Such tools and circular saw arrangements, respectively, are per se previously known. As an example, reference is made to the Swedish patent document 9304091-3 (504 961). The working tool according to the invention can be part of a block forming machine of the kind described in this patent document. It is however pointed out that the working tool and the circular saw arrangement also can be used in other types of machines for working purposes than the ones described in the just mentioned patent document. In the working tools comprised in the machine according to the patent document, the shoulder member has a surface facing the slit, which surface is cylindrical and coaxial with the rotation axis of the working tools.

A problem with working tools of this kind is that cuttings coming into the slit tend to stay in the slit and be wedged up in this so that a good function is jeopardised.

SUMMARY OF THE INVENTION The purpose of the present invention is to reduce the above re- lated drawbacks and to design the working tool so that the risk for cuttings wedging up in the slit is reduced.

According to the invention, this is achieved in that the shoulder member, in its surface facing the slit, has a recess. Such a re- cess implies that cuttings coming into the slit can enter the re- cess and, by means of this recess, be redirected in direction outwards in such a way that the cuttings tend to leave the slit thereafter.

The effect shown above is increased if the recess is rounded.

Consequently, cuttings coming into the recess can slide on a rounded surface and be redirected from a direction into the slit so as to move in a direction out of the slit.

According to a preferred embodiment, the shoulder member has, on the side of the recess situated furthest away from the tooth ring, a section, which limits the recess and is situated on a level above the bottom of the recess. In this way, it is secured that the cuttings will tend to move outwards from the recess when they leave the recess. It is then preferred that the side of the recess alienated from the tooth ring extends obliquely away from the tooth ring. By"obliquely away"is, consequently, meant a di- rection being oblique in relation to the rotation axis of the work- ing tool. However, it is pointed out that within the scope of the invention are also embraced embodiments where the side of the recess alienated from the tooth ring extends essentially in a ra- dial direction.

The effect according to the invention is increased if the circular saw arrangement, in the area between separate teeth, has out- wardly facing surfaces sloping obliquely towards the recess.

Consequently, these oblique surfaces will guide the cuttings into the recess.

It is preferred that the tooth ring of the circular saw arrangement is formed of several tooth segments. According to a preferred embodiment, each such tooth segment comprises a shoulder member formed in a single piece with the segment so that, con- sequently, a complete circular formation, comprising the shoul- der-like member, is obtained when several such segments are put together.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the enclosed drawings, a more specific de- scription of embodiments of the invention, put forward as exam- ples, will follow hereinbelow.

In the drawings: Fig 1 is a schematic perspective view illustrating the principal function of a working tool of the kind intended with the invention, Fig 2 is a partly cut and simplified sectional view illustrating a working tool of a known design formed as a spiral disc, Fig 3 a partially cut sectional view of a pair of working tools comprised in a block forming machine seen in the direc- tion of the arrows p in Fig 2, i. e. from below, Fig 4 an enlarged detail section illustrating an inner proc- essing member in connection with the circular saw ar- rangement, Fig 5 a vertical view, partly shown in section, corresponding to Fig 3, however, shown in a vertical plane,

Fig 6 a schematic section view illustrating a tooth segment, which according to the invention is intended to replace, together with further identical segments forming a cir- cular saw arrangement, corresponding parts in the known design shown in Fig 1-5, and Fig 7 a cut along the line 7-7 in Fig 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Fig 1 schematically illustrates the working principal of a working tool having processing members a, which in this case at first hand are intended to cleave or split the fibres in a log c, and a presawing circular saw arrangement b. The log c, which is axi- ally fed through a block forming machine and then passes two working tools formed as reduction discs and placed on each side of the centre of the log, will be formed into a block with two plane lateral surfaces d at the same time as wood material on the outside is processed into chips. The circular saw arrange- ment has several teeth, the purpose of which is to confer smoothness to the plane surfaces of the log block.

Fig 2-5 illustrate two working toois, in its entirety denoted as 1 and 2, respectively, which here will be denominated reducing discs. Jointly, these form or are comprised in a block forming machine. The purpose of this machine is to plane process an axially fed log 3 passing between the discs so that this will ob- tain two opposite plane surfaces 4,4'. At the same time, the ma- chine is to produce chips of the wood surplus material com- prised in the round log in the area outside said plane surfaces.

The two reducing discs 1,2 are rotatable around a common geometrical axis 5 and have generally a basic shape of the frus- trum of a cone. In Fig 3, the inner thin end of each disc is de- noted 6, whereas the opposite thicker end is denoted 7. As can be seen from Fig 3, the thin end of each disc is directed inwards towards the passing log, whereas the thick end 7 is alienated

from the log. Each disc is equipped with a large number of dis- mountable processing members, henceforth denominated cutting devices. These occur in two different designs or types, namely a right type 9 and a left type 8. The cutting devices are, by means of screw fastenings, demountably arranged in special essentially ring-shaped holders 10, which in their turn are permanently fixed in holes 11 in each disc 1,2, suitably by welding.

In connection with each cutting device 8,9, an opening or pas- sage is formed owing to the ring shape of the holder 10, through which opening or passage chips from the front side of the disc, facing the log, can pass to the back side of the disc. Each re- ducing disc furthermore comprises a circular saw arrangement, in its entirety denoted as 12, the teeth of which are denoted 13.

From Fig 3 and 5 it is evident how, in this known construction, the arrangement formed as a circular saw blade is secured by screws to the ring-shaped part 14, which in its turn, from the back side, is secured by screws to a disc-shaped hub or centre part 15 of the individual reducing disc. In the space inside the ring part 14, a filling disc 16 is secured by screws to the hub part 15.

As can be seen from Fig 2, the cutting devices on the individual reducing disc, in this case the disc 1, are arranged in one or more helical paths along the conical surface of the disc (it is emphasised that the cutting devices are only schematically il- lustrated in said figure). In the example, the cutting devices are distributed in three different helical paths denoted A, B and C, respectively. All the outer cutting devices 9 in each such helical path are, counting from the outer thick end of the disc up to the innermost but one cutting device, of one and the same type, in this case right type, whereas the innermost cutting device 8 is of opposite type, i. e. of left type in the disc 1 according to Fig 2.

The main edges of the cutting device are in this example located essentially in parallel with the feeding direction or fibre direction of the log, i. e. vertical planes being essentially perpendicular to

the rotation axis 5. This implies that the main edges of the cut- ting device when coming into contact with the log will cleave or split the fibres of the wood, rather than cutting the same off.

However, it is pointed out that the present invention, such as it will later be described, is as well applicable to such designs where the main edges of the cutting device are actually de- signed so as to cut off the fibres in the wood rather than cleav- ing or splitting the same.

In the known construction according to Fig 1-5, described above, the ring-shaped part 14 forms a shoulder-like member having a ring-shaped, outwardly facing surface 17. This surface 17 is essentially cylindric and concentric with the rotation axis 5.

As particularly evident from Fig 5, the shoulder-like member 14 forms a slit 18 between the tooth ring, denoted as 19, and the closest situated thin end surface 20 of the respective reducing disc 1,2. Chip or cutting material coming into this slit 18 easily tend to be caked or wedged up, which implies a risk for inter- ruption of the service, for instance overheating and deformations of the reducing discs and the circular saw arrangements 12.

Fig 6 and 7 will now illustrate the solution according to the in- vention. This consists more precisely in that the shoulder mem- ber 14, in its surface 17 facing the split 18, has a recess 21. In the complete circular saw arrangement 12, this recess 21 ex- tends in ring-shape and concentrically around the rotation axis 5. In this connection, it should already now be pointed out that Fig 6 illustrates a single one out of several segments 22, which jointly form the circular saw arrangement 12 according to the invention. Consequently, these different segments 22 are in- tended to be attached by means of screws arranged in holes denoted as 23, in such a way that the segments will be placed analogous to the blade 12 and the ring part 14 in the known construction according to Fig 1-5. From this, it also appears that the shoulder-like member 14 in the solution according to the in- vention, illustrated in Fig 6 and 7, forms a single piece with the

tooth ring itself, i. e. that an individual segment 22 has not only teeth but also a part of the shoulder-like member that completely forms ring shape.

In Fig 7, the thin end surface 20 of the reducing disc and the slit 18 between the tooth ring 19 and said surface 20 are indicated.

The recess 21 is suitably rounded. Consequently, it will be es- sentially concave outwards without sharp corners. This implies that cuttings obtained by sawing out from the log will tend to be guided into the recess 21 by the cutting edges of the teeth, and be redirected by the gentle roundness of the recess so that the cuttings again will be directed radially outwards and, conse- quently, the risk for undesired accumulations of cuttings in the recess 18 is reduced.

It is pointed out that the recess 21 is to be a real recess in the surface 17, i. e. that the recess 21 is to extend below a section 24, which limits the recess and is situated in the shoulder-like member 14 furthest away from the tooth ring 19.

According to a preferred embodiment, the side 25 of the recess 21 alienated from the tooth ring 19 extends obliquely away from the tooth ring. Consequently, the surface 25 will guide cuttings obliquely outwards towards the thin end surface 20 of the re- ducing disc so that the cuttings will be redirected outwards. The previously mentioned limiting section 17 will, consequently, be situated between the recess 21 and the thin end surface 20 of the reducing disc. The surface of the section 24 facing radially outwards is suitably plane, i. e. essentially cylindric and concen- tric with the rotation axis 5.

According to a preferred embodiment of the invention, the cir- cular saw arrangement, in the area between separate teeth, has outwardly facing surfaces 26 sloping obliquely inwards towards the recess 21 so as to guide cuttings cut by the teeth 13 towards

said recess. In this connection, it is pointed out that the teeth 13 in Fig 6 and 7 are shown without hard metal cutting edges, which are intended to be added.

Thus, according to the present invention a circular saw ar- rangement is formed on reducing discs of the kind described or other similar working tools by application of several saw seg- ments 22 of the kind described so that a continuous ring-shaped saw arrangement is formed. These different segments are at- tached by means of screw fastenings, or in any other way, to the reducing discs so that the segments will obtain the positions shown in the description above concerning the known circular saw blade 12 according to Fig 1-5 and the associated ring- shaped part 14, which there have the character of a separate piece. However, it is pointed out that the present invention is not at all limited to just such segments 22 that has been dealt with above. Consequently, it is within the scope of the invention that instead use a design partially analogous to the one according to previous technique shown in Fig 1-5, i. e. that the shoulder member 14 is formed as a separate component in relation to the circular saw blade 12. In such a case, the recess 21 according to the invention would, consequently, be attached in the sepa- rate ring-shaped part 14 with the achievement of essentially the same functional advantages as those already dealt with above.

Furthermore, it is pointed out that in case of a design where the ring-shaped part 14 is separate from the circular saw blade 12, both the ring-shaped part 14 and the blade 12 itself can of course be constituted by a number of co-operating segments, which jointly form ring shape. In this connection, it is also pointed out that the inventional solution according to Fig 6 and 7 could be modified in such a way that several segments 22 are not present, but instead the circular saw arrangement is formed of a single continuous ring-shaped part. Furthermore, it is pointed out that in another embodiment the shoulder member 14 could be integrated in the reducing disc in question, for instance

by being in a single piece therewith. Consequently, the circular saw arrangement 12 could then be attached to the shoulder member. Other modifications are also possible within the scope of the idea of the invention.