US2508455A - High-intensity carbon electrode - Google Patents

Description

Patented May 23, 1950 2,508,455 HIGH-INTENSITY CARBON ELECTRODE Clarence E. Greider, Lakewood, Ohio, assignor, by

mesne assignments, to Union Carbide and Carhon Corporation, a corporation of New York NoDrawing. Application July 6, 1949, Serial No. 103,327

Claims.

1. 1 This invention relates to an improved positive, high intensity, carbon electrode for use in motion picture projectors and the like, by means of which improved arc stability is achieved through the introduction of a small amount of tungsten to said electrode.

Carbon electrodes are of two general classes, referred to in the art as low intensity and high intensity carbons. Low intensity positive carbons presently in use vary in diameter from about 9 to 14 mm. and the operating amperage is in the nature of 10 to 52 amperes for these respective electrode size variations The low intensity carbon arc is seldom operated at a current density much over 200 amperes per square inch cross-section of the positive electrode.

In general, a high intensity carbon arc is distinguishable from a low intensity carbon arc in several important respects. The former has a core containing a substantial amount of flame material which becomes highly luminescent under the action of the electron bombardment in the arc stream. The current density in high intensity positive carbons is increased to values which may exceed 1500 amperes per square inch. At this high current density the material of the core is vaporized more rapidly than that of the carbon shell until a deep, cup-like crater is formed in the carbon face. Within this crater vapors of carbon and core materials are excited to a very high temperature and radiating efiiciency, producing a brightness several times that possible at the positive crater of the low intensity carbon arc.

In operation, high intensity carbon arcs are of two types. In the older type, the negative carbon is inclined to the positive and the latter is continuously rotated to maintain a symmetrical crater form. This type of high intensity are generally employs a positive carbon varying from 9 to 16 mm. in diameter, with are amperages varying from 60 to 1'70 amperes.

A newer type of high intensity are is operated without rotation of the positive carbon and with the positive and negative carbons in coaxial alignment. In this arc the positive carbon (usually referred to as a simplified high intensity type carbon) has a size range from 6 to 8 mm. in diameter and operates at amperages varying from to 70 amperes.

The operation of a high intensity carbon are at the lowest current density consistent with the light requirements of a particular motion picture projector installation results in economies with regard to both carbon cost and operating power consumption. With amperages on the border line of that required for a high intensity eiiect, however, frequent diihculty arises due to the tendency of the arc to go in and out of high intensity, i. e. to fluctuate between a high intensity and low intensity are. As the light brilliancy of the high intensity are is several times that of the low intensity are the resultis a disturbing light fluctuation on the motion picture screen; The exact current density at which this tendency to go in and out of high intensity takes place varies with the different carbons depend' ing on their size, composition and designed operating characteristics. Generally it is in the range of 450 to 600 amperes per square inch. While this difficulty might be overcome by changing the carbon size or current load, this is usually not convenient or feasible, because of the standardized projection equipment generally in use in the trade.

Accordingly, the object of this invention is to provide an improved high intensity positive carbon, which is operable over a wider current density range with a stable high intensity arc,

without the necessity of changing the carbon size or operating characteristics of a projection system wherein established carbon sizes are to be used.

I have discovered that the addition of a small amount of tungsten, preferably as tungstic oxide, to the positive carbon greatly reduces the current density at which a carbon arc fluctuates between the high and low intensity effect. While the tungsten may be added to the shell, core or both, it will generally be incorporated in the core mix as the simplest and most convenient way of introducing it into the carbon. The same desirable effects are produced, however, if the tungsten is present in the shell or in both the shell and core.

The most advantageous amount of tungstic oxide will vary somewhat with diiierent carbon electrode compositions. In general, between 0.1 and 0.5 percent by weight of the core or shell will provide satisfactory results, i. e. 0.1 to 0.5 percent by weight of the core composition when the tungstic oxide is added to the core or 0.1 to 0.5 percent by weight of the shell composition when the tungstic oxide is added to the shell. Amounts in excess of 0.5 percent increase the burning rate somewhat thus reducing carbon efficiency slightly (i. e. lumen-hours per inch). While under certain circumstances it might be desirable to increase the tungstic oxide to an amount in excess of 0.5 percent, in spite of the slight decrease in carbon efilciency (lumen hours per inch), in no case should it exceed 1 percent, as an amount in excess of this will produce core fusion of the carbon. If less than 0.1 percent tungstic oxide is employed in the core mixture, the stabilizing eifect becomes somewhat erratic.

While tungstic oxide in amounts between 0.5 and 1 percent may reduce the carbon efliciency somewhat as expressed in lumen hours per inch, the carbon efficiency as expressed in lumens per ampere is increased by the addition of tungstic oxide throughout the useful range of 0.1 to 1 percent. In addition, because the inclusion of tungstic oxide in the core material produces a higher are color temperature (the light being somewhat bluer) the apparent brilliancy of the light produced is greater than the actual lumen measurement indicates. I

The invention is applicable to the improvement of all types of high intensity positive carbons,

which may vary considerably in the exact shell and core composition. The useful results are especially significant in the simplified high intensity carbons employed in the reflector type projection systems. These carbons generally have a shell composition containing a high proportion of coke-base carbon, with a core mix having predominating amounts of rare earth fluorides and oxides. In such carbons tungstic oxide in the core, in an amount of about 25% by, weight thereof, provides a substantial improvement in the ability of the carbon to maintain a'stable high intensity are at an amperage lower than that normally required to insure a constant high intensity effect in the arc.

It will be readily apparent to those skilled in the arc that while I have described my invention with particular reference to improved arc stability in high intensity, positive carbons of present' commercial importance, it will be equally useful to the trade in the design of more efficient carbons capable of operating at lower current density (i. e. smaller carbon diameter or operating ampera e or both) with good are stability and a high intensity arc.

. I claim:

1. In a positive, high intensity, carbon electrode, the improvement which is a shell and a core one of which contains tungsten in an amount between 0.1 and 1 percent by weight computed as tungstic oxide.

2. In a positive, high intensity, cored, carbon electrode, the improvement which is a core con- 4 taining tungsten in an amount between 0.1 and 1 percent by weight computed as tungstic oxide.

3. In a positive, high intensity, cored, carbon electrode, the improvement which is a core containing tungstic oxide in an amount between 0.1 and 1 percent by weight.

4. An improved positive, high'intensity, carbon electrode comprising a shell and a core one of which contains between 0.1 and 1 percent by weight of tungsten computed as tungstic oxide.

5. An improved positive, high intensity, carbon electrode comprising a shell and a core, said core containing between 0.1 and 1 percent by weight of tungsten computed as tungstic oxide.

6. An improved positive, high intensity, carbon electrode comprising a shell and a core, said core comprising a mixture of carbon, rare earth oxides and fluorides and 0.1 to 1 percent by weight of tungstic oxide. 7

7. An improved positive, high intensity, carbon electrode comprising a shell and a core, saidcore containing between 0.1 and 0.5 percent by weight of tungstic oxide.

8. An improved positive, high intensity, carbon electrode comprising a shell composed in major proportions of coke-base carbon, and a core consisting predominately of rare earth oxides and fluorides, said core further containing about 0.25% by weight of tungstic oxide.

9. An improved positive, high intensity, carbon electrode comprising a shell and a core, said electrode being within 6 to 8 mm. in diameter, said shell being composed in major proportion of coke-base carbon and said core consisting predominately of rare earth oxides and fluorides, said core further containing about 0.25% by weight of tungstic oxide.

10. In the operation of a simplified high intensity carbon electrode are having a non-rotat ing positive electrode and a coaxially alined negative electrode, the improvement which comprises continually supplying tungsten to the positive electrode crater from a positive electrode core composition containing 0.1 to 1 percent by weight of tungsten computed as tungstic oxide.

' CLARENCE E. GREIDER.

REFERENCES orrED UNITED STATES PATENTS Name Date Hardman et al Sept. 2, 1930 Number

Claims (1)

1. IN A POSITIVE, HIGH INTENSITY, CARBON ELECTRODE, THE IMPROVEMENT WHICH IS A SHELL AND A CORE ONE OF WHICH CONTAINS TUNGSTEN IN AN AMOUNT BETWEEN 0.1 AND 1 PERCENT BY WEIGHT COMPUTED AS TUNGSTIC OXIDE.