US2898570A - Electrical resistors - Google Patents

Description

4, 1959 M. D. PATRICHI 2,898,570

ELECTRICAL RESISTORS Original Filed Oct. 15, 1956 IN VEN TOR.

MIHAI D. HATRICHI I I I 1 I l l 1 I I AT TORNYS atent Patented Aug. 4, 1959 ELECTRICAL RESISTORS Mihai D. Patrichi, Chatsworth, Calif., assignor to Networks Electronic Corporation, Van Nuys, Calif., a corporation of California Continuation of abandoned application Serial No. 615,981, October 15, 1956. This application October 16, 1958, Serial No. 767,683

10 Claims. (Cl. 338-237) This application is a continuation of my prior applications Serial No. 615,981, filed October 15, 1956, for Electrical Resistors and the Like, now abandoned; and Serial No. 616,091, filed October 15, 1956, for Method of Fusing Metal to Glass Articles.

This invention relates to electrical resistors, and has as its general object to provide an improved wire-wound precision resistor having improved qualities of moisture resistance, shock and vibration resistance, high mechanical strength, resistance to failure through the action of high temperatures, high ratio of Wattage rating to size, and stability of resistance rating within close tolerances.

In general, the invention contemplates a resistor embodying a wire-wound resistance element that is sup ported and hermetically sealed within a casing of novel and improved construction particularly characterized by extreme ruggedness and cushioning support of the resistance element in a manner to afford maximum protection of the element and its terminal connections against the effects of vibration, shock, moisture and heat.

More specifically, the invention aims to provide a resistor embodying a tubular mandrel upon which the resistance Wire is wound, a casing consisting in a larger tube within which the mandrel is encased, embedded in a cushioning body of resilient material filling the casing, and end caps sealed and securely attached to the ends of the larger tube; together with terminal rods which project through the caps and are connected to the ends of the resistance wire by connections that are received within and protected by the ends of the mandrel and the cushioning material.

An important object is to provide a resistor embodying the above mentioned improved qualities within relatively small dimensions and with close interfitting of parts.

In the drawings:

Fig. 1 is a side view of a resistor embodying the invention; v

Fig. 2 is an end view thereof;

lfig. 3 is a longitudinal sectional view of the same;

Fig. 4 is across-sectional view of the resistor; and

Fig, 5 is a fragmentary detail sectional view on an enlarged scale, showing the fused joints between the parts of my resistor. i

Referring now to the drawing in detail, I have shown therein, as an example of one form in which the invention maybe embodied, a resistor embodying an inductionless coi110 (wound in an even number of layers, e.g. two, in a manner" such that the inductive field of one layer will neutrali ze that of the next) supported upon a tubular'mandrel11"onwhich it is directly wound. The

wire ofcoil is one that will provide satisfactory stability of texture and resistance rating under high temperature a suitable material being Karma wire or other alloys usedin 'wi're resistors.

Mandrel 11 with its resistance winding 10, is encased within acasing tube 12 of internal diameter just slightly larger'tha'n the outer diameter of Winding 10, so that the wound mandrel may remain in substantially coaxial relation with casing tube 12 even though it should contact the inner wall thereof at some point around its circumference.

The ends of easing tube12 are closed by caps 13 each including a metal ferrule part consisting in a radial flange 14 (Fig. 5) and an open collar 15 projecting axially from the inner margin thereof into a respective end of casing tube 12. Flanges 14 are fused or soldered at 16 to the ends of tube 12, previously covered with metal as hereinafter described, to provide a very secure sealed connection, resistant to vibration, shocks, moistureladen air, etc. Each end cap 13 includes a grommet 18 fused or soldered into collar 15 thereof. Terminal rods 19 are fused or soldered into cylindrical bores in respective grommets 18 and project therethrough into the respective ends of mandrel 11, where they are welded or soldered to the respective end portions 20 of winding 10.

The space within casing 12, 13 is completely (or partly-at both ends and inside the mandrel) filled with a cushioning and insulating core body 21 of latex potting material in which the mandrel 11 and winding 10 are embedded and suspended with almost complete shock and vibration insulation. winding 10 within tube 12, there is the possibility that winding 10 may touch the tube 12 at one or two points, but even with this condition existing, substantially the entire force of shocks and vibration imposed upon terminal rods and tube 12 will be absorbed by core body 21 before reaching winding10 or mandrel 11, and at most only a negligibly small percentage thereof can reach winding 10 or its connections 20 to terminals 19,

Casing tube 12, mandrel 11 and grommets 18 are of high-temperature heat-resistant glass of high lead content, such as Pyrex glass. The ferrule portions 15, 14 of end caps 13 are drawn sheet metal parts, preferably of a corrosion resistant type, such as chromium, nickelsilver alloy, Kovar, or any alloy with the same coefiicient of expansion as the glass used, as a base metal, and coated with one of the noble metals.

The parts described above are joined to one another by strong, durable hermetic joints permanently resisting mechanical break down and leaking. This is attained by an improved process offusing metal to glass which is the subject of my patent application Serial No. 616,091, filed October 15, 1956. Referring now to Fig. 5, such joints consist in metal coatings 22, 23 and 24 respectively on the ends of tube 12, in the bores of grommets 18 and on the peripheral walls of the latter respectively. Such coatings are deposited on the glass surfaces of the respective parts prior to assembly into the finished re-' sistor. In this coating process, the glass parts are preliminarily prepared by thorough cleaning (e.g. by water Washing, soaking in methanol and then in chromic acid solution, and then rinsing, followed by another methanol bath). The parts are then dried and a conductive paste (e.g. a mixture of powdered silver, chromium or gold or other noble metal in 40% toluene) is applied in any suitable manner (eg. by brushing) to the areas of glass that are to be fused to the metal parts. The coated parts are then heat treated (eg in an electric oven) to anneal the glass and fuse the coating thereto, a temperature of 1140 F. being reached. The coated parts are then allowed to cool slowly to room temperature to avoid shattering of the glass and subsequently the thin films of noble metal, of molecular thinness (eg i the order of .0005 inch' to .005 inch) are then electroplated to build up additional metal deposit thereon, thereby producing the substantial metal coatings 22, 23 and 24 respectively. The electro-deposited build-up metal may be a metal (such as copper) that will providea good base for the subsequent soldering of the coating 22, 23 or 24 to a Due to the close fitting of non-noble metal such as Kovar (an alloy of iron, nickel and cobalt having practically the same co-efficient of thermo-expansion as hard glass up to about 465 C.).

During assembly, the terminal rods 19 are inserted into the bores of grommets 18 as defined by internal coatings 23, after first applying a film of a suitable high. tem perature solder material (such as silver solder paste) to the metal surfaces of either the rods or the grommets, or both, and the grommets 18 are inserted into their respective collars 15 after similar treatment of one or more of the metal surfaces to be joined. The assemblies of parts are then heated (e.g. by induction heating) to fuse the rods 19 to the coatings 23 and the collars 15 to the coatings 24, producing joints 25 and 26 respectively. Alternatively, the parts may be assembled without the application of solder paste, and may then be joined by other known soldering processes, such as the application of rings of solder wire to the joint at one end thereof, and the subsequent action into the joints, or by hand soldering. In each instance, a high temperature solder is used.

It will now be apparent that the joints 23, 24 etc. between the metal parts and the glass tube 12, each consist in three or four separate coatings, including (1) the very thin molecular film of noble metal fused to the glass surface; (2) the electro deposited coating of a good binding metal such as copper, joined to such molecular film; (3) a film of solder such as silver solder bonded upon the copper coating, and (4) (where the metal part is of nonnoble metal) a film of noble metal which joins the solder coating to the surface of the metal part.

At one end of the resistor, a cap 13 with its terminal 19 mounted therein and with the terminal 19 first joined to its winding connection 20, is attached to tube 12 prior to filling the tube with the potting material 21. Such attachment involves the fusing of flange 14 to end coating 22 by a soldered joint 27 (Fig. 5) using a method which may be similar to that used in making the other joints as described above. Joint 27 at the one end-may be made simultaneously with joints 25 and 26.

With wound mandrel 10, 11 in place within tube 12, the partially assembled resistor is now supported in a suitable tray or the like, in an upright position with its open end at the top. The tube 12 is then filled with the potting material, the other end cap assembled loosely in place, and the entire assembly subjected to avacuum process for completely evacuating residual air therefrom.

For example, the filled units may be immersed in a-container, at a sufiiciently high temperature to render the material highly fluid, and vacuum then applied to the container. After filling, the units are cured for minutes at 250 F. for the potting material to solidify.

As the final step of assembly, the loose end cap is fused to the open end of tube 12, to produce a hermetic joint 27, by soldering similar to the soldering of the other end. The resistor now consists in a hermetically sealed unit, its interior completely filled with the potting material 21 evacuated of air. The hermetic joints are truly fused omts between the glass and metal parts, and thus are highly resistant to the effects of shock and vibration tending to break them open. In effect they become a single, integral welded structure which, with the'cushionmg effect of the core body 21 in absorbing vibration, will be as strong and resistant to vibration and shock (except a direct blow against tube 12) as if made completely of metal. Being permanently closed with a hermetic seal, the resistor is equally resistant to the deteriorating effects of moisture and air.

My resistor likewise has an improved resistance to high temperatures. The close fitting of the interior part8 with n tube 12 and the fitting of the ends of terminals 19 within the ends of mandrel 10, Withthe core 21 extendmgthrough tubular mandrel 10, facilitate the conduction and radiation of heat away from winding 10' and connections 20. The fused joints 25-27 facilitate conductron of heat. The ruggedness of construction including the joints of high temperature solder, permit operation at higher temperatures than is possible with existing resistors. The integration of parts into a permanently integral unit makes it possible to maintain operating temperatures within a narrow range for any selected group of conditions, with a correspondingly close tolerance in the range of resistance values. The construction also provides for meeting exceedingly fine dimensional tolerance requirements. The resistor of my invention will comply with tolerance requirements of 0.1% for resistance and 005% for dimensions.

The end portions 20 of the winding 10 are looped back into mandrel 11 as shown, and are sutficiently slack so as to:

(a) Eliminate any possible development of tension therein; and (b) facilitate loose assembling of the final closure cap to the casing tube in a manner leaving the tube open for completion of the filling and evacuating steps and then facilitating the shifting of such end cap to a position fully preparatory to sealing the unit by the final fusing step.

The joints between metal and glass are hermetically tight, possess great strength, and shown no sign of weakness over the extreme temperature range of minus 65 F. to 500 F. or more.

In the process of depositing coatings 22, the glass parts are heated in a furnace to a temperature of 1140 and then allowed to gradually cool. Consequently the glass parts of my resistor are of annealed glass which will withstand high temperatures without breaking down.

Each of the joints 22, 23, 24 actually consists in three coatings of metal, ie (1) a very thin coating of a noble metal (e.g. silver) on the respective glass surface, attained by painting onto the surface a metal powder suspended in liquid which is later evaporated so as to leave the metal fused to the glass in a thin, evenly distributed molecular film; (2) a coating of metal (such as copper) that adheres well to such a molecular film and provides a goodmetal surface for good adherence of (3) a film of solder (e.g. silver solder) which unites the metal part (e.g. cap 13) to the electro-coating. The three coatings are shown-in Fig. 6.

Kovar is a preferred material for the cap 13, 13a, since'it is'especially well matched to hard glass in its expansion characteristics.

Where the cap is of a non-noble metal, such as Kovar, the surface of the metal part is precoated with a fourth coating, of noble metal, so that the solder will establish a good bond with the metal part. Alternatively, the metal part may be solidly of noble metal, in which case the surface thereof constitutes the fourth coating.

In using the term molecular film above, the meaning thereof is not necessarily restricted to a film of a single molecule thickness. Instead, the term is intended to designate acoating having a thinness Within the range of approximately .0005 inch to .005 inch.

I claim:

1. In a resistor: a casing comprising a tube and end caps each including a ferrule part attached to a respective end of said'tube and a grommet mounted in said ferrule part; a core body of latex potting material substantially filling said casing; a mandrel and a winding of resistance wire thereon, encased within said casing, said core body enveloping said winding and cushioning the same against the transmission of shocks thereto from said casing; and terminal rods extending through said grommets and connected to the respective ends of said winding; said casing tube and mandrel and grommets being of hightemperature glass, and said ferrule parts and terminal rods being of metal; and fused metal joints hermetically connecting said glass parts to said metal parts.

2. A resistor as defined in claim 1, wherein said joints comprise molecular films of noble metal fused to end surface; of said casing tube and to bore and peripheral surfaces of said grommet, electro-deposited coatings of copper covering and adhering to said molecular films, and fused connections between said coatings and said metal parts, said fused connections comprising films of silver solder covering said coatings and fused to said coatings and to said metal parts.

3. A resistor as defined in claim 2, wherein said fused connections further include films of noble metal bonded to the surfaces of said metal parts and to said solder films, said metal parts being of non-noble metal having a coefiicient of expansion that is matched to the glass of said casing in its thermal expansion characteristics.

4. A resistor as defined in claim 3, wherein each ferrule part consists in a radial flange fused to a respective end of the casing tube, and a cylindrical collar extending from the inner margin of said radial flange into a respective end of said casing tube, said collar encircling and being fused to the periphery of the respective grommet.

5. A resistor as defined in claim 1, wherein said mandrel is tubular and the ends of said terminal rods extend into the ends thereof, are of slightly smaller diameter than the internal wall of said mandrel, and are separated from said internal wall by thin films of said potting material.

6. A resistor as defined in claim 1, wherein said mandrel is tubular and the ends of said terminal rods extend into the ends thereof, wherein said winding has end portions thereof extending into said mandrel and connected to the ends of said terminal rods within said mandrel ends, and wherein thin films of said core body extend into the end portions of said mandrel and around said terminal rod ends and winding end portions, said core body being of insulating material.

7. In an electrical resistor: a casing comprising a tube of high temperature glass, end caps each including a radial flange having a fused connection with the respective ends of said tube and a cylindrical collar extending from the inner margin of said radial flange into a respective end of said casing tube and radially spaced from the inner wall thereof; grommets each having a cylindrical periphery closely fitted within a respective collar and having a fused connection therewith; a mandrel encased within said tube and having respective ends in adjacent axially spaced relation to the respective grommets; a winding of resistance wire on the periphery of said mandrel and in closely adjacent radially spaced relation to the inner wall of said casing tube; a pair of metal terminal rods each extending through the bore of a respective grommet, closely fitted and joined and sealed thereto by cylindrical sleeve-like fused connections and having respective end portions extending into respective ends of said mandrel, said end portions being of slightly smaller diameter than the inner wall of said mandrel and slightly spaced radially therefrom; and a core body of cushioning insulating material substantially filling said casing and said mandrel and including thin cylindrical sleeve portions interposed between and separating said collars from the inner wall of said casing tube and said terminal ends from the inner wall of said mandrel; all said parts being substantially coaxial, said casing tube, mandrel and grommets being of high temperature heat-resistant glass and said end caps and terminal rods being of a nickel alloy having thermal expansion characteristics substantially matched to that of said glass; said fused connections each comprising thin films of noble metal fused to end surfaces of said casing tube and to the bore and peripheral surfaces of said grommet, thicker coatings of electro-deposited copper covering and bonded to said noble metal films, and relatively thin coatings of silver solder covering said copper coatings and bonded thereto and to the respective surfaces of said end cap; said core body providing cushioning support between said winding and the inner wall of said phery closely fitted within a respective collar and having a fused connection therewith; a mandrel encased within said tube and having respective ends in adjacent axially spaced relation to the respective grommets; a winding of resistance wire on the periphery of said mandrel and in closely adjacent radially spaced relation to the inner wall of said casing tube; a pair of metal terminal rods each extending through the bore of a respective grommet, closely fitted therein and jo'med and sealed to said grommet and having respective end portions extending into respective ends of said mandrel, said end portions being of slightly smaller diameter than the inner wall of said mandrel and slightly spaced radially therefrom; all said parts being substantially coaxial, said casing tube, mandrel and grommets being of high temperature heat-resistant glass and said end caps and terminal rods being of a nickel alloy having thermal expansion characteristics substantially matched to that of said glass; said fused connections each comprising thin films of noble metal fused to end surfaces of said casing tube and to the peripheral surface of said grommet, thicker coatings of electro-deposited copper covering and bonded to said noble metal films, and relatively thin coatings of silver solder covering said copper coatings and bonded thereto and to the respective surfaces of said end cap.

9. In an electrical resistor: a casing comprising a tube of high temperature glass, end caps each including a radial flange having a fused connection with the respective end of said tube and a cylindrical collar extending from the inner margin of said radial flange into a respective end of said casing tube and radially spaced from the inner wall thereof; grommets each having a cylindrical periphery closely fitted within a respective collar and joined thereto; a mandrel encased within said tube and having respective ends in adjacent axially spaced relation to the respective grommets; a winding of resistance wire on the periphery of said mandrel and in closely adjacent radially spaced relation to the inner wall of said casing tube; a pair of metal terminal rods each extending through the bore of a respective grommet, closely fitted therein and joined and sealed to said grommet and having respective end portions extending into respective ends of said mandrel, said end portions being of slightly smaller diameter than the inner wall of said mandrel and slightly spaced radially therefrom; all said parts being substantially coaxial, said casing tube, mandrel and grommets being of high temperature heatresistant glass and said end caps and terminal rods being of a nickel alloy having thermal expansion characteristics substantially matched to that of said glass; said fused connection comprising a thin film of noble metal fused to end surfaces of said casing tube, a thicker coating of electro-deposited copper covering and bonded to said noble metal film, and a relatively thin coating of silver solder covering said copper coating and bonded thereto and to the surface of said end cap.

10. In an electrical resistor: a casing comprising a tube of high temperature glass, end caps each including a radial flange having a fused connection with the respective end of said tube and a cylindrical collar extending from the inner margin of said radial flange into a respective end of said casing tube and radially spaced from the inner wall thereof; grommets each having a cylindrical periphery closely fitted within a respective collar and joined thereto; a mandrel encased within said tube and having respective ends in adjacent axially spaced extending through and sealed in the bore of a respective grommet; all said parts being substantially coaxial, said casing tube, mandrel and grommets being of high temperature heat-resistant glass and said end caps and terminal rods being of a nickel alloy having thermal expansion characteristics substantially matched to that 10 of said glass; said fused connection comprising a thin filrn of noble metal fused to end surfaces of said casing 'tube, a coating of electro-deposited copper covering and bonded to said noble metal film, and a relatively thin coating of silver solder covering said copper coating and bonded thereto and to the surface of said end cap.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,779 Kohler Oct. 6, 1942 2,297,780 Pugh Oct. 6, 1942 2,332,255 Podolsky Oct. 19, 1943 2,407,171 McFarren Sept. 3, 1945

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