Chips produced from logs are used in making pulp which in turn is used to make paper and chip board used primarily for construction. In either case, it is undesirable to have tree bark mixed in with the chips to ultimately end up in the paper or chip board produced therefrom. Thus, it is a common practice to precede the chipping operation with a debarking operation.
In the past, logs to be chipped were hauled from the logging site to a pulp or chip board producing mill where the logs were processed. It has been found, however, that the difficulties, and accordingly the costs, of hauling full size logs can be substantially reduced by processing the logs at the logging site. Rather than using log hauling truck beds, trucks with large boxes can be filled with the chips and hauled far more conveniently and efficiently.
Accordingly, mobile chipper units and mobile debarking units have been developed. Each includes a power source, control apparatus and a substantial undercarriage. Each is hauled to the in-field processing site and set up to perform, independently, its own chipping or debarking function. Where logs are to be debarked and then chipped, i.e. the combination of functions contemplated for this invention, the two units are operated, still independently, but cooperatively as will be hereafter explained.
For the operation of the debarking unit, tree stems or logs are hauled from the cutting area and piled along side the unit. A loader (a boom with a grapple) picks up the logs and feeds them into the inlet of the debarking unit. As the logs are fed through the debarking unit, bark removing elements, e.g. flails, break the bond between the bark and the log core and the bark drops into a bark removing chute. The feeding of the logs through the flails is continuous with the logs being passed into and through the bark flailing station and out the other side, i.e. the exit or outlet of the debarking unit.
A debarking unit of the type herein contemplated is illustrated in U.S. Pat. Nos. 4,729,415, 4,721,139 and 4,719,950.
The debarked logs are then fed into the chipping unit. Typically a large number of knives or blades are mounted on a large, rigid disc. There are a number of designs for this chipping disc but in any event, it is of massive design to withstand heavy loads. The knife carrying disc is rotated to drive the knives into the log as the log is moved into the disc. This operation is capable of reducing a large log or a plurality of small logs fed simultaneously into the chipping unit, into small chips suitable for pulp or chip board within seconds. This chipping operation has very high power requirements with occasional power demands that exceed the power source capability. When this happens, the power source lugs down or slows up, a signal to the operator that the feeding of the logs needs to be slowed.
To reduce handling of the logs, some in-field log processing operators have arranged for the two units to be placed adjacent one another in a manner where the functions are performed cooperatively. The chipping apparatus is commonly equipped with a loader. The exit end of the debarker is lined up and positioned relative to the entry of the chipper to enable feeding directly from the debarker into the chipper. The loader, mounted on the chipper chassis, is used to reach over the debarking unit and feed the logs into the debarking unit. The feed rolls of the debarking unit simply continue the movement from the debarking unit into the feed rolls of the chipper.
The problems with this "reduced handling" concept of infield processing are several.
The chipping and debarking units must be placed close together or the logs will not feed properly from the debarking unit into the chipping unit. Also, if they are not close together, the loader operator, in his cab positioned over the chipping unit, has difficulty in maneuvering the logs for feeding them into the debarking unit. A problem occurs with the close placement of the units as it frequently happens that a small quantity of loose bark from the debarking operation is carried by the logs out of the debarking apparatus. This small quantity of bark is normally dropped off the logs if there is an intermediate handling of the logs. With the logs being fed directly into the chipping unit, the bark can become fed with the logs in the chipping unit resulting in a much greater contamination of the chips which is undesirable.
The power source of the chipping unit, as previously explained, lugs down when being overfed. With the debarking unit feeding the logs directly into the chipper, the log feeding process can get out of sync, i.e. the debarking unit will push the logs into the chipping unit at a rate faster than the chipping unit can process the logs. The chips formed when the chipper is overfed and thus lugged down will not be uniform which is undesirable. Also, the overloading can be such as to cause the engine to stop. This interruption of the process is also undesirable.
The in-field processing site is frequently a series of in-field processing sites that are simply spaced locations along a road, and most likely that road is a narrow rough logging road. Setting up the units is time consuming when the units are operated totally independently. To align them for continuous unit-to-unit feeding, further complicates that procedure. One of the units may have to be jacked up or the other lowered as by digging a trench under the supporting wheels. When the procedure has to be repeated on a frequent basis to process small stacks of logs spaced along the roadway, the efficiency gained from unit-to-unit feeding is greatly eliminated.
Considering the same frequent move of the units, the multiple tractors used to move these units creates congestion. The roads are narrow and frequently have no room to maneuver the units into the proper space, disconnect them from the tractors and get the tractors moved out of the way. Also, recall that a third vehicle is involved. The chip hauling truck must also be maneuvered into position for receiving the chips.