GB2104056A

GB2104056A - Refractory powder flame- projection mouldings

Info

Publication number: GB2104056A
Application number: GB08124629A
Authority: GB
Inventors: Hiromi Fukuoka; Masataka Matsuo; Kazuo Hamai; Mituo Sugawara; Tokauki Hatta
Original assignee: Kurosaki Refractories Co Ltd; Kurosaki Yogyo Co Ltd; Nippon Steel Corp
Current assignee: Kurosaki Refractories Co Ltd; Kurosaki Yogyo Co Ltd; Nippon Steel Corp
Priority date: 1981-08-12
Filing date: 1981-08-12
Publication date: 1983-03-02
Also published as: GB2104056B

Abstract

A refractory powder flame- projection moulding (e.g. a refractory moulding or repairing deposit), comprises non-fused refractory particles dispersed and embedded in the solidified structure of a fused refractory. A process of producing the mouldings comprises feeding fine refractory particles having a particle size of less than 0.2 mm. into the stream of a projected flame, flame-projecting the particles into a mould, and feeding coarse refractory particles having a particle size of 0.2 to 10 mm. either into the stream of the flame or into the mould from outside the system of the projected flame stream to form a solidified structure of the fine refractory particles fused by the projected flame, the coarse refractory particles thereby being dispersed and embedded in the solidified structure of the fused fine particles.

Description

SPECIFICATION Refractory powder flame projection mouldings The present invention is concerned with refractory mouldings or repairing deposits formed by refractory powder flame projection (hereinafter simply referred to as "refractory powder flame projection mouldings") and is also concerned with a process of producing refractory powder flame projection mouldings.

As is well known, refractory powder flame projection is now being employed as a direct repairing method for various kinds of furnaces in the iron and steel and chemical industries and it is also being used for producing refractory mouldings. The flame projection mouldings and the repairs made by this method have excellent properties which are not obtainable by conventional methods.

In the conventional refractory powder flame projecting technique, refractory particles are fed into the stream of a projected flame which carries the particles toward a substrate into which it causes them to collide in fused state so as to form an adhering layer on the substrate. Hence, easily fusable refractory particles having a relatively fine particle size, for example below 210 microns, are used. In this flame projection method, the fused refractory particles successively form a dense and uniform continuous solidified structure and hence the deposited layers or mouldings formed possess dense structures with a high strength.However, the mouldings or deposits with such a dense and uniform structure have certain faults: (1) they have a low thermal shock resistance; (2) the shrinkage which results when the fused refractory particles cool and solidify causes internal stresses to build up in the refractory mouldings and this stress accumulates to the extent of causing breakage of the refractory moulding or deposit; (3) the shrinking phenomenon causes spalling of the refractory deposits formed on the substrate by flame projection.

These faults are caused by the internal thermal stress of the refractory mouldings or refractory deposits and hence the greater the surface area and/or the thickness of the mouldings or deposits, the more likely the mouldings or deposits are to suffer breakage. Because of these faults, which are attributable to the residual stresses resulting from thermal stresses accumulating from the initiation of the solidification, refractory mouldings and deposits formed by flame projection are, in spite of their excellent properties, limited as to the size in which they can be produced.

It is an object of the present invention to provide refractory powder flame projection mouldings having the above-described excellent properties specific to refractory mouldings or deposits formed by refractory powder flame projection, without having a poor resistance to thermal shock resistance and spalling and without susceptibility to breakage by internal stress.

Another object of the present invention is to provide large refractory powder flame projection mouldings having a thermal shock resistance as high as those of burned bricks and unburned bricks and also having an erosion resistance which is as high as that of electrocast bricks.

Still another object of the present invention is to provide a process of producing these refractory powder flame projection mouldings.

Thus, according to the present invention, there is provided a refractory powder flame projection moulding, comprising non-fused refractory particles dispersed and embedded in the solidified structure of a fused refractory.

The present invention also provides a process of producing refractory powder flame projection mouldings, which comprises feeding fine refractory particles with a particle size of less than about 0.2 mm. and coarse refractory particles having a particle size of 0.2 to 10 mm. into the stream of a flame projected by a flame projecting burner and flame-projecting these particles into a mould thereby forming a solidified phase having the coarse refractory particles dispersed and embedded therein.

The present invention will now be described in more detail, with reference to the accompanying drawings, in which: Fig. 1 is a schematic view showing the structure of the refractory powder flame projection moulding of the present invention; Fig. 2 is a view showing one embodiment of the apparatus for performing the process of the present invention; and Fig. 3 is a view illustrating one embodiment of the process of producing the refractory powder flame projection mouldings of the present invention.

In the course of comparing and investigating the properties of conventional refractory mouldings and refractory deposits for repairing and the properties of mouldings and depots for repairing formed by refractory powder flame projection, we have succeeded in developing new refractory mouldings and refractory deposits formed by the flame projection technique. More specifically, we have succeeded in developing new and useful refractory mouldings and refractory repairing deposits with a thermal shock resistance as good as that of conventional burned or non-burned bricks and also having an erosion resistance as good as that of conventional electrocast bricks.The refractory mouldings and repairing deposits which we have developed are formed by refractory powder flame projection so as to have nonfused refractory particles dispersed in the solidified structure of the moulding or deposits.

In general, refractory mouldings are classified into the burned type, the non-burned type and the electrocast type, according to the production process, each type having its own specific features. For example, the burned and non-burned refractory bricks are produced by packing together refractory particles with a particle size of 7 mm. and less which thus have a large number of open pores so that the fine particle portion of the material is weak. Therefore, when the refractory matrix is attacked by the action of an erosive material, such as blast furnace slag, converter slag or the like, the fine particle portion of the matrix is predominantly eroded.On the other hand, an electrocast refractory has a very dense and uniform structure and hence has a high strength and high erosion resistance but has a low resistance to the thermal shock caused by repeated heating and cooling and is also expensive to produce.

Since refractory powder flame projection mouldings are formed by fusing and solidification of refractory particles, the structure is as uniform and dense as the structure of an electrocast brick and hence the mouldings have an excellent erosion resistance. On the other hand, they have an inferior thermal shock resistance.

In the course of various studies for eliminating such faults of refractory powder flame projection mouldings, we have discovered that excellent thermal shock resistance can be imparted to refractory powder flame projection mouldings by dispersing and embedding non-fused coarse refractory particles in the dense matrix formed by the fusion and solidification of fine refractory particles.

The present invention, which is based upon this discovery, thus provides novel refractory mouldings having a thermal shock resistance as good as that of burned bricks and non-burned bricks and having a strength and erosion resistance equal to those of electrocast bricks.

Also, according to the present invention, the internal thermal stresses of the mouldings occurring with solidification, which have previously been a fatal defect in the production of refractory powder flame projection mouldings, are broken up by the non-fused coarse refractory particles which are dispersed in the matrix of the mouldings and disrupt the moulding uniformity. As a result, breakage of the mouldings by thermal stress can be avoided, making it possible to provide larger refractory powder flame projection mouldings than those producible by conventional methods.

The refractory powder flame projection mouldings of the present invention can be produced using the refractory powder flame projecting burner apparatus described, for example, in U.S. Patent Specification No. 4,192,460. In the conventional refractory powder flame projection method, refractory particles having sizes below about 0.2 mm. are fed to the stream of a projected flame and are projected on to a material in a fused state.The refractory powderflame projection mouldings of the present invention can be easily produced by admixing coarse refractory particles having particle sizes of preferably about 0.2 to 10 mm. with the aforesaid fine refractory particles in the above-described method or by continuously projecting the aforesaid coarse refractory particles into a flame projection moulding being formed in a mould or on a material to be repaired from outside the system of the projected flame stream into which the aforesaid fine refractory particles are fed.

According to the present invention, the particle size of the aforesaid coarse refractory particles is limited to about 0.2 to 10 mm. since, if the particle size of the coarse refractory particles is less than 0.2 mm., the particles can remain unfused while being carried by the stream of the projected flame and are thus dispersed and embedded in the dense solidified structure of the fused fine refractory particles as non-fused coarse refractory particles. Furthermore, embedded particles of this size are effective in disrupting the uniformity of the dense solidified structure. On the other hand, if the particle size of the coarse refractory particles is over 10 mm., the density of the solidified structure is reduced, with the undesirable effect that the thermal shocks resistance is lowered.

The preferred ratio between the fine and coarse refractory particles is 95 to 20 parts by weight of the fine refractory particles to 5 to 80 parts by weight of the coarse refractory particles.

The fine and coarse refractory particles may be of the same or different refractory material.

As the refractory materials, there can be used acid refractories, such as siliceous refractories, semi-siliceous refractories, pyrophyllite refractories, chamotte refractories and the like; neutral refractories, such as high alumina refractories, carbonaceous refractories, chromium refractories, silicon carbide refractories and the like; and basic refractories, such as forsterite refractories, chrome-magnesia refractories, magnesia-chrome refractories, magnesia refractories, dolomite refractories and the like.

The coarse refractory particles can be closely embedded in the mouldings by introducing them into the stream of the projected flame or by injecting them into the mouldings formed of the fine refractory particles as the mouldings solidify from the fused state. The amount of heat taken from the flame by the coarse refractory particles while they are being carried to the moulding is very small and hence the fusion of the fine refractory particles is not hindered by the presence of the coarse particles.

Since the coarse refractory particles can be added to the flame projection mouldings from outside the system of the stream of projected flame carrying the fine refractory particles, even materials which decompose or react at high temperatures and cannot be used for flame projection can be used as coarse particles in the present invention. Therefore, combinations of materials hitherto considered to be impossible can be used and the material for the coarse refractory particles may be selected from a wide range of materials.

Therefore, as the non-fused coarse particles, it is possible to use not only such refractory materials as silica-alumina (SiO2-Al203) but also carbon or such carbides and nitrides as silicon carbide, silicon nitride, silicon oxynitride and the like.

The structure of the refractory powder flame projection mouldings of the present invention is schematicallly shown in Fig. 1. In this Figure, the portions indicated by oblique lines represent a solidified structure 1 of fused fine refractory particles in which fine closed pores 2 are interspersed. The portions indicated with fine dots represent non-fused coarse particles 3 with diameters of 0.21 to 10 mm. The interface between the non-fused coarse particles 3 and the solidified structure 1 is composed of welded portions and fine cavities 4. In the solidified structure 1 , there is a fine and complicated pattern of microcracks arising from the non-fused coarse particles.

The bonding strength between the non-fused coarse particles 3 and the solidified structure 1 is weak and the continuity of the solidified structure of fused fine refractory particles is complicatedly disrupted by the non-fused coarse particles 3. The clearance at the microcracks serves to absorb expansion and contraction during abrupt heat changes. The structural units formed by the microcracks are complicatedly interlocked with each other. Therefore, the structure obtained has an excellent thermal shock resistance but suffers no degradation in denseness on the whole.

The features of the refractory powder flame projection mouldings of the present invention will now be described, in comparison with conventional refractory mouldings. For example, whereas a burned brick has a matrix composed of fine refractory particles which has an inferior erosion resistance, the corresponding part of the mouldings of the present invention is a dense, solidified structure of fused fine refractory particles which has an erosion resistance as high as that of mouldings formed by electrocasting.The portion of a burned brick composed of average-sized refractory particles with diameters of 0.21 to 1.0 mm. and coarse refractory particles having a size of 1 to 10 mm. corresponds to the non-fused coarse refractory particles having diameters of 0.2 to 10 mm. which are uniformly distributed in the solidified structure of the fused fine refractory particles in the mouldings according to the present invention. Therefore, the refractory powder flame projection mouldings of the present invention possess both the high strength and high erosion resistance of an electrocast brick and the high thermal shock resistance of a burned brick. Thus, the refractory powder flame projection mouldings of the present invention are a new type of refractory mouldings having properties not obtainable in conventional mouldings by refractory powder flame projection.The refractory powder flame projection mouldings of the present invention can also be produced in large sizes, since even in such large mouldings, no problems occur, such as bending, deformation, spalling, crack formation or the like.

The present invention will be further explained, with reference to the apparatus shown in Fig. 2, in connection with the formation of flame projection deposits for reparing the wall of, for example, a blast furnace. The apparatus shown in Fig. 2 is a modification of the apparatus described in U.S. Patent Specification No. 4,192,460. In Fig. 2, 11 indicates a bottle of oxygen for supporting combustion and entraining particles, 12 a bottle of LPG for combustion, 13 a hopper for coarse refractory particles, 14 a hopper for fine refractory particles, 15 a gas regulator for controlling an LPG-02 combustion flame in a burner and 1 6 a burner casing having a burner at the tip.The burner casing 1 6 contains a refractory powder supply pipe 19, an oxygen supply pipe 20, an LPG supply pipe 21 and burner cooling pipes 22 and 23. 18 indicates a coarse refractory particle supply pipe and 26 a nozzle for supplying coarse refractory particles. The burner casing 1 6 is equipped with a driving means 1 7 for moving the burner casing in any desired direction so as to bring it and the nozzle 26 to the portion 28 of the furnace requiring repair. The driving means 1 7 is powered by a motor M.The fine refractory particles carried and fused by the flame projected by the burner body 16 are deposited in a fused state on the portion 28 of the furnace requiring repair and the coarse refractory particles are ejected from the nozzle 26, the flameprojected fine refractory particles thereby being deposited on the furnace wall intermixed with the coarse refractory particles which become dispersed and embedded in the resulting repairing deposit.

Fig. 3 shows an embodiment of the process for producing the refractory powder flame projection mouldings of the present invention. In this Figure, 31 indicates a fine refractory powder flame-projecting burner and 32 a coarse refractory particle flame-projecting burner. Separate flame projecting burners 31 and 32 are shown in the Figure for projecting fine refractory particles and coarse refractory particles but the fine refractory particles and coarse refractory particles may also be flame-projected through a single flame-projecting burner. A heat-resistant base plate 33 travels in the direction shown by the arrow and from the flame-projecting burners 31 and 32 disposed above the base plate, fine refractory particles and coarse refractory particles are projected together with the projected flame streams.First, a flame deposited layer 34 of the fine refractory particles is formed on the base plate and then the coarse refractory particles 35 are successively dispersed and embedded in the flame-projected layer, a flame projection moulding 36 thereby being continuously formed on the base plate 33. Thereafter, the flame projection moulding 36 is removed from the base plate 33 and cut into any desired sizes. For facilitating the removal of the moulding, the base plate is preferably made of a refractory material having good lubricating properties, such as heat-resistant cast steel, graphite, silicon carbide or the like, and when the base plate is made of heat-resistant cast steel, it is preferably provided with a cooling jacket. In addition, partitions extending in the width direction may be provided on the base plate at fixed intervals in the lengthwise direction to form flame-projection mouldings on the base plate separated by the partitions. A box-like base plate may also be employed for forming the refractory powder flame projection mouldings. Furthermore, by selecting a refractory material which can be firmly bonded to flame-projection mouldings as the material for the base plate, composite type flame projection mouldings can be obtained.

The following Examples are given for the purpose of illustrating the present invention: EXAMPLE 1 Using a conventional refractory powder flame projecting burner, a refractory material having the following composition was flame-projected by a propane flame to form a flame-projection block containing non-fused coarse refractory particles according to the present invention and a flameprojection block according to the conventional flame-projecting method and the properties of these flame-projection blocks and the properties of commercially available electrocast alumina bricks and burned alumina bricks were compared.

The refractory material used in the flame-projection method of the present invention and the conventional flame-projection method was an alumina material containing, by weight, 98.5% alumina and 0.3% silica. The refractory material was classified into coarse particles of 10 to 0.21 mm. size and fine particles of less than 0.2 mm. size and, for producing the conventional flame projection blocks, only fine particles of less than 0.2 mm. size were used. The refractory powder flame-projection block of the present invention was obtained by depositing 60 parts by weight of the fine refractory particles of less than 0.2 mm. size on to a heat-resistant base plate by flame projection and projecting 40 parts of the coarse refractory particles of 10 to 0.21 mm. size on to the deposit while the deposit was sill in a fused state.The properties of the flame-projection block of the present invention thus obtained, of the conventional flame-projection block, of an electrocast alumina brick and of a burned brick are shown in the following Table 1.

The slag resistance test results given in Table 1 were obtained by using a horizontal type rotary erosion test machine. A prolonged slag erosion test was performed at a rotation of 2 r.p.m. and at a temperature of 1 6000 C. for a period of 30 hours. The slag used was prepared by mixing blast furnace slag and converter slag in a weight ratio of 1:1. After the test was completed, the amount of erosion of the samples was measured. The comparison of the samples was made using the amount of erosion of the burned alumina brick as a standard, i.e. by defining the erosion index thereof as 100.The thermal shock resistance was tested by repeating the operation of placing a 50 x 50 x 50 mm3 sample in an electric furnace, heating it rapidly to a temperature of 1 2000C., keeping the sample in the furnace for 1 5 minutes at this temperature, withdrawing the sample from the electric furnace, placing it in the air and allowing it to cool for 1 5 minutes.

The thermal shock resistance in the Table is expressed as the number of repeated thermal shocks required to cause cracks in the sample and the number of thermal shocks required before the sample could no longer retain its form and a part of it had spalled.

As is clear from the results shown in Table 1, the flame projection block of the present invention has an excellent thermal shock resistance and slag resistance when compared with the three kinds of conventional articles.

TABLE 1

Tested property A B C D Bulk specific gravity (g/cm2) 3.60 3.67 3.42 3.14 Apparent porosity (%) 4.8 2.9 2.8 - 16.5 Chemical composition (%) Awl203 98.5 98.5 97.0 98.5 SiO2 0.3 0.3 0.7 0.3 Thermal bending strength at 14000C. (kg/cm2) 280 320 250 150 Slag resistance erosion index (-) 8 6 12 100 Thermal shock resistance No. of shocks before cracking 10 1 1 12 No. of shocks before spalling 23 1 4 25 A: Flame-projection block of the present invention.

B: Conventional flame-projection block.

C: Electrocast alumina brick.

D: Burned alumina brick.

EXAMPLE 2 A flame projection block was produced in the same manner as in Example 1, using fine alumina particles of less than 0.2 mm. size containing, by weight, 98.5% alumina and 0.3% silica as the fine refractory particles and electrocast magnesia particles of 0.21 to 10 mm. size containing, by weight, 99.9% magnesia as the coarse refractory particles.

The properties of the flame projection block are shown in the following Table 2. On comparing the properties with the properties of the flame projection block shown in Table 1, it was found that the thermal bending strength and thermal shock resistance of the flame-projection block are about the same as those of the flame-projection block in Table 1 but that there is a further improvement in the slag resistance.

TABLE 2

Flame projection block of property or the present Tested property invention Bulk specific gravity (g/cm2) 3.70 Apparent porosity (%) 4.9 Chemical composition (%) Fine powder Al203 98.5 SiO2 0.3 Coarse particles MgO 99.9 Thermal bending strength at 14000C. (kg/cm2) 290 Slag resistance erosion index (-) 5 Thermal shock resistance No. of shocks before cracking 9 No. of shocks before spalling 22

Claims

1. A refractory powder flame-projection moulding, comprising non-fused refractory particles dispersed and embedded in the solidified structure of a fused refractory.

2. A refractory powder flame-projection moulding according to claim 1, wherein cavities exist at the interface between the solidified structure of the fused refractory and the non-fused refractory particles.

3. A refractory powder flame-projection moulding according to claim 1 or 2, wherein the solidified structure of the fused refractory is composed of the same material as the non-fused refractory particles.

4. A refractory powder flame-projection moulding according to claim 1 or 2, wherein the solidified structure of the fused refractory is composed of a material different frorn that of the non-fused refractory particles.

5. A refractory powder flame-projection moulding according to any of the preceding claims, wherein the solidified structure is formed from refractory particles with a diameter of less than 0.2 mm.

and from non-fused refractory particles with a diameter of 0.2 to 10 mm.

6. A refractory powder flame-projection moulding according to any of the preceding claims, wherein the refractory material forming the solidified structure of the fused refractory is an acid refractory and/or a neutral refractory and/or a basic refractory.

7. A refractory powder flame-projection moulding according to any of the preceding claims, wherein the non-fused refractory particles are composed of an acid refractory and/or a neutral refractory and/or a basic refractory and/or carbon and/or a carbide and/or a nitride.

8. A refractory powder flame-projection moulding according to any of the preceding claims, wherein the non-fused refractory particles are dispersed and embedded in the solidified structure of the fused refractory in an amount of 5 to 80 parts by weight.

9. A refractory powder flame-projection moulding according to any of the preceding claims, wherein the refractory powder flame-projection moulding is a repairing deposit on the wall of a furnace.

10. A refractory powder flame-projection moulding according to claim 1, substantially as hereinbefore described and exemplified.

11. A process of producing refractory powder flame-projection mouldings, which comprises feeding fine refractory particles having a particle size of less than about 0.2 mm. and coarse refractory particles having a particle size of 0.2 to 10 mm. into the stream of a flame projected by flame-projecting burner and flame-projecting these particles into a mould, the fused fine refractory particles thereby forming a solidified structure phase and the coarse refractory particles being dispersed and embedded in the solidified structure phase.

12. A process of producing refractory powder flame-projecting mouldings. which comprises feeding fine refractory particles having a particle size of less than 0.2 mm. into the stream of a projected flame, flame-projecting the particles into a mould and injecting coarse refractory particles having a particle size of 0.2 to 10 mm. into the mould from outside the system of the projected flame stream while a solidified structure is being formed by the fine refractory particles fused by the projected flame, the coarse refractory particles thereby being dispersed and embedded in the solidified structure of the fused fine particles.

13. A process according to claim 11 or 12, wherein the proportion of the fine refractory particles having a particle size of less than 0.2 mm. is 95 to 20 parts by weight and the proportion of the coarse refractory particles having a particle size of 0.2 to 10 mm. is 5 to 80 parts by weight.

14. A process according to claim 11 or 12 of producing refractory powder flame-projection mouldings, substantially as hereinbefore described and exemplified.

1 5. Refractory powder flame-projection mouldings, whenever produced by the process according to any of claims 11 to 14.