US2597665A - Thermocouple - Google Patents

Description

y 20, 1952 M. B. NICHOLLS 2,597,665

THERMOCOUPLE Filed Sept. 2, 1950 INVENTOR. MALCOLM B. NICHOLLS BY DES JARDINS, ROBINSON KEISER HIS ATTORNEYS Patented May 20, 1952 THERMOCOUPLE Malcolm B. Nicholls, Cincinnati, Ohio, assignor, by mesne assignments, to Revere Corporation of America, Inc., Wallingford, Conn., a corporation of Connecticut Application September 2, 1950, Serial No. 182,985

4 Claims. 1

This invention relates to thermocouples. and it particularly pertains to thermocouples which have the lead wires from the terminals secured to the casing by a porcelain or vitrified enamel having a fusing temperature below the critical temperature of the lead wires in order to secure them firmly to a casing in which they are contained and prevent their vibration.

In thermocouples heretofore constructed, the wires have been embedded within refractory or ceramic materials contained within the casing for housing them. The refractory or ceramic material could be preformed in shape to fit within the casing and have a pair of longitudinal passages for the lead wires to be passed therethrough. While the preformed refractory or ceramic could be heated to the high temperature necessary for fusing it, there is the difiiculty of assembly, and the lead wires are loose within the fused refractory or ceramic and not adhered thereto, thereby resulting in their vibration and causing the connected ends of the wires, projecting from the end of the casing, to be sheared oif. Accordingly, the preferred construction heretofore has been to first place the lead wires within the casing, pack the casing with the refractory or ceramic material to embed the lead wires therein, and then to fuse the refractory or ceramic material. However, all refractory and ceramic materials require firing to a high temperature above 1800 F. which is above the critical temperature of the lead wires. This would necessarily heat the wires to the same temperature required to fuse the refractory or ceramic material. Then, too, the refractory or ceramic material has a different coefiicient of expansion than either the wires and the casing, thereby causing the bond between them resulting from the fusing treatment to be broken and permitting the loosened wires to vibrate. In order to overcome'this objection of heating the lead wires above their critical temperature in fusing the refractory or ceramic material, it has been proposed to heat treat refractory or ceramic material only to incipient fusion. This incomplete or incipient fusion, however, does not provide the degree of strength and permanency which is obtained by fusion, and does not overcome the objections resulting from the different coefficients of expansion of the refractory or ceramic material and the wires. All that is accomplished is a heat treatment below the critical temperature of 1800 F. Accordingly the principal object of my invention is to bond the lead wires to the casing in a thermocouple with porcelain or vitrified enamel material to secure them against vibration.

Another object of the invention is to provide a thermocouple which may be easily constructed and assembled.

Another object of the invention is to provide a thermocouple in which the ends of the lead wires may be secured in line contact with the casmg.

Another object of the invention is to provide a thermocouple having the ends of the lead wires constructed to provide a strong and permanent union.

Still another object of the invention is to bond the parts together by a material having the same coefiicient of expansion as the parts which are bonded.

Further objects, and objects relating to details of construction and economies of operation will readily appear from the detailed description to follow. In one instance, I have accomplished the objects of my invention by the device and means set forth in the following specification. My invention is clearly defined and pointed out in the appended claims. Structures constituting preferred embodiments of my invention are illustrated in the accompanying drawings forming a part of this specification, in which:

Fig. l is a vertical cross sectional view of a thermocouple embodying my invention.

Fig. 2 is a top end view of Fig. 1.

Fig. 3 is a bottom end view of Fig. 1.

Fig. 4 is an enlarged detailed view of a unit of the two wires, each of which has been coated with vitrifiable enamel except along their bottom end edges, having their bottom angularly disposed ends superimposed and welded together along their bottom edges to be rolled to fit within the casmg.

Fig. 5 is a vertical cross sectional view of the bottom end portion of another embodiment of the invention.

The invention broadly described comprises a metal tubular casing having a flange secured to one end to which terminal connections are fitted for two lead wires contained within the casing and projected from its opposite end for exposure to the surrounding atmosphere. The exposed projected edges of the wire are welded together.

The side of the flange facing the terminals and the inside wall of the casing are coated with vitrifiable enamel. Two terminals, each including a spacer plate, are attached to the flange, in position to be connected to two lead wires of a wire unit contained within the casing and bonded to its interior wall. These terminals, except for the screw threaded portions, are also coated with vitrifiable enamel. The adjacent ends of the spacer plates extend to overhang the bore in the casing, but they are spaced apart to be out of contact with each other in position to be attached to the ends of lead wires that are fitted within the casing with their opposite ends welded 3 together and extending beyond the end of said casing.

The portions of the wires extending beyond the end of the tubular casing may be connected together in various ways and welded. They are securely bonded to the tubular casing to with' stand the vibration to which a thermocouple is subjected. The Wires may have a flat surface on the side which is next to the interior wall of the casing. Wires with a fiat sideare'obtained either by making them from flat blanks or rolling conventional round wires to flatten them.

The ends of the wires at the bottom end of the casing may be angularly disposed to obtain a larger area of contact than that provided by their normal width. The angularly disposed ends provide long lengths which can be bonded together in superimposed relation and to the wall of the'ca'sing by the vitreous enamel. In a structure of this character each of the wires has an L-shaped end, and both of them are coated with vitrifiable enamel except on the bottom edges of the L-s'haped portions. The L shaped ends are superimposed with the main parts of the wires spaced from each other by the L-shaped portions which extend toward each other from thespaced apart main portions. The bottom edges of the L- shaped bottom portions are welded together. After the bottom edges of the wires in the wiring unit have been welded together, they are rolled to fit within the bottom end of the tubular casing with the main portions of the wires extending through the casing for the opposite ends to be attached to the adjacent ends of the spacer plates. Some means, such as an expanding jig, can be inserted in the bottom end of the tubular casing to hold the wires in contact with the interior wall of the casing while the unit is heated to fuse the enamel coating and bond the wires securely to the casing and also to bond together the superimposed L-shaped portions of the wires.

Where a larger area than that provided by the normal width of the wires is not desired, their exposed ends are connected and welded together without being angularly disposed. This connection' i'nay be by twisting the exposed ends or simply bending them to bring their edges into abutting contact. This latter method is more expedient for'flat Wire's, whereas round wires may have their ends twisted or the end edges in abutting contactfor welding.

The vitrifiable coating 'on the respective parts can be of the same coefficient of expansion as that metal part to which it is applied, thereby reducing if not entirely preventing any relative movement between the connected parts when the wires are heated. Moreover the vitrifiable enamel coating material can be fused at temperatures from about 1400 F. to 1600 F. which is considerably below the critical temperature of about 1800 F. for the wires and above which they should not be heated.

Referring specifically to the drawings in which like numerals are used to refer to like parts, numeral 2 is a tubular casing of such material as stainless steel having one end inserted within the recess 3 of a plate 4 and be welded thereto to provide a flanged head. The plate 4 has one or more openings 5 formed therein for permitting it to be bolted to the wall of a jet or diesel engine or other device with which the thermocouple is to be used. Two terminals are fitted to the outer side of the flange plate, each of these comprising a spacer plate Bto which the head 1 of a screw 8 is attached. The spacer plate and the screw are functionally integral and, of course, may be structural integral or made from separate parts connected together. The spacer plates 6 and screws 8 are secured to the plate "'4 by a stainless steel metal strip 9 recessed at IE) and secured by rivets I l extending through the plate, the spacer plates and the strip. In order to insulate the spacer plates, the heads of the screws and the strip from each other, the side of the flange plate facing the terminals, the screw heads and the inside face of the spacer strips are coated with vitrifiable enamel material l2. The inside wall of the tubular member is also coated with a lining [3 of vitrifiable enamel material. The recesses I'll are of slightly larger diameter than the screw heads, and so are the recesses I3 in the spacer and terminal plates in respect to the rivets H for keeping-them out of contact with each other. In lieu of or in addition to this insulated coating 12 between the spacer and terminal plates, shims of -mica, asbestos or other suitable insulation material may be inserted. The ad'- jace'nt ends of the spacer and terminal plates 6 are each spaced apart and cut 'awayin an intermediate portion I4 between sideportions i5 for the end portions [4 to slightly overhang the wall of the bore in the tubular casing for purposes hereinafter described.

A wiring unit comprising parts 20 and 2| is formed, one part '20 being of hard metal alloy, such as Alumel and. the part 2! being of a dis similar hard metal alloy, such as Chromell' Each of these parts is generally L-shapedha'ving an angularly disposed lower extension 22 at one end to provide an elongated bottom edge 23. The two parts, including the extensions, are first coated with vitrifiable coating enamel material, except for the two bottom edges 23, and then they are assembled with the extensions superimposed to space the main parts 20 and 2! of the wires from each other. These Wires can be out from a blank sheet and will be flat to provide a substantially 'wide surface area for being bonded to the tubular casing. Conventional round wire may also be rolled to flatten it. However, the

wires may be of any cross-sectional configuration and need not be flat. The fiat cross-sectional shape is preferred for obtaining a greater bonding area. The edges 23 of the extensions are welded together.

The end of the wire unit with the superimposed angular end extensions (Fig. 4) is bent in con-' formity with the cross-section of the tubular casing, and then the unit is inserted within the tubular member with the bottom end rojecting a slight distance below to be exposed to the sur rounding atmosphere. The parts 20 and 2! of the two wires are adjacent to the wall of the bore of the tubular member and of sufiicient length to have their top ends welded at 25 to the spacer plates. The Alumel wire is welded to one spacer plate 6 which is also of Alumel metal, and the chromel Wire is Welded to the other spacer plate 6- Which will be of Chrom'el metal. The thermocouple is then heated to a tempera= ture sufficient for fusing the vitrifiable coating enamel on the wires and the other coated parts, thereby bonding the wires to the wall of the tubular casing by the fused enamel. The superimposed extensions on the bottom ends of the wires will also be bonded together by the intervening coating material and to thewall of the tubular casing. In order toinsure the wires being held in close'contact with the interior wall of the tiibu lar casing, an expansible jig (not shown) may be inserted within the bottom end of the tubular casing and expanded against the wires to hold them in close contact with the casing wall during the fusing treatment.

The portion of the tubular member surrounding the bottom extensions of the wiring unit and the extensions may be crimped with one or more annular crimps pressed therein. These crimps may be formed in the elongated angular ends of the wires as they are rolled or after the insertion of the unit in the casing. The complementary crimp in the casing can be made therein before or after the wire unit is inserted. This will insure the wire unit being held against relative axial movement within the tubular casing.

In the embodiment in Fig. 5, the ends 26 and 2'! of respective wires 20' and 2| are bent toward each other to bring their edges in abutting relation to be welded together at 28. Since the wires are flat, their edges are more expediently abutted for being welded, but these ends may be twisted as is commonly done with round wires or wires of other conformation. Round Wires or wires of other conformation may also be used in carrying out the invention both for that embodiment illustrated in Fig. 4 and that in Fig. 5. The main feature of the invention is in bonding the wires to the interior wall of the casing with the vitrified enamel, whereas the use of wires with a fiat side is a secondary feature.

From the foregoing description, it will be readily understood that the wires are securely bonded to the wall of the tubular casing, and they are bonded by enamel material which can be fused below the critical temperature of the wires. The parts, particularly the wires and the wall of the tubular casing, can. be coated with vitrifiable material having the same coeificient of expansion, thereby preventing relative movement between the parts when the wires of the thermocouple are heated in being used. The invention lends itself to any variation of structure for connecting the wires, but in all of them there is less likelihood of the wires becoming loosened from the casing. Their bond thereto is more permanent and enduring.

It will be understood that the invention is not limited to any particular vitreous enamels and reference to them includes all of those conventionally used for coating metals. They are composed chiefiy of quartz, feldspar, clay, soda, and borax with saltpeter or borax used for fluxes. Opacifiers may be included. The enamel-making materials are prepared in the form of a powder which is called Frit. The temperature for making the Frit is about 2400" F., but the application temperatures are from l400 to 1600 F.

While I have shown no filling within the casing and have illustrated the wires bonded directly to the interior wall of the casing by the vitrified enamel, it will, of course, be understood that a filling, such as refractory or ceramic material can be placed therein and be bonded to the interior wall of the casing by the vitreous lining. No filling is necessary, but it may be used if desired. If a filling were used, the wires could be embedded within the filling and bonded thereto by the vitrified enamel being between the wires and the filling, the filling being bonded to the interior wall of the casing by the vitreous enamel. Where a filling is used, and the refractory or ceramic filling material is preformed with passages extended therethrough for the reception of the wires, it can be bonded to the interior wall of v the casing and the wires in the passages can be 6 bonded to the walls of the passages by the vitreous material. Accordingly the term casing" is broadly used to refer to any surrounding element to which the wires are bonded by the vitrified enamel, whether they be connected directly to the casing or to the filling material contained within the casing.

I am aware that there may be various changes in details of construction without departing from the spirit of my invention, and, therefore, I claim my invention broadly as indicated by the appended claims.

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

1. A thermocouple comprising a tubular casing, thermocouple wires disposed within said casing and projecting slightly at an end thereof where they are intimately joined to provide the hot junction of the couple, terminals at the other end of said casing for making external electrical connection to said thermocouple wires, and a relative thin coating of vitrified enamel encasing each of said wires and bonding them securely to the interior wall of said casing substantially through-,

out the extent of the latter.

2. A thermocouple as defined in claim 1, wherein said vitrified coating is formed of an enamel frit which fuses at a temperature below 1800 F.

3. A thermocouple as defined in claim 1, wherein said wires are substantially flat throughout their length and are disposed fiatwise along the interior wall of said casing to which they are bonded in spaced relation by said vitrified enamel.

4. A thermocouple comprising a tubular casing, a pair of substantially flat thermocouple wires of generally L-shaped configuration, the respective lower angular extensions of which are superimposed in overlapping relation so as to extend in opposite directions from the respective vertical legs whereby to space the latter apart, said overlapped angular extensions being arcuately bent to fit closely within the lower end of said tubular casing and to project slightly edgewise therefrom, said vertical legs being disposed so as to extend axially in spaced relation upwardly through said casing fiatwise along the interior wall thereof, said wires being intimately joined along the projecting edge of said angular extensions to provide the hot junction of the couple, and a relatively thin coating of vitrified enamel encasing each of said wires so as to insulate them from each other except along said projecting edge, said vitrified enamel coating serving also to securely bond said wires to the interior wall of said casing.

MALCOLM B. NICHOLLS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 834,162 Northrup Oct. 23, 1906 935,154 Hopkins Sept. 28, 1909 1,289,116 Chubb Dec. 31, 1918 1,693,130 Anderson Nov. 27, 1928 1,881,444 Flanzer Oct. 11, 1932 2,177,046 Sweo Oct. 24, 1939 2,216,375 Minter Oct. 1, 1940 2,416,864 Bricker Mar. 4, 1947 2,445,159 Tegge July 13, 1948 2,470,881 Zimbelman May 24, 1949

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