EP2650050B1

EP2650050B1 - Wood chipping machine with peripheral sieving and disintegration device

Info

Publication number: EP2650050B1
Application number: EP13162484.3A
Authority: EP
Inventors: Peder Bach Christensen
Original assignee: PC Maskiner ApS
Current assignee: PC Maskiner ApS
Priority date: 2012-04-10
Filing date: 2013-04-05
Publication date: 2016-06-01
Anticipated expiration: 2033-04-05
Also published as: EP2650050A1; DK2650050T3

Description

Field of invention

The present invention relates to a wood chipping machine according to the preamble of claim 1. Such a wood chipping machine is known from EP2047911A1 .

Prior art

Basically, there are two different principles used in wood chipping machines, both of which use a rotating rotor onto which a number of cutter knives are mounted. The rotor is driven by an external force, such as the engine of a tractor or another machine, or by an internal combustion engine or an electrical motor integrated within the wood chipping machine assembly. In both principles, the material to be chipped is fed into a feed inlet from where it is transported to the rotor either by gravitational forces ("drop feeding") or by means of a feeding device. After being chipped, the material leaves the wood chipping machine through some form of outlet pipe.
The material to be chipped is most often biological material, such as whole trees, branches or pieces of wood, but it could also be plastic, paper, ice or other materials suitable for being chipped.
Using the first principle, the rotor is formed as a cylinder with the cutter knives arranged with their cutting edges in a tangential plane of the rotor, substantially in the axially direction of the rotor. The material to be chipped is fed to the rotor in a substantially radial direction. This principle of wood chipping comprises many fine features. However, it is primarily used in very large specialized machines due to rather large construction costs.
In smaller machines, it is normal to use the second principle, in which the rotor comprises a cutter disk onto which cutter knives are mounted within or in close connection with chip slots formed through the disk. The material to be chipped is fed to the front side of the cutter disk in a substantially axially direction. The chipped material moves through the chip slots to the back side of the cutter disk, where a number of ejector vanes mounted on the disk make sure that the wood chips are ejected through the outlet pipe of the wood chipping machine.
Perfect wood chips are obtained when every piece of chipped material is smaller than a predefined maximum size, and there are no so-called lumps or pegs within the chipped material. Lumps and pegs are pieces of wood that are larger than the wanted maximum size of the wood chips. Contrary to a lump, which is more like a chunk of wood, a peg is oblong and often consists of a smaller branch.
In a wood chipping machine using a cutter disk, both lumps and pegs can pass through the machine without being chipped, either through a chip slot in the cutter disk or by following the front side of the cutter disk to its perimeter and passing around the edge of the disk to the back side.
US Patent No. 5,060,873 discloses a wood chipping machine having a rotating cutter disk, which comprises a plurality of fins attached to the back side of the cutter disk near the perimeter for deflecting wood chips axially away from the cutter disk. The purpose of the fins is to minimize the cross over of wood chips from the back side to the front side of the cutter disk.
Austrian patent No. 361 762 discloses a grinder for biological material, which grinder has a sieving device arranged along the perimeter of a rotating cutter disk for disintegration of the biological material.
The European patent application EP 2 047 911 A1 discloses a wood chipping machine for disintegrating biological material such as whole tees, branches and other forms of wooden material. The American patent application US 818 725 A discloses a dumping-cage for crushers and pulverisers. Still, these solutions can be improved with respect to the ability to avoid pieces of material passing through the machine without being chipped into sufficiently small pieces
Therefore, it is an objective of the present invention to provide a solution to the above mentioned problem of pieces of material passing through the wood chipping machine without being chipped into sufficiently small pieces. Furthermore, it is an objective of the present invention to prevent large of pieces of material from passing through the wood chipping machine without being chipped into sufficiently small pieces.

Summary of the invention

The object of the present invention can be achieved by a wood chipping machine as defined in claim 1. Preferred embodiments are defined in the dependent sub claims and explained in the following description and illustrated in the accompanying drawings.
The wood chipping machine according to the present invention is a wood chipping machine for disintegrating material, mainly biological material such as whole trees, branches and other forms of wooden material, which wood chipping machine comprises a disk housing having an ejection opening, a rotor arranged in the disk housing to be rotatable about its central axis, the rotor comprising a cutter disk having one or more cutter knives arranged with their cutting edges in a substantially radial plane of the cutter disk, the cutter disk having a front side oriented towards a feed inlet of the wood chipping machine, and one or more ejector vanes mounted behind the cutter disk as seen from the feed inlet, where the one or more ejector vanes are mounted on the cutter disk or in a distance from the cutter disk, which ejector vanes extend in a substantially radial direction with respect to the cutter disk and are arranged to rotate during operation of the wood chipping machine, thus creating a centrifugal flow of air and forcing material behind the cutter disk towards the ejection opening of the disk housing, and drive means for driving the rotation of the rotor, where the rotor further comprises one or more chip slots extending through the cutter disk for transporting material chipped by the cutter knives to the back side of the cutter disk during operation of the wood chipping machine, where the wood chipping machine further comprises a peripheral sieving and disintegration device including one or more fixed parts that are stationary with respect to the disk housing, and one or more rotating parts that are arranged to rotate with the rotor during operation of the wood chipping machine, the rotating parts and the fixed parts of the peripheral sieving and disintegration device being arranged to interact with each other to sieve and disintegrate material passing in a radial direction towards the periphery of the disk housing without passing through the chip slots in the cutter disk to the back side of the cutter disk during operation of the wood chipping machine, where the peripheral sieving and disintegration device comprises a sieving device extending along at least a part of the perimeter of the cutter disk and in a substantially axial direction towards the front side of the disk housing and one or more cutter blades, the sieving device having a plurality of openings and the cutter blades being arranged to interact with the edges of the openings of the sieving device to disintegrate pieces of material. The sieving device extends along less than the full perimeter of the cutter disk, and the peripheral sieving and disintegration further comprises a cover plate extending along at least a part of the perimeter of the cutter disk, where the sieving device does not extend, and in a substantially radial direction in close proximity with the back side of the cutter disk, said cover plate extending within the outer perimeter of the cutter disk, wherein the cover plate is provided with a plurality of through-going passages.
Hereby it is ensured that the pieces of material passing through the wood chipping machine are of the required small size. In other words the provision of a cover plate as described ensures that no material passes around the edge of the cutter disk without being disintegrated. Moreover, there is passage from the front side to the back side of the cutter disk around the edge thereof. Hereby the cover plate can be used to prevent large of pieces of material from passing through the wood chipping machine without being chipped into sufficiently small pieces.
The term "substantially radial direction" is meant not only to include straight, radial ejector vanes but also forward curved or backward curved ejector vanes. The different shapes are all well-known from blades of centrifugal fans, giving different pressure and flow properties of the air flow produced by such fans.
Having a peripheral sieving and disintegration device is advantageous in that it prevents pieces of material from passing through the wood chipping machine to the ejection opening without being chipped into sufficiently small pieces either by the cutter knives of the cutter disk or by the peripheral sieving and disintegration device.
Using the interaction between moving and stationary parts is a well-proven and advantageous way to disintegrate a material into smaller pieces and bits.
It is preferred that the cutter disk having a front side oriented towards a feed inlet of the wood chipping machine, which feed inlet does not overlap the rotational axis of the cutter disk. The eccentric position of the feed inlet without any overlap with the rotational axis of the cutter disk is necessary in order to allow a drive shaft, onto which the cutter disk is mounted and by which the cutter disk is driven, to be supported by bearings at both ends, i.e. at both sides of the cutter disk, which is crucial for making the wood chipping machine sturdy and robust enough to handle even very large pieces or chunks of wooden material, such as whole trees or branches thereof.
It is preferred that the ejection opening is provided at the periphery of the disk housing since such construction eases the ejection of the disintegrated material.
It is preferred that at least a part of the cover plate is formed as a crenelated plate. Thus, the passages from the front side to the back side of the cutter disk are defined by the edges of the crenels of the crenelated plate and by the perimeter of the cutter disk. The provision of passages through the cover plate ensures that material, which has been disintegrated by the interaction of the cutter blades with the openings of the sieving device or with the passages through the cover plate, is able to leave the area in front of the cutter disk and pass through to the back side of the cutter disk.
Otherwise, there would be a substantially risk of material being stuck in this area, where there is no sieving device, and friction might cause this material to be overheated or even to catch fire.
However, only a negligible part of the material passes through the cover plate during operation of the wood chipping machine, because of the intense rotational flow in the disk housing, which on the front side of the cutter disk is caused mainly by the radially extending cutter blades. This rotational flow causes almost every piece of material, which does not pass through the chip slots of the cutter disk, to leave the area in front of the cutter disk in a radial direction through the sieving device rather than in an axial direction through the cover plate.
In an embodiment of the invention, at least a part of the cover plate is formed as a crenelated plate, and the passages from the front side to the back side of the cutter disk are defined by the edges of the crenels of the crenelated plate and by the perimeter of the cutter disk. Using a crenelated plate is a simple, reliable and robust way of creating the passages from the front side to the back side of the cutter disk.
In an embodiment of the invention, the largest dimension of the through-going passages in the cover plate deviates from the largest dimension of the openings in the sieving device by less than 75 %, preferably by less than 50 %, most preferred by less than 25 % of the largest dimension of the openings in the sieving device. Using similar maximum dimensions of the openings in the sieving device and of the passages through the cover plate ensures that all the wood chips produced by the wood chipping machine will be of substantially the same dimensions.
In an embodiment of the invention, the sieving device extends along an upper part of the cutter disk and the cover plate extends along a lower part of the cutter disk.
Several advantages are obtained by constructing the wood chipping machine so that the sieving device extends along an upper part of the cutter disk. Generally, the construction will be simpler, because many parts of the wood chipping machine, such as bearings, feed inlet, various fittings and mountings et al., are typically placed in the lower part of the machine. Therefore, the access to the sieving device for monitoring wear and failures of the sieving device and for maintenance and replacement of the sieving device or parts thereof is much easier, if the sieving device is placed at an upper part of the wood chipping machine. Furthermore, a construction with the sieving device placed at an upper part of the wood chipping machine typically results in a lower position of the drive shaft and the feed inlet, meaning that less lifting of the wooden material is required to feed it into the wood chipping machine.
In an embodiment of the invention, the distance between the cutter disk and the front side of the disk housing is between 20 mm and 1000 mm, preferably between 30 mm and 350 mm, most preferred between 50 mm and 250 mm. The distance between the cutter disk and the front side of the disk housing must be large enough to get a sufficiently large total area of the openings of the sieving device and, thus, a sufficient capacity of the sieving and disintegration device. On the other hand, the distance should be kept small in order to limit the dimensions of the disk housing and the wood chipping machine as a whole.
The given ranges for the distance between the cutter disk and the front side of the disk housing have been found to represent good compromises with respect to the above-mentioned considerations regarding the distance.
It is preferred that the disk housing comprises a front sheet enclosing the cutter disk along its front side, a back sheet enclosing the cutter disk along its back side and a disk casing enclosing the cutter disk along its rim. In this way a reliable and simple construction can be provided.
It is an advantage that the cover plate is mounted on the disk casing. This may be done by mechanical means (e.g. bolts or other fastening means) or by welding by way of example. Such construction is easy producible and reliable.
In one embodiment according to the invention the cover plate is an integrated part of the disk casing.
It may be beneficial that the cover plate extends basically along mid plane of the disk casing, where the mid plane divides the disk casing into two basically equal portions. Hereby there is place for both the sieving device and the ejector vanes.
It is an advantage that the cover plate comprises a plurality of plate shaped tooth members extending essentially perpendicular from the inside surface of the disk casing. Hereby it is possible to manufacture a robust and reliable cover plate from a plate e.g. by a punching, plasma cutting or laser cutting. This method is cost efficient. It may be beneficial that the plate shaped tooth members are rectangular in order to ease their production.
It may be an advantage that the one or more ejector vanes are provided with a cut-out allowing passage of the cover plate during rotation of the cutter disk. Hereby it is possible to provide ejector vanes at the periphery of the cutter disk and still have place for the cover plate.
It is preferred that the one or more ejector vanes extend essentially radially and are provided along the periphery of the cutter disk and that the cut-out of each ejector vane is provided at the periphery of the cutter disk. It is preferred that the one or more ejector vanes are plate-shaped, preferably of rectangular shape.
In another aspect of the invention, it relates to a method for producing wood chips, the method comprising the step of feeding material to the front side of a rotating cutter disk of a wood chipping machine as described above, where the cutter knives of said cutter disk chip the material, and the chipped material thereupon either is transported to the back side of the cutter disk through chip slots extending through the cutter disk or is transported towards the periphery of the disk housing through the peripheral sieving and disintegration device, where pieces of material too large to pass through the peripheral sieving and disintegration device are disintegrated.
In yet another aspect of the invention, it relates to the use of a wood chipping machine according to any of the above mentioned embodiments to produce wood chips.
In a preferred embodiment of the invention, at least a part of the sieving device forms at least a part of a cylindrical or conical surface.
Arranging at least a part of the sieving device to form at least a part of a cylindrical or conical surface facilitates a simple and easy interaction between the one or more cutter blades and the sieving device due to the rotational motion of the sieving device and the cutter blades relatively to each other.
In an embodiment of the invention, the sieving device is fixed with respect to the front side of the disk housing, and the cutter blades extend from the edge of the cutter disk in a substantially axial direction towards the front side of the disk housing.
Using a stationary sieving device and letting the cutter blades rotate with the cutter disk is advantageous in that it enables easy solutions for replacing and repairing cutter knives, cutter blades, the sieving device, ejector vanes or other parts of the machine that might be damaged or worn out, as will be described in the detailed description below.
Again, the term "substantially radial direction" includes forward curved or backward curved cutter blades. Since the cutter blades rotating with the cutter disk will also function as ejector vanes forcing the material in front of the cutter disk towards the sieving device, the shape of the cutter blades can be designed according to the desired pressure and flow properties of the centrifugal air flow in front of the cutter disk.
In an embodiment of the invention, the openings of the sieving device are placed in one or more replaceable wearing plates mounted on supports of the sieving device. Placing the openings of the sieving device in replaceable wearing plates is advantageous in that the wearing plates can easily be replaced if they are worn out or if openings of other dimensions are wanted.
In an embodiment of the invention, at least some of the parts of the sieving device extend in a substantially radial direction in close proximity with the back side of the cutter disk, said parts extending within the outer perimeter of the cutter disk.
Letting a part of the sieving device extend in a radial direction behind the cutter disk ensures that no material passes between the sieving device and the cutter disk without being disintegrated.
In a further embodiment of the invention, the cover plate is provided with a plurality of through-going passages from the front side to the back side of the cutter disk around the edge thereof.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1: illustrates an overview of the main parts of a wood chipping machine,
Fig. 2: illustrates an overview of the main parts of the feeding device and the disk housing of a wood chipping machine as known from the art,
Fig. 3a: illustrates a cutter disk of a wood chipping machine as seen from the front side,
Fig. 3b: illustrates a cutter disk of a wood chipping machine as seen from the back side,
Fig. 4a: illustrates a sectional view of the feeding device and the disk housing of a wood chipping machine as known from the art,
Fig. 4b: illustrates an enlargement of a central part of the sectional view of the feeding device and the disk housing of a wood chipping machine as shown in fig. 4a,
Fig. 5a: illustrates a partial sectional view of a cutter disk with a knife mounted in recesses on the front side,
Fig. 5b: illustrates a partial sectional view of a cutter disk with a knife mounted in a slot inside the disk,
Fig. 6: illustrates a side view of a wood chipping machine according to the present invention, in which a disk casing has been omitted for the sake of visibility,
Fig. 7: illustrates a cutter disk of the wood chipping machine of fig. 6,
Fig. 8: illustrates a perspective view of the wood chipping machine of fig. 6, wherein also a back sheet of a disk housing has been omitted for the sake of visibility,
Fig. 9: illustrates a perspective view of the wood chipping machine of fig. 8, this time with the disk casing but without the cutter disk and the back sheet of the disk housing for the sake of visibility,
Fig. 10: illustrates a perspective view of the wood chipping machine of fig. 9, this time also with the cutter disk,
Fig. 11a: illustrates a cylindrical bore through a sieving plate of a sieving device of a wood chipping device according to the invention,
Fig. 11b: illustrates a conical bore through a sieving plate of a sieving device of a wood chipping device according to the invention,
Fig. 11c: illustrates a partly conical, partly cylindrical bore through a radial sieving plate of a sieving device of a wood chipping device according to the invention, and
Fig. 11d: illustrates a double-conical bore through a sieving plate of a sieving device of a wood chipping device according to the invention.

The appended figures are provided for illustrating an embodiment of the present invention and are not intended to limit the scope of protection as defined by the claims. For instance, the present invention is not limited to wood chipping machines comprising only a single cutter disk.

Detailed description of the invention

In the following is disclosed a few embodiments of the present invention of a wood chipping machine 1 comprising a cutter disk 15 having one or more cutter knives 16 arranged with their cutting edges in a substantially radial plane of the cutter disk 15 and a peripheral sieving and disintegration device 29 including fixed as well as rotating parts.
Fig. 1 illustrates a generalized overview of a wood chipping machine 1 comprising a feed inlet 2, a feeding device 3, a disk housing 4 and an outlet pipe 5.
During operation of the wood chipping machine 1, material 10, such as whole trees, branches or pieces of wood, which is to be disintegrated into wood chips 26, is fed into a feed inlet 2. The feeding device 3 behind the feed inlet 2 catches the material 10 and drags it towards the disk housing 4, inside which the knives 16 on a rotating cutter disk 15 chip the fed material 10 into wood chips 26. By means of ejector vanes 25 mounted behind the cutter disk 15, the wood chips 26 are expelled from the wood chipping machine 1 through the outlet pipe 5.
Fig. 2 illustrates a generalized overview of the main parts of the feeding device 3 and the disk housing 4 of a wood chipping machine 1 as known from the art. The feeding device comprises two feed-in rollers 6, 7 rotating in opposite directions 8, 9 about parallel axes of rotation. When material 10 to be disintegrated is caught between the feed-in rollers 6, 7, the rotation 8, 9 of the rollers 6, 7 drags the material 10 in a direction 11 towards the disk housing 4. In the shown embodiment, the rotational axes of the feed-in rollers 6, 7 are horizontal. It should be noted, however, that the axes can also be vertical or form any angle with the horizontal plane as long as they are parallel.
The disk housing 4 basically comprises a front sheet 12, a back sheet 13 and a disk casing 14, enclosing a cutter disk 15 along its front side, its back side and its rim, respectively. The cutter disk 15 comprises a number of cutter knives 16 arranged with their cutting edges in a substantially radial plane on the front side of the disk 15, which is arranged with its axial direction substantially parallel to the feed-in direction 11 of the feeding device 3. In the shown embodiment, the disk housing 4 further comprises a backstop 17 arranged to hold the material 10 in position while it is being chipped by the cutter knives 16 during rotation 18 of the cutter disk 15.
Furthermore, the disk housing 4 of many wood chipping machines 1 as known in the art comprises an ejector shielding 19, which is a kind of extra disk casing covering the ejection opening 20 through which the wood chips 26 are ejected 21 from the disk housing 4. The ejector shielding 19 covers the ejection opening 20 in front of the cutter disk 15 and over the rim of the disk 15 but leaves the ejection opening 20 open behind the cutter disk 15. Thus, the ejector shielding 19 ensures that material 10 on the front side of the cutter disk 15, that has not yet been disintegrated, cannot be ejected from the disk housing 15, whereas wood chips 26 on the back side of the cutter disk 15, that has already been disintegrated, is ejected through the ejection opening 20. This is important in those types of wood chipping machines 1 in which the material 10 must pass through the chip slots 22 from the front side to the back side of the cutter disk 15 in order to be chipped into wood chips 26, at least if there are specific requirements for the quality, i.e. for the uniformity and homogeneity, of the wood chips 26 produced by the wood chipping machine 1.
Fig. 3a and 3b show a rotor 41 with a cutter disk 15 as seen from the front side and the back side, respectively. In connection with each cutter knife 16, there is a chip slot 22 formed through the disk 15, through which the wood chips 26 pass from the front side to the back side of the disk 15 after being cut by a knife 16. The purpose of the edge blades 23 is to break the otherwise circular periphery of the cutter disk 15 and clean out the area between the rim of the cutter disk 15 and the disk casing 14 in order to avoid that any material 10 gets stuck in this area, where it can get very hot and even catch fire due to the friction between the stuck material 10 and the rotating cutter disk 15.
Normally, the diameter of cutter disks as known from the art are within a range from around 300 mm to around 1400 mm with the most typical diameter being around 1000 mm, but even larger cutter disks can be seen in large industrial wood chipping machines.
The cutter disk 15 is mounted on and driven by a drive shaft 24, which is again driven by some kind of drive means for driving the rotation of the rotor 41. These drive means may comprise an external force, such as the engine of a tractor or another machine, or an internal combustion engine or an electrical motor integrated within the wood chipping machine assembly 1. On the back side of a cutter disk 15 as known from the art, there are a number of ejector vanes 25 which, due to the rotation of the cutter disk 15, eject the wood chips 26 through the ejection opening 20 as the chips reach the back side of the disk 15 through the chip slots 22.
Cutting the material requires a relatively large force and, therefore, a certain rotational speed of the rotor 41. For this reason, a so-called "revolution guard" is preferably installed within the wood chipping machine 1. The "revolution guard" is an electronic device monitoring the number of revolutions per minute of the rotor 41 and disabling the function of the feeding device 3, if the number of revolutions per time unit gets too low. This is done in order to avoid "choking" of the machine or engine driving the rotation of the rotor 41, because it is very difficult to start up the wood chipping machine 1 again, if it is filled up with material 10 to be chipped. As soon as the number of revolutions is back to normal, the function of the feeding device 3 is enabled again, and the machine 1 resumes working normally.
The operational principle of a wood chipping machine 1 as known from the art using a cutter disk 15 is illustrated in figs. 4a and 4b, where fig. 4b is an enlargement of a central part of fig. 4a. The material 10 to be disintegrated is drawn into the wood chipping machine 1 by the feed-in rollers 6, 7 of the feeding device 3 towards the cutter disk 15. When the material 10 has reached the cutter disk 15, the end of the material 10 is chipped by one of the cutter knives 16 rotating with the cutter disk 15, the material 10 being held in position by the backstop 17.
The material 10 that has been chipped off and has now become wood chips 26 is forced through the chip slot 22 behind the knife 15 by the cutting force of the knife 15 and ends up at the back side of the cutter disk 15, from where it is ejected from the wood chipping machine 1 by being shovelled out by the ejector vanes 25. The small arrows in fig. 4a illustrate the flow of material 10, 26 through the machine.
Fig. 5a and fig. 5b illustrates two different principles of mounting the cutter knives 16 on the cutter disk 15. Basically, the size of the wood chips 26 is defined by the cutting height 28, i.e. the height of the edge of the knife 16 over the surface of the cutter disk 15. However, other factors can also affect the size of the wood chips 26.
If, for instance, the material 10 to be disintegrated is drawn too slowly towards the cutter disk 15 by the feeding device 3, so that it does not reach the front surface of the disk 15 before it is chipped by a knife 16, the wood chips will be smaller than the maximum size defined by the cutting height 28.
In fig. 5a, a cutter knife 16 is mounted in a recess on the front side of the cutter disk 15 with the blade of the knife 16 arranged in a plane that is parallel to the front plane of the disk 15. If needed, a spacer 27 can be mounted between the cutter knife 16 and the cutter disk 15 for adjustment of the cutting height 28. Using the other principle, as shown in fig. 5b, the cutter knife 16 is mounted within the chip slot 22 through the cutter disk 15 along a wall of the slot 22 that is angled with respect to the radial plane of the cutter disk 15. In this case, the cutting height 28 is adjusted by sliding the knife 16 along the wall of the chip slot 22 onto which the knife 16 is mounted.
During the use of wood chipping machines 1 using a cutter disk 15 as known from the art, pieces of material 10 sometimes pass through the chip slots 22 from the front side to the back side of the cutter disk 15 without being chipped into suitable sized wood chips 26 by the cutter knives 16. This is particularly a problem with end pieces of the material 10, which can be dragged through the chip slot 22 by the knife 16 instead of being cut, because they are too short to be held in position by the backstop 17 when they are met by the edge of a knife 16.
The maximum width of a piece of material 10 passing through a chip slot 22 equals the radial width of the chip slot 22, and the maximum height of such a piece of material 10 equals the distance between the edge of the cutter knife 16 and the opposite edge of the associated chip slot 22. The maximum length of a piece of material passing through a chip slot 22 depends on the cutting height 28, the speed with which the material 10 is fed towards the cutter disk 15 by the feeding device 3 and, only if the cutter disk 15 rotates very slowly, of the rotational speed of the cutter disk 15.
In the wood chipping machine 1 according to the present invention, the maximum dimensions of the pieces of material 10 passing through the chip slots 22 has been reduced significantly by using shorter cutter knives 16 and smaller chip slots 22 than normally used in wood chipping machines 1 as known from the art. In order to compensate for the reduced total area of the chip slots 22, the cutter disk 15 of the present invention comprises a larger number of cutter knives 16 and chip slots 22 than normally known in the art.
In a wood chipping machine as known from the art, oversized pieces of material 10 do not only travel from the front side to the back side of the cutter disk 15 through the chip slots 22. Also, some pieces of material 10 are seen travelling along the front side of the cutter disk 15 to its periphery and passing by the rim of the cutter disk 15 to its back side. Obviously, the material 10 is not supposed to move this way around the cutter disk 15, but it is very difficult to avoid that at least a limited amount of material 10 passes along the front side of the cutter disk 15 towards the rim because of the gap between the cutter disk 15 and the front sheet 12 of the disk housing 4.
This gap is necessary to make room for the cutter knives 16 which extend at least the cutting height 28 from the front side of the cutter disk 15. Also, a certain tolerance between the cutter knives 16 and the front sheet 12 is needed.
It should be noted, that it is not a workable solution just to blank off the periphery of the cutter disk 15, since this will simply cause the space between the front side of the cutter disk 15 and the front sheet 12 of the disk housing 4 to be filled up with material 10 very quickly.
A preferred embodiment of the present invention, comprising a sieving device 29, 32-36 fixed to the front sheet 12 of the disk housing 4, represents a solution to the problem of material 10 passing to the back side of the cutter disk 15 without passing through the chip slots 22 of the cutter disk 15. This embodiment, which causes all material 10 on the front side of the cutter disk 15 to pass either through the chip slots 22 or through the sieving device 29, 32 or through some well-defined passages 40 in a cover plate 30 before it reaches the ejection opening 20 of the disk housing 4, is described in details with references to the following figures.
Fig. 6 illustrates a side view of a wood chipping machine 1 according to the abovementioned embodiment, in which a disk casing 14 has been omitted for the sake of visibility.
The figure illustrates how the cutter disk 15 of the rotor 41 has been moved backwards from the front plate 12 of the disk housing 4 for a certain distance in order to create an area in front of the cutter disk 15. As mentioned above, the material 10 must pass through the chip slots 22, through the sieving device 32 or through the cover plate 30 to get to the back side of the cutter disk 15 and reach the ejection opening 20 of the wood chipping machine 1.
The main part of the sieving device 29 is the sieving plate 32 containing the openings 35 of the sieving device 29. The sieving plate 32 is also the part of the sieving device 29 forming part of an essentially cylindrical surface.
The sealing plate 33 is the part of the sieving device 29 that extends in a radial direction within the outer perimeter of the cutter disk 15 in close proximity with the back side of the cutter disk 15.
Instead of extending along the back side of the cutter disk 15, the sealing plate 33 can also be placed in a recess along the back side edge of the cutter disk 15, if the thickness of the cutter disk 15 is large enough to leave space for such a recess.
The mounting plate 34 is used for fixing the sieving device 29 to the front sheet 12 of the disk housing 4. In the embodiment shown, the mounting plate 34 is fixated to the disk housing 4 by means of a number of bolts 36. This is advantageous because it makes it possible to replace the sieving device 29, either because of wear or because another size of openings 35 is wanted. If the mounting plate 34 were welded directly to the disk housing 4, such a replacement would not be possible without also replacing the whole front sheet 12 of the disk housing 4.
The back sheet 13 of the disk housing 4 is provided with a number of air passages (not shown) formed through the back sheet 13 near its centre. These air passages constitute the main inlet for the air being blown out through the ejection opening 20 and the outlet pipe 5 during operation of the wood chipping machine 1. Due to the centrifugal properties of the air flow within the rotor 41, which air flow forces the wood chips 26 to move radially towards the periphery of the disk housing 4, and due to the direction of the motion of the air being sucked into the rotor 41 through the air passages, the wood chips 26 are not inclined to leave the disk housing 4 through the air passages during operation of the machine 1. Anyhow, the air passages can be formed as a plurality of small openings, or they can be covered by a mesh in order to ensure that no material leaves the rotor 41 this way.
The cutter blades 39 interact with the edges of the openings 35 of the sieving device 29 to disintegrate the material 10, until the material 10 have been divided into pieces 26 small enough to pass through the openings 35. In order to achieve a proper disintegration between the cutter blades 39 and the sieving device 29, it is necessary to keep a rather tight tolerance between the cutter blades 39 and the sieving device
The illustration of the cutter disk 15 in fig. 7 shows how the cutter blades 39 extend towards the feed inlet 2 of the wood chipping machine 1 from recesses 37 cut out from the rim of the cutter disk 15. In this way, also the part of the sieving plate 32 surrounding the rim of the cutter disk 15 can be used for disintegrating and sieving the wood chips 26. The cutter knives 16 are mounted in a plane parallel to the radial plane of the cutter disk 15, each in close proximity with a chip slot 22. In fig. 7 four ejector vanes 25 each provided with a cut-out 44 are attached to the cutter disk 15.
Fig. 8 illustrates the same embodiment of the wood chipping machine 1 from another angle and with some elements removed in order to enhance the visibility. It shows how the sieving device 32 and the cover plate 30 covers different parts of the perimeter of the cutting disk 15. Whereas the cover plate 30 is crenelated in order to allow a small amount of material 10 to pass from the front side to the back side of the cutter disk 15 around the rim of the cutter disk 15, the corresponding sealing plate 33 of the sieving device 32 is not provided with such passages 40. This is mainly due to strength considerations, and because material 10 is not likely to be stuck on the front side of the cutter disk 15 where there is a sieving device 32 through which it may pass. The cover plate 30 extends along the mid plane 43 of the disk casing 14. The mid plane 43 divides the disk casing 14 into two basically equal portions. The cover plate 30 comprises a plurality of plate shaped tooth members 42 (also known as merlons) extending essentially perpendicular from the inside surface of the disk casing 14. The ejector vanes 25 are provided with a cut-out 44 allowing passage of the cover plate 30 during rotation of the cutter disk 15.
In fig. 9, the disk casing 14 is back, but the cutter disk 15 has been removed. This figure shows how the cover plate 30 may be mounted directly on the disk casing 14. It can be seen that the cover plate 30 extends along the mid plane 43 of the disk casing 14 and that the cover plate 30 comprises a plurality of plate shaped tooth members 42 extending essentially perpendicular from the inside surface of the disk casing 14.
Finally, fig. 10 shows the complete disk housing 4 with the back sheet 13 as the only exception, still for the sake of visibility. It can be seen that the ejector vanes 25 are provided with a cut-out 44 allowing passage of the cover plate 30 during rotation of the cutter disk 15.
The cutting efficiency between the cutter blades 39 and the edges of the openings 35 of the sieving device 29 depends on a number of factors, among which are the shape of the openings 35, the thickness of the sieving plate 32 and the shape of the bore of the openings 35 through the sieving plate 32.
As for the shape of the openings 35, it has been found that circular openings 35 are to be preferred for a number of reasons: they can be packed closely, thus yielding a large area of flow through the plate 32 in a small place, they are stronger than openings 35 with corners, in which cracks tend to be formed, and they can be sharpened by use of a drill, leaving the openings 35 a little bit larger than before the sharpening.
The thinner the plate 32, the sharper and the weaker it will be. Even if a very thin plate 32 is very sharp when it is new, the edges of the openings 35 will soon be deformed and the efficiency will be reduced.
Figs. 11a-11d illustrate different shapes of the bore of the openings 35 through the sieving plate 32 of a sieving device 29.
By bevelling the edges of the openings 35 all the way from the back side to the front side of the plate 32, i.e. from the side turning away from the cutter blades 39 to the side turning against the cutter blades 39, a normal cylindrical bore as illustrated in fig. 11a will be changed to a conical bore as illustrated in fig. 11b.
Conical bores have at least two advantages: due to the shape, the bores will be less likely to be blocked by biological material, and the edges with which the cutter blades 39 interact will be sharper, thus increasing the cutting efficiency. The sharper the edge, the better the cutting efficiency, but also the larger the tendency to deformation and general weakness along the edges.
When using a thicker plate 32, a part of the bores can be left cylindrical, as illustrated in fig. 11c, in order to avoid overlaps between the openings 35 on the back side of the plate 32 without having a very large distance between the openings 35.
Fig. 11d illustrates a double-conical bore giving both the advantage of a sharp edge for increasing the cutting efficiency and the advantage of a conical bore reducing the risk of blockage by biological material without getting very large openings 35 on the back side of the plate 32.

List of reference numerals

1.: Wood chipping machine
2.: Feed inlet
3.: Feeding device
4.: Disk housing
5.: Outlet pipe
6.: Upper feed-in roller
7.: Lower feed-in roller
8.: Rotational direction of the upper feed-in roller
9.: Rotational direction of the lower feed-in roller
10.: Material to be disintegrated
11.: Feed-in direction of the material to be disintegrated
12.: Front sheet of the disk housing
13.: Back sheet of the disk housing
14.: Disk casing
15.: Cutter disk
16.: Cutter knife
17.: Backstop
18.: Rotational direction of the cutter disk
19.: Ejector shielding
20.: Ejection opening
21.: Ejection direction for the wood chips
22.: Chip slot through the cutter disk
23.: Edge blade on the cutter disk
24.: Drive shaft for the cutter disk
25.: Ejector vane
26.: Wood chips
27.: Spacer for adjustment of cutting height
28.: Cutting height
29.: Sieving device
30.: Crenelated cover plate
31.: Bolt for mounting the cutter knife
32.: Sieving plate
33.: Sealing plate for the sieving device
34.: Mounting plate for the sieving device
35.: Opening of the sieving device
36.: Bolt for mounting the sieving device
37.: Recess for the cutter blade
38.: Bolt for mounting the cutter blade
39.: Cutter blade
40.: Crenel in the crenelated cover plate
41.: Rotor
42.: Tooth member
43.: Mid plane
44.: Cut-out

Claims

A wood chipping machine (1) for disintegrating material (10), mainly biological material such as whole trees, branches and other forms of wooden material, which wood chipping machine (1) comprises a disk housing (4) having an ejection opening (20), a rotor (41), arranged in the disk housing (4) to be rotatable about its central axis, the rotor (41) comprising a cutter disk (15) having one or more cutter knives (16) arranged with their cutting edges in a substantially radial plane of the cutter disk (15), the cutter disk (15) having a front side oriented towards a feed inlet (2) of the wood chipping machine (1), and one or more ejector vanes (25) mounted behind the cutter disk (15) as seen from the feed inlet (2), where the one or more ejector vanes (25) are mounted on the cutter disk (15) or in a distance from the cutter disk (15), which ejector vanes (25) extend in a substantially radial direction with respect to the cutter disk (15) and are arranged to rotate during operation of the wood chipping machine (1), thus creating a centrifugal flow of air and forcing material behind the cutter disk (15) towards the ejection opening (20) of the disk housing (4), and drive means for driving the rotation of the rotor, where the rotor further comprises one or more chip slots (22) extending through the cutter disk (15) for transporting material chipped by the cutter knives (16) to the back side of the cutter disk (15) during operation of the wood chipping machine (1), where the wood chipping machine (1) further comprises a peripheral sieving and disintegration device (29, 30, 32-35, 39) including one or more fixed parts that are stationary with respect to the disk housing (4), and one or more rotating parts that are arranged to rotate with the rotor during operation of the wood chipping machine (1), the rotating parts and the fixed parts of the peripheral sieving and disintegration device (29, 30, 32-35, 39) being arranged to interact with each other to sieve and disintegrate material passing in a radial direction towards the periphery of the disk housing (4) without passing through the chip slots (22) in the cutter disk (15) to the back side of the cutter disk during operation of the wood chipping machine, where the peripheral sieving and disintegration device (29, 30, 32-35, 39) comprises a sieving device (29) extending along at least a part of the perimeter of the cutter disk (15) and in a substantially axial direction towards the front side of the disk housing (4) and one or more cutter blades (39), the sieving device (29) having a plurality of openings (35) and the cutter blades (39) being arranged to interact with the edges of the openings of the sieving device (29) to disintegrate pieces of material (10, 26) characterised in that the sieving device (29) extends along less than the full perimeter of the cutter disk (15), and the peripheral sieving and disintegration device (29, 30, 32-35, 39) further comprises a cover plate (30) extending along at least a part of the perimeter of the cutter disk (15), where the sieving device (29) does not extend, and in a substantially radial direction in close proximity with the back side of the cutter disk (15), said cover plate (30) extending within the outer perimeter of the cutter disk (15), wherein the cover plate (30) is provided with a plurality of through-going passages (40).
A wood chipping machine (1) according to claim 1, characterised in that at least a part of the cover plate (30) is formed as a crenelated plate (30).
A wood chipping machine (1) according to claim 1 or 2, characterised in that the largest dimension of the through-going passages in the cover plate (30) deviates from the largest dimension of the openings in the sieving device (29) by less than 75 %, preferably by less than 50 %, most preferred by less than 25 % of the largest dimension of the openings in the sieving device (29).
A wood chipping machine (1) according to any of the claims 1-3, characterised in that the sieving device (29) extends along a first part of the cutter disk (15) and that the cover plate (30) extends along the remaining part of the cutter disk (15).
A wood chipping machine (1) according to any of the preceding claims, characterised in that the distance between the cutter disk (15) and the front side of the disk housing (4) is between 20 mm and 1000 mm, preferably between 30 mm and 350 mm, most preferred between 50 mm and 250 mm.
A wood chipping machine (1) according to any of the preceding claims, characterised in that the disk housing (4) comprises a front sheet (12) enclosing the cutter disk (15) along its front side, a back sheet (13) enclosing the cutter disk (15) along its back side and a disk casing (14), enclosing the cutter disk (15) along its rim.
A wood chipping machine (1) according to claim 6, characterised in that the cover plate (30) is mounted on the disk casing (14).
A wood chipping machine (1) according to one of the claims 6-7, characterised in that the cover plate (30) extends basically along the mid plane (43) of the disk casing (14), where the mid plane (43) divides the disk casing (14) into two basically equal portions.
A wood chipping machine (1) according to any of the preceding claims, characterised in that the cover plate (30) comprises a plurality of plate shaped tooth members (42) extending essentially perpendicular from the inside surface of the disk casing (14).
A wood chipping machine (1) according to any of the preceding claims, characterised in that the one or more ejector vanes (25) are provided with a cut-out (44) allowing passage of the cover plate (30) during rotation of the cutter disk (15).
A wood chipping machine (1) according to claim 10, characterised in that the one or more ejector vanes (25) extend essentially radially and are provided along the periphery of the cutter disk (15) and that the cut-out (44) of each ejector vane (25) is provided at the periphery of the cutter disk (15).