WO2021144700A1

WO2021144700A1 - Process for producing mixtures for ceramic tiles

Info

Publication number: WO2021144700A1
Application number: PCT/IB2021/050209
Authority: WO
Inventors: Valter PALLADINI
Original assignee: Certech S.P.A. A Socio Unico
Priority date: 2020-01-16
Filing date: 2021-01-13
Publication date: 2021-07-22
Also published as: CN114845971A; BR112022011912A2; EP4090640A1

Abstract

Process for producing pastes for ceramic tiles, comprising the following steps: - wet grinding an initial ceramic mixture in order to obtain a slip; subjecting the slip to a mechanical dehydration step; - following the mechanical dehydration, subjecting the slip to an extrusion step, to obtain prismatic agglomerates of ceramic mixture; - subjecting the prismatic agglomerates to a drying step; - following the drying step, subjecting the prismatic agglomerates to a pulverisation step, in order to obtain granules of ceramic mixture.

Description

Process for producing mixtures for ceramic tiles

DESCRIPTION

The present invention relates to a process for producing pastes for ceramic tiles.

In particular, the process according to the present invention refers to a production process, the initial product of which is represented by slip coming from one or more wet grinding mills.

These production processes, widely known in the sector, provide for a drying step for drying the slip, carried out by using at least one atomizer. As is known, the atomizer, located downstream of the mills, produces hollow granules of ceramic material. These granules are obtained substantially by spraying the slip inside the atomizer through nozzles causing the pulverisation thereof. Inside the atomizer, the pulverised slip is dried by means of a flow of hot air which causes the water to evaporate, leaving the hollow granules intact.

The atomizer, necessary for the production of the dry granules of ceramic material, is a device that requires a considerable expenditure of energy and resources.

In fact, consider that the slip sent inside the atomizer has a moisture grade of about 50%, whereas a moisture grade of about 3÷4% is required at the outlet of the atomizer. The atomizer therefore requires a very large amount of heat to obtain such a reduction in moisture, which heat is produced by combustion of large quantities of fossil gas and consequent release of CO2 into the atmosphere. Furthermore, the water evaporating from the atomizer is dispersed into the atmosphere, thus constituting a further consumption of a natural resource. A further drawback of the atomizer is represented by its considerable dimensions, which entail a general increase in the overall dimensions of the production plants.

Production processes which do not provide for the use of an atomizer are currently also known in the sector, since they start from ceramic pastes obtained by dry grinding. However, these processes produce very coarse-quality pastes, with much larger granules than those obtained with an atomizer. Furthermore, the granules obtained are much denser and more compact than those obtained with an atomizer, making the semi finished products obtained by pressing less uniform.

The object of the present invention is to offer a process for producing pastes for ceramic tiles which allows obtaining a paste with characteristics comparable to those of the pastes obtained from an atomizer, but avoiding the use of an atomizer.

The advantages obtained by the process according to the present invention are therefore remarkable, both in terms of energy savings, in terms of consumption of raw materials and natural resources, and in terms of CO2 production.

Features and further advantages of the present invention will more fully emerge from the following detailed description of an embodiment of the present invention, as illustrated in a non-limiting example in the accompanying figures, in which:

- Figures 1 , 2 and 3 show a schematic view of different consecutive sections of a plant for carrying out the process according to the present invention.

The process according to the present invention provides for the wet grinding of an initial ceramic mixture in order to obtain a slip. This wet grinding step, well known in the sector, can be carried out by means of one or more continuous or discontinuous mills.

The initial ceramic mixture is substantially a mixture of minerals that are normally used, in various different compositions, for the production of ceramic tiles. In the initial ceramic mixture, the different minerals are present in a very varied granular form, that is, without any dimensional homogeneity. Wet grinding has the purpose of uniforming the particle size of the various minerals present in the initial mixture, and of bringing the particle size to a predetermined size.

As known, two or more mills can be arranged in series or in parallel. Mills with different characteristics are normally used in the first case in order to obtain a progressive refining of the ceramic mixture, that is in order to obtain gradually smaller particles. Typically, mills connected in series are provided with grinding bodies with gradually smaller dimensions, to produce particles with gradually smaller dimensions. To increase productivity, two or more lines of mills, or single mills, can be arranged in parallel.

The mills can be of the continuous type, that is of the type that provides for a continuous feeding and discharge of the slip, typically through ducts that are concentric to the axis of rotation of the mills, or of the discontinuous type, which provides for the loading, the process and the subsequent discharge of a predetermined quantity of material, wherein the material is loaded and discharged with the stopped mill.

Wet grinding mills and processes are widely known in the sector and will therefore not be described in further detail.

The product leaving the wet grinding step, as known, is the slip, i.e. an aqueous suspension of particles of ceramic mixture. The particle size depends on the refining or grinding grade obtained from the wet grinding step. Typically, the moisture grade of the slip is about 50%, i.e. the slip is made up of about half of water and half of ceramic mixture.

Subsequently, the slip is subjected to a mechanical dehydration step. This step essentially provides for extracting a part of water from the slip, through a mechanical action, that is, without adding heat. This allows for significant energy savings compared to using an atomizer. The mechanical dehydration of the slip is obtained by subjecting the slip to pressing, which allows expelling at least a part of water. Pressing can be made using, for example, a filter press, of type known in the sector, which provides a conveyor configured to push the slip in continuous advancement through a compression element, for example an elastic diaphragm or a passage duct with decreasing section. The action of the compression element causes the expulsion of at least a part of water from the advancing slip. The conveyor, for example, is in the form of an auger.

A possible alternative for the mechanical dehydration of the slip is obtained by subjecting the slip to centrifugal pressing, of type known in the sector. Basically, the slip is subjected to a centrifugal force that allows the expulsion of at least a part of water.

For example, the mechanical dehydration step for mechanically dehydrating the slip brings the moisture grade of the slip to about 18-20%. The use of a mechanical dehydration step offers an important advantage. The water expelled from the slip is in fact immediately available to be recirculated to the mills, allowing reducing the overall consumption of water used. On the contrary, the atomizer causes the water to evaporate, which cannot thus be reused for the mills.

Following the mechanical dehydration, the process according to the present invention provides for subjecting the slip to an extrusion step, to obtain prismatic agglomerates of ceramic mixture. Basically, through the extrusion step, the particles of ceramic mixture are aggregated together, into prismatic aggregates, the section of which depends on the section of the extrusion holes. For example, the aggregates are obtained by extrusion through circular holes, and have a cylindrical shape with a circular cross section.

The process according to the invention therefore provides for subjecting the prismatic agglomerates to a drying step. This drying step, which can be carried out by means of a drier known in the sector, considerably reduces the residual moisture of the ceramic mixture. For example, the drying step brings the moisture of the ceramic mixture to about 3-4%. Compared to an atomizer, the drier requires much lower temperatures, it thus allows the gas consumption to be considerably reduced. Additionally, the drier can receive waste heat from other process steps, allowing for further energy savings. The extrusion of the slip into prismatic aggregates makes the drying step particularly effective, allowing a rapid evacuation of moisture.

Following the drying step, the prismatic agglomerates are subjected to a pulverisation step, in order to obtain granules of ceramic mixture. The pulverisation step, which can be carried out with a device known in the sector, breaks up the prismatic agglomerates, substantially reducing them into granules.

The granules obtained from the pulverisation step, through the steps envisaged by the process according to the present invention, have very similar characteristics compared to the granules obtained by using an atomizer. In particular, the granules obtained from the process according to the present invention have relatively small dimensions, a regular shape and a soft consistency, all characteristics which facilitate the pressing step for pressing ceramic slabs or tiles having uniform density and regular surfaces.

The granules obtained at the end of the pulverisation step can be subjected to a screening step, by means of one or more screens of known type. The granules discarded from the screening step, that is the granules that do not filter through the provided sieves, can be sent back to the pulverisation step.

To further improve the fluidity characteristics of the granules, so as to further facilitate the pressing step for pressing the ceramic slabs or tiles, the granules of ceramic mixture can be subjected to a humidifying step, by means of humidifying devices known in the sector. For example, common granulators, followed by a fluidised bed, or common wetting machines, can be used to humidify the granules. Preferably, the moisture obtained from the humidifying step is about 5-6%. Preferably, the humidifying step is subsequent to the screening step.

Figures 1 , 2 and 3 schematically show the consecutive sections of a plant configured to carry out the process according to the present invention. The plant comprises at least one mechanical dehydrator (20), configured to receive and dehydrate the incoming slip. As already pointed out, the mechanical dehydrator (20) comprises for example a centrifugal separator or a filter press.

The slip is obtained from one or more mills (10) for wet grinding. These mills can be part of the plant, as represented in Figure 1 , or they could be in a separate position with respect to the plant. In this second case, the slip must be transported and fed to the mechanical dehydrator (20) by means of suitable means.

In the embodiment represented, the mills (10) are inserted in the plant and connected to the mechanical dehydrator (20) by means of suitable ducts served by pumping stations. Preferably, but not necessarily, a collection tank (11) can be interposed between the mills (10) and the mechanical dehydrator (20). This collection tank allows compensating for the differences between the flow rates that are processed by the mills (10) and by the mechanical dehydrator (20).

The plant comprises at least one extruder (30), configured to receive the incoming dehydrated slip produced by the mechanical dehydrator (20) and to produce prismatic agglomerates of ceramic mixture. As already indicated, the extruder (30) is a device known in the sector which comprises a matrix, that is a rigid septum provided with a plurality of through openings, with pre-established shape and size, through which the dehydrated ceramic mixture is forced to pass. Downstream of the matrix, the mixture is divided into prismatic aggregates, the cross section thereof depends on the shape and size of the through openings of the matrix.

The plant comprises at least one drier (40), configured to receive and dry the incoming prismatic agglomerates produced by the extruder (30). The drier (40) is connected to the extruder (30) by means of a transport device (41) of type known in the sector, for example a conveyor belt. Preferably, the conveyor belt swings around a vertical axis, to allow a uniform distribution of the prismatic agglomerates. As already indicated, the drier (40) is a device known in the sector, and will therefore not be described in detail.

The plant also comprises at least one pulveriser (50), configured to receive the incoming dried prismatic agglomerates, and to crush the prismatic agglomerates into granules of ceramic mixture. The pulveriser is connected to the drier (40) by transport means (51) of known type, for example by means of a conveyor belt (51). Preferably, but not necessarily, an accumulation silo (42) is interposed between the drier (40) and the pulveriser (50), to compensate for any differences between the flow rates processed by the two devices (40,50). In this case the transport device (51) is divided into two sections, separated by the silo (42).

Preferably, but not necessarily, the plant according to the present invention comprises at least one screen (60), configured to receive and screen the incoming granules of ceramic mixture produced by the pulveriser (50). The transport of the granules from the pulveriser (50) to the screen (60) takes place by means of a transport device (61), for example a bucket elevator. As already indicated, the granules discarded from the screen (60) because of too large dimensions can be sent back to the pulveriser (50), by means of a suitable duct (52). The screen (60) is a device well known in the sector, therefore it will not be described in detail.

Downstream of the pulveriser (50), preferably downstream of the screen (60), the plant comprises a humidifier (70), configured to receive and humidify the incoming granules of ceramic mixture produced by the pulveriser or selected by the screen (60). As already indicated, also the humidifier (70) is a device well known in the sector. For example, common granulators, followed by a fluidised bed, or common wetting machines, can be used to humidify the granules.

The humidifier (70) is connected to the screen (60) by means of a suitable transport device (71), for example a conveyor belt (71). An accumulation silo (72) can be interposed between the screen (60) and the humidifier (70), to compensate for differences between the flow rates produced by the screen (60) and the humidifier (70).

Claims

1. A process for producing pastes for ceramic tiles, comprising the following steps: wet grinding an initial ceramic mixture in order to obtain a slip; subjecting the slip to a mechanical dehydration step; following the mechanical dehydration, subjecting the slip to an extrusion step, to obtain prismatic agglomerates of ceramic mixture; subjecting the prismatic agglomerates to a drying step; following the drying step, subjecting the prismatic agglomerates to a pulverisation step, in order to obtain granules of ceramic mixture.

2. The process according to claim 1 , comprising a screening step for screening the granules of ceramic mixture.

3. The process according to claim 1 , comprising a humidifying step for humidifying the granules of ceramic mixture.

4. The process according to claim 3, wherein the humidifying step follows a screening step for screening the granules of ceramic mixture.

5. The process according to claim 1 , wherein the step of mechanical dehydration of the slip brings the moisture grade of the slip to about 18- 20%.

6. The process according to claim 1 , wherein the drying step for drying the prismatic agglomerates brings the moisture grade of the ceramic mixture to about 3-4%.

7. The process according to claim 1 , wherein the mechanical dehydration of the slip is made by pressing or by centrifugal separation.

8. The process according to claim 3, wherein the humidifying step for humidifying the granules of ceramic mixture takes place by means of granulation or by wetting.

9. A plant for the production of a paste for ceramic tiles, comprising one or more wet mills (10) for the production of slip of a ceramic mixture, characterised in that it comprises: at least one mechanical dehydrator (20), configured to receive and dehydrate the incoming slip produced by said one or more mills (10); at least one extruder (30), configured to receive the incoming dehydrated slip produced by the mechanical dehydrator (20) and to produce prismatic agglomerates of ceramic mixture; at least one drier (40), configured to receive and dry the incoming prismatic agglomerates produced by the extruder (30); at least one pulveriser (50), configured to receive the incoming dried prismatic agglomerates, and to crush the prismatic agglomerates into granules of ceramic mixture.

10. The plant according to claim 9, comprising at least one screen (60), for receiving and screening the incoming granules of ceramic mixture produced by the pulveriser (50).

11. The plant according to claim 9 or 10, comprising a humidifier (70), configured to receive and humidify the incoming granules of ceramic mixture produced by the pulveriser or selected by the screen (60).

12. The plant according to claim 9, wherein the mechanical dehydrator (20) comprises a press or a centrifugal separator.