Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated
Patent
1996-02-28
1998-04-14
Picard, Leo P.
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Fusible element actuated
337227, 337231, 337252, H01H 85143
Patent
active
057397406
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a fuse having an insulator, through which extends from one end to a facing end a cavity, in each case a solder coating a least covering the end, electrical connections and a fuse element, which passes through the cavity and whose ends are in each case conductively connected to the electrical connections.
2. Description of the Prior Art
A fuse of the aforementioned type is e.g. known from U.S. Pat. No. 5,214,406 and has a cross-sectionally rectangular insulator, whose offset end portions in each case taper outwards. A cylindrical through bore is positioned coaxially within the insulator, in which is diagonally positioned a fuse element. The ends of the latter are so bent round that it rests on the outer end portion of the insulator. A cap is mounted with solder on each end portion.
During the manufacture of the fuse the cap is pressed onto an end portion, whilst the solder is melted. So that the solder can pass as a connection between the cap and the end portion, there is a gap between the end portion and the cap. However, it is cross-sectionally wedge-shaped and the solder does not adhere to the smooth surface of the end portion, so that when corresponding mechanical stressing occurs the cap can easily be released from the end portion.
It is also known (German utility model 93 13 717.6), for improving the adhesion of solders to insulators of fuses, to provide the end faces of the insulator with a metallization.
SUMMARY OF THE INVENTION
The problem of the present invention is to further develop a fuse, particularly of the type indicated hereinbefore, in such a way that with simple manufacture a reliable closing of the cavity openings and a reliable fixing of the fuse element ends, as well as the connections or terminals to the end portions of the insulator is ensured, more particularly in such a way that connections projecting over the insulator profile are avoided.
In the case of a fuse according to the invention, this problem is solved with the feature combination of claim 1, more particularly in that directly on the end or the entire outer surface of each end portion of the insulator is applied in firmly adhering manner a metal coating to which is fixed the solder coating. Thus, in simple manner in conjunction with a stepping of the end portions with a constant cross-section, it is ensured that the solder coating can be firmly connected to the insulator. The connection between the insulator and solder is so improved that it withstands the higher mechanical stresses, which once again leads to further constructional possibilities which are referred to hereinafter.
In particular if the insulator is made from ceramic or glass according to an embodiment of the invention, a reliable connection between the solder and the insulator is possible without self-closure only in conjunction with the shaping and metal coating according to the invention. In addition, such an insulator is more resistant to heat action than e.g. conventional plastic. With plastic there is also a risk that on disconnecting the fuse, i.e. on interrupting the fuse element at a predetermined current, the resulting arc will damage the insulator. Compared with plastic ceramic or glass has the advantage that it can be better recycled and is less prejudicial to the environment. To give plastic non-flammable properties, it generally contains red phosphorus, which e.g. in the case of a smouldering fire gives off toxic phosphine. However, particularly from the standpoint of the ever stricter environmental standards, this problematical.
Favourable ceramic materials have proved to be alumina ceramic and the less heat conductive magnesium silicate ceramic.
A preferred embodiment has a metal coating or metallization of silver, silver palladium, silver platinum or silver palladium platinum, because these materials can be formed in alloying-resistant manner with respect to the solder. A silver metallization requires a diffusion barrier, which is preferably of nickel.
To ensu
REFERENCES:
patent: 4540969 (1985-09-01), Sugar
patent: 4996509 (1991-02-01), Bernstein
patent: 5166656 (1992-11-01), Badihi et al.
patent: 5198792 (1993-03-01), Bacon et al.
patent: 5214406 (1993-05-01), Reese et al.
Jollenbeck Andre
Stark Klaus
Gandhi Jayprakash N.
Picard Leo P.
Wickmann-Werke GmbH
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