each death...

.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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