FR2511362A1 - Forming refractory moulding by powder flame projection - using mixt. of coarse and fine refractory particles - Google Patents

Abstract

Refractory moulding or repaired refractory surface formed by a refractory powder flame profection process comprises non fused refractory particles dispersed and embedded in the solidified structure of a fused refractory. Preferably refractory particles sized less than 0.2 mm. are fed into the flame projected from a burner and refractory particles sized 0.2-10 mm. are also either projected into the flame or fed into the mould or onto the surface from a separate system. Producing refractory furnace bricks and repairing refractory furnace linings. The refractory has a thermal shock resistance as good as that of burned and non burned bricks and a strength and erosion resistance equal to those of electrocust bricks.

Description

 The present invention relates to refractory moldings or repair deposits formed by spraying flame refractory powder (in the following description these moldings will be referred to as "flame-resistant powder spray-casting"). The invention further relates to a method for producing such casts by spraying fire-resistant powder.

 In a well known manner is currently used the projection of flame-resistant powder as a means of direct repair of various types of ovens in the iron and steel industry and in the chemical industry. It is also used for the manufacture of refractory moldings. The refractory powder casts and the repairs made by such a process have excellent properties which can not be obtained by conventional methods.

 In the conventional technique of flame-refractory powder projection, refractory particles are brought into the stream of a projected flame which entrains these particles towards a substrate and causes them to strike this substrate while being melted in order to to form an adherent layer. Therefore, readily fusible refractory particles having a relatively low particle size, e.g. less than 210 microns, are used. In this flame spraying method, the melted refractory particles successively forge a solid, continuous, dense and uniform structure and, therefore, the deposited layers or millings exhibit dense structures having high strength.

However, the casts or deposits having such a dense and uniform structure have a certain number of defects among which can be mentioned in particular:
1 / They have a low resistance to thermal shock
2 / The contraction which occurs when the melted refractory particles cool and solidify causes internal stresses in the refractory moldings and these stresses accumulate to cause rupture of the molding or the refractory deposit.

 3 / The phenomenon of contraction causes a: oclase refractory deposits formed on the substrate by flame projection.

 the defects specified above are caused by the internal thermal stress of the refractory moldings or deposits and therefore the greater the surface area and / or the thickness of the moldings or deposits, the more likely they are to rupture. Since these defects are attributable to the residual stress resulting from the thermal stress that has accumulated since the onset of solidification, flame-retarded moldings and refractory deposits are limited in the dimensions to which they are subjected. can be manufactured, despite their excellent properties.

 Accordingly, it is an object of the present invention to provide flame refractory powder casting which has the excellent properties specified above, which are specific to fire-resistant powder-castings or refractory deposits, without, however, possessing a mediocre resistance to thermal shocks and thermoclase and without being subject to rupture by internal stress.

 Another object of the invention is to provide flame-resistant, large-dimension flame-resistant powder-casting moldings which withstand thermal shocks as well as cooked and uncooked bricks, these moldings are also resistant to erosion. than electro-cast bricks.

 Another object of the present invention is to provide a method of manufacturing the above-mentioned flame refractory powder casting.

 the flame-resistant powder projection moldings according to the present invention are essentially characterized in that they comprise unmelted refractory particles dispersed and embedded in the solidified structure of the molten refractory.

 The method according to the invention for producing flame-resistant powder projection moldings is characterized in that it consists in feeding fine refractory particles having a particle size of less than about 0.2 mm and coarse refractory particles having a particle size distribution. from about 0.2 to about 10, in the stream of a flame thrown by a flame projection burner and to project these particles to the flame, in a mold such that the melted refractory fine particles form a phase solidified in which are dispersed and coated the coarse refractory particles.

 Other features and advantages of the present invention will emerge from the description given below with reference to the accompanying drawings which illustrate various embodiments or implementation.

In the accompanying drawings;
FIG. 1 is a schematic view illustrating the structure of a flame-resistant powder projection molding according to the present invention;
FIG. 2 diagrammatically represents an exemplary embodiment of a device for buttering the process according to the present invention, and
- Figure 3 is a schematic view illustrating an exesple implementation of a method according to the invention for producing moldings by spraying flame-resistant powder flam.

 As a result of researches and comparative tests carried out on refractory casts and conventional refractory tears, as well as on the moldings and repair pits obtained by spraying fire-resistant powder, the Applicant has succeeded in developing new refractory castings as well as new repair deposits obtained by the technique of flame-resistant powder spraying. More specifically, the applicant has succeeded in developing and producing new refractory castings as well as new refractory repair depots. having a thermal shock resistance as good as that of conventional baked and uncooked bricks and also having erosion resistance as well as that of conventional electro-cast bricks. The refractory moldings and repair deposits developed by the present inventors are made by flame spraying refractory powder so as to present unmelted refractory particles which are dispersed in the solidified structure of the moldings or refractory deposits.

 In general, refractory castings are classified into the following types: cooked, uncooked and electro-cast according to the production technique used. Of course each type of refractory molding has its specific characteristics. For example, the fired and uncured refractory bricks are obtained by treating refractory particles having a grain size of 7, and less, and thus having a large number of open pores so that the portion of fine particles of the material is small. As a result, when the refractory matrix is attacked by an erosion material such as, for example, the slag of a blast furnace, the slag of a converter, etc., the part of the fine particles of the matrix is subjected to main erosion. Furthermore, an electroformed refractory has a uniform and very dense structure and therefore has a high erosion resistance and a high rigidity but has a low resistance to thermal shocks caused by repeated heating and cooling. These electrofusion refractories are also expensive.

 At the present time, since the flame-projection moldings of refractory powder are obtained by fusion and solidification of refractory particles, the structure is as uniform and dense as that of an electro-cast brick and therefore these moldings exhibit excellent resistance to erosion. However, on the other hand, they have lower properties with respect to resistance to thermal shock.

 Extensive studies made by the present applicant to overcome the drawbacks and defects of conventional castings obtained by spraying flame-resistant powder have led to the discovery that one can obtain an excellent resistance to thermal shocks of such moldings. dispersant and coating unmelted coarse refractory particles in the dense matrix formed by the melting and solidification of fine refractory particles.

 The present invention, which is based on this discovery, therefore makes it possible to produce new refractory moldings which have, on the one hand, a resistance to thermal shocks as good as that of cooked and uncooked bricks and, on the other hand, an erosion resistance as well as that a rigidity equal to those of electro-cast bricks.

 Likewise, according to the present invention, the internal thermal stresses of the moldings resulting from the solidification (stresses which result in irremediable defects in the production of flame-resistant castings of refractory powder) are eliminated thanks to the refractory particles. coarse unmelted particles which are dispersed in the matrix of the moldings and which interrupt the uniformity of the molding. As a result, it is possible to prevent the rupture of the moldings by thermal stress, which makes it possible to produce flame-projection moldings of refractory powder having dimensions that are much larger than those of the moldings obtained by the use of conventional methods. .

 Refractory powder flame-castings according to the present invention can be obtained by using a refractory powder flame burner of the type described, for example, in US Pat. No. 4,192,461. In a conventional method of spraying refractory powder, refractory particles having a particle size of less than 0.2 mm are fed into the stream of a projected flamne and are thus projected in the molten state onto a material. The present invention can be easily produced by mixing coarse refractory particles having a particle size of preferably between about 0.2 and 10 microns with fine refractory particles of the type used in the process described above, or by continuously projecting the coarse refractory particles mentioned above in a flame projection molding being carried out in a mold or on a material to be repaired from outside the projected flame flow system into which the fine particles are brought refractories indicated above.

 According to the present invention, the particle size of the coarse refractory particles is limited to about 0.2-10 minutes since, if the particle size of these particles is greater than 0.2 millimeters, they can remain in flux when transported by the current of the projected flame. They are thus dispersed and embedded in the dense solidified structure of the fused fine refractory particles in the form of unmelted coarse refractory particles. Moreover, enamelled particles of such granulonetry effectively make it possible to interrupt the uniformity of the dense solidified structure. In addition, if the particle size of the coarse refractory particles exceeds the value of 10 μm, the density of the solidified structure is reduced which decreases the resistance to thermal shocks.

 According to the present invention the preferred ratio of fine particle size refractory particles to coarse particles is 95-20 parts by weight of fine particles per 5-80 parts by weight of coarse particles. According to the present invention the coarse refractory particles and the fine particles may be made of the same refractory material or different material.

 As refractory material, it is possible to use acidic refractories such as in particular: siliceous refractories, semi-siliceous refractories, pyrophillite refractamines, chamotte, or neutral refractories such as refractories with a high alumina content, refractories based on carbon, chromium, silicon carbide, etc ... or even basic refractories such as forsterite, refractories based on magnesium chromium or magnesium chromium, refractories based on magnesia, dolomite etc ..

the coarse particles can be intimately embedded in the moldings by adding them to the current of the projected flame or
by injecting them into the forms of the fine refractory particles
when these casts solidify from the molten state. The amount
of heat extracted from the flame by coarse refractory particles
when these are brought to the molding, is very small and by
therefore the fusion of the fine refractory particles is not disturbed by the presence of these coarse particles.

Since the coarse refractory particles can be added to the flame spray grinding from outside the flame jet system carrying the fine particles; materials that decompose or react can also be used
at high temperature (and which can not be used for flame projection), as coarse particles. As a result, the combinations of materials which hitherto were considered impossible to use in conventional processes can be used in the process according to the present invention, the material constituting the coarse refractory particles being selectable in a wide range of materials. available.

 As a result, according to the present invention, it is possible to use, as unmelted coarse particles, not only refractory materials such as SiO 2 -Al 2 O 3 but also carbon or carbides and nitrides, such as, for example, silicon carbide. silicon nitride, silicon oxynitride, etc.

FIG. 1 shows the structure of a molding according to the invention. In this figure, the sections provided with oblique hatching designate a solidified structure 1 of fine particles of molten refractory in which there are fine closed pores 2. The portions provided with fine dotted lines denote coarse unmelted particles 3 present in FIG.
diameters of the order of 0.2-10 mm. The interface between the particles
coarse unmelted 3 and the solidified structure 1 consists of welded sections and thin cavities 4.

The solidified structure 1 has a fine complicated network of micro-cracks resulting from the presence of non-coarse particles.
fondues.

The bond strength between coarse particles
unmelted 3 and the solidified structure 1 is weak, and the continuity
of the solidified structure of the melted refractory fine particles is
interrupted by unmelted coarse particles 3. Free space
resulting from the presence of micro cracks can absorb the expansion and contraction that occur during sudden thermal changes. the structural units formed by the micro cracks are interlocked. Therefore the structure obtained by the present invention has excellent thermal shock resistance without decreasing its overall density.

 The characteristics of the moldings according to the invention will now be described by comparison with conventional refractory moldings. For example, while a fired brick has a matrix of fine refractory particles with low erosion resistance, the corresponding portion of a molding according to the present invention has a dense solidified structure of fused fine refractory particles whose resistance erosion is as high as that of the electro-fusion castings.The part of a fired brick made of refractory particles of average particle size having diameters of 0.21-1.0 nrn and coarse refractory particles having a granulometry of 1-10 irni, corresponds to coarse unmelted refractory particles having diameters of 0.2 to 10 nm, which are uniformly distributed in the solidified structure of fused fine refractory particles of the moldings according to the invention. Consequently, the casts according to the invention exhibit both the high rigidity and the high resistance to erosion of an electro-fused brick, and the high resistance to thermal shocks of a molten brick. therefore a new type of refractory moldings with properties that were not obtained using conventional moldings made by flame projection of refractory powder.

 Moreover, the moldings of the invention can be made in large dimensions since there is no problem such as, in particular, flexion, deformation, formation of cracks, thermoclase, etc.

 Reference is now made to FIG. 2, which schematically shows a device which can be used to flame-throw refractory deposits in order to repair the wall of a blast furnace, for example. This device is a variant of the system described in US Pat. No. 4,192,460. In this figure the reference 11 designates a bottle of oxygen to ensure the combustion and entrainment of the particles, the reference 12 denotes a bottle containing the fuel. gaseous, reference 13 designates a hopper for coarse refractory particles, reference 14 designates a hopper containing fine refractory particles, reference numeral 15 denotes a gas regulator ensuring the control of can bubbling gas-oxygen flarrrr, in a burner and the reference 16 designates a brightener device, the latter being placed at the end. the burner device 16 is provided with a pipe 19 for supplying refractory powder, a conduit 2Q supplying oxygen, a supply line for liquefied gas 21 (preferably natural gas) and pipes 22 and 23 for cooling the burner. the system further comprises a conduit 18 for supplying coarse refractory particles and a nozzle 26 for delivering these coarse particles. the heat system 16 is provided with a drive mechanism 17 to move this system in any desired direction to bring it, with the nozzle 26 on the part 28 where the furnace must be repaired. A motor M operates the drive mechanism. the fine refractory particles transported and melted by the flame projected by the burner system 16, are deposited in the molten state on the part 28 to be repaired from the furnace and the coarse refractory particles are ejected from the nozzle 26.Thus, the particles The flame-retarded fine refractories are deposited on the furnace wall and mix with the coarse refractory particles which are thus dispersed and embedded in the resulting repair plating.

 FIG. 3 illustrates an embodiment of a method according to the invention for the preparation of the moldings defined above.

 In this figure there is shown at 31 a burner providing the flame projection of fine refractory powder and 32 a burner ensuring the flame projection of large refractory particles.

It is of course possible to replace these two burners separated by a single burner. A heat-resistant base plate 33 moves in the direction indicated by the arrow and fine and coarse particles are projected on this plate using the flame currents from the burners 31 and 32. In the first place, it forms on the base plate 33 a layer 34 of refractory fine particles and thereafter refractory particles 35 are dispersed and embedded in the flame-projected layer 34, whereby a flame projection molding 36 is continuously formed on the plate 33. Then, the molding 36 is released from the plate 33 and is cut to the desired dimensions.

 In order to facilitate the molding release operations, the base plate is made of a refractory material having good lubricating properties, for example heat-resistant cast steel, graphite, silicon carbide, etc. base plate 33 is made of cast steel heat resistant, it is preferable that it is provided with a cooling jacket. Furthermore, this plate may be provided with partition walls extending along its width, at regular intervals to form moldings separated by these partitions. It is also possible to use a plate in the form of a box for producing the refractory moldings.

 Furthermore, by choosing a refractory material which can adhere to the molding to form the base plate, it is possible to obtain moldings of the composite type.

 the following examples illustrate the invention.

Example 1
Using a conventional refractory powder flame burner, a refractory material having the composition given below was sprayed with a propane fl ate to form a flame projection block. containing refractory particles
coarse non-melted according to this invention and a flame projection block according to the conventional technique. The properties of these flame projection blocks were then compared to those of fused alumina bricks and fired alumina bricks available in commerce.

 the refractory material used in the flame projection method according to the invention and in the conventional flame-projection method consisted of an alumina comprising 98.5% Al 2 O 3 and 0.3% SiO 2. the refractory material consisted of coarse particles having a particle size of 10 to 0.21 nanometers and fine particles having a particle size of less than 0.2 microns. For the production of blocks by conventional flame projection only fine particles having a particle size of less than 0.2 mm have been used. the block according to the invention was obtained by depositing 60 parts by weight of fine refractory particles with a particle size of less than 0.2 nm on a heat-resistant base plate, by flame projection and projecting 40 parts by weight of coarse refractory particles having a particle size of 10 to 0.21 mm on the deposit produced while the latter was in the molten state.

 Table 1 below lists the properties of the block according to the present invention, the block obtained by a conventional flame projection method, a fused alumina brick and a fired brick.

 In Table 1 the slag resistance test was carried out using a horizontal rotary type erosion test machine. An extended slag erosion test was carried out at a rotation speed of 2 rpm at a temperature of 1 6000 C and a duration of 30 hours. The laiter used was prepared by mixing a blast furnace slag and a converter slag in a proportion by weight of 1/1. At the end of the test the amplitude of the erosion of the samples subjected to the tests was measured. The comparison of the samples was carried out using the erosion rate of a brick of alumina cooked as a standard value, that is to say by defining the erosion index of such a brick by the value 100.The resistance to thermal shocks was determined by repeating the operation of placing in a furnace a sample of 50 x 50 x 50 mm, heating it rapidly to a temperature of 1 2000 C, maintaining this temperature. sample in the oven for 15 minutes at this temperature, removing the sample from the electric oven and placing it in air allowing it to cool for 15 minutes.

 In the table the thermal shock resistance has been expressed as the number of repeated thermal shocks required to overcome cracks in the sample and in the form of the number of thermal shocks required so that this sample can no longer be used. form and is damaged by scale production.

 The examination of Table 1 clearly shows that the block according to the invention obtained by flame projection has excellent properties of thermal shock resistance and slag resistance octopus to those of the three types of conventional blocks.

TABLE 1

<tb><SEP> PROPERTY <SEP> TESTED <SEP> A <SEP> B <SEP> C <SEP> D
<tb> Density <SEP> specific <SEP> (g / an2) <SEP> 3.60 <SEP> 3.67 <SEP> 3.42 <SEP> 3.14
<tb> Porosity <SEP> apparent <SEP> (%) <SEP> 4.8 <SEP> 2.9 <SEP> 2.8 <SEP> 16.5
<tb> Composition <SEP> chemical <SEP> in <SEP> z <SEP>
<tb><SEP> A1203 <SEP> 98.5 <SEP> 98.5 <SEP> 97.0 <SEP> 98.5
<tb><SEP> SiO2 <SEP> 0.3 <SEP> 0.3 <SEP> 0.7 <SEP> 0.3
<tb> Resistance <SEP> to <SEP><SEP> Bending <SEP> Thermal
<tb> to <SEP> 1 <SEP> 4000 <SEP> C <SEP> (kg / yr2) <SEP> 280 <SEQ> 320 <SEQ> 250 <SEP> 150
<tb><SEP> Erosion Index <SEP> of <SEP><SEP> Strength at
<tb> slag <SEP> (-) <SEP> 8 <SEP> 6 <SEP> 12 <SEP> 100
<tb><SEP><SEP><SEP> Shock <SEP> Shock Resistance>
<tb><SEP> Number <SEP> of <SEP> shocks <SEP> before <SEP> cracks <SEP> 10 <SEP> 1 <SEP> 1 <SEP> 12
<tb><SEP> Number <SEP> of <SEP> shocks <SEP> before <SEP> flaking <SEP> 23 <SEP> 1 <SEP> 4 <SEP> 25 <SEP>
<Tb>
A block obtained according to the present invention by flame projection
B: Classic block obtained by projection at 7a flame
C: Fused alumina brick
D: Cooked alumina brick
Example 2
A flame projection block was made as described in Example 1 using fine alumina particles having a particle size less than 0.2 nm and having a chemical composition of 98.5% Al 2 O 3. and 0.3% SiO 2 as fine refractory particles and fused magnesia particles having a particle size of 0.21 to 10 mm and a chemical composition of 99.9%.
MgO, as coarse refractory particles.

 Table 2 below specifies the properties of the block obtained.

The comparison of these properties with those of the block obtained by flame projection and indicated in Table 1 shows that the thermal bending resistance and the thermal shock resistance of this block are substantially the same as those of the projection block. the flame indicated in Table 1 but that an improvement in the resistance to slag is obtained,
TALBEAU 2

<tb><SEP> PROPERTY <SEP> TESTED <SEP> BLOCK <SEP> FROM <SEP> PROJECTION <SEP> A <SEP> LA
<tb><SEP> FLAME <SEP> BY <SEP> THE INVENTION
<tb> Density <SEP> specific <SEP> (g / cm2) <SEP> 3.70
<tb> Porosity <SEP> apparent <SEP> (8) <SEP> 4.9
<tb> Composition <SEP> Chemical <SEP> (%)
<tb><SEP> Powder <SEP> fine
<tb><SEP> Al2O3 <SEP> 98.5
<tb><SEP> SiO2 <SEP> 0.3
<tb><SEP> Coarse <SEP> Particles
<tb><SEP> Mgo <SEP> 99.9
<tb> Resistance <SEP> to <SEP> la2lexion <SEP> thermal <SEP> to <SEP> 290
<tb> 1 <SEP> 400 <SEP> @ <SEP><SEP> (kg / cm <SEP>)
<tb><SEP> Erosion Index <SEP> from <SEP><SEP><SEP><SEP> 5 <SEP> Resistance
<tb><SEP><SEP><SEP> Shock <SEP> Shock Resistance>
<tb><SEP> Number <SEP> of <SEP> shocks <SEP> before <SEP> cracks <SEP> 9
<tb><SEP> Number <SEP> of <SEP> shocks <SEP> before <SEP> shelling <SEP> 22
<Tb>
It remains understood that this invention is not limited to the embodiments or implementation indicated above, but encompasses all variants.

Claims (12)

 1 - Refractory molding obtained by spraying flame-resistant powder characterized in that it carries unmelted refractory particles (3) dispersed and embedded in the solidified structure (1) of a molten refractory.  2 - A molding according to claim 1 characterized in that it comprises cavities (4) at the interface between the solidified structure (1) of a molten refractory and unmelted refractory particles (3).  3 - Molding according to one of claims 1 or 2 characterized in that the solidified structure of the molten refractory is made of the material nee that unmelted refractory particles.  4 - Molding according to one of claims 1 or 2 characterized in that the silidifée structure of the molten refractory is made of a material different from unmelted refractory particles.  5 - Molding according to any one of claims 1 to 4 characterized in that the solidified structure comprises refractory particles having a diameter less than 0.2 μm and in that the unmelted refractory particles have a diameter of the order of 0.2 to 10 mm.  6 - Molding according to any one of claims 1 to 5 characterized in that the refractory material constituting the solidified structure of a molten refractory is selected from the group which comprises the acid refractories, neutral and basic.  7 - A molding according to any one of claims 1 to 5 characterized in that the unmelted refractory particles consist of at least one refractory selected from the group consisting of acidic, neutral and basic refractories and carbon, a carbide or a nitride.  8 - Molding according to any one of claims 1 to 7 characterized in that the unmelted refractory particles are dispersed and embedded in the solidified structure of a melted refractory in an amount of 5-80 parts by weight.  9 - Molding according to any one of claims 1 to 8 characterized in that it is formed as a deposit ensuring the repair of the wall of a furnace.  10 - Process for producing flame-projection moldings of refractory powder, characterized in that it consists in feeding fine refractory particles having a particle size of less than about 0.2 nin and coarse refractory particles having a particle size distribution of the order from 0.2 to 10 mm in the current of a flame projected by a flame projection burner and to project these particles to the flame in a mold in such a way that the melted refractory fine particles form a solidified phase of structure and that the coarse refractory particles are dispersed and embedded in this solidified structure.  11 - Process for producing flame-thrown castings of refractory powder, characterized in that it consists in bringing fine refractory particles having a particle size of less than about 0.2 m in the current of a projected flame, to be projected to flame these particles in a mold, and to inject into the mold coarse refractory particles having a particle size of 0.2 to 10 mm, from outside the system of the projected flame current, during the formation of a structure solidified by the refractory fine particles are melted by the projected flame, so that the coarse refractory particles are dispersed and embedded in the solidified structure constituted by the fine particles  12 - Process according to one of claims 10 or 11 characterized in that the proportion of refractory fine particles has a particle size less than 0.2 mm is 95 to 20 parts by weight and in that the proportion of coarse particles having a particle size of 0.2 to 10nin is of the order of 5 to 80 parts by weight.