GB2088154A - A fuse for appliances and a method for its manufacture - Google Patents

Abstract

A fuse (1) comprises an insulating tube (2), a fuse member (4) contained therein, a pair of end caps (3) seated on the insulating tube (2) and a metal support member (31) on each end cap, the fuse member (4) being welded to the end caps (3) beneath the support members (31). <IMAGE>

Description

SPECIFICATION A fuse for appliances and a method for its manufacture The invention relates to a fuse for appliances comprising an insulating tube, a fuse member contained therein and two metal end caps each seated on one end of the insulating tube, and being electrically connected by the fuse member, and a method for its manufacture. These fuses for appliances are also known as miniature meltable inserts.

In order to obtain the best possible electrical connection between the fuse member and the end caps, soldering is frequently used, there being areas of solder on the inside and on the outside as is known. With the areas of solder on both the inside and the outside, residues of fluxing agent can no longer be removed from the insulating tube and this is why weakly activated fluxing agents have to be used and this in turn may jeopardize the quality of the soldered areas. On the inner soldered areas the quality of the soldered areas is never completely clear, whereas the areas of solder on the outside can be affected unfavourably, at least on the end soldered second, by the pressure inside the tube, and then the fuse has to be reprocessed, which is expensive.

The invention seeks to create a fuse for appliances, which can be manufactured with an exceptionally good quality, but nevertheless economically.

According to a first aspect of the invention, there is provided a fuse for an appliance comprising an insulating tube, a fuse member contained therein and two metal end caps each seated on one end of the insulating tube, and being electrically connected by the fuse member wherein the fuse member is welded to each of the end caps beneath a metal support member.

According to a second aspect of the invention, there is provided a method of producing a fuse for appliances comprising providing an insulating tube with metal end caps and connecting a fuse member situated in the tube to the end caps wherein the fuse member is passed through the end caps and is welded thereto beneath a metal support member.

By welding the end of the fuse element between the end caps and the support member a clean and good electrical connection can be obtained reliably, whereby a very small welding spot may be sufficient. It is not necessary to place the position of the fuse member nor of the energy beam used for welding, particularly of laser beams exactly, at half the thickness of the fuse member.

Nevertheless, a laser welding process may be controlled so that high quality welding is achieved in a very small volume and therefore the material of the fuse element which still projects beyond the end cap may be "burnt off" so that there is no necessity to reprocess the fuse. Fluxing agents are superfluous and therefore do not provide a problem.

In order that the preferably wafer-like support member, which is preferably arranged in a depression of the end caps, is itself more safely fixed, it may be connected to the end cap, preferably by means of at least one other welding spot. The support member then reliably closes off the opening in the end cap, through which the fuse element is passed from the insulating tube to the welding point.

The fuse element is preferably diagonal to some extent i.e. runs at an angle through the insulating tube and is welded at opposite sides of the end caps. The end caps are preferably corrosion resistant at least on the surface, e.g. made of brass, nickel coated, silver coated or surface treated in some other suitable manner. Since laser welding causes an external "crater" on the support member, in which the brass would become visible if it were manufactured in the same way as the cap, it is preferable for these support members to be made entirely out of corrosion resistant metal, e.g. virgin siiver, pure nickel etc.With the method in which the insulating tube is provided with end caps, having orifices through which the fuse member is drawn, these orifices being covered by support members which are welded on, it it possible to obtain results, which are easily reproduced as well as being of the best quality, in a manner which is easily and simply automated. Since the protruding portions of the fuse member may be burned up during welding any retreatment of the fuse inserts is superfluous and so a reduction in costs is possible.

The invention will now be described below in greater detail, by ways of example, with reference to the drawings, in which: Figure 1 shows a front view of a fuse for an appliance; Figure 2 shows an end view of a first embodiment which is enlarged as compared to Fig. 1; Figure 3 shows a section along the iine Ill-Ill of Fig. 2; Figure 4 is a view, similar to Fig. 2 but showing a second embodiment, and Figure 5 is a sectional view taken along the line V-V of Fig. 4.

In Fig. 1 a fuse 1 for an appliance, can be seen comprising an insulating tube 2, end caps 3 and the fuse member 4 which is visible through the transparent insulating tube. One end cap 3 can be seen in Fig. 2 and has a depression 30 with a wafer 31 therein (see also Fig. 3). The end 40 of the fuse member (Fig. 3) which projects through the opening 32 in the cap 3 under the wafer 31 is welded in between the wafer 31 and the cap 3 by a welding point 5 (Figs. 2 and 3). A second welding point 50 connects the wafer 31 and the cap 3 so that the wafer is securely seated. Several welding points can also be used for this.

This fuse 1 can be simply manufactured, the end caps 3 being arranged on the insulating tube 2 in a manner known per se and the fuse member 4 can be drawn through the orifices 32 in the cap 3, the wafer 31 can be placed into the depression 30 of each cap and the two welding points 5 and 50 can be produced with lasers. The originally protruding end of the fuse element is burnt off to the residue which can be seen in Fig. 3. There is no need for any other work, because there is no fluxing agent which has to be removed on any protruding portions of material. The cap may comprise nickel plated brass whereas solid corrosion resistant material will be selected for the wafer if it is important for materials which are not completely corrosion resistant not to become visible at the weld areas.

Another embodiment of the fuse 1 is shown in Fig. 4 and 5 and differs from the embodiment in accordance with Figs. 1 to 3 only in the shape of the cap and of the wafer. End caps 3' are provided in each case with a conical depression 30' for association with a conical wafer 31'. An orifice 32' is present in the end cap 3' and is designed for the fuse element 4' to pass through it out of the insulating tube 2' and under the wafer 31'. The end 40' of the fuse member is fixed to the welding point 5' and the wafer 31' is connected to the cap 3' at a further welding point 50'. The manufacture may be the same as for the embodiment according to Figs. 1 to 3. The conical wafer may have a slightly higher manufacturing cost but this is compensated by the advantage it has namely that it is more easily supplied by automatic means.

Both of the embodiments shown are suitable for automatic manufacture and the cap orifice 32 or 32' is closed by the wafer 31 or 31' in both cases.

In addition the end caps can be fixed to the insulating tube (which can be made of glass or ceramics) in a manner known per se, for example by means of adhesion, clamping etc.

Claims (15)

1. A fuse for an appliance comprising an insulating tube, a fuse member contained therein and two metal end caps each seated on one end of the insulating tube and being electrically connected by the fuse member wherein the fuse member is welded to each of the end caps beneath a metal support member.

2. A fuse according to claim 1, wherein the fuse member is welded at a welding point.

3. A fuse according to claim 2, wherein the support member is additionally connected to the end cap by welding at least one point.

4. A fuse according to any one of claims 1 to 3 wherein the fuse member passes out of the inside of the insulating tube through an opening in each end cap underneath the support member.

5. A fuse according to claim 4, wherein a depression is provided in each end cap around the opening and the wafer-like support member is provided therein.

6. A fuse according to claim 5, wherein the depression and the wafer are conical.

7. A fuse according to any one of claims 1 to 6, wherein the fuse member passes at an angle through the insulating tube and is welded to opposite points of the end caps.

8. A fuse according to any one of claims 1 to 7 wherein the end caps are made of corrosion resistant material at least on their surface and the support members are made entirely out of corrosion resistant material.

9. A fuse according to any one of claims 1 to 8 wherein the fuse member is welded on to the end caps by laser welding.

10. A method of producing a fuse for appliances comprising providing an insulating tube with metal end caps and connecting a fuse member situated in the tube to the end caps wherein the fuse member is passed through the end caps and is welded thereto beneath a metal support member.

1 A method according to claim 10, wherein the fuse member is welded between the support member and the associated end cap by at least one laser beam.

12. A method according to claim 1 wherein the part of the fuse member which projects on the outside beyond the support member is burnt off and removed during the laser welding.

13. A method according to claim 11 or 12, wherein each support member is fixed by at least one further laser welding point to the end cap.

14. A fuse for an appliance substantially as described herein with reference to the drawings.

15. A method of producing a fuse for an appliance substantially as described herein with reference to the drawings.