GB1560162A - Method for manufacture of slaking resistant solidifield spheres for use in refractories and said slaking resistant solidified spheres - Google Patents

Description

(54) METHOD FOR MANUFACTURE OF SLAKING RESISTANT SOLIDIFIED SPHERES FOR USE IN REFRACTORIES AND SAID SLAKING RESISTANT SOLIDIFIED SPHERES (71) We,SHOWA DENKO K. K., a Japanese Company of 13-9 Shiba-Daimon 1 chome, Minato-ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method for the manufacture of slaking resistant spheres formed preponderantly of CaO or CaO and MgO and used for the manufacture of refractories and to the slaking resistant spheres to be produced by said method for use in refractories.

Generally, various steels are produced in converters. Since the reducing reaction of the charge in a converter proceeds at an elevated temperature under extremely harsh conditions, the inner wall of the converter is lined with a refractory material highly resistant to such attendant phenomena as slaking, corrosion, spalling and fusion.

In recent years, the operating conditions under which such converters are used have been growing increasingly harsh. For example, all possible efforts have been directed to decreasing the wall thickness of the converter so as to increase the volume of charge, to minimizing the number of standby converters, and to improving the rate of operation of such converters as by discarding the conventional system of installing two converters to use them alternately, namely, to keep one in service and the remaining one at rest and instead adopting a new system of installing three converters to keep two of them in service and the remaining one at rest on a cyclic basis. Further, the conditions under which high carbon steel or special steel is manufactured have also been growing increasingly harsh.

In order for the converters to be effectively operable under such increasingly harsh conditions, it is imperative that particularly the refractory material to be used for lining the converter walls should be possessed of amply enhanced resistance to such adverse phenomena as slaking, corrosion, spalling and fusion which are attendant upon the reducing reaction proceeding on the charge inside the converters.

The refactory materials which have heretofore been used for lining the converters are of the type manufactured by burning natural dolomite, crushing the burnt dolomite into aggregates (natural dolomite clinker aggregates) of a prescribed size, molding the aggregates into blocks of a prescribed shape with the aid of tar bond or kneading said aggregates with ceramic bond and similarly molding the resultant mix into blocks and subjecting the molded blocks to a heat treatment. One salient disadvantage of the dolomite clinker aggregates is the fact that they are highly susceptible to slaking. Various efforts have been made to prevent the dolomite clinker aggregates from undergoing the phenomenon of slaking. As one possible measure, an attempt has been made to incorporate a mineralizing agent during the manufacture of clinkers.Generally, a mineralizing agent composed mainly of SiO2 or Fe2O3 has been used for the purpose. In the case of the mineralizing agent composed of SiO2, it becomes necessary to incorporate the agent in a large amount (corresponding to a proportion of 10 to 20neo, for example). The refractory material produced by using dolomite as the raw material possesses properties characteristic of a basic refractory substance. These characteristic properties of the refractory material are degraded by the large amount of SiO2 which is added to the refractory material in consequence of the incorporation thereto of said mineralizing agent.Besides, this addition results in a degradation of the resistance of the refractory material to the corrosion causable by the slag which is additionally contained in the charge in the converter during the operation. In the case of the mineralizing agent composed of Fez03, it effectively functions when it is added in an amount on the order of 2 5%. At elevated temperatures, however, Fe203 is readily affected by the reducing atmosphere present inside the converter, with the result that the volume of the clinker is varied and the volume of the molded refactory material is consequently varied.

In the case of a carbon-containing refractory material like the aforementioned tardolomite clinker produced by using tar bond, the consumption of the carbon component induces a degradation of the structure of the refractory material. Thus, the incorporation of the mineralizing agent composed of Fe203 aggravates the degradation of the characteristic.

properties of the refractory material.

The incorporation of the mineralizing agent which is primarily aimed at enhancing the resistance of the clinker to slaking, on the other hand, entails such adverse effects as are described above. More recently, therefore, a refractory material produced by using synthetic dolomite clinker as the raw material has been proposed for use in converters. The synthetic dolomite clinker is produced by adding MgO to natural dolomite clinker to form a mixture or preparing a similar mixture containing MgO and CaO at a fixed percentage composition by the reaction of sea-water magnesia and subsequently burning the mixture.

The dolomite-type refractory material is such that its possible loss by the fusion owing to the action of slag generally decreases with the increasing MgO content. As the MgO content in the refractory material increases, however, the denatured layer occurring in the refractory material which lines the converter wall gains in thickness and consequently renders the refractory material structurally susceptible to the phenomenon of spalling. The shortcoming that the dolomite-type refractory material having a high CaO content readily yields to slaking has not yet been completely eliminated. An improvement in this respect is earnestly longed for.

There has also been suggested a refractory material which is obtained by electrically fusing natural or synthetic dolomite, casting the fused dolomite in a mold and allowing it to set therein, crushing the solidified dolomite into aggregates of a desired size, again molding the aggregates with ceramic bond and firing the molded aggregates. This refractory material has not yet been accepted for practical use because it has a disadvantage that the manufacture thereof is difficult as compared with the aforementioned method resorting solely to firing, the resistance thereof to slaking, though superior to that manifested by the product of said method of firing, is not sufficient and the price thereof is high.

An object of the present invention is to provide a method for the manufacture of spheres of a refractory material excellent in resistance to slaking, corrosion, spalling and fusion and useful as the lining material for converters and to provide the refractory material obtained by the method.

According to the invention there is provided a method for the manufacture of slaking resistant spheres for use in the manufacture of refractories, which method comprises melting a mixture made up of 25 to 100% by weight of CaO, O to 75% by weight of MgO, O to 5% by weight of one or more members selected from Art'203, Fe2O3, CR203 and TiO2, plus trace elements incorporated as entrained originally by the raw materials making up the mixture, converting the resultant molten mass into molten droplets and subsequently solidifying the molten droplets into spheres by sudden cooling.

The invention also provides slaking resistant spheres for use in the manufacture of refractories, which are made up of a mixture of 25 to 100% by weight of CaO, O to 75% by weight of MgO, O to 5% by weight of one or more members selected from Art'203 Foe.03 Cr203 and TiO2, plus trace elements incorporated as originally entrained by the raw materials making up the mixture, and which have a smooth surface consisting of microcrystalline particles. The spheres of the present invention have a composition identical to that of the mixture used as the starting material, possess and excel notably in resistance to slaking, corrosion, spalling and fusion. They have properties quite suitable for use as the lining material in converters as compared with the conventional countertypes known to the art.

Figure 1 illustrates the solidified spheres of the present invention in the photographs taken through a scanning electron microscope at 43 magnifications (Figure 1(A)) and 435 magnifications (Figure 1(B)).

Figure 2 illustrates the particles obtained by crushing a cast mass having the same composition as the spheres of this invention, in the photographs taken through a scanning electron microscope at 43.5 magnifications (Figure 2(A)) and 435 magnifications (Figure 2(B)).

Figure 3 and Figure 4 are graphs showing the results of a test for slaking performed on the spheres obtained by the present invention and the particles obtained otherwise.

Figure 5 is a graph showing the heat of neutralization found of the spheres of the present invention in comparison with that found of the particles obtained otherwise.

Now. the method by which the slaking resistant spheres of the present invention for use in the manufacture of refractories are produced will be described.

To be specific, the method comprises melting a mixture made up of 25 to 100%by weight of CaO, 0 to 75% by weight of MgO, 0 to 5% by weight of one or more members selected from At203, Fe2O3, CR2O3 and TiO2, plus trace elements incorporated as originally entrained by the raw materials making up the mixture, converting the resultant molten mixture into molten droplets and subsequently solidifying the molten droplets by sudden cooling.

The molten mass having the composition described above is obtained by mixing the raw materials providing said components and then melting the resultant mixture. Practically, it is obtained by mixing light burnt dolomite, magnesia, calcia, alumina, iron oxide, chromium oxide, and zirconia in amounts slected to give a percentage composition falling within the range specified above and fusing the resultant mixture in an electric furnace. The sudden cooling which is given to the molten droplets in converting them into solidified spheres is generally carried out by either of the two methods described below.

One of them called the blasting method, comprises causing the molten mass to fall in a continuous flow and at the same time blowing a gas such as compressed air against the flow of the molten mass for thereby dispersing the molten mass in droplets and allowing the droplets to cool off rapidly into solidified spheres.

The other method called the centrifugation method comprises pouring the molten mass onto a rotary disk or rotary cylinder in motion for thereby causing the molten mass to be dispersed into droplets by virtue of the centrifugal force exerted by the rotary vessel and cooled rapidly into solidified spheres.

For the molten droplets to be cooled effectively by the blowing method, the proper pressure of blowing gas is in the range from 3.5 to 7.0 kg/cm2 and the proper volume of blowing gas against the descending flow volume of molten mass is in the range shown below.

Descending flow volume of molten mass (kglmin.) - = 3.2 to 6.4 Volume of blowing gas (kglmin.) To obtain effective cooling of the molten droplets by the centrifugation method, the proper speed of rotation (peripheral speed) of the rotary vessel is in the range of from 250 to 1300 m/min.

Figure 1 illustrates the spheres of the present invention. Illustrated therein are the spheres photographed through a scanning electron microscope at 43 magnifications (Figure 1(A)) and 435 magnifications (Figure 1(B)), said spheres being those obtained by melting at 2400 a mixture made up of 60% by weight of CaO and 40% by weight of MgO, allowing the resultant molten mixture to fall at a flow rate of 35 kg/min., blowing a current of air (compressed to 5200 g/cm2) at a flow rate of 4800 g/min. against the descending flow of molten mass for thereby dispersing the molten mass into molten droplets and solidifying the molten droplets by sudden cooling.

It is evident from the photographs that the spheres are globular in shape and have a smooth surface devoid of jags and notches and, therefore, have a small surface area. Their surface layers consist of microcrystalline particles. Consequently, they have a low surface activity.

Figure 2 illustrates the particles obtained by casting a mixture of the same composition as that of the mixture used as the starting material for said spheres and subsequently crushing the molded mass to a required particle size. Illustrated are the articles photographed through a scanning electron microscope at 43.5 magnifications (Figure 2(A)) and 435 magnifications (Figure 2(B)).

It is clear from these photographs that virtually all the surfaces of these particles are fractured because of the crushing given to said molded mass. The particles themselves are in the shape of polyhedrons which abound with corners. Abounding with jags and notches as well as corners, these particles exhibit a large surface activity. This is a possible cause which has prevented the conventional crushed particles from offering good resistance to slaking.

The spheres of the present invention, by nature, possess no fractured surfaces.

The spheres of the present invention comprise those which are solid and those which are hollow. These spheres, solid or hollow, are required to possess diameters generally ranging from 0.5 mm to 5 mm, with 10 mm as the allowable maximum. The spheres of this invention embrace those which are composed solely of CaO, those which are composed of CaO plus up to 75% by weight of MgO and those which are composed of CaO, MgO plus up to 5% by weight of one or more members selected from At203, Foe203, Cr2O2 and TiO2.

Spheres composed solely of CaO show considerably high resistance to slaking (The spheres composed of solely of CaO and manufactured by methods other than the method of the present invention have high surface activity and therefore are slaked rapidly). In the case of spheres containing MgO in addition to CaO, they fail to provide sufficient resistance to the phenomenon of spalling when their CaO content is not more than 5%. The inclusion of up to 5% by weight of one or more members selected from At203, Fe203, Cr203 and TiO2 brings about an improvement in resistance to slaking. If this content exceeds the upper limit 5%. however, the spheres are degraded in resistance to fire and to decay by fusion. This is because the spheres of this invention are, by nature, a basic refractory substance and the characteristic properties the spheres exhibit as a basic refractory substance are impaired by such an excess of content.

Although for practical purposes, the spheres of the present invention can have any composition which falls within the range specified above, the preferred range is from 25 to 70% by weight for CaO, from 30 to 75% by weight for MgO and from 0.5 to 3% by weight for one or more members selected from At203, Fe2O3, Cr203 and TiO2.

The results of experiments conducted with the spheres of the present invention will now be presented by way of proving their superior qualities.

Table 1 shows the characteristics of the particles used in the experiments.

Table 1 Composition (weight %) Apparent Bulk Apparent SiO2 A#2O3 Fe2O3 CaO MgO lg. specific densitity porosity Description loss density (%) A 0.46 0.37 0.55 62.03 31.63 0.56 particles obtained by allowing molten mass to solidify in mold and crushing the molded mass to a particle size of 1 - 3 mm.

B* 0.46 0.37 0.55 62.03 31.63 0.56 3.38 3.31 1.50 Spheres obtained by allowing molten mass to fall at flow rate of 35 kg/min.

and blowing compressed air compressed to 5.2 kg/cm2) at a rate of 4.8 kg/min.

against the descending flow thereby dispersing the molten mass into droplets 1 - 3 mm in diameter.

C* 0.35 0.099 0.084 98.20 0.87 0.32 Spheres obtained by the blowing (Calcia) method similarly to B.

D (Natural 0.96 0.25 2.27 60.57 31.05 0.93 3.32 3.26 2.59 dolommite clinker) E (Synthetic 1.06 0.32 0.82 26.26 71.15 0.46 3.43 3.38 1.81 Particles obtained by pulverizing clinker dolomite and selecting particles 1 to 3 mm in size clinker) E' (Synthetic 1.06 0.32 0.82 26.26 71.15 0.46 Particles obtained by pulverizing clinker dolomite to a size of 1 to 3 mm.

clinker) C' (Calcia) 0.35 0.099 0.084 98.20 0.87 0.32 Particles of calcia obtained by light burning at 1200 C.

C'' (Calcia) 0.35 0.099 0.084 98.20 0.87 0.32 Particles obtained by melting, casting * Spheres obtained by the method of the present invention. and pulverising mixture 1. Test speciments A, B, C and C" were tested for resistance to slaking at a constant temperature (30 ) and a constant humidity (90So). The results are shown in Fig. 3. In the graph, the vertical axis is graduated for ratio of weight increase (in % by weight) and the horizontal axis for length of time (in days). From the graph, it is clear that the test speciments B and C according to this invention far excel the test specimen A in terms of resistance to slaking, i.e. surface activity (energy of activation). Since the test speciment C" yielded to slaking rapidly after pulverization, no data on this speciment are indicated in the graph.

2. Test speciments B, E and D each 1 to 3 mm in particle size were tested for resistance to slaking at a constant temperature (30"C) and a constant humidity (90So). The results are shown in Figure 4. In the graph, the vertical axis is graduated for ratio of weight increase (in % by weight) and the horizontal axis for length of time (in days). It is evident from the graph that the spheres according to this invention exhibit greatly enhanced resistance to slaking.

3. Test speciments B, E and D were left to stand under natural conditions for 11 days by way of test for natural aeration.Their ratios of weight increase due to the aeration are listed below.

B - 0.12%by weight D - 10.70%by weight E - 5.70% by weight 4. In an autoclave, test specimens A, B, D, E and E' were maintained at 1520C and 78% of relative humidity under 2 atmospheres for one hour, to test for increase of weight and percentage of pulverization (ratio of particles having diameters less than 1 mm). The results are shown in Table 2 below.

Table 2 A B D E Increase of weight (%) 14.80 0.98 2.17 1.20 6.50 Percentage of pulverization 40.70 3.30 18.90 12.50 25.80 (% by weight) These data were obtained as follows.

After the standing in the autoclave, each test specimen was sifted and the portion retained on the sieve and the portion allowed to pass through the sieve were weighed.

Based on the weights thus obtained, the ratio of weight increase and the percentage of pulverization were calculated.

Let W l stand for the initial weight of test specimen, W2 for the weight of the same test specimen to be found after the specimen had been cooled off and then dried in an air chamber at 102 to 105"C, and W3 for the weight of the portion of particles of the treated test specimen retained on a sieve 1000 cm in mesh size after the particles had been sifted with said sieve.

W2-W1 Ratio of weight increase (%) = x 100 W1 Percentage of pulverization (%) = x -W3 x 100 W1 The values given in the table indicate that the ratio of weight increase in the test specimen B was extremely small as compared with any of the ratios of weight increase found in the other test specimens A, D. E and E'.

5. Test specimens A, B. C, D. Cand C" were tested for resistance to slaking by immersion in an amyl acetate solution at room temperature and by immersion in boiling water. The results are shown in Table 3.

Table 3 A B Amyl Boiling Amyl Boiling acetate water acetate water Ratio of weight increase (%) 0.462 15.08 0.147 1.796 Percentage of pulverisation (%, particles of diameters 0.596 72.75 0.109 13.80 less than 1 mm) C D C' C" Amyl Boiling Amyl Boiling Amyl Boiling Amyl Boiling acetate water acetate water acetate water acetate water 0.309 4.216 6.156 10.76 10.76 16.08 12.86 19.38 0.145 43.86 17.37 68.17 19.38 86.54 29.44 79.65 It is clear from the results that the test specimens B and C showed extremely small ratios of weight increase and similarly small percentages of pulverization as compared with other test speciments.

6. Test specimen B was subjected to a reheating treatment at varying temperatures indicated below and then was tested for resistance to slaking in an amyl acetate solution and boiling water. The results are shown in Table 4.

Table 4 1200 C 1500 C 1800 C Amyl Boiling Amyl Boiling Amyl Boiling acetate water acetate water acetate water Ratio of weight increase (%) 0.142 1.893 0.125 1.146 0.079 1.198 Percentage of pulverization (%, particles of diameters 0.115 14.80 0.094 8.40 0.132 3.46 Note: The treatment was given invariably for a period of two hours.

It is evident from the table that the reheating treatment enhanced the spheres resistance to slaking.

7. Spheres manufactured by the method of this invention and particles manufactured otherwise were compared with respect to heat of hydration. Since in the refractory materials, high resistance to slaking can naturally be associated with low heat of hydration and the magnitude "heat of hydration" serves as a criterion for the resistance to slaking, said spheres and particles were tested for heat of hydration.

Each test specimen (ranging from 1 to 3 mm in particle size) 0.1 to 0.2 g in quantity was added to I 10 mt of water and the heat of reaction was measured by a thermometric titration apparatus.

The test specimen representing the spheres of the present invention was prepared by the method of B indicated in Table 1. It was composed of SiO2 A2O3 Foe203 CaO MgO Ig.Loss 0.46 0.37 0.55 62.03 31.63 0.28 The other test speciment representing control particles was prepared by the method of A indicated in Table 1. It was composed of SiO2 At203 Fe203 CaO MgO Ig.Loss 0.43 0.38 0.56 61.89 31.73 0.56 The results are shown in Figure 5. In the graph of Figure 5, the vertical axis is graduated for heat of hydration (in calzg) and the horizontal axis for weight proportion (%) of CaO/MgO.

It is evident from this graph that the test specimen obtained by the blowing method of the present invention had a smaller heat of hydration than the test specimen obtained by molding the molten mass and then crushing the molded mass. This indicates that the spheres of the present invention excel in resistance to slaking.

In a total of seven experiments performed as described above, the spheres manufactured by the method of this invention were shown to excel notably over the spheres manufactured by the known methods in terms of resistance to slaking.

Now, the effect of the present invention will be demonstrated by reference to working examples of the invention.

Example 1: In a 300-KVA single-phase He molt electric furnace (of a tiltable model incorporating a tap, using a man-made graphite electrode 6 inches in diameter), 100 kg of light-burned dolomite (composed of 0.51% of SiO2, 0.20% of At203, 0.28% of Fe2O3, 63.00% of CaO, 33.04Go of MgO and 2.68% of ignition-loss fraction) and 70 kg of magnesia were used as raw material and their portions were laid to a thickness of about 15 to 20 cm and the charge was treated by passing an electric current therethrough. As the initial charge was converted into a molten mass, the remaining portions were spread piecemeal on the surface of the molten mass. The passage of the electric current (120 V) was discontinued after a total of 75 minutes of the treatment. Then, the electric furnace was gradually tilted to allow the molten mass to fall at a descending flow rate of 35 kg/min and, at the same time. compressed air (about 5.0 kg/cm2 of pressure) projected through a blowing nozzle at a flow rate of 4.8 kg min. was caused to disperse the descending flow of the molten mass, giving rise to molten droplets. The spheres collected in the collection chamber were left to stand therein for 30 minutes. then classified by particle size and weighed. Consequently; there were obtained 58930 g of particles. The properties of the particles thus obtained are collectively shown in Table 5.

Table 5 Large spheres Particle size distribution (4.6 to lmm) - 26470g of spheres: Small spheres More than 4.6 mm - 0.8% (1 to 0.35 mm) - 13940g 4.6 to 2.3 mm - 8.6% Deformed spheres - 14650g 2.3 to 1 mm - 56.1% Dust (less than 0.35 mm) - 3860g 1 to 0.35 mm - 34.5% Yield of spheres (So) - 68.6 Chemical analysis (weight %) MgO 58.17 True specific gravity - 3.45 CaO 38.98 Bulk density of particles - 2.79 Si02 1.14 AQ203 0.25 Fe203 12.6 Refractory bricks were manufactured from the spheres thus obtained by the blowing method, with the aid of tar bond. The manufacture involved a procedure which comprised molding raw materials mixed at fundamental proportions for brick production, permeating the molded mixture with tar and sintering the resultant mixture.The properties of the refractory bricks are shown in Table 7.

Example 2: By faithfully following the procedure of Example 1, 34.487 kg of quick lime (having 95.24% of total CaO, 0.95% of At203 + Fe203, 7.50% of Ca(OH)2, 1.00% of CaCO3 and 0.24% of SiO2) was melted and the molten mass was subjected to a blowing treatment described in Example 1 to afford blasted spheres. The results of the spheres are shown in Table 6.

Table 6 Large spheres Particle size distribution (4.6 to 1 mm) - 12219g of spheres: Small spheres More than 4.6 mm - 0% (1 to 0.35 mm) - 12267g 4.6 to 2.3 mm - 3.0% Deformed spheres - 3868g 2.3 to 1 mm - 46.9% Dust (less than 0.35 mm) - 486g 1 to 0.35 mm - 50.1% Chemical analysis (weight %) MgO 0.87 True specific gravity - 3.29 CaO 98.20 Bulk density of particles - 2.54 Si02 0.35 AQ203 0.099 Fe2O3 0.084 By repeating the procedure of Example 1, refractory bricks were manufactured from the blasted spheres. The properties of the refractory bricks are shown in Table 7.

Comparative Example: By faithfully following the procedure of Example 1. refractory bricks were manufactured by using svnthetic dolomite clinker of the composition of E indicated in Table 1. The properties of the refractory bricks are shown in Table 7.

Table 7

Example I Example 2 Comparative Exampie 1 Exampre 2 @@mp@@@ Example Physical properties: Porosity 17.8 21.1 13.5 Hygroscopicity 6.2 9.8 4.5 Apparent specific gravit!- 3.41 | 3.17 35.0 Bulk density 2.82 2.54 3.0 Compressive strength (kg/cm2) 503 704 428 Spalling Test (1450 C. cooling in air) 15 times 24 times 10 times Fine cracks Cracks Fine Cracks Change of bricks softened due to slag absorption: Change of load (%0 1750 C 15 min. 0.56 0.86 1.19 (converter slag 30inin. 1.18 097 293 + fluorite) 60 min. 1.68 1.48 5.93 Measuring process of change in bricks softened due to slag absorption: The refractory bricks were reacted with slag in a furnace retained at a temperature of 1750 and having a load of 4 kg cm@ Changes in the height of the softened bricks were measured at 15 minutes. 30 minutes and 60 minutes.

It is clear from the results shown above that the spheres obtained in Examples 1 and 2 possessed better properties than the synthetic dolomite clinker of Comparative Example.

WHATWE CLAIMIS: 1. A method for the manufacture of slaking resistant spheres for use in the manufacture of refractories. which method comprises melting a mixture made up of 25 to 100% by weight of CaO. 0 to 75% by weight of MgO. 0 to 5% by weight of one or more members selected from A@2O3. Fe2O3. Cr2O3 and TiO2, plus trace elements incorporated as entrained originally bv the raw materials making up the mixture. converting the resultant molten mass into molten droplets and subsequently solidifying the molten droplets into spheres by sudden cooling.

2. The method according to claim 1. wherein the conversion of the molten mass into molten droplets is accomplished by allowing the molten mass to fall in a continuous flow and blowing a forced current of gas against the descending flow of said molten mass for thereby dividing the molten mass into molten droplets.

3. The method according to claim 1. wherein the conversion of the molten mass into molten droplets is accomplished by centrifugally dispersing the molten mass into molten droplets.

4. Slaking resistant spheres for use in the manufacture of refractories, which are made up of a mixture of 25 to 100% by weight of CaO, 0 to 75% by weight of MgO. 0 to 5% by weight of one or more members selected from A@2O3, Fe2O3, Cr2O3 and TiO2. plus trace

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   By repeating the procedure of Example 1, refractory bricks were manufactured from the blasted spheres. The properties of the refractory bricks are shown in Table 7.

   Comparative Example: By faithfully following the procedure of Example 1. refractory bricks were manufactured by using svnthetic dolomite clinker of the composition of E indicated in Table 1. The properties of the refractory bricks are shown in Table 7.

   Table 7

   Example I Example 2 Comparative Exampie 1 Exampre 2 @@mp@@@ Example Physical properties: Porosity 17.8 21.1 13.5 Hygroscopicity 6.2 9.8 4.5 Apparent specific gravit!- 3.41 | 3.17 35.0 Bulk density 2.82 2.54 3.0 Compressive strength (kg/cm2) 503 704 428 Spalling Test (1450 C. cooling in air) 15 times 24 times 10 times Fine cracks Cracks Fine Cracks Change of bricks softened due to slag absorption: Change of load (%0 1750 C 15 min. 0.56 0.86 1.19 (converter slag 30inin. 1.18 097 293 + fluorite) 60 min. 1.68 1.48 5.93 Measuring process of change in bricks softened due to slag absorption: The refractory bricks were reacted with slag in a furnace retained at a temperature of 1750 and having a load of 4 kg cm@ Changes in the height of the softened bricks were measured at

   15 minutes. 30 minutes and 60 minutes.

   It is clear from the results shown above that the spheres obtained in Examples 1 and 2 possessed better properties than the synthetic dolomite clinker of Comparative Example.

   WHATWE CLAIMIS: 1. A method for the manufacture of slaking resistant spheres for use in the manufacture of refractories. which method comprises melting a mixture made up of 25 to 100% by weight of CaO. 0 to 75% by weight of MgO. 0 to 5% by weight of one or more members selected from A@2O3. Fe2O3. Cr2O3 and TiO2, plus trace elements incorporated as entrained originally bv the raw materials making up the mixture. converting the resultant molten mass into molten droplets and subsequently solidifying the molten droplets into spheres by sudden cooling.
2. 2. The method according to claim 1. wherein the conversion of the molten mass into molten droplets is accomplished by allowing the molten mass to fall in a continuous flow and blowing a forced current of gas against the descending flow of said molten mass for thereby dividing the molten mass into molten droplets.
3. 3. The method according to claim 1. wherein the conversion of the molten mass into molten droplets is accomplished by centrifugally dispersing the molten mass into molten droplets.
4. 4. Slaking resistant spheres for use in the manufacture of refractories, which are made up of a mixture of 25 to 100% by weight of CaO, 0 to 75% by weight of MgO. 0 to 5% by weight of one or more members selected from A@2O3, Fe2O3, Cr2O3 and TiO2. plus trace

   elements incorporated as originally entrained by the raw materials making up the mixture, and which have a smooth surface consisting of microcrystalline particles.
5. 5. The spheres according to claim 4, wherein CaO accounts for 25 to 70% by weight, MgO accounts for 30 to 75% by weight and one or more members selected from At203, Fe2O3. Cr2O3 and TiO2 account for 0.5 to 3%by weight.
6. 6. ' A method for the manufacture of slaking resistant spheres as claimed in Claim 1 and substantially as described in any one of the specific examples hereinbefore set forth.
7. 7. Slaking resistant spheres as claimed in Claim 4 and substantially as described in any one of the specific examples hereinbefore set forth.
8. 8. Slaking resistant spheres as claimed in Claim 4 and substantially as herein described with reference to and as illustrated in the accompanying drawings.