JPH0355427B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a lime-based unfired refractory used as a lining for kilns used at high temperatures, such as containers for molten metals, reaction vessels for metal refining, and cement rotary kilns. In general, basic refractories, especially magnesia-based refractories containing MgO as a main component, are widely used as refractories for lining furnaces because of their high melting point and low solubility in low-melting slag. ing. However, magnesia-based refractories have the following drawbacks. That is, because the refractory itself has a high melting point, low-melting point slag or the like in the furnace penetrates into the interior of the refractory, which corresponds to the temperature gradient inside the refractory and whose melting point is equal to that of the refractory. In addition, magnesia-based refractories are fired at high temperatures, and the refractory structure is often a direct bond between particles, which occurs due to the difference in expansion between the operating surface and the inside of the refractory as the furnace heats up or cools down. There is no place for internal stress absorption, and the refractory cracks internally and peels off from the furnace lining. In particular, the deeper the low melting point slag penetrates, the stronger this tendency becomes.
Moreover, even without a heating-cooling cycle, the melt causes cracks between the refractory and the original refractory structure due to oversintering, causing flaking. In addition, the connective tissue loosens due to penetration, making the refractory more likely to collapse due to external force. Due to various factors such as those mentioned above, magnesia-based refractories have the disadvantage that exfoliation of about 30 to 100 mm in thickness occurs intermittently every certain number of use cycles. In order to improve the above-mentioned drawbacks, magnesia-carbon refractories containing a large amount of carbon to prevent the infiltration of low-melting point slag have been widely used in steelmaking furnaces, and have achieved considerable success. However, this refractory also has the following drawbacks. That is, as the operating temperature increases, the reaction of MgO+C→Mg↑+CO↑ progresses, causing self-oxidation of the refractory and progressing damage.
In particular, since the partial pressure of CO in the above reaction formula becomes 1 atm at 1800°C, the reaction is rapid, and continuous use at temperatures above 1750°C is normally impossible. Further, since carbon is easily oxidized and itself is more rigid than oxides in hot conditions, it easily causes brittle fracture when external force is applied, and the refractory material peels off significantly. In order to solve these drawbacks, the present inventor has conducted extensive research and considered the combined use of lime-based refractory aggregate.
In other words, although the CaO component is a component of low-melting point slag, as the CaO/SiO ₂ ratio in the slag increases, the slag becomes more viscous and eventually solidifies, so that basic refractories are hardly damaged. , CaO+
The reaction of 3C → CaC ₂ + CO is usually carried out at 3000℃ in an arc furnace, and the CO partial pressure of this reaction exceeds 1 atm at 2100℃ or higher. We focused on the fact that if the low melting point slag is added as a slag, the infiltrated low melting point slag will react with CaO, raising its own melting point and reducing the amount of infiltration into the refractory. We have been conducting research on refractories that will have a longer lifespan than damage caused by flaking, even if the amount is increased, but although lime-based clinker itself is present in small amounts,
Contains sintering aids such as Al ₂ O ₃ and TiO ₂ , which causes oversintering during refractory firing and reduces spalling resistance. Although it contains almost no auxiliary agents, extremely high temperatures are required to fire the refractory, and even if it is fired at high temperatures, the refractory structure will eventually become nearly rigid, reducing its resistance to thermal spalling and causing flaking. For this reason, etc.
Although it was possible to make the slag permeation layer thinner, the lifespan of the refractories was largely the same as that of conventional refractories. Lime also reacts very quickly with moisture, i.e.
The chemical reaction of CaO + H ₂ O → Ca (OH) ₂ causes so-called digestion, and the refractory collapses from the surface.
Moreover, when this reaction occurs inside the refractory, cracks are generated, which poses a serious problem in the manufacture of refractories. This reaction is
Occurs below 575℃. Based on the above findings, and also taking into consideration the prevention of lime digestion, the present inventor continued research and found that a case in which lime-based refractory aggregate and magnesia-based refractory aggregate are used together and non-fired. During the firing process (575
℃), oversintering during refractory firing, and thermal spalling during use.
This unfired refractory is given sufficient strength by the formation of carbon bonds due to carbonization of the binder during use, and this refractory is used under highly oxidizing conditions (carbon is easily oxidized). We have found that sufficient strength can be maintained by adding an appropriate amount of carbon when refracturing, and that, as mentioned above, by using CaO as one of the refractory components, slag penetration can be reduced. Furthermore, it has been found that it is necessary to use a specific binder to prevent digestion during the kneading, molding, and drying processes of this refractory. That is, when a phenolic resin-tar and/or pitch-polyisocyanate compound-based binder is selected, it does not contain any water and can prevent digestion during the kneading and molding processes, but also prevents the curing of the phenolic resin, especially during the drying process. By absorbing H ₂ O generated during the reaction into the polyisocyanate compound, curing of the phenol resin and curing by urea or urethanization of the polyisocyanate compound occur simultaneously, giving the refractory molded product a strong connective tissue. Even if it is unfired, the strength of the base is extremely high. Even if free lime is present, digestion can be completely prevented and the refractory will not crack at all. Tar and/or pitch is added to the phenolic resin. It was also confirmed that a binder effect can be obtained when Furthermore, it was confirmed that the strength at temperatures of 800°C or higher was improved by adding at least one metal fine powder of Si, Al, and Mg. The present invention was completed based on the above findings. That is, the present invention provides the following lime-based unfired refractory. (1) For 100 parts by weight of a refractory raw material consisting of a lime-based refractory agent and a magnesia refractory aggregate, (2) () consisting of a phenolic resin and tar and/or pitch, the content of the tar and/or pitch is A mixture with a weight ratio of 1/3 to 2/3 () polyisocyanate compound ():()=1:3 to 20 parts by weight of a binder with a weight ratio of 0.3 to 3 and (3) Si, Al, and Mg A lime-based unfired refractory obtained by kneading, molding, and drying 1 to 8 parts by weight of at least one metal fine powder selected from the following. (1) Lime-based refractory aggregate and magnesia refractory aggregate 50
~95 parts by weight, and 100 parts by weight of a refractory raw material consisting of 5 to 50 parts by weight of carbon, (2)() consisting of a phenolic resin and tar and/or pitch, and the content of the tar and/or pitch is in a weight ratio A mixture of () a polyisocyanate compound (): () = 1:0.3-3 (weight ratio) of 3-20 parts by weight of a binder and (3) Si, Al and Mg; A lime-based unfired refractory obtained by kneading, molding, and drying 1 to 8 parts by weight of at least one metal fine powder selected from the following. Among the refractory raw materials in the present invention, the lime-based refractory aggregate is not particularly limited, but for example, sintered calcia clinker, fused calcia clinker, fused calcia/magnesia clinker, synthetic dolomite clinker, natural dolomite clinker, etc. are used. These raw materials each have different CaO contents, different crystal sizes, and different types and amounts of impurities (mineralizing agents, etc.). The lime-based refractory aggregate contains free lime and is therefore very easily digested, but in the unfired refractory of the present invention, any of the above raw materials can be used alone or in combination. The magnesia-based refractory aggregate in the present invention is not particularly limited, and examples thereof include seawater magnesia clinker, natural magnesia clinker, and fused magnesia clinker, and one or more of these may be used. The above two types of aggregates and their usage ratios are not particularly limited, but depending on the use of the refractory,
In particular, there is an appropriate value for the amount of lime-based refractory aggregate used. For example, in a metal smelting furnace, if the iron oxide content in the slag is high, CaO cannot be used in large quantities because it is highly leached into iron oxides. However, at temperatures above 1700°C, the reaction between magnesia and carbon occurs as described above, and when magnesia is used alone, even unfired refractories manufactured according to the present invention have a lower thermal spalling property than fired products. However, the permeation layer of slag components increases and sintering of MgO progresses on the inner surface of the refractory, causing abnormal shrinkage in that area and further progressing MgO crystal growth.
As a result, stress is generated between the sintered part inside the refractory and the original refractory part further inside, making the refractory easy to peel off. In addition, MgO crystal growth always causes cleavage during the growth process, and a slight stress will cause a crack to occur at that part. At this time, if the CaO particles are homogeneously dispersed between the MgO particles, there will be almost no reaction between the MgO particles and the CaO particles, and the direct contact between the MgO particles will be reduced, resulting in the crystallization of MgO. Growth is suppressed and the above phenomena are significantly alleviated. It is desirable that the lime-based refractory aggregate used for this purpose be one with as few impurities as possible.
It is preferable to use sintered calcia clinker, fused calcia clinker, fused magnesia/calcia clinker, etc., which contain impurities other than CaO at 1.5% or less. The amount of lime-based refractory aggregate required to avoid the above point, that is, contact between MgO particles, is
Although it varies depending on the particle size, at least 1% of the total amount of lime-based refractory aggregate and magnesia-based refractory aggregate
It is desirable that it be present in an amount of % by weight or more. On the other hand, when the refractory usage conditions exceed 1700℃, e.g. 1750℃
When the atmosphere is neutral or reducing or vacuum, the iron oxide content in the slag in the smelting furnace is greatly reduced. Under these conditions, almost no elution of CaO occurs, so the amount used can be increased, but the storage period of refractories must be taken into account, for example, to guarantee a storage period of at least one month. In some cases, it is desirable that the amount is about 80% by weight or less in the total amount of aggregate. A particularly preferable usage amount of the lime-based refractory aggregate is 5 to 60% by weight based on the total amount of the aggregate. In addition, both the lime-based refractory aggregate and the magnesia-based refractory aggregate are used after adjusting the particle size in a conventional manner. To give an example, aggregates with a diameter of 5 to 1 mm are less than 75% by weight of both aggregates, and aggregates with a diameter of 1 mm or less are
Use approximately 25% by weight or more. The refractory of the present invention is an unfired refractory that is devised to maintain hot strength with a carbon bond obtained by carbonizing a binder with heat during use. However, when the refractory is highly oxidized during use, the carbon is oxidized to the inside of the refractory and its strength decreases, so good results can be obtained by adding an appropriate amount of carbon. In addition, carbon itself has excellent corrosion resistance against slag and molten steel.
Furthermore, since it is stable against thermal shock, good results can be obtained by increasing the amount used under conditions of use where atmospheric oxidation or liquid phase oxidation is not significant. However, if too much carbon is used, there will be problems such as deterioration of moldability, so the amount used is about 50% by weight or less, preferably 5 to 30% by weight of the entire refractory raw material. The carbon to be used is not particularly limited, but includes, for example, scaly graphite, earthy graphite, carbon black, electrode waste, and the like. The particle size of carbon is not particularly limited, but it is preferably about 3 mm or less from the viewpoint of kneading properties, moldability, etc. As a condition for using the furnace, the furnace is exposed to the atmospheric atmosphere during charging or discharging operations of molten metal, and is cooled during standby until the next use, causing atmospheric suction. As a result, carbon oxidation occurs due to oxygen in the atmosphere, which causes the strength of the refractory to decrease and damage to progress.However, in the refractory of the present invention, since it contains CaO, the working surface of the refractory is often covered with slag. The inside of the refractory is relatively well protected because the infiltrated slag reacts with CaO near the operating surface and a curing effect occurs, but in this case, adding a small amount of fine metal powder can protect the refractory. Metal oxidation occurs in the deep part, causing a plugging effect and a ceramic bond formation effect, thereby increasing the strength of the refractory. When metal Al is used in the refractory of the present invention, CaO
By coexisting with CaO and Al ₂ O ₃ based low melting point substances, the packing effect and low temperature strength improvement effect are remarkable. On the other hand, when metal Si is used, it coexists with CaO to form 2CaO.SiO ₂ and 3CaO.SiO ₂ based compounds. This bond is very strong and the refractory becomes stable against oxidation when heated. In addition, Si oxidation occurs before the carbon connective tissue from the binder oxidizes and disappears due to the reaction with oxygen from the atmosphere during use of the refractory or the oxygen contained in the oxide in the slag.
A reaction of O ₂ → SiO ₂ occurs, leaving SiO ₂ and this SiO ₂
2CaO・SiO ₂ , 3CaO・SiO ₂ by reaction with CaO
can maintain the refractory connective tissue instead of carbon bonding, so it can be used like when blowing stainless steel.
It is very effective for compensating the bonding force of carbon under conditions where CaO/SiO ₂ is low, high temperature, oxygen supply from slag is extremely large, and carbon loss is significant. In addition, when using metal Mg,
The strength of refractories can be improved by the packing effect of MgO produced by oxidation. Therefore, in the refractory of the present invention, a fine powder of metal, which is at least one of Si, Al, and Mg, is used.
The particle size of the fine metal powder is usually preferably about 0.2 mm or less in order to exhibit the above effects. In addition, the amount used is 1 to 100 parts by weight of the refractory raw material.
The amount is about 8 parts by weight, preferably 2 to 5 parts by weight.
If it is less than 1 part by weight, the above effects cannot be obtained, and if it exceeds 8 parts by weight, corrosion resistance tends to decrease due to an increase in CaO・Al ₂ O ₃ type low melting point substances in the case of Al.
In the case of Si or Mg, it is not preferable because it tends to partially change into CaO/MgO/SiO ₂ -based low melting point substances and be easily damaged by melting. The binder used in the present invention is a mixture of a phenol resin, tar and/or pitch mixed with a polyisocyanate compound. The above binder is characterized by the fact that the curing action of the phenolic resin and the water generated during curing reacts with the polyisocyanate compound to form a urea bond, or the OH group of the phenolic resin reacts with the polyisocyanate compound to form a urethane bond. Accordingly, both the phenol resin and the polyisocyanate compound are cured. In this binder, when tar and/or pitch is added to the phenolic resin, the curing action is not inhibited and the binder action of the tar and/or pitch is added. In the mixture of phenolic resin and tar and/or pitch, tar and/or pitch
Or the proportion of pitch used is 1/3 to 2/2 by weight.
It should be about 3. If it is less than 1/3, no binder effect will be obtained, and if it is more than 2/3, the curing effect of the phenol resin and polyisocyanate compound will be reduced, which is not preferable. In addition, the ratio of the polyisocyanate compound to the mixture of the phenol resin and tar and/or pitch is preferably such that the isocyanate groups in the polyisocyanate compound are at least equimolar or more to the OH groups in the phenol resin. The weight ratio of the former to the latter is approximately 1:0.3 to 1:3, preferably 1:0.5.
~1:2. If the latter is outside the above range,
Curing may be insufficient. Further, from the viewpoint of the strength of carbon bonds in the refractory, the amount of the binder used is preferably such that the amount of residual carbon in the refractory is about 1.3 to 8% by weight. Specifically, in consideration of sufficiently curing the refractory and keeping the amount of residual carbon within the above range, the amount of binder used is approximately 3 to 20 parts by weight per 100 parts by weight of the refractory raw material. The amount is preferably about 5 to 10 parts by weight. If it is outside the above range, the strength of the refractory will be insufficient as a result. As the phenolic resin in the above binder, one or more types of novolak type, resol type, etc. are used. The phenolic resin may be in powder or liquid form. Furthermore, if necessary, a curing agent such as hexamethylenetetramine may be used in combination with the phenol resin. In addition, as polyisocyanate compounds, tolylene diisocyanate,
methylene-bis(4-phenyl isocyanate),
Low polymers such as hexamethylene diisocyanate, methylene-bis-cyclohexyl isocyanate, and dimers and trimers thereof can be mentioned, and one or more of these can be used. Also,
As tar and pitch, any of those commonly used as binders for refractories can be used. The refractory of the present invention can be produced by kneading refractory raw materials, a binder, and fine metal powder, and then using a conventional method such as press molding.
After molding into the desired shape by stamp molding etc.
The product is produced by drying without firing, usually at a temperature of about 100 to 400°C, for about 6 to 36 hours, that is, removing volatile matter and curing the binder. The product obtained above will hardly be digested as it is, but in some cases, the surface of the refractory material may undergo some digestion, so if necessary, the surface of the product should be It may be coated with wax, paraffin, pitch, tar, etc. This sufficiently prevents surface digestion. In addition, as a particularly effective method, the binder used in the present invention is dissolved in an organic solvent, and fine frit powder is further added thereto, and the above-mentioned refractory before drying is coated, and then dried. By coating the refractory and drying it again, it is possible to completely prevent the surface of the refractory from being digested, and it is also possible to improve the oxidation prevention effect during use. The surface coating described above can significantly extend the shelf life of the product. As mentioned above, the lime-based unfired refractory of the present invention is
It is a completely new material developed through the accumulation of various technical ideas, and its heat resistance, spalling resistance, corrosion resistance, etc. are far improved compared to conventional refractories. Furthermore, there is almost no problem with the digestion of lime during the production of refractories, which contributes to resource and energy conservation. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 6 and Comparative Examples 1 to 8 Each of the ingredients shown in Table 1 below was mixed at 10 to 60% at room temperature.
The molded product obtained by minute kneading and molding is placed in a drying oven at about 100°C, and the oven temperature is raised to 180°C in about 12 hours.
Drying (curing) was carried out at the same temperature for 24 hours to obtain unfired refractories of the present invention or comparison. In addition, all the above molding methods are press molding (pressure, approximately 850
Kg/cm ² ). The dimensions of the molded bodies (refractories) in Examples 1 to 4 and Comparative Examples 1 to 4 are 780×
150 x 114 mm, Examples 5-6 and Comparative Examples 5-8
It is 230×100×130mm.

[Table] Next, for each unfired refractory obtained above, the porosity, bulk specific gravity, cold compressive strength, cold bending strength,
The hot bending strength at 1400℃ and the erosion ratio by rotary slag erosion test at 1750℃ were investigated. For the erosion test, eight samples of 114 x 50 x 40 mm were combined into a ring shape with their 114 mm edges touching.
This was carried out by setting this in a rotary cylinder and rotating it at 8 rpm while rapidly raising the temperature to 1750°C using an oxygen-propane burner and maintaining the same temperature for 5 hours while replacing the slag every 30 minutes. The A slag is CaO/SiO = 3, Total Fe = 20, and the B slag is CaO/SiO ₂ = 1, Total
Those with Fe=2 were used. The difference between the cut area of the sample before the test and the cut area of the sample after the test was taken as the amount of erosion, and the relative value when the amount of erosion of Comparative Example 1 (conventional MgO-C refractory) was taken as 100 was taken as the erosion ratio. The test results are shown in Table 2 below.

【table】

[Table] From the results in Table 2, the following is clear. That is, slag A has a composition assumed to be slag at the final stage of blowing ordinary steel in a steelmaking converter, and is characterized by high CaO/SiO ₂ and high total Fe. For such slag, the refractories of Examples 1, 3, 5, and 6 have higher erosion ratios than the MgO-C refractories of Comparative Example 1 because CaO easily reacts with FeO and Fe ₂ O ₃ . However, this can be significantly improved by replacing the magnesia-based refractory aggregate with fused magnesia, as shown in Examples 2 and 4. On the other hand, slag B has a composition assuming a slag at the final stage of refining stainless steel, and has a low CaO/SiO ₂ content and a total
It is characterized by low Fe content. For such slag, the refractory of the present invention is the MgO-C of Comparative Example 1.
It can be seen that this material has significantly superior corrosion resistance compared to other refractories. Next, the refractories of Examples 1 to 4 and Comparative Example 1 were used for the lining of a converter for stainless steel refining, and the durability was investigated. As a result, the durability of Examples 1 to 4 was more than 50% superior to that of Comparative Example 1. I got sex. Furthermore, when the refractories of Example 5 and Comparative Example 1 were used in the slag line part of a molten steel ladle, the service life of Comparative Example 1 was approximately 100 times, whereas in Example 5, the number of cycles was No breakout of refractories or oxidation on the back of refractories, and the service life is 120.
I was able to extend it more than once.

Claims (1)

[Scope of Claims] 1 (1) For 100 parts by weight of a refractory raw material consisting of lime-based refractory aggregate and magnesia refractory aggregate, (2) () consisting of a phenolic resin and tar and/or pitch, the tar and / or a mixture in which the content of pitch is 1/3 to 2/3 by weight () polyisocyanate compound (): 3 to 20 parts by weight of a binder with a ratio of () = 1:0.3 to 3 (weight ratio); 3) A lime-based unfired refractory obtained by kneading, molding, and drying 1 to 8 parts by weight of at least one metal fine powder selected from Si, Al, and Mg. 2 (1) Lime-based refractory aggregate and magnesia refractory aggregate
For 100 parts by weight of a refractory raw material consisting of 50 to 95 parts by weight and 5 to 50 parts by weight of carbon, (2)() consisting of a phenolic resin and tar and/or pitch, the content of the tar and/or pitch is A mixture with a ratio of 1/3 to 2/3 () polyisocyanate compound ():() = 3 to 20 parts by weight of a binder with a ratio of 1:0.3 to 3 (weight ratio) and (3) Si, Al and Mg. A lime-based unfired refractory obtained by kneading, molding, and drying 1 to 8 parts by weight of at least one selected metal fine powder.