Description

Technical Field

[0001 ] The invention relates to a method to produce a composite stone veneer product such as a tile comprising a stone veneer attached to a substrate.

Background Art

[0002] Composite tiles that consist of a thin natural stone veneer attached to a functional backing substrate enjoy increased popularity as those tiles are generally lighter than their massive stone counterparts. As the stone veneer is relatively thin it may even resist some bending. The backing substrate distributes impact energy better leading to less fractured tiles during transport, during mounting and use. Composite tiles are more and more used as an indoor or outdoor decorative wall or floor covering as they are much easier to mount and are safer for the passers-by (every year people get hurt by tiles, detaching from buildings). Their lower weight also reduces transport cost and carbon dioxide emission.

[0003] The way in which composite tiles have been produced has not evolved much since their inception. The procedure as described in US3963846 (P.T. Bourke, 1976) is still very closely followed. A block of natural stone of square basis (about the size of the final tile) and of limited height is cut flush along a horizontal plane by a stationary band or single wire saw by pushing the stone carried on a trolley through the saw. Glue is applied to the cut face and the backing substrate is pressed on it. After drying the stone is cut again slightly (5 to 7 mm) below the glue plane. A composite tile is thus obtained that is further polished and trimmed to final size. The procedure of gluing, drying and cutting is repeated on the newly formed surface.

[0004] The separation of the veneer layer is usually done by a band saw along a horizontal cutting line. Alternatively a single wire saw has been suggested wherein the drive wheels have their axes parallel (see US 5605141 ) or perpendicular (see EP 1316398 B1 ) to the cutting plane. Other cutting procedures have been suggested that cut along a vertical plane by splitting a single plate of stone with backing substrates glued to both sides (US 5339795). By making a stack of plates with double sided glued substrates, one can increase the cutting speeds by processing the stack in parallel by guiding it through a parallel set of cutting discs (see

US5605141 ).

[0005] The procedure remains slow (in a serial way, one by one), involves a lot of manual handling and does not lend itself easily to automation. Cutting with the described conventional saw techniques is prone to vibration resulting in cracking of the stone veneer. Therefor the veneer has to be relatively thick when handled independently or it must be glued to a substrate prior to cutting. Also the surface of the stone veneer shows ridges and/or waves that have to be polished away. A lot of stone is cut away and lost. The inventors therefore suggest an alternative way of working.

Disclosure of Invention

[0006] The primary object of the invention is to provide an alternative way for producing composite tiles that makes better use of the raw materials, is faster in execution and lends itself to automation (for example with equipment known from the photovolta ^' fcs industry). According this method the stone veneer is first cut in a parallel process and then glued to a substrate in a serial process.

[0007] According a first aspect of the invention a method is claimed to produce 'composite tiles'. With 'composite tiles' is meant a tile that - amongst others - comprises a stone veneer that is attached to a substrate. The tile is of rectangular or square shape with sides in the range of about 10 to 2000 cm. The composite tile further comprises glues or adhesives with or without fibre reinforcement, and possibly intermediate layers for damping or matching of properties between stone and substrate.

[0008] 'Stone' should not be interpreted limitative: also manmade stones like

ceramics or concrete can be used. Typical types of natural stones that are envisaged are marble, granite, slate, limestone, onyx, tyndall stone, sandstone, bluestone, syenite, gneiss, soapstone, basalt, quartz...

[0009] The stone is provided in the form of a 'veneer slice' or simply 'veneer'. With veneer is meant a thin layer of stone of between 0.1 to 15 mm thick or more preferred between 0.2 to 7 and mostly something between 0.5 and 5 mm thick. Stone veneer - due to its thinness - must be handled with care. It is one of the advantages of the method that cutting is gentle, with very low distortion of the stone veneer and with a very good surface quality, free of ridges and waves.

[0010] The method starts from a block of stone of rectangular cuboid shape i.e. the block is of elongated shape having an edge. Of course the block of stone will have more than one edge, but by referencing one of them as 'the edge', 'that edge' or 'said edge' the orientation of the block of stone can be defined. The cross section perpendicular to that edge is

rectangular or square and equal or slightly larger in dimension than and of the same shape as the final composite tile. An exemplary size is 20 cm χ 20 cm x 120 cm to obtain tiles of 20 χ 20 cm ² . The block of stone is sawn by a single wire saw, band saw or circular saw out of an even larger block or is cut directly out of a quarry. The finish of the sides is 'as sawn' on at least the sides sharing the direction of the edge.

[001 1 ] The block is mounted in a multiple loop wire saw, wherein the wire loops form a web of parallel wires that are tensioned over two or more capstans that drive the web. A multiple loop wire saw can comprise as many individually closed saw wires as there are loops. This is e.g. the case in the multiple loop saw machine described in WO 98 035802. Alternatively the loops can be formed by a single closed loop that is spirally threaded over the two or more capstans as described in JP 1235602. As a further alternative the loops can be formed from a single wire that is delivered from a pay-off spool and is spirally threaded over the capstans, and at exit is wound on a receiving spool. Such saw is customary in the field of sawing silicon wafers (see e.g. US 3824982), where it is, somewhat unfortunate, called a multi-wire saw (as there is actually only one wire present on the machine).

[0012] The block of stone is sawn by the web with the edge substantially

perpendicular to the plane of sawing. The plane of sawing is that plane formed during the progression of the cut. The thus formed stone veneer slices are separated from one another.

[0013] A substrate is provided. The substrate primarily provides strength to the tile but other functionalities can also be included such as sound absorption, thermal insulation (e.g. for wall coverings) or - oppositely - heat conduction (e.g. for floor heating). Preferably the substrate is light (for example by using honeycomb type of materials as per US 3723233) for easy installation and is strong (e.g. by reinforcement with fibres as in EP1226931 A1 ). The substrate can be thicker than the stone veneer but it may also be thinner. Typical materials may be wood, high density polystyrene, particle boards, oriented strand board, medium density fibre board, carton, metal based, fibre reinforced based cement sheets and the like.

[0014] The singled stone veneer slice is subsequently attached to the substrate.

Attachment is usually done by means of a glue that is compatible with as well the stone veneer as the substrate. Common glues are polyester, epoxy, or acrylic based. Epoxy, more particularly two component epoxy, glues are most preferred. Care should be taken with respect to the moisture content of the veneer, as it may have absorbed considerable water during sawing. It may be necessary to apply pressure during attachment. Preferably this is done by a bladder press as this gives an equal pressure over the whole surface of the tile.

[0015] Normally steps will follow to polish the visible surface of the tile and for trimming the tile to exact size. However, this is not necessary as the 'as cut' surface is already aesthetically pleasing. Possibly the top surface can be provided with a clear resin to even further improve the aesthetic aspect of the tile.

[0016] In a first preferred embodiment, there is an angle between the plane of the web of parallel wires and the edge of said block of stone. The angle is not big: less than 10% but more than 1 % when expressed as a slope. The angle is preferably made by keeping the edge of the block in horizontal position while putting the wire web under the mentioned angle to the horizontal plane.

[0017] The angle can be made between one of the sides of the block comprising the edge and the plane of the web. At the start of the cut the end of the block closest to the web is sawn first and gradually the stone veneer slices are cut off one by one. The outermost stone veneer slice can be held by a holding device - such as a suction holding device - that sequentially retrieves the stone veneer slices out of the sawing area one by one.

[0018] Alternatively the wire web can be so oriented that that the web first saws the block at the edge. The axis of the block is then parallel to the plane formed by the web.

[0019] Both orientations as above can also be combined: cutting by the web will than start at a single vertex of the stone block.

[0020] In a further preferred embodiment the stone veneer slices are separated by introducing parallel separators into the saw kerf following the

progression of the cut. The parallels separators can be in the form of parallel plates like a comb. In a further refinement, the plates are provided with channels and/or grooves that feed coolant or cutting slurry to the saw wire during cutting.

[0021 ] There are a number of relative orientations and movements possible

between the wire loops and block of stone:

- The block can be moved out of the wire loops or the block can be

moved into the wire loops;

- The block can be held stationary and the wire web moved or the block can be moved while the wire web is held stationary;

- The relative movement between block of stone and wire web can be with the direction of gravity or against the direction of gravity.

This results in eight possible sawing configurations. The most preferred configurations are where the block of stone remains stationary and the wire web is moved relative to the block as the block is generally heavier than the wire web and capstans.

Further preferred is if the block of stone moves outward of the wire loops as then the stone veneer slices can be easier received in the parallel separators. The parallel separators do not have to be entered into the wire loops.

Further preferred is if the relative movement between the block of stone and the wire web is in the direction of gravity. Such as when the - preferably the upper - wire web is pulled downward through the stationary stone. The tension on the web is controlled by the pushdown force on the capstans. Also the carrier for the block of stone can be flat and provided with a low cost 'cut-in' surface for finishing the cut. The stone veneer slices can be easily retrieved from above the wire web. The other alternative movement is if the block is kept stationary while the wire web - preferably the lower wire web - is pulled upward through the stationary stone. In that case the carrier for the block of stone must be provided with slits to accommodate the wire web before cutting starts.

[0022] In the field of wire sawing there is a relation between the stretch of the cut and the kerf. With the 'stretch of the cut' is meant the length of saw wire that is in contact with the block of stone during sawing. An increased stretch will result in an increased pull-through force and hence the saw wire must be stronger. A stronger saw wire generally implies a thicker wire and hence a larger kerf loss. Hence, the longer the stretch of the cut, the larger the kerf loss. However, an increased kerf means an increased loss of material and also a lower cutting speed (as more material must be removed) which is less desirable. Saw wires are therefore at the limit of the lowest possible kerf loss with the highest possible strength.

[0023] A first classification of wires can be based on the type of sawing: either through third body abrasion or through fixed abrasive sawing. The first class is generally known as 'loose abrasive sawing'. In loose abrasive sawing abrasive particles (like silicon carbide dust, steel shot, quartz sand,...) are carried in a liquid (like water, or oil, or PEG,..) thereby forming a slurry. The saw wire may be a steel wire that is pulled through the cut thereby entraining the slurry that carries the abrasive particles. The abrasive particles roll between the saw wire and the stone resulting in the abrasion of the stone. For stone sawing such wires have a diameter between 0.1 mm and 1 mm. For stone veneer sawing (with a stretch of between 20 to 80 cm) a diameter of between 0.15 to 0.30 mm is preferred.

[0024] The steel wire can be a plain carbon steel wire, a stainless steel wire or an alloy steel wire. A typical plain carbon steel comprises at least 0.70 wt% of carbon, a manganese content between 0.30 to 0.70 wt%, and a silicon content between 0.15 to 0.30 wt%. Presence of elements like aluminium, sulphur ( below 0.03%), phosphorous (below 0.30%) should be kept to a minimum. Possibly other alloying elements like boron, chromium, vanadium or molybdenum may be added to it to influence the drawability of the steel. Of course the remainder of the steel is iron and the

unavoidable impurities.

[0025] Preferred stainless steels contain a minimum of 12%Cr and a substantial amount of nickel. More preferred stainless steel compositions are austenitic stainless steels as these can easily be drawn to fine diameters. The more preferred compositions are those known in the art as AISI 302 (particularly the 'Heading Quality' HQ), AISI 301 , AISI 304 and AISI 314. 'AISI' is the abbreviation of 'American Iron and Steel Institute'.

[0026] Special alloy steels such as chrome nickel steel, chrome vanadium steel, chrome molybdenum, or chrome nickel molybdenum steel can also be used for the wires. Specific examples are 51VrV4 (Werkstoff Nr. 1 .8159, equivalent to SAE6150), 32CrMoV12-28 (Werkstoff Nr. 1 .2365) or

48CrMoNi4.4. These alloy steels are suitable for welding into closed loops.

[0027] Possibly the loose abrasive sawing wire is of the structured type. With

'structured' is meant that the wire surface or wire shape is adapted to enable a better drag of slurry. Indeed, a concern in loose abrasive sawing is that the slurry layer between stone and wire depletes as the wire progresses through the cut. In order to overcome this depletion problem, it has been suggested that the surface of the wire be made textured to enable an improved slurry drag as e.g. exemplified in FR045160 (first addition to FR771300, indented surface), JP2009023066 (wire with grooves) or JP 2007 04441 (wire with flattened faces).

Alternatively the wire can be locally bent and shaped to improve its slurry drag. Examples can be found in FR750081 (helix wire), JP 2004 276207 (single crimp), WO 2006 067062 (two crimps in two different planes) or WO 2012 069314 (helix wire with bends).

[0028] Another alternative is to use a saw wire that comprises two, three or more filaments twisted together into a strand (as for example shown in

US1687089, US 2451383). The strand has crevices between the wires that are able to hold the slurry well.

[0029] A second class of saw wires are fixed abrasive saw wires where the

abrasive is fixed to the wire. The abrasive is practically solely diamond grit that is attached to the wire in a number of ways: by indentation, by plating, by brazing or by holding the abrasive in a resin layer. The most preferred method is by plating nickel onto a steel substrate wire concomitantly with diamond particles (of sizes ranging from 10 to 100 μιτι). Such wires are available up to a size of 0.30 mm and are known for cutting e.g. silicon or sapphire.

[0030] A particularly preferred type of fixed abrasive saw wire is a saw wire that has an oblong cross section wherein the shorter side of said cross section is parallel to the direction of cutting. It has an improved lateral stability and keeps its course better than a round wire. Saw wires with a width of between 0.25 to 4.0 mm can be provided with a fixed abrasive by means of laser cladding as demonstrated by the applicant in the application with number EP12189756.6 of 24/10/2012.

[0031 ] Another preferred type of fixed abrasive saw wire is a saw wire that is structured. 'Structuring' may be accomplished by only having abrasive present locally on the surface of the wire (and not on the whole surface). For example that the abrasive is only present along a helical track, or on periodic spots. Alternatively 'structuring' may be achieved by starting from a carrier wire that comprises bends with straight segments in between. Also for a fixed abrasive sawing wire, structuring may be achieved by starting from a steel cord wherein two, three or more steel filaments are twisted around each other and subsequently coated with a fixed abrasive.

[0032] An alternative form of a fixed abrasive saw wire is a saw cord. A saw cord comprises a steel cord and cutting beads threaded thereon. The beads are separated by a polymer coating or sleeve. Such a cord is e.g.

described in WO 201 1 061 166. Currently the outer diameter of the bead is 7 mm (fresh wire) leading to a minimum kerf loss of above that dimension. Therefore saw cords are particularly preferred for larger tiles (above 50x50 cm ² ).

[0033] According a further inventive implementation of the method the multi loop wire saw is threaded with two different kinds of saw wire: odd numbered loops are formed from a different saw wire than even numbered loops. The advantage of such alternating saw wires is that stone veneer slices are formed with two different surface qualities. The odd numbered saw wire loops can for example be chosen to result in a rough surface aspect, while the even numbered saw wire loops can be chosen to give a very smooth surface. The stone veneer slices will thus show facing surfaces of rough and smooth quality. The rough side can then be used to obtain a better gluing to the substrate, while the smooth visible side needs less polishing.

[0034] As mentioned there is a trend that a longer cutting stretch results in a higher kerf loss. As will be shown in the embodiments saw wires can be selected to result in a very low kerf loss as small as 0.25 mm at veneer sizes of 20x20 cm ² . In any case the inventors are confident that the kerf loss can be lower than 5 mm for any size of stone veneer tile. This results in an optimal use of the block of stone.

[0035] Moreover the method of using a multiple loop wire saw results in a much more gentle cut than is for example available with a circular saw blade. A gentle cut results in less fractures of the stone veneer and a better overall yield of the process. In this way stone veneer slices that are thinner than the saw kerf may actually be obtained. Indeed the stone veneer slices can be made thinner than 1 mm, for example thinner than 0.7 mm.

Brief Description of Figures in the Drawings

[0036] Figure 1 shows the steps of the method.

[0037] Figure 2 depicts a general view of a multiple loop wire saw used for the production of the stone veneer slices.

[0038] Figure 3 shows a first preferred arrangement of the block of stone relative to the wire web.

[0039] Figure 4 shows a second preferred arrangement of the block of stone relative to the wire web at the start of the cut.

[0040] Figure 5 shows the second preferred arrangement at the end of the cut [0041 ] In the drawings the hundred digit refers to the drawing number and

numbers with equal tens and unit digits refer to like items over different figures.

Mode(s) for Carrying Out the Invention

[0042] The method in its generality (Figure 1 ) starts from a stone rock 100. This block is sawn in square prismatic blocks 102 by means of for example a band saw or by means of a circular saw. Important is that the base of the prism is about the size and shape the final tiles will have. The edge of the block of stone here corresponds to one of the edges perpendicular to the base of the prisms. The blocks of stone 102 or then separated by means of a multiple loop wire saw - explained further - into stone veneer slices 1 20. The stone veneer slices 1 20 are attached to a flat substrate 122 by means of glue 1 24.

[0043] In Figure 2 an overall view of a multiple loop wire saw 200 adapted to saw stone veneer is shown. The wire saw comprises two capstans 210, 21 0' - in essence cylindrical rolls - that have circumferential grooves adapted to receive the saw wire loops 21 2, 21 2', 21 2". The capstans are driven and together can move vertically in the direction of the arrows. The block of stone 202 is inserted into the wire loops on table top 206 that is rested on pillars 208. It's sizes are typically 32x32x1 00 cm ³ .

[0044] The longer edge 203 is perpendicular to the plane of sawing. Important is that the relatively heavy block of stone 202 (with mass 270 to 330 kg) remains stationary. In between block of stone 202 and table top 206 a cutting slab 204 of easily cutable material - such as wood - is provided. This is to protect the table top 206 at the end of the cut. In this case the saw wire loops 21 2, 21 2', 21 2" are individual loops of fixed abrasive saw wire of size 400 μιτι core diameter of round cross section with diamonds of 40 μιτι embedded in a nickel layer. The outer diameter of the wire is about 600 μιτι hence the kerf loss is about this size too.

[0045] During sawing the capstans 21 0, 21 0' are slowly lowered into to the block of stone at a typical speed of 0.1 to 1 mm per minute depending on the hardness of the stone (marble 1 mm/min, granite 0.1 mm/ min). Parallel separator plates 21 6 arranged on a distributor plate 214 are introduced into the cut as the sawing progresses. Via feed 21 8 coolant - usually water - is introduced to cool the saw wire loops and to remove debris from the cut. The coolant is distributed to the separator plates through the distributor plate 214. The separator plates are provided with vertical grooves to guide the coolant to the saw wire.

[0046] Figure 3 shows the orientation of the block of stone 302 relative to the wire web 31 2 in front view. In this arrangement the block of stone 302 is first sawn at the edge 303 by putting the block 302 under a small angle 'a' relative the plane of the wire web. This can e.g. be achieved by providing a slab 304 with a wedge shaped cross section. The wire web 312 touches the block under this small angle and this gives a smooth entry cut. In this way chipping at the start of the cut is avoided and the cutting pitch is first stabilised prior to continuing the cut.

[0047] Another preferred arrangement is shown in Figure 4 (at the start of the cut) and Figure 5 (at the end of the cut). In this arrangement there is a small angle β between the plane of the web and the edge 403 of the block of stone. The direction perpendicular to the web is under the same angle β to the vertical. The saw wire loops 412, 412', 412"... move in vertical direction, and the plane of sawing is again perpendicular to the edge 403. In this arrangement saw wire loops 412", 412"' will first cut the stone and the saw wire loop 412 ^V will last enter the stone 402.

[0048] During cutting (switching to Figure 5) the parallel separators 516, 516', 516" are gradually inserted into the kerf. The separators are attached to distributor plate 514. The bottom end of the parallel separators follows the same slant angle β as the wire. The parallel separators follow the saw wire loops closely but do not tough the running wires. Along the separators 516, 516', 516" coolant is injected through feed 518 and distributor plate 514. Some pressure may exerted by the coolant injected by separators on the saw wire loops thereby supporting the wire sawing.

[0049] Once the last wire saw loop 512 ^V has entered slab 504 the cutting can be stopped. The array of parallel separators is slowly moved upward over about the height of the stone veneer and the last cut stone veneer slice 520 ^v is first removed by means of sucking cup 530 and placed in a tray or placed directly on the substrate. The array of separators is slightly moved upward thereby liberating the last but one stone veneer slice 520 ^IV that is subsequently picked and placed by the sucking cup 530. The process is repeated until all stone veneer slices have been removed one by one.

[0050] In a series of trials a reel-to-reel wire saw was used with four loops of wire at a pitch of 5 mm. The wire used was a 0.25 crimped wire with a breaking load of about 150 N held at a tension of 70 N. An abrasive slurry with silicon carbide abrasive (to JIS1000 standard) in poly ethylene glycol (PEG 205) in a 1 :1 weight ratio was used. The block of stone was a marble type ("Dark Emperor", China) with a 25 χ 18 cm ² basis. Wire speed was set to 720 m/min and table speed was 2 mm/min. The 5 mnn thick stone veneer slices could still be handled well. The kerf loss was about 0.30 mm. The stone veneer slices showed a lower surface roughness R _a compared to stone veneer that was cut with a band saw: between 1 μιτι (in the direction of the wire movement) to 4 μιτι (in the direction perpendicular to the wire direction). With a band saw roughnesses R _a between 4 and 6 μιτι are obtained.

[0051 ] In a second series of trials a fixed abrasive saw wire with a core diameter of 175 μιτι equipped with 30/40 μιτι diamonds were used to cut harder classes of stone such as granite ("Himalaya Blue", from India, class B material). The stone of 15x15 cm ² could be sliced in stone veneer slices of only 600 μιτι thin without breaking. As coolant water was used. Table speed was 0.1 mm/min.

[0052] The stone veneer slices were glued to an MDF (medium density

fibreboard) substrate. The total thickness was about 10 mm. When subject to an impact test, the composite tile performed well.

[0053] The above description and trials all illustrate that for producing stone

veneer composite tiles the use of a multiple loop wire saw is a viable option.