GB2163094A - The production of thin marble sheets - Google Patents

Abstract

Thinner marble sheets are produced by making a first cut from one longitudinal side edge of an intermediate size sheet and a second cut from the opposite side edge. The results should be to approximately the longitudinal centre line of the intermediate sheet. If the two cuts intersect then a spacer can be fitted in the region of the first cut to hold the final two sheets apart to prevent the cutting blade being trapped during the second cut. If the two cuts do not intersect then a small longitudinal column of marble is left which can be fractured after compression of the two cuts by simply pressing together one side edge of the cut sheet. Preferably, the first and second cuts are made with the intermediate sheet in a horizontal orientation.

Description

SPECIFICATION The production of thin marble sheets This invention relates to the production of thin sheets or tiles of decorative stone such as marble.

To be useful as flooring material or wall cladding material, blocks of marble are cut into sheets and the top surface is highly polished. The cutting of a block of marble into such sheets is usually performed on a machine which makes a number of vertical cuts, one at a time or simultaneously, on a machine where one or more diamond disc blades cut through the block. A problem which does arise, however, is that the resulting sheets can break and the thinner the sheet the higher the breakage rate. As a result of this, marble sheets of say 10 mm in thickness tend to be more expensive than thicker sheets of 15 to 20 mm in thickness.

Some of the reasons for breakage seem to be inherent weaknesses in the marble itself. However, vibration during cutting at the periphery of the disc blade can cause breakage. Vibration can to some extent be reduced by using a thicker blade but this naturally increases the thickness of marble lost as powder for each cut and indeed this can represent a substantial volume of the original block.

In practice, it has not previously been possible to produce marble sheets thinner than about 8 to 10 mm on a commercial scale and as noted, even then the costs are high.

An important advantage of being able to produce a thinner sheet of marble is than the resulting sheets weigh less, thus are less expensive to transport and, when used in buildings, they represent a less significant component of the weight of the structure. Therefore, marble wall cladding or floor tiling can represent a significant portion of the weight of a building and by using thinner sheets, the overall structure of the building can often be made less strong and therefore cheaper.

It is therefore an object of this invention to enable the making of thinner marble sheets.

According to the invention, there is provided a method of making sheets of decorative stone such as marble in which an intermediate sheet is cut into at least two sheets by making a first cut from one longitudinal edge to the approximate longitudinal centre line and a second cut from the opposed longitudinal edge again to the approximate longitudinal centre line, means being provided to hold the two eventual sheets apart whilst the second cut is made.

The invention is applicable to all types of natural or man-made decorative stone including, for example, rhinestone, granite, limestone, onyx, agglomerated stone and Breton stone. It is particularly applicable to marble. Therefore, for simplicity, hereinafter reference will solely be made to "marble".

We have found that by following this process, we can produce much thinner sheets of marble than previously and often the thickness of such sheets can be of the order of 4.5 to 8 mm. Despite this, however, breakage during manufacture can be kept relatively low and since the process is relatively simple and economical to operate, the cost of the thinner marble sheets can be significantly less than prior relatively thin marble sheets. Also, the resulting sheets are easier and cheaper to transport and when used in buildings give a lower floor loading value than thicker sheets.

The use of a pair of cutting blades which cut approximately half-way through the sheet has the advantage that such blades can be smaller in diameter than the prior blades used for the same resulting width of sheet and so are less prone to vibration at their tips which in turn is liable to fracture the resulting thin marble sheets. Also, such blades can be rotated faster and so they are less prone to vibration at their edges. Therefore, the invention uses a pair of opposed cuts, which can be made simultaneously or consequentially, each of which can be of less depth than the overall width of the sheet. The cuts can be made in one pass or alternatively the first and/or second cuts can be made stepwise in depth with a plurality of passes of the cutting blade.

According to one preferred embodiment, the intermediate sheet is conveyed in a horizontal direction and orientation on conveying means. These could be a conveyor belt or hydraulic rams could push the sheet over a flat horizontal surface. The conveying means move the sheet past a pair of cutting blades, one of which produces a cut extending from one longitudinal side edge of the sheet to approximately the longitudinal centre line of the sheet whilst the other blade produces a similar cut but from the opposed edge of the sheet again to the approximate centre line, the size and positioning of the two disc blades being such that a thin central column of marble is left to hold the resulting two thin sheets temporarily apart because the cuts fall slightly short of the actual longitudinal centre line and thereafter breaking that central supporting column by applying bending pressure to one side edge so as to cause that column to snap and leave two thin marble sheets.

If the two cuts intersect so that there is no thin column of marble left then a spacer can be fitted within the region of the first cut and resilient means apply compression forces at or near the opposite longitudinal side edge from that in which the second cut is made during that cutting to ensure that the cutting blade used is not trapped.

The overall thickness of the intermediate sheets will need to be two times the thickness of the eventual sheet plus small amounts lost in grinding and perhaps polishings plus the thickness of material lost in a cut For example, to produce very thin sheets of, say, 4.5 mm in thickness, the cutting blade would probably be of the order of 3.5 mm and so overall the intermediate sheet would need to be of 12.5 to 13 mm in thickness depending on losses in grinding. Correspondingly, for a thicker shet, say 8 mm in thickness, the intermediate sheet would need to be about 19.5 to 20 mm in thickness.

The minimum thickness of final sheets to be produced depends to some extent on the width of the sheet, or in other words the depth of cut to be made. Thus, we have found that up to a maximum width of 15 cm, one can produce a final sheet as thin as 4.5 mm or even 3.5 mm by adopting the method of the invention whilst correspondingly for a maximum width of 60 cm, the thickness can be as small as 8 mm or even 5.5 mm. Thus, the deeper the depth of cut, the larger must be the cutting blade and the more prone its periphery to vibration and consequent breakage of the resulting sheet.Generally, marble sheets are produced in standard sizes such as: Width (cm) Length (cm) 15 30 30 30 30 40 30 60 Width (cm) Length (cm) 40 40 40 60 40 80 40 100 50 50 50 100 60 60 60 90 60 120 and so this range of thickness would cover all standard size sheets.

According to another feature of the invention, the vibration of the blade at its tip can be reduced by clamping it more securely at its centre. This can be achieved by clamping it between a pair of circular washers or flanges of larger diameter than normal, these washers or flanges being rigidly fixed to the rotating drive shaft. For example, since one blade does not have to pass completely through a block of marble but only through about one-half of the width, if one still uses a similar diameter blade to make one of the two cuts according to the invention, clamping washers or flanges of a diameter approaching one-quarter of the diameter of the blade can be used to clamp the blade securely onto its shaft of rotation.

By way of example, to cut an intermediate sheet of a size such as 15 x 30 cm, 30 x 30 cm, 30 x 40 cm or 30 x 60 cm to produce a finished sheet of 5.5 to 8 mm, one can make, for example, two cuts using 50 cm diameter blades. The maximum depth of cut with such a blade ts about 15.9 cm since preferably relatively large central washers of, say 190 mm diameter are used to stiffen the mounting of the blade. If the intermediate sheet is of a size such as 40 x 40 cm, 40 x 60 cm, 40 x 80cm or 40 x 100 cm, then the same 50 cm diameter cutting blades can be used but the central stiffening washers can only be about 98 mm in diameter so giving a maximum depth of cut of about 205 mm.For a larger intermediate sheet such as 50 x 50 cm, 50 x 100 cm, 60 x 60 cm, 60 x 90 cm or 60 x 120 cm to produce a finished sheet of 5.5 to 8 mm, two cuts using 76 cm diameter blades can be made. Such blades preferably have central reinforcing washers of about 150 mm diameter so giving a maximum depth of cut of about 306 mm.

Finally, to cut an intermediate sheet of a size, say, 15 x 30 cm to produce a finished sheet of 4.5 mm, one can make for example two cuts using 35 cm diameter blades. Such blades preferably have central reinforcing washers of about 140 mm in diameter so giving a maximum depth of cut of about 109.5 mm.

The marble sheets produced by the process of the invention eventually need to have one surface which is highly polished as its front surface and a rear surface which has been ground relatively flat and optionally slotted to provide a key for the adhesive or grout used to adhere the sheet to a wall or floor.

The formation of the highly polished front face forms another aspect of the invention and the time of its formation depends to some extent on the condition of the intermediate marble slab which is cut in two according to the invention to produce the two thinner sheets.

According to one feature of the invention, two final sheets are adhered together face to face after the first and second cuts which one or both outer faces of the resulting laminate are ground and polished and thereafter the two final sheets are separated.

The intermediate sheet can be cut from a squared off larger block or simply cut from a rough block in which-case the intermediate sheet or the final thin sheets will need to be squared off and generally cut to size.

The intermediate sheet can be cut in two or alternatively a number of thin sheets can be cut from an intermediate block. Thus, for example, two or more ganged parallel blades can cut two or more spaced cuts from one side edge of the intermediate sheet followed by or simultaneously with two or more spaced cuts from the opposed side and the intermediate sheet then separated into three or more thinner sheets.

Sharp edges mean that the edges are sufficiently sharp for the adjacent face to be polished without further grinding and the polished face will extend substantially to the edge whereas if the edges are not sharp mere polishing would leave rough non-polished areas adjacent the edges.

If the intermediate marble sheet has sharp edges for both faces then both of these surfaces can be polished and largely finished. Thereafter, this intermediate sheet is cut according to the invention and the resulting two sheets will then each have one finished front face. To complete each, it will only be necessary to grind the cut faces including grinding off the small stub, if present, remaining when the thin column along the centre is broken and for the thin ground face to be optionally slotted in conventional fashion. These polishing, grinding and slotting steps can be entirely conventional and can be performed by conventional machines.

If, on the other hand, only one surface of the intermediate sheet can be given a good polished surface before the intermediate sheet is cut into two, then after cutting according to the invention, one of the two sheets will have a polished front face and can be finished as described above. The other part however will have neither face finished and two such sheets can be temporarily adhered together with, for example, cement mortar and the resulting outer faces of the laminate polished. Because two such sheets are laminated together, they are thicker and mechanically stronger and so can undergo the normal polishing step with less risk of breaking. Thereafter, the laminate can be split or cleaned along the cement join and the rear faces ground and slotted if required.

In the case where neither surface of the intermediate sheet has a sharp edge enabling it to be polished for the intermediate sheet, then one can adopt a somewhat analogous process by severing the intermediate sheet according to the invention and again rejoining the rough, originally outer surfaces with some suitable temporary adhesive, such as cement mortar, before polishing the then resulting outer surfaces of the laminate, separating and finishing the rear surfaces of the two sheets by grinding and optionally slotting.

According to another aspect of the invention, we have found that by making a laminate in this way with cement mortar, one can polish the two outer faces of the laminate without risk of breakage even if the two marble sheets of the laminate are very thin, and thereafter cleave the laminate along the adhesive layer and finish the resulting two thin marble sheets by grinding and optionally slotting. The adhesive bond should be relatively weak, e.g. cement mortar, with one day curing and a lean mixture so that the laminate can be cleaved easily after polishing. Alternatively, the laminate can be held together mechanically not by an adhesive layer but by vacuum or mechanical clamps.

As an alternative to supporting a thin sheet during grinding and/or polishing by adhering two thin sheets together by an adhesive, one sheet can be adhered to a strong backing, examples of which are a thicker layer of cement or concrete, a reinforcing sheet such as a metal sheet, an aluminium sheet or a steel sheet or a plastics material sheet. The reinforcing sheet can be permanently adhered in the sense that it is intended that the resulting composite marble sheet and reinforcing sheet will be sold for use as such. Suitable adhesives include hot melt glues, synthetic Bayprene or neoprene, Neocem ceramic tile adhesive or the ceramic tile adhesives or an epoxy resin.

As an alternative to adhering a finally cut sheet to a temporary or permanent backing, one or both faces of the intermediate sheet could be temporarily or permanently adhered to a supporting strong backing before the intermediate sheet is cut.

Although the invention is particularly useful for producing thin sheets, e.g. sheets 4 to 10 mm in thickness, the method of the invention can be used to produce thicker sheets, e.g. up to 20 mm in thickness or more, since a thinner cutting blade can usually be used in the method of the invention and so a similar loss of material in the form of marble dust will occur although problems of breakage naturally become less acute as the sheet thickness is increased.

Another advantage of the invention is that by making two cuts with smaller diameter blades, rather than one cut with a large diameter blade, the overall power consumption can be less because in general a thinner cutting blade can be used and so less material has to be cut away and reduced to powder.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a machine used to produce thin marble slabs according to the invention; Figure 2 is a side view of the machine; Figure 3 is a block diagram illustrating steps in various processes according to the invention for forming thin marble blocks; Figure 4 is a diagram illustrating, by means of a series of cross-sections, the formation of a thin marble block according to the sheet; Figure 5 is a diagram illustrating, by means of another route, the formation of a thin marble block according to the invention; and Figure 6 is a diagram illustrating, by means of a further route, the formation of a thin marble block according to the invention.

The machine 10 shown in Figure 1 includes a girder framework 11 supporting a conveyor belt 12 having a horizontally extending web 14 at the top. This belt is driven so as to advance items laying on it in the direction of the arrow 16 by means of a motor 18 which drives a roller 20 at one end of the conveyor belt.

The girder framework 11 also supports cutting discs 30 and 32. These discs are horizontally oriented and are rotatably supported on respective spindles 34 and 36 carried in bearings 38 journalled to the framework 11. The discs are rotated thigh speed by means of electric motors 40 and 42 which drive the spindles 34 and 36 by means of transmission pulleys and belts.

The cutting discs 30 and 32 are largely conventional. Around their peripheries, they have small diamonds embedded to enable them to cut through slabs of marble. Such discs and their cutting action is however very well known and not believed to require further explanation. Water sprays from jets 37 are provided conventionally to keep the cutting areas cool and to suppress dust formation.

The two cutting discs are mounted one on either side of the upper web 14 of the conveyor belt. Their diameter and positioning is such that they extend almost but not quite to the longitudinal centre line 43 of the web, e.g. to within a few millimetres of it. As best shown in Figure 2, the underside of each disc is spaced upwardly from the top surface of the upper web 14 of the conveyor belt by small distance which is the approximate thickness of the final thin slab to be formed.

In order to form a thin slab, an intermediate thickness sheet 44 (Figure 4) is placed flat on the horizontal web and is entrained along the web as it moves in the direction of the arrow 16. Initially, it contacts the cutting blade 30 and a cut 46 (Figure 4) is formed by that blade from one side edge as the slab is progressively moved past that cutting blade. Referring to Figure 4, it will be noted that by step II, the cut 46 has been made from the left side of the intermediate sheet 44. As the sheet 44 continues to be moved by the web, it then reaches the cutting blade 32 which forms a corresponding cut 48 (Figure 4) from the right-hand side, e.g. step Ill in Figure 4.

The almost completely severed block then arrives at the right-hand end of the conveyor belt and it is a simple matter to snap the remaining small upright pillar 50 (Figure 4) of marble by simply pressing on one side edge, e.g. in the direction of the arrows 51 shown in step IV in Figure 4 to cause the two sheets to separate to give the two thin sheets 52 and 54. The operator can then remove these sheets from the right-hand end of the conveyor belt.

The sheets are finally finished by grinding off the small broken pillar 50 which appears on one face of each sheet 52 and 54 and that grinding can be entirely conventional.

Figure 3 shows in block diagram a number of routes according to the invention for producing thin sheets according to the invention. The choice of route depends upon the condition of the intermediate block 44. The latter can be produced conventionally or alternately by a two-cut cutting process according to the invention. Usually, a large block of marble is cut by a conventional machine to produce the intermediate sheet 44 and if both surfaces of the sheet have sharp edges. The process marked A can be followed and the steps of that process are illustrated in Figure 4.

Turning to the process A and Figure 4, the intermediate sheet has sharp edges all round, e.g. along the lines marked by the arrows 56 in step I of Figure 4 so that good polished upper and lower faces 58 and 60 can be formed. Then that intermediate sheet is cut according to the invention into the two thin sheets 52 and 54 according to the process already described and as illustrated in Figure 4. The eventual rear surface 62 of each final sheet has the broken pillar 50 and is ground as described above to remove that pillar and leave a reasonably finished face for keying to an adhesive or grout and optionally, additionally, that rear surface can be slotted to assist keying to a wall or floor surface.

As an alternative, if only one face of the intermediate sheet 44 has good sharp edges, then the process marked B can be followed and the steps of that process are illustrated in Figure 5.

Assuming that it is the upper surface shown in step I which has the sharp edges, that surface 70 is polished in a conventional manner leaving a rough undersurface 72. The sheet 44 is then cut according to the invention into two thin sheets following the steps shown in Figure 5.

At the end of step 4, a separate top sheet with a separate polished face 74 is formed and a separate lower sheet 76 has been formed. The sheet 74 merely needs grinding on its rear, non-polished face to remove the broken column and then it can be optionally slotted. The separate lower sheet is treated differently. Two such sheets are adhered face to face along their roughly finished faces 72 by means of a layer of cement mortar 78, e.g. 5 to 6 mm in thickness. The mortar is allowed to set for approximately one day. A lean mixture of cement and silica sand seems best but the layer 78 could be a tapioca flour paste. The resulting laminate 80 is then of sufficient strength for the two outer faces of the laminate to be ground to remove the small columns of marble and polished in a conventional manner.

Thereafter, the laminate can be split along the mortar join to give finished sheets 82 which can be ground to clean off mortar from the unpolished face and slotted if required.

Finally, if the faces of the intermediate sheet have no sharp edges and so cannot be polished satisfactorily, the process marked C in Figure 3 is followed and the steps of this process are illustrated in Figure 6. The intermediate sheet 44 is cut according to the invention by the two cutting steps and by step IV of Figure 6, two separate sheets 84 are formed. Each has a rough face 86 which cannot be polished and so those two faces 86 are adhered face to face by means of a layer of mortar 88 and as described in connection with Figure 5, the resulting outer faces 90 of the laminate are then ground to remove the small marble pillar and polished. Thereafter, the laminate can be split along the line of the mortar and the eventual rear surfaces of the finished shet 92 ground and optionally slotted.

Claims (19)

1. A method of making decorative stone sheets in which an intermediate sheet is cut into at least two sheets by making a first cut from one longitudinal edge to the approximate longitudinal centre line and a second cut from the opposed longitudinal edge again to the approximate longitudinal centre line, means being provided to hold the two eventual sheets apart whilst the second cut is made.

2. A method as claimed in Claim 1 in which the said means comprises making the two cuts of a depth from each longitudinal edge such that a thin, longitudinally extending column of marble is left and after completion of the two cuts, fracturing that column to complete separation of the two sheets by applying bending pressure to one longitudinal side edge.

3. A method as claimed in Claim 1 or Claim 2 in which both first and second cuts are made simultaneously.

4. A method as claimed in Claim 1 in which the said means include a spacer fitting within the region of the first cut and resilient means apply compression forces at or near the opposite longitudinal side edge from that in which the second cut is made during that cutting to ensure that the cutting blade used is not trapped.

5. A method as claimed in any of claims 1, 2 and 4 in which the first and second cuts are made consecutively.

6. A method as claimed in any preceding claim in which the intermediate sheet is supported substantially horizontally in a horizontal orientation on conveying means during the cutting and is moved by the conveying means past stationary cutters.

7. A method as claimed in any preceding claim in which the cuts are formed by rotating circular cutting blades.

8. A method as claimed in any preceding claim in which two final sheets are temporarily adhered together face to face after the first and second cuts whilst one or both outer faces of the resulting laminate are ground and polished and thereafter the two final sheets are separated.

9. A method as claimed in Claim 8 in which the two final sheets are adhered together by means of an intermediate adhesive layer.

10. A method as claimed in any preceding claim in which the intermediate sheet has sharp edges for both faces which are then polished followed by making the first and second cuts and each final sheet is then finished by grinding the cut faces and optionally slotting them.

11. A method as claimed in any of claims 1 to 9 in which the intermediate sheet has sharp edges for one face which is polished followed by making the first and second cuts, the one final sheet having the polished face is finished by grinding and optionally slotting its rear faces, whilst two of the other final sheets are adhered together by cement mortar, the outer faces of the resulting laminate polished, the laminate split and the rear faces of the resulting sheets finished by grinding and optionally polishing.

12. A method as claimed in any of claims 1 to 9 in which neither face of the intermediate sheet has sharp edges in which case the first and second cuts are made, the original faces of the intermediate sheet are bonded face to face with cement mortar, the outer faces of the resulting laminate polished, the laminate split and the rear faces of the resulting sheets finished by grinding and optionally polishing.

13. A method as claimed in any of claims 1 to 7 in which an eventual separated sheet is permanently adhered to a supporting backing.

14. A method as claimed in any of claims 1 to 7 in which one or both faces of the intermediate sheet are adhered temporarily or permanently to a supporting backing before the intermediate sheet is cut.

15. A method as claimed in any of Claims 1 to 7 in which two or more spaced first cuts are made from one longitudinal edge of the intermediate sheet and two or more spaced second cuts are made from the opposed longitudinal edge whereby the intermediate sheet is cut into three or more thinner sheets.

16. A method as claimed in any preceding claim in which the sheets produced are 4.5 to 8 mm in thickness and have a width of up to 15 cm.

17. A method as claimed in any of Claims 1 to 15 in which the sheets produced are 5.5 to 8 mm in thickness.

18. A method of making decorative stone sheets substantially as herein described with reference to Figure 4, Figure 5 or Figure 6, of the accompanying drawings.

19. Decorative stone sheets, such as marble sheet, when made by a method as claimed in any preceding claim.