The invention concerns a facing machine for large plates of natural stone, e.g. granite and hard stone slabs, which machine is adapted to dress such slabs by an improved process that makes the whole operation easier and quicker to complete even as the machine is fed slabs of varying size in close succession.

The ■ state of the art provides, among numbers of different machines designed for dressing wide slabs and/or surfaces, a granite slab-sizing machine of the kind described in Patent No. FR 2521475, wherein a pair of rollers mounted at a slab surface grooving station are driven rotatively about a transverse axis to the slab direction of advance. The rollers comprise a plurality of cutting disks provided with diamond tool teeth and spaced apart to span the slab width, with each roller disk being in intermeshed relationship with disks of a leading/trailing one of the rollers. The slabs are then taken, . on an underlying belt conveyor, to a dressing station which includes a plurality of diamond grinding wheels mounted for rotation about a vertical axis. The state of the art also provides a facing machine for ceramic tiles, as described in PCT Patent Application Publication No. WO 03/028968,- which comprises a structure arranged to hold and set for cutting depth at least a pair of rollers mounted at a grooving station and being driven rotatively about a transverse axis to the direction of advance of the tiles, the tiles being transported on a belt conveyor beneath. The rollers comprise a plurality of cutting disks provided with diamond tool teeth and spaced apart to span the tile width. The machine further comprises a dressing station that includes a plurality of diamond grinding wheels mounted for rotation about a vertical axis. In this prior machine, the set of disks in one roller have all the same working diameter; also, the rollers comprised of the cutting disks are carried on a common •holding structure which is adjustable to set the cutting depth of the disks. There are two such rollers mounted in a row along the direction of advance of the tiles, with the disks of one roller set to cut into the lands left between grooves by the disks of the other roller. The roller holding structure is mounted to swing around a parallel shaft to the work surface in a transverse direction to the direction of advance of the latter, and is associated with a swing movement setting and locking device effective to compensate for variations in the cutting diameters of the mounted rollers. The grinding wheels comprise rotary heads holding diamond tools that are rotated about a vertical axis jointly with the tool heads. In processing wide slabs of hard stone material, slabs of different sizes may have to be fed in random succession. This involves re-setting and replacing the rollers with rollers of wider or narrower working face. A condition for the disks to operate as expected is that all the cutting edges across the roller generatrix line should be at work simultaneously. A disk left out of work is bound to elude wear and retain a larger diameter than the disks kept engaged with the work. To process granite and hard stone, diamond tools of appropriate hardness to ensure a sufficiently long working life are required. However, wear and loss of diameter cannot be avoided during the process, therefore all the disks in one roller must be kept at work simultaneously. Setting conventional facing machines used for processing the surfaces of wide slabs is a time-consuming procedure due to that roller sets with a specific working face width have to be mounted each time. Consequently, slabs can be processed in large quantities only if they are trie same width in the transverse direction to the direction of. movement of their transport. Actually, wide slabs obtained from a natural block are seldom to one and the same width dimension. The largest slab size processed is usually about 2000x3500 mm, while the smallest may not exceed 1000 mm in width. Thus, a width variation of 1000 mm exists between slabs which is quite substantial, and in order to have all the cutting disks in one roller set to work simultaneously as mentioned above, the time allowance for machine setup also has to be extended. Finally, the design of dressing machines has favored the use of heavy vertical-axis rotary heads carrying a variety of oscillating or rotating tools for the purpose of maintaining a uniform cutting action across the slab surfaces, the rotary heads being mounted to a swing beam through cross-reciprocating devices for when the slab width exceeds the span of the heads. Most material removal has been effected using vertical-axis rotary heads equipped with rotating tools, such as varying forms of diamond-bit rollers. As a result, the pressure load applied by the rotating tools to a slab surface may crack and/or break it. The high pressure force exerted through the generatrix line of the roller across the cutting face can easily damage a slab which may be but 2 cm thick.

There exists, therefore, a demand for improvements effective to overcome the aforementioned problems, particularly as regards the capability to. process interleaved slabs of different widths fed in random order to a dressing machine on their transport, without the need to have the machine stopped for a lengthy setting procedure at each change of slab width.

It can be appreciated from the foregoing that the technical problem is one of providing a machine for facing wide slabs, which machine should incorporate a roller adjuster adapted to re-position the- cutting disks in the rollers to suit the width of each slab being processed, whereby the tools can be set as required without the operation involving long downtime for the machine and/or the availability of qualified personnel.

The above technical problem is solved by the invention providing a facing machine for large plates of natural stone, e.g. granite and hard stone slabs, which machine comprises: a pair of rollers driven rotatively about a transverse axis to the slab direction of advance and mounted at a work surface grooving station; wherein the rollers consist of a plurality of cutting disks having the same working diameter or being adjustable in height so as to compensate for minor variations in the roller diameters; wherein the cutting disks are fitted with diamond tool teeth and aligned together in spaced apart relationship across the slab width so as to intermesh with the cutting disks of a leading/trailing one of the rollers; and wherein the slabs are transported on a belt conveyor to a subsequent facing station where the ridges between grooves are removed; characterized in that at least one of said rollers is provided with an adjuster for setting its position relative to the other of said rollers and to a holding structure along a transverse direction to the slab direction of advance on said belt conveyor for the purpose of allowing full or partial or no interleave between grooves cut by said disks, according to the width of a slab being processed. In a preferred embodiment, the cutting face of each disk is slightly smaller than the minimum spacing between aligned disks in the roller. In a preferred embodiment, said disks are closely spaced apart in the rollers, but spaced twice the distance at either roller ends. In a preferred embodiment, the disks of the leading roller being mounted at close spacings are set to work near one longitudinal edge of a slab, whereas the disks of the trailing roller being mounted at close spacings are set to work near the other longitudinal edge of the slab, thereby the disks mounted at twice said spacing are set to cut interleaved or non-interleaved grooves according to the slab width. Also in a preferred embodiment, at least one of said rollers is mounted rotatively on a carriage for a traversing movement to the slab direction of advance along crosswise guide rails that are connected to a holding structure, in turn adjustable in height to set the cutting depth of the tool teeth into the slab surface. In another preferred embodiment, both said rollers are mounted rotatively on carriages for traversing movement to the slab direction of advance. In another preferred embodiment, the position(s) of said carriage-mounted roller(s) for traversing movement to the slab direction of advance is(are) set by means of a rack-and-pinion mechanism driven off a geared motor on each carriage. In another preferred embodiment, a carriage braking or locking mechanism is provided additionally to the roller setting mechanism in the transverse direction. In another preferred embodiment, the slab surface grooving station is followed by a dressing station where the ridges left over from the grooving station are removed, said dressing station comprising a machine equipped with a swing beam which is oscillated in the transverse direction and carries a plurality of rotary heads mounted for rotation about a vertical axis and provided with swinging or rotating diamond tools. In a further preferred embodiment, a slab width gauging device is associated with the slab surface grooving station, either directly ahead of or a suitable distance away from it along the slab transport, said gauging device being effective to control the roller(s) positioning in the transverse direction.

One embodiment of the invention is shown, by way of example only, in the four accompanying drawings, where: Figure 1 is a cross- sectional view, taken along the slab direction of advance and through the roller pair at the slab grooving station; Figure 2 is a perspective view of the wide slab facing machine comprising the slab grooving station shown in Figure 1 and a dressing station with a swing beam which is oscillated in a transverse direction to the slab and carries conventional heads for rotation about a vertical axis; Figures 3, 4 and 5 are plan views of the grooving station construction, outside of the rollers and a slab being processed, showing it at three typical settings for processing narrow, wide, and intermediate width slabs; Figure 6 is a perspective representation of the longitudinal section of the grooving station shown in Figure 1; and Figure 7 is a perspective view of the grooving station complete with its roller holding, driving and setting arrangements.

Shown in Figure 1 are cutting disks 1 which are fitted with diamond tool teeth 2 and assembled into leading and trailing rollers 3 and 4 along a direction A of advance of .the slabs through a grooving station 5. Each roller is driven by a respective motor 6. Each roller is mounted rotatively on a respective carriage 7, which carriage is driven for a traversing movement to the slabs along guide rails 8, the latter being adjustable for height on a shift frame 9 that is movable in a vertical direction to the work surface. The frame 9 is moved by means of mechanical actuators 10, in turn driven through angle drives 11 off a common motor 12. The shift frame is adjusted for height relative to an overhead structure 13 that carries the grooving station 5 in order to set the cutting depth of the disk tool teeth 2 into the slab surface. Each carriage 7 is positioned in. the transverse direction by means of a rack 14 in mesh engagement with a drive pinion (not shown) of a respective gear motor 15. These racks are attached with their ends rigidly to the shift frame 9, as are the carriage guide rails 8. In Figure 2, a dressing station 16 for removing the ridges between grooves is shown in which a beam 17 carrying the vertical- axis rotary heads 18, here eight such heads, can be oscillated in a crosswise direction, the station 16 being placed downstream of the grooving station 5 along the direction A. A conventional gauging device .19 is provided upstream of the grooving station, and is operative to gauge a slab width before the slab enters the working area.of the grooving station 5. When a slab edge trimmer is provided upstream .of the facing machine, said device may be placed directly ahead of said station 5, as shown. When no such trimmer is provided, the gauging device may be placed a suitable distance ahead the grooving station 5 to gauge the slab width dimension and control the transverse positioning of the rollers 3, 4 at the grooving station 5 to suit the slab width. In Figures 3, 4 and 5, slabs 20 of different widths, rotary holders 21 for rollers 3 and 4 attached to carriages 7 (omitted from these Figures), and roller drives 22 are shown. Disks 1 are mounted at different spacings on each, roller 3 or 4, with disks 23 that are set close together at one roller end and disks 24 that are set at twice the spacing at the other roller end. This allows the roller disks 24 at twice the spacing to be moved into and out of mutual mesh. The grooves left in the slab surface by the disks 1 will show areas 26 with narrow ridges, since processed by the narrowly spaced disks 23 or by intermeshed end disks 24 in the overlap central region 27. When the slab grooves overlap incompletely, central or intermediate regions 28 are left where the grooves are at twice the spacing and have wider ridges than the disk cutting edge. In Figure 7, there are shown the" bearing ends 30 of the guide rails 8 on the vertically movable frame 9.

The slab facing machine according to the invention operates as follows. Slabs to be processed are fed in the direction A on the belt conveyor. The gauging device 19 gauges a slab width dimension and controls the position settings of the rollers 3 and 4 in the transverse direction such that all the disks in either roller will be at work simultaneously. The slabs may have irregularly cut edges. Accordingly, the gauging step is to be carried out a sufficient distance away from the grooving station 5 for the side contours of a slab to be fully gauged. A conventional computing device will then determine the best lateral positioning of the rollers across the slab. In this way, the rollers 3 and 4 are set into a suitable one of the typical configurations shown in Figure 3, 4, or 5. The steps of gauging the slab width and adjusting either or both rollers 3, 4 may be carried out manually, if desired. The outboard disks 1 in the rollers will process the slab near its outer edges, yet inside of said edges, to keep the diamond tool teeth 2 always in contact with the slab surface. The roller area with the packed disks 23 will cut grooves 26 that leave separation ridges having the smallest width in the slab, whereas the roller areas with the disks 24, at twice the spacing will cut grooves 28 that leave wider ridges than the cutting tool teeth 2. In the regions of overlap with the double-spaced disks 24, as shown in Figures 3 and 5, the disks 1 intermesh and will produce grooves 27 with ridges of least width, since the disks in the trailing roller 4 are cutting through the wide ridges left by the disks of the leading roller 3. In the overlap region, the slab will show a series of grooves 27 separated by ridges of minimal width, albeit produced by disks of different rollers. The cutting pressure force applied by the disks 1 in one roller, 3 or 4, acts mainly in the cutting direction. Nevertheless, the carriages 7 would be provided with a locking device (not shown) for added safety against their moving out of the set positions. Somewhat less conveniently, in a simplified embodiment (not shown) of this invention, the station 5 for grooving the region 26, 27 or 28 of the slab surface 20 could have one roller adjustable in the transverse direction as previously described and the other roller fixed in the transverse direction, although movable vertically on the same frame 9 as the adjustable roller. Thus, a slab would have to be processed in a preferred orientation across th^ helt conveyor. The contents of PCT Patent Application No. WO 03/028968, althougn directed to ceramic tiles, is incorporated herein for the purpose of further clarifying the slab grooving and facing process. During- the above facing step, the dressing station 16 will then remove the ridges or lands left between grooves. The slab regions 26 and 27 with the narrow ridges will be the easiest to process, and the regions 28 with the wide ridges longer to face by the vertical- axis rotary heads. The advantages of this invention are that the wide slab facing machine described above uses the grooving station 5 to remove material at a high rate by centering the cutting action on the individual tool tooth 2 rather than on the generatrix line of the roller as in the prior art. This improves the cutting action, reduces the slab loading, extends the tool lifespan, and allows the cutting disks 1 of the first and second rollers 3 and 4 to be adjusted for mutual alignment in less time. By having the roller working face divided into areas 23 where the disks are closely spaced (packed) and areas 24 where they are at twice that spacing, any face widths within a range of maximum groove overlap at 27 (Figure 3) to zero groove overlap at 28 (Figure 4) become processable. Furthermore, the working face of the disks, at a narrow spacing in the area 23 or. at twice the spacing in the area 24 of either roller, can be altered to increase or decrease the processed slab width by the roller pair. In practicing the invention, the materials, dimensions, and details of construction may be other than specified hereinabove, without departing from the juridical domain of the present invention. Thus, for retrofit installations directed to improve the productivity and flexibility of sizing and/or dressing equipment using rotary heads 18 - viz. to adapt such equipment for use as facing stations on a grooving and facing line where wide slabs of hard stone material are processed as described above - the grooving station 5 could be provided as a separate structure from the dressing station 16 needed to complete the dressing process. In a somewhat less convenient way, moreover, the rollers 3 and 4 could have the disks spaced apart at twice the width of their individual working face throughout. The grooving would leave here sideband, ridges that are wider than in the middle region, where the ridges can be very narrow by virtue of the grooves cut by the leading roller meshing with the grooves cut by the trailing roller. By setting for a desired width, different slabs can be processed, but the heads of the facing station would take more time to complete the ridge removing step due to the bands of wider ridges present along the slab sides. Instead of the slab width gauging device 19 provided ahead of the dressing process, it could toe arranged for the slab width to be measured manually, and the working width of the rollers 3 and/or 4 also set manually.