GB2055511A - Electrical Contact Construction - Google Patents

Abstract

A contact construction for a contactor having spaced fixed contacts 42 and a bridging element 50 having contacts 56 in alignment therewith and movable between an open position wherein said bridging contacts are spaced from said fixed contacts and a closed position wherein said contacts are in engagement to carry current line to load, said contacts 42, 56 are of generally wedge shape configuration and have flat surface engaging portions 44, 58 at their thicker ends, said flat surface portions being located at the outer ends of said contacts relative to the center line of the contactor with the tapered portions 46, 60 extending towards the center line. <IMAGE>

Description

SPECIFICATION Contact Construction The present invention relates generally to a novel and improved contact construction particularly adaptable, although not limited to, electro-magnetic contactors.

Contactors are conventionally used as switching devices for opening and closing relatively heavy line to load currents and traditionally comprise a pair of fixed spaced terminal strips having precious metal contact buttons or elements bonded to the extremities of said strips. A bridging element in the form of an electrically conductive base metal strip extends across said fixed contacts and is provided with precious metal contact buttons or elements which are in alignment with the fixed contacts.

Electromagnetic means or the like are provided for moving the bridging element between a first or open position wherein the bridging contacts are spaced from the fixed contacts and a second or closed position wherein the bridging contacts make engagement with the fixed contacts to conduct current flow therebetween. Since switches of this type frequently carry heavy loads, it is essential that the contact buttons have a sufficient interface with the terminal strips to which they are bonded so that the current density at said interface is not increased to the point where it causes the bond between the terminal strip and the contact button to deteriorate. In addition, the contact buttons must be of a sufficient thickness so as to compensate for erosion and wearing of the contacts during continued use.Since contact buttons are constructed of a material which meets the necessary contact requirements, such as silver or a silver alloy, and since the cost of silver is exhibiting a costant upward trend, it has been found desirable to provide contact buttons or elements which are of less mass and hence require less silver, but which nevertheless function as effectively or even better than conventional contact buttons.

It will be understood that conventional contact buttons are of generally rectangular configuraton, i.e. of substantially constant thickness throughout, although some contacts may be slightly domed at their exposed or contacting surface to minimize wear and break-arcing by reducing the area of engagement between mating contacts. However, the following problems have been found to exist where rectangular contacts of substantially constant thickness are employed.

First of all, the amount of silver required for such a contact configuration is unnecessarily costly, a problem of growing concern in view of the rapidly rising price of silver.

Secondly, since contactors of the type with which the instant invention is concerned are frequently used where heavy loads are involved, a great deal of heat is generated during make and break of the contacts which results in pronounced erosion and deterioration of the contacts, thus shortening their effective life.

Also, the pronounced heat generated during make and break of the contacts causes are erosion on the insulating barriers of the contactor located adjacent to the contacts, thus lessening the dielectric withstand between line and load terminals during repeated use of the device.

It is therefore a primary object of the present invention to provide a novel and improved contact design and configuration which requires less silver or silver alloy to be used, without otherwise effecting the mechanical or electrical characteristics of the contactor, it being obvious that the lesser amount of silver now necessary results in a substantial financial saving.

A further object of the present invention is the provision of a novel and improved contact design and configuration wherein the area of actual contact between the bridging and stationary contacts is at the outward edge of the contacts, i.e. the ends of the contacts furthest removed from the centerline of the contactor, whereby heat generated during make and break of the contacts is blown outwardly away from the centerline of the contactor whereby the contacts run cooler, thus lessening erosion. At the same time, the blow out effect of the heat results in less arc erosion of the insulating barriers adjacent to the contacts which in turn results in a higher dielectric withstand between line and load terminals.

Another object of the present invention is the provision of a novel and improved contact design which achieves the foregoing objectives, but at the same time may be incorporated in existing contactors without requiring any changes or retooling with respect to the latter.

Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawing.

Description of the Drawing In the drawing which illustrates the best mode presently comtemplated for carrying out the present invention: Figure 1 is an exploded view, partially in section, of a contactor having conventional contact buttons or elements; Figure 2 is a view similar to Figure 1 but showing the novel and improved contact buttons of the instant invention; Figure 3 shows the contactor of Figure 2 in close position; Figure 4 is a section taken on line 4-4 of Figure 2; Figure 5 is a section taken on line 5-5 of Figure 3; Figure 6 is an exploded sectional view showing the contacts of the instant invention on an enlarged scale; and Figure 7 is a view similar to Figure 6 but showing a slightly modified form of the instant invention.

Description of the Invention Referring to the drawings, and more particularly to Figure 1, there is shown a contactor 10 comprising an insulating dielectric housing 12 having fixed terminal strips 14 secured to ledges 1 6 by any suitable fastening means such as screws 1 8. Terminals 20 of conductors 22 are maintained in contact with terminal strips 14 by the screws 18, all in a well known manner.

At their inner ends, the terminal strips 14 have bonded thereto contact buttons or elements 24, it being understood that the contact buttons 24 are constructed of a highly conductive metal, such as silver or a silver alloy, while the terminal strips 14 are constructed of an electrically conductive base metal, such as brass. In actual use silver cadimum oxide has been found to be a highiy effective silver alloy, it being understood that said alloy comprises somewhere in the range of 85 to 90 percent silver and somewhere in the range of 10 to 1 5 percent cadmium.

Overlying the fixed contacts 24 is a bridging element comprising a continuous elongated strip 26 of an electrically conductive base metal, such as brass, having contact elements or buttons 28 bonded thereto, it being noted that the contact buttons 28 are in substantial alignment with the contact buttons 24. The strip 26 extends through an upwardly and downwardly reciprocal plunger 30, it being understood that when the plunger 30 is in its uppermost position, as illustrated in Figure 1, the contacts 28 are spaced from the contacts 24 so that the switch is in open position. When, however, the plunger 30 is caused to move downwardly by any suitable means, such as energization of electromagnet 32, the contacts 28 will move into engagement with the contacts 24 to close the switch and complete the circuit between terminals 14.

It will be understood that the contactor illustrated in Figure 1 and above described is completely conventional in nature and per se forms no part of the present invention. It will further be noted that the contact buttons 24 in Figure 1 have a flat top surface, i.e. are of constant thickness throughout, while the contact buttons 28 are slightly domed at their lowest surface to minimize contact area between the contacts 24 and 28 when they are in engagement, thus minimizing wear, reducing arcing, etc. It has been found that when using the contact button configurations illustrated in Figure 1, and even where one pair of contacts is slightly domed, a tremendous amount of heat is generated during make and break of the contacts, particularly where heavy loads are involved, as is frequently the case in contactors of this type.The heat so generated causes erosion ad deterioration of the contact buttons, thus limiting the effective life of the switch, and at the same time, the heat causes arc erosion on the insulating barriers located adjacent to the contacts, as illustrated by the stipling shown at 34. This arc erosion lessens the dielectric withstand between line and load terminals after repeated operation of the switch.

It will be understood that the contactor 10 shown in Figure 1 illustrates a single pole.

Obviously the instant invention is applicable to either a single or multiple pole switch.

Referring now to Figure 2, it will be understood that the contactor shown therein is in all respects identical to the contactor of Figure 1 with the single exception of the design and configuration of the contact buttons or elements and the terminal and bridging strips. More specifically, the terminal strips 36 illustrated in Figure 2 are stepped as at 38 to provide thicker end portions 40 to which terminal buttons 42 are bonded. The design and configuration of the contact buttons 42 is shown more clearly in Figure 7, it being noted that the buttons 42 have a flat top surface portion 44 located adjacent the outboard end of the contact buttons with respect to the centerline of the contactor. Merging with flat top surface portion 44 is an inclined surface portion 46 which tapers to a point, as at 48.Bridging strip 50 is similarly stepped as at 52 to provide thickened end portions 54 to which are bonded contact buttons or elements 56 identical in configuration to the buttons 42 and oppositely disposed thereto. Specifically, the buttons 56 have a flat surface portion 58 and inclined portions 60 whereby when bridging element 50 has moved downwardly to close the contactor, as illustrated in Figure 3, flat surface portions 58 engage flat surface portions 44. Thus it will be seen that actual engagement between the contact buttons is made adjacent their outboard ends this being important because it has been found that when the heat is generated adjacent the outermost edges of the contacts, the opposed incline surfaces located inwardly thereof cause the heat so generated to be blown outwardly away from the centerline of the contactor.This causes the contacts to run cooler, thus resulting in less erosion and deterioration for a given number of cycles. At the same time, this blow out effect causes the arc erosion on the adjacent insulating barriers to take place at locations more outwardly disposed with respect to the contactor centerline, as shown by the stipled areas 62 in Figure 2.

Comparing the stipled areas 62 in Figure 2 with the stipled area 34 in Figure 1, it will be seen that in the latter the arc erosion areas tend to overlap each other, whereas in Figure 2 the areas of erosion are spaced from each other. This separation of the arc erosion areas, as per the instant invention, results in a higher dielectric withstand between line and load terminals of any given pole of the contactor after many cydles of operation of the device.

Since the wedge shaped configuration of the contact buttons 42 and 56 permit the contacts to run cooler, it follows that the contact buttons may now be made somewhat thinner, and for this reason the strips 36 and 50 have been made thicker at their end portions to compensate for the thinner contacts. In addition to the saving of silver effected by making the contact buttons thinner, further saving is effected by virtue of the wedge shaped configuration now employed. In actual practice, it has been found that utilizing the contact button design and configuration illustrated in Figures 2, 3 and 7 results in a saving of siler of approximately 50 percent when compared with conventional contact buttons of the type illustrated in Figure 1.Of course, if it is desired to utilize conventional terminal strips 14 and bridging strip 26, i.e. without thickened portions at their extremities, then the contact buttons would assume the configuration shown at 64 in Figure 6. It is important to understand that in order for the instant invention to be applicable to existing contactors, without any redesign or retooling of the latter, it is essential that the overall height of the contact buttons remain the same as the overall height of the contact buttons used heretofor. This eliminates any necessity of adjustment or modification with respect to the pretravel/over travel relationship of the contacts.

It is for this reason that the strips 36 and 50 are thickened at their end portions where the contact buttons have been made thinner. On the other hand, where the contact buttons have not been made thinner, even though they still embody the wedge shaped configuration of the instant invention, the strips 14 and 1 6 may not be changed. Also, it also would be possible to have the strips 36 and 50 of the same thickness throughout their length, as opposed to being stepped adjacent their extremities.

It will also be understood that the interface area between the contact buttons of the instant invention and the terminal or bridging strips to which they are bonded remains unchanged from the interface area that exist in Figure 1. Expressed differently, in order to maintain the proper current density through the bond between the contact buttons and the strips on which they are secured, it is essential the interface area be maintained to a sufficient degree. In other words, it simple would not be possible to effect a saving of silver by making the contact buttons smaller in length and width, because this would reduce the interface area which would build up current density at the bond, thus causing the bond to fail.

It will therefore be seen that the instant invention maintains the same interface area, but still effects a substantial saving in silver by utilizing the wedge shaped configuration illustrated and described, and by locating the thickest portions of the contact buttons at their outboard extremities relative to the centerline of the contactor. As previously explained, this specific configuration enables the contacts to run cooler, which in turn enables thinner contacts to be used, thus resulting in further savings of silver.Also, the blow out effect which takes place during breaking of the contacts causes the heat generated to be blown outwardly way from the centerline of the contactor, which results in less erosion and deterioration of the contacts and relocating arc erosion on adjacent insulating barriers of the contactor in a way that allows for a higher dielectric withstand between line and load terminals.

It will be understood that initial contact between buttons 52 and 56 is limited to surface areas 44 and 58. If, however, extremely high loads are involved and the surface area is not sufficient to take the heat that is generated, the contact area will automatically self-adjust to a larger area as the plateaus begin to erode and move down the adjacent inclined surface.

Actually, the plateaus or surface areas 44 and 58 need not be of any particular size, so long as said surface areas make contact with each other when bridging element 50 moves downwardly to closed position. Actually, the size of the plateaus and the angle of inclination of the contact button can be modified to meet any specific or desired seating and "wear-in" characteristics.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims. Thus although it is considered to be preferable that both the fixed and the bridge contact buttons should have the described wedge formation, the advantages of this invention can be obtained to a degree with an arrangement in which only one button in each pair of mutually engageable contact buttons is formed as described, the other button being of conventional form.

Claims (10)

Claims

1. In a contactor of the type comprising a pair of spaced fixed contacts and a bridging element having spaced contacts in substantial alignment with said fixed contacts, said bridging element being movable between a first open position wherein said bridging contacts are spaced from said fixed contacts.and a second closed position wherein said bridging contacts are in engagement with said fixed contacts whereby said bridging elements conduct current flow from one of said fixed contacts to the other, the improvement residing in the following:: (a) said fixed contacts each comprising precious metal contact elements comprising a base surface bonded to electrically conductive base metal terminal strips and having a substantially flat top surface located at the outer portions of said elements, said top surface merging with an inclined surface extending toward said base surface, whereby said fixed contact elements define spaced oppositely disposed wedges each having flat top portions at the outermost or thickest portions thereof and with the thinner portions of said wedges facing each other; and (b) said bridging element comprising a base metal electrically conductive strip having precious metal contact elements bonded thereto, said bridging contact elements making contact with the flat top surfaces of said fixed contact element when said bridging element is moved to its second closed position.

2. In the contactgr of claim 1, said bridging contact elements each being of substantially the same configuration as said fixed contacts and being oppositely disposed with respect thereto, whereby the flat surface portions of said bridging contact elements engage the flat top surface portions of said fixed contact elements when the bridging element is in its second closed position.

3. In the contactor of claim 2, said base metal strips being thicker at the areas were said precious metal contacts are bonded thereto.

4. In the contactor of claim 2, said precious metal contact elements comprising silver.

5. A contactor comprising a pair of spaced terminal strips having precious metal contacts bonded thereto, a bridging element comprising a base metal electrically conductive strip having precious metal contacts bonded thereto, said bridging contacts being in alignment with said fixed contacts means for moving said bridging element between a first open position wherein its contacts are spaced from said fixed contacts and a second closed position wherein its contacts engage said fixed contacts to conduct current therebetween, said bridging contacts and said fixed contacts having flat surface portions which engage each other when the contactor is in closed position, said flat surface portions being spaced from the inner facing edges of said bridging and fixed contacts respectively, said flat surface portions merging with inclined surface portions extending toward said inner facing edges.

6. In the contactor of claim 5, said flat surface portions being located adjacent the outermost edges of said contacts.

7. In the contactor of claim 6, said inclined surface portions defining a sharp edge at said inner facing edges of said contacts.

8. In the contactor of claim 7, said terminal and bridging strips being thicker at the areas where said contacts are bonded thereto.

9. A contactor comprising a pair of spaced terminal strips having precious metal contacts bonded thereto, a bridging element comprising a base metal electrically conductive strip having precious metal contacts bonded thereto, said bridging contacts being in alignment with said fixed contacts, means for moving said bridging element between a first open position wherein its contacts are spaced from said fixed contacts and a second closed position wherein it contacts engage said fixed contacts to conduct current therebetween, said bridging contacts and/or said fixed contacts having a relatively thick portion at one extremity and gradually decreasing in thickness toward the other extremity, whereby said contacts make engagement with each other at said relatively thick portion, said one extremity being located adjacent the outboard end of said contacts relative to the centerline of the contactor.

10. A contactor substantially as hereinbefore described with reference to and as shown in Figures 2, 3, 4, 5 and 6 or Figures 2, 3, 4, 5 and 7 of the accompanying drawings.