EP0116723A1

EP0116723A1 - Electrical cartridge fuselinks and a method of manufacturing same

Info

Publication number: EP0116723A1
Application number: EP83200225A
Authority: EP
Inventors: Gerardus Jacobus Deelman
Original assignee: Littelfuse-Olvis AG
Current assignee: Littelfuse-Olvis AG
Priority date: 1983-02-11
Filing date: 1983-02-11
Publication date: 1984-08-29

Abstract

An electrical cartridge fuselink comprises a fusible element (3); an insulating barrel (1) having said fusible element disposed therein; end caps (8) mounted on either end of said barrel, and each being electrically connected to an associated end portion of said fusible means; and first and second centering means (2) being rigidly secured within said barrel at its opposite ends, each of said centering means having at least one centering bore for receiving an associated end portion of said fusible element; said end portion being electrically connected to the inner surface of the associated end cap (8). It is a general object to provide an improved structure of a cartridge fuselink of the above type, thereby offering the possibility to mass-produce such fuselinks with a cost-effective and reliable, fully automated manufacturing/assembly process. An electrical cartridge fuselink of this invention is characterized thereby that each one of said centering means (2) comprises a disk shaped support means having at least one bush (4) of electrically conductive material extending therethrough, said bush (4) defining a centering bore (5); said disk shaped support means being circumferentially shaped and dimensioned respectively for securing it within its associated end of said barrel (1). The electrical contact resistance between the ends of a fusible element and its associated end caps is well defined and can be made extremely low.

Description

This invention relates to electrical cartridge fuselinks of the type wherein a fusible element is mounted within an insulating barrel, which at both of its ends is provided with a conductive end cap which is electrically and mechanically connected to the associated end of the fusible element, and a method for producing such electrical cartridge fuselinks.
A cartridge fuselink of the above type is known from the British patent specification 1,474,695. A cartridge fuselink as disclosed therein comprises fixing means which are adapted to squeeze the opposite ends of a fuse element disposed within the insulating barrel between a washer and an inside surface of an end cap. Now it is a main object of this prior art to provide a good electrical contact between a fuse element and the associated end caps of a fuselink by purely mechanical means. More in particular it is an object of this prior art to eliminate temperature effects on the contact pressure exerted on the opposite ends of the fuse element where it is squeezed between the associated washer and inside surface of the end cap. An essential component of this prior art fuselink is a washer in the form of an eyelet and having a central socket portion which is of similar shape to a boss portion on the inside of an associated end cap. Although these prior art proposals render the fuselink cheaper and easier to manufacture in comparison to a fuselink as disclosed in a prior British patent specification 1,167,583, still a cumbersome and time consuming operation is required for disposing a fuse element in an oblique position relative to the cartridge barrel and with its ends appropriately extending through the central openings of the eyelets. Moreover the required shape of the washers and end caps is relatively complicated, while also close tolerances are required regarding the inner diameter of the central washer opening and the outer dimensions of the end cap boss portion respectively.
The British patent application 2,061,137 relates to an electrical cartridge fuse of the type which is connected to a fuse holder or mounting in an electrical circuit by means of terminal lugs secured to the metal end caps of the fuse. Fuses of the type as described and claimed therein have the same deficiencies as those connected with a fuse of the afore-mentioned British specification 1,474,695. It is an object of the proposals for which protection is sought in the afore-mentioned British patent application to provide an improved manner of securing the terminal lug to the end caps of a cartridge fuse which permits consistently accurate fixing of the terminal lug. In view of this object the outside of the end wall of each of the associated end caps has a recess formed therein. Such recess provides a seat for receiving and supporting an associated terminal lug. Such an arrangement further adds to the complexity of the structure and leads to a cumbersome manufacturing process.
From US patent 4,336,521 an electric fuse is known having a fuse casing into the end of which plug terminals are plugged. Each plug terminal is provided with a recess in the center thereof to receive an insert member having a wide flange at right angles to its longitudinal axis . These insert members and the associated axially inner end surfaces of the plug terminals are adapted and dimensioned respectively to firmly hold a number of fusible elements within the fuse casing in their proper positions. More in particular the fusible elements are held in their respective positions by radial slots in the afore-mentioned flanges into which they are inserted, and their ends are bent 90 degrees and inserted into a small gap which is left between the axially outer end surfaces of the respective pair of flanges and the axially inner end surfaces of the plug terminals. The narrowness of these small gaps results in a considerable capillary action by which liquified solder is caused to enter these gaps thereby effecting reliable conductive bonds between the attendant inserts, fusible elements and plug terminals. Because the ends of the fusible elements are to be bent 90 degrees, and inserted into the narrow spaces defined by the afore-mentioned flanges and the plug terminals, this prior art electrical fuse cannot be manufactured and/or assembled by means of a reliable and cost-effective,automated process.
A method of manufacturing electric cartridge fuselinks is known from US patent 3,845,439. This prior art relates to fuselinks wherein a fusible wire of silver of extremely small diameter is wound around a substantially straight core of fiber material. By using the rigidifying effect of a coating of thermosetting material on the fiber material, microwire can be wound on extremely thin cores so that well defined fuselinks for low current values are obtained. In fuselinks manufactured in accordance with this prior art method, the electrically conductive connections between the fusible wire and the metal end caps which are cemented at either end of the tubular casing, is provided by means of a solder alloy. The fuse element is positioned within the tubular casing by means of eyelets which are disposed between the respective ends of the fuse casing and the opposite bottom portion of the associated end cap. This prior art structure also is unsuitable for a manufacturing process by which the various parts are automatically and reliably assembled, while providing a good and secure electrical connection which can be recurrently manufactured within close tolerances.
The European patent application 82200592.2, filed on May 13, 1982, describes an electrical cartridge fuselink and a method for manufacturing same, whereby the above deficiencies of the prior art are substantially overcome. It is an essential aspect of the proposals for which protection is sought therein that in an electrical cartridge fuselink of the above defined type comprises first and second centering means which are rigidly secured within the insulating barrel at its opposite ends, wherein each of said centering means is provided with at least one centering bore for receiving an associated end portion of the fusible means, said end portion being soldered to the inner side of the associated end cap.
It is a main object of the subject invention to provide a structure of a cartridge fuselink of a type as described in the afore-mentioned European patent application, which yields the following advantageous effects in combination:

a) by its structure an improved cost-effective and reliable, fully automated manufacturing/assembling process is implemented;
b) secure mechanical and electrical connections between fusible element and associated end caps can be recurrently established in a mass-production process within close tolerances;
c) the reject percentage is further reduced;
d) the quantity of soldering material is further reduced;
_e) extended service life with nominal operational ratings being preserved; and
f) a cost-effective use of material is made.

The above object is achieved by adapting a cartridge fuselink of the type as described in the afore-mentioned European application in such a manner that each one of said centering means comprises a disk shaped support means having at least one bush of electrically conductive material extending therethrough, said bush defining a centering bore; said disk shaped support means being circumferentially shaped and dimensioned respectively for securing it within its associated end of said barrel.
It is a further object of the subject invention to provide a method of manufacturing cartridge fuselinks of this invention with a fully automated process with the attendant technical advantages indicated above.
A preferred method of manufacturing and assembling a cartridge fuselink of the invention is characterized by the following steps:

punching, said disk shaped support means from strip shaped material; securing a bush within a disk shaped support means;
inserting a composed structure including a disk shaped support means and a bush secured therein, into each open end of an insulating barrel; positioning and securing respectively one end cap having a pallet of soldering material on its inside surface on one open end of said insulating barrel having said two composite structures inserted and secured therein; positioning a sub-assembly comprising an insulating barrel, two of said composite structure inserted therein and one end cap positioned and secured on its one end, with its opposite end turned upwardly;
substantially aligning, a fusible element and a sub-assembly thus positioned;
positioning said fusible element thus aligned by gravitational force within the two bores defined by the two bushes supported at the opposite ends of such sub-assembly;
positioning and securing an end cap having a pallet of soldering material on its inside surface on said opposite end;
and heating said end caps for establishing an electrical and mechanical connection between said fusible element and the end caps.

Because use has been made of electrical conductive bushes for receiving the respective end portions of a fusible element with close fittings, extremely well defined and reliable electrical connections can be made between these end portions and the associated end caps, by means of a soldering process. More in particular the electrical contact resistance of these connections can be made very low and reproducable within close tolerances.
It is preferred to use pretinned bushes having a flange at one end, namely the end which is intended for contacting a bottom portion of an associated end cap. Due to the thin coating of tin, the capillary action is furthered by which the soldering material creeps within the narrow gap between at the one hand an end portion of a fusible element and the inner wall of the bore defined by said bush, and such a bush and the inner surface of an associated end cap at the other hand. Due to the flange shaped end portion providing an. effective contact surface which is substantially larger than the cross-sectional surface of the fusible element inserted therein, a well defined low-ohmic contact resistance between such a bush and the associated end can be established. The cross-sectional size of the flange.surface contacting the associated end cap is substantially determinative of the nominal current rating of the cartridge fuselink.
In view of the above aspects the subject invention is particularly suitable for the manufacturing of cartridge fuselinks designed for relatively high nominal current ratings.
In case it should-be desired to employ a low melting alloy for the fusible elements, a good and reliable electrical connection between the respective end portions of such an element and the associated.end caps is ensured'by appropriate selection.of the bush (material/dimensions) and type of soldering material. Thereby when heating the end cap, within the bore of such a bush an appropriate temperature gradient is created whereby at the one hand melting of the fusible element is prevented and sufficient flow of soldering material, is ensured for establishing a good electrical connection at the other hand.
Because in cartridge.fuselinks of the subject invention the support means for accurately positioning the fusible element within the insulating barrel, are disk shaped, such support means are conveniently punched from strip shaped material, such as for instance presspane, or any high melting plastic material. In general such a disk is made of a heat-isolating material. Thereby the conductive bonds can be established with minimum amounts of solder and applied heat. Thereby a cost effective use is made of such material. With a further simple operation a bush is inserted into a disk shaped support means to extend therethrough. These features lead to a highly economical manufacturing process which can be readily automated.
For further convenience of the manufacturing process it is preferred to make use of bushes defining a bore being outwardly tapered at its ends for providing a guiding channel having an increasing transverse dimension at its ends.
In view of the fact that the disk shaped support means are to be pressfitted into either open end of the insulating barrel, while moreover they are punched from strip shaped material, preferably they are provided with appropriately shaped cams along their circumference. As will be obvious any other appropriate circumferential shape can be used.
Further the dimensions of the bushes, in particular the length of the channel or bore defined thereby, are selected in view of the tolerance ratings of the barrel length. That is for any barrel length which is within the range of tolerances, such bush provides appropriate support for a fusible element extending therein.
In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:

Figure 1 is a longitudinal section of a cartridge fuse embodying the present invention, showing some parts thereof in elevation rather than in section; and
Figure 2 shows a top plan view of a preferred embodiment of a disk shaped centering means with bush inserted therein, of the structure of Fig. 1 and on a larger scale than Fig. 1.

Referring to Figure 1 of the drawings, the electric cartridge fuselink shown therein comprises an insulating barrel 1 made from transparent glass or other insulating-material. In this embodiment illustrative for the principles of the subject invention said barrel is a cylindrical tube. Said tube is closed at both of its ends by centering members 2 which are adapted in this embodiment to accurately support and position a fusible element 3 within the barrel to extend substantially along the longitudinal axis thereof. The centering members are pressfitted into the tube 1. According to the present invention each of these centering members is a disk shaped washer having in its center portion an electrically conductive bush 4 extending therethrough and secured therein respectively. The disk shaped washers preferably are punched from stripped shaped material of relatively small thickness, for instance 2 mm. Preferably these washers are made from an electrically insulating material such as for instance presspane, or any suitable high melting plastic material. Preferably the bushes are made from brass. Such a bush is conveniently inserted into a disk shaped washer so that a central channel or bore 5 is extending therethrough, by means of any conventional stapling machine. The inserting operation.results therein that at one end of a bush a transversely extending flange 6 is formed so that the central portion of the washer body is firmly squeezed between said flange 6 and the flange 6' at the opposite end, whereby the bush is secured in its central position within the washer. In a preferred embodiment the central bore as defined by such a bush is outwardly tapered at its ends for providing a centering channel having an increasing transverse dimension at its ends. As will be explained further herein the operation by which a fusible element is positioned with its ends within such a centering channel is facilitated.
Preferably each one of said disk shaped washers along its outer circumference is provided with cams 7 as has been schematically illustrated in Fig. 2 on a larger scale than Fig. 1. These cams are in pressfitting engagement with the inside of the tube 1, thereby providing a rigid and strong mechanical connection between these washers and the respective tube ends. Preferably the inner wall defining a central bore such as 5 is coated with a thin layer of soldering material. As has been illustrated in Fig. 1 the central bores defined by the bushes are adapted to receive an associated end portion of the fusible element. At option the fusible element comprises a rigidified fiber core of electrically nonconductive heat-insulating and heat-resistive material, and a winding of fusible wire, wound thereon. Alternatively the fusible element consists of one or more sections of straightened wire.
The inner dimensions defining the passage way through a bush is adapted to the outer diameter of the fusible element end portion which is to be received therein, in such a manner that a very narrow gap is formed therebetween. By appropriately selecting the narrowness of such a gap the capillary action by which liquified solder is caused to enter this gap is effectively controlled thereby ensuring a reliable and reproducible conductive bond between the respective end portion of the fusible element and its associated bush. Because further such a bush through its flange portion which is opposite to the inner surface of the associated end cap 8 and a very thin layer of soldering material is directly connected to its associated end cap a well defined electrical conductive bond is established between the respective end portion and its associated cap.
With the above structure a very thin layer of solder 9 which contributes to a well defined amount to the contact resistance of the bond between the respective end portion and its associated end cap, is formed within the centering bore of the bush and within the gap formed between the inside surface of the end cap and the opposite surface portions of the bush flange , disk shaped washer and the tube. Moreover due to the presence of such thin layer of solder the associated end cap is rigidly and firmly secured to its associated end of the tube, while a sealed connection therewith is provided.
Due to the circumferential shape of the disk shaped washers a firm and reliable mechanical bond is ensured between the respective washer and its associated tube end portion taking into account the small tolerances permitted for the inner diameter of the housing tube.
It will be appreciated that various other modifications may be made to the details referred to herein without departing from the scope of this invention as defined in the appendant claims.
A fuselink having the above described structures is particularly well suited for a fully automated, cost-effective manufacturing and assembling process. In the following a preferred method of manufacturing and assembling fuselinks of this invention is described.
Initially the disk shaped washers are punched from suitable strip shaped material. In the next step a conductive bush is inserted and secured into an associated disk shaped washer by means of a conventional stapling machine. Thereafter a composite structure of such a disk shaped washer and a bush secured therein is inserted into each open end of an insulating barrel to form a pressfitted bond therewith. The sub-units thus formed are positioned and secured respectively in one end cap having a pallet of soldering material on its inside surface. The sub-assemblies each comprising a sub-unit and one end cap disposed on its one end, thereafter are disposed with their opposite ends turned upwardly into a certain pattern, for instance a matrix configuration. By making use for instance of a matrix control arrangement effecting a two-coordinate oscillation"fusible elements are substantially aligned with the sub-assemblies thus positioned in the matrix configuration. With such an oscillatory movement imparted thereon the respective fusible element by gravitational force is then caused to descend between the two bores defined by the two bushes of the respective sub-assembly in the aligned position. After having inserted a fusible element into its associated sub-assembly an end cap is positioned on its free end whereafter by means of a heating process the solder material is caused to liquidize and form the respective electrical and mechanical bonds between the fusible element and the associated end caps. Preferably the solder operation is performed at a relatively low speed.
Whilst particular embodiments and a particular method have been described, it will be understood by those skilled in the art that modifications can be made without departing from the scope of the invention as defined by the appending claims.

Claims

1. An electrical cartridge fuselink comprising a fusible element; an insulating barrel having said fusible element disposed therein; end caps mounted on either end of said barrel, and each being electrically connected to an associated end portion of said fusible means; and first and second centering means being rigidly secured within said barrel at its opposite ends, each of said centering means having at least one centering bore for receiving an associated end portion of said fusible element; said end portion being electrically connected to the inner surface of the associated end cap, characterized in that each one of said centering means comprises a disk shaped support means having at least one bush of electrically conductive material extending therethrough, said bush defining a centering bore; said disk shaped support means being circumferentially shaped and dimensioned respectively for securing it within its associated end of said barrel.

2. An electrical cartridge fuselink according to claim 1, characterized in that said bush has its centering bore internally coated with soldering material.

3. An electrical cartridge fuselink according to claims 1 or 2, characterized in that said centering bore being outwardly tapered at at least one of its ends for providing a centering channel having an increasing transverse dimension at its respective end.

4. An electrical cartridge fuselink in accordance with one of the foregoing claims, characterized in that said centering bore has a longitudinal dimension which has been selected in view of the tolerances regarding the longitudinal dimension of said barrel.

5. An electrical cartridge fuselink according to one of the claims 1 through 4, characterized in that said bush being provided at its one end with a flange providing an electrically conductive bond with the associated end cap.

6. An electrical cartridge fuselink according to one of the foregoing claims, characterized in that said disk shaped support means is formed from an electrically isolating material, such as for instance presspane.

7. An electrical cartridge fuselink according to claim 6, characterized in that said disk shaped support means is formed from a heat isolating material.

8. A method of manufacturing a cartridge fuselink of one of the foregoing claims, characterized by the steps:

punching said disk shaped support means from strip shaped material; securing a bush within a disk shaped support means;

inserting a composed structure including a disk shaped support means and a bush secured therein, into each open end of an insulating barrel; positioning and securing respectively one end cap having a pallet

of soldering material on its inside surface on one open end of said insulating barrel having said two composite structures inserted and secured therein; positioning a sub-assembly comprising an insulating barrel, two of said composite structures inserted therein and one end cap positioned and secured on its one end, with its opposite end turned upwardly; substantially aligning a fusible element and a sub- assembly thus positioned; positioning said fusible element thus aligned by gravitational force within the two bores defined by the two bushes supported at the opposite ends of such sub-assembly; positioning and securing an end cap having a pallet of soldering material on its inside surface on said opposite end; and heating said end caps for establishing an electrical and mechanical connection between said fusible element and the end caps.