US 2933709 A
Description (OCR text may contain errors)
April 19, 1960v H. M. wUTz 2,933,709
ELECTRICAL ELEMENT ASSEMBLY Filed oct. 16, 1958 Tlcrl -E=- ATTO RN E 5.'
United SffaSPatCf O" VThis invention relates to electrical elements and more particularly to assemblies of electrical elements, such as capacitors, inductances and resistors, which are mechanically rigid and hermetically sealed.
Resistor assemblies have heretofore generally included a component body having a resistive element affixed thereon with extended wire leads attached to each end of theA element and a ceramic shell enclosing the component body in such a manner that the leads `protrude therefrom. If thevends of the shell are open solder is often used to close up `these ends and seal the assembly. These prior assemblies, however, lack positive mechanical anchorage between the component body and the-shell and the solder engaging the lead wires is usually. theonly support of the resistive elementin'the shell. The solder which seals the ends, also holds the wirescentered and, thus, 'holds the Abody in place within the seal., This is particularly disadvantageous where the assembly is subjected to vibra` tionand shocks under which conditions the resistive element may be jarred out of position and in marginal cases the seal might be jarred loose.
Accordingly, it is an object of the present invention vto provide an inexpensive, easily assembled yet structurally strong electrical element assembly of improved structural strength. It is a further object to provide a resistor assembly which is durable and more rugged then the ceramic shell resistors used heretofore. It is a still further object to provide an assembly wherein the component tbody with its resistive element is held mechanically in a xed position within the shell independently of any seal at the ends of the shell.
Accordingto this invention, one provides an assembly wherein a sealing material adheres tenaciously both to the outer shell and to metal caps which are placed over the ends of the resistive element.
In the accompanying drawing a preferred embodiment of the present invention is shown and certain modifications are suggested in the specification. It is to be understood that these are not intended to be exhaustive or limiting of the invention, but, on the contrary, are for the purposeof illustrating and describing the invention in order that others skilled in the art may fully understand the invention, its principles and the application thereof, and that they may embodying it and adapt it in numerous forms, each as may be best suited to the requirements of the particular usage.
In the drawings:
Figure 1 is a longitudinal perspective view of a resistor assembly in accordance with the present invention;
Figure 2 is an exploded longitudinal perspective view of the resistor assembly of Figure 1 but not including the plastic sealing compound at each end of the plastic shell;
Figure 3 is a longitudinal sectional view taken on line 3--3 in the direction indicated by the arrows 3--3' on Figure 1; and
Figure 4 is a transverse sectional view of the resistor assembly of Figure 1 taken on line 4-4, in the direction of the arrows 4-4, on Figure 3. The proportional thickness shown in Figures 2, 3 and 4 are distorted for easier reading. In ordinary practice the metal of caps 14 will.; be much thinner thanrthe plastic tubular wall 18; butf these thicknesses are not a part of the present invention."
Referring now toFigures 1, 2 and l3 of the drawings, an illustrative embodiment of the present invention in thek form of a resistor assembly is geenrally indicated at 10.
This assembly 10 comprises a component body 12, a pair 'l of metal contact caps 14, a pair of lead wires 16, one being attached to each cap e.g. by welding or brazing,`
an outer plastic shell 18 tightly tted around the end caps 14 and also surrounding the component body 12, and a seal 20 of a compatible plastic sealing compound at eachV end of the shell 18.
The component body 12 includes a suitable core which is a resistive element itself, or it may carry a` resistive element. yFor example, the core may be of porcelain and the resistive element may be a wire wound thereon in one or several layers, or it may be a sprayed or adhesively bonded coating of a more or less conductive material,
for example carbon. Since the selection of the core and resistive element is already well known and dependent on the particular situation for which the assembly will be used, the resistive element in the illustrated embodiment will be. considered in this specification as a conventional unit and referred to as the component body 12.
Fitted on the ends of the component body 1'2 are,
metal end Vcaps-.14, .In one embodiment of the present contact between the caps and the resistive element.
Attached to each cap 14 is an extended lead wire 16 which is iixed to the cap by suitable means such as welding or soldering at 24.
After the caps 14 have been fitted onto the body 12, this sub-assembly is placed within the plastic shell 18. In order to insure that the body and caps will be substantially rigidly positioned with the shell 18, the maximum diameter of each cap 14 is advantageously slightly greater than the inside diameter of the shell 18. By so constructing the caps and shell, when the shell 1S is forced over the end caps 14 a mechanically rigid structure is obtained. This Vforced fit between the caps and shell nsures that the component body 12, with its attached resistive element, will be securely held in spaced relation with the shell 18. This iixed spaced relation of the comcomponent body 12 within the shell 18 prevents the shell influencing the characteristics of the resistive element. Further, when the seal 2G is applied at each end of the shell 18 the tight joint between the caps 14 `and the shell 18 insures that the seal 20, if applied in a liquid state, will not ow past the cap 14 and into the annular space 26 between the component body 12 and the inner wall of the shell 18.
By having the body 12, the caps 14, and the shell 18 rigidly secured together the seal Ztl is only required to -act as an hermetic seal and it need not perform the additional function of structuraily stabilizing the assembly.
In a preferred embodiment of a resistor assembly in accordance with the present invention the plastic shell 18 is advantageously made from an epoxy resin base compound and the sealing compound used to form the seal 2t) is also an epoxy type potting resin or sealer. The use of an epoxy resin base material provides a plastic shell which is relatively rigid and yet is not fragile, but other resins may be used such as nylon, vinyl chloride, polyesters, synthetic rubbers, etc., and much advantage can be had from this invention using metal caps tightly tted on the body and in the shell even when both are made of usual ceramic materials. The epoxy resin seal-L ,Patented prLlS, 1960.
3 ing compound has extremely good adhesive qualities and it adheres tenaciously to the shell 18 and to the metal cap 1,4. Thus, the epoxy resin compound provides a very` effective hermetic seal.
The caps 14 are preferably set inward from the edges of the shell 18; e.g., in one embodiment of a resistor assembly it was found satisfactory to have the shell 18 protrude about one-eighth of its length beyond the caps 14 at each end.
From the yforegoing description it will be appreciated that the present invention provides a new and unique component assembly which is rigid and mechanically stable. It' will thus be appreciated that the present invention accomplishes the aforementioned and other advantageous objects. However, it should also be emphasized that the foregoing description of the particular cm.- bodimentwhich is shown in the accompanying drawings is'intended to be illustrative of the invention and is not exhaustive of the invention.
1. An. electrical resistor assembly or like componentv being in fixed spaced relation with the inner surface of said shell.
22 An electrical resistor assembly or like component asset forth` in claim 1, wherein said caps are each set.
back within said shell a `distance approximately 1A, the length of said shell.
3. An electrical resistor assembly or like component as set forth in claim 1', wherein the ends of said tubular shell are sealed with an organic plastic sealing compound.
4. An electrical resistor assembly or like component as set forth in claim l, wherein said tubular shell is made of an epoxy resin base compound and said shell is cemented to the end caps by an epoxy resin sealing compound whereby said assembly is hermetically sealed.
5. An electrical resistor assembly or the likecomprising a :body having an electrical element attached thereto, metallic end caps fitted over each end of said body, lead wires attachedto each of said caps, aplastictubular shell surrounding said body and tightly fitting about said caps, said lead wires protruding from said shell, and a sealing compound filling in each end of said shell and hermetically sealing said caps and body within said said shell, the outside diameter of said metallic caps being slightly greater Athan the inner diameter of said shell whereby a strong mechanical bond between said shell and caps` is:
.References Cited in the iile of this patent UNITED. STATES, PATENT Sv 2,282,398` Ehrlich May12', 1942y 2,558,798 Thom July 3, 1951.l 2,638,523 Rubin Mayl2, 1953 744,988 Tierman May 8, 195.6 25792620' 1957 Kohring May 21,