US2109758A - Heating device - Google Patents

Description

March I, 1938. E. G. TOUCEDA 2,109,758

HEATING DEVICE Filed July 5, 1955 2 Sheets-Sheet 1 INV NTOR 9-9M,

' ATTORNEY E. G. TOUCEDA HEATING DEVICE March 1, 1938.

Filed July 3, 1935 2 Sheets-Sheet 2 T In ATTOW Patented Mar. 1, 1938 UNITED STATES PATENT OFFICE HEATING DEVICE Application July 3, 1935, Serial No. 29,623

11 Claims.

This invention relates to heating devices whereby comparatively small objects or test specimens may be subjected to heat treatment of controlled temperatures up to about 3300 F.

As examples of the uses to which a device of this type may be put mention may be made of the following, viz:determination of the fusion or melting points of coal ash; the glaze upon ceramics, fire brick, and various other refractories, and many metals; sintering operations, and the study of the effects of high temperature on materials in various atmospheres.

In determining fusion points, for example, it is desirable that the atmospheric condition or environment Within the confined space in which the test is being made shall remain substantially constant throughout the test, so that there may be as few variables as possible to be considered in the final evaluation; also, that the heat employed shall be applied to the specimen uniformly over its entire surface, throughout the test; also, that there shall be a uniformly useful application of the heat employed, without waste thereof by radiation; that the period of the test shall be as short as consistent with accuracy, and the expense thereof shall be minimum; and finally, that opportunity shall be given for accurate observation of the specimen during the test, without interference by products of combustion, heat waves or other disturbances in the local environment.

Heretofore, the usual heating medium employed in such measurements has been a gaseous fuel, but this medium has been unduly expensive, slow in its heating effect, subject to explosions, and is otherwise hazardous, on account of the carbon monoxide emanations. It has also been subject to undesirable change from an oxidizing effect to a reducing effect, and to the disadvantage that in its use there was considerable interference with observation, by the heat waves, etc., which characterized its use.

A principal object of the present invention is the provision of apparatus of the general type 45 above described, which will be free from the disadvantages above recited as characteristic of devices in which a gaseous heating medium is employed, and which will also be characterized to an optimum extent by the desirable properties first above set forth.

Another object of the invention is to provide a fusion determining device in which specimens may be economically tested at temperatures up to 3000 F. and under substantially standardized atmospheric conditions. To attain this object it is desirable that the fusion temperatures be developed by passing an electric current through a suitable resistor surrounding and in close proximity to, but not in contact with, the test specimen; and, further, that the material of the resistor be of such character that it will not react at high temperatures with the atmosphere around the test specimen to produce gases which, in turn, may react with the material in the test specimen to effect a fusion point thereof. I find that electrically conductive silicon carbide, such as that sold under the trade name of Globar, is substantially stable at temperatures up to about 2700 F. and can be used practically and economically up to about 3300 F. This material is well adapted for forming resistors of the type hereinafter described. These resistors are long lived and may be used for indefinitely long periods at temperatures below about 3000 F. although carbon loss seems to begin at about 2700 F. By the use of this material it is possible to maintain in the enclosure containing the material to be measured an atmosphere of substantially constant character until the silicon carbide breaks down to a serious degree, at or above the last mentioned temperature, so that it is possible to check accurately comparative results of high temperature measurements, and to tabulate and standardize the requirements to be embodied in specifications for materials of the various classes falling within the categories of the determinations for which such apparatus may be used.

Another object of the invention is to provide a very sturdy structure, capable of withstanding the high temperatures encountered by it in use and in which structure there are but few parts employed for the support and enclosure of the central muffle; and in which structure the ar rangement of terminal electrodes is such as to permit conduction of the current to the resistor with maximum efficiency, minimum danger, and optimum convenience; the various instrumentalities being especially designed to be easily assembled, readily disassembled, and also capable of replacement with minimum expense when necessary.

Still another object of the invention is to provide a structure designed for very accurate and convenient visual observation of the specimen under treatment, either with or without the assistance of pyrometric instruments, and preferably in such a manner that a part of the specimen under observation will be disposed in proximity to an optical axis, and, when heated to incandescence, will be sharply silhouetted against a darker background.

Other objects and advantages will appear as the description of the particular physical embodiment selected to illustrate the invention progresses, and the novel features of the invention will be particularly pointed out in the appended claims.

In describing the invention in detail and the particular physical embodiment selected to illustrate the invention, reference will be had to the accompanying drawings, and the several views thereof, wherein like characters of reference do"- ignate corresponding parts, and in which:

Fig. i is a view in vertical medial section of a fusion measuring apparatus in the construction of which this invention has been embodied; Fig. 2 is a horizontal transverse section on. the line IIII; Fig. 3 is a view in front elevation, partly in section, of the apparatus as shown in Figs. 1 and 2; Fig. l is a horizontal transverse section on the line IV-IV of Fig. l, the arrows at the end of the line indicating the direction in which the view is taken; Fig. 5 is a diagram of the internal electric circuits by which the apparatus is activated; Fig. 6 is a plan view of a water cooled terminal; and Fig. 7 is a section of Fig, 6 on line VII-4711.

In the illustrative embodiment of the invention, the apparatus is shown comprising a frame designated generally by the reference character F and which includes a base member designated by the reference character H, .and a top: member l2, connected by corner bolts l3 which also serve as struts.

The members i l and it may desirably be metal plates, and upon the base member H is supported an insulating base 54 held in place by side strips l5 bolted to the base member l l, while a bracket or abutment member it, also secured to the base, as by screws ll, serves to limit forward movement of the base M. The latter is preferably formed of a block of suitable refractory material such as silica, and its upper surface l8 may conveniently be flat and smooth, and so adapted to support firmly a metal strap 49 which constitutes the main leading-in electrode or terminal by which heating current is intro duced to the resistor from asuitable source, not shown. The strap it has preferably a foot portion 2t bent down at the front of th apparatus, and disposed in spaced relation from the bracket 96 by insulation such as sheets of mica it, the latter being secured to the bracket by screws 22. A binding screw 23 is provided on the front of the strap 2b to permit easy connection thereto of one of the conductors 24 leading from the controlling circuits as indicated in the diagram shown in Fig. 5.

The strap l 1-) may desirably be formed of metal having a high melting point, such as Nichrome, and I prefer to provide auxiliary electrode 25 of the same material which serves as a base contact terminal to receive the lower end of the resistor R. At .26 is shown a similar terminal, preferably made of the same material, and this terminal derives its current from another strap of the same material designated 2'5 and which has a bent up portion 23 provided at 29 with a bindi g screw, for connection thereto of the other conductor by which current is led to flow through the apparatus. The upper strap portion 23 is secured in spaced relation to a non-conducting strap 35 by a laminated insulator block which may desirably be of mica sheets, the latter being secured in place by screws 33, as shown in Figs. 1 and 3. If desired, both straps l9 2% may be provided with internal passages, such as shown at #2 in strap 23', Figs. 6 and 7, for the circulation of cooling water. Appropriate nipples it and M- are provided communicating with the passages l2 and over which small rubber tubes may be slipped to conduct water to and from the terniinals.

Embraced between the straps 2'! and 3! is an insulator block of refractory material 34, preferably silica, and this block with its associated parts is shown as biased toward the resistor R by suitable means such as a coil spring 35 disposed under compression between the top plate l2 and the strap 3 I.

The spring is shown as fitting at its upper end around the boss 36 of a bushing 31, screwed into a threaded orifice 38, in the top plate 12.

This bushing has a central bore 39 preferably of polygonal cross-section, within which is free to move lengthwise a squared post 40, the upper portion of which has a round threaded shank 4 I, upon which is screwed a hand nut 42. This nut may be operated to overcome the bias of the spring 35, either for adjustment of the block E i and its associated parts, or to withdraw them to a position in which the lower strap 21 is above the upper boundary of any of the movable structural parts, which will now be described more in detail.

In the first place, it should be noted that inits tubular or prism-like preferred form the hollow resistor R, which is desirably formed of electrically conductive silicon carbide, has a generally cylindrical shape in its longest dimension, not being a completely closed cylindrical form preferably, but having a lengthwise-extending slot or opening 1", co-extensive in length with the cylinder; and diametrically opposite to this lengthwise slot is a shorter slot or opening r, the purpose of these openings being to permit ocular observation of the specimen contained within the mufile, and Which specimen may desirably have a known standard form as shown. In the instance illustrated the specimen is designated by the letter S, and is of conical shape, its apex s being disposed a little above the lower margin of the opening 1", so that it can be seen through that observation opening, during the entire period of treatment.

It will be evident that when both the resistor and the specimen are heated to incandescence it would be very difficult to distinguish the apex s against a background (the interior of the resistor) having the same color, character, hence a portion r of the resistor in alignment with opening 1* and a part s of the specimen when heated to incandenscence and viewed through opening 1' will be silhouetted against the darker background of opening 1".

Ordinarily in making such tests, it is customary to carry the heating of the specimen to a degree at which the material fuses, and then the sharp apex s curls over and thus indicates the incidence of fusion. This procedure is wellknown, and does not require further detailed description, except to call attention to the unusual degree of convenience with which this known practice can be followed without departure from established routine.

In pursuance of the invention, the resistor R is preferably reinforced, or supplemented structurally and insulated against excessive loss of by refractory insulating blocks 43 and 44, either or both of which may be desirably made readily removable from the apparatus, so as to clear the resistor for inspection, removal and replacement.

The forward block 43 has a channel 45 through which observations may be taken of. the apex s of the specimen, the channel 45 being in suitable registry with the opening 1" for that purpose. Similarly there is a vertically extending slot 46 in the block 44, in registry with the longitudlnally extending slot r of the resistor. Both of the blocks are preferably made of silica, and

each of them is so shaped at its bottom surface I as to conform with the underlying structure of the terminal strap and parts I9 and 25. At their upper boundary, the blocks 43 and 44 are formed with cavities which together constitute a cavity 41 of suitable proportions to receive the terminal member 26 and the lower portion of the block 34 with its associated contact strap 28. As shown in Fig. 4 the blocks 43 and 44 are of semi-circular shape meeting in a diametric division line with tongue and groove joints 48.

In Fig. I have shown in diagrammatic form circuit connections which may desirably be used in providing for the electric activation or energization and control of a fusion measuring apparatus of this improved type.

A conventional plug 50 serves to make the connections with a suitable power source of electric heating current, not shown. The reference character M is used to designate diagrammatically the apparatus as a whole. The reference character A designates a suitable current-measuring meter such as an ammeter. R. designates a conventional rheostat. T designates a stepdown transformer of which the winding designated P is the primary, deriving its current by conductor 5| from the plug 50. B is a conven tional circuit breaker, and I prefer to provide for automatic operation of the latter by means of a bi-metallic thermostatic device designated B. M. T. S. designates a manually operated tumbler switch.

The operating circuits include the following conductors, viz.: 5| leading from plug 50 to one end of primary P; 52 leads from a given point in the primary winding to a contact point 53 of the tumbler switch; the other point 54 of the tumbler switch is connected by conductor 55 to another part of the primary winding P so that when the tumbler switch is thrown to point 54 a larger stretch of the primary winding is in circuit. The other end of the primary as 56 is connected by conductor 51 to the axis of rheostat R and one end 58 of the rheostat is connected by conductor 59 to the bi-metallic circuit breaker B. M. from which a conductor 60 leads to one contact point 6| of the circuit breaker. From the other point 62 of the circuit breaker a conductor 63 leads to the leading-in wire 30 shown in Fig. 1 as connected to binding screw 29 for the purpose of. conducting current to the terminal 26 of the resistor. The other conductor 24 leads from binding screw 23, and a conductor 64 connects the same with one end 65 of the secondary winding of the transformer. The other end 66 of the transformer is connected by conductor 61 to the ammeter A, and a conductor 68 leads from the ammeter to the terminal 69 of circuit-breaker B. A conductor completes the circuit back to the plug 50.

In the operation of my device in determining fusion points, the circuit connections being as illustrated in Fig. 5, and just described; the specimen S having been placed upon the terminal 25; and the resistor R. having been set in its proper position as illustrated in Fig. l; the blocks 43 and 44 will be suitably arranged in juxtaposition with the resistor R, and the upper terminal 26 will be set in place and the strap 2'! brought into contact therewith by running off upward the hand screw 42 to permit spring 35 to act effectively, biasing the block 34 and its associated parts downwardly; then current will be turned on by inserting the plug 50 into a suitable socket of the power circuit, and current will flow through the resistor. After the heating effect has started, preferably the tumbler switch T. S. will be thrown from the position shown in Fig. 5 to its position of contact with point 54, which will increase the amount of current delivered by primary winding P to the secondary of the transformer T. The current strength may then be increased still further by moving the pointer H of rheostat R in a clockwise direction, cutting down the resistance in known manner, until the resistor R has been heated to its maximum capacity, or to the desired degree of heat, according to the critical fusion point of the material composing the specimen S being tested. When the apex s curls over, this will be observed through the orifice R and the channel 45 and then the observer will read from the ammeter the current strength at the incidence of fusion, and by the use of suitable known pyrometric instruments may also secure the necessary or desirable data for establishing a standard specification for the composition of materials of the nature embodied in the specimen under test.

From the foregoing it will be apparent that the apparatus herein disclosed provides in a novel, compact and sturdy form, a device for testing at extremely high temperatures a wide range of materials under conditions which possess the desirable characteristics first above set forth, and it will be evident that this novel measuring apparatus operates in a manner free from the disadvantages there recited. Furthermore, it will be apparent that in cases where it is desirable to conduct sintering or other operations in a special atmosphere, such as hydrogen, the gas may be easily introduced into the muffle by inserting a conducting nozzle in channel 46.

Although I have particularly described a particular embodiment of my invention and explained the principle, construction, and mode of operation thereof, nevertheless, I desire to have it understood that the form selected is merely illustrative and does not exhaust the possible physical embodiments of the idea of means underlying my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A fusion testing apparatus of the class described, comprising in combination: a hollow resistor of generally cylindrical form having at one side a slot substantially co-extensive in length with the resistor, and having at its opposite side an observation opening through which a specimen under test within the inner cavity of said cylindrical resistor can be kept under visual observation, said resistor being composed of electrically conductive silicon carbide, and means to heat said resistor by passage of electric current therethrough of an order adapted to secure temperatures attaining 3300 F., whereby optimum conditions favorable to testing and to observation can be secured.

2. As a new article of. manufacture, a resistor forming a muille for receiving interiorly an object to be heated for heating devices of the class described, said resistor comprising a body having the general shape of a hollow prism, and formed of electrically conductive silicon carbide, said body having an axial cavity open at each end, and having one side-wall formed with an open slot in communication with said cavity for at least a portion of its length.

3. As a new article of manufacture, a resistor forming a muffle for receiving interiorly an object to be heated for heating devices of the class described, said resistor comprising a body having the general shape of a hollow prism, and formed of electrically conductive silicon carbide, said body having an axial cavity open at each end, and having one side-wall formed with an open slot in communication with said cavity throughout its length.

4. As a new article of manufacture, a resistor forming a muffle for receiving interiorly an object to be heated for heating devices of the class described, said resistor comprising a body having the general shape of a hollow prism and formed of electrically conductive silicon carbide, said body having an axial cavity open at each end, and having one side-wall formed with an open slot in communication with said cavity and the opposite wall of, said cavity having formed therein an orifice at a medial region thereof.

As a new article of manufacture, a resistor forming a muflie for receiving interiorly an object to be heated for heating devices of the class described, said resistor comprising a body having the general shape of a hollow prism and formed of electrically conductive silicon carbide, said body having an axial cavity open at each end, and having one side-wall formed with an open slot in communication with said cavity throughout its length, and the opposite wall of said cavity having formed therein an orifice at a medial region thereof.

6. A measuring apparatus of. the class described comprising in combination: a hollow resistor of generally cylindrical form with a body cavity to receive an object to be tested, and having an orifice through which a specimen under test in said cavity may be kept under visual observation during said test, said furnace bein characterized by having a fixed lower electrode upon which said resistor may be seated removably in upright position with said orifice presented laterally; and a block of refractory material upon which said lower electrode is mounted; said apparatus being further characterized by having a supporting frame, and a movable upper electrode secured to a block of refractory material carried reciprocably by said frame, and biased downward toward said resistor seat; auxiliary blocks of refractory material adapted to be disposed removably in circumjacent juxtaposition with said cylindrical resistor, conforming to the contour thereof, and one at least of said auxiliary blocks having an orifice or channel registering with said resistor orifice, for the stated purpose.

'7. A measuring apparatus of the class described comprising, in combination: a resistor or furnace member of generally cylindrical form and having diametrically opposite orifices communicating with the atmosphere and through which orifices a specimen within said resistor may be kept under visual observation during said test, said furnace being further characterized by having a fixed lower electrode of high melting point metal, such as Nichrome, and a block of refractory material, such as silica, upon which said lower electrode is mounted, and further by having a movable upper electrode of similar ma terial secured to a vertically reciprocable block of silica biased downward by gravity and/or by a coiled spring under compression, auxiliary blocks of silica supplementing said cylindrical resistor in circumjacent juxtaposition, and having respectively orifices or channels registering with said resistor orifices, for the same intended purposes respectively, and means to heat said resistor by passage of electric current therethrough, to secure in said cylindrical interior a wide range of heats, with an atmospheric environment of substantially constant character for the contained specimen, up to the melting point of said silicon carbide.

8. A furnace of the class described, said furnace being characterized by having a frame, including a base plate, a top plate and structural connecting members for said plates, said base plate having mounted thereon a fixed lower electrode of high melting point metal, such as Nichrome, and a block of refractory material, such as silica, upon which said lower electrode is mounted, and further by having a movable upper electrode of similar material secured to a vertically reciprocable block of silica carried by said top plate, and biased toward said lower electrode by a coiled spring under compression, a resistor positioned between the electrodes, auxiliary blocks of silica adapted to be disposed removably in circumjacent justaposition around the resistor when embraced between said electrodes;and electrical circuits and controlling means therefor to provide for the heating of said resistor by passage of electric current therethrough.

9. A furnace of the class described, said furnace being characterized by having a frame, including a base plate, a top plate and structural connecting members for said plates, said base plate having mounted thereon a fixed lower electrode of high melting point metal, such as Nichrome, and a block of refractory material, such as silica, upon, which said lower electrode is mounted, and further by having a movable upper electrode of similar material secured to a vertically reciprocable block of silica carried by said top plate, and biased toward said lower electrode by a coiled spring under compression, a resistor positioned between the electrodes, auxiliary blocks of silica adapted to be disposed removably in circumjacent juxtaposition around the resistor when embraced between said electrodes; and electrical circuits and controlling means therefor to provide for the heating of said resistor by passage of electric current therethrough; said controlling means including a thermostatic circuitbreaker effective when a predetermined heat is attained.

10. A furnace of the class described, characterized by the instrumentalities combined and cooperating as set forth in claim 8, and further characterized by the provision of. a resistor comprising a generally prism-shaped body having an axial cavity open at each end, and also by the provision of end pieces of conductive metal having a high melting point interposed removably between each of said electrodes and an end of said resistor.

11. In a device of the character described, a combined muflie and electrical resistance heater comprising a tubular element composed of electrically-conductive silicon carbide; said muflle being adapted to contain a specimen to be tested and provided with lateral openings positioned to permit a portion of said specimen to be observed through one opening against the other opening as a background.

ENRIQUE G. TOUCEDA.

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