Debarking drum, method and system for debarking of wood

Abstract

A debarking drum (1) for the debarking of wood (2) has an essentially horizontal cylindrical drum (10) supported to revolve around its longitudinal axis. The drum has a first end (12) and a second end (14) with an inner surface with inwardly projecting longitudinally extending debarking iron sections (16). Bark openings or slots (20) extend through the drum inner surface (18) and multiple rigid studs (22) protrude inwardly from the inner surface (18) and are positioned between the debarking iron sections (16). The studs operate to break the bark (3) of the wood (2) for debarking. The studs (22) are positioned along a partial length (L) of the drum (10) between the first end (12) and the second end (14). The invention also relates to a method and system for the debarking of wood by the debarking drum.

Claims

1. A drum for the debarking of wood, including an essentially horizontal cylindrical drum, which is supported to revolve around its longitudinal axis, the drum comprising: a first end for the feeding of wood into the drum; a second end for the removing of wood from the drum, the drum having an interior for the passage of the wood therethrough, the interior having a drum total length in the direction of the longitudinal axis between the first end and the second end; debarking iron sections fixed to an inner surface of the drum which extend in the longitudinal direction of the drum, wherein the debarking iron sections are positioned on an internal circumference of the drum and are spaced circumferentially from each other to define gaps therebetween, the debarking iron sections disposed to lift input wood upwards on the circumference of the drum when the drum is revolving and to release the bark of the wood when the wood drops; bark openings formed to extend through the drum and extending from the inner surface of the drum to an exterior of the drum, the bark openings providing pathways for the removal of the bark which comes off from the wood to pass out of the drum; and rigid studs fixed to the inner surface of the drum and positioned in the gaps between the debarking iron sections, the studs disposed to project into the interior of the drum to break the bark of the wood for the debarking of the wood, wherein the studs are positioned at the first end of the drum along a partial length of the drum total length.

2. The drum of claim 1 wherein the partial length is 10-40% of the drum total length between the first end and the second end.

3. The drum of claim 1 wherein the studs on the inner surface of the drum are disposed on at least every second gap between the debarking iron sections on the circumference of the drum.

4. The drum of claim 1 wherein the studs are formed directly on the drum or on protective plates that form the inner surface of the drum and that are fastened to the drum in a detachable manner.

5. The drum of claim 1 wherein the studs extend inwardly into the interior of the drum a height, and wherein the height of each stud is 10-25 mm.

6. The drum of claim 5 wherein the height of each stud is 13-19 mm.

7. The drum of claim 1 wherein the studs are spaced from one another in a circumferential direction in each gap a distance of 10-60 mm.

8. The drum of claim 7 wherein the studs are spaced from one another in the circumferential direction in each gap a distance of 25-40 mm.

9. The drum of claim 1 wherein the distance of each debarking iron section from the closest studs is 10-60 mm.

10. The drum of claim 9 wherein the distance of each debarking iron section from the closest studs is 25-40 mm.

11. The drum of claim 1 wherein the studs between two adjacent debarking iron sections are placed in rows, and wherein consecutive rows are placed in an overlapping manner with respect to each other in the longitudinal direction of the drum.

12. The drum of claim 11 wherein the studs are arranged in an overlapping manner to form a spiral to speed up or slow down the progress of the wood in the drum in accordance with the selected direction of the spiral.

13. The drum of claim 1 wherein each stud extends into the interior of the drum about a first axis, and wherein each stud is comprised of a surface material and a core material positioned radially inwardly of the surface material, wherein the core material is harder than the surface material, enabling that the stud becomes sharper as the stud wears down.

14. The drum of claim 13 wherein the surface material of the stud is of steel, and the core material is of a material the hardness of which is more than 800 HV.

15. The drum of claim 14 wherein the core material is tungsten carbide.

16. A system for the debarking of wood, which system comprises a debarking drum apparatus, which includes an essentially horizontal cylindrical drum which is supported to revolve around its longitudinal axis, wherein the drum comprises: a first end for the feeding of wood into the drum; a second end for the removing of wood from the drum, wherein an inner surface extends between the first end and the second end; debarking iron sections extending inwardly from and fixed to the inner surface, the debarking sections extending in the longitudinal direction of the drum on an interior circumference of the drum, wherein the debarking iron sections are spaced in the circumferential direction to define gaps therebetween, the debarking iron sections positioned to lift input wood upwards on the circumference of the drum when the drum is revolving and to release the bark of the wood; bark openings which extend through the drum from the inner surface to an exterior of the drum, the bark openings allowing the passage of bark which comes off from the wood, out of the drum; rigid structure for the breaking of the bark of the wood for the debarking of the wood, which structure comprises studs for the breaking of the bark of the wood for the debarking of the wood, which studs are positioned either: fixed on the inner surface of the drum between said debarking iron sections, and the studs are at the first end of the drum on a partial length of a total length of the drum between the first end and the second end; or on rotating elements that precede the drum.

17. A method for the debarking of wood using a debarking drum apparatus having an essentially horizontal cylindrical drum, which is supported to revolve around a longitudinal axis, the method comprising: feeding wood into the drum from a first end while the drum is rotated; lifting the wood which has been fed into the drum upwards by engaging debarking iron sections fixed to an interior of the drum with said wood in order to debark the wood as the wood drops on the wood in the drum, the debarking iron sections being spaced circumferentially to define gaps therebetween; removing bark released from the wood through bark openings in the drum; and removing debarked wood from the rotating drum from a second end of the drum which is downstream of the first end; and breaking the bark of the wood fed into the drum by engaging a plurality of inwardly protruding rigid studs fixed to the interior of the drum and positioned to facilitate debarking, wherein the studs are fixed in the drum in the gaps between the debarking iron sections at the first end of the drum or are positioned ahead of the first end of the drum as part of a separate structure rotating for the breaking of bark, the separate structure being positioned ahead of the first end of the drum and feeding into the drum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described below in detail by making reference to the enclosed drawings that illustrate some embodiments of the invention.

(2) FIG. 1 shows a prior art debarking drum and the process around it as a figure in principle,

(3) FIG. 2 shows an inlet end of a prior art debarking drum in an axonometric view.

(4) FIG. 3 shows an inlet end of a debarking drum according to the invention in an axonometric view.

(5) FIG. 4 shows studs of the debarking drum according to the invention, fastened to a protective plate and presented in the longitudinal direction of the studs.

(6) FIG. 5 shows studs of the debarking drum according to the invention, fastened to a protective plate and presented from the end of the protective plate.

(7) FIG. 6a shows an individual new stud separately presented from the side.

(8) FIG. 6b shows an individual worn stud separately presented from the side.

(9) FIG. 7 shows a debarking drum according to a second embodiment of the system according to the invention, the means for the breaking of bark and the process around it as a figure in principle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) It is to be understood in this context that the debarking drum according to the invention can be part of a fully corresponding process, which is described with a prior art debarking drum in FIG. 1. In this way, it can be thought that FIG. 1 also illustrates a debarking drum 1 according to the invention and the process around it.

(11) The debarking drum 1 according to the invention includes, in accordance with prior art, a drum 10 and support and rotating means 34 presented in FIG. 1, by means of which support and rotating means 34 the hollow drum 10 is supported essentially horizontally, however at an angle of 1/50- 1/150 (upward gradient with respect to the length of the drum) so that an open inlet or first end 12 included in the drum 10 is at a higher elevation than an open outlet or second end 14. This accomplishes a gravitational movement of wood in the debarking drum 1 in the direction of progress of the process through the debarking drum 1. The support and rotating means 34 can include, for example, hydraulically-supported rubber wheels, which are rotated by electric motors in order to accomplish rotation of the drum 10 taking place around its longitudinal axis, or other corresponding purposeful implementation.

(12) Longitudinally extending debarking iron sections 16 are fastened to the interior of the drum 1 and are spaced circumferentially from one another to define circumferentially extending gaps 19. The debarking drum 1 according to the invention includes studs 22 formed on the inner surface 18 of the drum 10 shown in FIG. 3, in the circumferential gaps 19 between debarking iron sections 16, in order to break the bark of the wood in accordance with the method according to the invention. The drum 1 has a longitudinal length in the direction of the drum's axis of rotation, and the studs 22 are formed advantageously on a partial length L, indicated in FIG. 1, which is less than the full longitudinal length of the drum, the partial length L of studs running from the inlet or first end 12 of the drum 10, which partial length can be 10-40% of the total length of the drum 10. In accordance with FIG. 3, there can be studs 22 in every second gap 19, for example, but the biggest effectiveness in the breaking of bark is achieved by using studs 22 in all gaps 19. When the drum 10 is rotating, the wood 2 on the bottom of the drum 10 is in contact with the studs 22, in which case the weight of the wood 2 that is on top of this wood 2 on the bottom is also directed at the lowest pieces of wood 2, pressing them against the studs 22. In this case, the studs 22 sink into the bark 3 of the wood 2, which bark 3 is presented in FIG. 5, breaking the uniform structure of the bark 3 around the surface wood that is underneath the bark of the wood 2. More specifically, the studs 22 break the outer shell of the wood, in other words the bark, the inner shell, in other words the phloem, and the cambium that is inside the inner shell, in order to remove these in debarking. When the drum 10 is rotating, the wood 2 moves upwards on the circumference of the drum 10 pushed by the debarking iron section 16, until ultimately the wood 2 drops from the circumference back to the bottom of the drum 10 on top of the wood 2 colliding with it. As a result of the impact, the bark, which has already been broken by the studs 22, is ripped off and comes off from the wood. The dimensions of the released pieces are often smaller than the corresponding pieces of prior art debarking drums, because the points of discontinuity caused by the studs in the bark are located fairly close to each other, like the placement of the studs, facilitating the release of small pieces of bark from the wood. The debarking iron sections 16 also release bark from the wood when the drum is rotating, but the impacts between the pieces of wood are the primary mechanism for releasing the bark.

(13) The studs 22 can be fastened directly to the inner surface 18 of the drum 10 or alternatively to separate protective plates 26, one of which is shown in FIG. 4. Furthermore, alternatively the studs 22 can be formed into cassettes, which are adapted on guideways formed on the surface of the drum. The fastening directly to the inner surface of the drum 10 or to the protective plates 26 takes place advantageously by means of welding, for example, laser welding or resistance butt welding. For welding, an opening can be made in the drum or the protective plate for the stud, which opening enables a sturdier fastening of the studs than a fastening directly to an existing uniform surface. It is advantageous to use laser welding in new drums in connection with the welding of studs directly to the drum or in connection with the protective plates. Instead of welding, threads can also be machined in the inner surface of the drum or in the protective plates, and the studs can be fastened by means of counter threads and a thread locking agent.

(14) Advantageously, existing prior art debarking drums can be modified to become debarking drums according to the invention by installing in them protective plates equipped with studs in connection with the first end of the debarking drum. The protective plates can be fastened between the debarking iron sections 16 by welding on site or by means of bolt fastening, for example. The purpose of the protective plates has traditionally been to protect the debarking drum against impacts caused by the wood. Protective plates can also be used to extend the service life of existing debarking drums by protecting already worn internal surfaces of the drum by means of protective plates that serve as wear surfaces. Now the protective plates can serve as a fastening base of the studs to the drum.

(15) In accordance with FIG. 4, the studs 22 are advantageously adapted in rows 24, which are advantageously overlapping with respect to each other in the longitudinal direction of the drum, in other words their offset with respect to the debarking iron sections 16 varies from one row to another. Advantageously, every second row has the same offset. The overlapping of the rows is advantageously selected so that a stud in one row is placed between two studs in the next row, in the middle of the distance between these, in the shape of a diamond. In this way, the stud protects the studs in the second row against impacts in the lateral direction. This is especially important, because due to the welding fastening of the studs, the studs withstand stress in their longitudinal direction well, but they withstand directly cross-directional impacts poorly, and these may dislodge a stud. The distance d of the studs 22 from each other in each gap is 10-50 mm, advantageously 25-40 mm. The distance of the studs 22 from a debarking iron section is also the same, in which case the studs protect each other in the longitudinal direction of the drum, and the debarking iron sections protect the outermost studs in the circumferential direction.

(16) According to one embodiment, the rows of studs can be installed so that they form the shape of a spiral in the longitudinal direction of the drum. The selection of the direction of the spiral influences the characteristics of the drum to carry wood in the longitudinal direction of the drum from the first end towards the second end. If the spiral is formed in the rotating direction of the drum, the spiral intensifies the travel of the wood in the longitudinal direction of the drum, and, when selected in an opposite manner, it slows the travel of the wood.

(17) Bark openings 20 are formed in the protective plates or directly in the inner surface of the drum which pass through the drum and thus communicate between the interior and the exterior of the drum and allowing the passage of bark therethrough. The size of the bark openings 20 is determined by the diameter of the wood to be handled; typically, the bark openings are 40-50 mm wide. The criterion for the selection of the size of the bark openings is that the bark can fit through the bark openings out of the drum, but the wood or the pieces dislodged from the wood cannot fit through. The shape of the bark openings is advantageously elongated, in other words its length is greater than its width. The longitudinal direction of the bark openings can be parallel with the longitudinal direction of the drum, or diagonal.

(18) The height of the studs in the radial direction of the drum can be 10-25 mm, advantageously 13-19 mm. The selection of the height of the stud is influenced by the wood species handled and the assumed amount of sinking of the stud so that the entire bark structure of the wood becomes broken. In accordance with FIG. 5, when the studs 22 are close to each other, several studs 22 are in contact simultaneously with an individual piece of wood 2, in which case the loading is distributed between these, reducing the loading of an individual stud 22. In accordance with FIG. 5, the studs 22 sink through the bark 3 of the wood 2 advantageously over the entire thickness of the bark. The sinking may change as the stud wears down, but the sinking should not be so great that it damages the surface wood under the bark, at least not significantly, exposing the wood to the creation of wood losses.

(19) Advantageously, the studs have a round shape in the transversal cross section with respect to the longitudinal direction, in which case the diameter of the stud at the root of the stud can be 5-15 mm, advantageously 8-12 mm. In accordance with FIG. 6a, the tip of the stud 22 can be blunt when it is new, but it wears and becomes sharp during operation in accordance with FIG. 6b. This can be accomplished by advantageously using in the stud a surface material 28, which is softer than the core material 30. In this way, the surface material 28 wears more during operation than the core material 30, enabling the stud to become sharper during operation without a separate need for sharpening. A softer surface material also enables a good fastenability of the stud by welding. The portion of the core material in the center of the stud can be 5-50% of the diameter of the stud, while the rest of the diameter is of the surface material.

(20) According to one embodiment, there can also be two kinds of studs, a first kind, which have a core material that is harder than the surface material, and a second kind, which are fully of a single selected material, which is more affordable than the core material but more durable than the soft surface material, advantageously of more durable wear-resistant steel. The surface material is advantageously of wear-resistant steel with a sufficient wear resistance, while the core material is of a material with a hardness in excess of 800 HV, such as tungsten carbide. The stud used can be, for example, an AVT wear stud (high performance) manufactured by the Australian Antec Group Pty Limited.

(21) Alternatively to a round cross-sectional shape, the shape of the cross section of the stud can also be elliptic or the shape of a diamond. A different cross-sectional shape can also be used to influence the sinking of the stud into the bark.

(22) When using studs, the rotating speed of the drum can be a rotating speed in accordance with prior art debarking drums, such as 5-30 rpm. Too great a rotating speed increases energy consumption drastically and can cause damage to or dislodging of the studs.

(23) The method and system according to the invention for the debarking of wood can also be thought to be applied so that the bark of the wood is broken before the debarking drum. This could be implemented, for example, by means of rotating elements or rollers, such as hydraulically-loaded rollers, used for the feeding of wood, where the rotating elements or rollers would include studs like the debarking drum according to the invention. In this case, the debarking drum can be completely in accordance with the prior art. FIG. 7 shows the second embodiment of the system according to the invention, where the means 40 for the breaking of bark are studs, which are placed on separate rotating elements 42 before the debarking drum 1. The rotating elements can be, for example, a structure of the type known by the name Rotary Debarker or Rotabarker of Acrowood Corporation, where rotating discs are adapted consecutively on axes adapted in the longitudinal direction of the wood, and the studs are formed on the discs. When the wood travels through this device, the wood is subject to impacts from the studs, which impacts break bark. According to the first embodiment, the system is implemented so that the means for the breaking of bark are part of the debarking drum, like in the debarking drum according to the invention.

(24) The diameter of the debarking drum according to the invention can be 3-9 m, advantageously 4-7 m. The length of the debarking drum can be 10-30 m, advantageously 15-25 m.