WO2009016553A1

WO2009016553A1 - Method and apparatus for removing a sheath layer from wire -like elements

Info

Publication number: WO2009016553A1
Application number: PCT/IB2008/052969
Authority: WO
Inventors: Andreas Kellenberger
Original assignee: Schleuniger Holding Ag; Rychener, Joerg
Priority date: 2007-07-27
Filing date: 2008-07-24
Publication date: 2009-02-05
Also published as: DE202008017747U1

Abstract

The invention relates to an apparatus and method for removing a sheath layer from wire-like elements, in particular for stripping insulation from electrical or optical cables, in which, for minimizing the residual breaking surface of the sheath layer, the sheath layer is cut into at the same point at successive times with the aid of at least two pairs of V-blades (7, 7' and 8, 8') having at least two different cutting angles (α, β), one cutting angle (α) being in the form of an acute angle and the other cutting angle (β) in the form of an obtuse angle. Particularly with a choice of angles of about 120° and 60°, the result is a substantially smaller residual breaking surface than in the case of conventional 90° V-knives.

Description

METHOD AND APPARATUS FOR REMOVING A SHEATH LAYER FROM

WIRE-LIKE ELEMENTS

The invention relates to methods and apparatuses for removing a sheath layer from wire-like elements, in particular for stripping insulation from electrical or optical cables, the sheath layer of the wire-like element being cut into at a predetermined point by means of a pair of blades having two V-shaped cutting edges or knives which can be actuated towards one another, transversely to the axis of the element, and the incised sheath section is then removed, for example pulled off.

EP-1261092 discloses insulation stripping methods and an apparatus, the cable insulation being cut into twice in succession at the same point. The same V-shaped pair of knives having the same cutting angle of about 90° is always used, and the cable is rotated through 45° before the second incision. However, this requires a complicated and expensive rotary drive and in addition other apparatuses and imposes a load on the cable for rotation.

US-4577405 describes another cable insulation stripping apparatus which is provided with a processing unit having a substantially V-shaped pair of knives mounted so as to be double-acting (reciprocatable) . With this insulation-stripping pair of knives, the cable is cut into without displacement or rotation of the cable. The pair of knives has a cutting angle of 36°.

The V-shaped insulation stripping knives have in principle the advantage that, within a certain range (determined by the dimensions of the insulation stripping knives), they can also strip insulation from cables of different diameters. With V-shaped insulation stripping knives or blades, the insulation can be cut into as well as removed - as a rule immediately after the incision. On the other hand, V- shaped insulation stripping knives - including the solutions according to the publications cited above - may have the disadvantage that a certain, relatively large region of the insulation cross-section always remains and is not cut through during the incision. This range - the so-called "residual breaking surface" - then usually breaks during the removal of the insulation in a more or less controlled manner. However, this is problematic in practice, particularly in the case of high-quality cable types and in cable assembly technology with high demands regarding the precision .

DE-10113082 describes a double knife which has an incision side with a rectangular cutting edge as an insulation stripping blade and a cut-through side having a V cutting edge. In column 2, lines 33-36, a half-oval cutting edge is also mentioned as an insulation stripping blade.

With so-called radius knives, the residual breaking surface can theoretically be reduced to zero in cable insulation stripping. However, only cables having very specific internal/external diameters can be stripped of insulation by means of radius knives. The radius knives are therefore very inflexible with regard to their usability and are suitable only for processing the same cable type.

The residual breaking surface can theoretically also be reduced to about zero with apparatuses with which the cable is cut into with rotation. In contrast to the radius knives, the internal and external diameters of a cable play no role here within a certain diameter span. However, such insulation stripping apparatuses are very complicated in design - compared with V-knives or radius knives. In addition, the processing speed is as a rule lower than in the case of V-knives or radius knives .

It is the object of the invention to provide an improved solution by means of which the above disadvantages of the prior art can be significantly reduced or eliminated, i.e. the residual breaking surface can be reduced to a minimum in the case of the sheath surfaces to be removed, for example cable insulation in various cable types can be removed with high precision and work quality without having to rotate the knives or the cable.

The object is achieved by the features of Claims 1 and 5. Advantageous further developments of the method according to the invention and of the apparatus are described in the dependent Claims.

The invention is based on the following discoveries:

The thinner an insulation in comparison with the total diameter of the cable, the greater is the percentage of the residual breaking surface, based on the total cross-section of the insulation. The larger the proportion of the residual breaking surface, the more difficult it is to cut the insulation in a controlled manner. Depending on material thickness and characteristics of the insulation (soft material, thick-walled) and the material type (large elongation at break) , large residual breaking surfaces result in warpage of the insulation material in the region of the residual breaking surfaces and uncontrolled breaking during the insulation stripping process. This is - as mentioned above - an actual problem in practice which has to be solved, particularly in cable assembly.

In order to effect as clean a cut as possible at the incision point and to keep the insulation stripping forces as small as possible, it is expedient according to the invention as far as possible to minimize the total residual breaking surface during the incision process without rotation.

The essential aspect of the invention is that - for minimizing the residual breaking surface of the sheath layer (insulation) - the incision of the sheath layer is carried out at the same point at successive times with the aid of at least two different V-shaped pairs of blades having different cutting angles, one cutting angle being chosen to be an acute angle, preferably about 54° to 85°, in particular about 60°, and the other cutting angle being chosen to be an obtuse angle, preferably 95° to 150°, in particular about 120°.

The method according to the invention can be carried out by the apparatus according to the invention, in which, for cutting into the sheath layer at the same point at successive times, at least two pairs of blades are provided with different cutting angles in each pair or with different cutting angles from pair to pair in one or more processing unit(s), the first cutting angle being in the form of an acute angle with the other cutting angle being in the form of an obtuse angle.

Further features, formation details and variants and the most important advantages are described below in the description of the figures and in the dependent patent Claims.

The invention is explained in more detail below with reference to the attached drawings which illustrate three working examples.

• Fig. 1 shows a cable cross-section after the insulation layer thereof has been cut into by a

90° V-knife pair according to the prior art; EP- 1261092 describes a design in which the pair of blades is swivelled by means of a complicated swivelling apparatus. The resultant cutting picture appears at the end of the process comparable with that shown in the present figure 4, because the apparatus according to the prior art does in fact rotate the knife head through 45°. According to the invention, however, this rotation is advantageously omitted.

• Fig. 2 shows a cable cross-section after cutting into by a pair of 120° V-blades of the apparatus according to the invention;

• Fig. 3 shows a cable cross-section after cutting into by a pair of 60° V-blades of the apparatus according to the invention;

• Fig. 4 shows the cable cross-section after cutting into by the two pairs of V-blades in each case at the same point according to Fig. 2 and Fig. 3 of the apparatus according to the invention;

• Figures 5-7 show a first working example of the insulation stripping apparatus according to the invention, Fig. 5 showing a view of one of the knives, Fig. 6 showing a perspective picture of a pair of knives in a first processing position and Fig. 7 showing a perspective picture of the pair of knives according to Fig. 6 in a second processing position;

• Figures 8-11 show a second working example of the apparatus according to the invention, Figures 8 and 9 each showing a knife in front view, Fig. 10 a perspective picture of the apparatus with the knives according to Fig. 8 and 9 in a first processing position, and Fig. 11 a perspective picture of the apparatus with the knives according to Fig. 8 and 9 in a second processing position - the pair of knives is moved in the y-direction between the two processing points;

• Fig. 12 shows a front view of a combined pair of knives of a third working example of the apparatus according to the invention;

• Fig. 13 shows a perspective picture of a complete knife head according to the invention.

In the figures, the similar or equivalent details are designated by the same reference numerals.

Fig. 1 schematically shows the cross-section of an electrical or optical cable 1 after incision of its insulation layer 2 by a pair of 90° V-knives according to the prior art. Those parts of the insulation layer 2 which have been cut into are shaded.

From Fig. 1, it is clear that the parts not cut into, the so-called residual breaking surface 3 (white areas, without shading) , form a considerable proportion of the insulation cross-section, which - as discussed above - can be problematic in practice. The inner conductor of the cable 1 is designated by 4.

In order to cut the insulation layer as cleanly as possible at the incision point and to minimize the insulation stripping forces, it is proposed according to the present invention as far as possible to minimize the total residual breaking surface during the incision process by the use of different V-blades or V-knives.

Figures 2-4 illustrate the removal of a sheath layer, i.e. insulation stripping layer 2 of a wire-like element, for example of an electrical cable 1, by the method according to the invention. For minimizing the residual breaking surface of the sheath layer, the incision of the insulation layer is carried out at the same point of the cable 1 - at successive times - with the aid of at least two pairs of V-shaped blades but with different cutting angles, one cutting angle being chosen as an acute angle and the other cutting angle as an obtuse angle.

Fig. 2 shows the cable cross-section after the incision by a first pair of V-blades having an obtuse angle of about 120°, Fig. 3 after the incision by another pair of V-blades having an acute angle about 60°, and Fig. 4 after the incision by the two mentioned pairs of V- blades of the apparatus according to the invention. Alternatively, an incision can be made first with the pair of V-blades having an acute angle and then with the pair of V-blades having the obtuse angle. In Figures 2-4, too, the sheath layer, i.e. the insulation layer, is designated by 2, the residual breaking surfaces by 3 and the inner conductor by 4. Those surfaces of the insulation layer 2 which have been cut into are shaded. From Fig. 4, it is clear that the total residual breaking surface 3 is substantially smaller according to the invention than in the traditional solution according to Fig. 1. It is thus possible substantially to minimize the residual breaking surface 3.

It should be noted that this method is suitable for stripping insulation from simple stranded cables as well as for stripping insulation of the cable sheath of a coaxial or multi-conductor cable and analogously for removing any sheath layer, insulation or similar layer from any desired wire-like elements.

Figures 5-7 schematically show the first working example of the insulation stripping apparatus according to the invention, Fig. 5 showing a front view of the knife 5, Fig. 6 a perspective picture of the pair of knives 5, 5' with two different pairs of cutting edges in a first processing position and Fig. 7 a perspective picture of the pair of knives 5, 5' in a second processing position.

According to Fig. 5, the knife 5 has in this case a recess 6 and pairs of V-shaped cutting edges 7 and 8 having different cutting angles CC and β, respectively, which are formed at opposite points of the recess 6 in the blade 5. The recess 6 and the pairs of V-shaped cutting edges 7 and 8 are arranged with mirror symmetry on the longitudinal centre line 9 of the knife 5 in this embodiment. The knife 5 is provided with at least one fixing point 10 (e.g. an opening) for connection to an actuating unit known per se (not shown) .

The V-blade 7 having the acute cutting angle OC is in this case arranged on the side of the fixing point 10 (i.e. at the bottom in Fig. 5) . It should be noted that the other V-blade 8 can optionally rest with the obtuse angle β on the side of the fixing point 10 (not shown) .

Figures 6 and 7 show the reciprocatably mounted knives 5 and 5' moving towards one another by means of a push- pull mechanism and having the pairs of V-blades 7, 8 cooperating with one another, in their first processing position .

The apparatus according to Figures 5-7 operates as follows:

In a first step, one end of the prepared cable 1 is run through the two recesses 6 of the knives 5 and 5' in the x-direction into the position intended for insulation stripping.

In the second step, the insulation layer 2 of the cable 1 is cut into with the pairs of V-blades 8 and 8' having an obtuse cutting angle β to a predetermined extent by moving apart (cf. arrow 12) the opposite knives 5 and 5' in the z-direction.

In the third step, the insulation layer 2 is cut into to a predetermined extent by means of the pairs of V- blades 7 and 7' having an acute V angle CC by moving the knives 5 and 5' towards one another in the z-direction

(cf . arrows 13) - towards the cable 1 (Fig. 7) . The complete incision form according to Fig. 4 has thus been achieved.

In the fourth step, the knives 5 and 5' are as a rule retracted slightly in the z-direction (this is also known as "wayback" in practice - see further below) . Thereafter, that section of the insulation layer 2 which has been cut into is stripped off, i.e. removed, by an axial feed movement of the cable 1 in the opposite direction to the cable end (in the x- direction) (not shown since known per se) . At the same point of the double incision by means of the pairs of V-blades 7, 7' and 8, 8' having different cutting angles CC and β, the insulation layer 2 breaks very easily and regularly when pulled off since, according to the invention, the residual breaking surface was reduced to a minimum (cf . Fig. 4) .

In a next step, the cable 1 from which insulation was stripped can be moved to a new position for cutting through after the V-blades 7 and 1' have been moved apart (cf. arrow 12), it being possible to carry out the full cutting through of the cable 1 either with any of the pairs 7, 1' or 8, 8' of insulation-stripping V- blades according to the invention or optionally with an additional pair of knives (not illustrated) .

Thereafter, the other end of the cable section or the beginning of the new cable section is stripped of insulation in a next processing sequence, in the same way as mentioned above. The above steps are repeated according to the desired number of cable pieces. The method according to the invention can be carried out several times with the same result and work quality, for example, on a cut and strip machine.

In order to free the cable from the insulation layer without problems, the V-blades remain in the position which corresponds to the external diameter of the inner conductor, the external diameter of a braided screen or the external diameter of another conductor or a certain arrangement of internal cables. Optionally, V-blades or the knives are retracted very slightly from this position (wayback) in order to prevent abrasion of the conductor, screen or inner cable underneath.

In the first working example according to Figures 5-7, just a pair of knives 5, 5' is required as a processing element. This compact arrangement has the advantage that only a single knife position on the knife head

(not shown) is occupied. The other knife positions are available for other pairs of knives or tools which may be used, for example, for processing the inner conductor of a multi-conductor cable.

The embodiment according to Figures 5-7 furthermore has the advantage that, in this embodiment, the knife head need not be moveable in the y-direction because one knife position is sufficient for cutting into, cutting through and pulling off.

Finally, the embodiment according to Figures 5-7 has the advantage that the knife head need not be moved in the y-direction and processing time can therefore be reduced.

Figures 8 and 9 each show a knife 5A and 5B, respectively, of the second working example of the apparatus according to the invention in front view. Figures 10 and 11 show the knives 5A, 5A' and 5B, 5B' , respectively, in perspective view. The knives 5A, 5A' and 5B, 5B' are separated from one another in pairs. The pairs of knives 5A and 5A' and 5B, 5B' are actuated by a push-pull mechanism in pairs in the z-direction (reciprocating) .

At the upper end of the knife 5A according to Fig. 8, a V-shaped blade 8 which has an obtuse angle β and the angle value of which is about 120° here is formed. The knife 5A is provided in its lower region with a fixing point 10, e.g. an opening. At the upper end of the knife 5B according to Fig. 9, a V-shaped blade 7 which has an acute angle OC and the angle value of which is about 60° here is formed. The knife 5B is provided in its lower region likewise with a fixing point 10, e.g. an opening.

As shown in Figures 10 and 11, the double-acting pair of knives 5A and 5A' occupy a first knife position 11, and the double-acting pair of knives 5B and 5B' occupy a second knife position 11' . In Fig. 10, the first pair of knives 5B and 5B' is in the active state but the second pair of knives 5A, 5A' is in the passive state. In Figure 11, the situation is the opposite.

The apparatus according to Figures 8-11 operates as follows :

In the first step, one end of the prepared cable 1 is run through between the opened knives 5B and 5B' in the x-direction into the position intended for stripping the insulation.

In the second step, the insulation layer 2 of the cable 1 is cut into to a predetermined extent with the pairs of V-blades having an acute cutting angle CC by moving the opposite knives 5B and 5B' towards one another (cf. arrows 13) in the z-direction. In the third step, the first pair of knives 5B and 5B' is opened again (cf . arrow 12) . In this arrangement, the two pairs of knives 5A, 5A' and 5B, 5B' are then moved in the y-direction by means of an adjusting unit which is not shown, so that the cable 1 comes to rest preferably in the middle between the pair of knives 5A and 5A' .

In the fourth step, the insulation layer 2 of the cable 1 is cut into to a predetermined extent with the pairs of V-blades having an acute cutting angle β by moving the opposite knives 5A and 5A' towards one another (cf. arrow 13) in the z-direction.

The insulation layer 2 of the cable 1 is thus cut into at the same point at successive times by the two pairs of blades 7, 7' and 8, 8' having different cutting angles CC and β, respectively, one cutting angle β being in the form of an obtuse angle and the other cutting angle OC in the form of an acute angle. The angle values chosen here are the same as in the first working example. The cutting cross-section thus obtained and the minimum residual breaking surface likewise correspond to Fig. 4.

In the fifth step, the two pairs of knives 5A, 5A' and 5B, 5B' are as a rule slightly retracted in the z- direction ("wayback" - see further above) . Thereafter, that section of the insulation layer 2 which has been cut into is pulled off, i.e. removed, by an axial feed movement of the cable 1 in the opposite direction to the cable end (in the x-direction) (not shown since known per se ) .

At the point of the double incision, the insulation layer 2 breaks here too very easily and regularly when being pulled off since, according to the invention, the residual breaking surface was reduced to a minimum (cf. Fig. 4) .

In a next step, the cable 1 from which insulation was stripped can be moved to a new position for cutting through after retraction of the pairs of knives 5A, 5A' and 5B, 5B' (cf. arrow 12), it being possible to cut through the cable 1 fully either with any of the pairs of knives 5A, 5A' and 5B, 5B' according to the invention or optionally with an additional pair of knives (not illustrated) .

Thereafter the other end of the cable section or the beginning of the new cable section is stripped of insulation in a next processing sequence, as mentioned above. The above steps are repeated according to the desired number of cable pieces. This method according to the invention can also be carried out several times with the same result and work quality, for example on a cut and strip machine.

Optionally, the insulation stripping apparatus according to the invention can be equipped with more than two pairs of knives or knife heads. In such embodiments, the pairs of knives can be moved transversely to the cable axis (e.g. in the y- direction) . With this movement, the processing can be changed from one pair of knives to another pair of knives which is best suitable for the respective operation. Consequently, the work quality and the flexibility of the apparatus can be further increased.

Figure 12 shows a combined pair of knives 5 and 5' of the third working example of the apparatus according to the invention in front view. This embodiment is a variant of the second working example according to Figures 8-11.

The preferably identical knives 5 and 5' (fig. 12) are provided with two V-blades 7, 8 and 7', 8', respectively, having different cutting angles CC and β, respectively, which are formed side by side with a spacing 14 in the y-direction. In contrast to the second working example, the V-blades 7, 8 and 7', 8' are present on the same knife 5 or 5' . A fixing point 10, e.g. an opening, is provided on each knife 5 and 5' . The pair of knives 5, 5' could optionally be equipped side by side with more than two pairs of V- blades .

The knife 5 cooperates in pairs with the knife 5' arranged opposite at an angle of 180°, in the manner discussed in detail in the case of Figures 10 and 11. Thus, the mode of operation of this apparatus is approximately the same.

However, it should be emphasised that here, after the first incision with the V-blades 7 and 7' transversely to the cable axis, i.e. in the y-direction, the single pair of knives consisting of the knives 5 and 5' has to be moved by that distance which corresponds to the spacing 14 in order then to cut in at the same point with the V-blades 8 and 8' .

The sequence in which insulation is stripped, i.e. whether the beginning of the subsequent cable (leading end) is first stripped of insulation and then the end of the leading cable (trailing end) or vice versa plays no role in the solution according to the invention. Whether an incision is first made with the V-blade having the obtuse angle β or with the V-blade having the acute angle CC for stripping insulation likewise plays no role. Two or more pairs of knives having a very wide range of geometries may be present in different knife positions (viewed in the y-direction) on the knife beam. It would even be possible to arrange a plurality of knife heads one behind the other in the x-direction. The two opposite blades of a pair preferably have V-cutting edges having each case an identical V-angle. The pairs of knives preferably have different V cutting angles from pair to pair.

The actuation direction, i.e. the feed movement of the knife beam in the direction of the cable, always remains the same on incision at successive times with pairs of V-knives or blades of different angles.

The at least two different cutting angle values of the at least two pairs of V-blades 7, 8 or pairs of V- knives should be determined in the context of the above disclosure, in each case according to the installation stripping conditions. In experiments according to the invention (cf. figures), two different angle values of the acute angle CC and the obtuse angle β are used, the acute angle CC having been chosen to be between 54° and 85°, preferably about 60°, and the obtuse angle β having been chosen to be between 95° and 150°, preferably about 120°. By means of these angle values, it was possible to reduce the residual breaking surface to a minimum in the case of the cable insulations to be removed. Consequently, a sheath layer of a wire-like element, in particular an electrical or optical cable insulation, can therefore be removed with higher precision and work quality in the case of very different cable types.

Fig. 13 shows the perspective working example of a complete knife head 15 of the apparatus according to the invention. In this arrangement, the knife head 15 is provided with a pair of knife beams 16, whose knife beams are arranged so as to be moveable towards one another (cf . arrows 13) or apart (arrows 12) in the z- direction by means of a driven screw spindle 17. In this embodiment, the screw spindle 17 is provided with left-handed and right-handed thread sections for the relative movement of the pair of knife beams 16. In this case, the pair of knives 5 and 5' according to Figures 5-7 is coordinated with the pair of knife beams 16. Each of the knives 5, 5' is fixed on the associated knife beam with one screw 18 each. The pair of knives 5, 5' is arranged in a first knife position HA on the pair of knife beams 16. As shown in Fig. 13, further knife positions HB and HC for further pairs of knives (not shown) are also provided. The screw spindle 17 is connected to a rotary drive 19. The entire knife head 15 can, if required, be moved in the y-direction in order in each case to bring the tools in the knife positions HA, HB or HC into action .

It should also be noted that the term "substantially V- shaped cutting edge" is also to be understood as meaning those cutting edges which consist not only of linear edge sections but also of linear and/or curved sections, but the theoretical overall contour (border) of the combined cutting edge is substantially V-shaped.

The invention is of course not limited to the working examples shown and described. Further embodiments and combinations are also conceivable within the claimed scope of protection.

Claims

PATENT CLAIMS

1. Method for removing a sheath layer from wire-like elements, in particular for stripping insulation from electrical or optical cables, in which the sheath layer, for example insulation of the wire- like element, is cut into at a predetermined point by means of a pair of blades having two, substantially V-shaped V-cutting edges actuated towards one another, transversely to the longitudinal axis of the element and the sheath section which has been cut into is then removed from the element, characterized in that - for minimizing the residual breaking surface of the sheath layer - the incision of the sheath layer

(2) is carried out at the same point at successive times, with the aid of at least two pairs of V- blades (7, 7' and 8, 8') having at least two different cutting angles (CC and β) , one cutting angle (CC) being chosen as an acute angle and the other cutting angle (β) as an obtuse angle.

2. Method according to Claim 1, characterized in that the pairs of V-blades (7, 1' and 8, 8') are moved in the same direction during each incision movement, and neither the cable 1 nor the pairs of blades are rotated about the axis of the cable 1.

3. Method according to Claim 1 or 2, characterized in that, of the different cutting angles (CC, β) of the at least two pairs of V-blades (7, 1' and 8, 2

8'), one cutting angle is chosen as an acute angle (α) of 54° to 85°, preferably about 60°, and the other cutting angle is chosen as an obtuse angle (β) of 95° to 150°, preferably about 120°.

4. Method according to any of Claims 1 to 3, characterized in that the wire-like element (1) is cut through at at least one predetermined point by means of one of the insulation-stripping pairs of V-blades (7, 7' and 8, 8') before or after the removal of its sheath layer (2) .

5. Apparatus for removing a sheath layer from wire- like elements, in particular for carrying out the method according to any of Claims 1-4, which has two knife beams mounted so as to be reciprocatable transversely to the longitudinal axis of the element and actuatable in pairs towards one another, which knife beams are provided with V- knives, characterized in that, for cutting into the sheath layer (2) at the same point at successive times, at least two pairs of V-blades (7, 7' and 8, 8') are provided with at least two different cutting angles (OC, β) , one cutting angle (α) being in the form of an acute angle and the other cutting angle (β) in the form of an obtuse angle .

6. Apparatus according to Claim 5, characterized in that two pairs of V-blades (7, 7' and 8, 8') having different cutting angles (OC, β) are combined in opposite positions around a recess (6) 3 in the same knife (5 and 5') .

7. Apparatus according to Claim 5, characterized in that at least two pairs of V-blades (7, 7' and 8, 8') having different cutting angles (OC, β) are provided on at least two pairs of knives (5A, 5A' and 5B, 5B' ) separated from one another.

8. Apparatus according to Claim 5, characterized in that the at least two pairs of V-blades (7, 1' and

8, 8') having different cutting angles (OC, β) are provided side by side with a spacing (14) on one knife of a single pair of knives (5, 5' ) .

9. Apparatus according to Claim 7 or 8, characterized in that the single pair of knives (5, 5') or the pairs of knives (5A, 5A' and 5B, 5B' ) form at least one processing unit which is arranged so as to be moveable or adjustable in a transverse direction (y) to the axis (x) of the element.

10. Apparatus according to any of Claims 5-9, characterized in that the cooperating V-blades (7, 8 and 7', 8') of the pairs of V-blades have the same or different cutting angles (OC, β) .