Shearing device

Abstract

A shearing device for fragmenting a metal strip includes two counter-rotating drums facing one another, a drive device connecting the drums and synchronising their rotation speed, and at least one pair of drum-supported blades. The blades engage by shearing effect during drum rotation to cut the waste. The blades of the pair have, from the cutting edge thereof, planar surfaces, referred to as overlapping surfaces, overlapping and facing one another during the shearing between blades, each blade being secured transversely to the drum, at an angle to the axis of rotation of the drum, so the plane through the overlapping surface of the blade forms an angle with the axis of rotation of the corresponding drum, producing gradual shearing. The overlapping surface of each blade is tilted so the plane passing through the overlapping surface does not intersect the rotational axis of the drum on its active width.

Claims

1. A shearing device (1) for fragmenting a metal strip into multiple pieces, said device comprising: two counter-rotating drums positioned facing each other, respective axes of rotation of the two drums being parallel to each other; a drive device connecting the two drums and synchronising a speed of rotation of the two drums; and a pair of blades, first and second blades of the pair of blades being carried by a respective drum of the two drums, the first and second blades of the pair of blades cooperating with a shearing effect during rotation of the two drums for cutting, the first and second blades having, starting from cutting edges (4) of the first and second blades, flat overlapping faces (5,6) that overlap with one another and face each other at least locally during shearing between the first and second blades, the first blade of the pair of blades being attached transversely to the respective drum at an angle with respect to an axis of rotation of the respective drum and in such a way that a plane which is co-planar with said overlapping face (5,6) of the first blade forms an angle with the axis of rotation of the respective drum, a cutting edge of the first blade and the axis of rotation of the respective drum being non-coplanar, the second blade of the pair of blades being attached transversely to the respective drum at an angle with respect to an axis of rotation of the respective drum and in such a way that a plane which is co-planar with said overlapping face (5,6) of the second blade forms an angle with the axis of rotation of the respective drum, a cutting edge of the second blade and the axis of rotation of the respective drum being non-coplanar, the first and second blades of the pair of blades carried by the two drums having opposite diagonal orientations and in such a way as to produce progressive shearing, wherein said overlapping face of each blade of the first and second blades has a double inclination with respect to the respective drum in such a way that the plane which is co-planar with said overlapping face does not intersect the axis of rotation of the respective drum over an active width of the respective drum, said plane intersecting the axis of rotation of the respective drum at a point located outside of a segment of the axis corresponding to the active width of the respective drum, wherein each blade of the pair of blades has a rectilinear cutting edge defined at an intersection of the overlapping face and an outer face of the blade, wherein said double inclination of the first blade prevents the rectilinear cutting edge of the first blade from impacting the second blade during shear cutting, wherein said double inclination of the second blade prevents the rectilinear cutting edge of the second blade from impacting the first blade during shear cutting, and wherein said double inclination is determined with respect to the rectilinear cutting edge of each blade parallel to the axis of rotation of the respective drum as follows: a first inclination of the overlapping face is obtained by rotation of each blade about an axis of rotation which is contained in a plane coplanar with the overlapping face, radial and perpendicular to the axis of rotation of the respective drum, and in such a way as to obtain the progressive shearing, the rotation ranging from 10 to 20, and a second inclination is obtained by rotation of each blade about an axis of rotation which is contained in a plane coplanar with the overlapping face and is parallel to the cutting edge of the blade, the rotation ranging from 4.5 to 14.5.

2. The device according to claim 1, wherein said drive device connecting the drums and synchronising the speed of rotation of said drums comprises two rotating shafts rigidly connected to the two drums, respectively, and a gear system connecting the two shafts, comprising a first toothed wheel and at least one second toothed wheel.

3. The device according to claim 2, wherein each drum and rotating shaft (8;9) thereof consist of a single-piece metal element.

4. The device according to claim 1, wherein the blades of the pair of blades are positioned on the drums in such a way as to allow local overlapping of said overlapping faces of the blades, during shearing, greater than 0.33% of the cutting centre-to-centre distance over the entire length of the cutting edge, for a cutting clearance of less than 0.02 mm.

5. The device according to claim 1, wherein each blade of the pair of blades have a constant cross-section longitudinally.

6. The device according to claim 5, wherein each blade of the pair of blades has at least one flat lateral face for forming said overlapping face at least over a surface portion, said cutting edge being defined at the intersection of the lateral face and the upper outer face.

7. The device according to claim 1, wherein each blade of the pair of blades has at least one flat lateral face forming said overlapping face at least over a surface portion, said cutting edge being defined at the intersection of the lateral face and the outer face.

8. The device according to claim 7, wherein each blade of the pair of blades is fastened to the respective drum at a housing of said respective drum comprising a flat first bearing face for said lateral face carrying the active cutting edge, directly or via a wedge.

9. The device according to claim 8, wherein the housing further comprises a second bearing face perpendicular to the first bearing face and acting as a support for a lower outer face of said blade, directly or via a wedge (37).

10. The device according to claim 9, wherein each blade of the pair of blades has a plurality of bores for screws to pass through, threaded bores extending from the flat first bearing face.

11. The device according to claim 7, wherein each blade of the pair of blades is a reversible blade having two mounting positions on the drums, said blade having two flat, parallel and opposite lateral faces to form, at least over a surface portion, said overlapping face, a first rectilinear cutting edge being defined at the intersection of one of the lateral faces and an upper outer face, and a second rectilinear cutting edge being defined at the intersection of the other lateral face and another lower outer face.

12. The device according to claim 11, wherein each blade of the pair of blades is fastened to the drum at a housing of said drum comprising a flat bearing face for said lateral face carrying the active cutting edge, directly or via a wedge.

13. A method to fragment metal strips into multiple pieces, comprising: providing the shearing device of claim 1; and feeding one or more metal strips into the shearing device.

14. The method according to claim 13, wherein the one or more metal strips have a thickness of less than 1 mm.

15. The method according to claim 13, wherein the one or more metal strips are made of a material having an elongation coefficient greater than 20%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood after reading the following description, accompanied by the appended drawings, in which:

(2) FIG. 1 is a front view of the drums of a shearing device as known from the prior art,

(3) FIG. 1a schematically shows the intersection, at the point I1, of the plane P1 passing through the overlapping face of FIG. 1 with the axis A1 of rotation of the upper drum, this point I1 being located on the segment of the axis A1 corresponding to the width L1 of the drum and, in general, close to the middle of the segment as known from the prior art,

(4) FIG. 1b schematically shows the intersection, at the point I2, of the plane P2 passing through the overlapping face of FIG. 1 with the axis A2 of rotation of the lower drum, this point I2 being located on the segment of the axis A2 corresponding to the width L2 of the drum and, in general, close to the middle of the segment as known from the prior art,

(5) FIG. 2 is a view of the cross-section A-A of FIG. 1,

(6) FIG. 2a is a detailed view showing the overlapping between the blades of the device of FIG. 2,

(7) FIGS. 3 and 4 are right-hand and left-hand views of the counter-rotating drums of a device according to the invention,

(8) FIG. 4a is a detailed view showing the overlapping between blades and the cutting clearance,

(9) FIG. 5 is a view of the two drums of the device according to the invention, the rotating shafts of said drums, and the anti-backlash gears synchronising the opposite rotations of the shafts,

(10) FIG. 5a schematically shows the intersection, at the point I1, of the plane P1 passing through the overlapping face of a blade of the upper drum of FIG. 5 with the axis A1 of rotation of the upper drum, this point I1 being located outside of the segment of the axis A1 corresponding to the width L1 of the drum via the doubly inclined position of the blade on the drum,

(11) FIG. 5b schematically shows the intersection, at the point I2, of the plane P2 passing through the overlapping face of a blade of the lower drum of FIG. 5 with the axis A2 of rotation of the lower drum, this point I2 being located outside of the segment of the axis A2 corresponding to the width L2 of the drum via the doubly inclined position of the blade on the drum,

(12) FIGS. 6 and 7 are respective views of the two drums, lower and upper,

(13) FIG. 8a and FIG. 8b are views of the cross-section A-A of FIG. 6, for a new blade and a worn blade, respectively,

(14) FIG. 9a and FIG. 9b are views of the cross-section C-C of FIG. 7, for a new blade and a worn blade, respectively,

(15) FIG. 9c is a side view of a blade,

(16) FIG. 10 is a cross-sectional view of the device of FIG. 5 along a plane passing through the two axes of rotation of the drums,

(17) FIG. 11 and FIG. 12 are views of the cross-sections B-B and C-C, respectively, as illustrated in FIG. 10,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(18) A shearing device having counter-rotating drums according to the prior art, known to the applicant, is illustrated in FIGS. 1 and 2,

(19) This is a shearing device 1 intended to fragment waste, in particular fragment a metal strip, such as edge scrap, into multiple pieces. This device 1 comprises two counter-rotating drums 2,3 positioned facing each other, the axes of rotation of the drums being substantially parallel.

(20) A drive device (not shown) connects the drums and synchronising the speed of rotation of said drums.

(21) This device 1 comprises at least one pair of blades 20 30; 21 31; 22 32; 23, 33 (and more particularly four pairs of blades), the blades 20, 30; 21, 31; 22, 32; 23, 33 of the pair being carried by the two drums 2,3, respectively, the blades of the pair being intended to cooperate via a shearing effect during the rotation of the drums 2,3 in order to cut the waste.

(22) As illustrated in FIG. 2a, the blades of the pair have, starting from the cutting edge 4 of said blades, flat faces 5,6, called overlapping faces, that overlap with each other and face each other at least locally during the shearing between blades 20, 30; 21, 31; 22, 32; 23, 33.

(23) As illustrated in FIG. 1, each blade is attached transversely to the drum 2;3, at an angle with respect to the axis of rotation A1 (or A2) of the drum 2;3, and in such a way that the plane P1 (or P2) passing through said overlapping face 5,6 of the blade forms an angle with the axis of rotation A1;A2 of the corresponding drum in such a way as to produce progressive shearing.

(24) Moreover, the blades of the pair carried by the two drums 2 and 3 have opposite diagonal orientations.

(25) Thus, the shearing begins locally at the two longitudinal ends of the blades of the pair and moves along the blades up to the two opposite longitudinal ends, which allows the noise of cutting to be reduced quite substantially.

(26) According to the observations of the present applicant, such a prior art has the disadvantages mentioned in the introduction.

(27) The cutting diameter (namely, double the distance between the cutting edge 4 of each blade and the axis of rotation of the corresponding drum A1 or A2) can only be, in these devices of the prior art, very slightly greater than the centre-to-centre distance (distance between the axis A1 and the axis A2) between the two drums, otherwise premature wear of the cutting edges may occur. In such a device of the prior art, the cutting diameter is at most 0.13% greater than the cutting centre-to-centre distance, with a clearance of 0.05 mm.

(28) In this type of device, this size constraint means little overlapping between the blades in order to prevent the blades from impacting each other during the shearing.

(29) This overlapping is illustrated in FIG. 2a by the dimension dr. For products having large thicknesses and high yield strengths, such devices allow cutting via fracturing of the product, without the overlapping and the cutting clearance being crucial to the cutting.

(30) However, it is known that such devices are not suitable for thinner products, namely less than 0.3 mm, and/or soft products, which have significant coefficient of elongation at rupture products (>20%), in that these products are inserted into the clearance between blades, the overlapping thus being insufficient to allow the product to be cut via tearing.

(31) It should be noted that in the devices of the prior art, and as illustrated in FIG. 1, the blade is always positioned on the drum in such a way that the plane P1 (respectively P2) passing through the overlapping face 5 (respectively 6) of the blade intersects the axis of the corresponding drum A1 (or A2) at a point I1 (respectively I2) positioned on the segment of the axis corresponding to the active width of the drum L1 (or L2).

(32) Here, active width means the width of the drum over which the cutting takes place.

(33) Thus, and as illustrated in FIG. 1a, the plane P1 passing through the overlapping face 5 of the blade 20 intersects the axis A1 at a point I1. This point I1 is positioned on the segment of the axis corresponding to the width L1 of the drum 2.

(34) Likewise, and as illustrated in FIG. 1b, the plane P2 passing through the overlapping face 6 intersects the axis A2 at a point I2. This point I2 is positioned on the segment of the axis corresponding to the width L2 of the drum 3.

(35) Thus, and according to the known prior art, the inclination of the blades on the drum of said blades is such that the point of intersection I1 (or I2) is always positioned on the segment of the axis A1 (or A2) corresponding to the active width of the corresponding drum L1 (or L2).

(36) Such a device according to the prior art requires machining the cutting edges of the blades along curved trajectories. The prior art illustrated in FIG. 1 and in FIG. 2 has removable drums. The machining of the cutting edges of the blades is carried out on the removable drum of said blades, on specific machining stations.

(37) The clamping of the blades in the housings of drums is carried out via wedges C, which lead to an ovalisation of the drums when the clamping procedure is not respected.

(38) The invention is the result of the observation of the inventors that it is possible, in such shearing devices, to substantially improve the kinematics of the shearing of the blades and in particular increase the overlapping between the blades by substantially modifying the inclination of the blades with respect to the corresponding drum of said blades, and more particularly the inclination of the overlapping faces of the blades with respect to the drum, with the goal of preventing the blades of the drums from interfering with each other.

(39) Such a configuration according to the invention allows greater overlapping (distance dr in FIG. 4a) during the cutting in comparison to the shearing devices of the known prior art, which promotes the cutting of the waste via tearing and thus the cutting of soft product.

(40) Alternatively, or in addition, this configuration allows the cutting clearance (distance dc) to be reduced in comparison to the shearing devices of the known prior art, which allows thinner waste to be cut.

(41) Such an inclination of the blades is characterised, according to the invention, in that said overlapping face 5;6 of each blade 20; 30; 21; 31; 22, 32; 23;33 is doubly inclined with respect to the corresponding drum 2;3 in such a way that the plane P1 (or P2) passing through said overlapping face 5 (or 6) does not intersect the axis of rotation of the drum 2 (or 3) over the active width L1 (or L2) of the corresponding drum 2 (or 3).

(42) Thus, as illustrated in FIG. 5a, according to the invention, the plane P1 intersects the axis A1 at the point I1, which is located outside of the segment of the axis A1 corresponding to the active width L1 of the upper drum.

(43) Likewise, and as illustrated in FIG. 5b, according to the invention, the plane P2 intersects the axis A2 at a point I2, outside of the segment of the axis A2 corresponding to the active width L2 of the lower drum.

(44) Thus, the invention relates to a shearing device 1 intended to fragment waste, in particular fragment a metal strip into multiple pieces.

(45) This device comprises two counter-rotating drums 2,3 positioned facing each other, the axes of rotation A1 and A2 of the drums being substantially parallel. A drive device connects the drums and synchronises the speed of rotation of said drums. This device can comprise two rotating shafts 8,9 rigidly connected to the two drums 2,3, respectively, as well as a gear comprising a first toothed wheel 90 and at least one second toothed wheel 80,81.

(46) The first toothed wheel 90 is mounted on the shaft 9 and said at least one second toothed wheel 80,81 mounted on the other shaft 8 meshes with the first toothed wheel 90. In order to eliminate the angular play between the drums 2 and 3, two slightly offset toothed wheels 80, 81 of the shaft 8 mesh with the first toothed wheel 90.

(47) Preferably, the drum 2 and the shaft 8 thereof consist of a single-piece metal element. Likewise, the drum 3 and the shaft 9 thereof consist of a single-piece metal element. The risks of bad positioning of the drums on the respective shafts thereof are thus eliminated.

(48) The device comprises at least one pair of blades 20, 30, 21, 31, 22, 32, 23, 33, the blades 20, 30; 21, 31; 22, 32; 23, 33 of the pair being carried by the two drums 2,3, respectively, the blades of the pair being intended to cooperate via a shearing effect during the rotation of the drums 2, 3 in order to cut the waste.

(49) Preferably, the device can comprise a plurality of pairs of blades 20, 30, 21, 31, 22, 32, 23,33. The blades 20, 21, 22, 23 (respectively 30, 31, 32, 33) of each drum are distributed, preferably regularly, on the circumference of the drum 2. According to the embodiment illustrated, each drum 2 (or 3) has four blades 20, 21, 22, 23 (respectively 30, 31, 32, 33), distributed every 90 around the axis of rotation of the drum A1 (respectively A2).

(50) The blades of the or each pair have, starting from the cutting edge 4 of said blades, flat faces, called overlapping faces 5,6, that overlap with each other and face each other at least locally during the shearing between blades 20, 30; 21, 31; 22, 32; 23, 33. Such overlapping, over the distance dr, is illustrated in detail in FIG. 4a.

(51) Each blade is attached transversely to the drum 2;3, at an angle with respect to the axis of rotation A1;A2 of the drum 2;3 and in such a way that the plane passing through said overlapping face 5,6 of the blade forms an angle with the axis of rotation A1;A2 of the corresponding drum, in such a way as to produce progressive shearing.

(52) As illustrated in FIG. 5, the blades 20,30 of a pair carried by the two drums 2,3 have opposite diagonal orientations. As visible in this FIG. 5, the cutting edge of the blade 20 (or 30) and the axis of rotation A1 (or A2) of the corresponding drum are thus not coplanar. As visible in FIGS. 6 and 7, seen in the radial direction passing through the blade, in particular in the middle of said blade, the blade cutting edge 20 and the axis of rotation of the corresponding drum are inclined by an angle corresponding to the first blade inclination allowing the progressive cutting to be obtained, in this case an angle of 15 and as illustrated in FIGS. 6 and 7.

(53) Thus, the shearing begins locally at the two longitudinal ends of the blades 20,30 of the pair and moves along the blades up to the two opposite longitudinal ends, which allows the noise of cutting to be reduced quite substantially.

(54) According to the invention, and as previously explained, said overlapping face 5;6 of each blade 20; 30; 21; 31; 22, 32; 23;33 is inclined with respect to the corresponding drum 2;3 in such a way that the plane P1;P2 passing through said overlapping face 5;6 does not intersect the axis of rotation of the drum 2; 3 over the active width L1;L2 of the drum 2;3.

(55) Such an inclination allows greater overlapping during the shearing to be provided for the same cutting clearance, without the risk of interference between the blades.

(56) According to one embodiment, the blades of a pair are positioned on the drum of said blades in such a way as to allow local overlapping of said overlapping faces 5,6 of the blades, during shearing, greater than 0.33% of the cutting centre-to-centre distance, for a cutting clearance of less than 0.02 mm.

(57) It is thus possible, and contrary to the progressive cutting devices of the prior art, to provide blades having rectilinear cutting edges and not curved cutting edges as taught in particular in documents DE1117358 and FR 2 640 174.

(58) According to one illustrated embodiment, the blades of the pair each have an active rectilinear cutting edge 4 defined at the intersection of the flat overlapping face 5 (or 6) and a flat outer face 50 (or 60), called upper face, of the blade.

(59) According to one embodiment, the blades 20; 30; 21; 31; 22, 32; 23; 33 each have a constant cross-section longitudinally, which simplifies the manufacture of said blades. The body of the blades can have a substantially parallelepiped shape, as illustrated in the drawings.

(60) Each blade 20; 30; 21; 31; 22, 32; 23; 33 can have at least one flat lateral face 51 (or 61) suitable for forming said overlapping face 5 (or 6) at least over a surface portion, said cutting edge 4 being defined at the intersection of the lateral face 51 (or 61) and the upper outer face 50 (or 60).

(61) Advantageously, each blade of the pair can be a reversible blade having two mounting positions on the drum, said blade having two lateral faces 51,52; 61,62, parallel and opposite, suitable for each forming, at least over a surface portion, said overlapping face 5,5;6,6, a first rectilinear cutting edge 4 being defined at the intersection of one of the lateral faces and an upper outer face 50;60, and a second rectilinear cutting edge 4 being defined at the intersection of the other lateral face 52;62 and another lower outer face 53;63.

(62) When the first blade cutting edge 4 is worn, it is possible to remove the blade, turn said blade over, and mount said blade in the other mounting position thereof in order to expose the second cutting edge 4.

(63) Preferably, each blade is fastened to the drum 2 (or 3) at a housing of said drum comprising a flat bearing face 24 (or 34) for said lateral face carrying the active cutting edge, directly or via a wedge.

(64) This flat bearing face 24 or 34 thus forms a reference plane for the positioning of the active cutting edge of the blade and the overlapping face 5 or 6 thereof.

(65) During the assembly, the lateral face 51 carrying the active cutting edge is pressed directly against this flat bearing face 24, as illustrated in FIGS. 9a and 9b as a non-limiting example, or via a wedge 35 having a predetermined thickness as illustrated in FIGS. 8a and 8b.

(66) Here, active cutting edge means, in the case of a reversible blade having a plurality of cutting edges, the cutting edge (4 or 4) exposed to work in shearing, and not the passive cutting edge not used.

(67) Such an arrangement allows the circumferential positions of the blades on the drum of said blades (2 or 3) to be definitively adjusted, without this adjustment being dependent on the wear of the blades and in particular on the reduction in thickness of said blades. Regardless of the reduction in the thickness of the blades between the lateral faces of said blades, the circumferential positions of the blades on the drum is fixed and no longer has to be modified in case of wear to the blades, contrary to the prior art taught by document FR 2 640 174.

(68) Thus, the adjustment via the wedge 34 does not change between a new blade as illustrated in FIG. 8a and a worn blade, illustrated in FIG. 8b, which has a smaller thickness.

(69) Likewise, the direct adjustment via the bearing face 24 does not change between a new blade as illustrated in FIG. 9a and a worn blade, illustrated in FIG. 9b, which has a smaller thickness.

(70) The reduction in thickness between the lateral faces, caused by wear, does not have to be taken into account, and such that this will be the case if the lateral face of the opposite blade were to be pressed against the face carrying the active cutting edge of the blade, as taught by document FR 2640174. Such an assembly, although not preferred, is still possible.

(71) Preferably, the housing comprises, besides the flat bearing face, called first bearing face 24;34, for said lateral face of said blade, a second bearing face 26;36 substantially perpendicular to the first bearing face and acting as a support for a lower outer face 53;63 of said blade, directly or preferably via a wedge 37. This wedge 37 having a predetermined thickness allows the overlap (distance dr) between the blades of the same pair to be adjusted.

(72) Each blade has a plurality of bores 38 for screws 39 to pass through. These bores are distributed along the length of each blade, for example each bore passing from one lateral face 51 (respectively 61) to the other lateral face 52 (respectively 62) of the blade. The attachment screws cooperating with threaded bores preferably extending from the flat bearing face for said lateral face.

(73) The rotating shafts are guided in rotation via bearings, which limits the axial play, with a motor allowing the drums to be driven in rotation.

(74) Naturally, other embodiments could have been envisaged without going beyond the scope of the invention defined by the claims below.

NOMENCLATURE

(75) Invention: (FIGS. 3 to 12)

(76) 1. Shearing device, 2,3. Counter-rotating drums, upper and lower, 4. Blade cutting edge (First cutting edge), 4. Blade cutting edge (Second reversible-blade cutting edge) 5,6. Overlapping faces of the blades of one pair, 5,6. Overlapping faces of the blades of one pair starting from the second cutting edge (4), 8. Rotating shaft (drum 2), 9. Rotating shaft (drum 3), 20, 21, 22, 23. Upper drum blades, 30, 31, 32, 33. Lower drum blades, 24. Bearing face drum 2 (First bearing face), 34. Bearing face drum 3 (First bearing face), 26. Second bearing face (drum 2), 36. Second bearing face (drum 3), 35. Wedge (First bearing face), 37. Wedge (Second bearing face), 38. Bores (for screws), 39. Screws, 50. Upper outer face of the blade (labelled 20), 51,52. Lateral faces of the blade (labelled 20), 53. Lower outer face (blade labelled 20), 60. Upper outer face of the blade (labelled 30), 61,62. Lateral faces of the blade (labelled 30), 63. Lower outer face (blade labelled 30), A1. Axis of rotation upper drum, A2. Axis of rotation lower drum, P1. Plane passing through the overlapping face (5), P2. Plane passing through the overlapping face (6), I1. Point of intersection between the plane P1 and the axis A1, I2. Point of intersection between the plane P2 and the axis A2, L1. Active width of the upper drum, L2. Active width of the lower drum, dr. Overlap between the blades of the same pair, dc. Cutting clearance.
Prior Art: (FIGS. 1 and 2): 1. Shearing device, 2,3. Counter-rotating drums, upper and lower, 4. Blade cutting edge, 5,6, Overlapping faces of the blades of one pair, 20, 21, 22, 23. Upper drum blades, 30, 31, 32, 33. Lower drum blades, A1. Axis of rotation upper drum, A2. Axis of rotation lower drum, C. Clamping wedges, P1. Plane passing through the overlapping face (5), P2. Plane passing through the overlapping face (6), I1. Point of intersection between the plane P1 and the axis A1, I2. Point of intersection between the plane P2 and the axis A2, L1. Active width of the upper drum, L2. Active width of the lower drum, dr. Overlap between blades.