US2015483A - Metal-refractory joint - Google Patents

Description

Sept. 24, 1935. J. E, |ENr'-E| D METAL REFRACTORY JOINT Filed Jun-e 29, 1932 INVEN'roR dw. /Us Eos/m l /L /E/VFEL o av v Patented Sept. 24, 19.35

Julius Edgar Llllenfeld, Winchester, Mass., as-

signor to Ergon Research Laboratories, Inc., Malden, Mass., a corporation of Delaware Application June 29, 1932, Serial No. 620,051

4 Claims.

The invention relates to ajoint between nonmetallic refractory materials and certain metals.

While the invention has several objectsfwhich will become apparent in the following description 5 thereof, it has for its particular objects the provision of a mechanically substantial welded joint between silicious refractory material and metals having a component suiiciently electropositive to react with a silicious component of a refractory, the metal cohering with said refractory by direct molecular contact therewith; the provision of gas-tight joints of this nature, and more particularly the provision of metal to refractory welded joints in which the metal has such combined properties of plasticity and expansivity that during the manufacture and later use of the joint, particularly at elevated temperatures, the stresses induced by reason of the difference between the coeilicients of expansion of the metal and the refractory do not fracture the latter nor separate the metal from the refractory; and more especially the provision of such joints between aluminum and a silicious refractory.

I have found that certain metals having a component sufliciently electropositive to react with a silicious component of the refractory may be welded thereto to accomplish the above objects. Such metals as aluminum and magnesium may, under certain conditions, be caused to thus react with the refractory forming a silicized transition layer between the metal and the refractory and thus securing molecular contact therebetween and aording a true welded joint.

Joints of this nature may nd use in many different applications, both as mechanical supports or connections for insulating refractories and joints that are liquidand/or gas-tight, as for sealing off containers. These welded joints may be utilized, for example, in the suspension of insulating bases for high-voltage equipment or terminals for oil-filled transformers and condenser-s, terminals for pressure-gas-lled tanks containing transformers, condensers, switches, lightning arresters, etc.; electrodes of electrolytic condensers, resistors, spark plugs, refractory seals and similar devices; also, in connection with high-vacuum apparatus, such as Dewar flasks, X-ray tubes and other vacuum discharge devices; mercuryfilled devices operated both in vacuum and/or high-pressure, such as mercuiytoggl? switches, mercury rectiflers, mercury lamps, etc.

In attaining the above objects, a welded joint is secured as, for exampleV between aluminum and porcelain, in the manner hereinafter more fully set forth and in which' the aluminum, or magnesium, is of such plasticity and expansivity that it will stand up under the heating and subsequent cooling of the welding operation without destroying the refractory material or the joint.

It is to be noted that genuinely sealed joints 5 between silicious insulators and metals having different coeflicients of expansion have heretofore been founded upon an entirely different physical basis than that herein disclosed. Thus, it has been the practice to join the molten insulator 10 to the solid metal, whereas in accordance with the present invention, the metal is applied in molten condition to a silicious refractory. Moreover, the difference in expansion was compenv sated for in the seals of the prior art by utilizing 15 very thin metal, the seal being mostly between a metal wall of greatly reduced thicknessand the silicious insulator whereby the difference of expansion between metal and insulator was accommodated by the inherent elasticity of the 20 metal itself.

For this reason, these seals were mechanically vulnerable, due to the extreme thinness' of the metal at the sealingl portion.

In contradistinction to the prior art and in car- 25 i rying out the present invention, a welded joint between the metal in a molten condition and a silicious refractory is provided, the expansion differences being accommodated by the inherent plasticity of the metal, rather than by shaping the metal so as to rely upon its elasticity, andy such that the plastic metal will conform to the stresses induced by reason of the difference between the coefficients of expansion of the metal and the refractory; and thus, by virtue of so conforming, will prevent fracture of the refractory and/or prevent separation of said refractory from the metal in securing a molecular contact therebetween. For this reason, a substantial mass of metal at the weld may be obtained and a rugged joint is secured and may be of such a nature, furthermore, as to be maintained at elevated temperatures.

A further novel characteristic of the joint resides in the fact that the temperature of the l refractory during the welding action is such as to exceed the melting temperature of the metal to be Welded thereto by an amount suilicientto attain the reaction between the' metal and the refractory, resulting in the formation of the aforesaid transition layer. It is to be noted that without such a reaction, a sweated joint rather than a weld would result, which sweated joint could. not have the required qualities of mechanical strength and/or tightness,A especially not at an elevated temperature. g

This application is a continuation in part of my copending applications Serial No. 486,101, filed October 3, 1930, and Serial No. 515,885, filed February 14, 1931.

In the accompanying drawing, which illustrates, by way of example, specific embodiments of the novel joint,

Fig. 1 is a front elevation and part vertical section of the riser for an electrode as utilized, for example, in electrolytic condensers.

Fig. 2 is a vertical section of a spark plug embodying the novel joint.

Fig. 3 is a vertical section through the upper` portion of a high-pressure gas condenser in which the novel joint is utilized.

Fig. 4 is a vertical section illustrating the application of the novel joint to a highly evacuated container such as a Dewar fik.

In the provision of these joints between a silicious refractory, such as porcelain, and a metal, such as aluminum, having a component sufiiciently electropositive to react with a silicious component of the refractory in the manner hereinafter set forth to produce a weld, it is to be noted that by the term "weld or "welded as applied to the joint herein described and referred to in the claims, I wish to be understood as vhaving reference to the direct consolidation of the two solid bodies-metal and refractory-to the extent of molecular cohesion by fusion at their junction.

Furthermore, as aluminum of different grades gof purity is suitable for effecting the novel joint,

the characteristics of the Joint being determined to a large degree by the particular grade of aluminum utilized, I desire, further, to define the word "aluminum as herein used to include not only substantially pure aluminum but also various suitable alloys of aluminum with other metals.

Por example, an alloy of aluminum with 1.25% of manganese; an alloy of aluminum with 1.25% of manganese and 1% of magnesium; an alloy of aluminum with 8% of copper, 12V-2% of si1icon and 1.15% of magnesium; an alloy of aluminum with 5% silicon; an alloy of aluminum with 5% silicon, 1.2% copper, and .5% of magnesium; jan alloy of aluminum with 7% silicon and 0.3% magnesium; an alloy of aluminum with 0.8% of nickel, 0.4% of iron, and 0.1% of titanium, has been ,found to an'ord satisfactory welds under certain conditions. l Also, the term pure aluminum" as utilized herein is to be understood as referring to aluminum containing 99% or better of aluminum and such as is normally produced in the well-known reduction methods for obtaining aluminum from ;-its ores, while the term high purity" aluminum ia intended to refer to the preferred form of pure aluminum and containing approximately 99.6% or more of aluminum.

In connection with the degree of purity of the :pure aluminum, it is to be noted that the amount of the impurities ordinarily present in the aluminum has a deleterious effect on the favorable combination of plasticity and expansivity and that the higher the degree of purity of the aluminum, the greater its plasticity characteristic.

Certain alloys of aluminum compounded so as to make them undesirable for the use in the novel,v weldin! process do not possess the high degree of plasticity required for effecting, for ex- .,ample. a Joint which will be gas-tight on repeated heating and cooling, yet are of such a nature as to afford a suitable joint where these rigid requirements are not met with. By this I do not wish to necessarily imply that the weld per se is not perfect and a molecular cohesion is not attained, but rather that there may be isolated areas in which no such contact exists and that therefore these portions might leak.

Particularly in the case of pure aluminum and certain aluminum alloys such as aluminum with 1.25% of manganese, and aluminum with 1.25% of manganese and 1% of magnesium, is it possible to effect a. joint that is gas-tight and/or one which will not fail under repeated heating and cooling. Where a joint of the very best characteristics is desired, however, high purity aluminum has been found to be the metal best suited for this purpose, this being particularly true where the refractory is a material such as fused quartz, which is extremely brittle.

The particular grade of aluminum required in connection with the production of a joint be tween the same and the selected refractory and whether the desired characteristic is that of perfect gas tightness, may readily be determined. e. g., by welding a threaded aluminum fitting to a tube of the refractory closed on one end, and by connecting said fitting to a gas pressure tank of, say, Z50-1b. pressure or to a vacuum system, and by observing the presence or absence of aleak first at room temperature, and secondly at a more elevated temperature which may in some Acases be 80 C., and in other cases run up as high as 300 C. or even higher.

In carrying out the method for providing the welded joint between a silicious refractory and a metal, an intermediate transition layer of the silicized metal is formed which provides molecular contact between the said metal and the said refractory, the reaction between the metal and the refractory being direct. This is best eected by heating the refractory at the area to be welded to a temperature greatly exceeding the melting temperature of the metal, as to a yellow heat and approximating 1100* C., which temperature willginsure the aforesaid reaction desired.

The aluminum is also heated and then placed in contact with the refractory whereby the temperature of the aluminum is elevated, either by further external heating or from the accumulated heat from the refractory, to an intense degree such as to cause the aluminum to iiow and react with the silicious component of the refractory.

In eii'ecting the weld, it is desirable to coat the aluminum prior to its contact with the heated refractory with a substance which will not dissolve the oxide skin upon the aluminum to a detrimental degree and which has a tendency rather to protect the aluminum from oxiizing too deeply, and to provide an envelope for supporting the metal in a molten state even if heated considerably above its melting point.

This envelope should be of a flexible character and I have found that a layer of borax is particularly suitable for this purpose, being when molten viscous enough to adhere to the aluminum and at the same time sufficiently liquid to allow the molten aluminum to adjust itself to the contour of the refractory.

Furthermore, the borax probably facilitates the reaction between the aluminum and the refrac-A tory, as it will run in its molten condition the freest at the tip where the aluminum is the thinon the metal and thus causing the latter to flow irregularly in all directions in the absence of any envelope to restrain it. Such action would be entirely unsuitable in the present instance.

In contradistinction to the usual method of effecting a joint between a metal and a refractory, I cuse the metal to melt while the refractory retains its solid phase, and moreover, is

heated to a temperature far above the melting point of the metal which is to be welded thereto, the particular temperature required being that necessary to attain the reaction between the electropositive componentv of the metal and the silicious component of the refractory. Furthermore, the enveloping agent utilized is of such a nature as to melt at the welding temperature but vnevertheless to adhere to the refractory in a molten condition and to restrain the metal from undue dispersion thereover.

The aforesaid method of welding is applicable to the production of a great variety of articles and yapparatus utilizing non-metallic refractory material, having also electrical insulating properties, and more especially amaterial of this nature having a siliclous component. For example, such refractories as porcelain (Si1limanite) quartz, glass of the borosilicate type, and other silicates have been found satisfactory for effecting therewith a welded joint.

The refractory is preferably utilized in cylindricalY form as bushings, tubes, rods, etc.: and the area to be welded is preferably, though not necessarily, first glazed as by a fluoride or borax glazing.

- As a specifc'example of the application of a welded joint of the aforesaid type an electrode, such as may be utilized for electrolytic condensers, is shown in Fig. 1. In this embodiment, I0 and I0' designate respectively the top and bottom aluminum rods or risers of the electrode (not shown) .secured thereto. These risers are secured to or 'are integral with vend heads, the upper of which is provided with an annular recess II and projecting axial stem I2, while the lower is provided with the socket I3.

A conductor I4 for external connection is suit-` rounding wall portions Il and I3 respectively. t.

The respective refractory members to this end have a snug fit in the corresponding recess or outer wall thereof which has, previous to the heating operation, applied thereto over the outer surface a coating of the ,enveloping agent such as borax.

A welded joint is thereby attained upon heating of the refractory and metal, as hereinbefore set forth, along the edge of the wall portions I1 and I8 to provide convenient external connections to the electrode anda mounting of the same.

In Fig. 2 a further embodiment of the invention is disclosed and more particularly in connection with the adaptation of the weld to a spark plug.

Referring to said figure, the axial tubing 20 is 10 of insulating material such as porcelain .or Sillimanite" and through the same extends the conductor or electrode element 2 I which is welded at the one end to the inside of a cap member or terminal 22. The latter seats over the tube and 15 is shown'as welded along its edge 23 thereto. Furthermore, a weld is effected between the said tube 20 and the aluminum housing 24 of the plug through its sleeve 25. The latter may be constituted of the more plastic-type of aluminum 20 andwelded to the portion 24 of the harder type.

Another practical embodiment of the invention is illustrated in Fig. 3 in which 30 designates a suitable container adapted to withstand high pressures and, in the present instance, housing 25 the electrodes 3I and 3|', of an electrical condenser in which the dielectric between said electrodes is constituted by a gas such as nitrogen.. hydrogen, carbon dioxide, air, etc., and under extremely high pressure. This necessitates a se- 30 cure external connection to the electrode or electrodes in order to avoid wastage or loss of the gas which is to be confined pennanently'therein. Similar difficulties exist in connection with the operation of high-voltage transformers with 35 sealed-in fluid, especially such as have a highpressure gas enclosed above the level of the fluid; in the operation of electric refrigerators wherein the mechanism is hermetically sealed within a gaseous medium under pressure, etc.; as Well as 40 in the case of vacuum-sealed apparatus.

The electrode 3| of the gas condenser is shown connected with a riser extension member 32 which is designed to pass through the top 30' of the container and in such a manner as to be elec- 4:5' trically insulated therefrom and sealed against loss of the high-pressure fluid retained by the container. To this end, a tubular insulator and refractory'member 33 is designed to surround a portion of the said riser, more especially the part 50 ber but is preferably welded to a container of aluminum, as shown, to secure a sealing or gastight fit thereto. This bushing is counterbored or recessed at its outer end to provide the seat 36 and'a sleeve'31 of relatively thin metal. The bottom of the tubular insulator member 33. moreover, is designed to rest on the seat 38, and. the sleeve 31 to fbe welded to the lower end of the said insulator member.

To strengthemlthe mechanical bond between the bushing and insulator member, more especially with reference to axially directed stresses, it is preferred to provide the lower end of the latter with a peripheral groove 38 which will be ,substantially filled during the welding operation.

cupped for this purpose to afford the overhanging sleeve portion 43 embracing said insulator member, and a peripheral groove 44 is provided in the latter to better secure the, cap thereon when welded thereto. Cap 40. furthermore, is provided with an inwardly directed threaded boss 4I, which is coaxial with the insulator member and is designed to receive the outer end of the extension or riser 32 of the electrode, and suitable electrical connection may then be made to the terminal cap, as at the threaded outer portion 46 thereof.

As an embodiment of a vacuum-sealed apparatus, a Dewar flask or so-called vacuum bottle is illustrated in Fig. 4. In this embodiment the container 50 is of aluminum, and the neck of the same is sealed as at 5I to a refractory or porcelain mouth element 52 and into which is designed to fit the stopper or cork 53. The enclosing shell 54 for the vacuum chamber, formed between said shell and the container 50, is made also of aluminum and of two parts in order to admit of the insertion of the container, and at its upper end 1t is welded to the neck member or mouth element 52 at an area displaced from the portion at which the container 50 is welded. The shell 54 may then be closed at the bottom, or in any convenient manner, as by welding thereto the cast or forged base 55 of aluminum. A cap 56 of metal (aluminum) fits over the other end of the flask and is designed to have, for example, a bayonet nt therewith.

I claim:

l. The herein described welded unit comprising a plurality of bodies, one a silicious refractory, the other of a metal of the group comprising aluminum and magnesium, each body of pre- 4formed individual shape, and an intermediate transitionbond of silicized metal providing molecular contact between a mass of the said metal small as compared to the total mass of the metal body and the said refractory.

2. The described welded unit comprising a plurality of bodies, one a silicious refractory, the other of a metal of the group comprising aluminum and magnesium and of sufficient plasticity to compensate for the difference between its thermic expansivity and that of the refractory, each body of preformed individual shape, said bodies being united molecularly at adjacent surfaces through an intermediate transition bond of silicized metal providing molecular Contact be tween a mass of the said metal small as compared to the total mass of the metal body.

3. 'Ihe described welded unit comprising a plurality of bodies, one a silicious refractory, the other of a metal of the group comprising aluminum and magnesium, each body of preformed individual shape, said bodies being united molecularly at adjacent surfaces through an intermediate transition bond of silicized metal providing molecular contact between a mass of the said metal small as compared to the total mass of the metal body and the contact remaining permanent and gas-tight under repeated heating and cooling.

4. The described welded unit comprising a plurality of bodies, one of quartz and the other of aluminum, each body of preformedindividual shape, said bodies being united molecularly at adjacent surfaces through an intermediate transition bond of silicized metal providing molecular contact between a mass of the said metal small as compared to the total mass of the metal body.

JULIUS EDGAR LILIENFELD.

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