Woodworking – Slicer – Cylindrical cutter
Reexamination Certificate
1999-09-17
2002-05-21
Rachuba, M. (Department: 3724)
Woodworking
Slicer
Cylindrical cutter
C144S180000, C144S162100
Reexamination Certificate
active
06390161
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a process for cutting rough timber or logs to form large-surface wood chips, in which, on the one hand, a rotating knife ring provided with cutting knives which are oriented parallel to its axis of rotation and, on the other hand, a quantity of logs which are likewise oriented parallel to the axis of rotation of the knife ring are moved toward one another and the logs are cut. The invention is further directed to a device for carrying out this process.
b) Description of the Related Art
Processes and devices for cutting wood have been known in the art for a long time. With the development of wood materials such as chipboard, fiberboard, beams and molded articles of particle board, etc., this type of technology has gained in importance and is constantly being perfected.
One of the earliest wood materials developed is oriented strand board (OSB), which is a further development of conventional chipboard. By the expression “strand” is meant in this case large-area wood chips with a preferred geometry, for example, 100 mm×14 mm×0.5 mm, which are glued together in flat cross-laminated layers to form OSB. The panels formed in this way are distinguished from conventional chipboard by substantially increased strength. Moreover, because of the layer orientation of the wood chips, they have a significantly lower proportion of glue and a more favorable ratio of wood to glue components which economizes on glue.
However, the development of OSB has also led to stricter requirements for the quality of wood chips because the advantages mentioned above can only be achieved by maintaining the chip geometry, especially the chip thickness.
Accordingly, one of the primary requirements of corresponding processes and devices for wood cutting is to supply chips of a defined quality. This effort with respect to chip quality has led in recent times to the development of cutting machines for logs and remainder wood, e.g., for round logs that have not been cut to length, in which the cutting is carried out by a rotating knife ring. This knife ring essentially has the geometry of a hollow cylinder, wherein cutting knives which are oriented parallel to the axis of rotation are arranged along the inner circumference of the knife ring so as to be distributed in a radially symmetric manner.
A bundle of logs which are oriented parallel to the axis of rotation are pushed into the knife ring gradually in a cyclic manner, that is, by lengths corresponding to the dimensioning of the knives in the axial direction; in doing so, the knives do not initially engage with the logs. After the logs are pushed in, they are clamped by a holding system and the rotating knife ring is then moved in the radial direction toward the portion of the logs projecting into its interior space, the cutting chamber, as it is called, so that the knives consequently come into contact with the logs and the cutting is carried out, wherein the required chip quality is achieved through the peeling effect brought about by the rotating knives oriented parallel to the longitudinal direction of the logs.
Of course, the forward feed speed, knife projection, pitch of the knife ring and quantity of knives at the circumference, cutting speed, radius of the orbit of the cutters, etc. play a substantial role in the chip forming process as regards chip quality. Extensive research has already been carried out in this regard; the findings are known and are already in use. However, another essential criterion in the production of strands has not yet been adequately met, namely, the amount of chips of like quality, especially of like chip thickness, that can be achieved in one revolution of the knife ring.
It will be seen from a consideration of the movement curves of the cutting knives that during the cutting process every cutter describes a path which extends in a spiral and corresponds to a helical line with a pitch that depends on the forward feed direction and on the forward feed speed.
In principle, horizontal cutting and vertical cutting are known with respect to the forward feed movement, wherein “horizontal” and “vertical” refer to the forward feed direction of the knife ring. For example, Patent DE 35 05 077 C2 shows a machine for horizontal cutting in which the wood bundle is deposited on a horizontally arranged sliding wall and is pushed into the interior of the knife ring by means of a feed pusher so as to slide along this sliding wall and is held in this position by clamping elements. The forward feed movement of the rotating knife ring is then carried out in the horizontal direction, for example, from left to right, wherein the cutting of the wood bundle is carried out. The depth of the cutting chamber is predetermined by the axial length of the individual knives.
The principal difference in vertically cutting machines compared with horizontal cutters essentially consists in the vertically directed forward feed movement of the knife ring. In this case, a bundle of logs is advanced into the interior of the knife ring initially with the help of a feed device, again in this case by a distance corresponding to the axial length of the knives. The rotating knife ring is then set in motion in a vertical forward feed movement, wherein the cutting is carried out. Patent DE 43 35 348 C1 discloses a long-timber or long-wood cutter in which the forward feed movement is directed vertically, specifically upward, toward the wood bundle. Similarly, the construction of cutting devices with a vertical downward movement of the knife ring is also conceivable.
The straight-line forward feed movement is characteristic of both arrangements described above. The cutting process taking place in this connection will be briefly described in the following. In this connection,
FIG. 1
shows a schematic diagram of a knife ring with m
G
=36 knives. In theory, of these knives, only m
&egr;
=18 knives which are arranged on the half-circle in the forward feed direction can be engaged. Assuming a forward feed movement that is directed vertically upward, as is shown in
FIG. 1
, different forward feed paths result for the individual cutters depending on their instantaneous position at the circumference of the knife ring, which leads to different chip thicknesses.
A cutter A and the cutter B trailing behind cutter A are shown in
FIG. 1
for different phase angles a during the rotation of the knife ring. It will be seen that the largest chip thickness results at d
3
and the smallest chip thickness results at d
1
. The occurring chip thicknesses therefore depend on the respective position of a cutting knife at the circumference of the knife ring at which engagement is carried out.
In order to establish a scale for evaluating the quality of the delivered chips in relation to the positions of the cutting knives, the circumference of the knife ring is divided into sectors which deliver chips having a thickness within permissible tolerance limits.
In
FIG. 2
, the knife ring for a vertical cutter with upward cutting is divided into individual phase sectors, wherein the sectors extend in the forward feed direction and the division is determined by the quantity of knives. Since, theoretically only m
&egr;
=18 knives of the total of m
G
=36 knives can be engaged and these 18 knives are distributed symmetrically with respect to the axis of rotation, a quantity of nine sectors S
1
to S
9
results. It is assumed that chips with a thickness within a range of permissible tolerances occur within each sector.
Therefore, it can be concluded that chips with a sufficiently consistent or unitary thickness are obtained only when the wood bundle is kept only in one of the sectors, or, in some cases, in two or three neighboring sectors, for example, sectors S
1
and S
2
, during the cutting process. However, it is likewise clear that the economy of a cutting device, especially with respect to the production of OSB, is essentially dependent on how many chips of unitary thickness ar
Freitag Andreas
Freitag Joachim
Rachuba M.
Reed Smith LLP
Tran Kim Ngoc
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