GUNNING REFRACTORY COMPOSITION

Abstract: The object of the present invention is to provide a spray-on (gunning) refractory composition having high anti-stripping property, adhesive strength and corrosion resistant property suitable even for high temperature operation in steelmaking furnace. To refractory materials, resol type phenolic resin powder, being in semi-melting state at 80°C to 500°C and having weight average molecular weight of 1,000 to 15,000 and residual monomer of not more than 1,000 ppm, or phenol-formaldehyde resin powder, being in heat melting, self-hardening state at 100°C to 500°C, having weight average molecular weight of 1,000 to 15,000 and residual monomer of not more than 1,000 ppm, and containing reactive methylol group by 6 to 9 weight %, said phenol-formaldehyde resin powder being added by 2 to 10 weight %, and pitch with high softening point of 100°C to 500°C being added by 2 to 10 weight %.

Description: The present invention relates to a spray-on (gunning) refractory composition used e.g. for the furnace wall or bottom of steelmaking facitilities such as ladles, converters, electric furnaces, and in particular, to a spray-on refractory composition having high service life, adhesiveness and corrosion-resistance. In the past, as spray-on (gunning) refractory composition used for repair of e.g. the furnace wall or bottom of steelmaking facilities such as converters, electric furnaces or ladles a composition has been known, which contains an inorganic binder such as phosphate or silicate added to a refractory aggregate in an amount of 3 to 10 weight %. However, this conventional type composition is disadvantageous in that service life is not sufficient when exposed to severe operating conditions of the steelmaking furnaces. The disadvantages may be attributed to the facts that the inorganic binder forms substances of low melting point when heated and bonded and causes shrinkage, that the binder migrates as water is rapidly evaporated because it is used in aqueous solution and adhesive strength is reduced and the binder is separated, and further, that it is easily dissolved and service life is reduced because the inorganic binder contains much liquid phase in matrix. Further, a refractory composition is known, which is obtained by adding an inorganic binder such as phosphate or silicate in an amount of several weight % and an organic binder such as pitch, or phenolic resin in an amount of 10 weight % to the refractory aggregate. The composition of this type is also disadvantageous in that the above problems are not solved yet because the inorganic binder exerts extensive influence on the adhesiveness. Also, in case a phenolic resin is used as the organic binder, it often hinders adhesive performance of the inorganic binder and the refractory composition is very likely to drop or be stripped off. Further, carbon generated by carbonization of the organic resin is oxidized by alkaline components of the inorganic binder, and this reduces the favorable effect of carbon. Further, another type of refractory composition is known, which is produced by adding pitch or a novolak type phenolic resin to the refractory aggregate, but this is also disadvantageous in that it flows down along high temperature furnace walls during heating and bonding, and it does not have sufficient adhesiveness and is not usable as a spray-on refractory composition. There is also a castable (prepared unshaped) refractory composition using phenol-formaldehyde type resin. For example, Japanese Patent Publication 62-38382 discloses a method to use only a powder of the above resin added to an inorganic powdery material as a binder, or a method to obtain a binder by combining a water-soluble organic binder, an auxiliary forming agent, a petroleum product and its byproducts as auxiliary components for the binder. These methods are disclosed for applications as e.g. wall material fire-retardant paint or fire-retardant pad of e.g. blast furnaces or converters. In case the mixture of these inorganic powdery materials is used as spraying material and if only a phenol-formaldehyde type resin is used for the binder, warping occurs on the portion of the facilities to be sprayed, and there is also a problem in adhesiveness. Also, in case another auxiliary component than pitch having a high melting point is used, fluidity and form-keeping property are not sufficient as spraying material, and adhesiveness is lower and it runs down. When the petroleum type auxiliary component is added, adhesiveness cannot be improved and warping of the portion to be sprayed is not prevented. US-A-4,298,391 discloses a hot repair gun refractory mix which comprises a granulated material which is prepared by covering the suface of a carbonaceous substance particle, which is a petroleum or coal pitch particle having a softening point of 200° to 300°C, with a fine refractory powder. It is an object of the present invention to provide a spray-on (gunning) refractory composition, which is high in anti-stripping property, adhesive strength and corrosion-resistance and is suitable for high temperature operation in steelmaking furnaces. A spray-on refractory composition according to the first aspect of the present invention comprises a refractory aggregate, a resol type phenolic resin powder which is in a semi-molten state at 80°C to 500°C and has a weight average molecular weight of 1,000 to 15,000 and a residual monomer content of not more than 1,000 ppm, said resin powder being added to the refractory aggregate in an amount of 2 to 10 weight %, and a pitch having a high softening point of 100°C to 500°C which is added to the refractory aggregate in an amount of 2 to 10 weight %. A spray-on refractory composition according to the second aspect of the invention comprises a refractory aggregate, a phenol-formaldehyde resin powder, which is in a heat melting and self-hardening state at 100°C to 500°C, has a weight average molecular weight of 1,000 to 15,000 and a residual monomer content of not more than 1,000 ppm and contains reactive methylol groups in an amount of 6 to 9 weight %, said resin powder being added to the refractory aggregate in an amount of 2 to 10 weight % and a pitch having a high softening point of 100°C to 500°C which is added to the refractory aggregate in an amount of 2 to 10 weight %. In the spray-on refractory compositions of the present invention, the water-insolbule resol type phenolic resin powder which is in a semi-molten state at 80°C to 500°C or the heat-melting, self-hardening type phenol-formaldehyde resin powder are used as bonding components. As a result, it is possible to have satisfactory adhesiveness during heating and bonding. By adding the pitch with a high softening point to prevent stripping of the portion to be sprayed after bonding, it is possible to obtain a refractory composition having high anti-stripping property, adhesive strength and corrosion resistance suitable for high temperature operation in steelmaking furnaces. As the refractory materials used in the present invention, refractory materials commonly used can be used, e.g. fused alumina, sintered alumina, sintered mullite, calcia partially stabilized zirconia, yttria partially stabilized zirconia, chamotte, silicon carbide, or a mixture of these substances may be used. In particular, it is preferable to use MgO or MgO-CaO type aggregate with the particle size adjusted and graded to 4 mm or less, e.g. basic aggregate such as electrofused magnesia, sintered magnesia clinker, natural magnesia clinker, natural dolomite clinker or synthetic dolomite clinker. The resol type phenolic resin powder used in the first spray-on refractory composition of the present invention is insoluble or hardly soluble in water and is in a semi-molten state at 80°C to 500°C, or more preferably at 80°C to 200°C. "Semi-molten state" means a state, in which the material is softened and exhibits adhesiveness but is not perfectly molten. If the material is perfectly molten at a temperature lower than 500°C, it is not desirable because the material may be fluidized and flow down during heating and bonding when it is sprayed on a vertical wall or the like. Also, a material softened at 500°C or a higher temperature exhibits no adhesiveness in the temperature range where adhesiveness is required, and the material cannot fulfill the function as a binder. Weight average molecular weight of the resol type phenolic resin is 1,000 to 15,000, or more preferably 1,000 to 10,000. In case of a novolak type phenolic resin having a weight average molecular weight of less than 1,000 (weight average molecular weight of 300 to 800) or a resol type phenolic resin having a weight average molecular weight of 200 to 700, the material is perfectly molten at 100°C or at lower temperature and is fluidized. It flows down during heating and bonding, and it is not desirable as the spray-on refractory composition. In the second spray-on refractory composition of the present invention, a heat-melting and self-hardening type phenol-formaldehyde resin powder is used, which is insoluble or hardly soluble in water and contains reactive methylol group in an amount of 6 to 9 weight %, or more preferably 8 to 9 weight %, is molten at 100°C to 500°C, or more preferably at 100°C to 200°C and shows gelating (self-hardening) property. If it contains the methylol group in an amount of more than 9 weight %, reactivity becomes too high, and the gelated hardened material is turned to fragile, and this causes problems in adhesive strength or mechanical strength of the portion to be sprayed. If it is less than 6 weight %, the material has poor reactivity for gelation, and this causes problems in adhesiveness and strength of the portion to be sprayed. The material molten at a temperature of more than 500°C has poor adhesiveness in the temperature range where adhesiveness is required, and it does not fulfill the function as a binder. In the heat-melting, self-hardening type phenol-formaldehyde resin powder as described above, the weight average molecular weight is 1,000 to 15,000, or more preferably, 3,000 to 15,000. If the weight average molecular weight is less than 1,000, content of the methylol group becomes higher, and this causes reactivity to be too high, and the gelated hardened material is turned to fragile. This is not desirable as a spray-on refractory composition. The resol type phenolic resin powder and the heat-melting, self-hardening type phenol-formaldehyde resin powder contains residual monomer in an amount of not more than 1,000 ppm, or more preferably not more than 500 ppm. If the residual monomer is contained in an amount of more than 1,000 ppm, extreme foaming occurs during heating and bonding. As a result, the texture of the sprayed portion is turned to a poor state, and adhesive strength is extensively reduced. The resol type phenolic resin powder has an average particle size of 15 to 20 µm. As commercially available products, there are, for example, PR-Q-731 and PR-Q-731V produced by Sumitomo Durez Co., Ltd. The heat-melting, self-hardening type phenol-formaldehyde resin powder has an average particle size of 15 to 20 µm. As commercially available products, there are, for example, "BELPEARL" S-870, S-890 and S-895 manufactured by Kanebo Ltd. The resol type phenolic resin powder or the heat-melting, self-hardening type phenol-formaldehyde resin powder is added in an amount of 2 to 10 weight %, or more preferably, 3 to 7 weight %, to the refractory aggregate. If the resin powder is added in an amount of less than 2 weight %, adhesiveness is low and trouble occurs when the spray-on refractory composition is applied on vertical walls. If it is added in an amount of more than 10 weight %, porosity becomes too high. This reduces corrosion-resistance and is not very economical. When the resol type phenolic resin powder or heat-melting, self-hardening type phenol-formaldehyde resin powder is used alone in the spray-on refractory composition, warping occurs on the sprayed portion after bonding and the material may be stripped off. To overcome this problem, the pitch with a high softening point is added. Its softening point (SP) is preferably 100°C to 500°C, or more preferably 120°C to 400°C. If the softening point of the pitch is higher than 500°C, expansiblity is lost because there remain almost no volatile components, and the effect to prevent warping of the sprayed portion after bonding is not obtained. The pitch with a high softening point is added to the refractory aggregate in an amount of 2 to 10 weight %, or more preferably 3 to 7 weight %. The ratio of the high softening point pitch to the resol type phenolic resin powder or the heat-melting, self-hardening type phenol-formaldehyde resin powder is preferably 70/30 to 30/70 in weight ratio. If the ratio of the pitch with high softening point to the resol type phenolic resin powder or the heat-melting self-hardening type phenol-formaldehyde resin powder is more than 70/30, the material may flow down along vertical walls during heating and bonding, and bonding ratio is reduced. If it is lower than 30/70, shrinkage of the resol type phenolic resin powder or the heat-melting, self-hardening type phenol-formaldehyde resin powder overcomes the expansion effect obtained by the pitch with high softening point. As a result, warping of the sprayed portion occurs due the shrinkage, and the material is often stripped off. In addition to the above components, other components such as a plasticizer, metal powder, and when necessary, a small amount of an additive such as a deflocculating agent and fibers are added to the spray-on refractory composition of the present invention. The plasticizer is added to improve the bonding ratio. For example, silica flour, clay, sepiolite, bentonite and calcium hydroxide may be used. It is added in an amount of 0.5 to 3 weight %, or more preferably 0.5 to 2 weight %, to the refractory aggregate. Metal powder is added to improve strength and to prevent oxidation of carbon as caused by the resol type phenolic resin powder or the heat-melting, self-hardening type phenol-formaldehyde resin powder and the pitch with high softening point. For example, powder of aluminum, silicon and aluminum-magnesium alloy may be used as the metal powder, and it is added to the refractory aggregate in an amount of 0 to 5 weight %, or more preferably, 0 to 3 weight %. If it is higher than 5 weight %, it is not desirable because texture of the sprayed portion becomes too porous. The deflocculating agent is added when necessary to improve denseness of the texture of the sprayed portion. For example, an inorganic deflocculating agent such as sodium hexametaphosphate and sodium silicate, or an organic deflocculating agent such as sodium polyalkylallyl sulfonate and polyacrylic acid salt may be used, and it is added to the refractory aggregate in an amount of 0 to 1 weight %, or more preferably 0 to 0.5 weight %. Fibers are added when necessary for preventing the running of spray slurry along vertical walls. For example, inorganic fibers such as alumina fibers, carbon fibers, natural fibers such as hemp, or organic fibers such as organic synthetic fibers may be used, and the fibers are added to the refractory aggregate in an amount of 0 to 0.2 weight %, or more preferably 0 to 0.1 weight %. After water is added to the mixture of the above components of the spray-on refractory composition of the present invention, it is sprayed e.g. to the furnace wall or bottom of steelmaking facilities by a normal procedure, and it is then heated and hardened. [Examples 1 to 18 and Comparative Examples 1 to 6] To the aggregates having weight ratios as shown in the following Tables 1 to 4, the additives were added in weight ratios shown in the same Tables 1 to 4, and spray-on refractory compositions of the present invention (1 to 18) were obtained. Also, to the aggregates of weight ratios shown in Tables 4 and 5, the additives were blended in weight ratios shown in the same Tables 4 and 5, and spray-on refractory compositions for comparison (Comparative Examples 1 to 6) were obtained. To each of the spray-on refractory compositions, water was added in an amount of 22 to 24 weight %, and they were sprayed on a panel in an experimental furnace kept at 1,000°C. Bonding ratio (%) of the spray material, adhesive strength (MPa), apparent porosity (%), the results of slag test at 1750°C for 3 hours, and the results of the actual furnace test using a 250-ton converter (the results of longevity test for high temperature tapping at 1700°C) are shown in Tables 1 to 5. In the results of the slag test, it is shown that, the smaller the index is, the more satisfactory the corrosion resistance is. In the results of actual furnace test, it is shown that, the higher the index is, the higher the longevity is. Physical properties of "BELPEARL" S-890 and S-895 used in the above examples were as follows: "BELPEARL" S-890 Weight average molecular weight 10,000 Softening temperature 100°C Residual monomer 300 ppm Average particle size 15 to 20 µm "BELPEARL" S-895 Weight average molecular weight 6,000 Softening temperature 100°C Residual monomer 500 ppm Average particle size 15 to 20 µm INDUSTRIAL APPLICABILITY The spray-on refractory composition of the present invention is high in adhesive strength and is very unlikely to be stripped off from the bonded surface. Slag penetration is shallow, and high temperature volume stability is high. Stripping of the material from intermediate layer and damage rarely occurs. Compared with the conventional type spray-on (gunning) refractory material, service life of the spray-on refractory composition of the present invention is by 3 to 5 times longer in case of ordinary type of steel. Service life is also long enough in case of steel of high temperature tapping at 1700°C or more. Accordingly, the spray-on refractory composition of the present invention is suitable for applications on the furnace walls or bottom, of steelmaking facilities such as converters electric furnaces or ladles.

Claims: A spray-on refractory composition, comprising a refractory aggregate, a resol type phenolic resin powder which is in a semi-molten state at 80°C to 500°C and has a weight average molecular weight of 1,000 to 15,000 and a residual monomer content of not more than 1,000 ppm, said resin powder being added to the refractory aggregate in an amount of 2 to 10 weight %, and a pitch with a high softening point of 100°C to 500°C which is added to the refractory aggregate in an amount of 2 to 10 weight %. A spray-on refractory composition, comprising a refractory aggregate, a phenol-formaldehyde resin powder, which is in a heat-melting self-hardening state at 100°C to 500°C, has a weight average molecular weight of 1,000 to 15,000 and a residual monomer content of not more than 1,000 ppm, and contains reactive methylol groups in an amount of 6 to 9 weight %, said resin powder being added to the refractory aggregate in an amount of 2 to 10 weight %, and a pitch with a high softening point of 100°C to 500°C which is added to the refractory aggregate in an amount of 2 to 10 weight %.

Inventors: MATSUDA TASUKU, SUGIMOTO HIROYUKI, TAKENAKA HIROSHI, TANAKA KOICHI, MATSUDA, TASUKU, SUGIMOTO, HIROYUKI, TAKENAKA, HIROSHI, TANAKA, KOICHI
Applicants: SHINAGAWA REFRACTORIES CO, SHINAGAWA REFRACTORIES CO., LTD.
Application year: 1995
Main classification: C04B35
IPC codes: C04B35