US3505124A - Super-pressure thermocouple - Google Patents

Description

April 7, 1970 J. J. SCANLON, JR., ETAL 3,505,124

SUPER-FRESSURE THERMOCOUPLE Filed Aug. 31, 1957 //V VE N TORS John J. Scan/on, Jr: Joseph B. Quin/an Fig] ATTORNEKS United States Patent 3,505,124 SUPER-PRESSURE THERMOCOUPLE John J. Scanlon, .Ir., Monroe, Conn., and Joseph B. Quinlan, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of the Army Filed Aug. 31, 1967, Ser. No. 665,678 Int. Cl. H01v 1/04 US. Cl. 136232 4 Claims ABSTRACT OF THE DISCLOSURE A thermocouple is provided in combination with a thin walled pressure vessel to sense the temperature directly at the inner surface wall thereof while being subjected to operating pressures on the order of 70,000 p.s.i.a. The area of that portion of the thermocouple which is directly exposed to the incident pressure is substantially minimized, thereby greatly reducing the force thereon and thus allowing the utilization thereof in the aforementioned environment.

The present invention relates to heat sensing apparatus of the thermocouple type and more particularly to thermocouple means adapted to sense temperature variations directly at the inner surface wall of a thin-walled pressure vessel or the like which is subjected to operating pressures of from 50,000 p.s.i.a. to 70,0O0 p.s.i.a. Examples of such pressure vessels are small arms weapons (both of the automatic and semiautomatic type), small arms test weapons, and small bombs. For the purpose of illustration, however, the present invention will be described in conjunction with a small arms weapon although it is to be understood that the invention is in no way limited to such an embodiment.

It is desirable from a weapons design viewpoint to know how hot the bore of a small arms weapon gets under ordinary operating conditions. It is also desirable to ascertain when cook off, or premature and undesired cartridge initiation (due to thermal exposure) occurs. It is known, for example, that 40 rounds fired in a continuous burst in a conventional small arms weapon heats the inner surface of the barrel to 315 F. This heat has an undesirable effect upon both the weapon and the cartridges. Excessive heat has been known to render the weapon barrel so plastic that a cartridge, upon firing, emerged from the side wall of the barrel rather than from the muzzle. Also, heat per se may be suificient to cause undesired initiation within the barrel. In addition, by knowing the heat generated per fired cartridge and further by knowing the cook off characteristics of the cartridge and the thermal tolerances of the weapons barrel, it is possible to determine both the number and rate of rounds which an operator may fire before his personal safety or the safety of friendly personnel in proximity with the weapon becomes endangered by the possibility of an explosion within the weapon.

The instant invention is directed toward providing the heat information requisite to the solution of these and other problems.

Researchers in this field have employed two devices and/or techniques in attempts to collect temperature data at the inner surface of a high pressure, thin-walled, small volume pressure vessel. One method, and the one most extensively employed, contemplates drilling a hole in side of the pressure vessel from the exterior thereof to a depth of within /8" of that inner surface, thereby leaving a relatively thick web of metal. A conventional thermocouple is then glued or otherwise secured into this hole with an epoxy or the like. This technique permits the obtainment of vessel temperature data, but not at the inner surface thereof. This data must then be extrapolated or approximated, which process usually results in larger error. The

3,505,124 Patented Apr. 7, 1970 web of metal heretofore referred to is a necessary requirement with conventional thermocouples for the two important reasons listed below.

If the vessel happens to be a small arms weapon in operation, a conventional thermocouple seated at the inner surface of the barrel could not withstand the extreme operating pressures and would rupture under the force applied thereto. Also, upon failure of the thermocouple much gas leakage would occur thereby greatly reducing the efliciency of the Weapon.

A second method contemplates the use of high pressure thermocouple, such as is produced by the Naumac Corp. of Indian Head, Md. This type thermocouple, however, as well as the other commercially available high pressure thermocouples, are suitable for use only in conjunction with thick-walled vessels and are therefore inapplicable to meet the needs of the small arms weapons field. For example, the Naumac thermocouple referred to above requires a housing holder of 5 diameter and a bored hole /2" deep. Thus, a vessel with a minimum wall thickness of /2 is required. Such a thick vessel wall is uncommon in small arms weapons, A" being the generally utilized maximum thickness.

It is therefore a primary object of the present invention to provide a thermocouple device adapted to be seated directly at the inner surface of a thin walled pressure vessel and to sense temperature variations at that inner surface While being subjected to extreme operating pressures.

It is a further object of the present invention to provide a thermocouple device which permits the direct measurement of surface temperatures at the inner wall of a high pressure, small volume, thin-walled chamber or vessel without any gas leakage therefrom.

A more specific object and aspect of the present invention is to provide a thermocouple device which may be seated at the inner barrel wall or surface of a conventional small arms weapon and which permits direct temperature measurement at that surface under actual firing conditions without impairing the efficiency or overall performance of the weapon.

The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description of a preferred embodiment thereof in conjunction with reference to the accompanying figures, the scope of the invention being recited in the appended claims.

FIG. 1 is a longitudinal cross-sectional view of the thermocouple device comprising a presently preferred embodiment of the invention.

FIG. 2 is a top View of the thermocouple of FIG. 1 showing further details thereof in accordance with the invention.

FIG. 3 is a front-end view of the weapon barrel of a conventional small arms weapon taken at a point down the barrel and through the thermocouple showing the lower portion and the seating thereof at the inner barrel surface.

FIG. 4 is an enlarged view of a portion of FIG. 1 showing the operating forces on the thermocouple.

Referring to the drawings wherein the various figures are numbered throughout where applicable with like numerals, and more particularly referring to FIG. 1, a super pressure thermocouple is shown which includes a housing 9 comprising a gland 10 which may be threaded at both ends, an extension 11, and a cap 12. It is noted that the latter two elements might readily be combined into a single unit. Such unit would preferably be fabricated from any suitable hard fiber, plastic, or other non-conductive material. The super-pressure thermocouple also includes an insulated thermocouple wire 13 which has been pulled through a relatively small hole or aperture 14 (on the order of 0.018 inch in diameter) at the base of the gland 10 thereby being positioned at the center of the couple and which is further secured at said gland base by a thermo-electrical conductive, metallic bead 15 formed by welding or the like. The aperture or hole 14 is sealed with a braze 16 which functions to further secure that bead weld 15 and, as it is shaped like a truncated cone, also serves to distribute any longitudinal force applied thereto as will hereinafter be described. The thermocouple wire 13 may be further supported and secured Within the gland 10 by refractory cement or the like 17. Alternatively if the gland 10 is machined to snugly encompass the thermocouple wire 13, the cement 17 may be omitted.

Referring now to FIG. 2 along with FIG. 1, it is seen that a pair of output leads 18 extend from the unbeaded end of thermocouple wire 13 and through a suitably supplied opening 19 in the cap 12. These output leads 18 are secured at the top of the cap 12 by two electrically conductive, metallic screws 20 or the like. A pair of metal connectors 21 are provided between the screws 20 and a second pair of electrically conductive screw-like elements 22 are secured in the cap 12 to provide an electrical connection between the thermocouple output wires 18 and an external recorder or electrical measuring device 24 through suitable input leads 23. It is noted that these screws may further serve the purpose of securing the cap 12 to the thermocouple extension 11.

Referring to FIG. 3, it is seen that the bead 15 is positioned to align with the inner surface 26 of a thin-walled pressure vessel or weapon barrel 25. Thus the thermocouple is in direct, intimate contact with the heat generated or formed within the barrel upon the firing of a cartridge therein and is therefore heated to the same temperature as the inner barrel surface. It is noted that a cavity was first bored in the barrel 25 sufficient to receive the thermocouple which is secured therein by any convenient means as, for example, by epoxy or by threading the barrel to receive a correspondingly threaded thermocouple housing.

The operation of the device is as follows:

Within thermocouple wire 13 are two dissimilar metallic wires 18 which are joined at the bead end thereof and positioned at the inner surface 26 of the barrel 25. It is known in the art that when two unlike metals are joined so as to form a complete circuit, an electromotive force exists in the circuit whenever the two junctions are at different temperatures. The electromotive force, for any given pair of metals, depends upon the difference in'temperature between the junctions. In the preferred embodiment shown, the two junctions are respectively the bead weld 15 positioned at the inner surface of the barrel 25, and the input leads 23 to the recorder 24. The thermocouple is then used in a manner analogous to a thermometer by, as noted heretofore, placing the bead weld junction in contact with the body whose temperature is to be measured, while keeping the other junction at some known temperature (usually either C. or ambient, the latter being the case here), and measuring the electromotive force. It is noted that the two dissimilar metals may be elements such as iron and copper or alloys such as 'Chromel and Alumel or the like. As the theory and operation of conventional thermocouples in general form no part of the instant invention, it is felt that no further explanation of the operation thereof is necessary.

The present invention, on the other hand, differs uniquely from the conventional thermocouple in that the bottom of the gland has been constructed so as to greatly reduce the area presented to the excessive pressure resulting from the expanding gas upon the firing of the small arms weapon in which the thermocouple is seated.

Referring now to FIG. 4 wherein the length L and the angle theta (6) may be taken to be 0.094 inch and 45, respectively, and furtherwherein the base of the gland has a circular cross-sectional area, it is seen that for a pressure of 70,000 p.s.i.a., the force F on the bead weld is 485.54 lbs., having been derived from the mathematical formula F =P A, where F is the force, P is the pressure and A is the area. Similarly, since the force on the gland, E is equal to F cos 0, it is seen that F =343.28 lbs. For possible operating pressures of 140,000 p.s.i.a. and 35,000 p.s.i.a., F is, respectively, 686.58 lbs. and 171.64 lbs. It is first noted that the bead weld 15 can withstand much more force than can the gland 10. Secondly, it is noted that tests have shown that the gland will not rupture until the force thereon exceeds 5250 lbs. Under normal operating conditions, then, wherein the operating pressure is on the order of 70,000 p.s.i.a., a safety factor of over 15 exists.

The forces on the gland 10 are derived from the longitudinal force F on the bead Weld 15 and are, in fact, components thereof. Also, varying the angle 0 will correspondingly vary the forces on the gland 10. Best results are obtained when 6 equals 45 as F then equals F thereby minimizing the force on the gland 10; however, other angles are also possible.

It should thus be clear that a thermocouple of the instant design is capable of sensing temperatures at the inner barrel surface of a thin walled small arms weapon under actual operating and firing conditions. Furthermore, the thermocouple of the instant invention may be placed in direct intimate contact with that inner surface with no fear of either thermocouple failure or reduction in weapon efficiency.

We claim:

1. In a thermocouple device for measuring the temperature at the inner surface wall of a thin walled pressure vessel, said thermocouple having two dissimilar electrical conductors joined at one end in a common junction at the base of a gland portion thereof, the improvement comprising a bead weld permanently affixed to said junction and surrounded by a braze, said bead weld being positioned in direct and intimate contact with said inner surface wall of said pressure vessel, and the thermocouple thereby being adapted to sense the temperature directly at said inner surface Wall upon the application of heat thereto.

2. The invention as defined in claim 1, wherein said bead weld comprises thermo-electric conductive material having a relatively small cross-sectional area thereby substantially limiting the force applied thereto for a given applied pressure.

3. The invention as defined in claim 1, wherein said braze surrounding said bead Weld is shaped like a truncated cone the sides of which are inclined at an angle deviating from the longitudinal axis of said thermocouple to minimize the force on the gland portion thereof.

4. A thermocouple device for converting sensed heat into electrical current comprising a housing constructed of nonconductive material, two dissimilar metallic conductor means within said housing joined together at one end thereof in a common junction and adapted to sense heat impinging thereon, said common junction being held together by a bead weld having a relatively small crosssectional area, and a braze surrounding said bead weld to further secure said junction, said bead weld and said braze so constructed and arranged that the cross-sectional area thereof is less than fifteen one-hundredths of an inch.

References Cited UNITED STATES PATENTS 2,054,120 9/ 1936 Florez. 2,696,118 12/1954 Petry 136227 X 3,007,988 11/1961 .lafie et al. l36227 CARL D. QUARFORTH, Primary Examiner S. I. LECHERT, IR., Assistant Examiner U.'S. Cl. X.R. 136-236, 241

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