JPH04228469A - Unburned magnesia carbon brick - Google Patents

Abstract

PURPOSE:To provide an unburned magnesia carbon brick having a reduced amount of carbon raw material blended without lowering corrosion resistance and spalling resistance, with respect to the production of refractory brick, especially to the unburned magnesia carbon brick in this invention. CONSTITUTION:A refractory raw material comprising a magnesia raw material blended with 0.5-5wt.% pitch and 3-10wt.% graphite as a main aggregate is mixed with a phenolic resin having compatibility with pitch such as alkoxymethylphenol resin as a binder and more preferably unburned magnesia carbon brick comprises >=40wt.% magnesia raw material ground into 6-50mm particle diameter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to refractory bricks, and more particularly to unfired magnesia carbon bricks.

0002

[Prior art] Unfired magnesia carbon bricks are
It is obtained by blending a magnesia raw material and a carbon raw material such as graphite, kneading and molding together with an organic binder such as a phenol resin, and then drying at a relatively low temperature of, for example, about 200°C. These unfired magnesia carbon bricks are widely used as refractories for lining molten metal containers such as converters, electric furnaces, and secondary smelting ladles. Due to the properties of the above carbon raw material, it has the effect of suppressing the penetration of slag and molten metal from the working surface and preventing oversintering, giving the unfired magnesia carbon bricks excellent corrosion resistance and spalling resistance. do.

In addition, the thermal conductivity of the unfired magnesia carbon brick increases especially when graphite is blended as a carbon raw material. Taking advantage of this property, for example, bricks are used in electric furnaces in order to extend the life of the furnace wall. An operating method is adopted in which cooling is performed from the back side, that is, from the shell side of the furnace using a predetermined means.

0004

[Problems to be Solved by the Invention] However, the above-mentioned carbon raw material is contaminated with oxygen in the atmosphere, FeO, Mn in the slag, etc.
It is oxidized by oxides such as O, for example, becomes carbon monoxide and disappears by volatilization, which leads to structural embrittlement and wear on the working surface of the unfired magnesia carbon brick. When applied to a molten metal container for the purpose of decarburizing molten metal, the above-mentioned carbon component may be eluted from the operating surface that comes into contact with the metal to be treated.

[0005] Furthermore, when unfired magnesia carbon bricks with high thermal conductivity, that is, low heat insulation properties, are applied to steelmaking furnaces that are not equipped with means for cooling the steel shell, such as the above-mentioned electric furnaces, the furnace The heat inside the steel shell is conducted to the steel shell, causing red heat and deformation of the steel shell, resulting in new costs for replacing the steel shell. In order to improve these drawbacks, it is possible to reduce the amount of carbon raw material blended. For example, it is usually 15%
Unfired magnesia carbon bricks were also prototyped with a blending amount of graphite as a carbon raw material of about 5 to 10% by weight, which was about 20% by weight, but the deterioration of spalling resistance due to the decrease in thermal conductivity was This results in a significant decrease in corrosion resistance, and the range of its application is extremely limited.

The present invention has been made in view of the above-mentioned conventional circumstances, and provides an unfired magnesia carbon brick in which the amount of carbon raw material blended is reduced without reducing corrosion resistance and spalling resistance. The purpose is to

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention employs the following means. In other words, a phenolic resin that is compatible with pitch is added as a binder to a refractory raw material whose main aggregate is a magnesia raw material containing 0.5 to 5% by weight of pitch and 3 to 10% by weight of graphite. It is an unfired magnesia carbon brick having a structure of
The composition is such that it is blended in an amount of at least % by weight.

[0008]

[Effect] Comparing the carbonized structures obtained after heat treatment of phenol resin, pitch alone, and a mixture of phenol resin and pitch at 1000°C for 3 hours, it was found that the carbonized structures of phenol resin and pitch alone were glass.
y-flow structure, whereas the carbonized structure of the mixture of phenol resin and pitch is fine mosai.
c shows the structure and the energy required to destroy the mixture of phenolic resin and pitch.
It has been reported that the pitch is larger than that of any single carbonized structure ("Types of binders in alumina/carbon nozzles and their destruction"
No. 9 1983]).

[0009] The present inventors focused on this knowledge and attempted to produce an unfired magnesia carbon brick with an overall reduced carbon content by replacing a portion of graphite with pitch as a carbon raw material. However, pitch and resol-type phenolic resin, which are commonly used as binders, have low compatibility, and a slight coexistence state was observed at the interface between pitch and phenolic resin in the brick structure obtained by mixing the two. However, most of the carbonized structures were different in each region, and the characteristics of the mixture of phenol resin and pitch described above were not fully exhibited. Therefore, we have come to the conclusion that it is optimal to use a specific phenolic resin, such as alkoxymethyl phenol resin, which has properties that are compatible with the pitch disclosed in the above structure, and in this case, both can be easily combined. A binder composition that is compatible with the two and fully takes advantage of the characteristics of a mixture of the two can be obtained.

That is, the alkoxymethylphenol resin used in the present invention is
As disclosed in the publication, the phenol nucleus has a methylene bond (-CH2-), a dimethylene ether bond (-
A polynuclear body of phenol nuclei bonded by CH2OCH2-), usually 0.2 or more, preferably 0.5 to 2 alkoxymethyl groups (-CH2OR) per phenol nucleus.
, R: alkyl group, preferably an alkyl group having 1 to 4 carbon atoms), and the number average molecular weight is usually 100 to 2000,
Preferably, the number is 200 to 1000. or,
The methylol group (-CH2OH) remaining in the phenol core
) is usually 1 or less per phenol nucleus, preferably 0.5 or less, from the viewpoint of stability during heating.

[0011] The method for producing the alkoxymethylphenol resin is not particularly limited;
Add 0.5 to 4 mol, preferably 1 to 3 mol, of the aldehyde per mol, and react in the presence of an alkaline catalyst (pH 7).
~10), react at 60 to 90°C for 1 to 4 hours, then add an acidic catalyst to adjust the pH to 4 to 6, and add 0.5 to 10 mol of alcohol, preferably 1 to 5 mol, for alkoxylation. A common method is to perform dehydration and dealcoholization by decantation, distortion, etc. under reflux temperature. Note that it may contain residual alcohol, free phenol, and other byproducts.

[0012] Examples of the phenols used here include phenol, cresols, xylenol, resorcinol, etc., but phenol is preferred if a high carbonization rate is to be obtained. As the aldehyde, an alcoholic solution of formaldehyde such as formalin, paraform, methylformcel, butylformcel can be used. Further, examples of the alcohol include methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, 2-ethylhexanol, etc. Among them, the ratio of fixed carbon, compatibility with pitch, binder propanol in terms of viscosity of the composition,
Butanol is preferred.

[0013] The alkoxymethyl phenol resin may be mixed with an ordinary resol type or novolac type phenol resin within a range that does not impede compatibility with pitch. Examples of alkaline catalysts include alkali metal or alkaline earth metal hydroxides, alkanolamines, alkylamines, ammonia, etc.; examples of acidic catalysts include sulfuric acid, acetic acid, oxalic acid, p-toluenesulfonic acid, and formic acid. etc.

[0014] As a method of mixing alkoxymethylphenol resin and pitch, 1. 2. Method of heating both to near the softening point of pitch and stirring and mixing under heating. 3. Method of uniformly dispersing powdered pitch in alkoxymethylphenol resin, then kneading it with other refractory raw materials, and heating and kneading as necessary. Either method may be used, such as mixing pitch, including powder, with alkoxymethylphenol resin and other refractory raw materials, and heating and kneading it if necessary. However, since pitch is designated as a specified chemical substance, If the containing preparation contains 5% or more of benzene soluble content, specific local exhaust equipment, body washing equipment, etc. will be required, so method 3 is much more economical than methods 1 and 2. It is.

[0015] The mixing ratio of pitch and alkoxymethyl phenol resin is usually 1:9 to 9:1 by weight based on experience.
, preferably in the range of 3:7 to 7:3, and the amount of binder required to produce the unfired magnesia carbon brick according to the present invention is 3 to 6% by weight on an external basis. The pitch content is calculated from 0.5~
5% by weight is preferred. That is, the pitch is 0.5% by weight.
If it is less than 5% by weight, the carbon component of the magnesia carbon brick will be insufficient, and the binder composition formed by adding the phenolic resin that is compatible with the pitch will be insufficient, and the desired effect will not be obtained. If the amount is exceeded, the corrosion resistance will be significantly deteriorated, which is not preferable.

[0016] Furthermore, it is desirable that the blending amount of graphite is 3 to 10% by weight; if it is less than 3% by weight, even if the phenol resin and pitch according to the present invention are used, the heat spalling resistance will inevitably decrease, and When blended in excess of %,
It does not meet the purpose of the present invention, and is unsuitable and undesirable for molten metal containers that need to ensure low thermal conductivity, and refractories for special steelmaking furnaces that dislike elution of carbon from operating surfaces.

In addition, in the present invention, the carbon component contained in the brick structure is reduced compared to conventional unfired magnesia carbon bricks, so in order to supplement the corrosion resistance, which tends to decrease slightly, magnesia is added. It was decided to mix 40% by weight or more of crushed grains with a particle size of 6 to 50 mm as a raw material. Regarding this effect, please refer to the patent application filed in 1986-
As described in No. 323919, the anchoring effect of crushed grains is required to suppress the exfoliation of a structure that has become partially brittle due to oxidation. However, if the amount is less than 40% by weight, durability will decrease.

In the present invention, for the purpose of improving oxidation resistance, there is no hindrance to adding Al, Si, Mg-Al alloy, etc. to the refractory raw material, as is known in the art.

[0019]

EXAMPLES The effects of the present invention will be verified below by comparing examples with comparative examples based on the prior art. As the phenol resin compatible with the pitch used in the present invention, a phenol resin (hereinafter referred to as phenol resin A) obtained by the production method shown below was employed. Production Example 1 Synthesis example of n-butoxymethylphenol resin 1600 parts by weight of n-butanol, 37% formalin 1
640 parts by weight, 750 parts by weight of phenol, and 15 parts by weight of a 48% aqueous solution of caustic soda were charged into a flask, and after reacting at 80°C for 3 hours, the pH was immediately adjusted with a 50% aqueous phosphoric acid solution.
Lower it to 5, then decant until it reaches 12.
The reaction was allowed to reach 0°C for 7 hours. Water, phenol, and n-butanol liberated by concentration were removed, and the precipitate was filtered to obtain n-butoxymethylphenol resin (number average molecular weight 4
50, 1 n-butoxymethyl group per phenol nucleus
．． 0, methylol group 0.2) concentration 90%, 25°C
Viscosity at 200 cps, pH 5.3, fixed carbon 35
% of phenolic resin A was obtained.

[0020] The physical properties of the resol type phenolic resin partially adopted in the comparative examples are as follows: non-volatile content: 68-72%, fixed carbon: 34-38%, viscosity at 25°C: 250-350 cp.
s, and the specific gravity is 1.17 to 1.19. Table 1 shows examples of the present invention and comparative examples. Invention Examples 1 and 2 and Comparative Example 1
contains 80% or more of particle size of 300 μm or less, has a softening point of 125-135°C, and has a fixed carbon of 45-5
5%, heat-kneaded together with phenolic resin A and other refractory raw materials at a temperature of 70 to 75°C, then immediately molded with a pressure of 1500 kgf/cm2, and heated at 200°C for 30 hours according to a conventional method. It was obtained by curing treatment.

Comparative Examples 2, 3, and 5 were obtained by using a resol type phenol resin and the above powder pitch in place of the above phenol resin A, and kneading at room temperature under the same conditions as above. were obtained using phenolic resin A and resol type phenolic resin, respectively. The measured values of porosity, bulk specific gravity, and compressive strength, as well as the results of heat spalling resistance and corrosion resistance tests, of each of the above samples are shown in the lower column of Table 1. The heat-resistant spalling test shows the number of times until the structure peels off, with one cycle of heating the sample to 1200°C, holding it for 15 minutes, and then cooling it with water.The corrosion resistance test shows the number of times until the structure peels off. 1, FeO20% 1
The thickness of the dissolved layer after immersing the sample in 750° C. slag for 3 hours was measured and expressed as a relative index when the measured value of Comparative Example 2 was set as 100.

Examples 1 and 2 of the present invention have the same level of spalling resistance as the conventional unfired magnesia carbon brick containing 20% by weight of graphite as shown in Comparative Example 2. In terms of corrosion resistance, Example 1 of the present invention is slightly inferior to the conventional material shown in Comparative Example 2, but in Example 2, the oxidation resistance was improved by adding metal Al, and as a result, Comparative Example 2
It shows superior corrosion resistance.

Invention Example 1, Comparative Example 1, and Comparative Example 3
In each comparison between Comparative Example 5 and Comparative Example 5, 6 was used as the magnesia raw material.
An improvement in corrosion resistance was observed by adding crushed particles of ~20 mm. In addition, Example 1 of the present invention, Comparative Example 3, and Comparative Example 1
In each comparison between Comparative Example 5 and Comparative Example 5, it was revealed that the system of the alkoxymethyl phenol resin and pitch according to the present invention is superior in heat-resistant spalling property compared to the conventional system of resol phenol resin and pitch. .

Furthermore, in a comparison between Comparative Example 1 and Comparative Example 4, when only the alkoxymethylphenol resin according to the present invention was added, no improvement in heat-resistant spalling property could be expected; It can be seen that the effect on improving the target spalling property is significant. When the brick shown in Example 2 of the present invention was used as a lining in an 85t stainless steel decarburization furnace, compared to the conventional unfired magnesia carbon with a graphite content of 20% by weight (Comparative Example 2), approximately exhibiting a 30% increase in durability, and
It was confirmed that the amount of carbon components eluted into the steel was also reduced due to the reduction in the amount of erosion loss, and as a result, the amount of blown acid required for refining was reduced by 5%.
It was shown that high quality, low cost stainless steel can be obtained.

It goes without saying that the present invention is not limited to the above embodiments, but can be applied in various ways without departing from the scope disclosed by the present invention.

[0026]

[Table 1]

[0027]

Effects of the Invention As described above, the present invention has a pitch of 0.5 to 0.5.
5% by weight of graphite and 3 to 10% by weight of graphite as the main aggregate, and a phenolic resin that is compatible with pitch such as alkoxymethyl phenol resin as a binder. By adding unfired magnesia, the amount of carbon raw material blended is reduced without reducing corrosion resistance and spalling resistance.
Carbon bricks can be provided.

Further, by blending 40% by weight or more of a magnesia raw material partially in the form of crushed particles with a particle size of 6 to 50 mm, it is possible to suppress a decrease in the corrosion resistance of the unfired magnesia carbon brick having the above structure. As described above, the unfired magnesia carbon brick obtained by the present invention has a low carbon component content, so it can be used for decarburizing molten metal, such as in a stainless steel decarburization furnace, where the carbon component does not want to be eluted into molten metal. It can also be applied to molten metal containers intended for charcoal.
The carbon lining prevents red heat, deformation, etc. of the steel shell, and has the effect of extending the life of the steel shell itself.

Claims (3)

[Claims] [Claim 1] Pitch 0.5-5% by weight, graphite 3-1
An unfired magnesia carbon brick characterized in that a phenolic resin having a property of being compatible with pitch is added as a binder to a refractory raw material whose main aggregate is a magnesia raw material containing 0% by weight. Claim 2: Claim 1, wherein the phenol resin contains an alkoxymethyl phenol resin.
The unfired magnesia carbon brick described in . 3. The unfired magnesia carbon brick according to claim 1 or 2, which contains 40% by weight or more of a magnesia raw material in the form of crushed particles with a particle size of 6 to 50 mm.