EP0145621B1 - Process for preparing a fibrous isolating piece - Google Patents

Abstract

The invention relates to a process for manufacturing an insulating fibrous piece based on fibers resisting high temperature, which consists in: preparing a first suspension containing a first type of fibers resisting high temperature; preparing at least one second suspension containing a second type of fibers resisting high temperature; then pouring each suspension into a distinct compartment of a vat of which the bottom comprises a momentarily obstructed filtering sieve and of which the elementary compartments are separated from one another by a removable plate, said process being characterized in that: each suspension also comprises a minority proportion of ceramizable particles; whilst withdrawing the removable separating plate, the medium is stirred locally at least in the vicinity of this separation plate, on the one hand, and, simultaneously, the water is drained through the filtering sieve, on the other hand, in known manner; and, after having dried the piece obtained, it is heated to a temperature capable of provoking in this piece the ceramization of said ceramizable particles.

Description

The invention relates to a method for manufacturing an insulating fibrous part.

It is well known to coat the enclosures intended to be brought to high temperature with a layer of an insulating material. Originally, to do this, we used refractory bricks. This technique, although widely used, has the disadvantage of being expensive, leading to heavy coatings, sensitive to thermal shock and which, for certain applications have a high heat capacity as well as a high thermal inertia.

In recent years, it has been proposed to replace bricks with fibrous sheets. In a first embodiment, it was suggested to unroll on the wall to be coated webs based on fibers resistant to high temperature, such as ceramic fibers. These layers are fixed parallel to the wall of the oven using metal rods. These rods cause thermal bridges, corrode and precipitate corrosion of the walls of the oven itself, as well as the fall of the layers.

To avoid these drawbacks, in a second embodiment, it was suggested to use a stack of elementary sheets of fibers resistant to high temperature, superimposed on the field or folded, fixed to the walls at the rear, which avoids thermal points. This latter technique allows only a homogeneous insulation from the hot face to the cold face, which unnecessarily increases the cost.

In patent FR-A-1 602 362 (corresponding to GB-A-1 296 681), it has been suggested to stack successive layers of ceramic fibers on a form using vacuum. A progressive stack is thus obtained in which the elementary layers do not interpenetrate and whose practical thickness is limited as a result of the technique of removal by suction.

In patent GB-A-2 114 621, a ceramic fiber material has been described having a hot face and a cold face and the interstice of which comprises fibers of each tangled face. One method for manufacturing such a product consists in preparing two suspensions of ceramic fibers, then in pouring each of them into one of the two compartments of a tray separated by a removable sliding plate and the bottom of which is constituted by a wire screen. trant, then apply the vacuum to remove the water and finally remove the removable plate and finally dry the product obtained. This technique has hardly been developed because, on the one hand, it does not ensure sufficient cohesion of the two parts which separate when used at high temperature and, on the other hand, the products obtained sometimes lack rigidity and dimensional stability.

The invention relates to a process for the manufacture of an insulating fibrous part, in particular for the internal coating of enclosures intended to be brought to high temperature, which is easy to implement, economical, in particular for the manufacture of small series, and allows the production of parts of appropriate dimensions and shapes with determined specifications.

• . à préparer une première suspension contenant un premier type de fibres résistant à haute température;
• . puis, à préparer au moins une seconde suspension contenant un second type de fibres résistant à haute température;
• . puis, à verser chaque suspension dans un compartiment distinct d'un bac dont le fond comporte un tamis filtrant momentanément obstrué et dont les compartiments élémentaires son séparés entre eux par une plaque amovible;
• . ensuite, à retirer la plaque amovible de séparation et à éliminer l'eau des suspensions à travers le tamis filtrant;
• . et enfin, à sécher le produit obtenu, caractérisé:
• - en ce que chaque suspension comporte pour partie minoritaire des particules céramisables;
• - et en ce que, lorsque l'on retire la plaque de séparation amovible, d'une part, simultanément on agite localement le milieu au voisinage de cette plaque de séparation amovible, et d'autre part, on élimine l'eau des suspensions par égouttage au travers du tamis filtrant;
• - et enfin, en ce que, après avoir séché de manière connue la pièce obtenue, on chauffe celle-ci à une température susceptible de provoquer dans cette pièce la céramisation desdites particules céramisables.

This process for the manufacture of an insulating fibrous part based on fibers resistant to high temperature, such as ceramic fibers, in particular for interior lining of heated enclosures, which consists of:

• . preparing a first suspension containing a first type of fibers resistant to high temperature;
• . then, preparing at least a second suspension containing a second type of fiber resistant to high temperature;
• . then, to pour each suspension into a separate compartment of a tank, the bottom of which has a temporarily obstructed filter screen and whose elementary compartments are separated from each other by a removable plate;
• . then remove the removable separation plate and remove the water from the suspensions through the filter screen;
• . and finally, drying the product obtained, characterized:
• - in that each suspension contains a ceramisable particles in the minority;
• - And in that, when the removable separation plate is removed, on the one hand, simultaneously the local medium is agitated in the vicinity of this removable separation plate, and on the other hand, the water is removed from the suspensions by draining through the filter screen;
• - And finally, in that, after drying the part obtained in a known manner, the latter is heated to a temperature capable of causing this part to ceramize said ceramizable particles.

In a first embodiment, the ceramizable minority particles are mineral particles such as for example Kaolin particles, which has the advantage of not increasing the electrical conductivity of the final product, or else clay particles, in particular swelling clay particles such as bentonnites, which have the advantage of waterlogging.

In a second preferred embodiment, the ceramizable minority particles are mechanical paper fibers, in particular recovery fibers, which facilitates the handling of the part before baking by giving it better resistance.

• - les fibres minoritaires papetières représentent 1 à 5% du poids en poids sec des fibres majoritaires résistant à la température;
• - la concentration en fibres varie d'une suspension à l'autre, mais la quantité de suspension versée dans chaque compartiment élémentaire est identique d'une suspension à l'autre pour éviter le déversement d'un compartiment dans l'autre;
• - on fait appel de préférence à des fibres en vrac, que l'on disperse de manière connue dans de l'eau;
• - pour préparer chaque suspension élémentaire, on réalise tout d'abord une suspension contenant des fibres résistant à haute température, notamment en vrac, s'il y a lieu additionnée d'agent mouillants, puis on ajoute ensuite à cette suspension une autre suspension préparée séparement contenant des particules céramisables;
• - la concentration de chaque suspension est comprise entre 50 et 80 grammes/litre car, en deça, la quantité d'eau éliminée est trop importante, alors qu'en revanche, au-delà, on obtient une mauvaise dispersion des fibres élémentaires;
• - l'agitation du milieu est obtenue de manière connue, par exemple, soit par un agitateur à vibrations, soit encore mieux tout simplement en ménageant, soit sur la paroi de la plaque amovible soit à son extrémité inférieure, un peigne transversal destiné à former organe d'agitation lors du retrait de cette plaque amovible;
• - lors du remplissage des compartiments élémentaires du bac, le tamis du fond du bac est obstrué par une couche d'eau qui sera éliminé lors de la phase d'égouttage;
• - la céramisation des cendres résultant de la combustion des fibres papetières est effectuée à une température d'au moins 1000°C;
• - après chauffage, la pièce refroidie peut être enduite d'une nouvelle composition minérale liante, telle que par exemple une solution aqueuse de phosphate d'alumine, que l'on sèche ensuite à l'étuve.

Advantageously, in practice:

• - minority paper fibers represent 1 to 5% of the dry weight of the majority temperature-resistant fibers;
• - the fiber concentration varies from one suspension to another, but the quantity of suspension poured into each elementary compartment is identical from one suspension to another to avoid spillage from one compartment to the other;
• - It is preferable to use loose fibers, which are dispersed in a known manner in water;
• - To prepare each elementary suspension, first a suspension containing fibers resistant to high temperature, in particular in bulk, is produced, if necessary, with wetting agents added, then another suspension is added to this suspension separately containing ceramisable particles;
• - The concentration of each suspension is between 50 and 80 grams / liter because, below, the amount of water removed is too large, while on the other hand, beyond this, poor dispersion of the elementary fibers is obtained;
• the stirring of the medium is obtained in a known manner, for example, either by a vibration stirrer, or even better quite simply by providing, either on the wall of the removable plate or at its lower end, a transverse comb intended to form stirring member during removal of this removable plate;
• - when filling the elementary compartments of the tank, the screen at the bottom of the tank is blocked by a layer of water which will be removed during the draining phase;
• - the ceramization of the ash resulting from the combustion of the paper fibers is carried out at a temperature of at least 1000 ° C;
• - After heating, the cooled part can be coated with a new mineral binder composition, such as for example an aqueous alumina phosphate solution, which is then dried in an oven.

The manner in which the invention can be implemented and the advantages which result therefrom will emerge more clearly from the following exemplary embodiments, given by way of non-limiting illustration in support of the appended figures.

Figure 1 is a schematic summary representation of a device for implementing the method according to the invention.

Figures 2 and 3 respectively show this device in section along the axes 1-1 '(Figure 2) and II-II' (Figure 3) of Figure 1.

FIG. 4 is a summary perspective view of the removable plate of the device in FIG. 1.

Figure 5 is a schematic representation in summary perspective of an insulating part according to the invention.

The device shown in FIGS. 1 to 4 for implementing the method according to the invention essentially consists of a tank (1) forming a rise, open at its upper end (2) and the bottom (3) of which is constituted by a highly open, but resistant grid. This tank (1), for example of sheet steel, has on two opposite edges elementary slots (4, 5, 6, 7) in suitable number intended to delimit elementary compartments (8, 9), by positioning a rigid separation plate (10), for example also made of sheet metal, inserted into each of these slots (4, 6-5, 7). The surface of this removable separation plate (10) corresponds to the internal section of the tank (1). This plate (10) has end ears (11, 12), intended to be inserted into the slots (4-7), and which protrude from the tray to allow the establishment and removal. The bottom of the separation plate (10) has a second slightly curved transverse plate (13), intended to come into contact with the screen (15) placed on the perforated bottom (3). This part (13), welded for example, has a plurality of elementary edges (14) like a comb. As already said, the bottom (3) in highly perforated mesh, is coated with a metallic filter screen (15) of 0.5 mm mesh. The bottom of the rise (1) comprises a collar (16) for connection to the body (17) and for holding the screen (15). The body (17) which rests on feet (18, 19) has on the front face a drip valve (20).

Example 1

To a ten-liter bucket of water, five hundred grams of a ceramic fiber resistant to a temperature of 1400 ° C. are added, marketed by Lafarge Réfractaire under the name "K60", of a length close to one centimeter.

At the same time, in half a liter of water, 25 grams of a mechanical paper pulp obtained from recovered, inked and heavily loaded paper are suspended.

At room temperature, the aqueous suspension of paper fibers is added to the suspension of ceramic fibers. 10.5 liters of a first aqueous suspension containing approximately 500 grams of ceramic fibers and 25 grams of paper fibers were thus prepared.

In the same way, a second suspension is prepared containing, still for 10.5 liters, 500 grams of ceramic fibers, but of “K45” quality marketed by Lafarge Réfractaire, resistant only to a temperature of 1250 ° C. and 25 grams of fibers. paper mills.

The first suspension based on ceramic fibers K60 is poured into the first compartment (8) and simultaneously the second suspension of majority fibers K45 into the second compartment (9). The bottom of the tank (1) on which the filter screen (15) is disposed is closed by a layer of water from the filling to the brim of the body (17). This layer thus forms a joint between the two compartments. The two prepared suspensions, placed in each separate compartment (8) and (9), are separated from each other by the removable plate (10). This plate is then removed (10) by pulling it upwards by the ears (1 1, 12). In this upward movement, the elementary edges (14) of the comb (13) cause in the vicinity of this plate (10) turbulences which locally stir the two suspensions contained in the compartments (8) and (9), so that the fibers of these suspensions in the vicinity of this plate (10) mix. Simultaneously, the drain valve (20) is opened, so that the water from each of the suspensions drips very quickly, since there is no water retention.

If necessary, by means of a brawl, the top of the fibrous mast made is packed, so as to obtain a flat surface.

The flange (16) is then opened, then pulling the assembly using the filter cloth (15), the fibrous mast is brought to a tray. This material is then dried in an oven at 90 ° C for four hours. One then obtains a material shown in FIG. 5 measuring approximately 21 by 29 centimeters on a side for a thickness of 70 millimeters and a density close to 0.2 g / cm ³ .

• - tout d'abord une première portion (26), formant face chaude, c'est-à-dire destinée à venir au contact de la paroi chaude, constituée par les fibres les plus résistantes à la température, en l'occurrence des fibres céramiques K60 résistant à 1300°C;
• - une deuxième zone opposée (27), formant face froide, formée de fibres moins résistantes à la température (K45);
• - et une portion intermédiaire (28) dans laquelle ces deux zones s'interpénètrent; cette portion (28) étant essentiellement formée, autour d'une ligne de jonction (29), plus précisément de deux zones (30, 31), la première (30) étant plus riche en fibres à haute résistance à la température et la seconde (31) étant plus riche en fibres moins résistantes à haute température.

This material is then placed in an oven where it is heated for three hours at 1000 ° C. This temperature firstly causes the combustion of the paper fibers, then the ceramization of the ash obtained during this combustion, which binds together the elementary ceramic fibers of each. suspensions. The block obtained (25) shown in FIG. 5 essentially consists of three zones, namely:

• - Firstly a first portion (26), forming a hot face, that is to say intended to come into contact with the hot wall, constituted by the fibers most resistant to temperature, in this case fibers K60 ceramics resistant to 1300 ° C;
• - a second opposite zone (27), forming a cold face, formed of fibers less resistant to temperature (K45);
• - And an intermediate portion (28) in which these two zones interpenetrate; this portion (28) being essentially formed, around a junction line (29), more precisely of two zones (30, 31), the first (30) being richer in fibers with high temperature resistance and the second (31) being richer in fibers less resistant to high temperature.

The fibers of these three zones are homogeneously linked together by ceramic ashes from the combustion of paper fibers.

Example 2

The previous example is repeated, replacing the ceramic fiber K60 with a ceramic fiber sold by Morgan under the name "Cerachrome", of a length close to ten centimeters. A block similar to that of Example 1 is obtained, but the hot face of which withstands a temperature of 1450 ° C.

Example 3

Example 1 is repeated, but filling the second compartment (9) no longer with the suspension of K45 fibers, but of K60 fibers with a concentration reduced by half, that is to say 25 grams instead of 50 grams per liter.

After compacting to a uniform thickness, a paver is obtained whose two faces have a different density from one another.

Example 4

Example 1 is repeated by varying the concentration of the pulp from one compartment to another. The compartment most loaded with paper fibers being the most bonded, has better cohesion.

Example 5

• - le premier à l'aide d'une suspension contenant dans six litres d'eau, 300 g de fibres céramiques K60 et 15 grammes de fibres papetières mécaniques;
• - le second, toujours dans six litres d'eau, contenant 300 grammes de fibres céramiques K45 et 15 grammes de fibres papetières;
• - le troisième, toujours dans six litres d'eau, contenant 300 grammes de laine de verre et 15 grammes de fibres papetières mécaniques.

The bin is divided into three identical elementary compartments which are filled respectively:

• - the first using a suspension containing in six liters of water, 300 g of K60 ceramic fibers and 15 grams of mechanical paper fibers;
• - the second, still in six liters of water, containing 300 grams of K45 ceramic fibers and 15 grams of paper fibers;
• - the third, still in six liters of water, containing 300 grams of glass wool and 15 grams of mechanical paper fibers.

We also get a paving stone of 7 x 21 x 29 cm in which the hot side is formed by the tablecloth based on K60 fibers, while the cold side is formed by that of glass wool.

In this case, the cooking will be done after assembly, so that the temperature remains compatible with glass wool.

Example 6

The previous example is repeated by modifying the volume of the various elementary compartments, in order to modulate the thickness of each layer.

Example 7

The block of Example 1 is immersed before or after cooking in a mineral binder composition consisting of an aqueous solution of alumina phosphate. After immersion and impregnation, the whole is dried for two hours at 90 ° C.

Example 8

Example 1 is repeated with the following modification. An ultrasonic vibration generator is attached to the outer wall of the riser (1) and is operated for a few seconds after the separation plate (10) has been removed. The ultrasounds cause a sharp agitation of the liquid mass, which induces a more regular interpenetration of suspensions than that obtained with the comb (13), and a fiber concentration gradient adjustable in the area (28) as a function of the time of agitation.

Example 9

Example 1 is repeated by adding to one or each of the suspensions a mineral filler, such as for example kaolin, which modifies the properties of all or part of the part after firing (porosity, electrical resistivity, mechanical resistance, ease of machining, etc.).

• - la possibilité de réaliser des pièces de dimensions appropriées, même de grandes dimensions, ce qui se traduit par un gain de temps;
• - la possibilité de réaliser des pièces à meilleur coût, puisque seule la face chaude est en fibres résistant à la plus haute température;
• - une résistance mécanique améliorée, puisque après chauffage, les cendres céramiques forment une liaison minérale homogène;
• - la possibilité de réaliser des pièces en forme par le choix de bacs de forme appropriée, tels que par exemple des éléments de voûte dans un four;
• - la facilité de manipulation, grâce à la présence des fibres papetières, ce qui permet de réaliser la cuisson finale après montage de ces pièces dans le four lui-même;
• - la possibilité de réaliser à la demande et en petites séries des pièces de forme et de spécification déterminées.

The method according to the invention has many advantages over those known to date. We can cite:

• - the possibility of making parts of appropriate dimensions, even of large dimensions, which results in a saving of time;
• - the possibility of producing parts at a lower cost, since only the hot face is made of fibers resistant to the highest temperature;
• - improved mechanical resistance, since after heating, the ceramic ashes form a homogeneous mineral bond;
• - The possibility of making shaped parts by the choice of tanks of appropriate shape, such as for example arch elements in an oven;
• - ease of handling, thanks to the presence of paper fibers, which makes it possible to carry out the final cooking after mounting these pieces in the oven itself;
• - the possibility of producing, on request and in small series, pieces of specific shape and specification.

In this way, these parts can be used successfully for the insulation of the interior linings of ovens intended to work at high temperatures.

Claims (7)

1. Process for manufacturing a fibrous insulating piece comprising fibers resisting high temperature, such as ceramic fibers, particularly for the internal lining of heated enclosures, which consists in:

- preparing a first suspension containing a first type of fibers resisting high temperature;

- then, preparing at least a second suspension containing a second type of fibers resisting high temperature;

- then, pouring each suspension into a distinct compartment (8, 9) of a vat (1) the bottom (3) of which comprises a momentarily obstructed filtering sieve (15) and the elementary compartments (8, 9) of which are separated from one another by a removable plate (10);

- next, withdrawing the removable separating plate and eliminating the water of the suspensions through the filtering sieve (15);

- and then, drying the product obtained; characterized in that:

- each suspension also comprises a lesser portion of ceramizable particles;

- while withdrawing the removable separating plate (10), the medium is stirred locally in the vicinity of this removable separating plate (10), on the one hand, and, simultaneously, the water of the suspensions is drained through the filtering sieve (15);

-. and finally, after having dried the piece obtained in known manner, it is heated to a temperature inducing in said piece the ceramization of said ceramizable particles.

2. Process according to claim 1, wherein the main portion of fibers resisting high temperature are ceramic fibers and wherein the lesser portion of ceramizable particles are paper-making fibers.

3. Process according to any claims 1 and 2, wherein the paper-making fibers represent 1 to 5% by weight of dry weight of the temperature resistant fibers.

4. Process according to claim 1, wherein an inorganic filler is added to at least one of the elementary suspension.

5. Process according to claim 1, wherein the removable plate (10) presents, at least at its end (13) in contact with the sieve (15), a series of transverse edges (14) adapted to form stirring member during withdrawal of this plate (10).

Process according to claim 1, wherein the concentration of the suspensions contained in each compartment (8, 9) varies from one suspension to the other, but the volume of suspension poured into each compartment (8, 9) is identical in order to avoid overflow from one compartment (8) into the other (9).

7. Process according to claim 1, wherein, before or after heating, the piece is coated with an inorganic stove-dried binding composition.

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