1. A bark stripping machine comprising a rotary drum and a plurality of knives, each of said knives having a cutting member at one end, a wing member at the other end thereof and a weight detachably mounted on said wing member, said knives being mounted on the inner peripheral wall of said rotary drum in such a manner that each said cutting member is pivotable toward the center of the rotary drum.
2. A bark stripping machine as recited in claim 1, further comprising a central shaft extending from each of said knives, each said knife rotating respectively thereabout, a boss enclosing each said shaft, a first stopper positioned on each said boss, a plurality of bearings mounted on the inner peripheral surface of said rotary drum, each adapted to receive said shaft of one of said knives, a second stopper operatively positioned on each of said bearings, said first and second stoppers preventing open cutting members of knives from contacting one another when said rotary drum stands still.
3. A bark stripping machine having a frame, comprising:
4. A bark stripping machine as recited in claim 3, further comprising: a boss enclosing the cnetral shaft of each of said knives, a plurality of first stoppers, one being positioned on each said boss, a plurality of second stoppers, one being positioned on each of said bearings, said first and second stoppers preventing the cutting members of the knives from contacting one another when said rotary drum stands still.
This invention relates to a bark stripping machine and more particularly to a bark stripping machine which is so constructed that a rotary drum having knives provided on the inside thereof is rotated at a high speed while inserting wood into said rotary drum, whereby the wood is barked by said knives during passage through said rotary drum.
Conventional bark stripping machines include a type comprising an endless chain and nail-shaped cutters provided thereon, said endless chain being pressed against the surface of a wood while being driven, whereby the bark of the wood is stripped by the cutters carried on said chain. However, in this type of bark stripping machine, the operator presses the chain against the wood while moving the machine in the longitudinal direction of the wood during the bark stripping operation, so that the pressure of contact between the knives and the wood depends solely on the sense of the operator, and there has been the disadvantage that cutting of the heartwood would result when the pressure is too large, while complete stripping would be impossible when the pressure is insufficiently large. In addition, since the pressure is adjusted by the operator, the stripping operation forces heavy labor upon the operator in the event when the bark to be stripped is tough.
There has also been known a type of bark sripping machine which utilizes a high hydraulic pressure, but such prior art machine has had the disadvantage that, since the machine calls for a large amount of water and necessitates treatment of the waste water, it can be used only at such a place where abundant water is available and, moreover, it becomes large in comparison with the above-described prior art machine and hence is uneconomical.
The present invention consists in a bark stripping machine which is completely free of the disadvantages of the prior art machine and which is so constructed that a rotary drum having knives provided on the inside thereof is driven at a high speed to strip the bark of a piece of wood passing in said rotary drum.
An object of the invention is to provide a bark stripping machine in which knives carried on a rotating rotary drum, during the stripping operation, are engaged with a piece of wood with pressure created by the centrifugal force of said rotary drum and optionally variable by varying the rotational speed of said rotary drum, and which, therefore, is capable of stripping with high efficieincy and with minimum labor.
Another object of the invention is to provide a bark stripping machine of the character described above, in which said knives each have a wing member projecting outwardly from the rotary drum and can be engaged with the wood with a strong pressure obtained by making use of the air pressure applied to said wing member during rotation of the rotary drum.
Still another object of the invention is to provide a bark stripping machine of the character described above, in which a weight is detachably mounted on the wing member of each knife to adjust the pressure of contact between the knife and wood to a value optimum for the type of wood to be stripped.
A further object of the invention is to provide a bark stripping machine of the character described, which is small in size as a whole and hence can be installed easily even in a narrow space.
FIG. 1 is a front elevational view of an embodiment of the bark stripping machine according to the present invention;
FIG. 2 is a sectional view taken along the line II--II of FIG. 1; and
FIG. 3 is a perspective view of the knife mounted on the rotary drum shown in FIG. 1.
Referring to the drawings, the bark stripping machine shown includes a machine frame having two parallel plates respectively having a circular openings 2 formed centrally therein in registration with each other, and a rotary drum 3 is rotatably mounted in said openings 2 and supported therein by rollers which are rotatably mounted between the two parallel plates of the machine frame 1 in contact with the upper and lower portions of the rotary drum respectively. The rotary drum 3 projects outwardly at one end from the machine frame 1, forming a grooved pulley 5, and V-belts 8 are engaged around said grooved pulley 5 and a grooved pulley 7, mounted on a drive shaft of a variable speed motor 6 provided on the machine frame 1, to drive the rotary drum 3.
A plurality of knives 9 are connected to the inner peripheral wall of the rotary drum 3 in such a manner that each knife is pivotable about a pin at the center thereof. Namely, each knife 9, as shown in detail in FIG. 3, consists of a cutting member 10 and a wing member 11, connected integrally with each other at their bosses 10a, 11a by and extending in opposite directions from central pin 12, and is connected to the rotary drum 3, with the central pin 12 journaled in a bearing 13 fixed to the inner wall of the rotary drum 3 by a fixing plate 14. The cutting member 10 extends toward the center of said rotary drum and the wing member 11 projects outwardly from said rotary drum. The cutting member 10 is replaced by a new one when worn out.
The wing member 11 serves as a weight per se but it will be understood that the centrifugal force created in the wing member may be adjusted by connecting a weight 15 thereto. The weight 15 is fixed to the wing member 11 by means of a nut 17 engaged on a bolt 16 projecting from said wing member. Reference numeral 18 designates a stopper provided on the boss 11a of the wing member 11 and 19 designates a stopper provided on the bearing 13, for engagement with each other to keep the cutting member 10 out of contact with the cutting member 10 of the adjacent knife while the rotary drum 3 is not rotating.
Now, when the motor 6 is set in motion and the rotary drum 3 is driven through the V-belts, a torque is generated in the knives 9, urging the cutting members of the respective knives toward the center of the rotary drum 3. Namely, when the rotary drum 3 is driven in a clockwise direction as viewed in FIG. 1, a torque occurs in a counter clockwise direction about the pin 12 under the influence of air pressure acting on and centrifugal force created in the wing member 11, urging the cutting member 10 to move in a counterclockwise direction. During rotation of the rotary drum 3, a clockwise reaction occurs in the cutting member 10 relative to the pin 12, but is negligible and the cutting member 10 is urged toward the center of the rotary body, since the wing member 11 is large in weight and subjected to the air pressure.
Thus, a piece of wooden log (not shown) when inserted into the rotary drum from the left side of the machine as viewed in FIG. 2 is stripped by the cutting members of the respective knives 9. In this case, the efficiency of bark stripping operation can be enhanced by providing a separate device for feeding the wood toward the center of the rotary drum 3. Usually, a wood feeding device and a stripped wood drawing device are provided on the left and right sides (as viewed in FIG. 2) of the subject bark stripping machine respectively, whereby feeding and withdrawal of wood are effected automatically.
The pressure of contact between the wood and cutting member 10 can be changed optionally by varying the rotational speed of the motor, and can also be varied by changing the weight 15 on the wing member 11.
According to the present invention, as described above, a plurality of knives are pivotably mounted on the rotary drum and the cutting members thereof are urged toward the center of the rotary drum by a torque created during rotation of said rotary drum, so that by providing the wood feeding device and wood drawing device on the front and back sides of the machine respectively, the stripping work can be completely automatized.
It is to be noted that according to the invention, the contacting pressure of the knife 9 can be adjusted to a value optimum for the type of wooid to be stripped, as it is variable optionally by varying the rotational speed of the rotary drum. It is also to be noted that, since the contacting pressure can also be varied by changing the weight connected to the wing member, it is possible to readily obtain a contacting pressure precisely suitable for the type of work desired to be achieved, by changing the rotational speed of the rotary drum and the weight used.