GB1573732A - High density low porosity refractory product and process for making the same - Google Patents

Description

(54) HIGH DENSITY LOW POROSITY REFRACTORY PRODUCT AND PROCESS FOR MAKING THE SAME (71) We, A. P. GREEN REFRACTORIES CO., a Corporation organised and existing under the laws of the State of Delaware, United States of America, of Mexico, Missouri, United States of America, 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 in general to refractory products and processes and more particularly to a high density, low porosity refractory product made substantially from very fine materials and to a process for making the same.

In refractory shapes, particularly refractory brick, it is desirable to have high density and low porosity, and all processes for producing these refractories strive for that end, with the exception of insulating firebrick which are characterized by low density and high porosity.

The conventional dry press process produces a brick which is suitable for many refractory purposes. Nevertheless, conventional dry pressed brick possess a lower than desired density and a higher than desired porosity. Conventional dry pressed brick also have a relatively high number of large pores, which is undesirable.

More specifically, the manufacture of refractory brick by the dry press process normally involves using a size graded mix of coarse, intermediate and fine sized particles. A typical screen analysis (Tyler Standard Screen Scale Sieve Series) of such a brick mix is: Pass 4 mesh and retained on 10 mesh 25% Pass 10 mesh and retained on 28 mesh 20% Pass 28 mesh and retained on 65 mesh 10% Pass 65 mesh 45% The use of such a size graded mixture allows the brick to be pressed to a reasonably high density without forming laminations in the brick perpendicular to the direction of pressing.

If too high a proportion of the mixture is composed of fine fraction (-65 mesh), there is a tendency for the mixture to contain entrapped air during pressing. This entrapped air is compressed during pressing, and, when the pressure is released, the air expands and causes highly undesirable laminations in the brick. These laminations tend to be further accentuated when the bricks are subjected to high temperatures during the firing process.

While the use of the size graded mixture allows forming solid brick free of laminations, such a mixture gives relatively low density and high porosity to the brick. Using the foregoing typical size gradation, there are limits to the values of density and porosity attainable.

It is further generally recognized that in addition to the amount of pores present in a refractory brick the size of the pores is important, with the smallest size possible generally being most desirable. When the foregoing typical gradation is used for a refractory body, the pore sizes resulting cover a wide range with an appreciable proportion of the pores being of large size i.e., on the order of 10 to 40 microns in diameter.

It is possible to improve the density, porosity, and size of pores developed in a refractory body by using a fine grained mixture. Such a procedure is used in making refractories by means of isostatic forming. Following is a procedure typical of one form of an isostatic process: a) Fine grained materials on the order of -325 mesh and finer are mixed thoroughly in a slurry form with suitable binders; b) The slurry is spray-dried under conditions which tend to form the fines into uniformly sized small balls which flow smoothly and freely; c) The balls are vibration packed into a rubber mold which is sealed and contained in a perforated metal container; d) The mold and container are placed into a high pressure vessel;; e) The balls of refractory material in the mold are exposed to a high pressure in the vessel by means of a fluid, such as oil or water, which is pumped into the vessel to exert pressures up to 50,000 psi on the mold; and f) The balls of refractory material are formed into an object which assumes the shape of the mold.

By exerting pressure on the body in this fashion, the air normally entrapped in the fine grained body is removed 6efore it can cause pressure laminations to form. Also, the pressure is exerted equally on all surfaces of the shape or refractory body. This method of pressure application produces a shape practically free of the stresses normally formed in a body which is exposed to forming pressures exerted primarily in one direction. Following forming, it is sometimes necessary to dress the shape in the green state before it is exposed to high temperature firing.

A modification of the isostatic process involves elimination of the spray-drying operation and forming the body directly from a damp or tempered mixture of finely divided material.

The isostatic forming process necessitates the use of equipment and processes not common to the refractories industry, e.g., spray-drying, isostatic pressure application, green finishing, etc. This, in turn, leads to the need for a separate plant to manufacture products by this process. Also, the isostatic process is a much more expensive manufacturing procedure than the conventional dry press process. This is particularly true when conventional size pieces or shapes are being manufactured. However, the isostatic process is ideal for forming large pieces weighing several hundreds of pounds and having the highly desirable properties of high density, uniformity, low porosity, and high strength.

Thus, while isostatic forming allows the manufacture of high strength, high density, and low porosity refractories from fine grain bodies by pressing, the isostatic process is characterized by the need for new processing plants and high manufacturing costs.

The present invention provides a process for producing a refractory brick or other refractory product, said process comprising the steps of forming a fine grain refractory material capable of passing a 65 mesh screen (Tyler Standard Screen Scale Sieve Series) into larger discrete particles, crushing the discrete particles, sizing the crushed discrete particles into a suitable mix for pressing to a shape, and pressing the mix into a desired refractory shape.

Preferably 70 - 100 parts by weight of the discrete particles consist of fine grain refractory material capable of passing a 325 mesh screen with an average size of 2 to 5 microns and 0 to 30 parts of the discrete particles consist of refractory materials capable of passing a 65 mesh screen.

The present invention also provides a refractory product produced by the foregoing process and comprising a sized distribution of particles each of which is composed of individual grains of less than about 325 mesh in size.

One of the advantages of the present invention is that conventional processing equipment may be utilized for manufacturing a refractory brick or other shape having greater strength, higher density, and lower porosity than refractory bricks made by conventional dry pressing processes. The process of the invention is simple and economical and provides refractory bricks or shapes which have functional characteristics similar to refractory products produced by an isostatic forming process.

The following table provides the ranges of properties that may be obtained by the process of this invention for a 60% MgO basic brick.

Range of properties of 60% MgO basic brick made by the predensification process Bulk Density 190-220 pcf Apparent Porosity 7.0-18.0% Modulus of Rupture 1400-2600 psi 2700 F. MOR 700-1100 psi Median Pore Size 2.5-8.0 microns The invention will now be described in detail. Broadly speaking, the process of the present invention involves agglomerating or forming a very fine grained mixture of refractory materials into larger particles prior to size grading and dry pressing the larger refractory aggregates or particles into a desired refractory shape by application of unidirectional pressing force. This pretreatment inhibits the formation of laminations perpendicular to the direction of the pressing force in the final product.Any agglomerating or pre-forming technique is acceptable provided the agglomerates formed thereby are sufficiently hard and strong to withstand subsequent processing steps, such as crushing and screening, batching, mixing, tempering and pressing. With all preforming techniques, the preformed shape is normally dried to develop its strength and then the preformed shape is crushed into particles of desirable brick forming sizes.

All known refractory materials are amenable to treatment according to this process, including chrome ores, magnesite, periclase, alumina, bauxites, fireclays, zircon, zirconia, etc. Any acid, basic, or neutral refractory material may be used in the practice of this invention.

Specific examples to illustrate the principles of this invention and the benefits derived from its use will be given hereinafter. These specific examples are chosen from the basic refractory area for illustrative purposes only and are not to be considered restrictive to the practice of the invention. As previously stated, all known refractory materials are amenable to treatment according to this process.

Before presenting specific examples of this invention, a general description of its practice, including the various modifications of its preferred practice, is presented. For illustrative purposes and to aid in clarifying the description, a manufacturing flow sheet depicting the Predensified Grain Basic Brick Process is presented hereinafter. Similar flow sheets can be made for other classes of refractories.

PREDENSIFIED GRAIN BASIC BRICK PROCESS Preferred Method Periclase and Chrome Ore or Concentrates (Any Combination) Co-Ball Mill to -325 Mesh With an Average Sub-Sieve Particle Size of 3 to 4 Microns Batch the Mix Composed of 80% of the Ball Milled Mixture and 20% of -65 Mesh Periclase and -65 Mesh Chrome Ore In the Same Ratio as the Ball Mill Charge Temper With A Bond Salts Water Solution Composed of 1% MgSO4-7H2O and 1% MgCk 6H2O Briquette at 40,000 psi in Briquette Rolls Dry Briquettes at 350"-400"F.

For at Least 1 Hour in a Shaft Dryer Crush Briquettes to 3 Mesh and Fines Using Any Equipment Suitable for Crushing and Then Screen Into Desired Fractions Blend and Temper the Desired Fractions With Bond Solution Described Above for Briquettes or With an Aqueous Solution of an Organic Bond Press Brick at 11,000 psi Dry Brick at 250"-400"F.

For at Least 8 Hours Burn Brick at 3200"F. for 10 Hours Using a Heating and Cooling Schedule of 50 F./Hour Periclase or deadburned magnesite and chrome ore are the principal ingredients of basic refractories, although other minor additives are sometimes used with these materials, such as fume silica, alumina, chromic oxide, olivine, etc.

The periclase and chrome ore ingredients may be used in any proportion in the practice of this invention. The chosen mixture, which is to be formed into larger pieces (which themselves are to be crushed) in the practice of this invention, is composed of finely divided particles of periclase and chrome ore. The finely divided mixture may be prepared by crushing and ball milling the properly proportioned mixture together (co-ball milling). This is the preferred method. An alternate method which may be used is to mill the ingredients separately to the desired degree of fineness, and then to combine them in the desired proportions. The degree of fineness of the mixture will affect the properties of the final product but may be as coarse as 65 mesh or as fine as 325 mesh or finer. The preferred fineness is 325 mesh with an average sub-sieve size of about 3 to 4 microns.This is true whether the materials are co-ball milled or milled separately.

A Fisher Sub-Sieve Sizer is preferably used to determine the average grain size in microns of the ball mill discharge.

When the desired fineness of the ball milled material has been achieved, an addition of 65 mesh or coarser periclase and chrome ore may be added for the purpose of controlling the shrinkage during burning. Brick made from a mixture of fines and 65 mesh or coarser materials are more resistant to craze and edge cracking on firing and can withstand a faster firing schedule than brick made of all fines. In the preferred method, a 20% addition of 65 mesh periclase and/or chrome ore is made to the mix, prior to forming into agglomerates, but may also be added to the final brick mix instead.

This mixture is then mixed and tempered with water and a bonding agent. The preferred bond is a water solution of 1% MgSO4-7H2O and 1% MgCl2.6H2O, based on the weight of the mixture being bonded. However, either of these salts alone or in amounts greater or smaller than the preferred quantities may be used. Also, other bonding agents such as sulfuric acid, hydrochloric acid, other sulphate or chloride salts, lignin liquor, etc., may be used. The bond selected, however, must provide agglomerates of the fine mixture having adequate hardness and strength to withstand the subsequent processing required in the practice of this invention. The amount of liquid used to temper the mixture must be sufficient to give the mixture the consistency required to form the desired agglomerates.

The tempered mixture is then formed into agglomerates or predensified granules of the fine mixture. These agglomerates or predensified granules may be formed by several means, such as by extruding into pellets which would require a relatively high water content and bond content, agglomerating in a mixer which would generally give relatively soft agglomerates, pressing into bricks or dobies on a toggle or hydraulic press, briquetting with briquette rolls, etc. Of the various possible methods for agglomerating or predensifying the fines, the use of briquette rolls is preferred, in which briquettes of almond shape about 1 inch x 3/4 inch x 1/2 inch in size are formed under a pressure of approximately 40,000 psi.

The second preferred method is forming dobies of about 9 inch x 42 inch x 22 inch size on a hydraulic or toggle press under a pressure of approximately 10,000-15,000 psi.

The method of forming the predensified granules influences the hardness, strength, and density of the granules which in turn influences the behavior of the brick made from the granules and their properties. The harder and more dense the granules the less will be the shrinkage upon firing of the brick made from the granules. This will be illustrated in the specific examples which follow.

After forming the briquettes, dobies, or agglomerates, they are dried at a sufficient temperature for a sufficient length of time to effect complete drying and to develop the optimum strength from the bond added to the mixture.

Drying may be accomplished in a batch dryer, a tunnel dryer, or a shaft dryer in the case of the briquetted material. The preferred method for briquettes is to use a shaft dryer, exposing the briquettes to a temperature of 300"F.-400"F. for a period of at least one hour, although somewhat higher temperatures or longer times may be used. In a shaft dryer the briquettes can be more readily exposed to both the temperature and the flow of hot air, thus reducing the time required to effect the necessary drying and development of bond strength. In the cases of using a batch dryer or a tunnel dryer, it is more difficult to effect the transfer of heat from the dryer to the briquettes or dobies. Therefore, in the batch and tunnel dryer techniques, a temperature of 350"F.-400"F. or somewhat higher is applied for at least 8 hours. In any case, regardless of the method used to dry the briquettes or dobies, the temperature and time of drying must be sufficient to completely dry them and develop their optimum strength.

After drying, the briquettes or dobies or other agglomerates of the fine mixture are crushed in suitable equipment to provide predensified grains of the proper grain sizing for making dry pressed brick. The grain sizing for making dry-pressed brick is as follows: Preferred Range Pass 3 mesh on 10 mesh 60% 40 to 60 Pass 10 mesh on 28 mesh 0 0 to 20 Pass 28 mesh 40 40 to 60 This preferred brick mix grain sizing, or any other grain sizing that may be desired, may be achieved by screening the crushed agglomerates into the required fractions and recombining these fractions in the desired proportions.

If an addition of 65 mesh or coarser periclase and chrome was not made to the briquette mix, these materials may be added to the brick mix otherwise consisting of the crushed predensified fines. If the addition is to be made to the brick mix, the sized fractions of the crushed predensified fines must be prepared to allow the 65 mesh materials to be accommodated and still retain good pressing characteristics.

The fractions of predensified grain and other raw material fractions, if added, are then mixed and blended and tempered with water and with bonding agents if desired. In the preferred method, a thick aqueous solution of an organic bond such as dextrin is used.

Preferably, the mix is dry mixed for 1 minute and then wet mixed or tempered for three minutes. However, the times for dry and wet mixing may be varied from the preferred method, as long as the mix is thoroughly mixed and tempered. A mixer with mullers can be used, but with the mullers raised above the pan bottom, to avoid excessive breakdown of the predensified granules.

The tempered mix is discharged from the mixer and conveyed by suitable means to a press where the bricks are formed. Any type of press may be used which is capable of forming the brick to the optimum pressed density. The preferred method of forming is by use of a hydraulic or mechanical press using a forming pressure of 11,000 psi. However, other pressures may be used provided the bricks formed are capable of being handled after pressing and do not contain laminations or pressure cracks due to excessive forming pressure.

After forming, the pressed bricks are dried, depending on the bonding agent, from 220"F.

to 400"F. for at least 8 hours. However, the criteria for selecting the drying conditions are that the brick be sufficiently dry to avoid cracking when exposed to high temperatures in firing and to possess sufficient strength to withstand handling in the case where the brick are transferred from the dryer cars to tunnel kiln cars or to a periodic kiln. When the pressed brick are set directly from the press to tunnel kiln cars or to periodic kiln cars, the requirement is then reduced to sufficient drying to avoid cracking in firing.

After drying the brick are set to tunnel kiln or periodic kiln cars, assuming they are not directly set to the tunnel kiln or periodic kiln cars after pressing, for firing. The preferred method of firing or burning the brick is to heat and cool the brick at a rate of about 50"F.

per hour using a top temperature of 3200"F. and holding the brick at the top temperature for 10 hours. However. deviations from this preferred method of firing the brick can be used which will, within limits, provide brick of somewhat improved properties.

Moving from the general description of the process and products derived from it, specific examples are now given in detail to illustrate the practice of the invention, the benefits to be derived from it, and the effects of varying the processing parameters as described previously.

Example No. 1 In this example a basic refractory material having a nominal MgO content of 60% was made using a combination of 50% Philippine chrome ore concentrates (-10 mesh) and 50% of a high purity sea-water periclase grain pre-crushed to - 10 mesh and fines. The characteristics of these materials were as follows: Chemical Analysis Philippine Chrome Ore Periclase MgO 15.4% 98.2% CaO 0.29 0.67 SiO2 2.93 0.76 Al203 29.5 0.16 Fe203 14.6 0.17 Cur703 34.1 Tr.

Bulk Specific Gravity, g/cc 3.84 3.33 True Specific Gravity, g/cc 3.98 3.56 The chrome ore and periclase were ball milled together to several degrees of fineness; i.e., minus 65 mesh. minus 150 mesh, and minus 325 mesh.

Each co-ball milled mixture was mixed with a water solution of 1% MgCl2.6H2O and 1% MgSO4.7H2O, based on the dry weight of the mixture. The dampened mixtures were then formed on Komarek-Greaves briquetting rolls into almond shaped briquettes. These briquettes were then dried at 350"F. for about 16 hours in a batch dryer until the briquettes were dry and hard.

After drying each of the types of briquettes were crushed and sized to give a normal brick making grain-sized mixture approximately as follows: Pass 3 on 10 mesh 25% Pass 10 on 28 mesh 20 Pass 28 on 65 mesh 10 Pass 65 mesh 45 Each of these grain-sized mixtures were then mixed in a muller-type mixer with the mullers raised and with sufficient water to give the mix a suitable dry pressing consistency.

These mixes were then formed into brick on a hydraulic press using a forming pressure of 11,000 psi. No laminations or pressure cracks were evident in the pressed brick.

The formed brick from each mix were then dried in a batch dryer for about 24 hours at 350"F. The dried brick were set and fired in a gas-fired periodic kiln at 31500F. for 10 hours using a heating and cooling rate of about 50"F. per hour.

After cooling, the brick from each mix were tested and examined. No laminations were evident in the fired brick although some crazing and edge cracking was noted. The brick properties are given in Table I along with properties usually obtained on brick of similar composition but made using normal dry press brick-making techniques and to properties usually obtained on brick of similar composition but made by the isostatic forming process.

TABLE I Conventional Isostatic Dry Press A B C Process Process MgO Content -------------------------------------- 60% ----------------------------------------- Mix: Agglomerate A 100% Agglomerate B 100% Agglomerate C 100% Water ~ ~~ 4% Firing Temperature ~~~~~~~~ 3150 F.~~~~~~~~ Manufacturing Shrinkage 7.4% 5.9% 3.1% Bulk Density, pcf 216 203 194 212 189-195 Modulus of Rupture psi 2315 1405 1685 5000 600-900 Hot Modulus of Rupture 2700 F., psi 1020 895 740 Apparent Porosity 7.5% 13.5% 17.2% 8.5% 16-19% Apparent Specific Gravity, g/cc 3.74 3.76 3.78 3.72 3.71-3.75 Median Pore Size, No Microns 2.7 6.2 Data 1.8 18.8 Agglomerate A - Briquetted co-ball milled -325 mesh mixture of 50% periclase and 50% chrome ore concentrates.

Agglomerate B - Briquetted co-ball milled - 150 mesh mixture of 50% periclase and 50% chrome ore concentrates.

Agglomerate C - Briquetted co-ball milled -65 mesh mixture of 50% periclase and 50% chrome ore concentrates.

As may be seen, as the fineness of the predensified materials decreases, the density and strength decreases and the porosity and pore size increases. The brick made by this invention using -325 mesh material have superior properties to conventional dry pressed brick and properties approaching those of isostatically formed brick.

Example No. 2 When brick are made from all predensified fine material according to this invention, they undergo the highest amount of shrinkage on firing. This sometimes results in brick having some surface craze cracking and edge cracking, which is probably due to heating them on a schedule too fast to accommodate the high shrinkage. While the cracking is confined to the surface with the interior of the brick being sound and crack free, this surface and edge cracking may be considered at times to be objectionable.

It was found that one method for eliminating this cracking or reducing it to an acceptable minimum, aside from slower firing schedules, was to increase the grain size of the mixtures to be briquetted; i.e., by increasing the grain size from the preferred -325 mesh size to -150 mesh or -65 mesh sizes. However, as seen from the data given in Table I, increasing the grain size in this manner resulted in decreased density and increased porosity.

In this example, another method of eliminating or reducing the surface crazing and edge cracking is described. A basic refractory having a nominal MgO content of 60% was made in the same manner as described in Example 1 using the -325 mesh co-ball milled mixture.

In addition, another basic refractory of similar composition was made, but in this case, 85% of the brick mix was composed of granules of the predensified briquette fines and 15% of the brick mix was composed of 7.5% of -65 mesh chrome ore concentrates and 7.5% of -65 mesh periclase. All other aspects of the manufacture of the brick of this second basic refractory were the same as described in Example 1. The properties of the brick made by these two techniques are given in Table II.

As may be seen from these data, adding the -65 mesh periclase and chrome ore decreased density and manufacturing shrinkage and increased strength, porosity, and pore size.

TABLE II MgO Content 60% Mix: A A-1 Agglomerate A 100% 85% Periclase, -65 mesh, ball milled 7.5 Chrome ore concentrates, -65 mesh ball milled 7.5 Water - ~ ~ 4% Firing Temperature - ~ 31500F. ~ ~ ~ ~ Manufacturing shrinkage 7.4% 6.9% Bulk density, pcf 216 210 Modulus of rupture, psi 2315 2640 Hot modulus of rupture, 2700 F., psi 1020 1315 Apparent porosity 7.5% 10.2% Apparent specific gravity g/cc 3.74 3.75 Median Pore size, microns 2.7 7.6 Example No. 3 In addition to making brick using all fine materials as described in the previous examples, it was found that additions of predensified granules of -325 mesh fine materials to a normal brick mix of a 60% MgO type product resulted in improved properties.In this example, predensified granules of co-ball milled -325 mesh materials were crushed to -3 mesh and fines and were then added to a normal brick mix in increasing amounts as shown in Table III. As may be seen, as the amount of predensified granules in the mix increased, the density increased and the porosity decreased.

TABLE III Mix: D E F G Periclase Pass 4 mesh and retained on 65 mesh, % 30 22.5 15 7.5 Ball milled and passing 65 mesh 25 18.75 12.5 6.25 Chrome Ore Concentrates Pass 10 mesh and retained on 65 mesh 25 18.75 12.5 6.25 Ball milled and passing 65 mesh 20 15 10 5 Agglomerate B, (Table II), 3 mesh and fines 0 25 50 75 Water -- 4% -- - Firing Temperature "F. -- 31500F. -- - Manufacturing Shrinkage +0.75% +0.25% -1.3% -3.5% Bulk density, pcf 182 185 190 195 Modulus of rupture, psi 515 550 675 1210 Hot modulus of rupture, 2700"F., psi 735 455 445 580 Apparent porosity 22.5% 20.6% 18.7% 16.7% Apparent specific gravity 3.76 3.74 3.75 3.76 Example No. 4 A wide variety of compositions can be made using the predensified grain brick process.

Table IV illustrates properties of brick made in nominal 30% MgO and 80% MgO compositions and from the same raw materials as were used in the previous examples but in different proportions. For comparison, similar data for isostatically formed, and conventionally processed brick are shown.

TABLE IV Conventional Predensifying Isostatic Dry Press Predensifying Isostatic Conventional Process Process Process Process Process Dry Press Nominal composition, MgO% 30 30 30 80 80 80 Bulk density, pcf 212 218 204 202 198 182 Apparent porosity, % 13.9 10.4 15.4 10.2 12.0 19.2 Apparent Sp. Gravity 3.93 3.91 3.88 3.60 3.60 3.61 Modulus of rupture, psi 2125 ND 1615 3685 ND 900 Chemical Analysis MgO 32.4% 29.9% 35.0% 81.8% 79.7% 79.3% CaO 0.37 0.36 0.49 0.60 0.59 0.58 SiO2 2.57 2.64 2.96 1.21 1.27 1.28 Al2O3 24.4 25.3 22.3 6.22 6.98 7.13 Fe2O3 12.1 12.5 12.7 3.15 3.52 3.60 Cr2O3 28.2 29.2 26.5 7.04 7.92 8.10 Burning Temperature, F. 3150 F. 3175 F. 3000 F. 3150 F. 3175 F. 3150 F.

Example No. 5 In brick mixes made with the same agglomerated grain, it is possible to alter the grain size of the addition made to the brick mix with corresponding alterations in the brick properties.

This is illustrated by Mixes H and I shown in Table V.

Both brick mixes were constituted of 80% of the same agglomerate crushed to 3 mesh and fines. To brick mix H was added 10% each of -65 mesh periclase and -65 mesh chrome ore, while to brick Mix I was added 10% each of -28+65 mesh periclase and chrome ore.

It can be seen that the mix with the -65 mesh additions had a higher manufacturing shrinkage and produced brick with higher bulk density, modulus of rupture and lower apparent porosity, but that the brick made from the mix with the -28+65 mesh additions had slightly better thermal shock resistance.

TABLE V MgO Content 60% Mix: H I Agglomerate Mix Co-Ball Milled to 5 microns Periclase 50% 50% Chrome Concentrate 50 50 MgSO4 (Extra) 1 1 MgCl2 (Extra) 1 1 Moisture 4 4 (Briquetted at 40,000 psi) Brick Mix Agglomerate, Crushed, 3 M/F 80% 80% Periclase, -28+65 Mesh 0 10 Periclase, -65 Mesh 10 0 Chrome Concentrate, -28+65 Mesh 0 10 Chrome Concentrate, -65 Mesh 10 0 Dextrin (Extra) 2 2 Moisture (Extra) 2 2 Firing Temperature - - - - - - 3200 F. - - - - - Manufacturing Shrinkage 5.8% 4.0% Bulk Density, pcf 206 202 Modulus of Rupture, psi 2030 1865 Apparent Porosity, % 12.2 13.8 Apparent Specific Gravity, g/cc 3.76 3.76 Prism Spalling, Cycles to Fail 5 7 Example No. 6 This example illustrates the preferred way to add a coarser fraction to the otherwise very fine ingredients to control shrinkage and densification of the brick, and at the same time permit effective and economical utilization of fine grained low silica Philippine chrome concentrates marketed as "Losil". This material is also referred to as 100 mesh concentrates, whereas screen analysis indicates it to be all essentially -65+325 mesh. It should be pointed out that these high purity chrome concentrates could have been substituted for the 10 mesh concentrates in all of the previous examples except Example No. 5 in which a -28+65 mesh chrome concentrate was added to the brick mix. This fraction is not available in the Philippine "Losil" chrome concentrates.

Mix J in Table 6 shows additions of 11% -65 mesh periclase and 9% of Losil chrome ore to the brick mix otherwise consisting of 80% crushed agglomerated grain, whereas in Mix K, the additions of 11% -65 mesh pericalse and 9% Losil chrome ore were blended with the co-ball milled periclase and chrome prior to briquetting.

After the briquettes were dried and crushed to 3 mesh and fines, to facilitate pressing, the - 10+28 mesh fraction was removed by screening, crushed to pass 28 mesh and fines, and blended back to the 3 mesh and fines.

Mix K brick made by adding -65 mesh material to the briquette mix had a slightly higher manufacturing shrinkage and density, lower porosity, and smaller pore size than brick made by the first method. The brick made by the second method had a slightly smoother texture than brick made by the first method.

TABLE VI Mix: J K Agglomerate Mixes Pericalse, -65 mesh 0% 11% "Losil" chrome Conc.

(100 mesh, as rec'd) 0 9 Co-Ball milled to 4.0 microns Periclase 55 44 "Losil" Chrome Conc. 45 36 MgCl2, Extra 1 1 MgSO4, Extra 1 1 Moisture, Extra 4 4 (Briquetted at 40,000 psi) Brick Mixes Agglomerate, 3/10 mesh 60% 60% Agglomerate, 28/F mesh 20 40 Periclase, 65/F 11 0 "Losil" Chrome Conc.

(100 mesh, as rec'd) 9 0 Dextrin, Extra 2 2 Moisture, Extra 2 2 Firing Temperature ~~~~~ 3200"F. ~~~~~ Agglomerate, Bulk Density, g/cc 3.00 3.06 Manufacturing Shrinkage, % 5.0 5.5 Bulk Density, pcf 200 203 Apparent Porosity, % 14.7 13.1 Apparent Specific Gravity, g/cc 3.77 3.75 Modulus of Rupture, psi 1955 2235 2700"F. Modulus of Rupture, psi 895 890 Median Pore Size, microns 8.7 6.2 WHAT WE CLAIM IS: 1.A process for producing a refractory brick or other refractory product, said process comprising the steps of forming a fine grain refractory material capable of passing a 65 mesh screen (Tyler Standard Screen Scale Sieve Series) into larger discrete particles, crushing the discrete particles, sizing the crushed discrete particles into a suitable mix for pressing to a shape, and pressing the mix into a desired refractory shape.

2. The process according to claim 1, including the step of firing the pressed shape.

3. The process according to claim 1 or 2, wherein 70-100 parts by weight of the discrete particles consist of fine grain refractory material capable of passing a 325 mesh screen with an average size of 2 to 5 microns and 0 to 30 parts of the discrete particles consist of refractory materials capable of passing a 65 mesh screen.

4. The process according to claim 1, 2, or 3, and further comprising moistening the fine grain refractory material with an aqueous chemical bonding solution material prior to forming it into discrete particles.

5. The process according to any of claims 1 to 4, wherein the fine grain refractory material is pressed into discrete particles in the shape of briquettes.

6. The process according to claim 5, and further comprising drying the refractory material at between 300"F. and 400"F. prior to crushing it.

7. The process according to claim 5 or 6 and further comprising screening the crushed particles into fractions of varying size graduation and mixing predetermined quantities of each fraction to form the brick mix.

8. The process according to claim 7, and further comprising moistening the brick mix

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

Claims (13)

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

   blended back to the 3 mesh and fines.

   Mix K brick made by adding -65 mesh material to the briquette mix had a slightly higher manufacturing shrinkage and density, lower porosity, and smaller pore size than brick made by the first method. The brick made by the second method had a slightly smoother texture than brick made by the first method.

   TABLE VI Mix: J K Agglomerate Mixes Pericalse, -65 mesh 0% 11% "Losil" chrome Conc.

   (100 mesh, as rec'd) 0 9 Co-Ball milled to 4.0 microns Periclase 55 44 "Losil" Chrome Conc. 45 36 MgCl2, Extra 1 1 MgSO4, Extra 1 1 Moisture, Extra 4 4 (Briquetted at 40,000 psi) Brick Mixes Agglomerate, 3/10 mesh 60% 60% Agglomerate, 28/F mesh 20 40 Periclase, 65/F 11 0 "Losil" Chrome Conc.

   (100 mesh, as rec'd) 9 0 Dextrin, Extra 2 2 Moisture, Extra 2 2 Firing Temperature ~~~~~ 3200"F. ~~~~~ Agglomerate, Bulk Density, g/cc 3.00 3.06 Manufacturing Shrinkage, % 5.0 5.5 Bulk Density, pcf 200 203 Apparent Porosity, % 14.7 13.1 Apparent Specific Gravity, g/cc 3.77 3.75 Modulus of Rupture, psi 1955 2235 2700"F. Modulus of Rupture, psi 895 890 Median Pore Size, microns 8.7 6.2 WHAT WE CLAIM IS: 1.A process for producing a refractory brick or other refractory product, said process comprising the steps of forming a fine grain refractory material capable of passing a 65 mesh screen (Tyler Standard Screen Scale Sieve Series) into larger discrete particles, crushing the discrete particles, sizing the crushed discrete particles into a suitable mix for pressing to a shape, and pressing the mix into a desired refractory shape.
2. 2. The process according to claim 1, including the step of firing the pressed shape.
3. 3. The process according to claim 1 or 2, wherein 70-100 parts by weight of the discrete particles consist of fine grain refractory material capable of passing a 325 mesh screen with an average size of 2 to 5 microns and 0 to 30 parts of the discrete particles consist of refractory materials capable of passing a 65 mesh screen.
4. 4. The process according to claim 1, 2, or 3, and further comprising moistening the fine grain refractory material with an aqueous chemical bonding solution material prior to forming it into discrete particles.
5. 5. The process according to any of claims 1 to 4, wherein the fine grain refractory material is pressed into discrete particles in the shape of briquettes.
6. 6. The process according to claim 5, and further comprising drying the refractory material at between 300"F. and 400"F. prior to crushing it.
7. 7. The process according to claim 5 or 6 and further comprising screening the crushed particles into fractions of varying size graduation and mixing predetermined quantities of each fraction to form the brick mix.
8. 8. The process according to claim 7, and further comprising moistening the brick mix

   prior to pressing it into the refractory shape.
9. 9. The process according to claim 8, and further comprising drying the pressed refractory shape at between 220"F. and 400"F. for at least 8 hours prior to firing.
10. 10. A refractory product, produced by the process of claim 1 and comprising a sized distribution of particles each of which is composed of individual grains of less than about 325 mesh in size.
11. 11. The product of claim 10, where the size distribution is: 40 to 60% pass 3 on 10 mesh o to 20% pass 10 on 28 mesh 40 to 60% pass 28 mesh.
12. 12. The product of claim 11, wherein a portion of the material passing 28 mesh consists of - 65 mesh materials that have not previously been milled to a finer size and agglomerated.
13. 13. A process for producing a refractory brick or other refractory product according to claim 1 and substantially as herein described with reference to any one of the Examples.