US 2036759 A
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A N 9 fin E, MLIEBNMANN ELECTRICAL CONTACT PIN Filed June 7, 1933 r end that enters the co-operating socket.
Patented Apr. 7, 1936 UNITED STATES PATENT OFFICE Application June 7, 1933, Serial No. 674,751 In Germany November 30, 1932 2 Claims.
This invention relates to tubular electrical contact pins of the type that is slit longitudinally, the portions between the slits providing springy contact-making surfaces which are usually bulged outwards at the middle of the pin. The pins are sometimes made from the solid, the slits being stamped or milled out; or the slit pins may be made by rolling up an appropriately slit sheet of metal and subsequently bulging by axial compression. This type of contact pin is frequently referred to as a banana plug by which term it will hereinafter be denoted.
The invention is c'oncerned with banana plugs of the kind having an open lower end, i. e. the
The attachment of electrical connecting wires to banana plugs of this kind-for example the attachment of the connecting wires of a thermionic tube, in the socket or base of which such banana plugs are employed as contact pinsis brought about by passing each connecting wire down the proper banana plug until the end of the wire lies inside the opening at the lower end of the plug and dipping this end of the banana plug into molten solder to effect soldering of the wire end to the plug end. In order to obtain springy contact surfaces the longitudinal slits are made as long as possible so that the ends of the slits extend close up to the lower end of the banana plug.
It has been found that soldering of the connecting wire to a banana plug by the method described causes the contact surfaces to lose some of their springiness. The reason is that when the lower end of the banana plug is dipped into the molten solder the plug may be dipped deep enough to allow the solder to gain access to the lower ends of the slits, whereupon it rises in them as a result of capillary action. It is extraordinarily difiicult to dip the plugs into the molten solder only so far that the solder does not reach the slits; dipping of the plugs only slightly deeper than is really. necessary for soldering allows it to do this. The solder that has mounted in this way, on solidification, naturally reduces the springiness of the contact surfaces of the banana plug. This occurs of course not only in the case of the lanceolate slits formed by slitting without removal of material and subsequent bulging, but also in the case of slits that are made by milling or stamping and which therefore have a uniform Width along their whole length, if their width is small enough, as it usually is.
The disadvantage is avoided according to the invention, by widening the lower ends of the slits. This is conveniently done by providing holes in which the slits end. The holes may be of round, oval, rectangular, triangular, or other form. When the plug end is dipped into the molten solder, solder will invariably enter the widened portion of the slits but will not rise in them as the width is such that there is no capillary action. The height of the widened portion is, of course, either such as to render it easy to avoid dipping the plug deep enough to allow the solder to reach the narrow portion of the slit; or such that the slit, at the top of the widened portion, is too wide to exert capillary action.
In order that the invention may be clearly understood and readily carried into effect, it will now be described with reference to the accompanying drawings in which:-
Figure 1 is an elevation of the usual form of banana plug,
Figures 2 and 3 are elevations on an enlarged scale of the lower ends of two different examples of banana plugs in accordance with the invention.
Referring first to Figure 1, I indicates the banana plug which has a bead 2 and open upper and lower ends 3 and 3 respectively. The slits '4, which are necessary for the production of the spring action of the banana plug, are shown as being of the usual lanceolate form. The connecting wire 5 that is to be soldered to the banana plug is passed into the open upper end 3 of the plug, down through its whole length and its end brought to the perforated lower end 6 in which it is soldered as a result of dipping in molten solder. As the lower ends of the slits 4 extend close up to the lower end 6 of the banana plug the danger arises, as aforesaid, that during soldering the pointed lower ends of the slits 4 may dip into the solder so that it is drawn up into them with consequent disadvantage.
In order to avoid this the slits 4 are, according to the invention, widened at their lower ends as shown in Figures 2 and 3. For this purpose a hole I is provided in which the lower end of the slit ends. The hole I is shown as being substantially square, but, as already mentioned, it might be of other forms.
The plug of Figure 2 has slits 4 of uniform width as might be obtained by milling or stamping. The hole I is large enough to render it easy to avoid dipping of the plug into the solder far enough to enable the solder to reach the end of the slit.
The plug of Figure 3 has slits of lanceolate form except in so far as this is avoided by the provision at their lower ends of the holes 1. The
form of the lower slit end as it would otherwise be is here shown in dotted lines. In this form even if the plug should be dipped far enough into the solder to enable it to reach the slit, the solder can no longer mount up over the hole 1, because above the hole I the distance apart of the slit edges 9 is so large that a capillary action no longer arises.
1. A tubular electrical contact pin provided with at least one longitudinal slit extending to adjacent said pin end which is narrow enough to exert a capillary action on solder and said pin being open at the end adapted to enter a cooperating socket, in which each slit is widened at its end adjacent said pin end so as to avoid rising of solder in said slits when said end is dipped into molten solder.
2. A tubular electrical contact pin provided with at least one longitudinal slit extending to adjacent said pin end which is narrow enough to exert a capillary action on solder and said pin being open at the end adapted to enter a cooperating socket, in which each slit ends in a hole at its end adjacent said pin end so as to avoid rising of solder in said slits when said end is dipped into molten solder.