Woodworking – Slicer – Rotary disk
Patent
1988-02-10
1989-05-30
Bray, W. Donald
Woodworking
Slicer
Rotary disk
144162R, 241277, B27L 1102, B27C 108
Patent
active
048341550
DESCRIPTION:
BRIEF SUMMARY
The subject of the present invention is a chipper for the chipping of wood into wood chips. In particular the invention relates to a basic type of a chipper which can be characterized as a radial spiral chipper and whose basic construction is described, e.g., in the published International Patent Application No. WO 84/02871.
It is characteristic of the said chipper type that the wood to be chipped is fed to the chipping members in a radial direction relative the blade disc. In this chipper type, the chipping of the wood is carried out by a continuous spiral blade whose cutting edge runs apart from the blade disc in screw line form, at the same time as it, starting from the periphery of the blade disc, approaches the centre of the blade disc. A recommended constructional form of the blade extends by about one and a half revolutions around the shaft of the blade disc, within which said path of travel the screw-shaped departing of the blade from the blade disc is arranged so that it produces a full "stroke" of the blade in the shaft direction, i.e. during the one and a half revolutions the blade wipes once across the feed opening of the chipper in the direction of the shaft.
If the chipper is constructed so that its shaft is placed horizontally, which is the recommended embodiment, the blade meets the wood first by reaching a tangential contact with one side of the wood, and thereat at a very sharp angle relative the vertical plane, which said angle is determined by the pitch angle of the departing of the blade edge from the blade disc.
The dimensioning of such a blade starts from the desired chip length and from the chosen pitch angle of the blade edge. If these factors have been chosen, the stroke length of the blade, i.e. the maximum thickness of the wood to be chipped, is determined by the blade diameter and blade length. As a rule, out of production-technical reasons and out of reasons of strength, it is not advisable to wind the blade to a spiral of very little radius, i.e. so that it revolves several times around the axis, but an adequate stroke length is preferably provided by means of a blade disc of somewhat larger diameter and by means of a blade wound on the disc with a larger radius. The distance in the radial direction between the blades in the blade spiral determines the length of the chips.
The said chipper type has been used successfully, e.g., for the production of fuel chips, in which case the chips are made rather coarse intentionally. The coarseness has been determined by choosing the radial spiral spacing of the blade, i.e., at the same time, the chip length large. Owing to the mode of operation of the chipper, large chip length at the same time also means high thickness of the chips. In order that the chips could be detached, it is necessary that the blade penetrating into the wood transversely to the grain in the radial direction has a force component in the direction of the grain which is sufficiently high to cleave the chip apart. For a long chip a higher detaching force is required than for a short chip, so that in the case of a long chip the blade has time to penetrate into the wood deeper before the chip is split apart.
The chipper may also be used for the production of chips to be defibrized, in which case the chip length is chosen clearly shorter. A usable chip length in the production of chemical pulp and refined groundwood is of an order of about 40 mm. However, in view of the absorption of the defibrizing chemicals, the chip thickness has a higher significance, and the thickness ought to be about 5 mm. However, the most essential matter in the control of the defibrizing process would be that the dimensions of all the chips are equal, i.e. the scattering of the dimensions of the chips should be as little as possible. Attempts have been made to reach this goal by means of a number of chipper solutions, but the scattering in the chip dimensions is still disturbingly high. The goal has been reached best in respect of the chip length, but the splitting of the chip apart from the w
REFERENCES:
patent: 3727504 (1973-04-01), Osterholt
patent: 4053004 (1977-10-01), Barwise et al.
patent: 4431039 (1984-02-01), Barwise et al.
patent: 4607672 (1986-08-01), Kangas et al.
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