Electrical Connecting Washer

Abstract

A connecting washer is provided with projections which scrape through a surface of a metal part to make an electrical connection. Parts of a second resilient insulating washer are trapped between the connecting washer and the metal part and around the projections to protect the connection area of the projections and the metal part from corrosive action.

Description

This invention relates to an electrical connecting washer.

In many items of electrical equipment, particularly those incorporating large metal cabinets, e.g. electric washing machines and cookers, ground connections are made to a metal cabinet wall by screwing a self-tapping screw into the wall. The screw is connected to an electrical conductor or an electrical conductor is trapped between the screwhead or an associated washer and the metal wall. The screwing action causes the screwhead to scrape or scratch an electrically nonconductive coating, e.g. a paint or oxide coating on the metal wall, which exposes metal to corrosion. This is especially bad where the electrically nonconductive coating is a paint applied by electrophoretic deposition.

It has been proposed to weld or solder connecting taps to the metal wall before applying the paint coating, the tags being sufficiently long to ensure that electrical connection can be made to the tags without marring the paint finish. This is expensive, and the tags themselves can become corroded.

An electrical connecting washer to be screwed to a metal wall having an electrically nonconductive coating, according to the invention, comprises a metal annulus formed on one side with a projection intermediate the annulus perimeter and the annulus aperture, the projection having a cutting edge to cut through the electrically nonconductive coating to make electrical connection with the metal wall and a sealing annulus formed of resiliently compressible material to lie intermediate the metal annulus and the electrically nonconductive coating with the apertures of the respective annuli aligned to receive a screw to hold the washer to the metal wall.

Advantageously, the metal annulus is formed with a plurality of the projections arranged generally about the screw-receiving aperture. The projections may be discrete or fused to define a continuous cutting edge. Preferably, the sealing annulus is so arranged that resiliently compressible material is disposed on opposed sides of the cutting edge to prevent corrosive forces reaching the areas where the cutting edge has cut into the metal wall from either side.

The sealing annulus is made of resiliently compressible material, for example, a nitrile material, so that the screwing of the screw into the metal wall compresses the sealing annulus to form an effective seal against corrosion.

A method of making an electrical connection between an electrically connecting washer according to the invention and a metal wall having an electrically nonconductive coating, comprises so arranging the washer that the cutting edge of the metal annulus protrudes through and beyond the sealing annulus and the respective annuli apertures are aligned to receive a screw, and screwing the washer to the metal wall to cause the cutting edge to cut through the electrically nonconductive coating to make electrical contact with the metal wall and to compress the sealing annulus to seal the area of electrical connection from corrosion.

The invention also includes an assembly made by the method disclosed herein.

An object of the invention is to provide an electrical connecting device having metal-scraping means to scrap paint, oxides, or foreign matter so that an excellent electrical connection can be effected.

Another object is the provision of an electrical connecting device wherein sealing means are provided to prevent corrosion from occurring in the scraped areas.

A further object is to provide an electrical connecting device wherein the metal-scraping means are located in concentric circles.

An additional object is the provision of means for securing the sealing means to the body of the electrical connecting device.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there are shown and described illustrative embodiments of the invention; it is to be understood, however, that these embodiments are not intended to be exhaustive nor limiting of the invention but are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.

In order that the invention may be well understood, it will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional perspective view of one electrical connecting washer according to the invention;

FIG. 2 is an enlarged side cross-sectional view of the washer of FIG. 1 in assembly with a screw;

FIG. 3 shows an enlarged cross-sectional detail of FIG. 2;

FIG. 4 is an underneath plan view of a metal annulus of another electrical connecting washer according to the invention;

FIG. 5 is a side cross-sectional view taken on lines 1--1 of FIG. 4;

Fig. 6 is a perspective view of a boss on the metal annulus of FIG. 4 drawn to a larger scale;

FIG. 7 is a plan view of a sealing annulus for use with the metal annulus of FIG. 4 but to a reduced scale;

FIG. 8 is a plan view of a metal annulus of another electrical connecting washer according to the invention; and

FIG. 9 is a section through an assembly comprising the electrical connecting washer according to FIG. 8 and two metal bodies.

The metal annulus 1, FIG. 1, comprises a flat steel stamping having a pair of radially spaced annular grooves 2, 3, pressed outwardly of one side. The area of the annulus between the grooves is raised, as at 4, (FIG. 2), by depressing the metal from the other side and this raised area is roughened, as by knurling, ridging or serration, at 5 to define a cutting edge which lies below the plane of the surfaces 6, 7 of the annulus lying on the outer opposed sides of the grooves 2, 3, The aperture 8 of the annulus receives the shank 9 of a screw, the head 10 of which may rest on the upper side (as seen in FIG. 2), of the annulus or may be sufficiently large to fit over the annulus 1, as shown in broken outline in FIG. 2. Rubber O-rings 11 and 12 are located in the grooves as shown in FIG. 3 by lances 13 struck out of the walls of the grooves at points along their circumference. The diameter of the O-rings is sized so that they project beyond the roughened zone 5 when fitted into the grooves.

When a connection is to be made to a metal cabinet wall having a painted surface, the shank 9 of the screw, which preferably is a sheet metal screw, is screwed into a hole preformed in the metal wall. If a wire (not shown) is also to be connected, it is trapped between the screwhead and the metal annulus; however, the annulus 1 may be formed with a ferrule to be crimped onto the end of the wire or a ring tongue crimped to the wire may be connected to the annulus via the screw. When the screw is nearly home, the O-rings 11 and 12 start to engage with the metal wall and as the screw is further screwed in, the cutting edge 5 meets the painted surface of the metal wall and starts to rotate with the screw to scrape through the paint and form good electrical contact between the washer and the metal wall. The O-rings 11 and 12 are compressed to give a good gasket seal. The O-ring 12 prevents a corrosive atmosphere reaching the cutting edge 5 and the mating metal wall, and the O-ring 11 acts as a further seal to prevent the atmosphere reaching the metal bared by the shank 9 of the screw.

The O-ring 11 could be omitted, but it exerts a balancing force to the resilient force produced by compression of the O-ring 12. More than two annular grooves with corresponding gaskets may be provided. The washer can be reused.

The metal annulus 21 of FIGS. 4 to 6 is formed from nickel-plated mild steel by stamping to have six spaced bosses 22 formed on one side and lying on a common pitch circle diameter; but the bosses can be provided at concentric locations on the annulus. The stamping forms a set of depressions 23, corresponding with bosses 22, in the other side of the annulus 21 (FIG. 5). The bosses 22 are cut with V-notches 24, and the free ends 25 of the notches are sharpened to define a cutting edge. The aperture 26 of the annulus receives a screw shank, and the rim 27 of the washer is bent inwardly in the same direction as bosses 22, FIG. 5, to retain the sealing annulus 29, FIG. 7, formed by molding from nitrile material. The sealing annulus comprises an inner annulus 30 and an outer annulus 31 joined by three radial spokes 32. The two annuli 30 and 31 define openings 33 so dimensioned that when sealing annulus 29 is fitted over metal annulus 21, the bosses 22 can protrude through and above the open annulus. A web 34 is provided by the inner annulus 30 and is perforated by an aperture 35 to receive a screw shank.

In use, the sealing annulus 29 is so fitted over the metal annulus 21 that the apertures 26 and 35 are aligned and the sealing annulus is rotated with respect to the metal annulus 21 to allow the bosses 22 to be passed through openings 33. The electrical connecting washer so formed is then placed against the painted surface of a metal cabinet wall with the sealing annulus facing the painted surface. A screw is passed through the apertures 26 and 35 and into a hole preformed in the metal wall. As the screw is tightened, the sealing annulus 29 is compressed against the painted surface and the sharp edge 25 of the bosses 22 bite into and through the paint to make electrical contact and force paint and metal from the wall into the grooves 24. The sealing annulus 29 is compressed to form a barrier between a corrosive atmosphere and the areas where bosses 22 have cut into the metal wall and the web 34 stops the atmosphere reaching the areas where the screw shank has cut into the sidewalls of the hole in the metal wall. An electrical connector may be secured to or made part of the screw, e.g. a ring tongue connector connected to a ground projecting electrical connector.

The metal annulus 41, having an aperture 42, FIG. 8, is stamped from nickel-plated mild steel to make four tines 43 which lie on a pitch circle diameter concentric with the aperture 42 and are equally spaced apart. The tines 43 are of triangular form, as shown, and their apices 49 are sharpened to define cutting edges. A sealing annulus 44, (FIG. 9), having a central aperture 45, is made of solid resilient material. In use, the sealing annulus 44 is fitted over the metal annulus 41, with the apertures 42 and 45 in alignment and the tines 43 are forced through the material of the sealing annulus 44. The electrical connecting washer so formed is then placed against a metal cabinet wall the surface of which may have an electrically nonconductive coating, e.g. a paint or oxide coating, the exposed face of the sealing annulus 44 abutting the metal plate surface 46 (FIG. 9) behind which is a metal body 47. A screw 48 is passed through the apertures 42 and 45, and as the screw is tightened, the apices 49 of the tines 43 bite into the and through the coated metal surface 46 to make electrical contact with the metal despite the presence of the coating. Also as the screw is tightened, the sealing annulus 44 is compressed and seals the areas of contact between the tines and the metal from the atmosphere so minimizing the risk of corrosion. A good electrical connection is thus made between the screw 48 grounding the metal plate 46 and the metal body 47. Annulus 41 may be provided with an integral ferrule for connection with a ground wire, an electrical connector connected to the ground wire may be connected to annulus 41 via the screw 48 or the ground wire may be captured between the screwhead and the annulus 41.

It will, therefore, be appreciated that the aforementioned and other desirable objects have been achieved; however, it should be emphasized that the particular embodiments of the invention, which are shown and described herein, are intended as merely illustrative and not as restrictive of the invention.

Claims

We claim:

1. An electrical connecting washer to be screwed to a metal wall having an electrically nonconductive coating, comprising a metal annulus formed on one side with a projection intermediate the annulus perimeter and the annulus aperture, the projection comprising a plurality of bosses, each having a sharp head disposed on a pitch circle diameter around the screw-receiving aperture of the metal annulus, the sharp heads constituting cutting edges to cut through the electrically nonconductive coating to make electrical connection with the metal wall, and a sealing annulus formed of resiliently compressible material to lie intermediate the metal annulus and the electrically nonconductive coating with the apertures of the respective annuli aligned to receive a screw to hold the washer to the metal wall, the sealing annulus comprising a pair of annuli spaced apart by arcuate openings and joined by spokes, the arcuate openings being dimensioned to allow the bosses to protrude through and beyond the sealing annulus.

2. A washer according to claim 1, in which the rim of the metal annulus is bent in the direction of the sealing annulus to form a retaining lip for the sealing annulus.

3. A washer according to claim 1, in which the bosses are formed with V-notches and the free ends of the V are sharpened to define a cutting edge.

4. A washer according to claim 1, wherein there are a plurality of projections disposed in concentric circles.