US2374497A - Arc lamp and carbon guide - Google Patents

Description

April 1945- E. G. POPHAL ARC LAMP AND CARBON GUIDE Filed Feb. 19, 1944 Patented Apr. 24, 1945 UNITED STATES PATENT OFFICE ARC LAMP AND cannon GUIDE Eric G. Pophal, St. Pauls, s. 0.,

Application February 19, 1944, Serial No. 523,035 1 Claim. (01. 176-419) This invention relates to an improved arc lamp r and especially to a novel method and apparatus for aligning the carbon elements thereof and maintaining the original alignment of the carbons while burning in the arc of such a lamp or iliary electrode guides in order to effect a more complete, efficient and more uniform burning and consumption of the carbon elements.

In accordance with the above general description, the specific embodiment of the invention N A furtherobject is to provide means for effecting a more economical and efficient consumption herein disclosed incorporates a pair of guides, one

for each carbon element of an arc lamp, which guides are made of an efiicient light transmitting vmaterial, such for example as a high melting point glass, 1. e., that known by the trade-mark Pyrex being a preferred type although various other materials such as quartz are equally applicable. I

In view of the multifarious uses to which the type of carbon guide herein below more particularly described may be adapted it is contemplated that a number of advantages will accompany its use. Although illustrated as part of a moving picture projector it is to be understood that the guides described as elements of this invention find ready and similar application for Another object is to provide an improved support for the carbon elements whereby the align ment of such carbon electrodes is maintained fixed during operation resulting in an improved and constant light source. Still another object is to provide a carbon guide which. is capable of transmitting most, if not all, of the light through its own structure thereby avoiding the appear-- ance of shadows and poorly lighted areas on a screen on which theprojected light falls.

of the carbon elements. A still further object is to provide an improved lateral support for carbon bons, provision of a drip well into which the carbon ash and copper drippings fall from the burning are thus keeping the inner surfaces of the projector and the reflector comparatively free of debris and smoke particles, to enumerate only a few of the more obvious advantages. Still other objects and advantages will become apparent or will be suggested to those skilled in the art upon reading the following description of one illustrative embodiment of the invention.

In the accompanying drawing:

Figure l is a side view of a motion picture projection device ShOWil'lg in broken lines, through the case, the association of the present invention with the assembly of parts commonly found in such projectors;

Figure 2 is an enlarged view of the carbon electrode, guide in operative position, the gap be tween the electrodes being somewhat exaggerated in order to show the reflection of the crater are more clearly;

Figure 3 is a sectional view taken on the line 3-3 of Fig. 2; and r Figure 4 is a perspective view of the carbon electrode guidein one of its moreuseful forms.

Referring, now, in more detail to the drawing and more particularly to Figs. 1 and 2, the projector I6 is provided with a carbon arc type lamp as a light source. This light source comprises a lamp base ll, preferably of insulating material into which is immovably fitted a carbon electrode holder l2 and a second carbon electrode holder 13, the latter being preferably of Pyrex or similar high temperature resistant, light transmitting glass. Fitted into and supported by these electrode holders is a negative carbon electrode M and a positive carbon electrode l5, respectively. Each one of these carbon electrodes is provided with the usual carbon composition core l8 and copper outside cylindrical shell ll. This association of copper and carbon structure re sults in the most suitable type of white projection lightgiving the most intense, easily con- I along adjusting slot 23 so that the concave crater arc I9 formed in the end of positive carbon electrode I is. exactly at the focus of mirror or refiector 2|]. 1 v

The particular structure 24 is more especially of interest in connection with the invention herein disclosed. It is a Pyrex or similar high temperature resistant glass support or guide forthe carbon electrodes. It is constructed, in this particular embodiment, of two sloping narrow sides 24, Fig. 4, each having an extension lip 2 5, provided with a V-shaped or notched portion for supporting the negative electrode at 26, and a similar V-shaped or notched portion for supporting the positive electrode at 21. Since the-positive electrode is usually of larger diameter, notch 21 is preferably cut correspondingly deeper than notch 26. This arrangement makes possible the exact'centering of the axes of carbons l4 and i5 and the maintaining of the aXes of these carbons on one and the same straight line.

As shown i Fig. 4, the glass carbon guide member has its two slanting upright carbon supporting portions 24 rigidly held together by a pair of Pyrex cross pieces 30 thereby forming an open top to catch the ash and copper drippings and conveying these waste products through the open end 28 for collection in removable tray 29. Such an arrangement removes most of the carbon ash and copper drippings given off by the burning are outside of the projector and out of the field.

of the light beam. 1

The necessity for guides of some form or other can be readily appreciated particularly when carbon electrodes of such small diameter as 7 to 10 millimeters are used. Frequently, the negative carbon which almost invariably extends through a central opening, such as in the reflector 20 is of the '7 millimeter size, Thus, because of the absence of the usual supporting structure found in the larger diametered positive carbon l5, the negative carbon I4 is usually the first to bend downwardly of its own weight, especially when the heat of the are over a long period. of operation weakens the thin negative carbon electrode.

Heretofore, in order toovercome this bending of the negative carbon means was provided in some cases to rotate the negative electrode slowly. This, however, made adjustment of this particular carbon electrode diflicult, resulted in a flickering arc and necessitated additional servicing.

' Then, again, the rotating carbon frequently burned the edges off the crater IQ of the positive carbon electrode, destroying the effectiveness of the hot crater l9 and defocusing the latter. After prolonged operation, the intense heat of the arc and the heat within the projector frequently became sufficient to cause in addition, a bending of the larger positive carbon. The resultant misalignment of the carbon elements causes the crater I9 to burn irregularly and form a groove across its concave face I9; this finally forms a large overhanging lip because of the more intense burning away of one side of the crater edge.

Usually this overhanging lip must be burned off by. the operator before a satisfactory beam of projected light can be obtained; this wastes a considerable portion of the carbon electrodes since during this burning off process the arc cannot be used to project a picture on a screen.

.An aligned crater such as is produced by an overhanging lip on positive carbon element l5 results in a light having at least three clearly visible zones of intensity. When projected on a screen such a light field shows regions of blue, white and brown coloration or hue. It is impossible to focus a uniformly white field on the mirror 20 for subsequent projection or reflection unless a relatively perfect concave crater such as shown at l9, Fig. 2, is formed at the arcing end of positive carbon I5. Such perfect operation of the carbon arc is possible only when the carbons are held in perfect alignment. With these guides only a very small part of the total weight of each carbon electrode iscsupported by the electrode .itself, the major portion resting upon and riding in the grooves 26, 21. I

The great advantageof using a glass support is readily appreciated in the absence of shadows on the projection screen. -Moreover, the use of a highly heat resistant glass enables one to use these supports Within about 01 an inch of the hot crater is; this assures a perfect-alignment and common axial arrangement of the carbon electrodes. In addition, the hardness of such heat resistant glass lessens the clouding effect on its polishedsurface caused by the bombardment from thehot carbonv ashes and copper particles. A typical specimen offthis type of guide was used over a period. of 5 to .6 months without requiring replacement because of opaqueness developed on the glass surface resulting in the formation of a shadow on thescreen. Itis to be noted in pass Although the gap betweenthe rear negative and the front positive carbon electrodes is somewhat exaggerated in Fig. 2 it is to be understood that it is really about 4 inch in the usual pro.- jection lamp and is shown larger in the drawing to facilitate the visualization of its operation and the collimation of the projected light beam.

It isto be noted that the use of guides such as those above described will not keep a white light continuously'on the projection screen but these guides will keep a uniform light field projected on the screen. As the crater l9 burns farther away from'the mirror 29 it gets out of the focus of mirror 20 andthus necessitates movingthe carbon electrode l5 towards the mirror 28. However, the guides 24 assure a perfect.

crater l9 and maintain a uniform. field of light projected-on the screen, unspotted by areas of different hues and colors.

With the guides of this invention, the usual carbon regulating or feeding units function much more effectively since with a practically perfect crater always in operation there is little or no opportunity for a sudden change in the resistance of the arc and as a result,.the usual automatic carbon feeding devices found in the better type lamps function by practically imperceptible gradations of adjustment when viewed by-the results produced on the projection screen. Thus flickering is completely overcome when these guides are used. In addition; the highly useful.

insulating properties of glass are utilized to full advantage. Although this inventionproduces its.

most favorable results when used with the newer because of the greater extremes of temperature and. current strength to which the carbon elements are subjected therein, it can be advantageously used and readily adapted for incorporation in the older type of moving picture projector, spot light and search light as well as other types of service lamp,

I claim:

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