US2008117A - Forming refractory articles - Google Patents

Description

2 Shets-Sheet 1 TONE FORMING REFRACTORY ARTICLES Original Filed May 6, 1930 ju y 16, 1935.

INVENTOR FRANK J. TONE v ATTORNEYS Fig. 2.

July 16, 1935. F. J. TONE FORMING REFRACTORY ARTICLES 2 Sheets-Sheet 2 Original Filed May 6, 1930 INVENTOR FRANK J. TONE M ATTORNEYS Patented July 16, 1935 UNITED. STATES PATENT OFFICE FORMING REFRACTORY ARTICLES Frank J. Tone, Niagara Falls, N. Y., assignor to The Carborundum Company, Niagara Falls, N. Y., a corporation of Pennsylvania Original application May 6, 1930, Serial No. 450,160. Divided and this application June 3,

= 1931, Serial No. 541,843. In Great Britain May 12 Claims. (Cl. 25-156) The present invention relates to the forming of this process contains particles of a flaky or platerefractory articles, and is especially applicable likecharacter, these particles so orient themselves to crucibles and other hollow articles having walls during the jolting that they lie generally in planes which are utilized for the conduction of heat, and which are approximately perpendicular to the dito their manufacture. The present application is rection of the jolt. The introduction of materials 5 a division of my copending application, Serial No. in which the flaky characteristic is pronounced 450,160 filed May 6, 1930. The latter application has been found to give very unusual properties is a continuation in part of my copending applito the resulting crucible. As an example, if a macation Serial No. 210,293 filed August 3, 1927. terial such as flake graphite is incorporated into It is desirable in some types of refractory the mix and the mix consolidated by the jolting 10 articles, such as crucibles or the like, that the maprocess as herein described, a crucible is produced terial be as densely compacted as possible, and in which the thermal conductivity radially that the particles of the material rather than bethrough the wall greatly exceeds that axially of ing pressed together in a haphazard or random the crucible, i. e., in the vertical direction.

arrangement, be so arranged or oriented that they The extent to which the directional thermal 15 occupy the greatest possible proportion of availconductivity may be controlled depends upon the able space. The high density thus obtained not properties of the individual particles used in the only renders the article more impermeable to gases mix. In the case of natural flake graphite, which and slags, but also increases its strength. There combines both flakiness and compartively high are also instances where it is advantageous to conthermal conductivity, heat can flow more readily 20 trol the. thermal conductivity of the article in a in a direction parallel to the planes of the flakes certain preferred direction. In the case. of a than in other directions. Measurements made crucible, it is desirable that the transmission of with mixes composed principally of flake graphheat through the wall is as great as possible, but ite have shown a thermal conductivity at right the conduction of heat toward the top or lip porangles to the direction of jolting several times 25 tion of the crucible should be minimized, since that parallel to the direction of jolting, and even the useful portion of the heat flow is limited to as high as five and six times as great. Even when that passing through the wall of the crucible the amount of flake graphite is decreased to the t0 the Charge. The Optimum Condition is epreextent where it constitutes a minor but material Sented bya crucible in which the thermal conportion of the mix, the directional thermal con- 30 ductivity through the Wall. greatly eXCeedS that in ductivity effect is still pronounced. The use of the vertical direction axially of the crucible. flaky graphite greatly increases the directional crucibles are usually manufactured by a spinthermal conductivity efiect over that which can be ning process, and although there may b obtained when ranular or non-flaky particles siderable orientation of the flake-like particles in are used g 35 the crucible mix during the spinning operation, k rticles in an a the structure tends to be laminated radially and The onenta'tlon of the fla y pa p the orientation of the particles is exactly the opt g gg g g s gz g g gz gfziii piogfig posite from that necessary to give an increased 61 e W c er 40 heat conductivity through the crucible wall. The in properties other than thermal conductivity 40 orientation of the flake-like particles lying with The orientation of the flakes right angles to the their planes parallel to that of the wall instead Wan Surface BXPQSGS only then' edgfis at t of increasing the thermal conductivity in a direcface whereas Wlth the reverse onenfoatlon tion through the wall, may actually act as a dettamed in the spinning Process the m surface -15 riment'as far as the thermal properties of the of the fl i exposed- The materlal n Whwh crucible are concerned. the flakes are horizontally oriented therefore does In the process described in the present applicanot flake or scale oif as readily under abrasion. tion, the refractory mix is consolidated by jolting In a crucible where the glaze is worn oil in use, in a direction parallel to the vertical axis of the the rate ,of oxidation will also be efiected to a crucible. If the mix used inmakiiig a crucible by certain degree by the orientation of the particles 50 and the ease with which the protective scale will flake off.

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 of the effect may be controlled through a wide range by varying the amount of comparatively non-conducting material incorporated into the mix. For example, the ratio of the electrical conductivity in a direction perpendicular to that of jolting in comparison with that parallel to the direction of jolting is approximately 2 to 1 in the case of a mix composed of flaky particles of graph ite 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 difierent 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 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 jolting operation. This volume can be retained by the application of hydraulic pressure 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 hereinafter described. The absolute prevention of the rebound of the follower and mix during jolting accentuates the properties obtainable through the orientation of the flakes by jolting.

The accompanying drawings illustrate a preferred embodiment of the apparatus which may be used in jolting an article illustrated as a crucible.

In the drawings:

Figure 1 is a vertical section through a crucible forming mold mounted on a jolting machine;

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

Figure 3 is a vertical section through a modifled form of the apparatus, employing a mechanical clutch to check the rebound of the jolt.

In making a crucible, a suitable composition, consisting principally of or containing a material proportion of flaky material, is thoroughly mixed and placed in the mold which is mounted on the machine used for jolting. The usual plumbago mixes may be used, which consist of flaky graphite and clay binder, 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 ina steam jacketed kettle or other suitable heating apparatus to a temperature where the binder is sufficiently fiuid to be thoroughly incorporated in the mix and to coat all of the particles.

The mixture, which is plastic, is preferably fed into the mold while the latter is jolted because by so doing the successive additions of mix are caused to conform to the mold cavity and the compacting process takes place more effectively than when the entire amount of mix is'added before the jolting action is commenced.

Referring to the embodiment of the invention illustrated in Figures 1 and 2, reference numeral 5 indicates generally a crucible forming mold, made preferably of metal and constructed in 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 jolting machine, indicated generally by reference numeral 4. The jolting machine 4 comprises a base 5 having sides 6 and a table I provided with downwardly extending guides 3 which telescopically receive the upper ends of the sides 6. The base is provided with a cylinder 9 which receives a piston in attached to the table I. For raising the table fluid underpressure is supplied to the cylinder through a pipe ii, and to permit the table to fall and jolt the mold the fluid is exhausted from the cylinder through a pipe i2. While the jolting machine above described is illustrated, it is to be understood that any other suitable type of jolting machine may be employed.

Supported within the mold l 'is a sectional core g The mold sections 1 are 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 sufficient quantity of mix has been added, a weight or follower I9 is introduced into this cylinder. The follower functions to confine the mix and to act as an aid in its consolidation.

After the follower H! has been inserted, a hydraulic head, indicated generally by reference numeral 20, is clamped to the mold by means of bolts 29 extending from the base plate 3 and provided with clamping nuts 22. A hydraulic pressure is then applied to the top of the follower or ram 59 by introducing water, oil, or other liquid under pressure through a pipe connection 23, and the air is removed through a pipe 24 until the space 25 of the cylinder above the follower I9 is filled with liquid. The valve 26 is then closed and the mix is jolted until consolidation is completed.

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 suflicient. The liquid, which may be of water or oil, is supplied under hydraulic pressure through the pipe 23, which is provided with a check valve 21, which permits the liquid to flow toward the chamber 25 but not in the reverse direction. It is found that a ball check valve of the type illustrated opcrates satisfactorily and is practically instantaneous in action, allowing the water to flow in one direction but instantaneously checking any tendency to flow in the reverse direction.

In the jolting operation the principal problem consists in the prevention of the rebound of both the follower and 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 jolt, the particles are for an instant compacted into a smaller volume, but owin to the tendency of the taneously checking the tendency to rebound.

The liquid under pressure follows up the downward movement of the follower or ram ill at the moment of impact, but because of the check valve 2'! it instantaneously acts to prevent rebound after the jolting impact.

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 freedom of movement of the particles in the mix. If hydraulic pressure is used in combination with an instantaneously acting check valve, the hydraulic pressure need not be high, and the freedom of movement of the particles will be correspondingly greater than when extremely high consolidating pressures are used; at the same time the decrease in volume produced with each re-arrangement of the particles under pressure is preserved by the positive check of the rebound. By positively checking the rebound and by preserving the minimum 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 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 by a head 3i held by rods '32 to the base plate 3. As illustrated, the clutch consists of a head 33 carried by the follower l9 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 3'Lmay 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 plungeror follower l9 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 present any upward rebound.

The instantaneously acting hydraulic check or Horton clutch as applied to a jolting machine is described and claimed in the copending application of Simeon M. McAnulty, Serial No. 390,949 filed September 7, 1929, which has become Patent No. 1,818,234.

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 disassembled and the crucible removed and fired in the usual way. When a thermo-plastic mix is employed, such as thathaving a tar or pitch binder, the mold may be heated during the jolting operation and then preferably cooled before the crucible is removed.

The crucible is preferably jolted in an inverted position, as illustrated. When formed in such inverted position the lip or upper portions of the crucible wall, which are lowermost in the inverted jolted position, are given an increased density and strength which is desired in the lip portion of the crucible. 1

In order to obtain the pronounced directional heat conductivity and other advantages, such as diminution of scaling, the crucible mix should consist principally of or contain a material proportion of particles of a pronounced flaky character. Natural graphite is such a material as it is made up of flakes or laminae. A crucible made of the usual plumbago mixes in which the flake natural graphiteis incorporated with from 25% to 50% clay, shows these desirable characteristics to a pronounced degree.

However, other crucible mixes may be employed, as for example, mixes which contain graphite, a granular refractory, a flux and a plastic carbonaceous binder. An example of such a mix is one containing Per cent Natural flake graphite 21 Crushed silicon carbide grain 45 Flint 11 Borax as a mineral flux Tar as a plastic carbonaceous binder 18 selective heat conductivity of the crucible can be further increased.

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 melting clay, borax or feldspar, and about 16% of a plastic carbonaceous or bituminous binder such as a batch preferably having a densitypf about Il 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 coat all of the particles before the mixture is introduced to the jolting mold. Preferably themold is also heated before and during the jolting operation. After the jolting operation the mold is preferably cooled before it is disassembled 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 spe- True Apparent S Percent peclflc denslty gravity porosity J olted crucible l. 99 2. 67 25. 3 Spun crucible make #1. 1. 83 2. 69 31.9 Spun crucible make #2- 1. 71 2. 65 35. 5

The above results were obtained with ordinary crucible mixes in order that the values would be comparative with crucibles made by other processes. If a judicious selection of particle sizes is made and the various proportions of fine, medium and coarse 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 conduc tivity through the wall of the crucible in com parison with that in a vertical direction, :is shown by the following measurements with a crucible made of an ordinary plumbago mix containing 70% of natural flake graphite bonded with clay.

The thermal conductivity through the wall is between four and five times that in a vertical direction. v

While the present process is especially adapted for use with mixes containing flaky graphite, it will be understood that other particles of pronouncedly flaky form may be substituted for the graphite, and that a directional thermal conductivity effect may be obtained by the use of particles of this character other than by graphite flakes. Examples of flaky particles which may be used in refractory mixes are flaky fused aluminum oxide, flake anthracite, flaky silicon carbide, or flaky materials which occur in nature, such as mica, some kinds of gypsum, talc, slate, etc. By a flaky material is meant a material in 'which the particles have two dimensions considjected to an air stream, the air will tend to re move 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 or I plate-like form having a thickness considerably less than the length or width of the plate or flakes.

There are also a. number of substances having a characteristic splinter or needle-like form which can be oriented by the above described 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 conductivity effect.

The orientation of flaky particles and particularly flaky graphite by the process here described, has also been found advantageous in the case of articles other than crucibles, as, for example, mufiles, where it is desired to 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 claims.

I claim:

1. The process of forming a refractory article, which comprises forming a refractory mix containing particles of pronounced flaky character, placing the mix in a mold and jolting it so as to consolidate the mix and orient the flaky particles in a direction at right angles to the direction of jolting.

2. The process of forming refractory articles which comprises forming a refractory mix containing natural flake graphite, placing the mix in a mold and jolting it so as to consolidate the mix and orient the graphite flakes in a direction at right angles to the direction of jolting.

3. The process of making hollow articles such as crucibles or the like, which comprises forming a mix containing particles of pronounced flaky character, placing the mix in a mold and jolting it so as totconsolidate the mix and orient the flaky particles in a direction at right angles to the direction of jolting.

4. The process of molding a crucible, which comprises forming a crucible mix containing particles of pronounced flaky character, placing the mix in a mold and jolting it axially of the crucible to be formed so as to cause the flaky particles to lie in planes approximately at right angles to the side walls of the crucible.

5. In a method of making crucibles, the steps of filling a mold, representing an inverted crucible, with loose crucible material so that crucible material before compacting extends above the portion of the-mold forming the bottom of the inverted crucible, applying pressure to the upper end of said material, and simultaneously jarring said mold and contents to compact the crucible material.

6. In a method of making crucibles the steps of assembling a core within a mold casing, filling the chamber of the casing with a carbonaceous crucible material bonded with a partially volatile hydrocarbon binder, said crucible material being loose and lacking in free flowing properties, and jarring the casing and its contents while applying pressure to said contents to compact the material to the desired density about the core.

7. A method of making crucibles, including filling a mold, representing an inverted crucible, with loose crucible material including a carbonaceous material bonded with a partially volatile hydrocarbon binder, said crucible material extending above the portion of the mold forming the bottom of the inverted crucible, applying a weight to the top of said material, and simultaneoush jarring said mold and contents to compact said crucible material, and heating the crucible to harden the same.

8. The process of molding a refractory crucible comprising filling a crucible mold with an intimate plastic mix containing graphite and a carbonaceous binder, and applying a weight to the top of the mixture and jolting the filled mold in a direction parallel to-the axis of the crucible to compact the mixture, the portion of the mold cavity forming the lip of the crucible being lowermost during the jolting operation.

9. The process of molding a refractory crucible, comprising filling a crucible mold with an intimate plastic mixture containing graphite and a carbonaceous binder, and applying a weight to the top of the mixture and jolting the filled mold.

in a direction such that the inertia of the particles of the mixture and the inertia of the weight when the falling movement of the mold is arrested during jolting, will tend to compact the mixture toward the lowermost part of the mold cavity, the crucible mold being inverted during the jolting so that the portion of the mold cavity forming the lip of the crucible is lowermost during the jolting operation.

10. The process of molding a refractory crucible having increased density, mechanical strength and thermal conductivity, comprising filling a crucible mold with an intimate plastic mixture containing graphite and a carbonaceous binder,

11. The process of molding a refractory crucible comprising filling a crucible mold with a loose plastic mixture of crucible material, and applying a weight to the top of the mixture and jolting the filled mold in a direction such that the inertia of the particles of the mixture and the inertia of the weight when the falling movement of the mold is arrested during jolting, will tend to compact the mixture toward the lowermost part of the mold cavity, the. crucible mold being inverted during the jolting so that the portion of the mold cavity forming the lip of the crucible is lowermost during the jolting operation.

12. The process of molding a refractory crucible, comprising filling a crucible mold with a plastic mix of crucible material, applying con-' solidating pressure to the top of the mix, and jolting the filled mold in a direction parallel to the axis of the crucible to compact the mix, the portion of the mold cavity forming the lip of the crucible being lowermost during the jolting operation.

FRANK J. TONE.

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