Log bark slitting machine
A bark slitting machine has swing mounted slitting arms on a rotating ring through which a log is fed. The arms have a swept back outer portion with a cutting edge and an attack angle having a size preferably like that of the lead angle of a helix determined by the path of a point rotating at a given rotational speed about the circumference of a log advancing at a given linear speed.
1.A log bark slitting machine for slitting in a helical path the bark of logs each having a diameter within a given diameter size range, said machine comprising:
a rotary ring having a central opening therethrough with a center axis for passing an axially moving log in a forward direction; anda swing arm having an elongated bark cutting edge, said arm being pivotally mounted on said ring such that the arm can swing inwardly into said central opening about a swing axis parallel to said center axis for engagement of said knife with the bark on a said log,said cutting edge facing toward said central axis and extending lengthwise from an outer end portion of said swing arm toward said ring,and said swing arm being swept rearwardly through at least the length of said cutting edge at an attack angle relative to a plane perpendicular to said central axis, said attack angle having a size approximating that of the lead angle of a helix determined by the path of a point rotating at a given rotational speed about the circumference of a said log advancing axially at a given speed.
2. A log bark slitting machine according to claim 1 in which an extension of a line along said cutting edge passes through said swing axis.
3. A log bark slitting machine according to claim 1 in which means is provided on said ring for urging said arm to swing inwardly.
4. A log bark slitting machine according to claim 1 in which adjustable means is provided on said ring for urging said arm to swing inwardly at variable slitting pressures, while the ring is turning.
5. A log bark slitting machine according to claim 1 in which said ring has a plurality of said pivotally mounted arms.
6. A log bark slitting machine according to claim 1 in which said cutting edge is provided by crbide inserts detachably mounted on said arm for ease of replacement.
7. A log bark slitting machine according to claim 1 in which an outer part of said arm containing the full length of said cutting edge is swing mounted on the remaining part of the arm for varying said helix angle.
8. A log bark slitting machine according to claim 7 in which the swing of said outer part relative to said remaining part is limited to a given swing range.
9. A log bark slitting machine according to claim 7 in which said outer part is free to swing in a given swing range.
10. A log bark slitting machine according to claim 1 in which said cutting edge is straight.
11. A log bark slitting machine according to claim 1 in which said cutting edge is convex aong its length.
12. A log bark slitting machine according to claim 1 in which said cutting edge is concave along its length.
13. A bark slitting tool comprising:a swing arm having a boss at one end defining a swing axis,a cutter assembly mounted on said arm and presenting an elongated straight cutting edge extending from the opposite end of said arm toward said boss,a portion of said arm containing said cutter assembly being bent at an angle relative to a portion of said arm containing said boss such that said cutting edge is parallel to a line intersecting said swing axis at an acute angle.
14. A bark slitting tool according to claim 13 in which said cutting edge coincides with said line.
15. A bark slitting tool according to claim 13 in which said arm portion which is bent is hinged to swing relative to said arm portion containing the boss.
16. A bark slitting tool according to claim 13 in which said swing arm is detachably mounted on said boss.
17. A bark slitting tool according to claim 13 in which said cutter assembly comprises a holder detachably mounted on said swing arm and a carbide insert on said holder.
18. A bark slitting machine according to claim 13 in which said cutter assembly comprises a row of aligned holders detachably mounted on said swing arm, each of said holders having a carbide insert, said carbide inserts providing said cutting edge.
19. A bark slitting tool comprising:a swing arm having a boss at one end defining a swing axis,a cutter mounted on said arm and presenting an elongated straight cutting edge extending from the opposite end of said arm toward said boss portion of said arm containing said cutter being hinged to swing at an angle relative to a portion of said arm containing said boss.
The present invention relates to slitting machines for slitting the bark on a log in a helical pattern prepatory to debarking the log.U.S. Pat. No. 3,991,800 discloses the concept of slitting the bark on a log in a helical pattern and than peeling off the bark in a continuous operation. This technique is particularly effective for removing bark having relatively long stringy fibers such as present on cedar and eucalyptus trees. The bark slitting is disclosed as being performed by a ring-type debarker having modified tools on its swing arms. The slitting operation cuts through the stringy fibers at regular intervals so that the bark can then be peeled cleanly from the log in a helical strip. The modified debarker is positioned in advance of a standard ring-type debarker so that the logs pass axially through both machines.
It is preferred to have the slit through the bark made during the bark slitting operation be performed such that the bark adjoining the slit is not scuffed and partially peeled. Otherwise, the stringy bark tends to bunch and foul the bark slitting ring.Bark thickness and resistance to cutting also varies. Hence, it is preferred to be able to control the cutting pressure so as to cleanly cut through the bark, and yet not unduly score the underlying wood. A further need is ease of removing the slitting tools for sharpening or replacement.
With the foregoing in mind the present invention utilizes a standard ring-type debarker having debarker arm pressure adjustment during operation and substitutes novel slitting arms for the debarker arms. Each slitting arm has a removeable cutting knife with an elongated cutting edge extending from the outer end of the arm toward the swing axis of the arm. Preferably the cutting edge is straight and coincides with a line passing through the swing axis. Each slitting arm is bent in a rearward direction, i.e., the travel direction of the logs, at a location sufficiently close to the pivot axis of the arm that the entire length of the cutting edge is contained in the rearwardly bent part of the arm. The degree of bend of the arm preferably matches the expected lead angle of the helical path of a point traveling around a log at ring rotational speed while the log advances axially at a predetermined speed. The lead angle of the helical path varies with the log diameter for a given ring speed and log speed, and hence it is preferred to have the degree of bend in the slitting arm approximate the lead angle for an intermediate expected log diameter. It has been found that this normally is close enough to prevent bark removal during the bark slitting operation.
As an alternative arrangement, the rearwardly bent part of slitting arm may be hinged to the remaining part of the arm rather than being rigidly connected. This arrangement permits the cutting edge to automatically find the correct cutting position with respect to the helix. Stops are provided to limit relative movement between the hinged parts of the splitting arm.
Although a straight cutting edge is preferred for production economy, the cutting knife may have a concave or convex configuration.FIG. 1 is a fragmentary elevational view of a bark slitting machine embodying the present invention and showing one of the slitting arms;
FIG. 2 is a fragmentary sectional view taken as indicated by line 2–2 in FIG. 1 and with the parts of a standard debarker on which the slitting arms are mounted being shown in phantom;
FIG. 3 is an enlarged end view of the outer end of one of the splitting arms;
FIG. 4 is a a fragmentary sectional view taken as shown by line 4–4 in FIG. 1;
FIG. 5 is a fragmentary view of the back side of the machine;
FIGS. 6A, 6B and 6C illustrate the helical slitting paths cut on various sizes of logs when the log speed and rotational speed of the ring are constant;
FIGS. 7A, 7B and 7C correspond to FIGS. 6A, 6B and 6C and are end views showing the corresponding slitting arm positions;
FIGS. 8A, 8B and 8C correspond to FIGS. 6A, 6B and 6C, and illustrate the slitting action of a modified slitting machine arm which is articulated;
FIG. 9 illustrates alternative cutting edge configurations for the slitting arms.
Processing your request, Please wait....
