US2297779A - Resistor construction - Google Patents

Description

Patented oci. 6,1942

nasis'ron coNs'raUc'noN a John ll. A. Kohler, Philadelphia, Pa., assigner to Resistance Company, Philadelphia, Pa., a corporation of Delaware Application July 19d., Serial No. 347,848 3 Claims. (Cl. 201-67) International This invention relates to anelectrical resistor construction and moreparticularly a hermetically sealed unit suitable for emcient operationl under a variety of weather conditions. One of the objects of this invention is to provide a resistor construction which' will be mechanically and electrically durable and well able to withstand indenitely the destructive effects 'of extremely adverse weather conditions. An-

other object is to provide a construction of the above character susceptible of economical manufacture from inexpensive materials, Another object is to provide a construction of the above character in which all electrical parts subject to damage from weather conditions are completely sealed therefrom by rugged and permanent structure. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the various possible embodiments of my invention: f

Figure 1 is a perspective view of the complete resistance unit;

' Figure 2 is a longitudinal sectional view of the 'unit shown in Figure 1;

Figure 3 is an enlarged fragmentary longitudinal sectional view of a portion of the structureshown in Figure 2; and

Figure 4 is a transverse sectional view taken along the line 4--4 of Figure 2,

Similar reference characters refer to similar parts throughout the several views of the drawing. A

Certain problems and difficultiesv inherent in resistor units now in general use form a basis for a more ready comprehension of some of the important featines of this invention. When resistance units and like equipment ,are used for maritime radio equipment or like purposes, the

variety of -weather conditions encountered in use is such as to produce rapid deterioration of any exposed' parts resulting in breakdowns and general inefficient operation. Not only are such units exposed to every variety of temperature from the equator to the 'arctic regions but :also the saline atmosphere encountered has a very damasim effect Fior example, humidity and salt air may corrode the resistance wire and Cil tion. Resistance wires are often made from l alloys having. as ingredients dissimilar metals and in-the presence of salt watena voltage is set up between two 4points in the wire resulting in rapid deterioration thereof by the electrolytic action; Resistance units now used in an attempt to overcome this difiiculty are generally characterized by chemical protective coatings of various types such as vitreous enamels, cements and the like. offered by these coatings delay to some extent the effects of humidity and`sa1t air, eventual penetration is effected and, as a matter of fact, some of theseL-coatings even contribute tothe diillculty because they contain salts which combine with the water to produce the electrolytic culties as well as many others are successfully overcome.

Referring to Figure 1 of the drawing, there is shown a resistance unit enclosed in a casing. I5 and having at each end terminals il and I2 preferably of annular shape for more ready connection in desired circuits. -The resistance unit together with all parts thereof vulnerable to weather conditions are hermetically sealed within the casing i5 as will be more fully described hereinafter.

More particularly, as better shown in Figure 2,

the unit consistsA of a core, which is preferably a ceramic tube I3, having wound thereon resistg ance wire I4. Tube I3 with the wire wound thereon is enclosed in a cylindrical casing I5 and terminals II and I I, preferably cup-shaped, ilt

4 over -the ends of tube Il and are connected to the nection's with the terminals Il and I1 are so protected in this enclosure that they cannotI be effected by any atmospheric conditions-and, more partimnsru, the action ofsait and water which,A

' as previously noted, is very harmful to these parts. Furthermore, the casing `I." and the terminals Il and I2 may be made fromdurable materials wellable to stand up under the variety -theremayalsobe an anodic or electrolytic acof weather conditions which this unit k de- While'th'e mechanical protection signed to withstand. There are no openings or crevices through which the atmosphere might attack the vulnerable parts of the resistance unit and the only seams through which leakage might occur are constructed to withstand any tending cylindrical portions IIc and I2c. Cylindrical portions IIc andY I2c t tightly within casing I5, thus to support the casing in spaced relation to the resistance wire I4 and provide the desired sealed space. Lips I Id and I2d prei'- erably cut from cylindrical portions IIc and I2c are bent downwardly and the ends of wire I6 fit between the lips Ild and I2d and thel cylindrical portions IIc and I2c preferably being silver soldered or otherwise electrically connected in this position, as shown in greater detail in Figures 3 and 4. Thus, terminals I I and I2V are Yelectrically connected to the resistance wire III at points within the sealed space so that harmful atmospheric -conditions cannot attack these vulnerable parts of .the resistance unit. The

' spacejcr the wire I4 defined by the Acasing I5,

the intesa and the terminals u and a2 is preferably tightly packed with an insulating medium, preferably an inorganic cement such as porcelain cement.

For the reasons mentioned above, it is most important to provide a durable hermetic seal between the terminals II and I2 and the casing I5. For this purpose I prefer to form the casing I5 from a glass and the terminalsvII and I2 from a metal so chosen that a bond may be effected therebetween. For example, the casing I5 may be formed from a glass known to the a hydrogen atmosphere to" eliminate all traces of gas from the metal so that no bubbles or gas pockets will be formed during the sealing operation: such formations materially reduce the ability of the resultant seal to withstand stresses introduced by temperature changes. The metal ends are then rapidly oxidized so as to give an oxidized surface for the glass to wet. The resultant bond between the casing I5 and the terminals I I and I2 provides a perfect hermetic seal for the interior parts of the resistance unit and, more particularly, thel resistance wire I4 with its connectionsto the terminals.

The outer structure, i. e. the terminals II and I2 and the casing I5 of the resultant resistance unit are thus formed from materials well able to withstand any'weather conditions without deterioration. Of course, the metal chosen for the terminals II and I2 is not only selected for its ability to form the above-described bond with the glass casing I5, vbut also `for its ability to withstand the corrosive eiect of Weather conditions. In practice, the seal between the casing I5 and the terminals Il and I2 has been found to be durable, to maintain a hermetic seal and thus prevent any seepage. of atmosphere, water or chemicals to the interior of the unit where they might damage the wire 'I4 and connected parts. Not only is this resistance unit designed to stand up under most extreme atmospheric conditions but also it has a marked ability to remain unaiected by sudden temperature changes over wide ranges. v

It will thus be seen that I haveprovided a thoroughly practical and emcient resistance unit V in which the several objects hereinabove referred to as well as many others are successfully and eiciently accomplished.

As many possible embodiments may be made of the above invention'and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

trade as G705A.I, manufactured by the Corning Glass Company, and the metal, which must have the same coemcientof expansion as the glass, may be an iron-nickel-cobalt valloy such' be used for the casing andthe terminalsl respeotively, the principal prerequisites for which are substantially equal coeicients ofgexpansion and the creation of abond therebetween by the application of heat. Glass-metal seals Aof the type utilized for this construction are disclosed in considerable detail in Patent No. 2,062,335.

After the unit has been assembled as described I claim:

1. In resistor construction, in combination, glass tube member, a Vdielectric core, a resistance element wound on said core, said core being positloned within said tube member and having its ends extending from the ends thereof, and metal cap members fitting over and being mounted on 'seal between said cap members and said tube,

said cap members and tube members having the same coeilicients of expansion and hermetically above, the opposite ends thereof are subjected l thereby forming a perfect b'ond therewith as it cools, Thus, upon cooling, the ends of casing-- I5 have formed thereon inwardly extending annular ridges I5a and I5b engaging and bonded to the flanges IIb and I2b (Figure 3). In practice, .preparatory to this sealing operation, I have found it desirable to heat the terminals II and sealing said resistance element from the atmos phere.

.go 2. In resistor construction, in combination, a

glass tube member, a ceramic core, a resistance element mounted ongsaid core, said core being positioned within said-tube member and having its .ends extending from the ends thereof, metal cap members fitting over and being mounted on each end of said core, and having annular flanges extending outwardly from the open ends thereof, the perlpheries of said flanges being connected to and completely covering the open ends of said tube member by a glass-to-metal seal, said tube and `cap members having the same coefficients of expansion and hermetically sealing said resistance element from the atmosphere, and means electrically connecting the ends of said resistance I2 at temperatures on the order of 1800 F; in 75 elementto said cap members'.

nected thereto by a glass-to-metal seal to completely cover and seal said ends from the atmosphere, said tube and csp members having the s ame coemcients of expansion, and means forming electrical connections between said resistance element and said ange portions.

JOHN H. A. KOHM.

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