METHOD AND DEVICE IN WOOD CHIPPING MACHINES

Abstract: This invention relates to a method of handling knife devices in wood chipping machines, each knife device comprising a knife blade. According to the invention, the method is characterized by the combination of the following steps: the knife blade (6) is provided with a list (8) of a fixed width measure at its rear portion, the knife device (1) getting a width measure, which essentially shall be valid during the use of the knife blade; when re-grinding the knife blade (6), the entire knife device (1) is taken loose from the wood chipping machine, the cutting edge of the knife blade being visually examined and the grinding degree being stipulated; the list (8), sitting on, is taken loose, and a new list the width of which corresponds to the width of the old one plus the grinding degree is fastened on the rear portion of the knife blade (6), whereafter the knife blade is ground and the cutting edge is burred; the finished knife device (1) is either placed directly into the wood chipping machine or into a knife magazine for a later use. The invention also relates to a device which is usable for carrying out the method.

Description: METHOD AND DEVICE IN WOOD CHIPPING MACHINES This invention relates to a method of handling knife devices in wood chipping machines, each knife device comprising a knife blade. The invention also relates to a knife device which is suitable to be used when carrying out the method. A problem in wood chipping machines is that the cutting edge of the knives has a rapid wear, relatively spoken, which has the consequence that these ones often have to be exchanged for new or re-ground knives. The wear is influenced partly of hard objects following the wood, and partly of the fact that a part of the energy consumed during the chipping is transformed to heat which heats up the cutting edges of the knives, whereby the cutting edge is easily subjected to wear. When re-inserting the knife device into the machine after the grinding it is important partly that the cutting edge of the knife device projects in a correct way, partly that the knife device has a secure contact in the machine for its rear portion. According to known technique the knife devices are adjusted by means of a plurality of adjusting screws. These ones have to be adjusted exactly equally in order that the rear portion of the knife device shall be in contact with these ones in a correct way. Furthermore, the adjusting screws shall be screwed forward an exact distance in order that the intended effect of the knife device shall be able to be reached. However, it has appeared to be extremely difficult to get the tolerances that are required in order that the knife device shall function in the correct way. Moreover, it has appeared to be difficult to get a uniform adjustment of the different adjusting screws for adjusting the knife device, which has had the consequence that the wood chipping machine has not functioned in the intended way. Furthermore, the use of adjusting screws requires that the thickness of the knife blade has to be at least 12 mm. This results in unnecessarily heavy and expensive knife blades, which besides that require an expensive re-grinding procedure. This invention intends to remove the problems with known technique and to provide a technical solution of the problems with grinding/mounting of knife devices in wood chipping machines. This has been made possible by a method of the kind mentioned by way of introduction, which is characterized by the combination of the following steps: - The knife blade is provided with an exchangeable list of a fixed width measure at its rear portion, the knife device getting a width measure which essentially shall be valid during the use of the knife blade; - When re-grinding the knife blade, the entire knife device is taken loose from the wood chipping machine, the cutting edge of the knife blade being visually examined and the grinding degree being stipulated; - The list, sitting on, is taken loose and a new list, the width of which corresponds to the width of the old one plus grinding degree, is fastened on the rear portion of the knife blade, whereafter the knife blade is ground and the cutting edge is burred; - The finished knife device is either placed directly in the wood chipping machine or in a knife magazine for later use. Due to this arrangement the previously mentioned adjusting screws can be eliminated, whereby the problems connected with these ones will disappear. Furthermore, by inserting new and somewhat broader lists, the necessary weight balance can be maintained in the knife wheel of the wood chipping machine, whereby the function of the wood chipping machine becomes more reliable than is the case when using known technique in this field. The invention shall be described more closely below with reference to the accompanying drawings, where fig. 1 shows a cross section through a knife device according to the invention and a knife holder, intended for this one, and fig. 2 shows a perspective view of a part of a knife blade according to the invention with a plurality of different lists and also of a part of an intermediate piece. Referring to the drawings is shown there the knife device 1 according to the invention, fastened in a known knife holder device 2, the knife device being kept in a clamping position between two parts 3, 4 in the knife holder device by a screw means 5. The knife holder device is normally detachably fastened on a rotatable chipper disk, the elongated knife device having an essentially radial extension on the chipper disk. The knife device comprises a knife blade 6, which has a groove-designed recess 7 at its rear portion and along its entire length. Due to the existance of the groove at the rear edge of the knife blade, the list inserted into the groove gets a secure contact with the knife blade, which secures a good knife adjustment. In this groove lists 8, designed for this purpose, of different width measures are intended to be inserted. These lists with their rear portions are intended in a secure way to be in contact with a fixed rear portion of the holder device 2, whereby the distance between the rear portion 9 of the list 8 and the cutting edge of the knife blade 6 will be an exact measure and will be the same along the entire length of the knife device. Thus, the list according to the invention has an exact width measure along its entire length, and this width measure increases for the other lists in suitable, fixed steps, which correspond to the grinding degree when grinding the knife device. The width measure of the entire knife device shall be essentially the same all the time, even though the width of the knife blade is reduced all the time due to the re-grindings of the knife blade. Thus, in order to maintain the uniform width measure, lists with greater and greater width measure have to be fastened on the rear portion of the knife blade. In figs. 1 and 2 is also shown an intermediate piece 10, which is intended to be inserted between the knife blade and the list. Due to that fact the number of lists can be kept low. This intermediate piece has a front portion 11 which is designed like a projection for adaptation to the rear portion of the knife blade 6, and a rear portion 12, which is like the rear portion of the knife blade, and which accordingly is intended to cooperate with the different lists 8. When re-grinding a knife blade, the entire knife device is taken loose from the wood chipping machine, the cutting edge of the knife blade being subjected to a visual examination. In this connection the expert in this field can directly see how great the grinding degree shall be. The list fastened on the knife blade is taken loose and is replaced by a new list, the width of which corresponds to the width of the old one plus the grinding degree, decided by the expert. The knife device is inserted into the grinding machine and is ground, whereafter the cutting edge is burred. The finished knife device is either placed directly into the wood chipping machine or into a knife magazine for a later use. This knife magazine is intended to contain a great number of different knife devices, which have that feature common that their width measures are essentially the same. This means that if a knife blade of one knife device is narrower than another knife blade in another knife device, the first knife device comprises a broader list than the second knife device. The new invention has a plurality of advantages compared with known technique comprising adjusting screws: 1/ A considerably more secure knife adjustment; 2/ A considerably simplier and more rapid mounting of the knives; 3/ Greater grindings, calculated as a percentage, of the knife can be done, which means a better utilization of the material; 4/ The knife blade can be made considerably thinner, which partly gives lower costs, partly lower weight and due to that better ergonomics; The knife blade thickness can be as low as 5 mm; 5/ The knives essentially maintain their weight all the time, which eliminates the problems with unbalance in the machine. The invention is of course not limited to the shown and mentioned embodiment but can be modified within the scope of the following claims.

Claims: Claims 1. A method of handling knife devices in wood chipping machines, each knife device comprising a knife blade, c h a r a c t e r i z e d by the combination of the following steps: - The knife blade (6) is provided with a list (8) of a fixed width measure at its rear portion, the knife device (1) getting a width measure, which essentially shall be valid during the use of the knife blade; - When re-grinding the knife blade (6), the entire knife device (1) is taken loose from the wood chipping machine, the cutting edge of the knife blade being visually examined and the grinding degree being stipulated; - The list (8), sitting on, is taken loose and a new list, the width of which corresponds to the width of the old one plus the grinding degree is fastened on the rear portion of the knife blade (6), whereafter the knife blade is ground and the cutting edge is burred; - The finished knife device (1) is placed either directly into the wood chipping machine or into a knife magazine for a later use. 2. A knife device, usable for carrying out the method according to claim 1, and the knife device being intended to be inserted into conventional knife holder devices of wood chipping machines of the type comprising a rotatable chipper disk, on which the knife devices are intended to have an essentially radial extension, c h a r a c t e r i z e d by the combination of the following features: - The knife device (1) has an elongated design and comprises a knife blade (6), which has a front portion in the form of a cutting edge and a rear portion, in which is made a groove-designed recess (7) along the entire length of the knife blade (6); - The knife device (1) further comprises a list (8), which is designed in that way that it fits into the mentioned recess (7), and which has such a width that it projects a distance outside the rear portion of the knife blade (6). 3. A knife device according to claim 2, c h a r a c t e r i z e d in that it comprises a package of lists (8), all of which have essentially the same length and thickness but different width, the list (8) of the knife blade (6) being intended to be exchanged for broader lists, as the knife blade is ground down, so that the width of the knife device remains essentially constant. 4. A knife device according to claim 3, characterized in that it comprises an intermediate piece (10), which is intended to be inserted between the knife blade (6) and the list (8), and that the intermediate piece (10) has a front portion (11), which is designed like a projection for fitting into the rear portion of the knife blade (6), and a rear portion (12), which is like the rear portion of the knife blade (6). 5. A knife blade for use in the knife device according to any one of the claims 2-4, characterized in that the thickness of the knife blade (6) can be extremely thin, and that the knife blade (6) at its rear portion has a groove-designed recess (7) along its entire length.

Inventors: JONASSON PER GUSTAV, SVENSSON AAKE, JONASSON, PER, GUSTAV, SVENSSON, AAKE
Applicants: BMH WOOD TECHNOLOGY AB, JONASSON PER GUSTAV, SVENSSON AAKE, JONASSON, PER, GUSTAV, SVENSSON, AAKE
Application year: 1996
Main classification: B27G13
IPC codes: B27G13