JPS62110B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to the formulation of basic castable refractories used as lining materials for various molten metal containers, melting furnaces, metal processing furnaces, etc., and is capable of imparting high hot strength in high temperature ranges by improving the binder phase. The object of the present invention is to obtain a castable refractory that suppresses peeling due to spalling and destruction due to mechanical stress. In recent years, excellent refractory aggregates such as various synthetic products, sintered products, and fused products have been commercially available.
The development of binders is relatively slow. For example, basic castable refractories are typified by mixing basic refractory aggregate with alumina cement as a binder and curing at room temperature. There is a decrease in strength due to dehydration of alumina cement at intermediate temperatures before and after ℃.Also, in the case of basic refractories, magnesia is the main component, and in the matrix part containing alumina cement, MgO
-Al ₂ O ₃ -CaO-based low-melting substances are formed, and the hot strength is significantly reduced. Therefore, although basic castable refractories exhibit high corrosion resistance against basic slag, their hot strength at high temperatures is extremely low, resulting in peeling due to spalling,
It has the disadvantage that it is prone to breakage due to mechanical stress and has a short service life. In order to improve this, the following techniques have been known in recent years. (1) By using ultra-fine powder and deflocculant, we can reduce the amount of alumina cement used and perform castable casting with low moisture content to strengthen the structure. (2) Use phosphate binders such as monoaluminum phosphate and condensed sodium phosphate together with alumina cement to improve strength in the intermediate temperature range. (3) By adding condensed sodium phosphate with a polymerization degree of 21 and a CaO source to maguro-based unfired bricks, and optimizing the CaO/P ₂ O ₅ + SiO ₂ of the blend.
A hot bending strength of 100Kg/cm2 or ^more can be obtained. (4) The binder phase that provides the above-mentioned high strength is sodium lenanite (Na ₂ O・2CaO・
P ₂ O ₅ ). (5) Recently, magnesia-based sprayed refractories with the above-mentioned condensed sodium phosphate and CaO source added have been used, and in this case as well, the binder phase that forms at high temperatures is thought to be sodium lenanite. It is being As mentioned above, many examples of improved binders have been reported, but each has the following problems. The use of ultrafine powder and deflocculant in (1) above can make the structure densified, but since alumina cement and magnesia produce low-melting substances, the hot strength at 1400°C, for example, in a high temperature range is 10 Kg/cm ² becomes very small. In addition, in the case of (2) phosphate binding, castable refractories use large amounts of phosphate, and this phosphate acts as a deflocculant for alumina cement, so even if a flocculant is added, the It is trapped by acid salts and cannot be cured, making it impossible to achieve low moisture content and densification of the structure using ultrafine powder, deflocculant, and flocculant. Regarding (3), (4), and (5), condensed sodium phosphate and CaO source are added separately, so condensed sodium phosphate, which has a high solubility in water of about 60%, is added. Regardless of the particle size, it easily dissolves in water and the binder phase formed in the connective tissue of refractories tends to become small, and therefore there are many parts that do not participate in bonding, so if the amount of binder added is small, the strength will increase rapidly. descend. For the same reason,
Since only the condensed sodium phosphate moves to the heated surface side before use or during heating and drying during the manufacturing process of the refractory, a different concentration distribution occurs in the construction body or product, resulting in uneven bonding. Condensed sodium phosphate reacts violently with basic aggregate when blended water is added, so it must be neutralized with ammonia, etc. to suppress this, and ammonia has quality issues such as producing a strong pungent odor. There are also many problems in the working environment. In addition, sodium lenanite (Na ₂ O・2CaO・P ₂ O ₅ ), which is the binder phase mentioned above, _is
Both react and the binder phase is destroyed at 1250°C or above, forming Nagelschmittite (7CaO・P ₂ O ₅・
It is known that the hot strength at temperatures above 1300°C decreases because Na ₂ O _is liberated and enters the silicate liquid phase to form a low-melting glass. This invention is a basic castable refractory made to solve the problems in the prior art as described above, which uses a basic refractory material as the main raw material and other weakly basic or neutral refractory materials as auxiliary raw materials. It is characterized in that sodium lenanite and alumina cement, which are binder phases synthesized in advance, are blended with aggregate whose particle size has been adjusted with or without addition. In general, it has never been seen that a binder phase that is produced at high temperatures is synthesized in advance and added, and it is believed that the synthesized binder phase does not provide strength. However, the inventors found that even if the synthesized binder phase was added to the formulation, sufficient hot strength could be obtained depending on the method of synthesis and use, and that the binder phase caused by the _SiO2 component in the aggregate described above The present invention was completed after various experiments confirmed that the destructive effect of the phase can be suppressed by adding alumina cement. First, the binder phase, sodium lenanite, is synthesized by mixing condensed sodium phosphate and a CaO source in chemical equivalents and heating the mixture to 750°C or higher, or by adding various compounds containing Na ₂ O, CaO, and P ₂ O ₅ . Although it can be obtained by heating, specifically, it was synthesized as follows. Synthesis Example 1: Condensed sodium phosphate with a degree of polymerization of around 21 and CaCO ₃ were mixed in chemical equivalents and heated at 1100° C. for 3 hours. Synthesis Example 2: Mix sodium dihydrogen phosphate (NaH ₂ PO ₄ ) and CaCO ₃ in chemical equivalents,
It was heated at 1000°C for 3 hours. Synthesis Example 3: Sodium carbonate (NaCO ₃ ), phosphorus pentoxide (P ₂ O ₅ ), and CaCO ₃ were blended in chemical equivalents and heated at 1000° C. for 1 hour. As a result of X-ray diffraction, the mineral phase of each of the above-mentioned synthetic products was detected to be mostly β-sodium lenanite and a trace amount of α-sodium lenanite. In addition, photos 1 and 2 of the reference materials attached with the results of observing each composite product with a scanning electron microscope,
Shown in 3. Reference photo 1 (synthesis example 1 above), reference photo 2 (synthesis example 2 above), and reference photo 3 (synthesis example 3 above) are all magnified 200 times, but the size of the crystal grains of sodium lenanite is different from each other. The diameter is different from 5 to 10 μm in Synthesis Example 1 and 20 μm in Synthesis Example 2.
~50 μm, and Synthesis Example 3 has a thickness of 40 to 200 μm. It has also been found that it is possible to control the size of each crystal grain by changing the heating temperature and heating time as necessary. It was found that the following characteristics were found by crushing the sodium lenanite crystals synthesized as described above and blending them into a refractory aggregate. 1. Since it is not blended as sodium phosphate, it is possible to reduce the moisture content by using ultrafine powder, deflocculant, and flocculant, making the structure of castable refractories denser and improving their strength. 2 Synthetic products have very low solubility in water, so
Since the blended particles act as a binder phase, it is possible to control the size of the binder phase. Specifically, by crushing and sieving
100 meshes (147μm) or less, 200 meshes (74μm) or less, 325 meshes (43μm) or less,
The binder phase can be adjusted to any particle size as required, such as 20 μm or less, 10 μm or less, and in particular, by increasing the number of fine particles of several μm, which are effective for bonding, high hot strength can be achieved in castable refractories. Given. 3. For the same reason, the binder phase does not move during heating and drying of the refractory, so a uniform structure can be obtained from the heated surface to the inside. 4. The synthesized sodium lenanite has little reaction with basic aggregates such as magnesia and dolomite when added to kneading water, and is easy to handle. Next, the amount of sodium lenanite added to the fire-resistant aggregate is 1 out of 100 weight of the total weight of the aggregate.
~15% by weight is desirable. That is, if the amount of the binder phase added is less than 1% by weight, sufficient hot strength cannot be obtained for the refractory, whereas if it exceeds 15% by weight, the bond between the binder phases increases, but the bond is weak. On the other hand, it was found that corrosion resistance decreased. Next, alumina cement, as mentioned above,
The purpose of this addition is to suppress the destructive action of the binder _{phase caused by the SiO 2 source} , and the inventors first created Nagelschmittite (7CaO.
The conditions for the formation of P ₂ O ₅ .2SiO ₂ ) were investigated in the laboratory. That is, as silica sources, amorphous silica, silica sand, synthetic mullite (3Al ₂ O ₃ .2SiO ₂ ), synthetic phorsulite (2MgO .SiO ₂ ), and synthesized 2CaO .SiO ₂ are used as silica sources.
Sodium lenanite (Na ₂ O・
As a result of reacting with 2CaO・P ₂ 5 ₅ ) at high temperature, 2CaO・
Although the reaction with SiO ₂ does not proceed, SiO ₂ becomes 7CaO・
In the composition range of more than twice the chemical equivalent of P ₂ O ₅ 2SiO ₂ , the temperature starts from 1400℃ for amorphous silica, and from 1300℃ for silica sand, mullite, and forsterite.
It was found that a reaction proceeded to generate 7CaO.P ₂ O _{5.2SiO 2} and decompose the binder phase. Next, we conducted various studies on substances that suppress this reaction, and as a result, we found that the addition of alumina cement is effective.This is because CaO・Al ₂ O ₃ , the main mineral phase of alumina cement, reacts with the SiO ₂ source to form 2CaO・
SiO ₂ and Gehlenite (2CaO・Al ₂ O ₃・
It was found that it fixed as SiO ₂ ) and eliminated the action of decomposing sodium lenanite. As the alumina cement added in this invention, JIS No. 1 alumina cement, electrified high alumina cement, electrified high alumina cement super, Alcoa CA-25, Sekar 250, etc. can be used, but those with a low SiO ₂ content are more effective. It is. The amount of alumina cement blended is preferably 1 to 8% by weight based on the total amount of the refractory aggregate and sodium lenanite. If it is less than 1% by weight, the room temperature strength will be low and the hot strength will decrease because the reaction between SiO ₂ and sodium lenanite at high temperatures (destructive action of the binder phase) cannot be suppressed. On the other hand, if it exceeds 8% by weight, the amount of liquid phase produced increases due to the low-melting components in the alumina cement, resulting in a decrease in corrosion resistance. The refractory aggregate to which the above sodium lenanite and alumina cement are added is one whose particle size has been adjusted using one or more basic materials such as magnesia clinker, chromite, and dolomite clinker as main raw materials, or One or more of spinel, chromium oxide, alumina, graphite and calcium carbonate is added as an auxiliary raw material to the powder to adjust the particle size to a predetermined value. The purpose of adding the auxiliary raw materials in the above aggregate is mainly as follows. Spinel: It has a smaller coefficient of thermal expansion than magnesia, so it is especially added to fine powder parts to improve heating characteristics. Chromium oxide...Prevents slag infiltration. Alumina: To obtain a spinel bond through reaction with magnesia, and to create a dense structure as an ultra-fine powder. Graphite: It has the property of not being easily wetted by molten metal or molten slag, so it prevents infiltration of molten material. Calcium carbonate: Enriches the matrix with CaO components, reacts with the slag when it enters the slag, and raises the melting point of the slag. In addition to the aggregate, binder phase, and alumina cement described above, the castable refractory of this invention also contains sodium phosphate, polyphosphate, oxycarboxylate, and naphthalene as deflocculants to increase fluidity during construction. Sulfonates, and carboxylic acids as hardening modifiers for alumina cement.
Carboxylate, citric acid, borax, boric acid, Ca
Adding (OH) ₂ LiCO ₃ and a small amount of metal aluminum or the like as a drying accelerator is effective in improving workability. Table 1 shows the formulation contents and test results of Examples of the present invention and conventional products (Comparative Examples).

【table】

[Table] As is clear from Table 1, the high-temperature hot strength of the conventional products of Comparative Examples 1 to 3, which used alumina cement or Ca(OH) ₂ and sodium phosphate as binders, was 10 Kg/cm ² In contrast, the examples of the present invention exhibited extremely high hot strength of 62 to 110 Kg/cm ² . As explained above, this invention improves high-temperature hot strength by adding a pre-synthesized binder phase to basic aggregate and alumina cement to suppress the phenomenon that the binder phase is destroyed at high temperatures. It is 10 times better than conventional products, and has an average structure, so it can achieve a long life as a refractory for various molten metal containers and industrial furnaces.

Claims (1)

[Claims] 1. A refractory aggregate prepared by adjusting the particle size of one or more of magnesia clinker, chromite, and dolomite clinker, or spinel, chromium oxide, alumina, graphite, and calcium carbonate as auxiliary raw materials. A basic castable refractory characterized by adding synthesized sodium lenanite and alumina cement to a refractory aggregate whose particle size has been adjusted by adding one or more types. 2. The basic castable refractory according to claim 1, wherein the amount of sodium lenanite added is 1 to 15% by weight based on the total amount with the refractory aggregate. 3 The amount of alumina cement added is 1 to 8 with respect to the total amount of refractory aggregate and sodium lenanite.
% by weight of the basic castable refractory according to claim 1 or 2.