DE4317383A1 - Fire-resistant material for use as liner for pig iron@ tapping spouts - contg. spinel aggregate plus silicon carbide to hydrophilic carbon of specific particle size to high corrosion-resistance - Google Patents

Abstract

The claim concerns an unshapen, fire-resistant casting material contg. a fire-resistant aggregate of principally MgO-Al2O3 spinel together with Al2O3, silicon carbide, carbon and binder. Silicon carbide is present at a concn. of 5-20 wt.% and as particles of min. dia. 30 microns. Carbon is also present at a concn. of 5-20 wt.%, particle size max. 2 mm, and undergoes treatment to become more hydrophilic in nature. USE/ADVANTAGE - Used as a lining material for pouring spouts in e.g. tapping of pig iron from a furnace. Shows improved corrosion-resistance against molten metal and slag due to control of particle size and concn. of silicon carbide and the introduction of specialised carbon in specific quantities.

Description

The present invention relates to an unshaped refractory casting material for use in the formation of Lining for runners, especially the main runner for receiving pig iron tapped from a blast furnace. In particular, the invention relates to a refractory Casting material that improved such liners Resistance to corrosion by the metal (molten pig iron), especially FeO.

Refractory casting materials are used to form the Linings of runners for receiving from blast furnaces used tapped pig iron. At the current trend to an enlargement of the blast furnaces, a shortening of the Intervals between the pig iron taps, an increase the tapped amount of pig iron and an increase in Temperature of the tapped pig iron, however, are the Operating conditions for the refractory casting materials always harder, especially in the main runner, which is from the Tap hole to the slag dam runs. To tighten this Conditions have become different Materials developed. Recently developed materials exclude an unshaped refractory casting material Alumina Carbon, an unshapely refractory Casting material of alumina-silicon carbide-carbon and a refractory casting material of spinel-silicon carbide Carbon containing a magnesia-alumina spinel as the main component and furthermore alumina, Silicon carbide, carbon and a binder. These refractory casting materials are described in JP  A-53-82824, JP-A-55-37459 and JP-A-55-85478. (The Term "JP-A" means "unaudited published Japanese patent application ".)

In the main gutter of a blast furnace separate the molten pig iron and the slag from the Gap hole to be drained from each other due to a Difference in specific gravity, with the molten pig iron is located under the slag, and flow through the main runner. The refractory material suffers the strongest corrosion at the interface between the molten pig iron and the slag, so that the narrow Areas in the area of this interface are usually deep erode. This phenomenon can be seen in the formation of highly reactive FeO at the interface between molten Cast iron and the slag and FeO's reaction with the attributed refractory material. There will be action taken to suppress the corrosion by a Magnesium oxide-alumina spinel in refractory Materials used are less easily due to FeO eroded.

However, if silicon carbide in such a refractory Composition, it reacts with FeO as follows:

SiC + 2FeO → SiO ₂ + 2Fe + C (1)

whereby the effect of using the magnesia Alumina spinel is reduced.

As silicon carbide to ensure the Corrosion resistance to slag, Resistance to chipping / flaking (Thermal shock resistance) and other properties of the refractory material is causing the Removal of silicon carbide has a problem that these properties deteriorate.

An object of the present invention which has been made to To overcome the problems described above is the Improvement of an unshaped refractory casting material from Magnesia-alumina spinel / silicon carbide / Carbon type by regulation of the particle diameter and the amount of silicon carbide and by introducing a specific carbon in a specific amount.

The present invention provides an unshaped refractory Casting material available, which is a refractory aggregate which consists of a magnesium oxide-alumina Spinel as the main component and the balance alumina, Silicon carbide, carbon and a binder, wherein the silicon carbide in an amount of 5 to 20 wt.% of the refractory material is included and off Silicon carbide particles with particle diameters of 30 microns or more and the carbon in an amount of 5 to 20 wt.% Of the refractory material is included and off Carbon particles with particle diameters of 2 mm or less exists, that of a hydrophilization treatment were subjected.

Brief description of the figure

FIG. 1 is a graph showing the relationship between the Carbon amount and the necessary amount of water in one shows unshaped refractory casting material.

Magnesium oxide-alumina spinel is a compound having a chemical composition which theoretically consists of 28.3 wt% MgO and 71.7 wt% Al ₂ O ₃ . Since magnesia-alumina spinel products, which are highly pure and of theoretical chemical composition, are very expensive and therefore unsuitable for use as refractory materials in large quantities, for use in the present invention a less expensive commercially available spinel product may be used which is produced industrially by an electric melting or combustion process as a mass product. Although the chemical composition of such alumina-magnesia spinel products produced industrially in bulk does not exactly match the theoretical chemical composition, the use of these industrial products never presents a hindrance to the practicability of the present invention because of their crystalline composition the necessary magnesium oxide-alumina spinel is formed.

Such magnesia-alumina spinel products were already in refractory linings for melting furnaces and Melting furnace troughs are used in steelworks and are therefore no new material. However, the mechanism of the Dissolution and corrosion of in a refractory material contained magnesium oxide alumina spinel not fully elucidated.

The present inventors investigated the local dissolution and corrosion by which the refractory material in the portion of the main runner around the slag-molten pig iron interface, ie in the so-called metal zone, is eroded at an acute angle. As a result, it was found that although the magnesia-alumina spinel has excellent corrosion resistance to molten pig iron (FeO resistance), it is eroded by the slag which coexists with the pig iron and simultaneously reacts with SiO ₂ derived from silicon carbide, as shown in the above scheme (1), whereby low-melting substances are formed, e.g. Enstatite (MgO SiO ₂ ) accelerates the corrosion of the magnesia-alumina spinel in the refractory material.

In order to retard the above reaction, it is preferable that the Coarse magnesium oxide-alumina spinel Spinel particles of 74 microns or more. In the refractory Material of the present invention are magnesium oxide Alumina spinel levels of less than 40 wt.% Not  very effective for improving corrosion resistance, while spinel levels greater than 70 wt% Accelerated corrosion by slag and deteriorated Thermal shock resistance, although a improved resistance to corrosion molten pig iron is obtained.

As the alumina, one may be used industrially after the electric melting or burning process as Mass produced and a chemical purity of 98% or more and that has the α-crystal structure, the is also stable up to high temperatures.

Unlike a magnesia-alumina spinel becomes Aluminum oxide corroded by FeO, that in the constituents is contained in molten pig iron, but becomes less easily eroded by the slag components. Therefore, it is preferred to use alumina so that it at least a part of the refractory aggregate component (s) and the Fine particle component (s) of the refractory material of less than 74 μm, for the magnesium oxide Alumina spinel particles are difficult to use.

If the amount of alumina used is less than 3% by weight is, the sintering of the fine particles runs in refractory material inadequate, and therefore the resulting structure of the refractory material no have sufficient strength. On the other hand Alumina amounts of more than 15 wt.% Therefore not preferred because the refractory material then by molten pig iron suffers corrosion.

Silicon carbide is not only known Resistance to corrosion by various molten metals and slags, but also good Resistance to spalling (Thermal shock resistance). However, it decomposes by reaction with FeO in molten steel or  molten pig iron is formed, as by the above given scheme (1) is shown, reducing the resolution and Corrosion of refractory materials containing magnesium oxide Use alumina spinels, is accelerated. In the Silicon carbide is used in the present invention to provide the Disadvantages of the refractory material contained To avoid magnesia-alumina spinel, d. H. around the corrosion resistance to slag and the To improve thermal shock resistance.

As the silicon carbide for use in the present invention, an industrial mass product can be used. The higher the purity of the silicon carbide, the more it is preferable from the viewpoint of corrosion resistance. The lower limit for purity is about 85%; Silicon carbide products having such purities are often used for refractories. The present invention employs silicon carbide consisting of coarse silicon carbide particles of 30 μm or more in an amount of 5 to 20% by weight based on the refractory material to retard the progress of the reaction shown by the above-mentioned Scheme 1 , and thereby to reduce the formation of SiO ₂ whose reaction with the magnesia-alumina spinel leads to the dissolution and corrosion of the refractory material. If the silicon carbide particles are smaller than 30 μm, the reaction with the magnesia-alumina spinel proceeds faster, which accelerates the dissolution and corrosion of the refractory material. The upper limit of the particle diameter of the silicon carbide is preferably 5000 μm. If the amount of the silicon carbide used is less than 5% by weight, the corrosion resistance to slag and the thermal shock resistance of the structures obtained from the refractory casting material are insufficient. If its amount exceeds 20% by weight, the corrosion resistance to FeO-containing molten pig iron is significantly deteriorated, though the corrosion resistance and thermal shock resistance are improved.

Carbon is made by various molten metals and Slags less easily wetted and has an excellent Corrosion resistance, for example molten steel or molten pig iron and opposite the FeO contained therein, although it is a disadvantage in that it is oxidized and consumed when it is heated in air at high temperatures. Moreover, it is well known that carbon is another Advantage to the effect that due to its low Expansion coefficients compared to its resistance thermal flaking is high. An example of refractory Materials that take advantage of carbon are Magnesium oxide carbon brick, which is considered refractory Material for use in converters and electric ovens developed and actually gave good results.

However, in the case of unshaped refractory casting materials, which are fluidized and hardened by kneading with water and are then formed, the incorporation of carbon into increased amount in an increase in the necessary amount of water to obtain a certain fluidity due to water-repellent properties of carbon. When The result is shaped structures made from such Casting materials were obtained, deficient in their Compactness, and molten cast iron and slag penetrate into the structures, causing their dissolution and corrosion is accelerated. That's why currently inserted in refractory materials Carbon amount kept as small as possible.

A feature of the present invention is that in order to an advantage of metal resistance (FeO resistance) of a magnesia-alumina spinel and um to improve the resistance to slag corrosion, which is a disadvantage of the spinel, the amount and the  Particle diameter of the silicon carbide used in specific areas are regulated and carbon in increased amount is used. To insert in a big one Quantity is necessary that the used carbon before so treated that it is easily wetted by water, d. H. that the surface of the carbon particles is hydrophilized.

Examples of carbon materials suitable for such Hydrophilization treatments can be used include pitch, mesophase carbon, soot, coke and Graphite. Hydrophilic carbon can be made by adding for example sodium linoleate, ammonium humate, Sodium alginate, sodium lignosulfonate or a Sodium alkylbenzenesulfonate to one of these Carbon materials, kneading the mixture and then Drying be achieved with a spray dryer.

Either a manufactured carbon or a trade available carbon product, the one Hydrophilization treatment may be used become. That is, it is important to have a hydrophilized one Use carbon to keep it in an increased amount can be installed without increasing the amount of water that while kneading to obtain the required fluidity of the Unformed refractory casting material is necessary. Figure l shows the relationship between the amount of carbon contained and the amount of water needed to receive a given Fluiditätsgrads is required, each with respect to one Carbon, that of a hydrophilization treatment was subjected, and an untreated carbon.

A basic composition which corresponds to the composition of Example 1, which is shown in Table 1, corresponded to FIG Except that the hydrophilized carbon omitted was mixed with hydrophilised carbon, wherein the amount of hydrophilized carbon is from 2 to 14 Wt.%, Based on the refractory material, was varied,  and the amount of water necessary to achieve that each of the resulting refractory compositions Flow value of 150 mm was determined. It was also the same basic composition as above with untreated Carbon mixed, the amount of untreated Carbon from 2 to 10% by weight, based on the refractory Material, was varied, and the amount of water necessary was so that each of the resulting refractory Compositions showed a flow value of 150 mm was certainly. As a result, the refractory required Composition containing 10% by weight of untreated carbon contained, the addition of 8% water, which is very large in the Compared to 5.5% water addition for the refractory Composition containing 10% hydrophilized carbon contained. If such a hydrophilized carbon has a particle diameter of more than 2 mm refractory structures made from the refractory casting material be obtained, a deteriorated strength or that refractory material has deteriorated Corrosion resistance due to oxidation of the Carbon particles. In addition, the amount of carbon that can necessary to improve corrosion resistance, the more reduced the smaller the Particle diameter is. If the amount of used Carbon is less than 5 wt.%, Adequate Corrosion resistance can not be achieved. If his Quantity exceeds 20% by weight, it becomes necessary to add water in one to admit to large amount, even though the carbon was hydrophilized so that the refractory structures, the were obtained from the refractory casting material, a deteriorated compactness (density) and therefore a bad one Have corrosion resistance.

As a binder, aluminum oxide cement, an ultrafine Silica powder (amorphous) or refractory clay. In the case of using alumina cement, it may be used in in an amount of 0.5 to 2% by weight, based on the refractory Material used. If its amount is less than 0.5  Wt.%, Show from the refractory casting material structures obtained have insufficient dimensional stability after installation. If its amount is more than 2% by weight is, the refractory material has deteriorated Corrosion resistance due to the influence of CaO, the contained in aluminum oxide cement and has defects in its refractory properties and corrosion resistance on.

In the case of using refractory clay, this may be used in in an amount of 0.1 to 3% by weight, based on the refractory Material, be included. If its amount is more than 3% by weight is, the resulting composition has too high Viscosity and therefore a poor casting ability. In the case of Use of ultrafine silica powder can do this in one Amount of 0.1 to 3 wt.%, Based on the refractory Aggregate, are used. The addition of this powder, the of spherical, amorphous silica particles of mostly 1 μm or less, increases the high-temperature strength.

A peptizer, such as sodium hexametaphosphate, can be used in one Amount of 0.01 to 0.5 wt.%, Based on the amount of refractory aggregate, used to the To improve the dispersibility of these powder components.

The present invention will be described in greater detail below In detail with reference to the following examples explained, but should not be limited to these.

Examples and Comparative Examples

Comparative Example 1 shows a refractory composition, the 8% parts by weight ultrafine silicon carbide powder contains. Comparative Example 2 represents a refractory Composition is 3 parts by weight of an ultrafine Silicon carbide powder contains: This comparative example was the standard for the corrosion resistance index  used. Comparative Example 3 shows a refractory Composition with a small amount of spinel aggregate.

1) Resistance to metal (FeO resistance)

Examples 1 and 2 according to the present invention sat both a fine silicon carbide powder of 30 microns or more and Carbon, which is a hydrophilization treatment had been subjected. The refractory compositions of Examples 1 and 2 gave good results, the Corrosion index against metal (compared to FeO) 84 and 81, respectively scam.

2) Flow value

In general, it is said that the incorporation of larger quantities fine carbon powder generally in a deteriorated one Flowability results. However, the refractories were Compositions of Examples 1 and 2 containing carbon in Contains quantities of even 10 parts by weight and more, both in the flowability equal to the compositions of Comparative examples containing 3 parts by weight of carbon contained.

3) Strength after curing

The refractory compositions cured for 24 hours had a strength that was sufficient the structures no longer deformed, which shows that the Amount of alumina cement in the examples was suitable.

4) Compressive strength after firing at 800 ° C

The strength at 800 ° C, allegedly in refractory Compositions using aluminum oxide cement should be low, was measured. As a result, the Strength sufficiently high.  

5) Properties after firing at 1450 ° C

The extent of change in the length direction was within of the ± 0.1% range, indicating that the refractory Materials had excellent dimensional stability.

Remarks Aluminum oxide aggregate | 8,000-44 μm Spinellaggregat Magnesium oxide-alumina spinel 8,000-74 μm Alumina fine powder 44 μm or less Siliciumcarbidfeinpulver 30-125 μm Ultrafine silicon carbide powder 10 μm or less Hydrophilized carbon 2 mm or less Fireproof clay Kaolin clay (SANAGE) Ultrafine silica powder about 1 μm or less

test method

Flow value (mm): Measurement was made in accordance with JIS R2521. To the Casting suitable flow values are between 130 and 150 mm. A flow cone with an inner diameter of 100 mm was filled with 1 kg of a sample and then onto the flow table a flow tester provided. After that, the cone became removed and left the sample mass remaining on the table one flows, by pushing the table so that he in moving up and down. By the abutment was the Sample reduced in height and spread over one large area out. The longest and the shortest diameter of the spread material were measured, and the Average of these two was used as a flow value.

Corrosion resistance test: Resistance to corrosion by metal and corrosion resistance to slag were evaluated as follows: A high frequency melting furnace for test purposes was lined inside with refractory test bricks. Blast furnace pig iron and blast furnace slag (basicity: CaO / SiO ₂ = 1.3) in a weight ratio of 1: 1 were melted in the furnace and the melt held at 1550 ° C for 6 hours. The depth of the resulting corrosion was then measured. The corrosion depth for Comparative Example 2 was set to 100.

Compressive strength after 24 hours of hardening (kg / cm ² ):

Each refractory sample was placed in a printing form (50⌀ x 50H) poured in and then closed. After the printing form 24 Hours at 60 ° C, the sample was removed from the Printing form taken out. The compressive strength then became measured using a compression tester.

Compressive strength after firing at 800 ° C (kg / cm ² ):

The respective refractory sample was placed in a printing form according to Cast JIS R2653. After holding the printing form on Room temperature (20 ° C) for 24 hours, the sample was made the printing form taken out. Then it was dried at 110 ° C for 24 hours at 800 ° C for 3 hours in one burned in a reducing atmosphere. The compressive strength was then measured using a pressure test machine.

Properties after firing at 1450 ° C. (degree of change in length (%), breaking modulus (kg / cm ² ), and cold breaking strength (kg / cm ² )):

Each sample of a refractory material was placed in a Die cast in accordance with JIS R2653. After holding the printing form at room temperature (20 ° C) for 24 hours the sample became removed from the mold. Then the sample went to Drying at 110 ° C for 24 hours at 1450 ° C for 3 hours fired under a reducing atmosphere. The properties the sample was checked as follows.

• 1) The change of the sample in size before and after Burning was measured to increase the degree of change in length check.
• 2) Breaking strength was determined using a triple Point bending tester measured.  
• 3) Compressive strength was measured using a Pressure test machine measured.

As described above, linings for runners, especially main runners for receiving from blast furnaces tapped cast iron, in its corrosion resistance compared with molten pig iron improved by the Linings from the unformed refractory casting material are formed, which comprises a refractory aggregate, consisting of a magnesia-alumina spinel as Main component and the balance of alumina, Silicon carbide, carbon and a binder, wherein the refractory material characterized in that the Silicon carbide in the refractory aggregate in an amount of 5 to 20 wt.% Contains and silicon carbide particles with particle diameters of 30 microns or more and that the carbon in the refractory aggregate in an amount of 5 is contained to 20 wt.% And made of carbon particles with Particle diameters of 2 mm or less and one Hydrophilization was subjected.

Claims (1)

Unshaped refractory casting material containing a refractory aggregate consisting of a magnesium oxide Alumina spinel as the main constituent and as the remainder Alumina, silicon carbide, carbon and a Binder, wherein the silicon carbide in an amount of 5 to 20 wt.% Of the refractory material is included and off Silicon carbide particles with particle diameters of 30 microns or more and where the carbon is in an amount from 5 to 20% by weight of the refractory material and consists of carbon particles, the particle diameter of 2 mm or less and one Hydrophilization treatment were subjected.