CA1072130A - Method for producing a basic sintered material - Google Patents
Method for producing a basic sintered materialInfo
- Publication number
- CA1072130A CA1072130A CA277,108A CA277108A CA1072130A CA 1072130 A CA1072130 A CA 1072130A CA 277108 A CA277108 A CA 277108A CA 1072130 A CA1072130 A CA 1072130A
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- grain size
- weight
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- chrome ore
- oxide
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/03—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on magnesium oxide, calcium oxide or oxide mixtures derived from dolomite
- C04B35/04—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on magnesium oxide, calcium oxide or oxide mixtures derived from dolomite based on magnesium oxide
- C04B35/043—Refractories from grain sized mixtures
- C04B35/047—Refractories from grain sized mixtures containing chromium oxide or chrome ore
- C04B35/0476—Refractories from grain sized mixtures containing chromium oxide or chrome ore obtained from prereacted sintered grains ("simultaneous sinter")
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A basic sintered material for use in the production of refractory magnesia-chromite and chromite-magnesia bricks is formed by mixing (a) magnesium oxide or a substance which produces magnesium oxide on combustion in a grain size of less than 0.2 mm but 80% < 0.063 mm with (b) a substance containing chromic oxide or chrome ore. Component (b) is used partly in fine grain form (35 to 75% by weight < 0.063 mm) with the balance in coarse grain form (grain size 0.5 to 3 mm). Thus, a grain-size gap exists. The mixture is formed into briquettes, sintered and then crushed to give a material which can be used in the production of bricks having good hot and cold strength, resistance to cracking in use, and wear resistance.
A basic sintered material for use in the production of refractory magnesia-chromite and chromite-magnesia bricks is formed by mixing (a) magnesium oxide or a substance which produces magnesium oxide on combustion in a grain size of less than 0.2 mm but 80% < 0.063 mm with (b) a substance containing chromic oxide or chrome ore. Component (b) is used partly in fine grain form (35 to 75% by weight < 0.063 mm) with the balance in coarse grain form (grain size 0.5 to 3 mm). Thus, a grain-size gap exists. The mixture is formed into briquettes, sintered and then crushed to give a material which can be used in the production of bricks having good hot and cold strength, resistance to cracking in use, and wear resistance.
Description
~072130 The invention relates to a method for producing a basic sintered material for use in the production of refractory magnesia-chromite and/or chromite-magnesia bricks.
In producing refractory, basic granules or bricks based upon magnes-ium oxide and chrome oxide or chrome ore, it is desirable first of all to produce from magnesium oxide or combustion products thereof, and substances containing chromic oxide, or chrome ore, by preliminary combustion at temper-atures usually above 1700 C, a sintered material which is then crushed and, if necessary, after the addition of further magnesium oxide, is used as it is or for producing burned or unburned bricks. Additional heating, either while the - -material is in use in the form of granules or unburned bricks, or a second burning, if burned bricks are being made, produces materials having advantage-ous properties such as good cold-compression strength and good hot-bending - strength.
During so-called sinter-burning for producing the sintered material, an initial reaction takes place between the magnesium oxide, or the compounds producing MgO when burned and the substances containing chromic oxide or the chrome ore, whereby a so-called "direct bond" is obtained under certain cir-cumstances (see the article by MOERTL et al in "Rasexx-Rundschau" (1965), pages 559-576). German Auslegeschrift 2011805 describes such a method for producing refractory magnesia-chromite and chromite-magnesia bricks, wherein the magnesite, and the magnesium compounds producing magnesium oxide when burned, have a grain size of less than 0.20 mm and the substances containing chromic oxide, and the chrome ore, have a grain size of between O and 6 mm, a maximum of 20% and a maximum of 80~ of the substances containing chromic oxide used to make the sintered material having a grain size of less than 0.12 mm, and the said sintered material having a maximum silicic-acid content of 2.5~, a maximum lime content of 4~, and a lime:silicic-acid molecular ratio of from more than 0.6 to 2.5.
~ 7Z~30 Hitherto known processes made many suggestions relating to the grain size of the raw materials, the chemical composition of the sinter, and the manufacture of the bricks, but the final results produced no outstanding values for strength and the ability to withstand changes in temperature.
Thus, German Auslegeschrift 1,257,655 and German Patent 1,275,934 describe a so-called simultaneous sinter using mainly a coarse-grained chrome ore and a very fine-grained magnesia, whereas in German Auslegeschriften 1,571,328 and 1,646,845 all of the raw materials are in the finely-granular form. But a high-density sintered material, with high resistance to the ~-formation of cracks in the bricks when in use, was not achieved in every case.
The invention seeks to provide a sintered material based upon mag-` nesium oxide or substances which produce magnesium oxide when burned, and substances containing chromic oxide, or chrome ore, the said sintered material, upon further processing, either in the form of granules or in a form for pro-si ducing unburned and burned bricks, producing final results which indicate particularly good resistance to slag and satisfactory wear-behaviour in steel furnaces, especially open-hearth furnaces, in addition to the usual, satisfact-ory, known properties of such types of sinter.
Problems arising with refractory magnesia-chromite and chromite-magnesia compounds or bricks in use in open-hearth furnaces have been described in, among other publications, the article by H.M. MIKAMI, W.E. BRoWN and GILBERT in ~eramic Bulletin", Vol. 44, No. 5 (1965~, pages 433-439, especially -; in conjunction with Figure 2 of the article. In open-hearth-furnace arches, the arch is often forced upwards, and very special mechanical devices must therefore be provided to force the arch down again and to hold it down.
This "pushing up" of the arch is attributable, in the case of chemi-cally bonded brick, among other things to the action of slags and to different reactions in different areas of bricks, the bricks and granules used in produc-ing the arch undergoing an increase in volume.
.
1(~72130 It has now been found that by using the sintered material according to the invention, it is possible to produce both unburned and burned bricks and also compounds which are particularly resistant to this type of attack in open-hearth furnaces, thus increasing the life of an arch made of such refractory materials.
According to the invention, this is achieved in that, in producing the sintered material, the magnesium oxide or the substance which produces magnesium oxide when burned, is used in fine granular form, while a certain proportion of the substances supplying chromic oxide, or the chrome ore, is used in a very fine grain size, and the remainder of the substance containing chromic oxide, or the chrome ore, is used in a relativelylarge grainsize,i.e.
there is a so-called "grain-size gap" in the grain-size distribution in the substances containing chromic oxide or in the chrome ore.
According to the invention, there is provided in a method for pro-ducing a basic sintered material suitable for use in the production of refractory magnesia-chromite and chromite-magnesia granules and/or bricks, wherein substances containing chromic oxide or chrome ore in the form of particles having a grain size of between 0 and 3 mm are mixed with fine-grained magnesium oxide or a substance which produces magnesium oxide when burned, formed into briquettes, if necessary with the addition of a suitable bonding agent, are thereafter sintered at a temperature above 1700&, and are then crushed, the steps of:
a) supplying the magnesium oxide or substance giving magnesium oxide on combustion in a grain size of less than 0.2 mm, but with at least 80~ having a grain size of less than 0.063 mm, b) supplying from 35 to 75% by weight of the substances containing chromic oxide, or chrome ore in a grain size of less than 0.063 mm; and c) supplying the balance of the substances containing chromic oxide, or the chrome ore, in a grain size of between 0.5 and 3 mm) ,It~
~ - 3 -whereby to obtain a basic sintered material containing between 10 and 30~ by weight of Cr203 and having an SiO2 content of less than 3~.
,.~
- 3a -Preferably 50 to 70% by weight of substances containing chromic oxide or chrome ore are present in a grain size of less than 0.063 mm; and 50 to 30% by weight of these substances are used in a grain size of between 0.5 and 3 mm. Thus the substances containing chromic oxide, or the chrome ore used in this process have a grain-size gap between 0.063 and 0.5 mm.
~` As regards the above-mentioned grain-size gap between 0.063 and 0.5 mm, it is, of course, possible that small amounts of substances containing chromic oxide, or of chrome ore, having grain sizes within the above-mentioned gap will be present, since it is scarcely possible to carry out 100% screening on an industrial scale. However, these small amounts, will usually be no more than 2 to 4%. Furthermore, a certain amount of crushing occurs when the raw materials are being mixed before the si~lltaneous sinter is burned, but this ;~ is not detrimental and may be disregarded. Thepercentage given herein are by ~ weight, unless otherwise indicated.
-, According to another preferred embodiment of the fine-grained pro-portion of the substances containing chromic oxide, or of the chrome ore, which is present in a grain size of less than 0.063 mm, 75 to 95% by weight ~` of this amount has a grain size of less than 0.04 mm.
Moreover, it is desirable for the coarser grain-size fraction of the ~ 20 substances containing chromic oxide, and of the chrome ore, to have a grain size of between 0.5 and 2 mm.
By restricting the maximum grain size of the coarse chromic ore to -~ 3 mm, preferably 2 mm, a uniformly good and complete direct bond is obtained between the ore granules and the MgO, the fine chrome-ore flour being absorbed , into the MgO component in the course of the sintering process. The upper l;~;t of 3, preferably 2 mm, is extremely important since, as the grain size of the ore increases, under given combustion conditions, the direct bond be-. .
comes increasingly irregular and inadequate. Moreover, it is desirable to keep the maximum ore grain size distinctly below the subsequent brick grain -- 4 _ . .:
size of 5 mm, in order to keep to a minimum any damage to the direct-bond areas when the sinter is crushed.
In the production of simultaneous sinter, the magnesium oxide, or the substances producing magnesium oxide when burned, and the substances con-taining chromic oxide, or the chrome ore, which have the grain sizes mentioned above, are moulded, if necessary with the addition of a bonding agent, into briquettes or bricks, after which they are sintered at temperatures of 1700 C
or above, preferably 1850& or above. However, it is desirable not to exceed a sintering temperature of 2000& , since this could cause melting, which means that the properties of the sintered material based on direct bonding would no longer be obtained.
The bonding agents used are those generally known per se in the art, e.g., a saturated magnesium-sulphate solution, sulphite lyes from paper manu-facturer, or other known bonding agents.
The magnesium oxide or substances which produce magnesium oxide when burned may be materials normally used in the art, e.g. salt-water magnesia, sintered magnesia, natural or synthetic magnesium compounds forming periclase upon burning, such as magnesium carbonate in the form of the mineral magnesite.
The substances containing chromic oxide, or the chrome ore, may be all materials known per se to the art, in the case of the chrome ore more particularly: Sudanese chrome ore, Phillipine chrome ore, Turkish chrome ore, Persian chrome ore, and South African chrome ore, and these chrome ores may also be used in the form of concentrates, i.e. ore concentrates prepared chemi-cally or by other means and containing small quantities of impurities.
As compared with known similar types of sinter, the use of the meth-od according to the invention optimizes the direct-bonding and dissolving effects. This permits an extension of the preferred Cr203 range to lower chrome-ore contents, which in turn makes it possible to reduce the material supplying chromic oxide if required and if suitable types of chrome ore are ~072130 used, without any impairment of behaviour during handling. If required, less than 4S% of chrome ore may be used.
The sintered material obtained by the method according to the inven-tion contains between 10 and 30% by weight of Cr203, preferably between 15 and 25% by weight.
The SiO2 content of the sintered material should be less than 3%, better still less than 2.5%.
The CaO:SiO2 molecular ratio is not particularly critical, but values between 0.2 and 2.0 have been found advantageous, preferably between 0.5 and 0.8.
In producing the sintered material, the fine-grained part may also be chromic oxide in a grain size of up to 0.063 mm, whereas the coarse-grained part may be chromic oxide in a grain size of between 0.5 and 3 mm, preferably between O.S and 2 mm.
The sintered material is then granulated and may then be used to produce refractory granules, unburned refractory bricks, or burned refractory bricks. To this end, the sintered material may be crushed to a grain size of between 0 and 5 mm, preferably between 0 and 3 mm, a-l of the fractions, i.e.
fine-grain, medium-grain and coarse-grain, and a separately-ground flour frac-tion, being used for further processing, It is desirable to add to the crushed sintered material up to 20%
by weight, preferably up to 10~ by weight, of magnesium oxide. The grain size ` of this additional magnesium oxide may be between 0 and 3 mm, preferably be-tween 0 and 1 mm, but it may also be added in the form of 0 - 0.12 mm sintered flour.
By using substances containing chrome oxide or chrome ores on the one hand as the fine-grained material and, on the other hand, as the narrow-` range coarse-grained material with a grain-size gap, the method according to the invention produces a sintered material which provides, in the bricks made . ~
'' ' ~07Z~30 therefrom, especially in the case of unburned bricks, uniformly good propert-ies, especially those relating to density, hot and cold strength, and resist-ance to crack formation when in use, as well as satisfactory resistance to changes in temperature, the latter being brought about by structural resilience.
However, emphasis should also be given to the very good wear behaviour as revealed by the low pressures resulting from optimal expansion behaviour and to the particularly good resistance to slag of bricks made from such sintered materials. The result of this is that arches made of such sintered materials do not push up or peel off and have a substantially longer life. Wear is between 15 and 20% less, for example.
The production of the sintered material is explained in greater detail in the following examples:
Example 1 A simultaneous sinter was produced by mixing together the following raw materials, miYing them with 4% by weight of a saturated magnesium sulphate solution and 3% by weight of water, based upon the weight of the solids, mould-ing the mixture into briquettes, and burning the saidbriquettes at about 1850&
in a pilot-plant furnace. The said raw materials are given in the following Table 1.
Table 1 Based on Based on Raw materials Calcined material Magnesite, Flotation-concentrate 0 - 0.063 mm 60% by weight 43% by weight Magnesia, Furnace flue dust (after grinding to 0 - 0.063 mm) 10% by weight 14% by weight Chrome ore (54~ CR203) 30% by weight 43% by weight of which 0 - 0.063 mm = 67%
0.5 - 3 mm = 33~
The burned simultaneous sinter was then crushed to a grain size of between 0 and 5 mm, 10~ by weight of sintered magnesia flour containing about 95% of 0 - 0.1 mm MgO was added to the crushed sinter~ together with 3.5% by weight (based on the mixture of solids) of a saturated magnesium sulphate solution, and unburned bricks were moulded. In addition to high hot and cold strength, these bricks have optimal expansion behaviour, high structural resiliency and, as determined by tests, very good resistance to slags and minimal crack formation.
Example 2 : The procedure according to Example 1 was repeated, but with the raw materials given in the following Table 2.
Table 2 Caustic salt-water magnesia (0 - 0.063 mm) 45%
Magnesia Furnace flue dust (Reground to 0 - 0.063 mm) 10%
Chrome ore (54% Cr203) 45%
of which 0 - 0.063 mm 50%
; 0.5 - 2 mm 50%
Unburned bricks produced with an addition of 10% by weight of sintered magnesia showed the good properties mentioned in Example 1.
- EXample 3 .
The procedure according to Example 1 was repeated, but with the raw materials given in the following Table 3. - -Table 3 Based on Based on Raw materials Calcined material ,:, : Magnesite Flotation-- concentrate 0 - 0.2 mm -- (90% below 0.063 mm) 70% by weight 54% by weight Magnesia, Furnace flue dust (Reground to 0 - 0.063 mm) 10% by weight 14% by weight Chrome ore (54% Cr203) 20% by weight 32% by weight of which0 - 0.063 mm 50%
0.5 - 2 mm 50%
: . Unburned bricks produced with the addition of 10% by weight of . - 8 -~ .
.
sintered magnesia showed the good properties mentioned in EXample 1.
Unburned bricks made from sintered material produced according to the present invention, were inserted in the centre part of the vault in a Siemens-Martin furnace (area above tap). On the right-hand side, the bricked vault was formed by previously known uncalcined magnesite-chromium bricks which had been produced on the basis of simultaneous sinter. It was found that at the same initial strength the wear on these known bricks after nearly 6 months in operation was substantially greater than on the bricks produced by the sintered material according to the present invention. On the average, the wear was 156 mm, compared with 124 mm.
It should be pointed out that the wear on the vault in the centre part of the Siemens-~artin furnace in the area of both kinds of brick was equally strong.
, ' '~
~, _ g _ :, ~
.
In producing refractory, basic granules or bricks based upon magnes-ium oxide and chrome oxide or chrome ore, it is desirable first of all to produce from magnesium oxide or combustion products thereof, and substances containing chromic oxide, or chrome ore, by preliminary combustion at temper-atures usually above 1700 C, a sintered material which is then crushed and, if necessary, after the addition of further magnesium oxide, is used as it is or for producing burned or unburned bricks. Additional heating, either while the - -material is in use in the form of granules or unburned bricks, or a second burning, if burned bricks are being made, produces materials having advantage-ous properties such as good cold-compression strength and good hot-bending - strength.
During so-called sinter-burning for producing the sintered material, an initial reaction takes place between the magnesium oxide, or the compounds producing MgO when burned and the substances containing chromic oxide or the chrome ore, whereby a so-called "direct bond" is obtained under certain cir-cumstances (see the article by MOERTL et al in "Rasexx-Rundschau" (1965), pages 559-576). German Auslegeschrift 2011805 describes such a method for producing refractory magnesia-chromite and chromite-magnesia bricks, wherein the magnesite, and the magnesium compounds producing magnesium oxide when burned, have a grain size of less than 0.20 mm and the substances containing chromic oxide, and the chrome ore, have a grain size of between O and 6 mm, a maximum of 20% and a maximum of 80~ of the substances containing chromic oxide used to make the sintered material having a grain size of less than 0.12 mm, and the said sintered material having a maximum silicic-acid content of 2.5~, a maximum lime content of 4~, and a lime:silicic-acid molecular ratio of from more than 0.6 to 2.5.
~ 7Z~30 Hitherto known processes made many suggestions relating to the grain size of the raw materials, the chemical composition of the sinter, and the manufacture of the bricks, but the final results produced no outstanding values for strength and the ability to withstand changes in temperature.
Thus, German Auslegeschrift 1,257,655 and German Patent 1,275,934 describe a so-called simultaneous sinter using mainly a coarse-grained chrome ore and a very fine-grained magnesia, whereas in German Auslegeschriften 1,571,328 and 1,646,845 all of the raw materials are in the finely-granular form. But a high-density sintered material, with high resistance to the ~-formation of cracks in the bricks when in use, was not achieved in every case.
The invention seeks to provide a sintered material based upon mag-` nesium oxide or substances which produce magnesium oxide when burned, and substances containing chromic oxide, or chrome ore, the said sintered material, upon further processing, either in the form of granules or in a form for pro-si ducing unburned and burned bricks, producing final results which indicate particularly good resistance to slag and satisfactory wear-behaviour in steel furnaces, especially open-hearth furnaces, in addition to the usual, satisfact-ory, known properties of such types of sinter.
Problems arising with refractory magnesia-chromite and chromite-magnesia compounds or bricks in use in open-hearth furnaces have been described in, among other publications, the article by H.M. MIKAMI, W.E. BRoWN and GILBERT in ~eramic Bulletin", Vol. 44, No. 5 (1965~, pages 433-439, especially -; in conjunction with Figure 2 of the article. In open-hearth-furnace arches, the arch is often forced upwards, and very special mechanical devices must therefore be provided to force the arch down again and to hold it down.
This "pushing up" of the arch is attributable, in the case of chemi-cally bonded brick, among other things to the action of slags and to different reactions in different areas of bricks, the bricks and granules used in produc-ing the arch undergoing an increase in volume.
.
1(~72130 It has now been found that by using the sintered material according to the invention, it is possible to produce both unburned and burned bricks and also compounds which are particularly resistant to this type of attack in open-hearth furnaces, thus increasing the life of an arch made of such refractory materials.
According to the invention, this is achieved in that, in producing the sintered material, the magnesium oxide or the substance which produces magnesium oxide when burned, is used in fine granular form, while a certain proportion of the substances supplying chromic oxide, or the chrome ore, is used in a very fine grain size, and the remainder of the substance containing chromic oxide, or the chrome ore, is used in a relativelylarge grainsize,i.e.
there is a so-called "grain-size gap" in the grain-size distribution in the substances containing chromic oxide or in the chrome ore.
According to the invention, there is provided in a method for pro-ducing a basic sintered material suitable for use in the production of refractory magnesia-chromite and chromite-magnesia granules and/or bricks, wherein substances containing chromic oxide or chrome ore in the form of particles having a grain size of between 0 and 3 mm are mixed with fine-grained magnesium oxide or a substance which produces magnesium oxide when burned, formed into briquettes, if necessary with the addition of a suitable bonding agent, are thereafter sintered at a temperature above 1700&, and are then crushed, the steps of:
a) supplying the magnesium oxide or substance giving magnesium oxide on combustion in a grain size of less than 0.2 mm, but with at least 80~ having a grain size of less than 0.063 mm, b) supplying from 35 to 75% by weight of the substances containing chromic oxide, or chrome ore in a grain size of less than 0.063 mm; and c) supplying the balance of the substances containing chromic oxide, or the chrome ore, in a grain size of between 0.5 and 3 mm) ,It~
~ - 3 -whereby to obtain a basic sintered material containing between 10 and 30~ by weight of Cr203 and having an SiO2 content of less than 3~.
,.~
- 3a -Preferably 50 to 70% by weight of substances containing chromic oxide or chrome ore are present in a grain size of less than 0.063 mm; and 50 to 30% by weight of these substances are used in a grain size of between 0.5 and 3 mm. Thus the substances containing chromic oxide, or the chrome ore used in this process have a grain-size gap between 0.063 and 0.5 mm.
~` As regards the above-mentioned grain-size gap between 0.063 and 0.5 mm, it is, of course, possible that small amounts of substances containing chromic oxide, or of chrome ore, having grain sizes within the above-mentioned gap will be present, since it is scarcely possible to carry out 100% screening on an industrial scale. However, these small amounts, will usually be no more than 2 to 4%. Furthermore, a certain amount of crushing occurs when the raw materials are being mixed before the si~lltaneous sinter is burned, but this ;~ is not detrimental and may be disregarded. Thepercentage given herein are by ~ weight, unless otherwise indicated.
-, According to another preferred embodiment of the fine-grained pro-portion of the substances containing chromic oxide, or of the chrome ore, which is present in a grain size of less than 0.063 mm, 75 to 95% by weight ~` of this amount has a grain size of less than 0.04 mm.
Moreover, it is desirable for the coarser grain-size fraction of the ~ 20 substances containing chromic oxide, and of the chrome ore, to have a grain size of between 0.5 and 2 mm.
By restricting the maximum grain size of the coarse chromic ore to -~ 3 mm, preferably 2 mm, a uniformly good and complete direct bond is obtained between the ore granules and the MgO, the fine chrome-ore flour being absorbed , into the MgO component in the course of the sintering process. The upper l;~;t of 3, preferably 2 mm, is extremely important since, as the grain size of the ore increases, under given combustion conditions, the direct bond be-. .
comes increasingly irregular and inadequate. Moreover, it is desirable to keep the maximum ore grain size distinctly below the subsequent brick grain -- 4 _ . .:
size of 5 mm, in order to keep to a minimum any damage to the direct-bond areas when the sinter is crushed.
In the production of simultaneous sinter, the magnesium oxide, or the substances producing magnesium oxide when burned, and the substances con-taining chromic oxide, or the chrome ore, which have the grain sizes mentioned above, are moulded, if necessary with the addition of a bonding agent, into briquettes or bricks, after which they are sintered at temperatures of 1700 C
or above, preferably 1850& or above. However, it is desirable not to exceed a sintering temperature of 2000& , since this could cause melting, which means that the properties of the sintered material based on direct bonding would no longer be obtained.
The bonding agents used are those generally known per se in the art, e.g., a saturated magnesium-sulphate solution, sulphite lyes from paper manu-facturer, or other known bonding agents.
The magnesium oxide or substances which produce magnesium oxide when burned may be materials normally used in the art, e.g. salt-water magnesia, sintered magnesia, natural or synthetic magnesium compounds forming periclase upon burning, such as magnesium carbonate in the form of the mineral magnesite.
The substances containing chromic oxide, or the chrome ore, may be all materials known per se to the art, in the case of the chrome ore more particularly: Sudanese chrome ore, Phillipine chrome ore, Turkish chrome ore, Persian chrome ore, and South African chrome ore, and these chrome ores may also be used in the form of concentrates, i.e. ore concentrates prepared chemi-cally or by other means and containing small quantities of impurities.
As compared with known similar types of sinter, the use of the meth-od according to the invention optimizes the direct-bonding and dissolving effects. This permits an extension of the preferred Cr203 range to lower chrome-ore contents, which in turn makes it possible to reduce the material supplying chromic oxide if required and if suitable types of chrome ore are ~072130 used, without any impairment of behaviour during handling. If required, less than 4S% of chrome ore may be used.
The sintered material obtained by the method according to the inven-tion contains between 10 and 30% by weight of Cr203, preferably between 15 and 25% by weight.
The SiO2 content of the sintered material should be less than 3%, better still less than 2.5%.
The CaO:SiO2 molecular ratio is not particularly critical, but values between 0.2 and 2.0 have been found advantageous, preferably between 0.5 and 0.8.
In producing the sintered material, the fine-grained part may also be chromic oxide in a grain size of up to 0.063 mm, whereas the coarse-grained part may be chromic oxide in a grain size of between 0.5 and 3 mm, preferably between O.S and 2 mm.
The sintered material is then granulated and may then be used to produce refractory granules, unburned refractory bricks, or burned refractory bricks. To this end, the sintered material may be crushed to a grain size of between 0 and 5 mm, preferably between 0 and 3 mm, a-l of the fractions, i.e.
fine-grain, medium-grain and coarse-grain, and a separately-ground flour frac-tion, being used for further processing, It is desirable to add to the crushed sintered material up to 20%
by weight, preferably up to 10~ by weight, of magnesium oxide. The grain size ` of this additional magnesium oxide may be between 0 and 3 mm, preferably be-tween 0 and 1 mm, but it may also be added in the form of 0 - 0.12 mm sintered flour.
By using substances containing chrome oxide or chrome ores on the one hand as the fine-grained material and, on the other hand, as the narrow-` range coarse-grained material with a grain-size gap, the method according to the invention produces a sintered material which provides, in the bricks made . ~
'' ' ~07Z~30 therefrom, especially in the case of unburned bricks, uniformly good propert-ies, especially those relating to density, hot and cold strength, and resist-ance to crack formation when in use, as well as satisfactory resistance to changes in temperature, the latter being brought about by structural resilience.
However, emphasis should also be given to the very good wear behaviour as revealed by the low pressures resulting from optimal expansion behaviour and to the particularly good resistance to slag of bricks made from such sintered materials. The result of this is that arches made of such sintered materials do not push up or peel off and have a substantially longer life. Wear is between 15 and 20% less, for example.
The production of the sintered material is explained in greater detail in the following examples:
Example 1 A simultaneous sinter was produced by mixing together the following raw materials, miYing them with 4% by weight of a saturated magnesium sulphate solution and 3% by weight of water, based upon the weight of the solids, mould-ing the mixture into briquettes, and burning the saidbriquettes at about 1850&
in a pilot-plant furnace. The said raw materials are given in the following Table 1.
Table 1 Based on Based on Raw materials Calcined material Magnesite, Flotation-concentrate 0 - 0.063 mm 60% by weight 43% by weight Magnesia, Furnace flue dust (after grinding to 0 - 0.063 mm) 10% by weight 14% by weight Chrome ore (54~ CR203) 30% by weight 43% by weight of which 0 - 0.063 mm = 67%
0.5 - 3 mm = 33~
The burned simultaneous sinter was then crushed to a grain size of between 0 and 5 mm, 10~ by weight of sintered magnesia flour containing about 95% of 0 - 0.1 mm MgO was added to the crushed sinter~ together with 3.5% by weight (based on the mixture of solids) of a saturated magnesium sulphate solution, and unburned bricks were moulded. In addition to high hot and cold strength, these bricks have optimal expansion behaviour, high structural resiliency and, as determined by tests, very good resistance to slags and minimal crack formation.
Example 2 : The procedure according to Example 1 was repeated, but with the raw materials given in the following Table 2.
Table 2 Caustic salt-water magnesia (0 - 0.063 mm) 45%
Magnesia Furnace flue dust (Reground to 0 - 0.063 mm) 10%
Chrome ore (54% Cr203) 45%
of which 0 - 0.063 mm 50%
; 0.5 - 2 mm 50%
Unburned bricks produced with an addition of 10% by weight of sintered magnesia showed the good properties mentioned in Example 1.
- EXample 3 .
The procedure according to Example 1 was repeated, but with the raw materials given in the following Table 3. - -Table 3 Based on Based on Raw materials Calcined material ,:, : Magnesite Flotation-- concentrate 0 - 0.2 mm -- (90% below 0.063 mm) 70% by weight 54% by weight Magnesia, Furnace flue dust (Reground to 0 - 0.063 mm) 10% by weight 14% by weight Chrome ore (54% Cr203) 20% by weight 32% by weight of which0 - 0.063 mm 50%
0.5 - 2 mm 50%
: . Unburned bricks produced with the addition of 10% by weight of . - 8 -~ .
.
sintered magnesia showed the good properties mentioned in EXample 1.
Unburned bricks made from sintered material produced according to the present invention, were inserted in the centre part of the vault in a Siemens-Martin furnace (area above tap). On the right-hand side, the bricked vault was formed by previously known uncalcined magnesite-chromium bricks which had been produced on the basis of simultaneous sinter. It was found that at the same initial strength the wear on these known bricks after nearly 6 months in operation was substantially greater than on the bricks produced by the sintered material according to the present invention. On the average, the wear was 156 mm, compared with 124 mm.
It should be pointed out that the wear on the vault in the centre part of the Siemens-~artin furnace in the area of both kinds of brick was equally strong.
, ' '~
~, _ g _ :, ~
.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method for producing a basic sintered material suitable for use in the production of refractory magnesia-chromite and chromite-magnesia granu-les and/or bricks, wherein substances containing chromic oxide or chrome ore in the form of particles having a grain size of between 0 and 3 mm are mixed with fine-grained magnesium oxide or a substance which produces magnesium oxide when burned formed into briquettes, if necessary with the addition of a suit-able bonding agent, are thereafter sintered at a temperature above 1700°C, and are then crushed, the steps of:
a) supplying the magnesium oxide or substance giving magnesium oxide on combustion in a grain size of less than 0.2 mm, but with at least 80% having a grain size of less than 0.063 mm;
b) supplying from 35 to 75% by weight of the substances containing chromic oxide, or chrome ore in a grain size of less than 0.063 mm; and c) supplying the balance of the substances containing chromic oxide, or the chrome ore, in a grain size of between 0.5 and 3 mm, whereby to obtain a basic sintered material containing between 10 and 30% by weight of Cr2O3 and having an SiO2 content of less than 3%.
a) supplying the magnesium oxide or substance giving magnesium oxide on combustion in a grain size of less than 0.2 mm, but with at least 80% having a grain size of less than 0.063 mm;
b) supplying from 35 to 75% by weight of the substances containing chromic oxide, or chrome ore in a grain size of less than 0.063 mm; and c) supplying the balance of the substances containing chromic oxide, or the chrome ore, in a grain size of between 0.5 and 3 mm, whereby to obtain a basic sintered material containing between 10 and 30% by weight of Cr2O3 and having an SiO2 content of less than 3%.
2. A method according to claim 1, wherein from 50 to 70% by weight of the chromic oxide-containing substance or chrome ore is supplied in a grain size of less than 0.063 mm.
3. A method according to claim 1, wherein sintering is carried out at a temperature of 1850°C to 2000°C.
4. A method according to claim 1, 2 or 3, wherein the fine-grained substances containing chromic oxide or fine-grained chrome ore (b) has a maxi-mum grain size of 0.063 mm, 75 to 90% by weight thereof having a grain size of less than 0.04 mm.
5. A method according to claim 1, 2 or 3, wherein the coarser-grained portion (c) has a grain size of 0.5 to 2 mm.
6. A method according to claim 1, 2 or 3, wherein raw materials used are such that the C/S ratio in the finished simultaneous sinter is between 0.2 and 2Ø
7. A method according to claim 1, 2 or 3, wherein raw materials used are such that the C/S ratio in the finished simultaneous sinter is between 0.5 and 0.8.
8. A method according to claim 1, 2 or 3, wherein raw materials used are such that the SiO2 content of the simultaneous sinter is less than 2.5%
by weight.
by weight.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1727076A GB1573316A (en) | 1976-04-28 | 1976-04-28 | Sinter material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072130A true CA1072130A (en) | 1980-02-19 |
Family
ID=10092253
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA277,108A Expired CA1072130A (en) | 1976-04-28 | 1977-04-27 | Method for producing a basic sintered material |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1072130A (en) |
| DE (1) | DE2718370B2 (en) |
| ES (1) | ES458216A1 (en) |
| GB (1) | GB1573316A (en) |
| GR (1) | GR64491B (en) |
| IT (1) | IT1083179B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2063357A1 (en) * | 1991-06-27 | 1992-12-28 | David J. Michael | Burned refractories with low soluble chromium |
-
1976
- 1976-04-28 GB GB1727076A patent/GB1573316A/en not_active Expired
-
1977
- 1977-03-22 GR GR53067A patent/GR64491B/en unknown
- 1977-04-25 DE DE19772718370 patent/DE2718370B2/en not_active Withdrawn
- 1977-04-27 ES ES458216A patent/ES458216A1/en not_active Expired
- 1977-04-27 IT IT4914977A patent/IT1083179B/en active
- 1977-04-27 CA CA277,108A patent/CA1072130A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IT1083179B (en) | 1985-05-21 |
| GR64491B (en) | 1980-03-31 |
| DE2718370A1 (en) | 1977-11-17 |
| ES458216A1 (en) | 1978-02-16 |
| GB1573316A (en) | 1980-08-20 |
| DE2718370B2 (en) | 1979-09-27 |
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