US1991998A - Negative electrode for high current arc lamps - Google Patents

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Feb. 19, 1935. H BECK NEGATIVE ELECTRODE FOR HIGH CURRENT ARC LAMPS Filed Jan. 13, 1930 In vemon:

Patented Feb. 19, 1935 NEGATIVE ELECTRODE FOR HIGH oun- RENT ARC LAMPS Heinrich Beck, Meiningen, Germany, assignor to firm Carl Zeiss, Jena, Germany Application January 13,1930, Serial No. 420,639% In Germany January 18, 1929 v 2 Claims.

I have filed an application in Germany, January 18, 1929 of which the following is a specification.

By increasing more and more the current for a carbon arc lamp the flame of the negative electrode will be subjected at approximately 80 to 90 amperes to a, visible alteration caused by a sharply defined jet which is engendered in the interior of the flame and hereinafter called the negative jet. As soon as the jet appears, a small crater has been formed in the negative electrode. As the strength of the current increases the jet as well as the crater will grow more and more, and, apart from the said general stronger form, the general aspect of the light are remains the same. All this changes as soon as about 300 amperes have been reached. The jet is apparently divided and appears bifurcated. Investigations have proved, however, that such bifurcation is merely imaginative and a consequence of the jet taking in rapid succession positions that approximately form the convex surface of a cone whose point is to be imagined as lying in the negative crater. The bifurcation of the negative jet always entails an increase of the dimension of the crater. As soon as the negative jet is beginning to bifurcate there result fluctuations of current and a consequent intensive noise (in one case 800 to 1060 periods per second were measured). The strength of current at which the bifurcation sets in is not quite distinctly marked and depends partially on the material of which the electrodes are made. With specially unfavourable material a bifurcation was noted already at 250 amperes, whereas best carbon, e. g. carbon which is electrically fritted, permits of a bifurcation taking place not before approximately 330 amperes have been reached. The bifurcation is not to be observed at once and appears after a certain period of lighting only. Causing a strong influence on the conditions of the anode, the bifurcation of the negative flame has an extraordinarily detrimental iniluence on the light arc, which is rendered unsuited for the production of light, all the more as it is exceedingly difficult to eliminate the bifurcation even after having reduced the strength of current. A great deal of tests regarding the elimination of the bifurcation at greater strengths of current had no result. Now, it has been attained by the present invention to do away with the bifurcation and, as a consequence, to manufacture lamps that suit stronger currents.

According to the present invention there is applied a negative carbon electrode whose diameter is equal to or, to a slight extent, greater than that of the negative crater. If the negative crater'has at 400 amperes a diameter of, say, 5.5 mm., then there has to be applied a negative carbon of a diameter which either is the same or, at the utmost, greater to such an extent that in consideration of a slight pointing of the carbon there is not permitted the formation of any crater having a diameter greater than the one corresponding to the respective current.

The" use of such an electrode will not give rise-to any bifurcation, and presumably this is due to the fact that the crater cannot grow beyond the normal measure. To whatextent the greater velocity of evaporation of the thin carbon plays a part, too, has not yet been sufficiently explored. Compared with the electrodes applied thus far, the diameter of the new electrode is considerably smaller, which is explained by the fact that at 200 amperes ordinary arc lamps required negative carbons of approximately mm. diameter, whereas, when using special electrode heads, at 300 amperes still electrode heads of 16 mm. were necessary. It follows; at once that the reduction in diameter, which the present invention aims at, is quite a considerable one. this thin electrode need not always be of pure It may be remarked here that carbon and that the carbon may contain certain quantities of metallic salts, carbides etc., which,

in a given case, also may take the form of a core,

so as to influence the electric cathode conditions.

Such thin and highly loaded electrode is conveniently used together with special auxiliary means. The carbon may be enclosed in a strong cover of, e. g., metal.

However, this method does not turn out a very advantageous one since such thick metal cover will not fuse uniformly and at the same time might injure an eventual reflector.

It is more appropriate to surround the a rule. In case the carbon is fed too quickly and protrudes too far from the sleeve it will be excessively heated. The consequence is that the carbon is subjected to a quicker evaporation which reduces its projecting part to the ordinary measure In case the sleeve is chosen of metal, it

must be thoroughly cooled by well-known means. However, it proves to be more advantageous to have the sleeve made of carbon. In this case the sleeve is heated at its front end and consumed slowly so that a corresponding feed must be provided. The consumption of this sleeve must be made in the proper way and effected in such a manner that, as far as this is possible, it is ef- Iected on the front side only. For such purpose the sleeve can be surrounded by a metal jacket in such a way that it protrudes from the latter only to a slight extent. If necessary, the metal Jacket may be cooled and, in turn, will impart the cooling effect to the carbon sleeve. Current can be supplied to the sleeve direct by means of the said metal jacket. In this case, whilst consuming, the carbon sleeve will become very blunt, which ensures a safe contact of the outermost part of the carbon sleeve with the burning end of the negative electrode. In order to avoid the supply of current to the negative electrode from one side, the carbon sleeve is conveniently turned slowly during the burning of the lamp, in which case the negative electrode may be fixedly arranged or made to turn together with the tube.

The accompanying drawing which illustrates the invention shows a constructional example of an arrangement corresponding to the invention. Figure 1 represents a section along the axis of the negative electrode, and Figure 2 a section along the line 2-2 in Figure 1.

In the constructional example corresponding to the drawing the negative electrode is a carbon rod a of which the front or burning end is in a carbon sleeve b and the remaining part is held by two rollers d and d fixedly mounted in a casing c. 0! these two rollers the last named, d is fixedly connected with a bevel wheel d coacting with a bevel wheel e The bevel wheel e is fixedly connected with a spur wheel a which, through the agency of a pair of bevel wheels F, f fast with a shaft f, receives its motion from a spur wheel e whose shaft is provided also with a spur wheel 9 coacting with teeth 9 These teeth a are arranged on a metal tube h which is pushed over the sleeve 1) and serves for supplying electric current to the said sleeve and, consequently, also to the carbon rod a. In its exterior surface the tube It has cut in a thread it on which a nut h is screwed. Above the pipe h and the nut 11 the casing is constructed in such a way that a chamber i is left between the casing, the tube h, and the nut h. By means of a pipe 9' this chamber is supplied with water which leaves again through a pipe 7", thus serving for cooling the tube h. Two slits, k and k, cut into the tube h allow two cars, 10 and k revolubly mounted on the nut h. to slide therein. The case c is provided with a groove 0 into which an ear I of the nut it extends, so that the nut It can be moved on the tube It in axial direction but will not allow of being turned.

When with this arrangement the shaft 1 and, consequently, also the bevel wheel I are turned, the roller (1 is rotated through the agency of the wheels e e c and d and the carbon rod a slowly pushed forward. At the same time, by

means of the wheels g and 9 the tube h and I consequently also the carbon sleeve b are turned. When the tube h is rotated, the nut it slowly screws itself along the thread it to the required degree and the ears k and it take the carbon sleeve 1) along and push it forward.

I claim:

1. In an arc lamp for very high current a negative electrode, the diameter of the said electrode being approximately equal to that of the crater appearing in the electrode, the electrode being surrounded by a conductive sleeve of carbon, this sleeve being adapted to supply current to the electrode in close proximity to the burning end and being displaceable relative to the negative electrode, and means for gradually pushing the sleeve forward and turning it at the same time.

2. In an arc lamp for very high current a negative electrode, the diameter of the said electrode being approximately equal to that of the crater appearing in the electrode, the electrode being surrounded by a conductive sleeve, this sleeve being adapted to supply current to the electrode in close proximity to the burning end and being displaceable relative to the negative electrode, and means for gradually pushing the sleeve forward and turning it at the same time.

HEINRICH BECK.

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