DD296747A5 - CERAMIC WELDING PROCESS AND POWDER MIXTURE DAFUER - Google Patents

Abstract

The invention relates to a ceramic Schweiszverfahren and powder mixture thereof. In ceramic welding processes, oxidizing gas and a mixture of refractory and fuel powder are flung against a surface and the fuel is burned to generate sufficient heat to at least partially melt or soften the refractory powder and gradually build up a coherent refractory mass against that surface becomes. In order to reduce any tendency of the Schweiszmasse to contain a lower refractory phase and thus to promote the refractoriness of this Schweiszmasse, the fuel powder is present in an amount of not more than 15 * of the total mixture and contains at least two metals from the group aluminum, magnesium, Chromium and zirconium, and at least the main weight fraction of the refractory powder consists of one or more of the group of magnesia, alumina and chromia, and the molar ratio of silica to calcia present in the refractory powder (if any) meets the following equation:

Description

fulfill.

2. A ceramic welding method according to claim 1, characterized in that the molar proportions of silica and calcium oxide present in the refractory powder (if any) meet the following equation:

(SiO ₂ )% <(CaO)%

3. Ceramic welding method according to claim 1 or 2, characterized in that the refractory powder is virtually free of silicon dioxide.

4. Ceramic welding method according to one of the preceding claims, characterized in that the hurled refractory powder practically consists of one or more of zirconium oxide, magnesium oxide, aluminum oxide and chromium oxide.

5. Ceramic welding method according to one of the preceding claims, characterized in that the fuel powder contains aluminum together with one or more of the group magnesium, chromium and zirconium.

6. Ceramic welding method according to one of the preceding claims, characterized in that no element makes up more than 80 wt .-% of the fuel powder.

7. A ceramic welding method according to any one of the preceding claims, characterized in that the fuel powder contains an alloy containing at least 30 wt .-% of a metal from the group consisting of aluminum, magnesium, chromium and zirconium, wherein the remainder of the alloy of at least one other Element as such a selected metal, which element is also oxidizable to form a refractory oxide.

A ceramic welding method according to any one of the preceding claims, characterized in that any silicon present in said fuel is in the form of an alloy of silicon with at least one of aluminum, magnesium, chromium and zirconium.

A ceramic welding method according to any one of the preceding claims, characterized in that the molar amount of silicon present in the spun mixture (if any) is not more than the molar amount (if any) of zirconium calculated as elemental zirconium.

10. Ceramic welding method according to claim 9, characterized in that the fuel contains elemental silicon in the form of particles having an average particle size of less than ΙΟμιη, preferably less than 5 μιτι and the mixture comprises zirconium oxide particles having particle sizes below 150 цт, these Zirconia particles are present in a molar amount which is at least equal to the molar amount of elemental silicon in the mixture.

11. Ceramic welding method according to one of claims 1 to 7, characterized in that the hurled fuel powder is virtually free of silicon.

12. Ceramic welding method according to one of the preceding claims, characterized in that the hurled fuel powder contains magnesium and aluminum.

13. Ceramic welding method according to claim 12, characterized in that the spun fuel powder, based on the weight, contains more aluminum than magnesium.

14. Ceramic welding method according to claim 12 or 13, characterized in that magnesium is introduced in the spun fuel powder in the form of a magnesium / aluminum alloy.

15. Ceramic welding method according to one of claims 1 to 11, characterized in that the hurled fuel powder contains chromium and aluminum.

16. A ceramic welding method according to claim 15, characterized in that the spun fuel powder, based on the weight, contains more chromium than aluminum.

A ceramic welding method according to any one of the preceding claims, applied to the repair of a structure of basic refractory material.

18. Ceramic welding powder of a mixture of refractory and fuel powder for use in a ceramic welding process, wherein oxidizing gas and the mixture of refractory and fuel powders are flung against a surface and the fuel powder is burned to obtain sufficient heat that the refractory powder at least partially melted or softened and a coherent refractory mass is gradually built up against this surface, characterized in that the fuel powder is present in an amount of not more than 15% by weight of the total mixture and at least two metals from the group aluminum, magnesium, chromium and zirconium and that at least the major part of the refractory powder consists of one or more of the group magnesium oxide, aluminum oxide and chromium oxide and that the molar proportions of silica and calcium oxide present in the refractory powder (if at all) satisfy the following equation:

(SiO ₂ )% <0.2 + (CaO)%

19. Ceramic welding powder according to claim 18, characterized in that the molar proportions of silica and calcium oxide in the refractory powder (if any) satisfy the following equation:

(SiO ₂ )% <(CaO)%

20. Ceramic welding powder according to claim 18 or 19, characterized in that the refractory powder is virtually free of silicon dioxide.

21. Ceramic welding powder according to one of claims 18 to 20, characterized in that the hurled refractory powder practically consists of one or more of zirconium oxide, magnesium oxide, aluminum oxide and chromium oxide.

22. Ceramic welding powder according to one of claims 18 to 21, characterized in that the fuel powder contains aluminum, together with one or more of the group magnesium, chromium and zirconium.

23. Ceramic welding powder according to one of claims 18 to 22, characterized in that no element makes up more than 80% by weight of the fuel powder.

A ceramic welding powder according to any one of claims 18 to 23, characterized in that the fuel powder contains an alloy comprising at least 30% by weight of a metal of the group consisting of aluminum, magnesium, chromium and zirconium, the remainder of the alloy being of at least one other Elemental is such a selected metal, which element is also oxidizable to form a refractory oxide.

25. Ceramic welding powder according to one of claims 18 to 24, characterized in that each silicon present in the fuel in the form of an alloy of silicon with at least one metal of the group aluminum, magnesium, chromium and zirconium.

26. Ceramic welding powder according to one of claims 18 to 25, characterized in that the molar amount of silicon (if present) in the spun mixture is not more than the molar amount (if any) of zirconium, calculated as elemental zirconium.

27. Ceramic welding powder according to claim 26, characterized in that the fuel contains elemental silicon in the form of particles having an average particle size of less than 10 μπα, preferably less than 5 pm and the mixture zirconia having particle sizes below 150 μιη, wherein the zirconia particles are present in a molar amount at least equal to the molar amount of elemental silicon in the mixture.

28. Ceramic welding powder according to one of claims 18 to 24, characterized in that the spun fuel powder is virtually free of silicon.

29. Ceramic welding powder according to one of claims 18 to 28, characterized in that the hurled fuel powder contains magnesium and aluminum.

30. Ceramic welding powder according to claim 29, characterized in that the hurled fuel powder, based on the weight, contains more aluminum than magnesium.

31. Ceramic welding powder according to claim 29 or 30, characterized in that magnesium is introduced into the centrifuged fuel powder in the form of magnesium / aluminum mini order alloy.

32. Ceramic welding powder according to one of claims 18 to 28, characterized in that the hurled fuel powder contains chromium and aluminum.

33. Ceramic welding powder according to claim 32, characterized in that the spun fuel powder, based on the weight, contains more chromium than aluminum.

The invention relates to a ceramic welding process, wherein oxidizing gas and a mixture of refractory and fuel powder are flung against a surface and the fuel is burned to generate sufficient heat to at least partially melt or soften the refractory powder and gradually form a coherent one refractory mass is built up on or against the surface. The invention also relates to a ceramic welding powder mixture containing refractory powder and fuel powder for use in such a ceramic welding process.

Ceramic welding processes are useful for the production of new refractory bodies, г. В. However, bodies of fairly complicated shapes are most commonly used in the present engineering practice for lining or repairing hot refractory structures, such as blast furnaces or furnaces of various kinds, and allow eroded areas of the refractory structure (provided that these areas accessible) to repair while the structure is at virtually its operating temperature, and in some cases even while the structure is still operating. It is in any case desirable that there be no deliberate cooling of the refractory structure from its normal operating temperature. Avoidance of such deliberate cooling tends to favor the effectiveness of the ceramic welding reactions, avoiding further damage to the structure due to thermal stresses caused by such cooling and / or subsequent reheating to operating temperature, and also helps to increase the furnace turn-off time to decrease.

In ceramic welding processes refractory powder, fuel powder and oxidizing gas are thrown against the point to be repaired and the fuel is burned so that the refractory powder is at least partially melted or softened and build up at the repair site gradually refractory repair mass. The fuel typically used is silicon and / or aluminum, although other materials such as magnesium and zirconium may be used. The refractory powder can be chosen so that the chemical composition of the repair composition fits as well as possible to the composition of the refractory mass to be repaired, although it can also be modified, for. B. such that deposits a coating of higher degree of fire resistance on the basic structure. In ordinary practice, fuel and refractory powders are spun by a lance as a mixture in a stream of oxidizing carrier gas.

Due to the intense heat generated by burning the fuel powder at or near the surface to be repaired, this surface is also softened or melted and, as a result, the repair mass, which itself is largely fused together, will strongly adhere to the repaired wall and result in a highly effective and permanent repair. Earlier ceramic welding repair methods can be found, for example, in German Patent Nos. 1330894 and 2110200. So far, one of the most common uses of ceramic welding repair methods has been the renewal of coke ovens constructed of silica bricks. The usual ceramic welding powder, which is mostly used for the repair of silica rocks, contains silica together with silicon and optionally aluminum as fuel powder. Silica bricks are actually repair the leichtesten by ceramic welding, at least partly because silica stones have relatively low resistance to fire, so that dieTempraturen (eg 1800 ⁰ C or higher) that are reached in the reaction zone of ceramic welding, easy formation of an adherent continuous repair mass and the requirements on the refractoriness of the repair mass are usually not higher than those of the original Silicasteinstruktur.

However, it has been found that certain problems arise when repairing higher-grade refractory structures or, in other cases, when the refractory requirements of the ceramic welding compound are particularly stringent. Examples of high-grade refractory bricks are:

Chromium-magnesite, magnesite-alumina, alumina-chromium, magnesite-chromium, chromium- and magnesite-stones, high-alumina-refractory refractory bricks and refractory bricks containing a considerable amount of zirconium, such as Corhart (trademark), Zac (a co-melted Stone of alumina, zirconia and zirconia). In order to achieve the formation of a ceramic weld compound having a refractoriness and / or composition approaching or equal to that of such high grade refractory bricks, it is not always sufficient to use a standard ceramic weld powder as described above.

A particular problem that arises in the case of a ceramic weld repair mass that is to be subjected to very high temperatures during its working life is the avoidance of a phase in the repair mass that has an insufficiently high softening or melting point. The integrity of a repair compound containing such a phase is degraded at high temperatures and its corrosion resistance at high temperatures is also not

as good as you expect. In general, a refractory phase, which is relatively less resistant to heat, is also more readily attacked chemically at high temperatures.

It is an object of this invention to provide a ceramic welding method and a ceramic welding powder for use in such a method which results in the formation of a welding compound in which the occurrence of such a phase is reduced with less refractoriness and, in some embodiments of the invention is avoided. According to the invention, there is provided a ceramic welding method in which oxidizing gas and a mixture of refractory and fuel powder are flung against a surface and the fuel is burned to generate sufficient heat to at least partially melt or soften the refractory powder and to form a coherent one refractory mass is gradually built up on or against the surface, which is characterized in that the fuel powder is present in a proportion of not more than 15Gew .-% of the total mixture and at least two metals from the group aluminum, magnesium, chromium and zirconium and that at least the main part of the refractory powder consists of one or more of the materials magnesium oxide, aluminum oxide and chromium oxide and that the molar proportions of silica and calcium oxide present in the refractory powder (if any), the following equation gen gen:

(SiO ₂ )% <0.2 + (CaO)%

The invention also provides a ceramic welding powder which is a mixture of refractory powder and fuel powder for use in a ceramic welding process, wherein oxidizing gas and the mixture of refractory and fuel powder are thrown against a surface and the fuel is burned to provide sufficient heat produce that the refractory powder is at least partially melted or softened and a coherent refractory mass is gradually built up on or against the surface and characterized in that the fuel powder in a proportion of not more than 15Gew .-% of the total mixture and at least two metals from the group aluminum, magnesium, chromium and zirconium and that at least the main part of the refractory powder consists of one or more of the compounds magnesium oxide, aluminum oxide and chromium oxide and wherein the molar proportions of silica and calcium oxide in the refractory powder (if any) satisfies the following equation:

(SiO ₂ )% £ 0.2 + (CaO)%

The use of such a powder in such a process yields a ceramic welding compound which is highly resistant to molten materials such as molten metals and metal slags and molten glass. Such weld masses may have good resistance to corrosive liquids and gas at elevated temperatures, such as those encountered in the machining or production of steel, copper, aluminum, nickel and glass, and in crucibles or other chemical reaction vessels exposed to the action of flames. Such welds can also adhere well to highly refractory frameworks.

The occasional loss of refractoriness in the formed ceramic weld compound is often observed when using a weld powder containing significant amounts of silica or silica-forming materials, and can be attributed to the formation of a glassy phase in the weld at the very high temperatures during the ceramic welding reactions can be achieved. Such a vitreous phase often has a relatively low melting point and can also be readily attacked by molten materials such as molten metals, slags and molten glass, and their presence would thus compromise the quality of the overall weld mass. Silica is often present in refractory bricks or masses, whether intentionally added or as an impurity. When applying the present invention, the allowable amount of silica is reduced to an amount which tends to form a refractory weld which greatly reduces or avoids such a glassy phase and improves the refractoriness of the formed weld.

The refractoriness of the formed weld compound is improved if, as is preferred, the molar proportions of silica and calcium oxide present in the refractory powder (if any) satisfy the following equation: (SiO ₂ )% <(CaO)%.

This promotes avoidance of an acidic phase in the weld and improves its resistance to corrosion by molten glass or metallurgical slags.

Preferably, the refractory powder is virtually free of silicon dioxide. The choice of this feature also counteracts the formation of any silica-based vitreous phase in the formed weld mass.

Advantageously, the spun refractory powder consists practically of one or more of zirconia, magnesia, alumina and chromia. Such materials can form very high-grade refractories.

According to the invention, the fuel powder contains at least two metals from the group aluminum, magnesium, chromium and zirconium. Such fuels burn to form oxides which are of good refractory quality and which are either amphoteric (alumina and zirconia) or basic (magnesia or chromia) and, accordingly, such fuels contribute to the formation of a refractory mass which is highly resistant to molten corrosion Glass or metallurgical slag is. This feature of the invention also allows considerable flexibility in the choice of fuel elements, and thus in the refractory oxide product resulting from the combustion of these elements, so that the composition of the finally formed refractory welding compound can be varied if desired. Advantageously, the fuel powder comprises aluminum together with one or more of the metals magnesium, chromium and zirconium. Aluminum has excellent combustion properties for the intended purposes and is also relatively easily available as a powder.

Preferably, no element makes up more than 80% by weight of this fuel powder. This has proven to be beneficial in controlling the conditions under which combustion occurs. For example, in choosing this preferred feature, a predominantly highly reactive fuel component is limited to 80% of the total fuel and the remainder of the fuel, at least 20% by weight, may be a fuel element that reacts more slowly to control the rate of combustion. Conversely, a less active major portion of fuel may be heated in rate of reaction by adding at least 20 weight percent of one or more fuel elements that react more rapidly.

Advantageously, the fuel powder comprises an alloy containing at least 30% by weight of a metal of the group consisting of aluminum, magnesium, chromium and zirconium, the remainder of the alloy consisting of at least one metal other than that selected, this element also forming a refractory metal Oxides is oxidizable. The use of particles of an alloy as a fuel is particularly valuable for adjusting the conditions under which combustion occurs.

The spun mixture of powders need not necessarily be completely free of silicon to reduce or avoid the formation of relatively low-grade acid or glassy silicon-containing phases. In some cases, silicon may be present in the fuel powder. In fact, it has been found that the use of silicon as a fuel component can have advantages in stabilizing the manner in which the ceramic welding reaction occurs. Thus, in some preferred embodiments of the invention, silicon is present in this fuel in the form of an alloy of silicon with at least one of the metals aluminum, magnesium, chromium and zirconium. The use of silicon as an alloying ingredient can have a beneficial effect on the rate at which the combustion reaction occurs during the practice of the invention. For example, silicon alloyed with magnesium may have the effect of moderating the rate at which the highly active magnesium burns off. Moreover, since an alloy is an intimate mixture of its constituents, intimate mixing of the reaction products is favored, and this counteracts the possibility that the silicon gives rise to a distinct, ie separate, acidic or glassy phase in the formed refractory weld mass.

In other preferred embodiments of the invention, again to promote the avoidance of the presence of a siliceous acid or glassy phase in the formed weld compound, it is preferred that the molar amount of silicon present in the mixture (if any) is not more than the molar amount of zirconium (if any). For example, the refractory powder may contain a proportion of zirconium orthosilicate (zirconium), which is a fairly useful, highly refractory component. Alternatively or additionally, the fuel powder may contain a portion of elemental silicon that may combine with zirconium in the mixture (whether as elemental zirconium or zirconia) to form zirconium without exciting an acidic phase in the formed weld compound.

Thus, in some preferred embodiments of the invention, this fuel contains elemental silicon in the form of particles having an average grain size of less than 10μιη, preferably less than 5μm , and the mixture comprises zirconia particles having a grain size below 150μιη, such zirconia particles in one molar amount, which is at least equal to the molar amount of elemental silicon in the mixture. It has been found that the use of this optional feature of the invention promotes the formation of zirconium (zirconium orthosilicate) in the formed weld mass as a result of the ceramic weld reactions, so that this composition is virtually free of silica as such and the risk of forming a vitreous low refractory phase is low. In this way, the advantage of using silicon as a fuel can be achieved without at the same time having the disadvantage of having a possibly glassy acidic phase of silicon dioxide in the welding compound.

In other preferred embodiments of the invention, the spun fuel powder is virtually free of silicon.

The choice of this feature avoids the formation of any silica-based glassy mass in the formed weld mass.

In some preferred embodiments of the invention, the spun fuel powder contains magnesium and aluminum. The oxidation of aluminum and magnesium in appropriate proportions can produce sufficient heat to carry out the process of the invention and gives rise to the formation of refractory oxides incorporated into a high-refractory weld mass.

Preferably, the spun fuel powder, by weight, comprises more aluminum than magnesium, e.g.

For example, aluminum may be present in the fuel in a molar amount of about 2 times that of magnesium. This promotes the formation of spinel (magnesium aluminate) in the weld. Spinel is a very useful high grade refractory material.

Advantageously, magnesium is introduced into the spun fuel powder in the form of a magnesium / aluminum alloy. The use of a powdered alloy of these metals rather than a mixture of powder further favors the formation of spinel rather than the separate oxides as a result of the ceramic welding reactions. The composition of the alloy may be varied or additions of additional aluminum or magnesium may be made to adjust the relative proportions of aluminum and magnesium in fuel powder as desired.

In other preferred embodiments of the invention, the spun fuel powder comprises chromium and aluminum. Such fuel powders are useful for forming high chromium refractory weld masses and, advantageously, such a spun fuel powder contains more chromium than aluminum in weight.

Preferably, at least 60% and in some embodiments at least 90% by weight of the spun fuel powder has a grain size below 50pm. This favors the rapid and effective combustion of the fuel powder to form a coherent refractory weld mass.

The process of the invention is particularly advantageous when it is applied to the treatment of refractory materials, which themselves are of basic rather than acidic character, and accordingly it is preferred that the method of repairing a structure constructed of basic refractory be applied ,

Various specific ceramic welding powders according to the invention will now be described by way of example. The examples illustrate the invention.

example 1

A ceramic welding powder contains, by weight, the following components:

Magnesium oxide 82% Mg / Al alloy 5%

Zirconia 10% aluminum grains 3%

The magnesium oxide used had grain sizes up to 2 mm. The zirconia had particle sizes below 150μπι. The Mg / Al alloy with nominally 30 wt% magnesium and 70% aluminum had grain sizes below 100μιη and an average grain size of about 42 цt, and the aluminum was in the form of grains having a nominal maximum size of 45μηη.

The magnesium oxide used had a purity of 99% by weight. It contained 0.8% by weight of calcium oxide and 0.05% by weight of silica. The molar ratio of SiO ₂ to CaO in magnesium oxide was therefore 1: 17.4.

Another magnesium oxide composition suitable for use has a purity of 98% by weight. It contains 0.6% by weight of calcium oxide and 0.5% by weight of silicon dioxide. The molar ratio of SiO ₂ to CaO in this magnesium oxide composition is therefore 1: 1.28.

Such a powder may be spun in an amount of 1 to 2 t / h from a lance known as such in the ceramic welding, wherein oxygen is used as a carrier gas for repairing a steel converter formed from basic magnesia refractory bricks. The repair site is at a temperature of 1400 ⁰ C immediately before spin-coating.

Example 2

A ceramic welding powder contains, by weight, the following components:

magnesia 82% aluminum Korner 3% zirconia 10% aluminum flakes 3.5 ° / Magnesium grains 1.5 ° /

The magnesia, zirconia and aluminum grains had the grain sizes given in Example 1. The composition of the magnesium oxide was one of those given in Example 1. The magnesium had a nominal maximum size of about 75 ц t and an average grain size of less than 45. M. The aluminum flakes had a specific surface area (measured by Griffin permeate) of over 7000 cm ² / g.

Such a powder can be thrown to the repair of a steel converter as described in Example 1, which is formed from magnesia-chrome refractory bricks, wherein the repair site C is located immediately before the spin coating at 1400 einerTemperaturvon ^0th

Example 3

A ceramic welding powder contains, by weight, the following components:

Chromium oxide 82% Mg / Al alloy 5%

Zirconia 10% aluminum grains 3%

The chromium oxide had a grain size of up to 2mm. The other materials were as indicated in Example 1.

The chromium oxide was virtually free of silica, with little trace of the analysis.

Such a powder may be used in an amount of 150 to 200 kg / hr from a lance well known as such in ceramic welding, using oxygen as a carrier gas to repair a copper converter formed of magnesium-chromium refractory bricks. the repair site being immediately prior to spin-coating at a temperature of 1100 ° C.

Example 4

A ceramic welding powder, by weight, comprises the following components:

chromium 82% aluminum grains 3% zirconia 10% aluminum flakes 3.5% magnesium grains 1.5%

The chromium oxide was as indicated in Example 3. The other materials were as indicated in Example 2. Such a powder may be used in an amount of 150 to 200 kg / hr from a lance well known in ceramic welding under oxygen as a carrier gas for repairing a steel degassing nozzle formed of magnesia-chromium refractory bricks Repair site immediately prior to spin-coating at a temperature of 1100 ° C.

In one variant of this example, the magnesium was replaced by zirconium having an average particle size of about 10 to 15%, taking all necessary precautions regarding the well-known high reactivity of zirconium.

Example 5

A ceramic welding powder, by weight, comprises the following components:

Chromium oxide 90% Cr 8%

Aluminum flakes 2%

The chromium had the form of grains with a nominal maximum grain size of about 100pm and an average grain size between 25 and 30pm. The chromium oxide was as indicated in Example 3. The aluminum flakes had a specific surface area (measured by Griffin permeate) of over 7000 cm ² / g.

Such a powder may be used in an amount of 40kg / hr from a lance known in ceramic welding, using oxygen as a carrier gas to repair Corhart (trade mark), Zac (fused alumina-zirconia-zirconia) refractory blocks, which were located at the level of the surface of the melt in a glass melting furnace, the repair point being immediately before this spin-on at a temperature of 1500 ° C to 1600 ° C.

The powder is also suitable for repairing chrome refractory bricks (i.e., a refractory containing more than 25% chromium oxide and less than 25% magnesium oxide), which in turn is at the level of the surface of the melt in a glass melting furnace.

Example 6

A ceramic welding powder contains, by weight, the following components:

5%

The carbon was coke with an average diameter of about 1.25 mm. The other materials were as indicated in Example 1. Such a powder may be used as described in Example 1 to repair a steel converter formed from magnesia-carbon refractory bricks.

Example 7

A ceramic welding powder contains, by weight, the following components:

magnesia 72% aluminum grains zirconia 10% Mg / Al alloy carbon 10%

magnesia 82% Si zirconia 10% mg Al flakes

The silicon had the form of grains with an average grain size of 4pm. The zirconia had a nominal maximum grain size of 150 μm. The other materials were as indicated in the previous examples. Such a powder may be spun in an amount of 150 kg / hr for repairing a magnesium oxide basic refractory steel melting bucket.

Example 8

A ceramic welding powder contains, by weight, the following components:

Alumina 92% Mg 2%

Aluminum grains 6%

The alumina used was an electro-cast alumina, by weight, containing 99.6% Al ₂ O ₃ . It contained 0.05% CaO and 0.02% SiO ₂ . The molar ratio of SiO _{2 to} CaO in this aluminum oxide is therefore 1: 2.68. The alumina had a nominal maximum grain size of 700μπη and the aluminum and magnesium had grain sizes as given in Example 2. Such a powder may be used as described in Example 5 to repair Corhart (Trade Mark) Zac refractory blocks in a glass smelting furnace below the level of the melt's working surface after the pan is partially depleted to give access to the repair site. In a modification of this example, the electro-cast alumina was replaced by tabular alumina. The tabular alumina used had a nominal maximum grain size of 2 mm and contained, by weight, 99.5% Al ₂ O ₃ . It contained 0.073 mole% CaO and 0.085 mole% SiO ₂ . The molar ratio of SiO ₂ to CaO in this alumina was therefore 1: 0.86, thus satisfying the equation (SiO ₂ )% 0,2 0.2 + (CaO)%.

Example 9

A ceramic welding powder contains, by weight, the following components:

Magnesium oxide 80% Mg / Si alloy 5%

Zirconia 10% Mg / Al alloy 5%

The magnesium / silicon alloy contained equal parts by weight of the two elements and had an average grain size of about 40 μm. The other materials were as indicated in Example 1. Such a powder may be spun as described in Example 1 to repair a refractory wall formed from basic magnesia refractory bricks.

Examples 10 to 16

In variations of Examples 1 to 4, 6, 7 and 9, the zirconia was replaced by tabular alumina as described in Example 8.

In variations of Examples 1, 3.6, 9, 10, 12, 14 and 16, the alloy containing 30% magnesium and 70% aluminum had a maximum grain size of not more than 75pm and an average grain size of less than 45pm , In still other variations, the alloy contained equal parts by weight of magnesium and aluminum.

Claims (1)

A ceramic welding method wherein an oxidizing gas and a mixture of refractory and fuel powders are flung against a surface and the fuel is burned to generate sufficient heat to at least partially melt or soften the refractory powder and gradually to form a coherent refractory mass Characterized in that the fuel powder is present in an amount of not more than 15% by weight of the total mixture and contains at least two metals from the group consisting of aluminum, magnesium, chromium and zirconium and at least the major part by weight of the refractory powder consists of one or more of the group magnesium oxide, alumina and Chromium oxide exists and that the moral proportions of silica and calcium oxide present in the refractory powder (if any), the following equation (SiO ₂ )% <0.2 + (CaO)%