Not applicable.
Not applicable.
The present invention relates to drum debarkers which are used to remove the bark from logs which are further processed, for example by being converted to wood chips.
Bark contains little cellulosic fiber and typically contains dark pigments. Therefore bark is viewed as an undesirable contaminant in wood fibers which are used to make paper or in wood chips which are used to make engineered wood products such as chipboard. Debarking drums have been developed to efficiently remove the bark from large quantities of raw logs without damaging or removing useful fiber. A debarking drum has a large cylindrical shell which is mounted on truck tires which are driven to cause the drum to rotate about the drum axis. Alternatively, the drum may be supported and driven by other support systems such as chains, or gears mounted to the exterior of the drum. Logs are placed into the drum debarker at one end and debarked logs are removed from the other end.
The diameter of a debarker drum shell ranges from nine feet to more than 16 feet. The drum is constructed with a steel shell sometimes having a thickness of an inch or more. The drum length may be from about 60 feet to more than 110 feet long, depending on how long it is desirable to retain the logs, and the length of the logs. Log length is typically in the range of six to 65 feet. The logs are fed into one end of the drum and the tumbling action results in logs hitting other logs, which loosens and removes the bark as the logs progress to the opposite end of the drum. The drum may have a plurality of bark slots, and the number and size of these openings vary with the size and species of wood to be debarked. The debarking slots are simply holes cut in the cylindrical wall of the drum shell. The drum may contain lifters which are steel or rubber members which extend radially inwardly of the inside surface of the drum and control or enhance the tumbling action of the logs. The tumbling action both loosens the bark and breaks it apart. The loose bark then falls through the bark slots.
A problem exists for certain types of logs such as hickory which have a thick stringy bark during certain times of the year. This bark will not easily move through standard size slots. If slots large enough to accommodate the bark are cut in the drum, useful wood fiber is lost as slivers which break from the logs, and smaller sticks containing useful fiber which pass through the over-large bark slots. What is needed is a drum debarker which allows removal of thick fiberous bark through openings in the drum but which retains smaller sticks and log slivers containing useful fiber.
The log debarker of this invention has a cylindrical steel drum which is mounted for rotation about the drum axis. Logs are fed into one end of the drum, and the tumbling action of the drum causes the bark to be removed. The debarked logs are then discharged from the other end of the drum. The cylindrical shell of the drum is penetrated by a multiplicity of slots at least some of which are larger than normal having a minimum width of 3xc2xd inches, preferably six inches, and a length of about one to two feet. The slots are arrayed circumferentially about the drum and extend axially along the length of the drum. Each large slot has a cover which is mounted to the exterior of the drum and is spaced to form a minimum two inch gap between the exterior surface of the drum and the cover. The cover has a shallow U-shaped member with legs which are welded to the exterior of the drum adjacent the short sides of the slots. The U-shaped member extends about one to one-half inches on either side of the slot. The bottom of the U-shaped member is preferably flat so that the gap between the U-shaped member and the exterior surface of the drum increases in the circumferential direction away from the edge of the slot. The quantity and location of the bark slots are determined by drum size and log species and may be, for example, about 5 percent of the area defined by the exterior cylindrical surface of the drum. The covers prevent sticks and log pieces from leaving the drum with the bark. At the same time, bark slots which are approximately six inches wide can receive large thick fibrous bark which in the past has been difficult to separate from the logs by means of bark slots. Once a slab of bark begins to move through the slot, the tumbling action of the logs will tend to drive the bark through the slot, or break the slab of bark into smaller pieces which can then pass through the slots.
It is a feature of the present invention to provide a debarking drum which is effective at separating thick fibrous or stringy bark from logs.
It is another feature of the present invention to provide a debarking drum with a higher yield of useful fiber.