US1992483A - High pressure chrome refractory - Google Patents

Description

Feb. 26, 1935. R. P. HEUER 1,992,433

v HIGH PRESSURE CHRQIE REFRACTORY Filed. Feb. 15, 1933 Patented Feb. 26, 1935 UNITE PATEN FFICE Russell Pearce Heuer, Bryn Mawr, Pa., assignor to General Refractories Company, a corporation of Pennsylvania Application February 15, 1933, Serial No. 656,938

18 Claims.

My invention relates to the manufacture of chrome refractory brick. This application is a continuation in part of my application Serial No. 323,890, filed December 5, 1928 for Dense mix for refractory bricks.

A purpose of my invention is to make chrome brick of greater density and less porosity for use without previous firing, by methods which are better and more economical, using a mix of definite proportions of larger and smaller graded sizes of non-plastic chrome particles, suitably bonding the non-plastic mix, and subjecting the non-plastic mix to high pressure to cause tight interfitting of the particles. In this way the voids are decreased to a minimum, the need for bonding material is reduced, and the chrome brick are enabled to give improved service and to withstand high temperatures in a better manner.

A further purpose is to employ between 45% and 65% (preferably 55%) of larger non-plastic chrome particles between 10 and mesh per linear inch and between 55% and (preferably of smaller non-plastic chrome particles through mesh per linear inch (preferably 25 through or mesh per linear inch) in chrome brick, desirably regrinding the intermediate particles between 30 and 50 mesh per linear inch to make smaller particles, and to subject the mixture, without plastic material or fluxing ingredients, to pressure in excess of 1000 pounds per square inch.

A further purpose is to operate a crushing, grinding and screening mill on a cycle that adapts the mill to deliver ground chrome ore in the form of larger and smaller grain sizes in predetermined relative quantities without the presence of grains of an intermediate size, the relative quantities of larger and smaller size particles be,- ing preferably about 55% and 45% respectively. A further purpose is to grind a refractory (preferably chrome ore) under conditions producing a relative excess of larger particles for the intended use, thus insuring that suflicient larger particles are obtained, and to subsequently regrind the excess of larger particles.

A furtherpurpose is to employ magnesia in a chrome brick made in accordance with my invention.

Further-purposes appear in the specification and in the claims.

My invention relates to the methods involved and to the products obtained.

Figure 1 is a ternary diagram for different mixes that may be made from three different graded sizes of nonlastic chrome particles mixed together in different proportions, and is given to indicate the results of research work that I have done to determine the way in which the density of chrome mixes is dependent upon the relative quantities of three different graded sizes of particles in the mix.

Figure 2 is a diagrammatic view showing my. method of operating a crushing, grinding and screening mill for the preparation of a chrome brick mix in accord with my invention.

Figures 3, 4 and 5 are diagrammatic fragmentary sections through different hypothetical mixes for forming chrome brick, Figure 3 illustrating a mix made up exclusively of larger or A particles, Figure 4 illustrating a mix of larger or A, smaller or C, and intermediate or B sizes, and Figure 5 a mix made up of larger or A and smaller or C grains, but without grains of intermediate or B size.

In the drawing like numerals refer to like parts.

Many non-plastic refractory materials may be used to produce brick of high density'by grading the particles into larger and smaller sizes, with the. partial or complete elimination of intermediate sizes, and combining the larger and smaller sizes in definite proportions. This has been explained by me in my U. S. Patent No. 1,851,181, granted March 9. 1932. Prior to the invention of the said patent, it was common practice to form brick from ground refractory which passes a specific size of screen and which therefore comprises indiscriminately different sizes of particles, all of which however are sufiiciently small to pass the screen used.

However, by eliminating intermediate size particles and combining the larger and smaller sizes as discussed in my Patent No. 1,851,181, I have found that the service characteristics, such as Y strength, resistance -to abrasion and spalling, and resistance to molten slags, hot metals, and hot products of combustion of refractory brick are much improved. This improvement I attribute largely to increased density and correspondingly decreased void space obtained by the proper grading of the sizes of the particles and combining of the graded sizes.

Chrome ore is an excellent example of a nonplastic material which may be made into greatly improved brick by proper grading and combining of the particle sizes. More benefit of my invention is obtained with chrome brick than with many refractories, because of the closeness with which chrome brick follow the law which I have diswvered. I find that, the more dense the re- -.fractory mix from which chrome brick are formed, the more dense will be the brick, and

that by suitably proportioning the relative quantitles of the particles of diiferent graded sizes that together make up the mix. I am able to materially increase the density of the mix from which the chrome brick are subsequently formed, with a corresponding increase in density and great improvement in the service characteristics of the chrome brick.

The increase in density of the mix is incident to a decrease in the void space between the mix particles, which, in turn, is doubtless due to a better interfitting of the brick particles with one another, the more perfect interfitting of the particles making the tighter, denser structure that gives the greatly superior service characteristics. Since my chrome particles are non-plastic, it will be evident that they do not have associated with them during forming the considerable film of moisture which surrounds plastic particles. There is therefore not any substantial loss in tightness of interfitting, or increase in void space, due to the driving air of moisture by heating operations which take place subsequent to interfitting, such as drying, firing, or subjecting to firing temperature during use in a furnace lining. Likewise, since my chrome brick do not contain suflicient fluxes or similar materials to promote plastic flow at high temperatures, such as the temperatures of use in a metallurgical furnace in which chrome brick are employed, there is no tendency of the particles to fiux together into a solid mass and destroy the interfitting of the particles, producing a shrunken mass of unreliable expansion and contraction characteristics.

By selecting suitably different graded sizes of chrome particles for making up the mix and proportioning in the mix the relative quantities of the particles of the different selected graded sizes, I obtain a mix that forms denser, stronger and less porous brick than-are otherwise obtainable.

In Figure 1, I illustrate a ternary diagram for a series of mixes of chrome particles having sizes A, B and C. The larger or A particles are those which are between 10 and 20 mesh per linear inch, the intermediate or B particles will pass 20 mesh per linear inch and be caught on mesh per linear inch, while'the smaller or C particles will pass 80 mesh per linear inch. I

Any point within the diagram represents a-mix having certain definite proportions'of A, B and C particles, as determined by the perpendicular distance from that point to the side opposite to the apex of the triangle indicating of that size of particles. The percentage of A. Band C particles indicated by any point on the diuram total to 100%. For example, the point 20 .of Figure 1 corresponds to a mix containing 20% of component A, 30% of component B and 50% of com- I ponent C. Each curve on Figure 1 is the locus of mixtures of A, B and C particles having the same density. For example, on the curve 21, the chrome brick made from the mix indicated by the point 22 have the same density as the chrome brick made from the mix indicated-by the point 23, or by any other point-on that curve. Curve 21 indicates the lowest density mix of any curve plotted on Figure 1, while curves 24, 25, 26 and 27 indicate mixes which produce chrome brick of increased density, the mix of greatest density being that shown by the curve 27. However, the mix indicated by the curve 26 is of very high density.

The areas on the ternary diagram enclosed by the curves of equal density are progressively smaller as the portion of the diagram for mixes of high density is approached, so that, for high density, there is a smaller range of selection of proportions of various size ranges.

Mixes located within the curve 26 are of high density, and generally indicate that the percentage of larger or A particles should be between 45% and 65%, while the proportion of smaller or C particles should be between 35% and 55%, while the intermediate or B particles should be either eliminated or held to the remaining percentage. The mix of highest density should have preferably 55% of larger or A particles and 45% of smaller of C particles.

From a practical standpoint, it is more convenient to limit the mix to larger and smaller particles, that is, to A and C particles, eliminating the intermediate or B particles altogether. However, as indicated by'the diagram, a small pro portion of B particles in the mix may have no material tendency to lower the density of the mix and may perhaps even have a tendency to raise the density of the mix, provided the proportion is so low that the mix remains in the area of high density. 7

In Figures 3 to 5 inclusive, I have endeavored to indicate on a greatly magnified scale, different types of granular structure of refractory mixes, the densities of the mixes varying according to the extent to which the respective grains interfit with one another. It should be understood that the contours shown in the figures are not intended to represent the contours of actual particles, as no attempt has been made to represent the actual contours of the particles, the figures being intended merely to indicate a possible reason for the marked changes effected bymy invention, changes that do take place in the structure of the mix and that I have found to give the markedly increased mix density and markedly better physical characteristic for the brick made from my mix.

In Figure 3, I illustrate a mix made up only of larger chrome grains of fairly uniform size, that is, a mix made up only of A particles. The interstitial or void spaces 28 between the individual A particles are relatively few and are considerably reduced in size by reason of the fair interfitting of the individual particles, but are of a content that is large as compared to that of the idividual C particles, a single void space 28 being perhaps large enough to contain many of the C particles without changing the relative positions of the adjoining A particles.

In the mix shown in Figure5 the relatively large interstitial spaces 28' between the grains have been filled with small particles C and there has been little change in the relative placement of the large grains, the presence of the C particles not interfering with the interfitting of the A particles, and, as a result, there has been a material reduction in the void space as compared to that shown in Figure 3. If the relative placement of the A particles be the same as in Figure 3, the presence of the small C particles will have reduced the void space by an amount equal to the sum of the volumes of the individual C particles.

A mix represented by the area of high density of Figure 1 might perhaps be considered to approach or at least tend toward the conditions indicated in Figure 5, except that the A particles in the actual mix would probably be more widely variant in size than the A particles of Figure 5.

and not so large as compared to the C particles of Figure 5.

Figure 4 is intended to represent a mix made up of larger particles A, smaller particles C and particles B of intermediate size. As indicated in this figure. the particles B of intermediate size interfere with the relative interfitting of the larger particles A and make the interstitial spaces 28 which may or may not be filled with the C particles, larger and more numerous than with the conditions of Figures 3 or 5.

It is of course obvious that a different selection of screens may be used in obtaining the A, B and C (larger, intermediate and smaller) grades of particles from that taken for the series of tests represented by Figure 1, and that the position of the equi-density curves will be variant according to variant selections of these size grading screens and that the focal region representing the relative quantities of A, B and C particles for a mix of maximum density may, to some extent, be variant with a different selection of grading screens.

The coarseness of the larger particles may be increased to include larger particles between 3 and 30 mesh per linear inch, while the fineness of the smaller particles may be reduced, using smaller particles finer than 60 mesh per linear inch or even finer than 80 mesh per linear inch. However, good results may be obtained with smaller particles which pass through 50 mesh per linear inch. I find considerable advantage in selecting the A and C particles of decidedly different sizes, so that the belts of larger and smaller particles are not very close to each other in size} Figure 2 gives a diagrammatic illustration of my method of obtaining a mix made up of larger and smaller particles without the presence of particles of intermediate size, as for example, a mix made up of 55% of larger or A particles and 45% of smaller or C particles, with substantially no B particles.

The raw material is initially ground and crushed in a mill 29, which delivers the ground material at 30 to a course screen 31 which may desirably be mesh per linear inch, but may permissibly be as large as 3 mesh per linear inch.

Any particles too large to pass the screen 31 may desirably be returned at 32 to the mill 29 for continued grinding.

The material passing the screen 31 drops to a screen 33 of intermediate mesh, for example or mesh per linear inch. The material that fails to pass the screen 33 comprises particles of 'the larger or A size, and falls off the screen 33 into a suitable receptacle or conveyor 34, while the material that passes through the screen 33 consists of B or intermediate and C or smaller whence they are delivered at 37 to a secondary grinder 38 which grinds them to the smaller or C size, the grinder 38 delivering to a screen 39 which is of the same mesh as the screen 35, and any particles too large to pass this screen being returned at 40 to the grinder 38 for continued grinding.

The particles that pass through the screen 35 are the smaller or C particles, and drop into a receptacle 41, whence they are taken by a suitable conveyor 42 to a mixer 43. Likewise the particles that pass the screen 39, which are also smaller or C particles, are delivered from a hopper 44 through conveying means 45 to the conveyor 42, so as to unite them with the C particles that have passed through the screen 35. The larger or A particles from the receptacle 34 are delivered by a conveyor 46, partly into the conveyor 42 at 47, and partly into the auxiliary grinder 38 by a conveyor 48.

In practice the relative quantity of larger or A particles delivered from the mill 29 is readily controlled roughly by suitable adjustment at the mill 29, but exact adjustment is diflicult and I prefer to operate the mill 29 to deliver larger or A particles in an indefinite excess of the desired quantity, using as much of the A particle material from the screen 33 to mix .with the C particle material from the screens 35 and 39 as is needed for the desired mixture of maximum density, and grinding the surplus of the larger or A material into smaller or C particles.

When the proper balance is finally obtained,

all of the material leaving the mill 29 is delivered to the mixer 43 in the desired ratio of larger and smaller sizes, usually of larger particles to 45% of smaller particles, although the proportion of larger particles may vary between 45% and and the proportion of smaller particles may vary between 35% and 55%. Likewise, while the intermediate or B particles are preferably totally absent, they may permissibly be present to the extent of between 0 and about 20%. r

I contemplate that conventional brick-making methods will be used, as at present applied in chrome brick. I have already explained how the material will be ground and the mix made up. Prior to molding the mix will be suitably moistened, and suitable temporary or permanent binders may be incorporated. I will, however, use care to see that suflicient binder is not added to flux the refractory under furnace conditions. I will not add substantial quantities of plastic material to the mix.

The use of high pressure for forming the chrome brick is highly important in my invention, as without it the brick are not desirably dense. I. therefore consider it important in my invention to use for the chrome brick a molding pressure of 1000 pounds per square'inch or greater. The molding pressure should, however, preferably exceed 5000 pounds per square inch, and may exceed 10,000 pounds per square inch.

While my brick may be fired before use, they may desirably be used in unfired condition, relying on the furnace in which the brick are employed to subject them to firing temperature. In the case of an unfired brick, sodium silicate may be desirably used as a binder. I find that about 2% of sodium silicate, or even less, will serve as an effective binder.

Where sodium silicate or any other soluble substance is used as a binder; it will of course be added with water, but the water is not to be included in the percentage given for the binder.- The percentage is intended to be the proportion of binder in the dry brick.

While I have referred throughout to the use of chrome ore as the raw material for my chrome brick, it will be understood that magnesia (burned magnesite) may be substituted for chrome ore with relatively little loss in advan tage. However, I prefer to use less than 50% of magnesia in the chrome brick.

The brick subsequent to molding, may either be dried and fired, or they may be dried and placed in a furnace lining without previous firing.

In either case, the brick will be subjected to firing temperature, whether the firing temperature be that of a kiln or that of the furnace lining or other place in which the brick are ultimately used.

Wherever I refer herein to percentages, I mean percentages by weight, unless the context clearly indicates that percentages by volume are intended, as in the case of porosity.

In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A refractory shape of chrome ore and magnesia, comprising between 45% and 65% by weight of larger particles between 3 and 30 mesh per linear inch and between 315% and 55% by weight of smaller particles through 50 mesh per linear inch, densely compacted together and adapted to be used in a furnace lining in unfired condition.

2. The method of making a refractory of high density from non-plastic material preponderantly chrome, and a bonding substance, using non-plastic particles of relatively larger and smaller grain sizes, which consists in mixing larger non-plastic particles retained on a 30 mesh per linear inch screen with smaller non-plastic particles and a bonding substance, while employing not more than a relatively small proportion of intermediate grain sizes, using a preponderant amount of chrome in the mix, in molding the mix in moist condition into a refractory shape, in drying the refractory shape and in subjecting the dried unburned refractory shape to firing temperature in a furnace structure during use. Y

3. The method of making a refractory of high density from non-plastic material preponderantly chrome, and a bonding substance, using non-plastic particles of relatively larger and smaller grain sizes, which consists in mixing larger non-plastic particles retained on a 30 mesh per linear inch screen with smaller non-plastic particles and a bonding substance, while employ ing not more than a relatively small proportion of intermediate grain sizes, using a preponderant amount of chrome in the mix, in molding the mix in moist condition under pressure into a refractory shape, in drying the refractory shape and in subjecting the dried unburned refractory shape to firing temperature in a furnace structure during use.

4. The method of making a refractory of high density from non-plastic material preponderantly chrome, and a bonding substance, using non-plastic particles of relatively larger and smaller grain sizes, which consists in mixing larger non-plastic particles retained on a 20 mesh per linear inch screen with smaller nonplastic particles and a bonding substance, while employing not more than a relatively small proportion of intermediate grain sizes, using a preponderant amount'of chrome in the mix, in molding the mix in moist condition under pressure into a refractory shape, in drying the refractory shape and in subjecting the dried unburned refractory shape to firing temperature in a furnace structure during use. a

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5. The method of making a refractory of high density from non-plastic material preponderantly chrome, and a bonding substance, using non-plastic particles of relatively larger and smaller grain sizes, which consists in mixing -larger non-plastic particles retained on a 30 mesh per linear inch screen with smaller nonplastic particles below 60 mesh per linear inch and a bonding substance, while employing not more than a relatively small proportion of in- 6. The method of making a refractory of high density from non-plastic material, preponder-- antly chrome, and a bond, using non-plastic particles of relatively larger and smaller grain sizes, which consists in mixing larger non-plastic particles between 3 and 30 mesh per linear inch in the proportion of 45% to 65% with smaller nonplastic particles below 50 mesh per linear inch in the proportion of 55% to 35%, and with a bond, incorporating a preponderant amount of chrome in the mixture, in molding the mixture in moist condition under a pressure exceeding 1000 pounds per square inch, in drying the mixture and in subjecting the dried unburned mixture to firing temperature in a furnace structure during {7. The method of making a refractory of high density from non-plastic material preponderantly chrome, and a bond, using non-plastic particles of relatively larger and smaller grain sizes, which consists in mixing larger non-plastic particles between 3 and 30 mesh per linear inch in the proportion of 45% to 65% with smaller nonplastic particles below 50 mesh per linear inch in the proportion of 55% to 35%, and with about 2% of sodium silicate, incorporating a preponderant amount of chrome in the mixture, in molding the mixture in moist condition under a pressure exceeding 1000 pounds per square inch, in drying the mixture and in subjecting the dried unburned mixture to firing temperature in a furnace structure during use.

8. The method of making a refractory of high density from chrome and a bonding substance, using larger and smaller grain sizes, which consists in mixing larger chrome particles retained on a 30 mesh per linear inch screen with smaller chrome particles and a bonding substance, while employing not more than a relatively small proportion of intermediate grain sizes, in molding the mix in moist condition under pressure into a refractory shape, in drying the refractory shape and in subjecting the dried unburned refractory shape to firing temperature in a furnace structure during use.

9. The method of making a refractory of high density from chrome and a bond, using relatively larger and smaller grain sizes, which consists in mixing larger chrome particles between 3 and 30 mesh per linear inch in the proportion of 45% to 65% with smaller chrome particles below 50 mesh per linear inch in the proportion of 55% to 35%, and with a bond, in molding the mixture in moist condition under a pressure exceeding 1000 pounds per square inch, in drying the mixture and in subjecting the dried unfired tureduring use.

10. The method of making a refractory of high density from amixture of chrome and magnesia containing more chrome than magnesia, and a bonding substance, using larger and smaller grain sizes, which consists in mixing together chrome and magnesia particles, with an excess of chrome, using larger particles between 10 and 30 mesh per linear inch with smaller particles below 60 mesh per linear inch, in roughly equal proportions, and with a bonding substance, in molding the mixture in moist condition under high pressure, in drying the brick thus formed and in placing the dry unburned brick in a furnace structure.

11. The method of making a refractory of high density from a mixture of chrome and magnesia containing more chrome than magnesia, and a bond, using relatively larger and smaller grain sizes, which consists in mixing together chromeand magnesia particles with an excess of chrome, using larger particles between 3, and 30 mesh per linear inch in the proportion of 45% to 65% with smaller particles below mesh per linear inch in the proportion of to 35%, and with a bond, in molding the mixture in moist condition under pressure exceeding 1000 pounds per square inch, in drying the mixture and in subjecting the dried unburned mixture to firing temperature in afurnace structure during use.

12. A dry refractory body preponderantly containing chrome, said body having low porosity, being in unfired condition and suitable for use in unfired condition, and comprising a densely compacted mixture of larger non-plastic particles capable of being retained on a screen of 30 mesh per linear inch-and smaller non-plastic particles capable of passing through a screen of mesh per linear inch, in roughly equal proportions and a bonding substance distributed through the mixture.

13. A dry refractory brick preponderantly containing chrome, said brick having low porosity, being in unfired condition and suitable for use in unfired condition, and comprising a densely compacted mixture of about equal proportions of larger non-plastic particles between 10 and 30 mesh per linear inch and smaller non-plastic particles below 60 mesh per linear inch and a bond in the mixture.

14. A non-plastic refractory brick preponderantly containing chrome, comprising about 55% of larger non-plastic particles between 10 and 30 mesh per linear inch, about 45%, of smaller nonplastic particles below 60 mesh per linear inch and a binder, the brick being of requisite cold strength for use in unfired condition.

15. A dry refractory brick preponderantly containing chrome, said brick having low porosity,

being in unfired condition and suitable for usein unfired condition, comprising a densely compacted mixture of between 45% and of larger non-plastic particles between 3 and 30 mesh per linear inch and between 55% and 35% of smaller non-plastic particles below 50 mesh per linear inch and a bond in the mixture.

16. A dry refractory brick preponderantly containing chrome, said brick having low porosity,

being in unfired condition and suitable for use in unfired condition, comprising a densely compacted mixture of between 45% and 65% of larger non-plastic particles between 3 and 30 mesh per linear inch and between 55% and 35% of smaller non-plastic particles below 50 mesh per linear inch and about 2% of sodium silicate in the mixture.

17. A dry chrome brick having low porosity,.

being in unfired condition and suitable for use in unfired condition, comprising a densely compacted mixture of between 45% and 65% of larger non-plastic particles between 3 and 30 mesh per linear inch and between 55% and 35% of smaller non-plastic particles below 50 mesh per linear inch and a bond in the mixture.

18. A dry chrome-magnesia brick containing more chrome than magnesia, having low porosity, being in unfired condition and suitable for use in unfired condition, comprising a densely compacted mixture of between 45% and 65% of larger non-plastic particles between 3 and 30 mesh per linear inch and between 55% and 35% of smaller non-plastic particles below 50 mesh per linear inch and a bond in the mixture.

RUSSELL PEARCE

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