US2640903A - Resistance construction - Google Patents

Description

June 2, 1953 w. M. KOHRING 2,640,903-

RESISTANCE CONSTRUCTION Filed July 15. 1950 INVENTOR. W/L w? M. {WW/N6 yin Z: W

ATTOR/YEX)" Patented June 2, 1953 RESISTANCE CONSTRUCTION Wilbur M. Kohring, Lakewood, Ohio, assignor, by mesne assignments, to Aerovox Corporation, New Bedford, Mass, a corporation of Massachusetts ApplicationJuly 15, 1950, Serial No. 174,079

9 Claims.

I In my patent applications Serial No. 77,713, now Patent No. 2,537,061, and Serial No. 161,348, now Patent No. 2,597,338, of which this application is a continuation, in part and as to common subject matter, I set forth resistor construction in which a resistance element was carried by an insulation or ceramic core, and into end openings in the insulation terminals were driven. Electrical contact with the resistance element had to be completed by mechanical contact or by metallic means. I have now found that a molded resistance body as of carbon powder or metal powder with a binder can be provided with end openings and terminals can be driven into them. This is particularly surprising, since common experience with such resistances is that they are so highly frangible that a priori it would be apparent that an attempt to drive a terminal into such a body would merely result in breaking it. However, by the present invention, this means of making terminal contact not only becomes feasible, but an especially excellent electrical contact results. Why the electrical contact should work out better and more uniformly than where a terminal is merely molded in during the making of a resistance, is not wholly clear; but there is some reason for believing that the driving in of the terminal incurs such abrasion of the engaging surfaces that variable oxide films on the metal are cleared off and a particularly intimate contact between metal and resistance is gained. And further also, it may be that the film of binder which tends to segregate to the metal surface where a terminal is merely molded in, is wholly obviated here, and with the result of a more uniform electrical contact between metal terminal and resistance material. Other objects and advantages of the invention will appear from the following description.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however,v of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

Fig. 1 is a broken longitudinal sectional view 01": a resistance in accordance with the invention;

Figs. 2, 3 and l are end elevational views on a slightly larger scale, of resistance bodies having illustrative end openings applicable in the invention;

"in'g transverse ridges or" pr'otuberances.

Figs. 5-8 inclusive are illustrative fragmentary perspective views of metal terminals which are to be driven into the resistance bodies;

Fig. 9 is a fragmentary longitudinal sectional view of a completed resistance embodying the invention;

Figs. 10 and 11 are fragmentary side elevational and longitudinal sectional views respectively showing an improved form of terminal abutment-flange construction;

Figs. 12 and 13 are perspective views showing the terminal end of complete assemblies; and

Figs. 14 and 15 are plan views of the end closure pieces.

The resistance body 2 is formed to standardized dimensions and values, by individual molding, or in some cases by extrusion molding and severing to required dimension. The material of which such body is formed may be a suitably conducting resistance material, such as carbon black powder, or in some instances metallic powder, with a suitable binder. Phenol-formaldehyde for example as known in the molded resistance art, in liquid form is illustrative. For example, carbon black powder, in some cases together with inert filler, and heat-hardenable phenol-formaldehyde resin solution (e. g. the forty or fifty per cent commercial solution) are mixed together to a stiff plastic mass whichis molded, as afore-indicated, into the desired value bodies. And similarly, where metal powder is substituted instead of carbon. The resistance bodies are provided with end openings 3, either in the molding, or subsequent drilling may be employed where the end opening is to be of uniform circular diameter. As illustrated in Fig. 2, the end opening is circular in section. Figs. 3 and 4 illustrate different forms of non-circular openings, involving various serrations. The metal terminals 4, as of wire of suitable diameter, and preferably copper with tin coating, may be given a forming operation to provide a slight enlargement or flange 5 spaced back from the end. But this is not in all cases necessary. The cross-section of the terminal to be driven into the end opening of the resistance'body is provided to an effective diameter slightly larger than that of the end opening in the resistance body. The difference in effective cross-section results in abrasion and deformation of the engaging surfaces and tight seizure when such terminals are driven into the openings in the resistance bodies. Illustrative forms which the end of the metal terminals may take are shown in the drawing. In Figs. 5 and'lOisshown an endhav- Such form is Well suited for end openings of circular cross-section, although it may be used with others. Figs. 6 and 7 illustrate terminal ends with non-circular cross-section, as square and triangular respectively. Fig. 8 illustrates an end with a plain round cross-section, such form being mostly used with end openings of non-circular cross-section.

In each instance, the terminal is assembled with the resistance body by driving or forcing it into the end opening. The resistance body may be held for such operation, in suitable holding means.

To exclude moisture and influence of atmospheric conditions, as shown in Fig. 9 the resistance with terminals is encased in a layer of plastic insulating material, by a final operation of molding-on, and thus the resistance body 2 with its terminals 4 is completely covered by the outside layer id of insulating plastic material such as heat-set phenol-formaldehyde resin. Where plastic material is molded onto such an assembly, there is a tendency for the material to flow between the parting-mold sections at the end, undesirably in some cases. I have found that this can be obviated if the flange or enlargement a, Figs. 10 and 11, be in the form of a stepped or compound flange, avoiding inclined surfaces. Thus the larger diameter portion of the flange or enlargement on the terminal abuts against the core as shown in Fig. 11, and the other portion exposed in the mold cavity is of stepped-down diameter.

To complete an assemblage of resistors in compact form, the resistors r in number desired, as for instance two, three or four, are positioned in an insulating or ceramic shell 12 and spaced from each other by an intermediate insulating or ceramic insert spacer 13 which presents longitudinal grooves corresponding to the number of resistors to be accommodated. In such operation, the end piece or plate 15 of insulating or ceramic material not only serves to close the end of the shell [2, but also assists inthe assembling. Thus, on an assembly line frame or carrier a series of the end pieces are placed, and two or more resistors as desired are placed upright on each with the terminals 4 setting into appropriate openings l6. Thereby the resistors are properly spaced and held while the shell l2 and spacer l3 are assembled. The same utility obtains also if the terminals are provided with soldering eye-ends 4', Fig. 13; the holes I6, Fig. 15, being elongated in outline to receive them. The assembly in any case is held together by suitable cement, as ceramic cement or sodium silicate cement, applied to the end piece before the shell is closed down over it, the final position being as in Fig. 12. This kind of construction can tolerate drastic heating conditions.

In my co-pending application, Serial No. 77,713, new Patent No. 2,537,061, there is claimed the affixing of terminals for a resistor by drive-fit and contacting-surface deformation in an insulating core.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In resistance construction, a resistance body, terminals held in end openings thereof by contacting-surface deformation, compound flanges on said terminals against the ends of said body, a moisture-excluding layer of plastic material over the body and flanges, means for protecting said resistor including a ceramic shell, and means for positioning the resistor to the shell including a plate fitting the end of the shell and having an opening to co-relate the terminal of the adjacent end of the resistor.

2. In resistance construction, a resistor body, flexible terminals projecting from openings at each end and being held therein by contactingsurface deformation, compound flanges on said terminals in stepped large and smaller diameters with the large diameter against the resistor end, a moisture-excluding layer of plastic material over the resistor and said end flanges, a self sustaining hollow insulating shell surrounding said resistor and at least one other, and means for positioning the resistors to the shell including a preformed insulating plate fitting the end of the shell and having openings to spacedly position adjacent terminals of the resistors.

3. In resistance construction, a resistor in length proportioned for a predetermined resistance value, flexible terminals projecting from openings at each end and being held therein by contacting-surface deformation, a hollow insulating shell, and means for assembling and positioning the resistor in the shell including a preformed plate fitting the end of the shell and having an opening to co-relate the terminal of the adjacent end of the resistor.

4. In resistance construction, a resistor body of poorly-conducting material dimensioned to a predetermined resistance value, a hole in each end of said body in axial alignment, terminals seized in said holes in contacting-surface deformation, flanges on said terminals against the body, moisture-excluding plastic material covering the body and said flanges, flexible projections of said terminals extending out from the plastic cover, a. preformed ceramic shell in which said resistor is positioned, and a preformed plate perforated for receiving and positioning the resistor terminal.

5. In resistance construction, a resistor body of poorly-conducting material dimensioned to a predetermined resistance value, a hole in each end of said body in axial alignment, terminals seized in said holes in contacting-surface deformation, flanges on said terminals against the body, moisture-excluding plastic material covering the body and said flanges, and flexible projections of said terminals extending out from the plastic cover.

6. In resistance construction, driving terminals which have compound step flanges of large and smaller diameter into openings in the opposite ends of a resistor to seize therein by contactingsurface deformation, the large diameter flange being against the resistor end, covering the body and flanges with a moisture-excluding layer of plastic material, co-relating the resistor to a protective shell by setting the resistor with a terminal through an opening in an end plate therefor, and assembling with the resistor inside the shell and the plate closing the shell, with the terminal end projecting.

7. In resistance construction, driving terminals into openings in the opposite ends of a resistor to seize therein by contacting-surface deformation and provide extending flexible projections, and assembling such resistors in an insulating shell by setting resistor terminals into openings in an end insulating plate thereby holding them in position, and assembling a spacer and an insulating shell with the resistors and end plate.

WJLBUR M. KOHRING.

References Cited in the file of this patent UNITED STATES PATENTS Number Number 15 508,836

Name Date Smalley Oct. 3, 1922 Backer Dec. 2, 1930 Eddy Oct. 10, 1939 I-Iubald Feb. 18, 1941 Hediger et a1 Sept. 25, 1945 Robbie et a1. Dec. 2, 1947 Kohring Nov. 8, 1949 Kohring Jan. 9, 1951 FOREIGN PATENTS Country Date Great Britain July 6, 1939

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