METHOD FOR CLEAVING LAMINATED MINERAL BLOCKS, DEVICE FOR CARRYING OUT THE METHOD AND A PRODUCT PRODUCED BY MEANS OF THE METHOD

Abstract: In a method for cleaving laminated mineral blocks (1) along an interface between two laminae a fluid under pressure is fed to the mineral block to be cleft at at least one place (21) in the boundary region between said two laminae so as to make the fluid penetrating between the laminae and while pressing them apart propagate between the laminae until they are separated by a continuous crack.

Description: Method for cleaving laminated mineral blocks, device for carrying out the method and a product produced by means of the method TECHNICAL FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a method for cleaving lami¬ nated mineral blocks along an interface between two laminas, a device for carrying out the method and a product produced by means of the method. The definition laminated mineral blocks comprises all types of solid minerals composed by a number of laminae or layers. These have been created in the course of the ages in the earth's crust and may be exploited therefrom for different purposes, for instance within the building field. The invention relates more particularly, but accordingly not solely, to cleaving of mineral blocks consisting of slate, especially mica slate and clay slate. As a consequence of this, the invention will hereinafter by way of example be described in connection with cleaving of mica slate so as to throw light upon the different problems of the present technique of clea¬ ving mineral blocks along an interface between two laminae. Mica slate is mined as large blocks, in general in open cut mine, and these blocks are given a size and form being easy to handle by means of for example sawing. The mineral blocks of mica slate are composed by superposed material laminae substan¬ tially parallel to each other. The mica slate is very hard, but it may be cleaved along the interfaces between two laminae while generating surfaces being very attractive to the eye. By doing so a surface with small waves is obtained, which is very decorative and gives rise to different kinds of reflexes and visual perceptions in dependence on the light inciding thereon and at which angle the slate surface is observed. This surface is in every day parlance called cleft surface. The mode of procedure for obtaining such a so called cleft surface has up to now been the following: by means of swinging a sledge or hammer by hand power several metal wedges have been driven at mutual distances into' the region between two laminae and in a direction substantially parallel thereto. The lami¬ nated mineral block has an expressed tendency to be cleft along the interfaces between the two laminae, the driving of the wedges inwardly generates a crack propagating between the two laminae in question and finally completely separating the two laminae, so that two material pieces with one desired cleft surface each have been created. A so called cleavage has been carried out. However, this mode of procedure has several inconveniences, not least for the person who has to carry out the work in question. It is namely very power consuming to drive wedges by means of a sledge hammer into the slate block, and the breaks have to be taken with comparatively short intervals, which results in a short effective work time per working cycle time. The sledge strokes on the wedges generate very high and unpleasant noices, which require hearing protection means and if one neglects to use them injuries in the acoustic apparatus may be a conse¬ quence. Furthermore, a minor cloud of quartz dust is created for each struck at the place of driving the wedge into the block, and since the striking person has his head positioned comparatively close to this place, he cannot avoid inhaling a part of this quartz dust. This will over a longer time influ¬ ence the health of the person in a negative way. Another disadvantage of this cleaving method consists in the proportionally great waste of material. Ugly marks on the resulting cleaving surfaces are formed where the wedges have been driven into the block, which leads to the necessity of sawing and throw an edge portion thereof away later on. The use of wedges also results in very long lever arms when the crack is propagated comparatively far into the material block, said lever arms increasing with the propagation of the crack from the driven wedge towards the opposite end of the material block. These long lever arms lead to an impending risk of formation of cracks in the direction substantially perpendi¬ cular to the two laminae, so that the material block is repea¬ tedly subjected to ruptures in this direction, and parts of or in some cases the whole slate scale aimed at has to be thrown away. The use of driven striking tools having wedges for cleaving slate blocks is also known, but it has turned out that these increase the risk of the last mentioned ruptures even more, since the driven striking tools may not be handled with the balancing of forces and the feeling possible when hitting wedges by man power. BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to remedy the incon¬ veniences mentioned above on cleaving laminated mineral blocks along an interface between two laminae by providing a method and a device enabling an efficient cleaving completely acceptable from the working environment point of view while procuring a minimal waste of material and still obtaining the beautiful natural so called cleft surfaces desired. According to the invention this object is obtained by a method and a device according to the appended independent claims 1 and 11. By feeding a fluid under pressure to the mineral block to be cleft at at least one place in the boundary region between said two laminae so as to make the fluid penetrating into and between the laminae and while pressing them apart propagate between the laminae until these are separated by a continuous crack, it is possible to avoid all the inconveniencies asso¬ ciated with a bad working environment. Neither the hearing nor the state of the lungs of the person realizing the cleaving is jeopardized, since neither noice nor dust clouds are created by the cleaving. The person only has to supervise the function of the device utilized for the cleaving. Furthermore, the need of frequent breaks is removed, since the work is not physically burdensome for the person in question. By the fact that the fluid penetrates between the laminae and thanks to that it needs room for propagating and presses the two laminae apart so as to by degrees propagate further and further inwardly between the laminae while displacing the crack front through the material block, no long lever arms are created, but the crack forming force always attacks the two laminae very close to the propagation front of the crack, so that the risk of the occurance of cracks and ruptures in other directions will be minimal. This reduces the waste of material considerably. It may in certain cases be necessary to apply a small incipient crack by means of for instance a wedge prior to the fluid under pressure is fed, but even in such a case the surface portion damaged by the wedge, which has to be cut away, will be consi¬ derably smaller than when driving in several wedges for obtai¬ ning the cleavage. In some cases incipient cracks may be omitted and any waste of material as a result of wedge marks may be completely eliminated. It should be underlined that the cleaving according to the invention takes place by pressing two laminae apart and not by cutting in a plane parallel to these laminae. Such a cutting, which could be realized mecanically, for instance by sawing, or by feeding a fluid under a very high pressure, would not result in the beautiful cleft surfaces with small waves desired. According to a preferred embodiment of the method according to the invention the mineral block is sealed by means of a means substantially impermeable to the fluid along the outer deli¬ miting walls of the mineral block at the level of the transi¬ tion between the two laminae, whereby the fluid is forced to propagate along the interface between the two laminae and generate the desired crack formation. The fluid consists advantageously of water and it is possible to feed water under a surprisingly low pressure, for instance about 2 bars, and still obtain a cleaving, since the water seeks its way through the mineral block while pressing the two laminae apart. The possibilities to have this low pressure lead to a fluid flow being very considerate to the surfaces formed on each side of the crack obtained and damages thereon are avoided. A product according to the invention may be obtained by car¬ rying out the method according to the invention. Further advantages and preferred characteristics of the inven¬ tion appear from the following description and the other appended dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a specific description of a preferred embodiment of the device according to the invention cited as an example as well as the method possible to carry out through this. In the drawings: Fig 1 is a perspective view illustrating the method utilized until now for cleaving laminated mineral blocks, Fig 2 is a perspective view of a preferred embodiment of the device according to the invention, Fig 3 is an enlarged, sectional side elevation of a detail of the device according to Fig 1 in the state of function, Fig 4 is a perspective view obliquely from above of a detail shown in Fig 3 with the material block arranged in the device made transparent, and Fig 5 is a schematic, sectional side elevation intended to illustrate how a mineral block is cleft according to the invention by the propagation of water between two laminae. BRIEF DESCRIPTION OF THE PRIOR ART In Fig 1 it is schematically shown how a mica slate block is cleft or split into scales. The slate block 1 is usually sawn in a direction substantially perpendicular to the extension of the different laminae, so that it gets substantially even delimiting walls. The thickness of such a block 1 is normally about 30 cm and such a block includes a great number of laminae, for instance about 50. Slate scales with a thickness of about 10-40 mm are usually demanded, so that scales consisting of several laminae are to be cleft out of the slate block. However, for the sake of clarity only the interfaces along wich it has to be cleft are indicated. It is necessary to drive the wedges 2 in between two laminae substantially at half the thickness of the block so as to prevent breaking forces acting obliquely upon the block from occurring. Several wedges are struck at mutual distances along at least one delimiting wall of the block. It is shown in the Figure how two such wedges still remain in the block, while a wedge driven into the block is removed in order to illustrate the damaging mark 3 left behind by the wedges. Through the hitting of the wedges into the block a crack 4 will propagate along the interface between the two lamniae between wich the wedges have been driven into the block. A cleavage of the slate block 1 is accomplished in this way. When this cleavage has taken place the two slate block parts obtained may in their turn be halved with respect to the thickness by driving in wedges between two laminae thereof. The disadvantages of this way of cleaving have been thoroughly discussed above. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the device according to the invention is shown in a simplified way in perspective in Fig 2. The device has a bed 5, which is constituted by mutually spaced rolls 6, which are arranged to support a mineral block 1 to be cleft along the interface between two laminae. The bed 5 is supported through power means 7, in the form of hydraulic cylinders, by a stand 8 resting on the ground. The bed may be lifted and lowered by prolongation and shortering, respec¬ tively, of the hydraulic cylinders 7. Furthermore, the device comprises a frame work 9, and on this a second power means 10, also in the form of a hydraulic cylin¬ der, is arranged to act between the frame work 9 and a pressure plate 11 arranged at one end of the power means so as to press the plate 11 against the upper side of the mineral block 1 and thereby clamp and fix the block between the pressure plate 11 and the rolls 6 of the bed 5. The mineral block 1 may in this way be hold in a substantially fixed position during the cleaving process. However, the power means 10 preferably allows a slight movement, of some mm, of the mineral block in the vertical direction by pressing the pressure plate 11 back during the penetration of the fluid in the mineral block 1 and thereby a slight coming apart of the material block portions located on each side of the cleaving surface in question. Two rulers 12 in the form of square beams extending substan¬ tially parallel to each other in a horizontal plane are movably arranged on the frame work 9 in the directions towards and away from each other. However, these rulers 12 are not movable in the vertical direction. The movements of the rulers are achieved by third power means 13 acting between the frame work 9 and the ruler in question, and these means are also in the form of hydraulic cylinders. The third power means 13 are preferably commanded in common by one single command. A sealing element in the form of a rubber strip 14 is secured to the surface of each ruler facing the other ruler, i.e. the mineral block 1 (see in particular Fig 4). The rubber strip 14 has here the same width as the ruler 12 in question, but it could be considerably narrower, should a very straight crack propagation be expected, since it is only necessary that it bears on each side of the crack formed. It would be possible to reduce the bearing pressure of the power means 13 if the strip were more narrow. The device has also a plate 15 arranged to be pressed against a delimiting wall of the mineral block being substantially perpendicular to the extension of the rulers. A fourth power means 16 in the form of a hydraulic cylinder is for this reason arranged to act between a part 18 securable through stretching screws 17 with respect to the rest of the frame work and the plate 15. The surface of the plate 15 turned towards the mineral block 1 is provided with a nozzle 19 (see also Fig 4), which consists of a rubber strip 20 extending substantially horizontally and having an aperture. A conduit for fluid under pressure in the form of a water hose 22 is led through the plate 15 and to the aperture 21 of the nozzle 19. The end of the hose is indicated in Fig 3. The assembly for feeding water through the conduit 22 is not shown in the Figures, and this may be constructed in an arbitrary way known per se. The rubber strip 20 is arranged to extend along the entire width of the mineral block all the way to the rubber strips of the two rulers, so that the rubber strips 14 and 20 are able to, except for the opening 21, form a water tight delimiting of the mineral block 1 along three delimiting walls of the mineral block over a surface vertically corresponding to the width of the strips. It may be assured that the rubber strips 14 are tightly connected to the rubber strip 20 by adjustment of the stretching screws 17. It is shown in Fig 4 how a plate 15 with the strip 20 is inserted between the rulers 12, but the rulers 12 could be arranged not to project beyond the end edge of the block and the length of the strip 20 may be increased to an appropriate extent so as to adapt the device to mineral blocks with different widths. The function of the device described above will now be de¬ scribed with reference made also to Figs 3-5. A mineral block to be cleft along the interface between two lamina, may be at several places so as to split the mineral block into several scales, is firstly cut so that it gets even lateral delimiting walls, in the way shown in Fig 2. This block is then laid down on the bed formed by the rolls 6 and the second power means 10 is actuated to fix the mineral block with respect to the bed 5. The power means 7 are after that actuated so that the bed 5 is vertically moved with respect to the rulers provided with the rubber strips 14 and the nozzle 19. This movement takes place to a position in which a first interface along which is to be cleft lies in a horizontal plane approximately in the middle between the upper and lower edge of the rubber strips 14. When this position is reached, the third power means 13 are actuated to bring the rulers 12 towards each other, so that the rubber strips 14 will sealingly bear against the two laminae of the mineral block on each side of the transition therebetween. The fourth power means 16 is after that actuated to press the nozzle 19 into sealing bearing against the mineral block on each side of the same laminae transition. It is possible to provide the mineral block with a small incipient crack 24 at the place intended to be located just opposite to the aperture 21 of the nozzle. Such incipient cracks 24 are illustrated in Fig 3 and assist in initiating the cleaving crack aimed at. All the laminae of the upper scale to be cleft away from the mineral block are shown in this Figure, while for the rest only the boundary layer surfaces along which it is to be cleft are indicated. Water under a comparatively low pressure (experi¬ ments have shown that pressures of below 2 bars are sufficient in some cases) is after that fed to the aperture 21. However, higher pressures, such as about 10 bars, may be required for initiating the crack formation. The water penetrates into the incipient crack 24 and is by the rubber strips 20 and 14 prevented from escaping from the mineral block. The water will as a consequence thereof exert forces in the direction sub¬ stantially perpendicular to the planes of the two lamina and gradually press the two laminae apart on the propagation of a crack quickly filled by water in the direction towards the end 25 of the mineral block 1 located opposite to the aperture 21. How this takes place is shown in Fig 5. Accordingly, the lever arms will during this pressing apart be very short, since the water continuously fills the crack formed and exerts forces for pressing apart in the region of the crack front existing in every moment. The risk of accidental ruptures is therefor very small. Thanks to the short lever arms it is also possible to cleave the mineral block at a desired place, i.e. also so that the mineral block parts located on each side of the crack formed have considerably different thicknesses. The water supply to the nozzle 19 is interrupted and the power means 16 and 13 are actuated to move the sealing strips away from the mineral block 1, when said crack has propagated along the entire interfacing in question and the cleaving thus has been completed. The power means 7 is after that actuated to move the bed 5 and thereby the mineral block in the vertical direction to a position suitable for carrying out the next cleaving, whereupon the working moments described above are repeated for the realization thereof. It may in this way be started for instance 30 mm from the upper side of the mineral block with a cleavage along the interface between two laminae and the mineral block may thereafter be gradually moved up¬ wardly while cleaving thin scales from the lower part of the mineral block until the block consists solely of such thin scales. The invention is of course not in any way restricted to the preferred embodiment described above, but a variety of possi¬ bilities to modifications thereof should be apparent to a man skilled in the art without departing from the basic idea of the invention. It would for example be possible to feed another fluid than ■ water for cleaving the mineral block, for instance any other liquid or even a gas under a certain over-pressure. However, it must be observed that the pressure of the supplied fluid has to be so low that the cleaving is realized by pressing the two laminae apart and not by cutting along a plane in the interface between the laminae. It would also be possible to arrange sealing elements at the end 25 of the mineral block, so that the mineral block is sealed substantially all around, but it would then be necessary to arrange some kind of escape openings for the fluid close to this end. The block to be cleft by means of the device could of course appear in totally different forms than the one shown in the Figures, and the device will then get the corresponding modi¬ fications. However, it is advantageous that the material block has smooth delimiting walls, but this is not completely necessary, but it would also be conceivable to arrange any other type of sealing elements, e.g. any kind of sealing paste sprayable onto and along the mineral block. It would also be conceivable to arrange any other type of means than sealing elements so as to counteract that the fluid escapes out of the mineral block at its outer delimiting walls before the continuous crack is formed. It would also be possible to feed fluid at several places along the periphery of the mineral block, and a supply of fluid on one short side of the mineral block, as shown in Fig 2, should not at all be considered as a limitation of the invention, but the feed place or places may just as well be located on a greater side of the block. The pressure informations for the fluid given above are only to be considered as examples and do not constitute any limits for the invention.

Claims: Claims 1. A metohd for cleaving laminated mineral blocks (1) along an interface between two laminae, c h a r a c t e r i z e d in that a fluid under pressure is fed to the mineral block to be cleft at at least one place (24) in the boundary region between said two laminae, so as to make the fluid to penetrate between the laminae and propagate between the laminae while pressing them apart until they have been separated by a continuous crack. 2. A method according to claim 1, c h a r a c t e r i z e d in that while feeding the fluid this is counteracted to leave the mineral block at the outer delimiting walls (23) thereof prior to the formation of said continuous crack. 3. A method according to claim 2, c h a r a c t e r i z e d in that said counteraction is realized by sealing the mineral block by means of a means (14, 20) substantially impermeable to the fluid along the outer delimiting walls of the mineral block at the level of the transition between the two laminae. 4. A method according to claim 3, c h a r a c t e r i z e d in that the mineral block is prior to the feed of fluid cut according to planes making substantial angles, preferably right angles, with the laminae planes so as to provide the mineral block with outer delimiting walls having even surfaces for facilitating the application of the sealing means (14, 20) thereto. 5. A method according to claim 4, c h a r a c t e r i z e d in that the sealing is realized by pressing substantially planar material pieces (14 20) to bearing against the two laminae on each side of the transition therebetween along at least the main part of the delimiting walls of the mineral block. 6. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the fluid being fed is a liquid. 7. A method according to claim 6, c h a r a c t e r i z e d in that water is what is fed to the mineral block. 8. A method according to claim 6 or 7, c h a r a c t e ¬ r i z e d in that the liquid is fed under a low pressure, preferably between 1,5 and 2,5 bars. 9. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the mineral block being cleft consists of mica slate. 10. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the mineral block is prior to the feed of fluid provided with an incipient crack (24) at said place or places for feed of fluid. 11. A device for cleaving laminated mineral blocks along an interface between two laminae, c h a r a c t e r i z e d in that it compirses means (22) for feeding a fluid under pressure at at least one place (21) in the boundary region between said two layers. 12. A device according to claim 11, c h a r a c t e r i z e d in that it comprises means (14, 20) for counteracting an escape of the fluid out of the mineral block (1) at the outer delimi¬ ting walls (23) thereof. 13. A device according to claim 12, c h a r a c t e r i z e d in that said counteracting means comprises one or several elements (14, 20) substantially impermeable to the fluid and arranged to seal the mineral block along its outer delimiting walls at the level of the transition between the two laminae. 14. A device according to claim 13, c h a r a c t e r i z e d in that the elements consist of substantially planar material pieces (14, 20) and that the device comprises a power apparatus (13, 16) arranged to press the planar material pieces to bearing against the two lamina on each side of the transition therebetween along at least the main part of the delimiting walls of the mineral block. 15. A device according to claim 14, c h a r a c t e r i z e d in that the material piece (20) adapted for bearing in the region of the place for the feed of fluid has an aperture (21), that said feeding means comprises a fluid conduit (22) arranged to emerge into the aperture, and that the portions of the material piece surrounding the aperture are arranged to be sealingly connected to the periphery of the fluid conduit. 16. A device according to claim 14 or 15, c h a r a c t e ¬ r i z e d in that the material pieces consist of planar rubber sheets or strips. 17. A device according to any of the claims 11 to 16, c h a r a c t e r i z e d in that it comprises an apparatus (7) arranged to, after the cleaving of the mineral block along an interface between two laminae cause a movement of the mineral block (1) and the fluid feed place (21) with respect to each other in a direction substantially perpendicular to the exten¬ sion of the laminae so as to to move the place for feeding fluid under pressure to a boundary region between another pair of laminae in order to make several cleavings of one and the same mineral block. 18. A device according to claims 14 and 17, c h a r a c t e ¬ r i z e in that it comprises a bed (5), on which the mineral block (1) is intended to rest with the laminae planes sub¬ stantially parallel thereto, that the power apparatus (13, 16) is arranged to, after a completed cleaving along the interface between two laminae, remove the sealing material pieces (14, 20) from the mineral block, and that said apparatus (7) for rela¬ tive movement is arranged to, after this removal, cause a vertically movement of on one hand the bed (5) and on the other the sealing material pieces (14, 20) and the fluid feed place (21) with respect to each other so as to bring the material pieces and the fluid feed place into a position for cleaving the mineral block along an interface between another pair of laminae of the mineral block. 19. A device according to any of the claims 11-18, c h a r a c t e r i z e d in that the feeding means (22) is arranged to feed a liquid to the boundary region between the two laminae. 20. A device according to claim 19, c h a r a c t e r i z e d in that the liquid is water, and that the feeding means is arranged to feed water under a low pressure, preferably between 1,5 and 2,5 bars. 21. A product obtained by cleaving a laminated mineral block along an interface between two laminae, c h a r a c t e ¬ r i z e d in that it is produced by carrying out the method to any of the claims 1-10.

Inventors: MELLGREN BO, MELLGREN, BO
Applicants: JACOBSSON & OSCARSSON SKIFFER, SKIFFERBOLAGET JACOBSSON & OSCARSSON AB
Application year: 1990
Main classification: B28D1
IPC codes: B28D1, B28D7