Woodworking – Process – Mechanical cutting or shaping
Patent
1997-08-11
1999-01-12
Bray, W. Donald
Woodworking
Process
Mechanical cutting or shaping
144176, 144241, 241 92, 241294, B27C 100, B27C 710
Patent
active
058575081
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method in accordance with the preamble of claim 1 of mounting a wear plate and a knife base on a disc chipper's disc, and to a disc chipper in accordance with the preamble of claim 3.
For producing chips for use in pulp production a chipper is generally used, wherein knives chipping the log of wood against a fixed counter knife are mounted onto a knife disc approximately in a radial direction. Wear plates against which the log of wood is fed are located in sectors between the knives. The distance between the wear plate and the counter knife increases from one knife to the following knife. Chip length depends on the so-called T dimension, that is, the distance between the wear plate and the cutting edge of the following knife, measured in parallel with the knife disc shaft.
Chip length as such is not the most important characteristic in pulp production, but chip thickness is. Longer chips are always also thicker when produced in similar conditions. Other factors besides length which affect chip thickness are the quality of logs of wood, feeding and knife angles of the chipper, and the cutting speed of the knife. Tests indicate that a higher speed gives thinner chins, given a constant chip length. In a disc chipper, the cutting speed is higher at the outer disc rim than closer to the shaft. For this reason, when for example the chip length is increased to obtain thicker chips, the length ought to be increased more at the outer rim of the knife disc, because due to the higher speed, the same change of length there will not result in an equal change of thickness as nearer to the shaft where the speed is lower.
Because the same chipper is used for chipping different kinds of wood in different seasons and, in addition, chips from the same chipper are used for different pulps, it must be possible to perform adjustment of the chip length and at the same time of the thickness promptly and with small costs.
One method of chip length adjustment in a disc chipper is described in patent publication FI 79799. In the method according to patent publication 79799, however, mounting of the knives against the wear plate by pressing by means of screws and a knife stop causes bending of the wear plate, so that the distance between the cutting edge of the knife and the counter knife will change. The distance between the knife edge and the counter knife will also change when adjusting the chip length by turning the wear plate around its pivot joint, so that the whole knife disc must be moved. Because the entire wear plate and the knife along with it will turn during adjustment, the knife cutting angles will change at the same time, so that the clearance angle is smaller with short chips. "Suction" into the chipper is also reduced as a result of this. In addition, changing of knives is difficult, because the knives are exchanged from the other side of the chipper disc than where the screws are opened and tightened.
Another known adjustable wear plate system is a structure in accordance with printed application WO90/15702, wherein a knife cassette is mounted on a knife disc by means of spacers and the adjustment of the chip length is done by a torsioning wear plate. The publication also describes an embodiment wherein fastening bolts at the front edge of the wear plate are supported against the disc by means of semispherical washers. The weak point in this system is its complicated structure and numerous dust-producing recesses for bolt heads in the wear plate.
The disadvantages of known adjustable wear plate systems are eliminated by the present invention. The method according to the invention is characterized in that the wear plate rests against the knife base via two counter faces, of which one forms in the wear plate or in a strip supported against the wear plate a groove in parallel or almost in parallel with the knife, while the other forms in the knife base a ridge which can be fitted into this groove, and in that the tightening force of the wear plate's fastening bolts by means of the wear plate
REFERENCES:
patent: 3981337 (1976-09-01), Erik Wilhelm
patent: 4503893 (1985-03-01), Dino M. Demopoulos
patent: 4669516 (1987-06-01), Carpenter et al.
patent: 5287901 (1994-02-01), Mathews
patent: 5469902 (1995-11-01), Sharp et al.
Bray W. Donald
Sunds Defibrator Woodhandling Oy
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