Counter blade for a disc chipper

Abstract: The invention relates to a counter blade designed for use in a chipping machine which comprises a chipper disc (9) rotatably mounted in the chipper frame (1) by means of a shaft supporting the disc, and in which the counter blade is attached to the chipper frame (1) essentially at the intersection of a blade (11) mounted in the chipper disc (9) and the log to be chipped, in such manner that, on the side opposite to the chipping blade (11), the counter blade rests against the log to be chipped, said counter blade (5) consisting of a first and a second blade part placed at an obtuse angle relative to each other. According to the invention, the counter blade consists of two essentially elongated pieces (5) having an arris (8,8') forming the cutting edge of the counter blade at least on one of its longitudinal sides, the end faces (14) of said counter blade pieces (5) being so formed as to permit connection to the adjacent counter blade piece (5) so that the two counter blades form a continuous cutting edge of the counter blade.

Description: The present invention relates to a counter blade for a disc chipper designed for the chipping of wood, as defined in the introductory part of claim 1. The production of wood chips for the paper and pulp industry is generally implemented using disc chippers, in which the wood is chipped by means of blades mounted in a radial or nearly radial arrangement on a disc . As the disc rotates, the blades strike against the log under chipping, the opposite side of which leans against the counter blade. The counter blade is located at the delivery end of the feed funnel, on the opposite side relative to the direction of motion of the blade. The wood may be fed into the disc chipper either vertically or horizontally, and the chipper is accordingly called a horizontal-feed or a vertical-feed chipper. There are corresponding differences in the positions of the disc and blades in these different chipper types, but in principle they are identical in operation. In a disc chipper, the parts subject to wear are the chipping blade and the counter blade, which receives the log being chipped. For the chips produced to be suitable for use as fibrous material, the counter blade must meet certain requirements regarding its condition. The cutting edge of the counter blade, i.e. the arris receiving the log, must not have an excessive radius of curvature, otherwise the wood fibres will be broken and the result is low-quality chips containing sawdust. In prior art, the counter blade consists of a relatively large and bulky body that requires plenty of material and is difficult to handle during installation and maintenance. The wearing part of the counter blade is provided with a hard-metal coating which needs renewal at times. At present, there are also counter blades of a lighter construction which are free of the above-mentioned drawbacks. However, there is still the problem that different parts of the cutting surface of the counter blade are unevenly worn due to the uneven distribution of the logs. For this reason, the counter blade cannot be utilized in full. To achieve an optimal chipping efficiency, the counter blade in a vertical-feed chipper consists of a horizontal part and another part placed in a direction slightly differing from the horizontal, so that the blade parts are at an angle slightly diverging from 180° relative to each other. In a blade construction like this, the horizontal blade area close to the junction of the parts is subject to the hardest wear, due to the manner in which the logs are directed in the feed funnel, and so the wear in this area determines the need for blade replacement. Therefore, when this small area of the whole effective surface of the blade has worn out, the whole blade must be replaced. If the counter blade has a hard-metal coating, renewing the coating means re-coating the whole blade. US 3,220,447 discloses a one-piece counter blade (38) having four parallel cutting arrises which are arranged symmetrically around the central longitudinal axis of the counter blade piece. By this way the working life of the counter blade piece can be extended. US 3,220,447 discloses the preamble of claim 1. US 4,669,516 discloses a disk chipper having a rotatable cutting disk. On this disk there are positioned three longitudinal cutting blades in radial direction. Each cutting blade comprises three cutting blade pieces which are aligned in the radial direction of the cutting disk. It is the object of the invention to produce a new more advantageous counter blade construction, allowing to form a continuous cutting edge in a counter blade consisting of pieces which are mutually inclined at an obtuse angle, which construction allows replacement only of the worn blade pieces. According to the invention, this is achieved in the manner defined in the characterization part of claim 1. Other preferred embodiments are presented in the subclaims. The invention allows the counter blade to be effectively utilized as only the worn piece of the blade needs to be replaced. In respect of manufacturing techniques, the counter blade of the invention is advantageous since it does not involve any difficult angular structures. By using blade pieces of a symmetrical cross-section, it is possible to provide each blade piece with two cutting surfaces. Also, it is preferable to be able to swap the two counter blade pieces to replace the more worn piece with the less worn one. In the following, the invention is described by the aid of one its embodiments by referring to the drawings attached, in which Fig. 1 presents a cross-section through a vertical-feed chipper, showing the position of the counter blade, Fig. 2 presents the counter blade construction of the invention, and Fig. 3 presents a cross-section through the counter blade in Fig. 2 as sectioned along line A-A. As illustrated by Fig. 1, a vertical-feed chipper consists of a chipper frame 1 accommodating a counter blade carrier 2 movable relative to the frame. At the upper part of the counter blade carrier 2 there is a feed space which, together with a hollow space communicating with the log conveyor (not shown), forms a gravity funnel 3. Attached e.g. by means of bolts (not shown) to the counter blade carrier 2 is a counter blade holder 4, placed at the delivery end of the gravity funnel 3. The counter blade piece 5 is attached by means of bolts to a groove 7 provided in the counter blade holder 4. The surfaces of the counter blade holder 4 and counter blade piece 5 facing the gravity funnel 3 form a continuous and essentially even surface allowing the logs to slide over it. The cutting edge of the counter blade consists of an arris 8 located at the delivery end of the gravity funnel 3. At the delivery end of the gravity funnel 3, next to the counter blade carrier 2 provided with the counter blade holder 4 and counter blade 5 there is a space housing a vertically mounted chipper disc 9 rotating on its shaft. The shaft and the power means rotating the disc, which are suitably mounted on the chipper frame, are not shown and they can be implemented in a manner known in the art. The chipper disc 9 accommodates several, usually 12 -16 blade bodies 10 provided with cutting blades 11 and mounted on the disc in a manner known in itself. The logs are brought to the funnel by means of conveyors and directed into the chipper in a manner known in itself. The blades of the disc 9 cut the wood into chips of a desired size. The chip length can be determined by adjusting the distance T between the blades 11 and stoppers provided in the disc. This is done by moving the blade body 10 so as to obtain a suitable distance T, preferably approx. 13 mm. To achieve a good chipping efficiency, the distance C between the blade 11 and the counter blade must be correct, suitably approx. 0.5 mm. The arris 8 forming the cutting edge of the counter blade must not be allowed to be rounded too much by wear. The radius of curvature must remain below 5 mm to ensure that the wood fibres are not damaged and that the chips produced-will not contain sawdust. Fig. 2 depicts the counter blade holder 4 and one of the two counter blade pieces 5 accommodated by it as seen from the side facing the disc 9. The holder 4 is provided with a groove 7 for the counter blade pieces 5. The groove extends over the whole length of the holder and is bent into an angle δ at a point midway between the ends. The thickness of that part of the holder which lies above the groove decreases towards the edge so that its surface 16 constitutes part of the wall of the funnel 3. The counter blade holder 4 is fixed to the counter blade carrier 2 by means of bolts screwed into holes 12. The counter blade consists of two identical counter blade pieces 5. Each piece has two longitudinal arrises 8 and 8' placed at a distance from each other and forming the cutting edge of the counter blade. The counter blade piece has a cross-section symmetrical in relation to plane B-B, which, as shown in Fig. 3, is equally distanced from the arrises 8 and 8' and perpendicular to the normal connecting the two arrises. When the two counter blade pieces are placed in the groove 7 in the holder 4, the cutting surface of the counter blade has an elbow equal to angle δ. The end faces 14 of the counter blade pieces 5 form an angle α diverging from the straight angle relative to the longitudinal side of the part 5. Angle α is determined by the angle of the elbow at point 13. Thus, the parts can be so fitted together that a continuous blade surface 8 is formed at the upper edge of the counter blade. In a preferred embodiment of the invention, as illustrated by Fig. 3, each counter blade piece 5 is provided with four parallel arrises 8, 8' 18, 18', each of which is so made that it can act as the cutting edge of the counter blade. When the piece is in position, two of the arrises always face towards the chipper disc 9. One of these two arrises acts as the cutting edge. The other two arrises are essentially on the opposite side of the counter blade piece 5 as seen in the direction of the shaft of the disc 9. The counter blade piece is symmetrical in relation to plane B-B. Plane B-B is perpendicular to the normal connecting the adjacent arrises 8 and 8' forming a cutting edge and correspondingly arrises 18 and 18'. It is located at an equal distance from each arris 8,8' and similarly from arrises 18 and 18'. Thus, each counter blade piece 5 has altogether four arrises, each of which can be used as a counter blade surface by turning the piece. In a preferred embodiment, the lower part of the end face 14 of the counter blade pieces forms an angle of 180-2α relative to the upper part of the end face. This renders the horizontal and oblique blade parts interchangeable. This is practical because the horizontal part of the counter blade is subject to faster wear than the oblique part, which is due to the fact that the logs under chipping tend to move horizontally side by side in the feed funnel. The minimum requirement is that the cutting edges of the two blade pieces 5 should be in contact with each other. It is possible to place supporting or filling elements between the lower parts of the counter blade pieces to achieve a continuous overall structure. The counter blade pieces 5 are attached to the counter blade holder 4 by means of bolts or equivalent placed in holes 15. The bolts may extend through the counter blade carrier 2 as shown in Fig. 1. The holes are symetrically laid out so as to allow the pieces 5 to be mounted in alternative positions and locations using the same holes and fixing elements. The pieces can be joined by their ends to each other or to the above-mentioned supporting structures e.g. by means of mortise-and-tenon joints. Fig. 3 presents a cross-section of the counter blade holder 4 and counter blade piece 5 as taken along line A-A in Fig. 2. Part 16 of the holder 4 is at an angle β relative to the vertical plane. The counter blade piece 5 is in the groove 7 and has a part 17 shaped in the same angle with the holder and protruding out of it. The front surface 28 of the counter blade piece is in a vertical position, so that arris 8 constitutes the cutting edge of the counter blade. In the above, the invention has been described with reference to one of its embodiments. However, the invention is not restricted to this embodiment.

Claims: Counter blade designed for use in a vertical chipping machine which comprises a chipper disk (9) rotatably mounted in the chipper frame (1) by means of a shaft supporting the disk, and in which a counter blade is mounted in the chipper frame (1), essentially at the intersection of a blade (11) mounted in the chipper disk (9) and the log to be chipped, in such a manner that in use, on the side opposite to the chipping blade (11), the log rests against the counter blade, said counter blade having an arris (8,8') forming the cutting edge of the counter blade at least on one of its longitudinal sides, and the profile of the counter blade being symmetrical with respect to a plane extending in the longitudinal axis of the counter blade, characterized in that the counter blade (5) consists of a first elongated and second elongated blade piece (5) whose longitudinal axes, in use, are to be arranged at an obtuse angle (δ) relative to each other, and that end faces (14) of the blade pieces (5) have - above and below the plane of symmetry - an angle (α) with respect to a transversal axis of the plane of symmetry, which angle (α) being determined by the angle (δ) between the blade pieces (5) when arranged together such that each counter blade piece (5) permits end face (14) connection to the adjacent counter blade piece (5) such that the counter blade pieces (5) when arranged together in end face connection form a continuous cutting edge (8,8') of the counter blade. Counter blade according to claim 1, characterized in that the counter blade pieces (5) have two parallel arrises (8,8') which are so formed that they can act as counter blade surfaces and which are placed at a distance from each other. Counter blade according to claim 1, characterized in that the counter blade pieces (5) have four parallel arrises (8,8',18,18') which are designed to act as counter blade surfaces and which, when the counter blade piece (5) is mounted in place, are so located that two (8,8') of the arrises, placed at a distance from each other, are on that side of the counter blade piece which faces towards the chipper disc (9), while the other two arrises (18,18') are essentially on the opposite side of the counter blade piece (5) as seen in the direction of the shaft of the chipper disc (9). Counter blade according to claim 2 or 3, characterized in that the counter blade pieces (5) are of a cross-section symmetrical relative to plane B-B, which is perpendicular to the normal between adjacent arrises (8,8') constituting a cutting edge and equally distanced from said arrises. Counter blade according to any one of the preceding claims, characterized in that the end faces (14) are so shaped that each counter blade piece (5) can be mounted in the place of either one of the two pieces of the counter blade (5). Counter blade according to claim 1 characterized in that when mounted in a counter blade holder (4), in which the blade pieces (5) are supported, a gap is formed between the non-contacting end faces of the counter blade pieces, said gap being substantially filled by a supporting or filling part provided on the counter blade holder (4). Counter blade according to any one of the preceding claims, characterized in that when in use, on the side essentially opposite to the arris (8,8') constituting the cutting edge, the counter blade pieces (5) are attached to a counter blade holder (4) by means of fixing elements fitted into the counter blade pieces (5) and the counter blade holder (4), while the counter blade holder (4) is attached to a counter blade carrier (2), which again is attached to a chipper frame (1).

Inventors: HANNIMAEKI ARI, KOKKO PEKKA, OLOFSSON ANDERS, SVENSSON AKE, HANNIMAEKI, ARI, KOKKO, PEKKA, OLOFSSON, ANDERS, SVENSSON, AKE, Hannimäki, Ari
Applicants: ANDRITZ PATENTVERWALTUNG, ANDRITZ-PATENTVERWALTUNGS-GESELLSCHAFT M.B.H.
Application year: 1992
Main classification: B27L11
IPC codes: B27L11