US1881104A - Refractory article - Google Patents

Description

" Oct. 4, 1932. TONE 1,881,104

REFRACTORY ARTI CLE Filed May 6, 1950 2 Sheets-Sheet l INVENTOR F. .1. TONE REFRACTORY ARTICLE Filed May 6. 1930 2 Sheets-Sheet 2 INVENTOR Patented Oct. 4, 1932 UNITED STATES PATENT OFFICE PANY, OF NIAGARA FALLS, NEW YORK, A CORPORATION OF PENNSYLVANIA mmc'roav ARTICLE Application filed May 8, 1980. Serial No. 450,189.

,The present invention relates to refractory articles, and especially to crucibles and other hollow articles having walls which are utilized for the conduction of heat. The present application is a continuation, in, part, of my copending application Serial No. 210,293, filed August 3, 1927.

It is'desirable in some types of refractory articles, such as crucibles or the like, that the material be as densely compacted as possible, and that the particles of the material rather than being pressed together in a hap- ,hazard or random arrangement, be so arranged or oriented that they ,occupy the greatest possible. proportion of available space. The high density thusobtained not only renders the article more impermeable to gases and slags, but also increases its strength. There are also instances where it is advantageous to control the thermal conductivity of the article'in a certain preferred direction; In the case of a crucible, it is desirable that the transmission of heat through the wall is as great as'possible, but the conduction of heat toward the top or lip portion of the crucible should be minimized, since the useful portion of the heat flow is limited to that passing through the wall of the crucible tothe charge. The optimum condition is represented by a crucible in which the thermal conductivity through the wall greatly exceeds that in the vertical direction axially of the crucible.

Crucibles are usuallymanufactured by a spinning process, and although there may be considerable orientation of the flake-like particles in the crucible mix during the spinning operation, the; structure tends to be laminated radially and the orientation of the particles is exactly the opposite fromv that necessary to-give an increased heat conductivity through the crucible wall. The orientation of the' flake-like particles lying with their planes parallel to that of the wall instead of increasing the thermal conductivity. in a direction through the wall, may actually act asa detriment as far as the thermal properties of the crucible are concerned.

In the process described in the present application, the refractoryvmix is consolidated y jolting in a direction parallel to the vertical axis of the crucible. If the mix used in making a crucible by this process contains particles of a flaky or plate-like character, these particles so orient. themselves during the jolting that they lie generally in lanes which are approximately erpendicu ar to the direction of the jolt. he introduction of materials in which the flaky characteristic is pronounced has been found to give very unusual properties to the resulting crucible. As an example, if a material such as flake graphite is incor orated into the mix and the mix consolidate by the jolting process as herein described, a crucible is roduced in which the thermal conductivity radially through the wall greatly exceeds that axially of the crucible, i. e., in the vertical direction.

' FRANK J. TONE, OF FALLS, NEW YORK, ASSIGNOB TO THE GARBOBUNDUK COM- The extent to which the directional thermal conductivity may be controlled depends upon the propprties of the individual particles used in t graphite, which combines both flakiness and comparatively high thermal conductivity,

heat can flow more readily in a direction parly increases the -directional thermal conduc-- tivity eflect over that which can be obtained when granular or non-flaky particles are used.

The orientation of the flaky particles in an approximately horizontal position produces a crucible which differs from the usual spun product in properties other than thermal conductivity. The orientation of the flakes at right angles to the wall surface exposes only their edges at the surface, whereas with the reverse orientation obtained in the spinning e mix. In the case of natural flake process the entire surface of theflake is exposed. The material in which, the flakes are horizontally oriented therefore does not flake or scale oil as readily under abrasion. In a crucible where the glaze is worn off in use, the rate of oxidation will also be affected to a certain degree by the orientation of the particles and the easewith which the protective scale will flake ofi.

The electrical properties of an article made from a mix containing flake graphite show pronounced directional effects when the mix is consolidated by the process herein described. The magnitude ofthe effect may be controlled through a wide range by varying the'amount of comparatively non-conductirig material 'iIICOIPOlflt-QdjilltO the mix. For example, the ratio of the electrical conductivity in a direction perpendicular to that of j olting in comparison with that parallel to the direction of jolting is approximately 2 to l in the case of a mix composed of flaky particles of graphite and a carbonaceous binder such as tar or pitch which on carbonization becomes a fairly good electrical conductor. In a mix containing 70% flake natural graphite and 30% clay, where the bonding material is comparatively non-conducting, the ratio was approximately 6 to 1. If the nature of the mix is known, the measurement of the electrical conductivity of the article in different directions will also give'some idea of the relative thermal conductivities in these directions.

In order to obtain the maximum degree of orientation and at the same time secure the 1 densest possible consolidation of the mix, it is preferable to jolt the mix in combination with a follower which will confine the mix to the minimum volume which it reaches during the 7 jolting operation. This volume can be retained by the application of hydraulic pres sure to the .mix'in combination with an instantaneously acting check valve to prevent recession of the follower, or by other quick acting means, as will be hereinafer described. The absoluteiprevention of the rebound of the follower and mix during jolting accentuates the properties obtainable-through the orientation of the flakes by olting.

The accompanying drawings illustrate a preferred embodiment of the apparatus which may be used in j olting an article illustrated asa crucible. v In the drawingsa Figure 1 is a vertical section through a crucible forming mold mounted on a jolting machine; r

' Figure 2 is a horizontal section on the line 11-11 of Figure 1; and

Figu modified form of the apparatus, employin a mechanical clutch to check the rebound o the jolt. I

In making a crucible, a suitable composi- 35 tion, consisting principally of or containing re 3 is a vertical section through 21 .a material proportion of flakymaterial, is thoroughly mixed and placed in the mold which is mounted on the machine used for 'olting. The usual plumbago mixes may e used, which consist of flaky graphite and clay hinder, or mixes may be used consisting of natural flake graphite, silicon carbide, a mineral fluxing material, and a bituminous binder. In case a bituminous binder such as'tar or pitch is used, the mix is heated in a steam jacketed kettle or other suitable heating apparatus to a temperature where the binder is sufficiently fluid to be thoroughly incorporatedin the mix and to coat all of the particles. p

The mixture, which is lastic, is preferably fed into the mold w ilethe latter is jolted because by so doing the successive additions of mix are caused to.conformv to the mold cavity and the compactin process takes place more efl'ectivelythan w en the entire amount of mix is added beforethejolting action is commenced. g

Referring to the embodiment of the inventionillustrated in Figures 1 and 2, reference numeral 1 indicates generally a crucible forming mold, made preferably of metal and constructedin sections.. The mold rests on a bottom plate 2. The mold and bottom plate are carried-by 'a base plate 3 adapted to be "placed on a joltingmachine, indicated gen erally by reference numeral 4. The jolting machine i comprises a base 5'having sides 6 and a table 7 provided with downwardly extending guides 8. which telescopically receive the upper ends of the sides 6. 3 The base is provided with a cylinder 9. which receives a piston-10 attached to the table 7. For raising thetable fluid under pressure is supplied to the cylinder through a pipe 11, and to permit the-table to fall and jolt the mold the fluid is exhausted from the cylinder through a pipe 12. While the jolting ma chine above described is illustrated it'is to be understood that any other suitable type of jolting machine may be employed.

Supportedwithinthe mold 1" is a sectional core 13 shaped to give proper form and size to the interior of the crucible. -The core 13 is assembled on the bottom plate 2 and the mold sections 1 are put in place and retaining rings 14 areforcedaround theoutside. The-mold sections 1 are clamped'to thebottom plate 2 by means of'bolts15 engagin' lugs 16 on the mold sections and provided with nuts 17.

After the mold isassembled the crucible forming mix 18 is fed into the open top of the mold, which is jolted during the introduction of the mix. The upper'part of "the mold forms a cylindrical chamber to receive the uncompacted' mix, and after a sufthe, mix and to act as an aid in its consolidation.

After the follower 19 has been inserted, a

V, hydraulic head, indicated generally by ref- I removed through a pipe 24 until the space 25 ofthe cylinder above the follower 19 is filled with liquid. Thevalve 26 is then closed and the mix is jolted until consolidation is completed. I I 4 A high hydraulic pressure is not required, and the pressure available from the usual city supply means under, say, a pressure of fifty to one hundred pounds per square inch, is' sufficient. The liquid, which may be of water or oil, is supplied under hydraulic pressure through the pipe 23, which is provided with a Cit check valve 27, which permits the liquid to flow toward the chamber but not in the reverse direction. It is found that a ball 7 check valve of the type illustrated operates satisfactorily and is practically instantaneous in action, allowing the water to fiow in one direction but instantaneouslychecking any A tendency to fiow in the reverse direction.

In the olting operation the principal problem consists in the prevention of the rebound of both the followerand the mix. The jolting action takes place with considerable violence, and as the downward velocity of the mold, the contained mix and follower is checked by the olt, the particles are for an instant compacted into a smaller volume, but owing to the tendency of the weight and the mix'to rebound, this minimumvolume is not ordinarily retained unless some instantaneously acting means be. employed to check the rebound of'the follower and 'lIllX. The

hydraulic arrangement of the type illustrated has been found to be a satisfactory means for instantaneously checking the tendency to rebound. The liquid under pressure follows up the downward movement of the follower or ram 19 at the moment of impact, but because of the check valve 27 it instantaneously acts. to prevent rebound after the jolting imact. I V Y P The rebound of the follower would affect not only the density of the resulting article,

but also the degree of orientation of the flaky particles. The degree to which the particles orient themselves in a. given time depends upon both the violence of the jolt and the free dom of movement of the particles in the mix.

. If hydraulic pressure is used in combination with an instantaneously acting check valve,

7 the hydraulic pressure need not be high, and

the freedom of movement of the particles will be correspondingly greater than when exminimum volume which the mix attains with each individual jolt, a. product having an ,exceptional density and a high degree of orientation of the flaky particles is made possible.

Although the hydraulic head of the check" v valve is preferred for checking the rebound,

mechanical devices may be employed which will permit the follower to follow up the mix during consolidation, but which will instantaneously check rebound thereof. Such a mechanical device is illustrated in Figure 3. In Figure 3 the mold and jolting table are similar to that illustrated in Figure 1. A mechanical clutch of the so-called Horton type is indicated generally by reference numeral 30. The clutch 30 is carried bythe head 31 held by rods 32 to the base plate 3. As illustrated, the clutch consists of ahead 33 carried by the follower 19 and receiving a bar 34.- The bar 34 projects downwardly from the yoke 31. The bar 34 is of hardened steel and is of square or rectangular cross-section having smooth sides. The head 33 has integrally inclined hardened wedge faces 35. Between the faces of the bar 34 and the inclined wedge faces 35 are placed hardened steel rollers 36. The rollers will be naturally held downward by gravity, although springs 37 may be used to additionally urge them downward. Fingers 38 may be provided for holding the rollers 36 in released position when desired.

This type of clutch is commonly known as the Horton clutch, and its operation is as follows:

- The wedging rollers 36 permit the head 33 to move downwardly with respect to the bar 34, but instantaneously prevent upward movement with respect thereto. When the downward movement of the mold and its attached parts is suddenly arrested the mix which is being consolidated and the plunger or follower 19 continue to move downwardly because of their inertia. The inertia of the rollers 36 will also tend to move them downwardly into tight wedging engagement so that they will instantaneously lock the head 33 and prevent any upward rebound.

The instantaneously acting hydraulic check or Horton clutch as applied to a jolting machine is describedand claimed in the copending application of Simeon M, McAri- Serial No. 390,949, filed September 7,

The jolting is continued until the desired consolidation of the mix is attained, after which the hydraulic follower or Horton clutch is released and removed, the mold disare lowermost in the inverted jolted position,

are givenanincreased density and strength which is desired in the lip portion of the crucible.

In order to obtain the pronounced directional heat conductivity and other advantages, such as diminution of scaling, the cru-- cible mix should consist principally of or coni tain a material proportion of particles of a pronounced flaky character. Natural gra hite is such a materialas it is madeup of fla esor. lamina. A crucible made of the usual plumbago mixes in which the flake' natural graphite is incorporated with from to 50% clay, shows these desirable characteristics to apronounceddegree.

- However, other crucible mixes may be employed, as for example, mixes which contain plastic carbonaceous binder. example of sucha mix is one containing 7 v p V Per cent Natural flake graphite 21 Crushed silicon carbide grain Flint 1 11. Borax as a mineral flux 5 Tar as a plastic carbonaceous binder 18 graphite, a granular refr'actor a fluxand a r The silicon carbide may be the ordinary crushed variety which contains both flakes and irregular particles as formed by the ordinary crushing operation. A silicon carbide, however, which consists principally of flaky or, plate-like particles may be obtained by subjecting the ordinary crushed silicon' carbide to an air separation process, which separates the markedly flaky particles from i the rest of the material. By incorporating such air-winnowed silicon carbide consisting principally of the flaky or plate-like. particles, the selective heat conductivity of the crucible can be further increased. 3 Another suitable mix consists of about 58% of silicon carbide ground and screened through a screen of forty meshes to the inch, about 21% natural crystalline flake graphite, about 5% of mineral flux such as a low melt ing clay, boraxor feldspar, and about 16% of a plastic carbonaceous or bituminous bindor such as a batch preferably having a density of about l'? B. at 150. centigrade.

-When mixes containing such thermoplastic binders are used, they are intimately mixed and heated, as, for example, in a steam jacketed mixer, to a temperature such that the binder is fluid enough to be thoroughly incorporated with and coatall of the particles mg Parallel to the well (parallel to direction oijolting) before the mixture is introduced to the jolting mold. Preferably the mold is also heated before and during the jolting operation. After the jolting operation the mold ispreferably cooled before it is dis-assembled and the crucible removed therefrom.

The high density of crucibles as made by the present'process is shown by a determination of the ratio of the apparent density to the true specific gravity of mix, from which the percentage of voids or porosity may be calculated. In the following table the'density of crucibles made by the present jolting process is compared with that of two makes of crucibles made by the spinning process. The spun crucibles-were of two well-known American makes and were a high grade product: 7 7

True specific E W W Per cent Apparent porosity density Iolted crucible Spun crucible, Make #1 Theabove results were obtained with ordinary crucible mixes in order that the values would be comparative with crucibles made by other processes. Ifa judicious selection of particle sizes is made andthe various proportions of fine, medium andcoarse particles so adjusted that-the solid material fills the greatest possible proportion of available space, the porosity can be decreased to between 10 and 15% when the present process of jolting is employed.

The pronounced directional thermal conductivity through the wall of the crucible in comparison with that in a vertical direction,

is shown by the following measurements with a crucible made of an ordinary plumbago mix containing 70% ofnatural flake graphite bonded with clay:

7 Thermal conductivity Cal/cm'PGJsec.

Through the wall (perpendicular to direction of lolt 01 The thermal conductivity through the wall is between four and five times that in a vertical direction. 7

While the present process is especially adapted for use with mixes containing flaky graphite, it will be .understood thatother particles of pronouncedly flaky form may be subor flaky materials which occur in nature, such as mica, some kinds of gypsum, talc, slate,

in which the particles have two dimensions considerably greater than the third dimension, and hence may be classified as flakes or plates in contrast with the irregular shaped particles produced by the ordinary crushing.

operations on a substance such as coke or, a m-fitbn-flaky mineral.

It is possible to separate the flaky constituents from materials in which the particles are generally irregular but not all ofthe flaky form. For example, if fused aluminous oxide is subjected to an air stream, the air will tend to remove the thinner or more flaky or plate-like particles from the particles which are generally irregularly shaped, but which are not flaky. Similarly, flaky silicon carbide may be obtained by air separation. Such flaky fused aluminum oxide or flaky silicon carbide differs from the usual crushed fused aluminum oxide or silicon carbide in that the particles are nearly all of a flaky I or plate-like form having a thickness considerably less than the length or width of the plate or flakes.

There arealso a number of substances having a characteristic splinter or needle-like form which can be oriented by the above de scribed process so that the particles are oriented in a preferred direction, and which,

when so oriented as by the jolting operation,

can impart the pronounced directional thermal conductivityeflect.

The orientation of flakg particles, and par-1 ticularly flaky graphite described, has also been found advantageous in the case of articles other than crucibles, as, for example, muflles, have maximum heat conductivity through the wall.

While I have specifically described the preferred embodiments of my invention, it is to be understood that the invention is not so limited, but may be otherwise embodied and practiced within the scope of the following I claims.

1. A crucible containing refractory particles having their greatest dimensions lying generally in a direction normal to the surfaces of the side walls of the crucible and also normal to the axis of the crucible, whereby the crucible has a greater thermal conductivity in such direction than axially of the crucible.

2. A crucible made from a mix containing natural flake graphite, being oriented in an approximately horizontal direction.

3. A crucible containing granular refractory particles and containing flake graphite in which the graphite flakes are oriented in ented to lie in y the process here where it is desired to' the graphite flakes' ented in the side walls of the crucible in a direction generally normal to the vertical axis of the crucible, whereby the side walls have a greater thermal conductivity in a horizontal direction than in a vertical direction.

5. A crucible formed from a refractory mix containing natural graphite, the particles of which are oriented in the side walls of the crucible to have their greatest dimensions lying in ,a direction generally normal to the vertical axis of the'crucible, whereby the side walls have a greater thermal conductivity in a'horizontal direction than in a vertical direction.

6. A refractory article containing natural graphite and having the graphite particles oriented to lie in planes which are substantially parallel.

7. A refractory article containing at least 21% of natural graphite together with a binder, and having the graphite particles oriplanes which are substantially parallel.

In testimony whereof I have hereunto set my hand.

FRANK J. -TONE.

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