A MACHINE FOR SMOOTHING/POLISHING FLAT SLABS, IN PARTICULAR OF CERAMIC MATERIAL, NATURAL STONE, OR OTHER EQUIVALENT MATERIALS

Abstract: For each grinding wheel (10) there is provided a bush (21) which supports an individual grinding wheel (10) and is rotatably coupled to a longitudinal member (41) about a fixed axis of rotation (S) perpendicular to the support surface (P) for the slabs; the grinding wheel (10) is rotatably coupled about its axis (M) to the longitudinal member (41); the axis (M) forms a small angle with the axis (S) of the bush (21), the centre (C) of the active face (11') of the grinding wheel (10) being positioned on or relatively close to the axis (S) of the bush (21); both the bush (21) and the grinding wheel (10) are rotated about their respective axes (S and M)

Description: Description A MACHINE FOR SMOOTHING/POLISHING FLAT SLABS, IN PARTICULAR OF CERAMIC MATERIAL, NATURAL STONE, OR OTHER EQUIVALENT MATERIALS Technical Field This invention relates to machines for smoothing/polishing flat slabs, in particular slabs of ceramic material (ceramic tiles), of natural stone (marble, granite and the like), or other equivalent materials. The invention can however be used for other materials, for example metal plates. Background Art For a considerable time it has been industrial practice to smooth or polish the major face, ie that intended to remain exposed, of paving and facing slabs, not only in the case of natural stone slabs but also in the case of ceramic tiles or other equivalent materials. The purpose of this is to make said major face flat, to polish it or possibly to attain a required thickness. In particular the invention relates to those machines which use a plurality of grinding wheels rotating about their axis, their active face being in the form of a circular ring perpendicular to their axis of rotation (so-called cup grinding wheels), and comprise means for advancing the slabs below the field of action of the grinding wheels in contact with the active face of these latter. The known machines of this type comprise a unit (so-called "head") rotating at a relatively high speed (about 400 r.p.m.) about an axis perpendicular to the underlying surface on which the slabs rest, and able to slide axially both to compensate tool wear and to follow the slab irregularities. Said head carries a plurality of cup grinding wheels rotating about their axis, which is slightly inclined to the vertical so that at any moment only a small part of the active face of the grinding wheels is in contact with the slab. The axes of rotation of said grinding wheels are spaced from the axis of rotation of the head so that while the grinding wheels rotate about themselves, they are rotated by the head which rotates about its own axis while they act on the underlying slab. Other machines are also known which instead of the cup grinding wheels use a like number of cylindrical grinding wheels rotating about a horizontal axis, or tools in the form of a cylindrical sector rocking about a horizontal axis and acting with their cylindrical surface on the upper face of the slab while they are turned by the head which rotates about its vertical axis. Known machines have however various drawbacks, namely: a polishing effect which is not constant in the various regions of the slab; difficulties in working medium and small dimension slabs because of the fact that by virtue of the head dimensions and geometry only one head at a time can operate on each slab so that its grinding wheels rise from and descend onto the slab continuously. This means that the slabs are never perfectly at rest relative to the surface on which they rest, but instead undergo small vertical and horizontal movements, with consequent machining inaccuracies and the need to advance the slabs slowly relative to the machine; an intrinsic lack of machine flexibility with respect to the dimensions of medium and small slabs, in that the head dimensions should be related to the slab dimensions; the need to move the head transversely in the case of large slabs, with a consequent reduction in the slab advancement speed. Disclosure of invention The object of the present invention is to provide an improved machine which overcomes said drawbacks. Said object is attained by the machine according to the invention as characterised in the claims. The invention is described in detail hereinafter with the aid of the accompanying figures which illustrate some embodiments thereof. Figure 1 is a section on a vertical plane through a first embodiment of an individual grinding wheel. Figure 2 is a view of a first embodiment of the entire machine using the grinding wheels of Figure 1 , taken in a direction parallel to the direction of advancement of the slabs. Figure 3 is a section on the plane III-III of Figure 2. Figure 4 is an enlarged detail of Figure 3. Figure 5 is a section on a vertical plane through a second embodiment of an individual grinding wheel. Figure 6 shows the machine of Figure 3 using grinding wheels of Figure 5. Figure 7 is a section on an axial vertical plane through a second embodiment of the machine using grinding wheels of Figure 5. Figure 8 shows schematically the gearing of Figure 7. The machine comprises a plurality of grinding wheels each indicated overall by 10. Each grinding wheel 10 has a tool 11 (based on diamond, carbon, silicon or equivalent material granules) the active face 11' (ie the face which operates on the slab) of which is substantially flat, is in the form of a circular ring and is perpendicular to the axis of rotation M of the grinding wheel 10. More specifically, the shape which the face 11' assumes with use is a frusto-conical surface shape, the axis of which coincides with the axis M, and the vertex angle of which is nearly flat for the reasons given hereinafter. The grinding wheel 10 comprises a shaft 12 coaxial with M, to the lower end of which there is fixed a gripping member 13 into which there is securely inserted a disc 14, to the lower face of which the abrasive tool 11 is fixed. The machine also comprises a structure 41 , 60 (described hereinafter) which supports the grinding wheels above the slabs 3 to be machined. With the machine there is also associated a belt conveyor 16, for example of the type comprising a horizontal conveyor belt 17 resting on a fixed surface 18 and arranged to advance the slabs 3 relative to the field of action of the grinding wheels 10 in contact with the faces 11'. The support surface P defined by the conveyor 16 is a normally horizontal and geometrically precise surface, in that it represents the reference plane for the machining of the slabs 3. For each grinding wheel there is provided a means 20 for supporting a single grinding wheel 10 and rotatably coupled to the support structure 41 , 60 on an axis of rotation S which is fixed relative to the structure 41 , 60 and perpendicular to the surface P on which the slabs 3 rest. Specifically, each means 20 comprises a cylindrical bush 21 the outer cylindrical surface of which is rotatably engaged, via bearings 22, in a respective cylindrical through cavity 42 provided in the support structure 41 , 60 such as to be able to rotate about its axis S. In Figure 1 the cavity 42 is provided directly within the structure 41 whereas in Figure 5 a bush 410 comprising said cavity 42 is joined to the structure 41, 60. The bush 21 comprises a central cavity 23 of cylindrical surface, the axis of which is inclined (specifically at a small angle of inclination) to the axis S. The grinding wheel shaft 12 is rotatable coupled, via bearings 24, with the cavity 23 such that its axis of rotation M coincides with the axis of the cavity 23. The axis M is therefore inclined at a small angle of inclination to the axis S of. the means 20. In addition the geometrical centre C of the active face 11' of the tool 11 is positioned either on the axis S or close to it. The centre C represents the point of intersection between the ideal plane (or rather the frusto-conical surface) on which the face 11' lies and the axis M. The angle between the two axes M and S ensures that at any moment only a part 11a of the face 11' operates on the surface of the slab 3 so as to create a relief angle from which the material particles are removed from the machining region. This angle between the axes M and S is conveniently just a few degrees or some tenths of a degree. Respective means are associated both with the bush 21 and with the grinding wheel 10 to rotate both about the respective axes S and M. In the embodiment shown in Figure 1 , the upper portion of the bush 21 projects from the cavity 42 and has fixed to it a pulley 25 which is rotated about the axis S by a transmission belt 31 driven by a motor 33. Likewise the upper portion of the shaft 12 projects from the cavity 23 and has fixed to it a pulley 15 which is rotated about the axis M by a transmission belt 32 driven by a motor 34. In operation, the grinding wheel 10 is rotated about its axis M while at the same time the axis M rotates about the axis S to move over a conical surface, the vertex of which lies substantially within the axial dimension of the grinding wheel 10. For example, this vertex is positioned within the central region of the pulley 15 to reduce the rocking of this latter to a minimum. As the axis M is inclined to the axis S, the active face 11', as stated, operates at any moment only with a portion 11a thereof (this portion changing continuously) which is distant from the axis S by approximately the radius of the active face 11'. As the axis M rotates about the axis S, the portion 11a also rotates about the axis S to produce a machining region in the form of a circular ring. These movements are obviously combined with the relatively slow movement of the slabs 3 carried by the conveyor 16. In the machine embodiment shown in Figures 2-4, the support structure for the grinding wheels 10 comprises at least one horizontal longitudinal member 41 positioned transverse to the direction of advancement of the slabs 3 and carrying at least one aligned plurality of support means 20 with respective grinding wheels, the tools of which are positioned very close to each other. The longitudinal member 41 is arranged to move vertically relative to the support surface P and is urged downwards with the grinding wheels in contact with the underlying slabs 3, at constant force. The longitudinal member 41 carries at least one pair of rows of grinding wheels 10 (Figures 3 and 4 show two pairs of rows) in which the tools 11 are close and almost tangential to each other, the rows being offset in pairs such that the axes of the grinding wheels are positioned at the vertices of an ideal lattice formed from equilateral triangles. The pulleys 25 of the bushes 21 are close together, and between them there runs a transmission belt 31 which simultaneously engages the pulleys 25 of one row and those of the adjacent row. Hence a single belt 31 acting with both its branches operates four rows of bushes 21. Likewise, the pulleys 15 of the shafts 12 are also relatively close together, a transmission belt 32 simultaneously engaging the pulleys 15 of one row and those of the adjacent row following the same path as the other belt 31 but at a higher level than this. The belts 31 and 32 are driven by respective pulleys 35 and 36, themselves driven by respective motors 33 and 34. The return pulleys for the belts 31 and 32 are indicated by 37 and 38. Each row of tools 11 has a length equal to the useful width of the surface P on which the slabs 3 move, these completely filling this width as they are positioned one against the other to define a continuous surface of indefinite length. In order to best utilize all the tools 11, the longitudinal member 41 can be moved with translational movement horizontally and transversely, forwards and backwards, through a distance substantially equal to the radius of the tools 11 so that, in turn, all the end tools 11 of the row completely enter the plane of the slabs 3. In the embodiment shown in Figure 2, the longitudinal member 41 is pivoted at one end, on a horizontal axis, to two vertical columns 43 (the figure shows only one column 43, the other being hidden by this latter) which are slidable as an exact fit within a guide member 44. This is slidingly supported by two horizontal, fixed cylindrical guides supported by a fixed base 46 which also supports the supports 47 for the conveyor 16. To the member 44 there is fixed a bracket 48, between which and the longitudinal member 41 there is positioned a cylinder-piston unit 49 which normally maintains the longitudinal member 41 in a horizontal position but can raise it vertically to allow maintenance, inspection etc. to be carried out. By other means (not shown) , the longitudinal member 41 is thrust downwards so that the grinding wheels 10 operate on the slabs 3 with the required pressure, the longitudinal member 41 being also able to slide vertically both to compensate tool wear and to follow slab irregularities. Alternatively, the cylinder-piston unit 49 can be used to provide the required pressure on the slabs together with the weight of the equipment. There is also provided parallel to the conveyor 16 a longitudinal beam 51 driven with horizontal reciprocating movement. The member 44 is fixed (in a manner which enables it to be released) to the beam 51 so as to move the longitudinal member 41 forwards and backwards in a transverse direction above the slabs 3. In the embodiment shown in Figure 5, the bush 21 is rigid with a pulley 25 which is rotated about the axis S by a transmission belt 31 driven by a motor 33. The pulley 25 projects upwards beyond the upper face of the structure 41 and of the bush 410 and is joined to the bush 21 by one or more shafts 251 which for space considerations can be curved or out of alignment as shown in Figure 1. An internal toothing 411 is fixed to the top of the bush 410 (and hence rigid with the support structure 41, 60), in a manner coaxial with the axis S of the means 20. A gearwheel 121 coaxial with the axis M of the grinding wheel 10 is fixed to the top of the shaft 12 and engages the toothing 411. In operation, the bush 21 is rotated (by the pulley 25 and the driven belt 31) about the axis S. The bush 21 drags with it the shaft 12, the axis M of which rotates about the axis S to describe a conical surface. In this manner, the gearwheel 121 rolls on the toothing 411 to rotate the shaft 12 (and the grinding wheel 10) about its axis M. Hence, by motorizing the bush 21 the grinding wheel 10 is also rotated, with the ratio of the rotation of the grinding wheel 10 about the axis M to the rotation of the axis M about the axis S depending on the geometrical relationship between the pitch circle diameters of the gearwheel 121 and of the toothing 411, which can be formed in the most convenient manner. The point of intersection between the axes M and S can be positioned as close as possible to the active face 11'. The portion 11a hence defines a circular ring virtually identical to the circular ring defined in plan view by the tool 11 , this having been found advantageous in practice for the proper operation of the tool. In addition, the angle of inclination between the axes S and M can be advantageously increased compared with the embodiment shown in Figure 1 so that the tool 11 operates in the most favourable geometrical configuration. Figure 6 shows the same machine embodiment as shown in Figures 2- 4, but with the aforedescribed modifications relative to the motorization of the grinding wheels 10 and bushes 21. In this embodiment there is only one belt 31 driven by the motor 33 to simultaneously engage all the pulleys 25 (as already seen). Hence a single belt 31 operates all four rows of bushes 21 and hence all four rows of grinding wheels 10. By means of the present invention a machine can be formed in which several grinding wheels act at the same time on each slab 3, even if relatively small. For example, Figures 3 and 6 show tiles 3a and 3b having sides of 20 cm and 10 cm respectively, ie small slabs. In addition the axis M of the grinding wheels 10 is virtually stationary. Moreover, the polishing action on each slab 3 acts in circles which are small, numerous and mutually cross, to determine an extremely valid final polishing effect substantially constant in each region of the slab. Even if small, the slabs are not subjected to horizontal or vertical thrusts and remain constantly and effectively pressed rigidly onto the conveyor 16. Slabs of various dimensions can be machined by the same machine and the same tools by simply positioning the slabs side by side in mutual contact in the transverse direction in addition to longitudinally. Moreover the production potential of the machine is much greater than known machines. Figure 7 shows a different embodiment of the structure supporting the grinding wheels 10. This support structure comprises a cylindrical head 60 rotating about a central main shaft 61 of vertical axis, which is driven by a suitable motor (not shown). The head 60 supports a plurality of units comprising a grinding wheel 10 and support means 20 as shown in Figure 5, these being positioned at equal distance from the axis A, the arrangement being such that the tools 11 are close together, with their centres angularly equidistant. Specifically, the head 60 supports a plurality of support means 20, for each of which the bush 21 is rotationally coupled to the head 60, via bearings 22, within a respective cylindrical seat 62 in the head 60. The bush 21 is free to rotate relative to the head 60 about its axis S, which is vertical (ie perpendicular to the surface P). To each support means 20 there is rotationally coupled a respective grinding wheel 10 free to rotate about its axis M, which is inclined to the axis S (as already illustrated with reference to Figure 5). The head 60 is rotated by one or more idle planet gears 63 (four gears 63 are shown in Figure 7) supported by shafts 631 carried by a cover 68 which is made fixed with respect to the rotation of the shaft 61 (by means not shown) and covers the head 60. The gears 63 engage a gearwheel 64 coaxial and rigid with the main shaft 61 , and simultaneously engage internal toothing 65 rigid with the head 60. The rotation of the shaft 61 hence causes the head 60 to rotate, via the planet gears 63, with a suitable transmission ratio, for example with an angular speed of 1/4 the angular speed of the shaft 61. As a result of the rotation of the head 60, the support means 20 are rotated about their axes S. For this purpose each bush 21 is joined by its shaft (or shafts) 251 to a coaxial gearwheel 66, all said gearwheels 66 engaging a gearwheel 67 coaxial and rigid with the shaft 61. Consequently the rotation of the head 61 drags with it the gearwheels 66 which, engaged by the gearwheel 67, are rotated (and with them the respective means 20) about their axes S with a suitable transmission ratio, for example with an angular speed about 7 times the angular speed of the head 20. A plurality of said internal toothings 411 are fixed to the head 60, each coaxial with the axis S of the relative means 20, and with which the gearwheel 121 fixed to the shaft 12 of the respective grinding wheel 20 engages. Consequently, as already described with reference to Figure 5, the grinding wheels 10 rotate as a result of the rotation of the support means 20. Figure 8 schematically shows the aforedescribed gearing and the direction of rotation of the various gearwheels. The result is that while the grinding wheels 10 operate on the slabs 3, each describing a working region in the form of a circular ring (as already described), the grinding wheels undergo a circular path about the central axis A. In certain aspects this embodiment behaves as the traditional heads carrying grinding wheels rotating with a circular path. However the result of the various movements to which each grinding wheel 10 is subjected, combined with the advancement movement of the slabs 3, produces on each slab 3 a polishing action extending as numerous small circles which mutually cross to determine an extremely valid polishing effect which is substantially constant in every region of the slab 3. Moreover the head 60 can be rotated at a lower speed, with the result that the various members are less stressed.

Claims: Claims 1. A machine for smoothing/polishing flat slabs in particular of ceramic material, natural stone or other equivalent materials, comprising: a plurality of grinding wheels (10) arranged to rotate about their axis (M) and having their active face (11') frusto-conical or substantially flat and perpendicular to their axis of rotation (M); a structure (41) arranged to support said grinding wheels (10) above the slabs (3) to be machined; said slabs (3) being advanced along a support surface (P) through the field of action of the grinding wheels (10); characterised by comprising, for each grinding wheel (10): a means (20) supporting an individual grinding wheel (10) and rotatably coupled to the support structure (41) about an axis of rotation (S) perpendicular to the underlying support surface (P) for the slabs; the grinding wheel (10) being rotatably coupled about its axis (M) to the support means (20), the axis (M) of the grinding wheel (10) forming an acute angle with the axis (S) of the support means (20), and the centre (C) of the active face (11') of the grinding wheel (10) being positioned on or relatively close to the axis (S) of the support means (20); means (25, 31, 33) for rotating the support means (20) about its axis (S); and means (15, 32, 34) for rotating the grinding wheel (10) about its axis (M). 2. A machine as claimed in claim 1, characterised in that each support means (20) comprises a cylindrical bush (21) having its cylindrical outer surface rotatably coupled about the axis of rotation (S) of the support means (20) to the support structure (41), and having a cylindrical central cavity (23) the axis of which is inclined by a small angle to the axis (S) of the means (20), the grinding wheel (10) having an axial shaft (12) rotatably coupled to the cavity (23) of the bush (21) such that its axis (M) coincides with the axis of the cavity (23). 3. A machine as claimed in claim 1, characterised by comprising, for rotating the grinding wheel (10), a gearwheel (121) rigid with the shaft (12) of the grinding wheel and coaxial with the axis (M) thereof, to engage internal toothing (411) rigid with the support structure (41, 61) and coaxial with the axis (S) of the support means (20). 4. A machine as claimed in claim 3, characterised in that the point of intersection between the axis (M) of the grinding wheel (10) and the axis (S) of the support means (20) is close to the active face (11') of the grinding wheel (10). 5. A machine as claimed in claim 1, characterised in that the support structure for the grinding wheels (10) comprises at least one horizontal longitudinal member (41) positioned transversely to the direction of advancement of the slabs (3), to support at least one aligned plurality of support means (20) carrying respective grinding wheels (10), the tools (11) of which are relatively close together; said longitudinal member (41) being arranged to move vertically relative to the support surface (P) and being urged downwards with the tools (11) in contact with the slabs (3), at constant force. 6. A machine as claimed in claim 5, characterised in that said longitudinal member (41) carries at least one pair of rows of grinding wheels (10), the tools (11) being almost mutually tangential and the two rows being offset from each other to define an equilateral triangle arrangement. 7. A machine as claimed in claim 4, characterised in that respective pulleys (25, 15) are associated with the bushes (21) and with the shafts (12) of the grinding wheels (10), the pulleys (25, 15) of one row being positioned close to the corresponding pulleys (25, 15) of the adjacent row, and by further comprising, at least for the pulleys (25) of the bushes (21), a respective transmission belt (31) which engages the pulleys (25) of one row and those of the adjacent row simultaneously. 8. A machine as claimed in claim 3, characterised in that the longitudinal member (41) is moved with translational movement horizontally and transversely, forwards and backwards so that, in turn, the end tools (11) of the row completely enter the plane of the slabs 3. 9. A machine as claimed in claim 3, characterised by comprising: a head (60) rotating about a motorized central main shaft (61) of vertical axis A which supports a plurality of said support means (20) rotationally coupled to the rotary head (60) about the vertical axes of rotation (S) of said means (20), said axes (S) being positioned at an equal distance from the axis (A) of the main shaft (61 ); a plurality of grinding wheels (10) each coupled in the said manner to a respective support means (20); means (63-65) for rotating the head (20); means (66, 67) for rotating the support means (20) about their axes (S) following the rotation of the head (60); and a plurality of said internal toothings (411) rigid with the head (20) and each coaxial with the axis (S) of the respective support means (20), they being engaged by the gearwheels (121) of the grinding wheel shafts (12). 10. A machine as claimed in claim 9, characterised by comprising, for rotating the support means (20), a plurality of gearwheels (66) each rigid with a respective support means (20), and a gearwheel (67) coaxial and rigid with the main shaft (61) and engaged by said gearwheels (66). 11. A machine as claimed in claim 10, characterised by comprising, for rotating the head (60), one or more planet gears (63) supported by the head (60) and engaging both a gearwheel (64) coaxial and rigid with the main shaft (61) and, simultaneously, an internal toothing (65) rigid with the head (60), the main shaft (61) being rotated by a motor.

Inventors: SPADONI GIULIANO, SPADONI, GIULIANO
Applicants: SIRT SOCIETA IND RICERCA TECNO, SPADONI GIULIANO, SIRT SOCIETA' INDUSTRIALE RICERCA TECNOLOGICA S.R., SPADONI, GIULIANO
Application year: 1995
Main classification: B24B41
IPC codes: B24B7, B24B27, B24B41