EP0505647A1 - Dryer system for drying flat humid products made out of ceramic paste - Google Patents

Abstract

The rigid, openworked racks (1), on which the products, known as green products (2), lie flat along one of their larger surfaces, are driven in a continuous or intermittent movement, or else in a to-and- fro movement, the green products (2) to be dried passing over hot-air streams distributed uniformly over the path of the said racks (1). The field of the invention is that of the industrial manufacture of flat ceramic products based on clay and marl, in particular of tiles. <IMAGE>

Description

The present invention relates to a dryer system for drying wet flat products made of ceramic paste, in particular tiles.

The manufacture of ceramic earthenware 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 by spinning and / or pressing. The products thus produced, hereinafter called "green products", have a water content which can be close to 20 to 30%. The operation of drying them so as to obtain so-called "dry" products aims to reduce their water content to a percentage generally less than 5%. In modern processes, cooking at high temperature (typically 1100 ° Celsius) then makes it possible to obtain "cooked" products of various qualities. It is also recalled that the hardening of the wet ceramic paste, under the more or less rapid effect of a progressive heat supply, causes a densification of this paste and its hardening. Unfortunately, the densification is accompanied by a volume contraction generating shrinkages which tend to crack or split the dry products; however, even a microscopic discontinuity of these products inevitably leads to their subsequent breakage.

A large number of dryer systems are known, the best known being those of the "tunnel dryer" type. In the latter technique, 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 underside. 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 generally parallel to the faces (that is to say along the longitudinal direction of the tunnel of drying). As a result, the aqueous content of the flat products after drying is very disparate and can vary from 3% to 10% on the same product; during cooking, the points with the highest water content undergo a very large shrinkage and there may ensue, localized around these points, cracking of the dry products.

To overcome these various drawbacks, a number of dryers have been proposed where the blowing of drying air is located closer to the products, or even takes place in closed cells; French patent FR-732799 is known in particular for which separate drying chambers are separated from one another by sliding doors, rolling walls or similar partitions. Hot air is generally blown into the cell and is then extracted before being recycled after it has been reheated. This latter process, as well as the various other techniques hitherto proposed, however have the drawback of not being able to be easily industrialized, since in fact it turns out to be impossible to produce individual micro-dryers for each tile or each small set. tiles leaving, on large racks, the shaping area.

The present invention aims to remedy all these drawbacks by proposing a dryer system for drying wet flat products made of ceramic paste, called "green products", lying flat on one of their largest faces on a set of racks rigid openwork, this system being characterized in that said racks are driven in a continuous movement, or intermittent, or in a back and forth movement, the "green products" to be dried through air knives hot evenly distributed on the path of said racks, both above and below said "green products".

A dryer implemented in accordance with this principle of the invention is then presented as a set of mobile openwork racks supporting "green products" to be dried, these racks being arranged in layers superimposed crossing curtains or blades of hot air more or less spaced. All of these racks can be mounted on a single movable frame making it possible to move them, with intermittence or a chosen alternation, through fixed hot air curtains. Likewise, it is possible to alternate the blowing times and the resting times when the racks are fixed relative to the blowing members. It will be noted that the mobility of the racks makes it possible to constitute a "dynamic dryer" offering the advantage of very homogeneous proximity drying of the products. The latter benefit, in fact, from localized drying of width determined by that of the hot air blowing members. Furthermore, the intermittent movement of the racks through the hot air curtains thus constituted by upper and lower blowing members make it possible to alternate the blowing phases and the rest phases at will. It is recalled, in this regard, that the rest phases make it possible to re-homogenize the moisture in the thickness of the "green products" after a first drying phase which can, in any case, never be perfectly homogeneous.

According to the present invention, it is therefore understood that the ventilation of the lower and upper faces of the "green products" to be dried is intermittent, this intermittence resulting either from alternating ventilation and rest phases, or from the relative movement of the organs of ventilation of the lower and upper faces with respect to the racks supporting the "green products" to be dried, or again a combination of these two effects.

It can also be provided, in order to avoid an accident due to an unexpected stoppage of the relative movement of the screens and of the hot air blowing members, that the ventilation members are animated by an oscillating movement so that the hot air curtains through which the screens are not fixed but permanently sweep small areas of "products green "to dry. This oscillation of the hot air curtains also avoids the formation of overheated areas on the surface of said products.

It will be noted that the suction of the vapors resulting from the drying can be obtained by an extractor or a single suction device placed inside the dryer. One could, of course, also consider having extractors close to the hot air ventilation members, but this arrangement would unnecessarily complicate the device.

An advantage resulting from the blowing of hot air perpendicular to the faces of the "green products" to be dried is the gain on the drying speed compared to a "parallel" drying carried out in a tunnel dryer, which not only proves to be inhomogeneous, but contributes less to dry the "green product" in the mass.

• la figure unique est une vue en perspective d'un ensemble de claies supportant des "produits verts" à faire sécher traversant un ensemble de rideaux d'air chaud soufflé perpendiculairement aux faces des produits, aussi bien au-dessus qu'en dessous desdites claies.

Other characteristics and advantages of the dryer system according to the invention will emerge more clearly from the description which follows of several variants given by way of nonlimiting examples with reference to the appended drawing in which:

• the single figure is a perspective view of a set of racks supporting "green products" to be dried through a set of curtains of hot air blown perpendicular to the faces of the products, both above and below said racks .

According to this figure, a dryer system according to the invention comprises a set of racks 1 supporting "green products" 2 to be dried. The number of "green products" 2 placed along a rack 1 is variable and depends on the respective geometric parameters of the rack 1 and of said "green products" 2, these being generally juxtaposed on said rack 1. In the figure , mechanical tiles have been shown, but the invention also applies to any normally flat "green product" 2. The shape of the rack 1 is of course not arbitrary and, in particular, one can make a rigid perforated support stamped by means of an imprint suitable for the shape of the "green products" 2. For this purpose, one could produce a rigid perforated support comprising meshes delimited by stainless steel wire of 1.5 min. diameter, these meshes having an area of 60 min X 60 min (a tile typically having an overall size of 20 cm X 40 cm). In fact, the structure of the rack 1 must be designed in such a way that by shrinking under the effect of drying (the shrinkage can reach approximately 20% of the initial dimension of the "green product" 2), the material constituting said product 2 does not catch the meshes of rack 1, at the risk of breaking. The product 2 must thus be able to slide on the rack 1. In addition, it is obvious that the rack 1 must be permeable to the flow of ventilation blown in the form of hot air curtains 3 normally parallel and orthogonal to the running direction of the racks 1 .

The racks 1 shown in the figure can be driven in a continuous movement or in an intermittent movement or even undergo a back-and-forth movement, either individually with respect to a set of rollers driving them inside the dryer. , or collectively, all of the racks 1 then being generally moved back and forth relative to a set of orthogonal blowing members 4.

The latter may be of the type shown by way of example in the figure, namely an upper ventilation member 4 a and a lower ventilation member 4 b constituted by a ply of conduits juxtaposed parallel to each other, each ply being located at a distance from the racks 1 allowing the blowing of the hot ventilation fluid near the upper and lower faces of "green products" 2 to be dried resting on said racks 1.

The hot fluid is blown through orifices 5 arranged along the conduits, these orifices 5 being placed at least on one side of said conduit located opposite the upper faces or lower faces of the "green products" 2 resting on the screens 1 running just above or just below said sheet of hot air ducts.

According to another characteristic of the present invention, the conduits can oscillate along their longitudinal axis in a back-and-forth movement capable of preventing the formation of overheated zones on the surface of the "green products" 2 being dried, particularly in the event of accidental or voluntary stopping of the scrolling of racks 1 through the dryer. Under these conditions, the hot air curtains 3 generated by the conduits are not fixed and continue to dry both sides of the products 2 without harmful overheating.

The pressure losses undergone by the hot ventilation flow in the ducts can, moreover, be normally calculated by a person skilled in the ordinary art, the blowing powers being chosen according to the power of the blowing central available.

According to another arrangement of the invention not shown in the figure, the conduits pierced with orifices 5 and generating successive hot air curtains 3 on the path of the racks 1 can be replaced by blowing drums carrying drive rollers racks. By turning on themselves, the blowing drums, also pierced with orifices distributed in a suitable manner on the barrel of said drums, make, on the one hand, advance or oscillate the racks 1 which they support and, on the other hand share, allow to move the hot air curtains 3 which are created through the orifices provided on the barrels of said drums.

Since various modifications can be made 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 the attached drawing are given by way of title. non-limiting examples.

The field of the invention is that of the industrial manufacture of flat ceramic products based on clay and marl, in particular tiles.

Claims (5)

Drier system for drying wet flat products made of ceramic paste, called green products (2), lying flat along one of their largest faces on a set of rigid perforated racks (1), system characterized in that said trays (1) are animated by a continuous or intermittent movement, or even by a back-and-forth movement, the green products (2) to be dried through hot air curtains (3) distributed regularly over the path of said screens (1). Dryer system according to claim 1, characterized in that the ventilation of the lower and upper faces of the green products (2) to be dried is intermittent, this intermittence resulting either from alternating ventilation and rest phases, or from movement relative to the ventilation members (4) of the lower and upper faces with respect to the racks (1) supporting the green products (2) to be dried, or even a combination of these two effects. Dryer system according to Claim 2, in which the upper (4 a ) and lower (4 b ) ventilation units for the green products (2) to be dried consist of a sheet of conduits juxtaposed parallel to each other, along which are provided with orifices (5) allowing the blowing of a hot fluid near said faces, system characterized in that said conduits oscillate along their longitudinal axis in a reciprocating movement capable of avoiding the formation of zones superheated on the surface of said products (2). Dryer system according to claim 2, wherein the ventilation members (4) of the upper and lower faces of the green products (2) to be dried comprise, near the racks (1) supporting said green products (2), a set means of blowing a hot fluid consisting of blowing drums rotating along axes perpendicular to the longitudinal direction of said racks (1), system characterized in that said blowing drums advantageously serve to support drive rollers of said racks (1). Drier system for drying wet flat products made of ceramic paste, called green products (2), lying flat on one of their largest face on a set of rigid perforated racks (1), characterized by racks (1 ) with movable grate supporting said green products (2) to be dried, these racks (1) being arranged in superimposed layers passing through curtains of hot air (3) more or less spaced, both on top and on the bottom of said racks (1).

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