IE34672B

IE34672B - Method of mounting a terminal assembly on an electrical device,and a terminal assembly mounted on an electrical device

Info

Publication number: IE34672B
Application number: IE138670A
Authority: IE
Original assignee: Gen Electric
Priority date: 1969-11-28
Filing date: 1970-10-30
Publication date: 1975-07-09
Also published as: DE2056378A1; DE2056378C3; IE34672L; JPS5121155B1; DE2056378B2

Abstract

The connector is intended particularly for electrolytic capacitors and has a lid formed of several insulating layers. The lid is abutted by a conductive rivet (40) containing a connecting terminal (32). The latter is coupled to the rivet by a head flange (140) formed by upsetting. The rivet has a massive shaft portion (144) which fills a bore (28) in a first, relatively rigid lid layer (24) only partly, while fitting completely a bore (29) in a second, more elastic lid layer (26). The outer head flange of the rivet presses the connecting terminal against an inner sh oulder (146), formed by upsetting in the shaft portion in the first lid layer. The deformed part of the shaft has preferably a volume, prior to upsetting, which corresponds to the total volume of both bores. [DE2056378B2]

Description

34672 This invention relates to terminal assemblies for electrical devices such as electrolytic capacitors and more particularly to a terminal assembly for mechanically and electrically connecting the internal elec-5 trical lead running from the device to an external terminal .

Riveted terminal assemblies, particularly for electrolytic capacitors, usually pass through plastics and elastomer discs which form the end closure for the 10 capacitor. Difficulties have been encountered in the prior art relative to maintaining a tight,secure and durable electrical connection between the rivet, the internal electrical lead and the external terminal. Cracking and distortion of the plastics closure cover 15 can occur, even during manufacture, depending upon the compression set characteristics of the customary cover materials, commonly the combination of an elastomer rubber and a rigid phenolic resin. Such difficulties often result in a progressive loosening of the rivet 20 seal, which can cause relative motion between the electrical connection members and result iii a deterioration of that connection, thereby increasing the electrical 2 resistance thereof. Resulting I R losses cause excessive heating of the connection/ which further deter-25 iorates the seal and can cause eventual destruction of the electrical, connection.

Prior attempts to solve this problem have included the use of a metal bushing surrounding the rivet and tightly fitted within the aperture of the insulative - 2 - 3 4 6 7 2 closure member, whereby the bushing serves to support the terminal and form an additional currents-conducting path, in addition to the rivet. Such metal bushings are known from U.S.patent 3,439,232, for example. 5 The invention provides a method of mounting on an electrical device a terminal assembly comprising an insulated cover for the device, said cover having a bore therethrough, and a terminal having a portion adjacent one side of the cover, said portion having a 10 bore therethrough of smaller diameter than the cover bore; said method comprising aligning the bores, locating in the aligned bores a rivet shank dimensioned to define an annular space with the cover bore which shank is solid where it extends through the cover and terminal 15 portion, and applying a force to the rivet to produce an enlargement at one end and also to deform the shank of the rivet remote from the point of application of the force so as at least partly to fill the cover bore, the rivet providing by said enlargement and deformation 20 two laterally extending portions which grip opposite sides of the terminal portion.

The invention also provides a terminal assembly mounted on an electrical device by the method just defined. This invention will be better understood when con- 25 sidered in connection with the following description and the drawing in which: FIGURE 1 is a cross section of a typical prior art riveted terminal connection for electrolytic capacitors; FIGURE 2 illustrates a cross section of a terminal 30 assembly embodying the present invention before deformation of the rivet; - 3 - 34672 and FIGURE 3 is a cross section of the completed terminal assembly after rivet deformation.

In FIGURE 1 of the drawing, there is shown a 5 typical prior art riveted terminal structure for an electrolytic capacitor having an end closure comprising a closure disc 10 provided with a lower rubber face 11 and an upper phenolic plastics face 12 to seal the capacitor body and to provide means for connecting suitable 10 electrical terminals to the capacitor. An electric terminal lug 13 is mechanically attached to the disc 10 by means of a rivet 14 which extends through an aperture 15 in the closure disc 10 and is a SnUg fit in the aperture before being upset. The rivet 14 also 15 serves as the electrical connection between the terminal lug 13 and an internal lead 16 of the capacitor, the internal lead being pressed against a washer 17 by the lower head of riVet 14.

As may be seen from FIG.l, when the rivet of the 20 prior art structure is upset,the deformable material of the rivet shank tends to flow primarily downwardly into a somewhat conical shape. Accordingly, the deformable rivet material in the rivet presses radially outwardly near the bottom and tends to warp and distort the rigid 25 plastics face 12 into an upwardly concave shape when the shank material fills the aperture in the cover and cannot expand beyond it. Customary riveting practice, normally followed in this and other prior art riveted structures to assure good alignment of parts, was that 30 the aperture of the cover" or sleeve into which the rivet shank fits should always closely encompass the diameter - 4 - 34672 of the rivet shank prior to upsetting. As a result, these difficulties occurred. It will be noted from PIG.1 that substantially no Supporting ledge or shoulder is formed against the under surface of the terminal 5 lug 13 by the rivet shank.

With this type of prior art construction it is very difficult to achieve a secure mechanical and durable electrical connection in the aperture 15 of the closure disc 10, because thermal cycling during operation of the 10 capacitor carrying heavy current causes the connection to heat up. The face 12 is stressed by the rivet deformation. Decay of the compression set characteristics of the, material of the plastics face 12 event* ;ually occurs, resulting in a loosening of the terminal 15 lug 13 around the rivet, causing increased resistance to current flow with eventual arcing, burning of the connection and ultimate destruction and failure of the device. Such a secure connection is needed to insure that the electrical path from the internal lead 16 to 20 the terminal lug 13 will be unbroken. With the prior art arrangement of FIG.l, the connection tends to have a high electrical resistance because of the possibility of progressive deterioration of the contact between the terminal lug 13 and the rivet 14. This problem has been 2'5 overcome by the arrangement o£ the present invention, an example of which is illustrated in FIGURES 2 and 3. ;FIG.2, illustrates one embodiment of the invention, and shows its essential components, before deformation of the rivet. The cover 22 of an electrical device, ;30 such as an electrolytic capacitor, comprises an electrically ;- 5 - ;3 4 6 7 s> ;non-conducting material and may include the usual relatively rigid outer member 24 of phenolic resin or fiber board, and a pliable inner member or layer 26, of a suitable elastomer or rubber material. The 5 members 24 and 26 each have formed therein respective bores or apertures 28, 29, through which the shank portion 44 of a rivet 40 extends, which shank portion is solid. However, contrary to customary riveting practice, and for reasons which will be explained below, the bores 10 28, 29 are of substantially enlarged diameter relative to the diameter of the shank 44- The metal rivet 40 has a preformed lower head 42. The shank portion 44 j after passing through a customary metal washer 68, extends up through the enlarged bores 29 and 28 of the members 15 26 and 24, and then through a close fitting bore 38 in the flange 34 of a terminal lug 32 which forms an external electrical connection. As mentioned, the bores 28 and 29 are substantially larger than the diameter of shank portion 44 of the rivet, contrary to customary riveting 20 practice. These larger diameter bores 28, 29 provide vertically adjacent annular spaces or cavities surrounding the rivet shank 44 and extending the height of the bore 28 and of the bore 29. The bore 38 in the flange 34 above the cover does not have such an annular space 25 surrounding the rivet shank 44 because the bore 38 is of smaller diamater than that of the bores 29 and 28. The metal washer 68, below the pliable member 26 is provided with a bore 69 which is also of smaller diameter than the bore 29. ;The rivet 40 with its shank 44 is preferably of a 30 standard semi-tubular aluminum type wherein the shank has a cup-shaped formation 41 at its upper end which terminates in an inverted apex 43} below which the shank 44 is of ;-6- ;34 67 3 ;solid metal and defines a cylindrical portion of deformable material having a diameter corresponding to the outer diameter of the rivet shank 44 and having a length extending from the bottom of the cup-shaped apex 43 down 5 to the upper surface of the lower rivet head 42. ;The relative volumes of deformable shank material and cavities into which it can laterally expand are preferably proportioned so as to prevent cracking or distortion of the cover 22, while forming a terminal-supporting 10 shoulder within the bore in the rigid member 24. ;We have found that we can accomplish this end by proportioning the volume of the above-defined cylindrical portion of deforrtable rivet shank material to substantially equal the total volume of the bores 28 , 29 of the rigid and 15 pliable members 24, 26. This proportioning of volumes controls the rivet deformation to avoid cracking and deformation of the rigid outer member 24 while forming a terminal supporting ledge or shoulder within the bore 28, which will be more apparent from FIG. 20 3, described below. ;The rivet 40 is inserted into position from the bottom of the cover, as is customary, through an aperture 64 in the internal lead 66 and through an aperture 69 in the metal washer 68, both of these apertures closely 25 fitting the diameter of the shank 44. The aperture 64 ;in the lead 66 is approximately the same diameter as that of the aperture 38 in the flange 34» both of which are smaller in diameter than the bores 28 and 29. The shank 44 goes up through the enlarged bores 29 and 28, 30 respectively, in the pliable member 26 and the rigid member 24. The lower rivet head 42 preferably ;- 7 - ;3 4 6 7 2 ;has provided on its upper or inner surface a plurality of projections or raised concentric gripping rings 50 which are adapted to bite into and sealingly engage the soft aluminum metal of the internal lead 66. Spurs 46 5 on the lower surface of terminal lug 32 are adapted to engage the upper surface of member 24 to inhibit relative movement of the member 24 and terminal lug 32. ;FIG.3 shows, in cross section, the completed terminal structure of the embodiment after the rivet 40 10 has been deformed by upset. The upper portion of the rivet 40, in the usual manner,has formed the rolled-over or expanded upper head portion 140. However, contrary to the rivet structures of the prior art, the deformed shank portion 144 of the rivet of FIG.3 has expanded 15 radially more cylindrically than conically and has formed a terminal-supporting shoulder or ledge 146 adjacent the flange 34 and is disposed at least partially within the bore cavity 2 8 in the rigid member 24. The laterally expanded shank portion 144 may only partially 20 fill all corners of the bore 28, but has been controlled to slightly over-fill only the bore 29 in the pliable member 26 at 148 to cause a radial compression of the member- 26 and thus to form a secure fluid-tight seal together with the washer 68 which rests below • and adjacent 25 the member 26. The rivet shank 144 has expanded laterally to completely fill the bore 38 in the flange 34 and to fill the bore 69 in the washer 68, but not to over-fill the bore 28 in the rigid member 24. The shoulder 146 of the rivet shank is contiguous 30 to the lower surface of flange 34 from below in ;- 8 - ;34673 ;opposition to the grip from roll-over rivet portion 140 from above. The terminal lug 32 is thus securely gripped from opposite surfaces thereof. The shoulder formation 146 in the rivet shank is possible because of the presence of the annular cavity surrounding the rivet shank into which the shank 44 was permitted to expand during upset, although in a limited manner. If the bore 28 were made too large or too small in relation to the amount of deformable material in the rivet shank 44, the ledge or shoulder 146 would not form with controlled assurance in the desired location within the bore 28 and without stresses which might deform or stress the material of member 24, We have found that maintain- ;ing a proportion of substantially lsl for the volume of cylindrical solid deformable material in the rivet shank in relation to volume of the bores 28, 29 in the member 24 and member 26 compensates sufficiently for a partially filled bore 28 and overfilled bore 29 to balance the two and to accomplish the desired result of forming a terminal-supporting shoulder 146 within bore 28. *

Claims

1. A method of mounting on an electrical device a terminal assembly comprising an insulated cover /♦ for the device, said cover having a bore therethrough, and a terminal having a portion adjacent one side of the cover, said portion having a bore therethrough of smaller diameter than the cover bore; said method comprising aligning the bores, locating in the aligned bores a rivet shank dimensioned to define an annular space with the cover bore which shank is solid where it extends through the cover and terminal portion, and applying a force to the rivet to produce an enlargement at one end and also to deform the shank of the rivet so as at least partly to fill the cover bore, the rivet providing by said enlargement and deformation two laterally extending portions which grip opposite sides of the terminal portion.

2. A method as claimed in Claim 1, in which the volume of the shank before deformation is substantially equal to the volume of the cover bore.

3. A method as claimed in either preceding claim, in which the terminal portion is provided with spur means to engage said one side of the cover to at least reduce relative movement of the portion and cover.

4. A method of mounting a terminal assembly substantially as herein described with reference to the accompanying drawings.

5. A terminal assembly mounted on an electrical device, made by the method of any one of the preceding claims.

6. A terminal assembly mounted on an electrical device substantially as' herein described with reference to the accompanying drawings. Dated this 30th day of October 1970. F.R.KELLY & CO. by/v\QU,oA d. ^ UaAA^-^ EXECUTIVE. 27, Clyde Road?f'*Ballsbridge, Dublin, 4. Agents for the Applicants. - 10 -