FR2652410A1 - Method for drying flat products made from ceramic paste and dryer system implementing it - Google Patents

Abstract

The present invention relates to a method for drying damp flat products made from ceramic paste, termed "green" products, resting flat along one of their largest faces, on a suitable support such as a rack, characterised in that the accelerated evaporation of the water contained in the said products is obtained by means of a ventilation device pointing perpendicularly to the lower and/or upper faces of the said products. The field of the invention is that of the industrial manufacture of flat ceramic products, for example based on clays and marls, and particularly of tiles.

Description

The present invention relates to a method for drying flat products in

  ceramic paste, in particular tiles, and a dryer system using it. The manufacture of ceramic products from the class of terracotta products can be summarized as follows: after obtaining a plastic ceramic paste based, for example, on marl and clay, it is conventional to shape said paste for example by spinning and / or pressing; the products thus produced, subsequently called "green" products, have a water content which can be close to 20 to 30%. They should then be dried, an operation aimed at obtaining so-called "dry" products, the aqueous content of which is generally less than 5%. In modern processes, baking at high temperature (typically 1100 C) makes it possible to obtain

  hard "cooked" products of various qualities.

  The hardening of the wet ceramic paste under the more or less rapid effect of a progressive addition of heat causes a densification of this paste and its hardening. Unfortunately, the densification of the ceramic paste is accompanied by a volume contraction generating shrinkages, tending to crack or split the "dry" products; however, even a microscopic discontinuity of these products inevitably leads to their subsequent breakage (it is said in particular that a tile must "sound", which is an acoustic means of measuring its defects). Traditional crafts had correctly resolved most of the problems associated with these withdrawals by commonly drying and natural cooking, that is to say that they were done out of the sun, under the main effect of wind. Drying, as well as

cooking, were therefore slow.

  The industrialization of traditional drying processes has come up against obtaining strong production capacities for ceramic products in all cases where too rapid drying has been attempted due to withdrawals which may be too brutal - indeed, drying never being homogeneous, differential withdrawals may occur which would cause the products to break

in case of drying too quickly -.

  Despite the advantages provided by slow drying with respect to the quality of the ceramic products produced, "rapid drying" has nevertheless been conventionally adopted by all ceramic industries having to deal with clay and / or marl clay. The driers intended for this use are nowadays very perfected, and a continuous control makes it possible in particular to subject the conditions of the drying to the dynamics of the withdrawal. In these conventional dryers, of the type known as the "tunnel dryer", the flat products to be dried are placed, after their shaping, on racks whose structure is most often ill-suited to the ventilation of their lower faces resting on these same racks; in addition, the products to be dried can present significant reliefs (in particular the case of mechanical tiles) which make ventilation very heterogeneous, the direction of which is parallel to the faces (that is to say along the longitudinal direction of the drying tunnel ). It follows from these various drawbacks that the aqueous content of the flat products after drying is very disparate, and can vary from 3% to% on the same product; during cooking, the points of the products with the highest water content will undergo the greatest shrinkage, and it may ensue, located around these points, a

cracking of "dry" products.

  The present invention aims to remedy these drawbacks by proposing a method for drying wet flat products made of ceramic paste, called "green" products, lying flat on one of their largest faces, on a suitable support such as a rack, characterized in that the accelerated evaporation of the water contained in said products is obtained by means of ventilation oriented perpendicular to the

  lower and / or upper faces of said products.

  The first object of the invention is thus to achieve homogeneous drying of the products, their aqueous content then generally being less than 5%. The problems associated with differential withdrawals are then significantly better controlled and the risk of breakage at the time of

cooking decreases.

  According to an additional characteristic of the process which is the subject of the invention, the ventilation of the lower faces and the ventilation of the upper faces of the "green" products to be dried are carried out simultaneously. It is obvious that such a configuration advantageously solves the problem of ventilating the undersides of the products to be dried, especially in

  the case where these products present significant reliefs.

  Furthermore, and according to another characteristic of the invention, the device for ventilating the lower and / or upper faces of "green" products with

  to be dried is located near said faces.

  In this way, it avoids using a dryer system of the type of a "tunnel dryer" for which the flow of ventilation fluids follow, substantially in the longitudinal axis of the drying tunnel, very long paths, which can result in heterogeneous drying of the products

  "green" according to their position inside the dryer.

  Localized drying in accordance with that of the invention makes it possible to control in its entirety the drying of each "green" product, whatever its position inside the dryer; the dryer then becomes a simple shed in which no fluid circulates overall. This results in "proximity" drying, which is very favorable for obtaining

homogeneous drying.

  To this end, and according to a preferred characteristic of the process which is the subject of the invention, the ventilation of the lower and / or upper faces of the "green" products to be dried results from the closed circulation.

  of a forced convection ventilation fluid.

  Preferably, the path of the hot fluid, generated by blowing, is kept substantially orthogonal to said faces. The aspiration of the cold fluid, laden with mist, can be located near the air supply

  hot, but it can also be global, i.e.

  say that we can have a single high-flow suction device for an entire dryer. We can finally use a vacuum distributed in a few

places of the dryer.

  It is thus possible to very effectively control the drying of a limited set of "green" products, and, for example, the drying of only one of these products. It is indeed possible, for example, to act locally on the flow rate or the temperature of the ventilation fluid. In addition, the drying is substantially perpendicular to the faces; there is therefore a very fast drying speed, capable of promoting a shorter stay of "green" products in the dryer. This advantage is notable with respect to the production capacity of an industrial dryer implementing the method according to the invention; drying is no longer the "bottleneck" in the manufacture of ceramic products,

  for example based on clay or marl.

  As has been understood, "perpendicular" ventilation located near the "green" products to be dried makes it possible to effectively control the drying parameters, and therefore the shrinkage associated with this drying. However, permanent ventilation of the upper and / or lower faces can have some drawbacks, in particular due to the speed of "perpendicular" drying. According to an additional characteristic of the invention, the ventilation of the lower and / or upper faces of the "green" products to be dried can thus be intermittent. In this way, if the drying of a "green" product was carried out in a heterogeneous manner during the blowing of hot air, the temporary stopping of this blowing allows the water contained in the humid zones of the product to migrate towards the dry areas of it; the aqueous content of the product is thus homogenized before continuing to dry it. It should also be noted that the racks supporting the "green" products to be dried can be fixed relative to the ventilation members of the lower and / or upper faces of said products, but can also be movable relative to these members, in a continuous movement. , intermittent, or following a back and forth movement. The choice between these possibilities will normally be made by those skilled in the art, depending on the specific conditions of drying and

quality sought.

  Other characteristics and advantages of the process

  according to the invention will emerge better from the description

  which will follow several dryer systems implementing said method, given by way of nonlimiting examples, with reference to the appended drawing in which: - Figure 1 is a perspective view of a part of a dryer system according to the invention, - Figure 2 is a schematic side view of part of a dryer according to the preferred embodiment of the method according to the invention, - Figure 3 is a schematic side view of a cell forming part of a dryer in accordance with another variant implementation of the method according to the invention, - Figure 4 is a schematic front view of the dryer shown in Figure 3, - Figure 5 is a perspective view of an exemplary embodiment of a rack supporting the "green" products to be dried, this rack being in accordance with a first variant implementation of the method according to the invention, In accordance with FIG. 1, a dryer system 1 put The process according to the invention consists of: - a set of racks 2 supporting "green" products 3 to be dried. The number of "green" products 3 placed along a rack 2 is variable and depends on the respective geometric parameters of the rack 2 and the "green" products 3, these generally being

juxtaposed on said rack 2.

  - By an assembly of ventilation cells 4, preferably juxtaposed and / or stacked, each cell 4 being arranged so as to be able to wrap a rack 2 supporting "green" products 3 to be dried. A cell 4 furthermore comprises at least one ventilation member 5 making it possible to ventilate at least the upper faces perpendicularly 6

of said products 3.

  After their shaping, the "green" products 3 are placed on the racks 2 which are transported in a known manner to the dryer system 1; each rack 2 is then introduced into a cell 4. In accordance with FIG. 1, a rack 2 can advantageously slide on slides 7 integral with the lateral uprights 8 of a cell 4; its progression along the dryer system

  1 is carried out continuously or intermittently.

  In accordance with FIG. 2, a rack 2 can also be driven by rollers 7a integral with said lateral uprights 8, these rollers 7a being distributed

  regularly along the racks 2.

  In a first embodiment of the invention, only the upper faces 6 of the "green" products 3 are ventilated; drying takes place uniformly, but the drying speed, which is directly linked to the square of the thickness of "green" products 3, is considerably reduced compared to drying which would take place simultaneously on the upper faces 6 and the lower faces 9 of said products 3. There is, moreover, a risk of bending of the products 3. This is why, in accordance with a second preferred variant of the invention, each cell 4 comprises: - on the one hand , an upper ventilation member 5 making it possible to ventilate the upper faces 6 of the "green" products 3, perpendicularly to said faces 6, - on the other hand, a lower ventilation member 10 making it possible to ventilate the lower faces 9 of said products 3, which for this purpose are based on screens 2 permeable to the fluid ensuring ventilation

  lower, perpendicular to said faces 9.

  In this way, the thickness of the products 3 to be dried is divided by two, the upper ventilation member 5 ensuring the drying of the upper half of the thickness of the products 3, and the lower ventilation member 10 ensuring the drying the bottom half of

  the lower thickness of said products 3.

  This division by two of the thickness gives a division by four of the drying speed, which

  represents a very considerable advantage.

  In addition, and in general, the structure of the dryer system 1 in cells 4 juxtaposed and / or stacked provides unexpected advantages: the drying of "green" products 3 is located close to these, and depends on the geometric parameters. and functional of the ventilation members 5 and 10: path, flow rate and temperature of the ventilation fluid can thus be modified as desired depending on the nature of the ceramic paste used to form the products 3, their water content, or else of their shape. - the development of a single cell 4 provides the development of the entire dryer system 1. It is therefore possible to study in the laboratory the ventilation parameters in a cell 4 to know with relative certainty the ventilation parameters in a dryer system 1 as large as desired (hence the intentionally partial representation of a dryer system according to the present invention on

Figure 1).

  - Finally, the structure of the dryer system 1 in cells 4 facilitates "balancing" of the "green" products 3 to be dried. - By "balancing" is meant a product 3 of ceramic paste the fact of perfectly controlling shrinkage during drying and cooking. Now, we have seen that these withdrawals surely depend on the homogeneity of the drying; but they can also depend on the processing conditions of the products 3; the tightening of the ceramic paste, carried out in particular during their molding, in fact modifies the local behavior of the products 3. The ceramist must therefore "balance" his mold, and, to do this, he must precisely establish a map of the shrinkages due molding; it must, therefore, locate the shrinkages due to drying. The cell structure 4 of the dryer system 1 which is the subject of the present invention makes it possible, by providing an exact control of the ventilation and therefore of the drying of the "green" products 3 over their entire surface, to evaluate the conditions of molding said products 3; "balancing" of products 3, done in this way

  in situ, provides a significant gain in productivity.

  Whatever the type of ventilation elements 5 and used, the racks 2 are identical and slide continuously or intermittently, through the dryer system 1, on the slides 7 or the rollers

  7a drive provided for this purpose.

  The racks 2 which it is possible to use to support the "green" products 3 must in particular allow passage, without causing a pressure drop

  consequent, the ventilation fluid such as air.

  In accordance with FIG. 5, and according to a first alternative embodiment of the invention, the racks 2 supporting the "green" products 3 to be dried are rigid perforated supports 11 stamped by means of an imprint suitable for the shape of said products 3. In FIG. 5, we have chosen to represent a rigid perforated support 11 stamped in the press substantially in the profile of tiles 12, so as to constitute a screen 2. The meshes 13 of these supports 11 can, for example, be delimited by stainless steel wire 1.5 mm in diameter, and have an area of 60 mm by 60 mm (a tile 12 typically having an overall size of 20 cm by 40 cm). In addition, during drying, there can be, as already mentioned, up to 20% shrinkage; this important value means that the length of a tile 12 can go from 50cm to 40cm. The structure of the rack 2 must therefore be designed so that by shrinking the material constituting a "green" product 3 does not catch the rack 2 at the risk of breaking; the "green" product 3 must therefore be able to slide

on rack 2.

  It is of course obvious that the previous embodiment of a screen 2 permeable to a ventilation fluid such as air is given as an indication; any part 2, produced in the same spirit and fulfilling the same functions, would not leave the

part of the invention.

  In a cell 4 of the dryer system 1 according to the present invention, the ventilation member 5 of the upper faces 6 of "green" products 3, and / or the ventilation member 10 of the lower faces 9 of said products 3, can be done in many ways; in all cases, and in accordance with FIGS. 2 and 3, a ventilation member 5 or 10 comprises devices for blowing 15 a hot ventilation fluid, such as in particular hot air, adequately connected to a central , not shown in the figures,

and generating this fluid.

  It is also possible to provide, near the blowing devices 15, suction devices 16 for the cold and wet ventilation fluid, resulting from the drying of the "green" products 3 by the hot ventilation fluid. The cold fluid is charged with fogging

  evaporation of the water contained in said products 3.

  However, this arrangement is not compulsory and the suction of the cold fluid can be carried out by means of a limited number of suction devices (not shown in the figures), or even by means of a single device. In accordance with FIG. 2, which shows schematically the structure of the dryer 1 as shown by way of nonlimiting example in FIG. 1, the upper ventilation member 5 (or lower 10) of the upper faces 6 (or lower 9) "green" products 3 to be dried, consists of a set

  conduits juxtaposed parallel to each other.

  These conduits are, moreover, advantageously arranged in the same plane, located at a distance from the rack 2 capable of allowing the blowing of the hot ventilation fluid near the upper faces 6 (or lower

9) of said products 3.

  The hot fluid is blown through orifices 18 disposed along a first series of conduits, called flues 19; these orifices 18 are placed at least on one side of said flues 19 lying opposite the upper faces 6 or the faces

  lower 9 of "green" products 3.

  In a complementary variant of the invention, the suction of the cold and wet fluid, charged with the vapors resulting from the drying of the products 3, is carried out through orifices 20 arranged along a second series of conduits, called extractors 21 These orifices are preferably placed at least on one side of said extractors 21 located opposite said faces 6 or 9. According to a complementary characteristic of this variant of the invention, the flues 19 alternate

  laterally with the extractors 21 in the same plane.

  Finally, and according to a last characteristic, the flues 19 can oscillate along their longitudinal axis, in a back-and-forth movement capable of avoiding the formation of overheated zones on the surface of the "green" products 3 in the process of drying, particularly in the event of accidental or voluntary stopping of the scrolling of the racks 2 through the dryer system 1; under these conditions, the blade of hot air generated by the flues 19 is not fixed and continues to sweep the faces 6 and 9 of the products 3 without damaging overheating. A static dryer system 1 can, in the same way, be envisaged; in this case, the racks 2 are kept fixed during the drying of the products 3, reserving for the oscillating blowing provided by the flues 19 of

  distribute ventilation properly.

  It is easily understood that the configuration described above of the flues 19 and the extractors 21 is not limiting; naturally, for each type of "green" product 3 to be dried, the

  adequate special provision.

  The pressure losses undergone by the ventilation fluid in the ducts can, moreover, be normally calculated; the blowing powers and

  suction will then be chosen accordingly.

  In operation, such a dryer system 1 is in the form of a set of cells 4 each enveloping a screen 2 permeable to ventilation fluid, on which rest "green" products 3 to be dried. The racks 2 can be fixed, or move along the cells 4 by sliding on the slides 7 or on the rollers 7a; their eventual movement can be continuous, intermittent, and we can

  in particular, print on racks 2 a back-and-forth movement

  is likely to homogenize, in a complementary manner, the drying of the products 3. Finally, the drying itself can be continuous or intermittent. When they pass through the dryer system 1, the "green" products 3 thus pass through hot air blades distributed regularly over the path of the racks 2

permeable that support them.

  In accordance with FIG. 3, which details the lateral structure of a cell 4 in accordance with another alternative embodiment of the dryer system 1, the upper ventilation member 5 (or lower 10) of the upper faces 6 (or lower 9) "green" products 3 to be dried, comprises, near said rack 2, a set of devices for blowing 15 a hot ventilation fluid, optionally alternating with a set of devices for sucking 16 of the

  cold and damp ventilation resulting from drying.

  The blowing devices 15 for the hot fluid consist of blowing drums 22 which can rotate along axes 23 which are advantageously perpendicular to the longitudinal direction of the rack 2. These blowing drums 22 can advantageously carry the rollers 7a for driving the racks 2 ; in this case, the rollers 7a are attached to the circumferences of the blowing drums 22 at the points o

rest the racks 2 to train.

  The cold fluid suction devices 16 consist, for their part, of transverse conduits, called extractors 24, recovering the cold fluid through orifices 25 aligned along

said extractors 24.

  The extractors 24 are connected in a conventional manner to a central vacuum unit not shown in the figures. Here again, the extractors 24 can be replaced by a single suction and

  global, or by a distributed aspiration.

  The blowing drums 22 are, for their part, connected to a central unit generating a hot fluid, also not shown in the figures. The internal structure of these blowing drums 22 will now be better understood with reference to FIG. 4. The blowing drums 22, with axes 23, can for example have a range of a few meters. Over such a length, perfect alignment is impossible to obtain; this is why a blowing drum 22 is supported by a

  bearing 32 of the type of a swinging bearing.

  The inclination of a blowing drum 22 can be controlled by means of an inclination adjustment system, by which the body 26 of the blowing drum 22 is embedded in a female part 27 integral with the frame of the system. dryer 1, so as to always remain tangential to a toric bulge 28 of the female part 27; this O-ring bulge 28 has for its center an axis 29 which intersects the axis 23 of the blowing drum 22. An O-ring 30 disposed between the body 26 of the blowing drum 22 and the female part 27 provides sealing

from the whole.

  The drive of a blowing drum 22 is carried out, for example, by means of a drive by

channels 31.

  In the two alternative embodiments of the ventilation members 5 and 10 of a cell 4 of a dryer system 1, it is quite clear that the upper ventilation member 5 of a first cell 4 can advantageously be used for lower ventilation unit of cell 4 immediately adjacent to this

  first cell 4 and vice versa.

  The modular design of the dryer system 1 (i.e. its structure in cells 4) and the numerous variants of construction, arrangement and operation of the ventilation members 5 and 10, ensuring efficient and uniform drying of the products "green" 3, provide the remarkable advantage of not having to permanently freeze the methods of this drying; the production of a dryer system 1 for drying mechanical tiles 12 proceeds, in fact, from the same logic as the production logic of a dryer system 1 for drying flat tiles, or of the channel type. It will also be noted that the drying method in accordance with the invention is particularly advantageous for drying hollow products for which conventional drying is ill-suited: the pressure losses of the ventilation fluid are in fact very high due to the cross section of the hollow

  found in the body of these products.

  Thanks to the process and to the devices according to the invention, it is possible to force ventilation individually inside the holes of a hollow "green" product 3, this being placed vertically (and no longer horizontally) on racks 2 permeable to

ventilation fluid.

  Since various modifications can be made to the process and to the embodiments described above without departing from the scope of the invention, it is obvious that all the details contained

  in the description above or illustrated in

  attached drawings are given by way of nonlimiting examples. The field of the invention is that of the industrial manufacture of flat ceramic products with

  base of clay and marl, and in particular of tiles.

Claims (11)

  1 - Method for drying wet flat products made of ceramic paste, called "green" products, lying flat along one of their largest faces, on a suitable support such as a rack, characterized in that the accelerated evaporation of l water contained in said products is obtained by means of ventilation oriented perpendicular to the undersides and / or superior of said products.   2 - A drying method according to claim 1, characterized in that simultaneously performs the ventilation of the lower faces and the ventilation of   upper sides of "green" products to be dried.   3 - Drying method according to any one of   previous claims, characterized in that   the ventilation unit for the lower and / or upper sides of the "green" products to be dried is   located near said faces.   4 - Drying method according to any one of   previous claims, characterized in that the   ventilation of the lower and / or upper sides of "green" products to be dried results from the closed circulation of a hot ventilation fluid by forced convection, the path of this fluid being maintained   substantially orthogonal to said faces.   - Drying method according to any one of   previous claims, characterized in that the   ventilation of the lower and / or upper sides of the   "green" products to be dried are intermittent.   6 - Dryer system (1) comprising a set of racks (2) supporting "green" products (3) to be dried according to the drying process according to one   any one of claims 1,3,4, or 5, characterized in   what it comprises an assembly of ventilation cells (4) preferably juxtaposed and / or stacked, each cell (4) being arranged so as to be able to wrap a rack (2) supporting "green" products (3) to be dried , a cell (4) further comprising at least one ventilation member (5) making it possible to ventilate at least perpendicularly the   upper faces (6) of said products (3).   7 - Dryer system (1) comprising a set of racks (2) supporting "green" products (3) to be dried according to the drying process according to one   any one of claims 1 to 5, characterized in that   that it comprises an assembly of ventilation cells (4) preferably juxtaposed and / or stacked, each cell (4) being arranged so as to be able to wrap a rack (2) supporting "green" products (3) to be dried, each cell (4) further comprising: - on the one hand, an upper ventilation member (5) making it possible to ventilate the upper faces (6) of said products (3), perpendicular to said faces (6), - d 'other hand, a lower ventilation member (10) for ventilating the lower faces (9) of said products (3), which are based for this purpose on screens (2) permeable to fluid ensuring lower ventilation, perpendicular to said faces (9).   8 - dryer system (1) according to any one   claims 6 or 7, characterized in that, in   a cell (4), the upper (5) (or lower (10)) ventilation member of the upper (6) (or lower (9)) faces of the "green" products (3) to be dried, consists of a set of conduits juxtaposed parallel to each other, these conduits being moreover advantageously arranged in the same plane situated at a distance from said rack (2) capable of allowing the blowing of a hot fluid near the upper faces ( 6) (or lower (9)) of said products (3), the blowing being effected through orifices (18) arranged along a first series of conduits, called flues (19), at least one side of said flues (19) located opposite said faces (6, 9).   9 - dryer system (1) according to claim 8, characterized in that the flues (19) oscillate longitudinally along their axis. - dryer system (1) according to any one   claims 8 or 9, characterized in that the   flues (19) alternate with a second series of conduits, called extractors (21), which vacuum the fumes resulting from the drying of "green" products (3) at   through orifices (20) arranged along their length.   11 - Dryer system (1) according to any one   claims 6 or 7, characterized in that, in   a cell (4), the upper (5) (or lower (10)) ventilation member of the upper (6) (or lower (9)) faces of the "green" products (3) to be dried, comprises, at proximity of the rack (2) supporting the "green" products (3) to be dried, a set of blowing means (15) of hot fluid made up of blowing drums (22), and rotating for example along axes (23) advantageously perpendicular to the   longitudinal direction of the rack (2).   12 - dryer system (1) according to claim 11, characterized in that the blowing drums (22) advantageously serve to support the rollers (7a) for driving the racks (2) supporting the products "green" (3) to dry.   13 - dryer system (1) according to any one   claims 7 to 12, characterized in that the   trays (2) supporting the "green" products (3) to be dried are rigid openwork supports (11) stamped by means of an imprint adapted to the shape of said products (3).