GB2041063A

GB2041063A - Clamp frame for screw clamp connector and method of making the same

Info

Publication number: GB2041063A
Application number: GB8002845A
Authority: GB
Original assignee: Legrand SA
Current assignee: Legrand SA
Priority date: 1979-01-30
Filing date: 1980-01-28
Publication date: 1980-09-03
Also published as: IT1147705B; GB2041063B; ES248451U; FR2448234A1; CH634956A5; FR2448234B1; ATA47180A; AT371290B; DE3003140A1; JPS55103105A; IT8067125A0; AU5500080A; BE881402A; ZA80370B; ES248451Y

Abstract

A bush 20 threaded at 19 to receive a clamping screw is formed at one end of a metal strip 11 and an aperture 22 adapted to accommodate the bush at the other. The metal strip 11 is folded into a frame and the bush is upset or riveted at 23 to secure the two end sections 15A and 15B together. The elasticity of this clamp frame 10 compensates for an unloosening of the clamping screw. <IMAGE>

Description

SPECIFICATION Clamp frame for screw clamp connector and method of making the same The present invention relates generally to screw clamp connectors for junction terminal blocks.

Such a connector comprises a clamp frame for receiving a wire conductor which is to be connected, and a clamping screw in threaded engagement with a tapped hole extending through one of the sides of the clamp frame for clamping the conductor against the opposite side of the clamp frame either directly or, as is most often the case, by means of a clamping bar or jaw.

The present invention relates more particularly to the case in which the clamp frame is constructed from a suitably cutout strip or ribbon of metal. The metal strip is folded generally into a frame, the folding being carried out so that the free ends of the metal strip overlap each other to form the side of the clamp frame in which the tapped hole for the clamping screw is to be located.

Accordingly, in screw clamp connectors of this type the tapped hole is defined by a pair of separate bores, one in one of the end sections of the initial metal strip and the other in the other end section thereof. The tapping of the screwthread in the holes is performed subsequent to the folding of the metal strip into framelike configuration.

Such a construction of the clamp frame has numerous drawbacks.

First of all, in order that the starting metal strip may be folded conveniently, initially the metal must be relatively malleabie.

Furthermore, in order that the resultant clamp frame may have sufficient rigidity to withstand any tendency to open by the sliding of one of the superposed end sections relative to the other, in practice it is necessary to surface harden the clamp frame.

Surface hardening itself is expensive. In addition, it has the disadvantage of making the clamp frame more fragile by accentuating the cracks which develop during the folding operation and making it more sensitive to the adsorption of hydrogen due to the surface treatment the clamp frame undergoes to assure corrosion resistance which makes one or more degassing operations necessary.

It has the additional disadvantage of reducing elastic limit of the metal, i.e., a reduction of the capacity of the metal to elongate elastically without plastic deformation for a given unit load.

Further it appears that the permanency of the clamping of the conductor by the clamp frame is a function, inter alia, of the amount of elongation. Indeed, if the clamping screw is to some extent loosened, e.g. by vibrations or impact, the conductor is no longer properly held in the clamp frame and the corresponding connection is thereafter defective.

Tc be sure, it has been attempted to take advantage1 of the fact that the overlapped end sections of the metal strip may shift relative to each other under load conditions; these overlapped sections assuring a jamming of the clamping screw so as to oppose any accidental loosening thereof.

But in actual fact this is insufficient because even if the loosening of the clamping screw is thereby prevented, this does not suffice to assure proper holding of the conductor in the clamp frame, the conductor which is generally of relatively malleable metal is inevitably flattened in contact with the clamping screw and therefore develops play in relation to the clamping screw.

Customarily in connectors of this type means are employed to oppose any relative displacement of the end sections of the folded strip. This involves, for example, welding the sections of the strip together, or lugs on one of the end sections folded at right angles into engagement with the other. Still, so far such means have not enabled the surface hardening to be eliminated.

Moreover, independently of the drawbacks due to the surface hardening, there results from the construction of heretofore known connectors of this type very fast wear of the taps used for cutting the screw threads owing to the inherent interference due to burrs at the interface between the two bores which together define the hole.

There also results a marked imbalance in the conditions in which the sections of such a frame member participate in supporting the clamping force developed, namely as regards the side section which is contiguous with the inner end section which in practice has to withstand a force very much greater than that which has to be withstood by the other side section.

To overcome at least some of these problems, there has been proposed, in French printed patent application No. 2,107,561, a clamp frame member comprising a metal strip generally folded into a frame, the two end sections of the metal strip overlapping each other and one of them having an integrally formed continuous bush with a threaded bore which extends through an aperture in the other end section of the metal adapted to accommodate the bush.

But in this French printed patent appliczaion no real securement is provided between the two overlapping end sections of the clamp frame generally in the planes thereof or perpendicular thereto since there is play between them.

Now experience has shown that play may be permitted, if absolutely necessary, between the end sections parallel to their planes, but not play parallel to these planes.

An object of the present invention is a clamp frame for a screw clamp connector which satisfies this condition.

According to the invention there is provided a clamp frame for a screw clamp connector, comprising a metal strip generally folded into a frame, two end sections of the folded strip overlapping each other, one of said end sections having continuous bush formed in one piece therewith, said bush having a tapped inner wall and extending through an aperture formed in the other end section of said strip, said free end of the bush being fixed to the other end section by upsetting or riveting.

Thus according to the invention the bush firmly secures the two overlapping end sections of the clamp frame of the connector perpendicular to their planes.

The interlocking or securement is then sufficient so that it is no longer necessary to surface harden the clamp frame.

According to the invention it is therefore advantageously possible to save the expense of this treatment.

The surface treatment of the frame member is therefore simplified, and no degassing need be provided upon the completion thereof.

Furthermore, the strain corresponding to the elastic limit of the clamp frame according to the invention advantageously remains the same as the initial strip from which it is formed.

Since this metal is relatively malleable for the reasons alluded to above, the elastic limit is therefore relatively high.

Consequently the clamp frame according to the invention in itself has a sufficient elastic reserve or resilience to assure permanently the proper holding of the conductor, even in case the clamping screw clamping the conductor slightly unscrews or in case the conductor itself flattens and otherwise would develop play in relation to the clamping screw.

Indeed, and to the extent that under the action of the initial load the clamp frame according to the invention undergoes sufficient strain within the elastic limit owing to the inherent tendency to return to its initial configuration the clamp frame automatically takes up any play which may otherwise develop between the conductor and the clamping screw.

Further, the tapping or threading of the hole in the clamp frame may be advantageously facilitated since it is effected on a cylindrical wall surface without any discontinuities and in case the threading or tapping is performed by deformation, any beneficial effect to the threads due to hammer hardening in the course of threading is, absent any subsequent hardening treatment, advantageously conserved.

Finally, better balanced working conditions between the sections of the metal strip, and particularly the side sections, are advantageously produced.

Another object of the present invention is to provide a method of manufacture for the clamp frame briefly described above.

According to another aspect of the invention a method of making a clamp frame for a screw clamp connector, comprises the steps of providing a strip of metal, forming a bush in an end section of the strip, forming an aperture in the other end section of the strip complementary in shape to the outer contour of the bush, folding the strip into a frame, in the course of folding inserting the bush through the aperture, and securing the free outer end of the bush to the other end section of the strip by upsetting or riveting.

Such a method in practice advantageously involves no marked complication of the method of manufacture of similar prior art clamp frames.

These and other features and advantageous of the invention will become apparent from the description which follows, given by way of example, with reference to the accompanying schematic drawings, in which: Figure 1 is a perspective view of a clamp frame according to the invention and the clamping screw associated therewith which together comprise a screw connector; Figure 2 is a longitudinal sectional view of the clamp frame taken on the line ll-ll in Fig.

1; Figures 3A, 3B, 3C, SD, 3E and 3Fare sectional views illustrating the method of manufacture of such a clamp frame according to the invention; and Figure 4 is a view similar to that of Fig. 3F, illustrating the operational mode thereof.

In the drawings general reference numeral 10 designates the clamp frame embodying the invention with which is associated a clamping screw 11' for constituting a screw clamp connector.

As it will appear in greater detail hereinafter, the clamp frame 10 is formed from a suitably cutout metal strip 11, generally folded into a frame.

The clamp frame itself thus forms a tubular housing 1 2 for lodging the stripped end of some wire conductor which is to be electrically connected to some other conductor (not shown).

The metal strip 11 generally comprises five sections.

There is accordingly a central section 13, two side sections 1 4A, 1 4B and two end sections 1 so, 1 SB, one which is contiguous with side section 1 4A, and the other with side section 1 4B and they overlap each other to form a single composite side of the clamp frame opposite the side formed by the central section 13.

In the illustrated embodiment, the central section 1 3 is of generally dihedral shape and has on its inner side transverse score lines 16.

Further on one of its sides it is bordered by a tab 1 7 folded at right angles thereto.

The end sections 15A, 15B jointly define a threaded hole 1 9.

According to the invention the threaded hole 1 9 is formed integrally on the inner wall of the continuous bush 20 and also provide interlocking of one of end sections 1 5A and 15A relative to the other so as to preclude the opening of the clamp frame formed by the strip 11; in other words to inhibit relative displacement of one of the side sections 1 4A relative to the other side section 14B.

Preferably, as illustrated in the drawings, the bush 20 is formed in one piece with one of the end sections 15A, 15B, in practice the lower or inner section, namely section 15A.

According to the invention bush 20 for enabling interlocking with section 15B through which it extends, slightly protrudes therebeyond and is riveted thereto by upsetting or swaging its free edge 23 flowing into contact with the end section 15B during upsetting.

According to another embodiment the bush 20 may be secured to the end section 15B by upsetting or some similar forming operation, the aperture 22 in this end section slightly flaring and the bush 20 being applied against it by radial bulging.

In any event the aperture.22 through which bush 20 protrudes preferably, as shown, has a section complementary to that of the bush itself, in other words it is sufficiently large to permit trouble-free insertion of the bush 20.

In Fig. 3A is represented a metal blank 24 from which the strap is cut out to its desired contour (end sections 14A, 1 4B are in practice generally trapezoidal) including the associated lateral tab.

Before folding the metal strip 11 into the frame, the strip is stamped to form the bush 20 at one of its ends, and the aperture 22 complementary to the outer contour of the bush at its other end, as illustrated in Figs.

3B.

Then the metal strip 11 is folded into sections 13, 14A, 14B, 15A and 15B described above and shown in Fig. 3C. Before or during folding the dihedral angle in central section 1 3 is formed and the tabl laterally bordering the central section is folded at right angles thereto (not shown in Fig. 3C).

During folding resulting in the section 15B overlapping section 15A the bush 20 integrally formed on the latter is inserted through the aperture 22 in the former (Fig. 3D).

The free end of bush 20 which protrudes slightly beyond upper end section 15B is then upset (Fig. 3E) or riveted to obtain the sought after securement or interlocking.

Finally, the inner wall of the bush 20 is tapped, Fig. 3F. The screwthread is advantageously tapped over a continuous surface, i.e., devoid of any discontinuities.

The resulting clamp is then ready for any surface treatment which may be found to be necessary. But, there is no surface hardening treatment.

Furthermore the clamp has a relatively high elastic limit.

Thereafter, in service, during the loading or clamping of the clamping screw 11' associated with the clamp frame, for clamping a wire conductor 25 with a plate member therebetween, there is elastic elongation A of the side sections 1 4A and 1 4B as schematically illustrated by the phantom line in Fig. 4.

Consequently if any play arises between the clamping screw 11' and the conductor 25 the clamp frame itself takes up this play because of its resiliency tending to bring it back to its initial configuration.

Obviously the present invention is not restricted to the described and illustrated embodiment but encompasses all variations, modifications and alternatives without departing from the scope of the appended claims.

In particular, the end section which carries the bush may be the upper end section even though the reverse arrangement described hereinabove appears to be more suitable for facilitating the configuration of the metal strip and riveting or upsetting.

Moreover, it is not absolutely necessary for the bush to be formed in one piece with one of the end sections. It may be formed as a separate part distinct from one of the sections in the manner of a hollow rivet.

Claims

1. A clamp frame for a screw clamp connector, comprising a metal strip generally folded into a frame, two end sections of the folded strip overlapping each other, one of said end sections having continuous bush formed in one piece therewith, said bush having a tapped inner wall and extending through an aperture formed in the other end section of said strip, said free end of the bush being fixed to the other end section by upsetting or riveting.

2. A clamp frame according to claim 1, wherein the aperture in said other end section has a contour complementary to that of the outer contour of said bush.

3. A clamp frame for a screw clamp connector substantially as herein described and illustrated in the accompanying drawings.

4. A screw clamp connector having a clamp frame substantially as herein described and illustrated in the accompanying drawings.

5. A method of making a clamp frame for a screw clamp connector, comprising the steps of providing a strip of metal, forming a bush in an end section of the strip, forming an aperture in the other end section of the strip complementary in shape to the outer contour of the bush, folding the strip into a frame, in the course of folding inserting the bush through the aperture, and securing the free outer end of the bush to the other end section of the strip by upsetting or riveting.

6. Method of making a clamp frame for a screw clamp connector substantially as herein described and illustrated in the accompanying drawings.