GB2203004A

GB2203004A - Electrical fuse

Info

Publication number: GB2203004A
Application number: GB08807446A
Authority: GB
Inventors: Claus Friedrich; Nikolaus Trager; Manfred Oppenhauser
Original assignee: Wickmann Werke GmbH
Current assignee: Wickmann Werke GmbH
Priority date: 1987-03-28
Filing date: 1988-03-28
Publication date: 1988-10-05
Anticipated expiration: 2008-03-28
Also published as: SE8801105L; SE8801105D0; DE8704621U1; SE464159B; GB8807446D0; JPS642238A; GB2203004B

Abstract

An electrical fuse, such as an equipment fuse, has a fusible conductor in a cylindrical housing (1), which is closed at both ends by caps (7). Leads (4) extend from both caps. The housing, including the caps and the adjoining sections (3) of the leads, is embedded in a plastics body (5), the outer shape of which is essentially independent of the profile formed by the embedded parts. <IMAGE>

Description

DESCRIPTION ELECTRICAL FUSE The invention relates to an electrical fuse, such as an equipment fuse, having a fusible conductor in a, usually cylindrical, housing closed by closures, such as caps or covers, at both ends, with leads extending from both caps. Such a fuse is hereinafter referred to as of the kind described.

Plastics-sheathed fuses of the above type are known from US-A-4,385,281 and US-A-4,460,887. In those arrangements, the fuse is coated with plastics material, either by applying and heating plastics powder or by the use of a plastics immersion method.

In each case, a coating on the fuse body is formed which essentially follows the fuse profile. Since the connecting area between the caps and the leads also receives a coating, the leads do not break easily with careless handling as in the case of non-sheathed fuses, yet the strength of the connection between the leads and the caps is basically not increased. In addition, the outer profile of the known sheathed fuse exhibits constrictions and roundings which impede printing or other marking of the fuse on the outer plastics sheath. Neither do- the coating methods permit any accurately uniform coating so that the profile shape of the series fluctuates. In addition, the choice of plastics relies on those which, in addition to the required electrical insulating properties, also permit a coating which enters into a durable bond with the housing, the caps and the adjoining leads.

The invention is therefore based on the object of preventing or at least significantly reducing the above disadvantages.

In accordance with the invention, in a fuse of the kind described, the housing together with the closures and adjoining sections of the leads are embedded in a plastics body, the outer shape of which is essentially independent of the profiles of the embedded parts.

In contrast to the prior art, a moulded body of plastics material is formed which completely embeds the fuse and the adjoining sections of the leads. In contrast to the result and the possibilities of a coating method, this makes it possible to provide the plastics body with the required or most advantageous profile for the respective application, which profile no longer has anything in common with the profile of the embedded parts.

The fuse according to the invention can thus be characterised by very high mechanical strength. Its switching capacity is much higher than that of the uncoated fuses and even considerably above the strength of fuses only coated with plastics. An exploding or bursting of the fuse under very high short circuit loads is therefore virtually impossible.

The strength of the connection between the closures and the adjoining sections of the leads is also considerably improved. Since these sections are also embedded in the plastics body, they cannot be pulled off the caps. Bending or kinking or high tensile stress will cause the leads to rupture or break, if at all, outside the plastics body.

In contrast to the coating method, the plastics body can easily be designed to be longer if desired than corresponds to the actual fuse, for example far beyond the closures.

The position of the fusible conductor inside the tubular housing does not play any role with respect to the embedment of the fuse and essentially depends on the respective fuse type and the methof used for mounting the fusible conductor.

The fuses form a typical mass-produced article which is why the embedment of the fuses in a plastics body can be performed very inexpensively by appropriate spraying on of plastics material. After the production of the actual fuse, the operating cycles requires for the plastics embedment are easily fully automatable.

If the embedment occurs in corresponding moulds, each plastics body receives an accurately defined shape, the dimensions of which can be extremely accurately reproduced in contrast to the immersion or coating method.

The plastics body may closely envelop the housing, the closures and the leads, suitably in an all-round sealing manner. The liquid plastics material may be supplied under high pressure during the moulding of the plastics bodies so that no air inclusions and so forth can form, for example in the area of the transition between the closures and the housing.

The plastics body preferably exhibits a cylindrical shape, from the ends of-which the free sections of the leads emerge. The printing of the cylindrical jacket surface is extremely simple both in ring form and in the form of axially extending markings.

If required, polygonal cross-sections of the elongate plastics body can be easily produced.

The plastics body is preferably produced of a thermoplastics material. Of these, Nylon 6 Nylon 66 Polyphenylene oxide Polyethylene terephthalate Polyphenylene sulphide are particularly suitable. As has already been partly specified above, the plastics body is preferably formed in a mould which accommodates the completed housing including closures and leads, by spraying around the housing and the other parts to be embedded with liquid plastics material. After the plastics has set, the completely embedded fuse is removed from the mould.

The above mentioned advantages also apply to a variant of the invention, in accordance with which the plastics body is of cuboid shape and the leads emerge from the plastics body at opposite faces or side by side at one face. With corresponding construction of the leads this produces a component which can be used both in a radial construction technique and, with angled connecting legs, allows it to be used as a SMD component.

In the accompanying drawings: Figure 1 is a longitudinal section through one fuse in accordance with the invention; Figure 2 is an end view of the fuse of Figure 1; Figure 3 is a perspective view of a second fuse; and, Figures 4 and 5 are part views relating to Figure 3.

A tubular housing 1, consisting of glass or ceramic in conventional manner, is closed and sealed at both ends in each case by a metal cap 2 with an intermediate solder layer 7. Through the free internal space of the housing 1, a fusible conductor not shown, extends diagonally or axially, the ends of which are electrically conductively connected to respective ones of the caps 2 by means of the intermediate solder layers 7. At the outer end faces of the caps 2, adjoining sections 3 of electrical leads 4 are in each case electrically conductively attached. The intermediate solder layer 7 consists, for example, of silver lead solder (96.5% lead, 3.5% silver; melting temperature 221or) or of tin solder (95% tin, 5% antimony; melting temperature 236-2430C).

The fuse described above is embedded in a solid plastics body 5 which also contains the sections 3 of the electrical leads 4 adjoining the caps 2, as is shown in the drawing.

A thermoplastic material of the above mentioned type is used for producing the plastics body 5.

After the production of the fuse consisting of the parts 1, 2, 3, 4, 7, it is inserted in a fully-automated production process into a mould which predefines the shape of the required body. After the mould has been closed, heated liquid plastics material is introduced under appropriate pressure via an injection duct to the mould so that the fuse is completely sprayed around with plastics material and the mould is filled. After the plastics material has set, the mould is automatically opened and the fuse completely embedded in the moulded plastics body 5 is removed and forwarded for the usual quality checks.

The sections 3 of the leads 4 coming from the front ends 6 of the plastics body 5, which is cylindrical in this case, are firmly bonded to the plastics body 5 so that they cannot be detached from the caps 2.

Fuses produced in this manner are mainly used as equipment fuses.

In the illustrative embodiment according to Figure 3, a fuse having a tubular housing 1, caps 2 and leads 4, coming from these in one part, are embedded in a cuboid plastics body 5. Depending on the construction, especially of the protruding ends of the leads 4, the embedded fuse can be used as a radial component (Figure 4) or as a SMD component (Figure 5).

Claims

1. An electrical fuse having a fusible conductor in a housing, the housing being closed at both ends by closures, from which leads extend, wherein the housing together with the closures and adjoining sections of the leads are embedded in a plastics body, the outer shape of which is essentially independent of the profiles of the embedded parts.

2. A fuse according to claim 1, in which the plastics body closely envelops in an all-round sealing manner the housing, the closures and the leads.

3. A fuse according to claim 1 or claim 2, in which the plastics body has a cylindrical shape, from the ends of which free sections of the leads emerge.

4. A fuse according to claim 1 or claim 2, in which the plastics body has a polygonal cross-section.

5. A fuse according to claim 1 or claim 2, in which the plastics body is of a cuboid shape and the leads emerge from the body at opposite faces or side by side at the same face.

6. A fuse according to any one of the preceding claims, in which the plastics body consists of a thermoplastic material.

7. A fuse according to any one of the preceding claims, in which the plastics body has been formed in a mould which accommodates the complete housing closures and lead sections by spraying liquid plastics material into the mould around the parts to be embedded.

8. An electrical fuse, substantially as described with reference to the accompanying drawings.