Woodchipper
A tree chipper or 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.
Chipper Styles
Drum Chippers
The first commercially marketed chippers were of a design that was drum-based. They are still produced and sold today. The chipping mechanism in a drum style chipper is large steel drum powered by the motor, usually by a belt. It 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. This caused it to be colloquially known as a “chuck-and-duck” chipper, because material would start moving through the chipper very quickly as soon as it made contact with the drum.
These chippers have many downsides. The drum-style chipper is not as safe as newer designs. If an operator becomes snagged on material being fed into the machine, injury or death is almost certain. These chippers are also very loud. The chips produced can be very large, and if thin material is inserted, it may be cut into slivers rather than chips. Finally, since the drum cannot be disengaged from the engine, if too large or too long material is fed through the machine, it will stall, usually with the material stuck firmly in the drum.
Newer models have overcome many of these disadvantages with 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 19 inches.
Disk Chippers
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 on a perpendicular angle to the incoming material. As the disk spins, the knives cut the material into chips. They 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 are of this type.
Disk-style chippers usually have a material diameter capacity of 6 to 24 inches.
Other Styles
Much larger machines for wood processing exist. “Whole tree chippers” and “Recyclers,” which can typically handle material diameters of two to six feet, 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 eight feet or greater, and used carbide tipped flail hammers to pulverize wood rather than cut it. These machines usually have 200 to 1,000 horsepower. Some are so heavy that they must be moved by a semi-trailer truck.Smaller models can be pulled with a medium duty truck.
Chipper Knives
Although chippers vary greatly in size, style, and capacity, the knives they use are all very similar. They are rectangular in shape and are usually four to six inches across by six to twelve inches long. They vary in thickness from about one-half to two inches. Chipper knives are made from high grade steel, and usually contain a minimum of 8% chromium for hardness.
Chippers in popular culture
A famous (or infamous, depending on one’s perspective) use of a tree chipper is the scene in the Joel and Ethan Coen movie Fargo in which a tree chipper is used to dispose of a body. ( “Wood chipper. Unauthorized use” - The four-word film review)
In the 1996 film Rumble in the Bronx, there is a (largely offscreen) scene where a wood chipper is used by Mafia members to execute a double-crossing gang member.
In an episode of The Bernie Mac Show, Bernie hired Jordan to destroy Baby Girl’s doll, which she has become obsessed with. After considering many alternatives (like baking it on the outdoor grill), Jordan throws the doll in a woodchipper.
In the video game, Punisher, the beginning of the zoo level allows the player an opportunity to feed a mobster (feet first) into a wood chipper.
In Final Destination 3m on the Choose Their Fate mode, there is a newspaper article that is about the deaths of Kimberly Corman and Officer Thomas Burke, who were both pulled into a malfunctioning woodchipper
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