The present invention relates to an arrangement in wood chippers of the kind which comprise a rotatable body, such as a disc, knives which are affixed to the rota¬ table body by means of knife holders, and wear plates which are mounted adjacent the knife holders and which form log guiding surfaces and function to guide the end of a log to be chipped in a given relationship with the knife engaging said end of the log.

It is known to guide logs in such wood chippers by applying torsion to the log guide surface such as to achieve the desired chipping result.

One method of achieving this torsion is to work or machine the wear plates, and optionally also the knife holders, to the desired degree of torsion prior to mounting the wear plates, and also the knife holders, onto the chipper disc.

Torsioning of the log guide surface can also be achieved by clamping the wear plates to the rotatable body of the chipper while the plates are in a twisted state, for instance with the aid of purposely con¬ figured inserts, such as straight edges, beneath the wear plates, and to exchange these inserts when desir¬ ing to modify the torsion in the log guide surface.

In order to obtain a uniform chip quality to the best possible extent, it is necessary to adapt this torsion¬ ing of the log guide surface to the desired length of chip to be produced and also to the quality of the wood concerned, to knife wear and to other factors which are liable to change during a chipping operation. In the

case of known chipper constructions, this means that the chipper must be stopped and the wear plates ex¬ changed for wear plates which embody other degrees of torsion, or the inserts, such as straight edges or the like, located beneath the wear plates must be exchanged for other inserts which impart the desired torsion in the wear plates as the plates are clamped. This work is time-consuming and requires the machine to be statio¬ nary while the exchange takes place, and also requires dismantling of the wear plates and machine parts located in the vicinity thereof. Since the wear plates are more often than not bolted from the underside of the chipper, in order to enable the plates to withstand the large forces to which they are subjected during operation, this work of dismantling the plates is both time-consuming and difficult to carry out. Furthermore, it is necessary to have available a number of wear plates or inserts in order to be able to accommodate varying degrees of torsioning of the wear plates.

The main object of the invention is to provide an arrangement of the aforedescribed kind in which changes can be made to the torsion of wear plates in a simple and time-saving manner.

Another object is to provide an arrangement in which changes can be made to the torsioning of the wear plates without needing to dismantle the machine to any great extent or without needing to replace machine parts.

A further object of the invention is to provide an arrangement which will enable changes to be made to the torsioning of the wear plates while the chipper is in

operation, i.e. without needing to stop the chipper.

These and other objects of the invention are achieved with an inventive wood chipper having the characteris- tic features set forth in the following Claims.

The invention will now be described in more detail with reference to the accompanying drawings, which illus¬ trate preferred exemplifying embodiments of an inven- tive arrangement.

Figure 1 is a plan view of a section of a chipper disc provided with adjustment means in accordance with the invention for adjusting the torsion of a wear plate. Figure 2 is a sectional view taken on the line II-II in Figure 1. Figure 3 is a plan view and Figure 4 a side view of a straight edge used to adjust the torsion of the wear plate. Figures 5 and 6 illustrate different methods of attaching the wear plate at its forward part distal from the adjustment means.

The section of a chipper disc illustrated in Figure 1 includes a holder cassette 10 in which a knife 12 is held by means of a bolt 14. The cassette is attached to a bottom liner 16 (Figure 2) mounted in the chipper disc, said bottom liner being attached, in turn, to a disc base plate 18 by means of bolts 20 which extend to the vicinity of the undersurface (not shown) of the disc, for instance in the manner described in the DS Patent Specification 4,694,995. The chipper disc pre¬ sents in front of each knife 12, as seen in the rota¬ tional direction of the disc, an opening 22 through which chips pass to the chipper outfeed opening (not shown). Located after the opening or recess 22 and the knife cassette 10 on the upper side of the disc is a

wear plate 24 which extends to the next recess or opening 22 and which functions to guide the log being chipped to the next following knife. Although Figure 1 illustrates only one section of a chipper disc, it will be understood that a plurality of such sections incor¬ porating openings 22, knives 12 and wear plates 24 are arranged at regular intervals around the disc circum¬ ference, for instance as described in Swedish Patent Specification 7314475-0 (U.S. Patent Specification 4 047 670).

In order to achieve the desired torsion in the wear plates, as described in the introduction of this docu¬ ment, a straight edge 26 is placed beneath the wear plate 24 at the end thereof remote from the holder cassettes 10, beneath an intermediate journalling means comprising a block 28 and a hemispherical plate 30, the flat undersurface of which abuts the straight edge 26. As shown by the arrow P in Figure 1, the straight edge 26 can be moved in the radial direction of the disc by means of a piston-cylinder device 32, the piston arm 34 of which engages a recess 36 in the straight edge 26. This setting device 32 is attached to the base plate 18 of the disc unit by means of screws 38 and guide pins 40, and is provided with a connection 42 for connection to a drive medium source, such as a source of compres¬ sed air, hydraulic fluid or some other known drive medium. The end of the wear plate 24 nearest the knife cassette 10 is fixed permanently to the base plate 18 of the disc, by means of screws 44 and spacer means 46.

As will be seen from Figures 3 and 4, the straight edge 26 is provided with a number of elongated holes 48 which receive screws 50 (Figure 2) which hold the end edge of the wear plate 24 firmly to the base plate 18

of the chipper body or disc. The load on the wear plate attachment can thus be relieved by slackening the screws 50 and therewith enable the straight edge 26 to be moved in the direction of its longitudinal axis so as to change the torsion in the wear plate 24, this movement of the straight edge either being effected with the aid of the illustrated setting device 32 or with the aid of a mechanically actuated device, such as a screw-nut device, an excentric or the like. Adjust- ments to the setting of the straight edge can also be effected manually.

In the variant of the invention illustrated in Figure 2, the screws 50 are arranged so as to hold the end edge of the wear plate 24 secured to the pistons of a plurality of piston-cylinder devices 52, said pistons being vertically movable in the cylinders. The screws 50 thus pass through the wear plate block 28, through the hemispherical plate 30 and the elongated holes 48 in the straight edge 26 and are screwed into the piston of the piston-cylinder device 52.

As will be seen from Figure 2, the straight edge 26 has an inverted L-shape in order to guide the straight edge in its longitudinal direction, and the upper surface of the straight edge 26 facing towards the wear plate 24 is provided with sloping camming surfaces 54 (Figure 4). When the straight edge 26 is displaced in the direction of its longitudinal axis, these camming surfaces 54 will act on the hemispherical plates 30, causing the end surface of the wear plate to be lifted or lowered via the blocks 28, so as to modify the torsion in the wear plate. The camming surfaces have different slopes and/or configurations which permit the desired torsion to be obtained.

When wishing to release or lock the straight edge from or in a set position, pressure medium, such as com¬ pressed air or hydraulic fluid, is delivered to or removed from the piston in the piston-cylinder device 52, this pressure medium being delivered to and removed from the piston-cylinder device 52 through a conduit system 56 connected to a pressure medium source. Thus, when the piston of the piston-cylinder device 52 is relieved of load, the load acting on the end of the wear plate 24 is also removed so as to enable the straight edge 26 to be moved in the direction of its longitudinal axis with the aid of the piston-cylinder setting device 32, until desired torsioning of the wear plate is achieved. Of course, the camming surfaces of the straight edge 26 may have mutually different con¬ figurations so that the inventive arrangement is able to satisfy the different usages for which the chipper is intended.

In the case of the Figure 2 embodiment, the wear plate 24 is firmly clamped by bolts 44 at its front end adjacent the cassette 10. Thus, when changing the torsion in the wear plate, the wear plate is twisted about this fixed clamping point.

In other embodiments, such as those illustrated in Figures 5 and 6, the front end of the wear plate 24 is instead movably secured, so as to reduce the stresses that occur in the wear plate 24 when adjusting torsion with the aid of the straight edge. In the case of the Figure 5 embodiment, this is effected by securing the wear plate 24 to the spacer member 46 with the aid of the bolts 44 and shimming the plate with two hemis¬ pherical washers 58, 60 which enable the front end of

the wear plate 24 to be turned readily without needing to slacken or remove the bolts.

This ability to move the front end of the wear plate 24 is achieved differently in the Figure 6 embodiment. In this case, the wear plate 24 is provided with a groove 62 which extends into a lip 64 on the spacer member 46 so as to obtain a hinge effect between the spacer member 46 and the wear plate 24. Naturally, the lip 64 may instead be formed in the wear plate 24 and the groove 62 in the spacer member 46, if desired. It will be seen that in this case, the attachment bolt 44 is configured in a manner which will enable the wear plate 24 to move in relation to the bolt 44 with a slight clearance.

The position of the straight edge 26 can be adjusted for the purpose of changing the torsion in the wear plate 24 in a number of ways. This positional adjust- ment can be carried out very quickly when the disc has been stopped, for instance by manually positioning the straight edge subsequent to relieving the pressure on the piston-cylinder devices 52. In this regard, the straight edge 26 can be manipulated by means of some mechanical device, for instance a screw arrangement or the like. The adjustment can also be made with the aid of the illustrated piston-cylinder setting device 32, which is driven by a pressure medium. In this latter case, it is also conceivable to adjust the position of the straight edge while the chipper disc rotates and the chipper is in operation, in which case it is neces¬ sary to construct the holding piston-cylinder devices 52 and the piston-cylinder setting devices 32 in a manner such that these devices are able to manage these operating conditions, which is effected with the aid of

fittings known within this technical field.

It will be obvious from the aforegoing that the inven¬ tion provides an arrangement which will enable torsion- ing of the wear plate to be adjusted very readily and quickly in comparison with present-day techniques, with the aid of different means, such as mechanical means or pressure-medium operated means with the chipper disc stationary or in rotation, as in the last described case.

It will also be understood that by such expressions as chipper body, chipper disc, etc., used in the descrip¬ tion and in the following Claims is meant both the basic components, such as disc, cylinder or the like and also cassette carriers, knife carriers, etc., and also other auxiliary carrying devices, such as base plates, spacer members, bottom linings and like devices mounted on the base body and functioning to carry knives, knife cassettes, wear plates, etc.

It will also be understood that the invention is not restricted to the illustrated and described embodi¬ ments, and that modifications can be made within the scope of the following Claims.