JPH04310560A - Production of magnesia-carbon brick - Google Patents

Abstract

PURPOSE:To produce a magnesia.carbon brick using a novolak type phenolic resin mixable and moldable at normal temperature as a binder without requiring an aging period after kneading. CONSTITUTION:A compound comprising magnesia raw material, a carbonaceous raw material and a metal powder raw material is kneaded with a liquid mixture of a resol type phenol resin and a novolak type phenol resin in a blending ratio of 5/95 to 15/85 as an organic binder to give body, which is molded at normal temperature while reducing pressure.

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 a method for producing unfired magnesia carbon bricks.

0002

[Prior art] Magnesia carbon bricks are made by adding an organic binder to magnesia raw materials and carbon raw materials such as graphite, kneading and forming them, and then molding them at a relatively low temperature of about 200°C for unfired products. Obtained by drying. These unfired magnesia carbon bricks are widely used as refractories for lining molten metal containers such as converters, electric furnaces, and secondary smelting ladles. The above-mentioned carbon raw material has the effect of suppressing the penetration of slag and molten metal from the working surface and preventing oversintering, and therefore has excellent corrosion resistance and spalling resistance.

Furthermore, in order to impart oxidation resistance to the above-mentioned magnesia carbon bricks, for example, Al powder or the Mg-Al alloy disclosed in Japanese Patent Publication No. 61-303 is added to the raw materials. ing. In addition, phenolic resin is commonly used as the organic binder, and it imparts a predetermined viscosity to the raw material, making it easier to mold, and
The heat received during operation of the furnace causes the volatile matter to disappear, leaving carbon components remaining in the structure, which also plays the role of supplementing the action of the carbonaceous raw material. When using phenolic resin as such an organic binder, the residual carbon content, that is, the weight ratio of the carbon component remaining in the structure, is set to be about 40%, and the amount added is the external multiplication factor of 3.
．． The content is generally 5 to 4.0% by weight. There are two types of such phenolic resins: resol type, which has thermosetting properties and a relatively low viscosity at room temperature, and novolac type, which has high viscosity at room temperature and is therefore kneaded while heating the raw materials.

0004

[Problems to be Solved by the Invention] By the way, although the viscosity of the above-mentioned resol type phenolic resin at room temperature is low,
In the clay after kneading, a chelate reaction occurs between Mg or Fe in the raw materials and the phenol resin, and the viscosity of the clay gradually increases with the passage of time after kneading. Therefore, if molding is performed immediately after kneading, the viscosity of the raw materials may be too low and lamination may occur during molding. On the other hand, if too much time has passed after kneading, the clay will be in a dry state (the viscosity of the binder The time (ripening time) required for the clay to reach a state suitable for molding after kneading must be appropriately set to prevent the appearance of a binder shortage due to excessive increase in the amount of binder. This aging time depends on various factors such as the individual characteristics of the resol-type phenolic resin used, the temperature and humidity during use, and the temperature of the clay discharged from the mixer, and is determined optimally by taking these factors into consideration. The complexity of calculating and setting the appropriate ripening time is required.

Furthermore, since resol-type phenolic resins have thermosetting properties, strict temperature control is required when producing the resol-type phenolic resins, and storage in a cold storage room kept at 15°C or lower is also necessary. Furthermore, even when stored at a temperature of about 25°C, the usable life was usually as short as about one month.

On the other hand, novolac type phenolic resins are
Because it is thermoplastic, it can be heated and kneaded, but even if it is liquid, it is generally mixed with hexamine as a hardening agent.
%, the viscosity at room temperature inevitably increases, and as mentioned above, it is necessary to provide a heating device to the kneading means such as a mixer. In addition, as disclosed in the above-mentioned Japanese Patent Publication No. 61-303, M, which is particularly active as an antioxidant,
The flash point of the Mg-Al alloy containing g is 535° C., which is lower than the flash point of conventional Al powder alone, 650° C., so there is a risk of ignition when heated and kneaded.

Furthermore, when molding unfired magnesia carbon bricks using the above novolac type phenolic resin as a binder, the clay is also used in the pressurizing/forming means such as a press in order to exhaust the air present in the clay. It was necessary to provide a heating device to heat the product and lower its viscosity. Under these circumstances, as a result of various experiments, the inventors determined that the novolac type phenol resin used for producing magnesia carbon bricks, which can be kneaded at room temperature, should have a viscosity of 1000 to 2000 cps (2
5°C) It was found that it is desirable to set the non-volatile content to 70 ± 2% and the residual carbon content to 40 ± 2%, but when trying to lower the viscosity, it is necessary to The residual carbon content and the residual carbon content decrease to a value below the above-mentioned range, making it unsuitable for practical use.

The present invention was proposed in view of the above circumstances, and does not require a maturing period after kneading.
The object of the present invention is to provide a method for producing unfired magnesia carbon bricks using a novolac type phenolic resin as a binder, which can be kneaded and molded at room temperature.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention employs the following means. That is, a liquid mixture of a resol type phenolic resin and a novolac type phenolic resin in a mixing ratio of 5/95 to 15/85 as an organic binder is added to a composition consisting of a magnesia raw material, a carbonaceous raw material, and a metal powder raw material. is added, kneaded, and the resulting clay is molded at room temperature while applying reduced pressure.

0010

[Function] According to the above structure of the present invention, by blending 5 to 15% by weight of resol type phenol resin with novolac type phenol resin as a base, the nonvolatile content and fixed carbon are not reduced. Can reduce viscosity. In this case, it is desirable that the viscosity, nonvolatile content, and residual carbon content of the resol type and novolac type phenolic resins be as shown in Table 1 below. Furthermore, Table 1
The residual carbon percentage of a novolac type phenolic resin is the value when hexamine is added as a curing agent.For example, when 7% by weight of hexamine is added to the novolac type phenolic resin, the residual carbon percentage within the stated range is is obtained.

[0011]

[Table 1]

[0012] Furthermore, the mixing ratio of resol type phenolic resin and novolak type phenolic resin is 5/95 to 15/
85 is desirable, and if the amount of resol type phenolic resin exceeds the above range, the drawbacks of the resol type phenolic resin will appear, and after discharging from the mixer,
As time passes, the clay noticeably dries out, making it necessary to set a ripening time.If the maturing time is less than the above range, the viscosity will not decrease and the desired effect of the present invention will not be exhibited.

Furthermore, when molding the unfired magnesia carbon brick according to the present invention having the above-mentioned characteristics, by molding while removing air trapped in the clay,
A dense molded body with low porosity can be obtained. In this case, it is most desirable to use, for example, a vacuum degassing press as the molding means.

[0014]

EXAMPLES The present invention will be explained below based on examples. =Example 1= Samples of unfired magnesia carbon bricks were prepared using the formulations shown in Table 2. In Table 2, since the amounts added together with magnesia clinker fine particles, Mg-Al alloy powder, and hexamethylenetetramine were small, the respective weights were combined, premixed, and kneaded.

In addition, the phenol resin added as an organic binder has a mixing ratio of resol type and novolac type in the product of the present invention of 10/90, and about 11% hexamethylenetetramine with respect to the novolak type phenol resin. was added. On the other hand, the conventional product uses 100% resol type phenolic resin. Conventional products with such a composition were molded with aging times of 4 hours, 24 hours, and 48 hours after kneading, but with conventional products, lamination occurred when the aging time was 4 hours, and the clay formed after 48 hours. It hardened and could not be molded together. In addition, in the products to which the present invention was applied, the aging time was 4 hours and 24 hours, and a vacuum degassing press was used and molding was performed under reduced pressure conditions of 60 torr.

Table 3 shows the products to which the present invention is applied (aging times 4, 2
4 hours) and the conventional product (aging time 24 hours) are shown below. As seen in Table 3, there was no noticeable difference between the products to which the present invention was applied and the conventional products, and in particular, due to the use of a vacuum degassing press, the products to which the present invention was applied had lower compressive strength and bending strength. It shows a slightly high value. Further, when the conventional product and the product to which the present invention was applied were laminated together on a slag line of a ladle with a capacity of 40 tons, no difference in residual thickness was observed between the two after 20 charges of operation.

[0017]

[Table 2]

[0018]

[Table 3]

= Example 2 = The applied product of the present invention used in Example 1 and the phenol resin (initial viscosity 300 cps) used in the conventional product were placed in a constant temperature bath at 50°C and the change in viscosity over time was measured. However,
Whereas the phenol resin, which is a mixture of resol type and novolac type according to the present invention, did not exhibit any viscosity change for 4 months,
The viscosity of the conventional resol-type single phenol resin had already increased to 3000 cps after two weeks, which exceeded the limit of its applicability as an organic binder for unfired magnesia carbon bricks.

[0020]

As described above, according to the present invention, it is possible to knead at room temperature, so even highly flammable and explosive antioxidants (e.g. Mg-Al alloy) can be safely kneaded. Not only is it unnecessary to set a complicated aging time that is required when phenolic resin is used, but also molding can be performed immediately after kneading, so lead time can be shortened. In this case, if the molding is performed under reduced pressure, a denser refractory can be manufactured.

Furthermore, the organic binder of the present invention has the effect of improving storage stability and requiring no special precautions during storage, greatly increasing its industrial utility value.

Claims (2)

[Claims] Claim 1: A composition consisting of a magnesia raw material, a carbonaceous raw material, and a metal powder raw material, and a resol type phenol resin and a novolac type phenol as organic binders in a mixing ratio of 5/95 to 15/85. A method for producing magnesia carbon bricks, which comprises adding a liquid mixture with a resin, kneading the mixture, and molding the resulting clay at room temperature while applying reduced pressure. [Claim 2] The viscosity at 25° C. of the novolac type phenolic resin to which hexamine is added as a curing agent is 30.
000 to 50,000 cps, non-volatile content is 70 ± 2%, and fixed carbon is 40 ± 2%, and the viscosity of the resol type phenol resin at 25°C is 250 to 350 cps, non-volatile content is 70 ± 2%, and fixed carbon is 40 ± 2. The method for producing magnesia carbon bricks according to claim 1, wherein the magnesia carbon brick is 2%.