WO2006099894A1

WO2006099894A1 - Improved ceramic slab for facings, and method for its manufacture

Info

Publication number: WO2006099894A1
Application number: PCT/EP2005/012364
Authority: WO
Inventors: Silvano Valli; Claudio Ricci
Original assignee: Sacmi Cooperativa Meccanici Imola Societa' Cooperativa
Priority date: 2005-03-24
Filing date: 2005-11-16
Publication date: 2006-09-28
Also published as: ITRE20050030A1; ATE406339T1; DE602005009407D1; EP1866261B1; EP1866261A1; PT1866261E; RU2007134248A; CN101142153A

Abstract

An improved ceramic slab (1) and a method for its manufacture. The slab (1) comprises a continuous ceramic matrix (2) internally incorporating reinforcement fiber (3) having resistance characteristics superior to those of the ceramic matrix itself. The method comprises the following steps: creating, on a support surface (11), a first layer of ceramic powder (5); distributing an assembly of reinforcement fibers (3) over at least an area of the top surface (50) of said first layer (5) of ceramic powder; covering the reinforcement fibers, to create at least a second layer (6) of ceramic powder on said first layer (5), in order to obtain a soft ceramic blank of desired thickness containing the reinforcement fibers; pressing said soft blank to compact the powders and obtain an unfired ceramic slab; subjecting said unfired ceramic slab to firing, to obtain a ceramic slab (1) comprising a continuous ceramic matrix (2) with the reinforcement fibers (3) incorporated.

Description

DESCRIPTION

IMPROVED CERAMIC SLAB FOR FACINGS, AND METHOD FOR ITS

MANUFACTURE

TECHNICAL FIELD

The present invention relates generally to ceramic slabs or tiles for facings and floorings, and to a method for their manufacture.

BACKGROUND ART Ceramic slabs usually used for facings and floorings are known to present high compression resistance, surface hardness and abrasion resistance characteristics, which are provided by the constituent materials of the ceramic mix and the high temperature firing process to which the mix is subjected. In contrast, said ceramic slabs present low tensile strength and generally a fragile behaviour, which has always limited their use under conditions in which a state of tensile or bending stress is present. Under such conditions, as the result of a knock or a particularly intense stress, a small crack can form within the ceramic slab, and because of the fragile ceramic behaviour can propagate progressively throughout the entire slab, until it breaks.

This intrinsic ceramic fragility is particularly serious if said slabs are used for facing external facades of buildings, as they may be fixed, generally by suitable mechanical means, at a great height from the ground. In this context, there is an obvious clanger arising from a sudden breakage of the slab (due to natural or accidental events) and the consequent fall of its fragments from a great height.

To confront this problem, two possible alternative solutions are currently known.

A widely used first solution consists of applying a net of synthetic or metallic material to the rear face of the ceramic slab by gluing with epoxy resin.

In this manner, if the slab suddenly breaks, its fragments remain in position retained by the net to which they are glued, so preventing danger to persons or things.

A recently introduced second solution consists of producing the slab by superposing two or more thin slabs and interposing a resin layer therebetween, which by gluing them together provides mechanical continuity to the assembly. In this manner a composite ceramic slab is obtained, in which each individual constituent slab acts as a support for the others.

Notwithstanding the good results offered by both said solutions, they present serious limitations to their widespread use, in particular because of the lack of reliability of the glue connection and the high cost of making this type of connection.

An object of the present invention is to provide a reinforced ceramic slab presenting resistance characteristics superior to usual slabs, within the framework of a simple, rational and low-cost solution. DISCLOSURE OF THE INVENTION

This object is attained by a reinforced ceramic slab comprising a continuous ceramic matrix internally incorporating reinforcement fibres, i.e. filiform bodies not necessarily rectilinear, having resistance characteristics superior to those of the ceramic matrix itself.

In particular, the reinforcement fibres possess greater tensile strength than said ceramic matrix.

According to the invention, the reinforcement fibres are distributed within said ceramic matrix in such a manner as to form at least one composite layer of ceramic and fibres lying between two purely ceramic layers. Within said composite layer, the reinforcement fibres lie separated and spaced apart from each other substantially in one and the same plane, which can be parallel to the faces of the ceramic slab or inclined to them. In particular, the reinforcement fibres can be distributed in random manner, or preferably can be distributed in an ordered manner to form a discontinuous net, the meshes of which are defined by the reinforcement fibres.

By virtue of this solution, a ceramic slab according to the invention is substantially provided with an inner reinforcement, which makes it less fragile than the usual completely ceramic slabs.

In this respect, if a crack forms within the reinforced ceramic slab, its propagation is interrupted on encountering the reinforcement fibres, which have greater resistance than the ceramic matrix, and which hence prevent the slab from breaking into fragments. According to the invention, the meshes of the net must have their sides of length less than the length of the reinforcement fibres which define them, to prevent substantially rectilinear preferential directions existing within the ceramic slab along which a crack can propagate without encountering any reinforcement fibre.

In a preferred embodiment of the invention, the reinforcement fibres are distributed in an ordered repetitive pattern, so that the meshes of the discontinuous net are in the form of a parallelogram, typically rectangular or square, and are all equal to each other.

Furthermore, according to the invention, the reinforcement fibres are metal fibres, typically rectilinear pieces of steel wire, preferably having a diameter between 0.3 and 0.7 mm, and a length between 20 and 200 mm, preferably between 40 and 100 mm.

Alternatively, said reinforcement fibres can be glass fibres, carbon fibres or aramid fibres.

The invention also comprises a method for manufacturing said reinforced ceramic slab, comprising the following steps: a) creating, on a support surface, a first layer of ceramic powder; b) distributing an assembly of reinforcement fibres over at least an area of the top surface of said first layer of powder; c) covering the reinforcement fibres, to create at least a second layer of ceramic powder on said first layer, in order to obtain a soft ceramic blank of desired thickness, containing the reinforcement fibres; d) pressing said soft blank to compact the powders and obtain an unfired ceramic slab; and finally e) subjecting said unfired ceramic slab to firing, to obtain a reinforced slab comprising a continuous ceramic matrix within which the reinforcement fibres are incorporated. According to the invention, in particular, said step c) of covering the reinforcement fibres can be implemented by repeating steps a) and b) a desired number of times, so that the soft blank comprises a plurality of ceramic powder layers, between which the reinforcement fibres are interposed.

With this solution, the reinforced ceramic slab can be manufactured very simply, rationally and economically, both by a discontinuous forming process using usual ceramic moulds, and by a continuous forming process, of the type described in European patent application EP 1283097 in the name of the same Applicant.

In the first case, said support surface is a vertically translating surface, defined by the upper surface of the lower die of a ceramic mould, whereas in the second case it is a horizontally translating surface, defined by the conveyor belt of a continuous forming plant. According to the invention, the reinforcement fibres are distributed over the entire top surface of the first layer of ceramic powder created, this preferably being a flat surface which can be parallel to the support surface or inclined to it. The reinforcement fibres are distributed separated and spaced apart over said top surface in such a manner as to reduce to a minimum the region of ceramic mass within which possible cracks can propagate. In particular, said reinforcement fibres can be distributed in random manner, but they are preferably distributed in an ordered manner to form a discontinuous net, the meshes of which are defined by the reinforcement fibres themselves; said meshes preferably having sides of dimensions less than the length of the fibres which define them. In this manner, by using separate and easily applied reinforcement fibres, the method of the invention can be easily adapted to changes in ceramic slab format.

Moreover, said reinforced fibres advantageously enable natural linear expansion of the ceramic mass immediately after the pressing step, and its shrinkage during firing, during which in particular, notwithstanding the high temperatures, the reinforced fibres (especially those of metal or carbon) maintain their mechanical properties unaltered, they being embedded in the ceramic mass and not in contact with the oxygen of the air.

According to a preferred embodiment of the invention, the reinforced fibres are distributed as a plurality of longitudinal parallel rows and as a plurality of transverse parallel rows which intersect to form said discontinuous net, this hence presenting meshes of parallelogram shape. Moreover, the reinforced fibres of each longitudinal row are preferably offset from those pertaining to the adjacent longitudinal rows, the reinforced fibres of each transverse row likewise being offset from those pertaining to the adjacent transverse rows, so that the net meshes can have any desired dimension without involving superposing and mutual contact of the reinforced fibres.

According to a preferred embodiment, the distance separating the longitudinal rows and the distance separating the transverse rows are both constant and are preferably equal, to hence obtain a discontinuous net with its meshes all identical. According to a further preferred embodiment of the invention, said longitudinal and transverse rows are inclined to the sides of the ceramic slab, preferably at an angle of about 45°.

By virtue of this embodiment, if the slab is subjected to a cutting step, for example after the pressing step, the cutting lines, which are generally parallel to the sides of the slab, intersect the reinforced fibres only within a limited region, to ensure good finishing of the resultant edge, and avoiding ceramic slab stability problems.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will become apparent on reading the ensuing description provided by way of non- limiting example, with the aid of the figures shown in the accompanying drawings, in which: Figure 1 is a partially cut-away view of a reinforced ceramic slab according to the invention;

Figure 2 is a side view of the slab of Figure 1 ;

Figures 3a to 3c show schematically a succession of steps in the method for manufacturing the slab of Figure 1 ; Figure 4 is a plan view of Figure 3b;

Figure 4' is the same as Figure 4 but showing an alternative embodiment of the slab of Figure 1 ;

Figure 5 is a side view of a continuous plant for forming reinforced ceramic slabs according to the invention; Figure 6 is a plan view of the forming plant shown in Figure 5; Figures 7a to 7d show a ceramic mould during a succession of steps in the discontinuous forming process for the slab of Figure 1 ; Figure 8 is an enlarged detail of Figure 5.

BEST MODE FOR CARRYING OUT THE INVENTION

The reinforced ceramic slab 1 , shown in Figure 1 , comprises a continuous ceramic matrix 2, within which reinforcement fibres 3 are incorporated. In the particular illustrated example, said reinforced fibres are rectilinear pieces of steel wire, preferably stainless steel; however, in general they can be filiform bodies, not necessarily rectilinear, of a material having resistance characteristics superior to those of the ceramic matrix 2, for example carbon fibres, glass fibres or aramid fibres. As shown in Figure 1 , the reinforced fibres 3 are distributed in the interior of the ceramic matrix in such a manner as to define a composite layer 20 of ceramic and fibres lying between two purely ceramic layers 20 and 21 (see also Figure 2), within said layer the reinforced fibres 3 lying substantially on one and the same surface, separated and spaced apart, to form a discontinuous net. In this manner, whenever a crack forms in the ceramic slab 1 , its propagation is interrupted on encountering the reinforced fibres 3, which have greater tensile strength than the ceramic matrix 2, and hence prevent the ceramic slab 1 from breaking into fragments. As shown in the particular example of Figure 1 , the reinforced fibres 3 are all of the same length, preferably between 40 mm and 100 mm, and the same diameter, preferably between 0.3 mm and 0.7 mm; in addition, the meshes of the discontinuous net, which are defined by the reinforced fibres 3, are substantially square.

The side dimension of said meshes is less than the length of the reinforced fibres 3, so that no substantially rectilinear preferential directions exist along which a crack can propagate without encountering any reinforced fibre 3.

A preferred method for manufacturing reinforced ceramic slabs 1 of the aforedescribed type is described hereinafter with the aid of Figures 3a-3c. Said manufacturing method comprises the following steps: - creating, on a support surface 11 , a first layer 5 of ceramic powders having a thickness substantially one half of the thickness of the soft ceramic mass which is to form the slab 1 (see Figure 3a);

- distributing an assembly of reinforcement fibres (3) over the top surface 50 of said first layer 5 (see Figure 3b); - covering said reinforcement fibres 3, to create a second layer 6 of ceramic powders on said first layer 5, in order to obtain a soft ceramic blank containing the reinforcement fibres 3;

- pressing said soft blank to compact the powders and obtain an unfired ceramic slab; and finally - subjecting said unfired ceramic slab to firing, to obtain a slab 1 comprising a continuous ceramic matrix 2 with the reinforcement fibres 3 incorporated in its interior.

As shown in Figure 4, said manufacturing method comprises distributing the reinforced fibres 3 over the surface 50 of the first layer 5 in an ordered manner, separated and spaced from each other, to form said discontinuous net. In detail, the reinforced fibres 3 are aligned along a plurality of longitudinal parallel lines 30 and along a plurality of transverse parallel lines 31 parallel to the former.

The reinforced fibres 3 of each longitudinal row 30 are offset from the fibres 3 pertaining to the adjacent rows 30, and likewise the fibres 3 of each transverse row 31 are offset from those pertaining to the adjacent rows 31.

Moreover, the distance P between the longitudinal rows 30 and the distance P' between the transverse rows 31 are both constant, equal to each other and less than the length of the individual reinforced fibres 3, to obtain a discontinuous net with square meshes, all equal, having the length of their side less than said length of the reinforced fibres 3. In the particular example shown in Figure 4, the longitudinal rows 30 and the transverse rows 31 are parallel respectively to the edges of the first ceramic layer 5, and hence to the edges of the reinforced slab 1 being manufactured. However, these rows 30 and 31 can also be inclined to the edges of the slab 1 and in particular, as shown in Figure 4', can be inclined by an angle substantially of 45°, for the reasons which will become clear hereinafter. According to a first preferred embodiment of the method, shown in Figures 5 and 6, the reinforced ceramic slabs 1 are manufactured by a continuous forming plant 8.

Said forming plant 8 comprises schematically: a conveyor belt 80; first ceramic powder dispensing means 81 ; a distributor device 82 for reinforced fibres 3; second ceramic powder dispensing means 83; continuous powder compacting means 84; and finally cutting means 85 downstream of said compacting means 84.

In use, the first dispensing means 81 are arranged to deposit a first continuous layer of ceramic powder onto the upper surface 11 of the advancing belt 80; the distributor device 82, which is positioned downstream of the means 81 , then distributes the reinforced fibres 3, which are all identical, over the top surface 50 of the first powder layer 5, in such a manner as to form the discontinuous net in accordance with the aforedescribed modality, In particular, as visible in Figure 8, the longitudinal rows 30 and the transverse rows 31 are inclined to the sides of the first ceramic powder layer 5 by an angle substantially equal to 45°.

Downstream of the distributor device 82, the second dispensing means 83 deposit a second continuous layer 6 of ceramic powder onto the surface 50 of the first layer 5, to cover the reinforced fibres 3; said second layer 6 being able to present graphic effects within the powder mass or on its top surface.

In this manner, a continuous strip 7 of ceramic powder containing the reinforced fibres 3 is formed, and is made to advance on the conveyor belt 80 between the compacting means 84, which subject the ceramic powders to pressing to form a compact strip 7'. Said compacting means

84 are described in European patent application EP 1283097, to which reference should be made for further details.

Finally, the compact strip T is fed to the cutting means 85, which trim its edge and divide it into an assembly of separate unfired slabs 9. In particular, as shown in Figure 8, said step of dividing the strip T into unfired slabs 9 takes place along cutting lines A perpendicular to the sides of the strip 7'; consequently, because of the already described distribution of reinforced fibres 3 along longitudinal lines 30 and transverse lines 31 inclined to the sides of the compact strip T, said cutting lines A intersect the reinforced fibres 3 within limited regions, to obtain a good edge finish on the resultant unfired slab 9, without compromising its stability. On termination of the cutting step, the unfired slabs 9 can finally be decorated, and may be subjected to a further pressing step using ceramic moulds, before being subjected to the traditional drying and firing steps, which enable the finished reinforced slab 1 to be obtained. After the cutting step, the edges of the slab 1 may be smoothed and ground. According to an alternative embodiment, shown in Figures 7a to 7d, the manufacture of the reinforced ceramic slabs 1 takes place by a discontinuous process using a usual ceramic mould 10. Said mould 10 comprises a die plate 100 provided with a forming cavity 101 , the base of which is closed by a lower movable die 102, with which an upper movable die 103 is vertically aligned. A usual movable loading tray (not shown) can be associated with the mould 10 to release powdered ceramic material into the interior of the forming cavity 101.

In use, the manufacturing cycle conventionally begins when the upper surface 11 of the lower die 102 of the mould 10 is coplanar with the top of the die plate 100. At this point the loading tray advances to above the forming cavity 101 ; then, as shown in Figure 7a, the lower die 102 is lowered by an amount substantially equal to one half the thickness of the soft ceramic mass intended to form the slab 1 , so that a first layer 5 of ceramic powder descends to fill the forming cavity 101 , in contact with the surface 11 of the lower die 102.

After this step, the loading tray withdraws, and reinforced fibres 3 are distributed over the top surface 50 of the first layer 5 (see Figure 7b), in a manner similar to that described for the preceding embodiment. At this point the loading tray again advances and, as shown in Figure 7c, the lower die 102 is again lowered, enabling a second layer 6 of ceramic powders to descend to cover the reinforced fibres 3. Finally (see Figure 7d), the upper die 103 is lowered to compact the soft ceramic mass, and hence obtain an unfired slab 9 which can then be subjected to the usual accessory steps, such as decoration or trimming, before being subjected to drying and firing in a kiln.

Claims

1. A reinforced ceramic slab, characterised by comprising a continuous ceramic matrix (2) internally incorporating reinforcement fibres (3) having resistance characteristics superior to those of the ceramic matrix itself.

2. A ceramic slab as claimed in claim 1 , characterised in that the reinforced fibres (3) possess greater tensile strength than the ceramic matrix (2).

3. A ceramic slab as claimed in claim 1 , characterised in that the reinforced fibres (3) are distributed within the interior of the ceramic matrix (2) in such a manner as to form at least one composite layer (20) of ceramic and fibres, lying between two purely ceramic layers (21 , 22).

4. A slab as claimed in claim 3, characterised in that within the composite layer (20), the reinforced fibres are distributed in such a manner as to lie substantially in the same plane, separated and spaced apart.

5. A slab as claimed in claim 4, characterised in that said plane is substantially parallel to the faces of the slab (1 ).

6. A slab as claimed in claim 4, characterised in that said plane is inclined to the faces of the slab (1 ).

7. A slab as claimed in claim 4, characterised in that the reinforced fibres (3) are distributed in a random manner.

8. A slab as claimed in claim 4, characterised in that the reinforced fibres (3) are distributed in an ordered manner to form a discontinuous net, the meshes of which are defined by the reinforced fibres (3).

9. A slab as claimed in claim 8, characterised in that the meshes of the net have sides of length less than the length of the reinforced fibres (3) which define them.

10. A slab as claimed in claim 8, characterised in that the meshes of the net are of parallelogram shape.

11. A slab as claimed in claim 10, characterised in that the meshes of the net are substantially all equal.

12. A slab as claimed in claim 1 , characterised in that said reinforced fibres (3) are metal fibres.

13. A slab as claimed in claim 12, characterised in that said metal fibres (3) are rectilinear pieces of steel wire.

14. A slab as claimed in claim 13, characterised in that said steel wire pieces have a diameter between 0.3 mm and 0.7 mm.

15. A slab as claimed in claim 13, characterised in that the steel wire pieces have a length between 20 mm and 200 mm.

16. A slab as claimed in claim 15, characterised in that the steel wire pieces have a length between 40 mm and 100 mm.

17. A slab as claimed in claim 1 , characterised in that said reinforced fibres (3) are chosen from the group comprising carbon fibres, aramid fibres and glass fibres.

18. A method for manufacturing reinforced ceramic slabs (1 ) in accordance with claim 1 , characterised by comprising the following steps: a) creating, on a support surface (11 ), a first layer of ceramic powder (5); b) distributing an assembly of reinforcement fibres (3) over at least an area of the top surface (50) of said first layer (5) of ceramic powder; c) covering the reinforcement fibres, to create at least a second layer (6) of ceramic powder on said first layer (5), in order to obtain a soft ceramic blank of desired thickness containing the reinforcement fibres; d) pressing said soft blank to compact the powders and obtain an unfired ceramic slab; e) subjecting said unfired ceramic slab to firing, to obtain a ceramic slab (1 ) comprising a continuous ceramic matrix (2) with the reinforcement fibres (3) incorporated.

19. A method as claimed in claim 18, characterised in that step c) is implemented by repeating steps a) and b), to obtain a soft bank comprising a plurality of ceramic powder layers between which the reinforced fibres (3) are interposed.

20. A method as claimed in claim 18, characterised in that the reinforced fibres (3) are distributed over the entire top surface (50) of the first ceramic powder layer (5).

21. A method as claimed in claim 18, characterised in that the top surface (50) of the first layer (5) is a flat surface.

22. A method as claimed in claim 21 , characterised in that said top surface (50) is parallel to the support surface (11 ) on which the first ceramic powder layer (5) is created.

23. A method as claimed in claim 21 , characterised in that said top surface (50) is inclined to the support surface (11 ).

24. A method as claimed in claim 18, characterised in that the reinforced fibres (3) of each assembly are distributed such that they are separated and spaced apart.

25. A method as claimed in claim 18, characterised in that the reinforced fibres (3) are distributed in a random manner.

26. A method as claimed in claim 18, characterised in that the reinforced fibres (3) are distributed in an ordered manner such as to form a discontinuous net, the meshes of which are defined by the reinforced fibres (3).

27. A method as claimed in claim 26, characterised in that the meshes of the discontinuous net have sides of length less than the length of the reinforced fibres (3) which define them.

28. A method as claimed in claim 26, characterised in that the reinforced fibres (3) are distributed as a plurality of longitudinal parallel rows (30) and a plurality of transverse parallel rows (31 ) oblique to the longitudinal rows (30).

29. A method as claimed in claim 28, characterised in that the reinforced fibres (3) pertaining to each longitudinal row (30) are offset from those pertaining to the adjacent longitudinal rows (30), the reinforced fibres (3) pertaining to each transverse row (31 ) being offset from those pertaining to the adjacent transverse rows (31 ).

30. A method as claimed in claim 28, characterised in that said longitudinal rows (30) are spaced apart by a constant distance (P), the transverse rows (31 ) being likewise spaced apart by a constant distance (P).

31. A method as claimed in claim 30, characterised in that the distance (P) separating the longitudinal rows (30) is equal to the distance (P') separating the transverse rows (31 ).

32. A method as claimed in claim 28, characterised in that said longitudinal rows (30) and transverse rows (31 ) are inclined to the sides of the ceramic slab (1 ).

33. A method as claimed in claim 32, characterised in that said longitudinal rows (30) and transverse rows (31 ) are inclined substantially at 45° to the sides of the ceramic slab (1 ).

34. A method as claimed in claim 18, characterised in that the support surface (11 ) on which the first ceramic powder layer (5) is created is a translating surface.

35. A method as claimed in claim 34, characterised in that said support surface (11 ) translates in a vertical direction.

36. A method as claimed in claim 34, characterised in that said support surface (11 ) translates in a horizontal direction.

37. A method as claimed in claim 35, characterised in that said support surface (11 ) is defined by the upper surface of the lower die (102) of a ceramic mould (10).

38. A method as claimed in claim 36, characterised in that said support surface (11 ) is defined by the conveyor belt (80) of a continuous pressing plant.

39. A method as claimed in claim 18, characterised in that step c) is followed by a step of decorating the unfired slab.

40. A method as claimed in claim 18, characterised in that step c) is followed by a second pressing of the unfired slab.

41. A method as claimed in claim 18, characterised in that step c) is followed by a step of cutting the unfired ceramic slab.

42. A method as claimed in claim 18, characterised in that step d) is followed by a step of smoothing and grinding the edges of the ceramic slab (1 ).