US1893085A - Luminous tube - Google Patents

Description

Jan. 3, 1933. s, 1 JOHNSON 1,893,085

LUMINOUS TUBE Filed Sept. 27, 1928 INVENTOR,

A TTORN Y6 Patented Jan. 3, 1933 UNITED STATES PATENT OFFICE STANLEY J. JOHNSON, OF CLEVELAND, OHIO, ASSIGNOR TO NEON PROCESS, INCORPORATED, OF CLEVELAND, OHIO, A CORPORATION OF OHIO LUMINOUS TUBE Application filed September 27, 1928.

The present improvements, relating as indicated, to luminous tubes have more particular regard to neon tubes such as are extensively utilized for display and advert1s1ng 5 purposes, due tothe ldistinctivefspectral color of the neon whenexcitcd by the passage of a suitable electric current therethrough. One principal object of the present invention 1s to provide an electrode assembly for use in 19 such neon tubes which will make it possible to employ an electrode of relatively small surface area, much smaller than has ever been found possible, at least where the electrode is made of commonly available metals. In

connection with such improved electrode assembly a simplified method of evacuation is furthermore rendered possible.

To the accomplishment of the foregoing and related ends, said invention, then, con- 20 sists of the means hereinafter fully described and particularly pointed out in the claims; the annexed drawing and the following description setting forth in detail certain mechanism embodying the invention, such disclosed means constituting, however, but one of various mechanical forms in which the principle of the invention may be used.

In said annexed drawing Fig. 1 is a central section through the end of a typical neon tube showing one form of the present improved electrode assembly; Fig. 2 is a similar sectional view showing a modified form of such assembly; and Fig. 3 is a diagrammatic representation of such tube illustrating one process of manufacture.

Referring to the structural features of such electrode assembly, the body 1 of the tube is shown in the several figures of the drawing in conventional form, it being understood that such body is of suitable diameter and length, and will ordinarily be bent in the outline of a letter or ornamental design, where the tube is used for advertising purposes. The ends 2 of the tube are, as shown,

preferably of somewhat larger diameter than such body 1 so as to form chambers for the corresponding metallic electrodes 3. The latter are connected with, and supported by, the lead-in wires 4 which conduct the necessary current to said electrodes. Each of such Serial No. 308,663.

wires 4, it will be understood, is sealed vacuum-tight at the point 5 where it passes through the end of the electrode chamber 2.

Referring more particularly to the electrode assembly illustrated in Fig. 1, it will be noted that a cylindrical glass sheath 6 is placed so as to surround the electrode 3, the outer end of this sheath being of reduced diameter to a permit its attachment to the end of the chamber 2 adjacent the point 5 where the lead-in wire 4 passes therethrough, as just described. The inner end of the sheath preferably extends a short distance beyond the corresponding, i. e., free end of the electrode and the space between the latter and such sheath is thereupon filled in, as shown, with a suitable dielectric, such as dehydrated sodium silicate, although a number of materials of dielectric character and capable of withstanding a high temperature have been found satisfactory for the purpose of filling such space, such as asbestos fiber, low density porcelain, plaster of Paris, and plaster of Paris mixed with a small quantity of sodium silicate. IVhere the sheath 6, as shown, extends beyond the end of the electrode, the filling material 7 thus placed in the sheath will be preferably gouged out so as to leave the endof the electrode exposed, but otherwise the latter is completely surrounded by such material.

In the modified form of electrode assem bly illustrated in Fig. 2 the only difference from that just described is the omission of any sheath around the electrode and the fill- 35 ing material 8 of the same character as that employed to fill the sheath here fills the entire space between the electrode and the chamber 2. As in the first described construction such filling material, if it extends beyond the end of the electrode, is nevertheless preferably gouged out to expose such end.

The neon tube with an electrode assembly, such as the foregoing, may be evacuated and charged with neon gas in various ways. For example, a vacuum pump 10 may be connected to the tube 1 by means of a temporary sealed connection 11, in which is interposed a valve 12 and trap 13. Between the tube 1 and such valve 12 there is a branch connection 14 that communicates through a chamber 15 with a reservoir 16 containlng the gas, e. g., commercial neon, wherewith the tube is to be filled, valves 17 and 18 controlling communication between chamber 15 and connection 14 and the reservoir 16, respectively, and a suitable pressure indicating device 19 being also provided.

The lead-in wires 4 at the respective ends of the tube 1 are connected to the terminals of a secondary circuit of a transformer 20, whereby an electrical current of proper character may be supplied to said electrode.

With the apparatus arranged as aforesald, the vacuum pump is set in operation with the valve 12 open and the valve 17 closed. At the same time current is supplied to the primary winding of the transfer 20 so as to set up a current flow through the secondary coil of said transformer and the circuit including the wires l and the electrodes 3, with resultant; ionization of the atmosphere within the tube 1. This electrical excitation of the atmosphere within the tube 1, it will be understood, takes place while the latter is in a partlally evacuated state, and, due to the current flow, heat is generated within said tube, which vaporizes any moisture present in such atmosphere and the vapors are drawn ofi by the pump. When a suitable heat has been attained the electric current is shut off and evacuation continued until the tube cools and the pressure within the latter has been reduced so far as possible by means of the pump. Thereupon the valve 12 is closed and gas from chamber 15, which has previously been filled from the reservoir 16, is admitted to the tube 1 until the desired pressure of as is obtained therein, approximately dou 1e that which is employed in normal service of the tube.- When this stage is reached chamber 15 is cut oif and electric current again turned on to excite the gas within the tube to luminosity. The tube is now a second-time evacuated until the pressure is reduced to desired operating range within the tube and the connection 11 thereupon sealed off. After a brief period of aging the tube is then ready for commercial service.

Instead of the foregoing, the customary method of utilizing previously purified neon gas to fill the tube may be employed in conjunction with a standard mercury vapor condensation pump, liquid air traps and gas purification systems, a method with which the art is familiar.

Also a simpler method of evacuation is possible with the present improved electrode, the purification system, traps, condensation pump and the use. of liquid air being eliminated, only a rotary oil pump being required for evacuation of the tube before filling the latter with neon gas in its commercial state. According to this method a bombardment of the electrodes is caused during the process of evacuation by supplying a suitable electriccurrent, as previously described, to the latter, with the result that the material surrounding the electrodes is thoroughly dehydrated. A high temperature is in fact generated throughout the entire length of the tube being evacuated, thus assisting in the elimination of water vapor and gases which require to be removed. The tube is then allowed to cool and neon gas at a pressure of from 5 to 20 mm. is allowed to enter, after which the tube is sealed off and ready for aging.

Another method which has been successfully employed is to place the tube, when ready for evacuation, in an oven and there bake it at a high temperature during the process of evacuation, the temperature thus supplied serving to dehydrate the material surrounding the electrodes and to eliminate water vapor and gases from the tube. The

latter is thereupon allowed to cool, after which it is filled with neon gas and sealed off as before.

The dielectric mass or substance, which is preferably porous, as in the case of dehydrated sodium silicate, that surrounds or contacts with the electrode, in each of the two forms of electrode assembly hereinbefore described, in the first place acts as a cooling agent for the electrode and so serves to prevent excessive vaporization of the latter. At the same time the materials named either have the inherent quality, or are effective because the mass is porous, to absorb and segregate the gaseous impurities in the tube and in commercial neon gas, thus allowing the neon gas to give forth its characteristic luminous qualities. Such material may absorb neon as well as so-called impurities, but should preferentially absorb the latter.

. As a result of the foregoing I have found it possible to employ electrodes of much smaller area than has heretofore been considered possible with like conditions of pressure obtaining in the tube. In particular, successfully operating tubes are possible in which the electrode has an area substantially less than-1.5 square decimeters per ampere of current employed in illuminating the tube,

and after several months continuous operation such tubes do not show any consequential amount of vaporization of the electrode. Any of the metals known to be available for use as electrodes in luminous tubes, and :slpecifically neon tubes, may be employed, but

preferably use iron or tungsten.

While reference has hereinbefore been made specifically to neon tubes, it'will be understood that my improvements may be advantageously used in luminous tubes filled with other gas or gases, and particularly with neon admixed with another gas or vapor, e. g. mercury vapor, or with a mixture of neon, argon and helium.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the mechanism herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention 1. An illuminating device of the character described, comprising a glass tube, an electrode supported within said tube in spaced relation to the wall thereof, and a body of dehydrated silicate laterally surrounding and contacting with said electrode.

2. An illuminating device of the character described, comprising a glass tube, an electrode supported within said tube in spaced relation to the wall thereof, and a body of dehydrated sodium silicate laterally surrounding and contacting with said electrode. 3. An illuminating device of the character described, comprising a glass tube, an electrode supported within said tube in spaced relation to the wall thereof, a supplemental glass sheath within said tube laterally surrounding but spaced from said electrode, and

a body of dehydrated silicate held in said sheath about said electrode.

4. An illuminating device of the character described, comprising a glass tube, an electrode supported within said tube in spaced relation to the wall thereof, a supplemental glass sheath within said tube laterally surrounding but spaced from said electrode, and a body of dehydrated sodium silicate held in said sheath about said electrode.

5. An illuminating device of the character described, comprising a glass tube, an elec- 10 trode supported within said tube in spaced relationto the wall thereof, and dielectric means of greater thickness than the electrode for preferentially absorbing impurities, said means surrounding said electrode and prel5 senting a divergent crater.

6. An illuminating device of the character described, comprising a glass tube, an electrode supported within said tube in spaced relation to the wall thereof, and dielectric means for conducting heat away from said electrode and for preferentially absorbing impurities, said means surrounding said electrode and presenting a divergent crater.

7. An illuminating device of the character described, comprising a glass tube, an iron electrode supported within said tube in spaced relation to the wall thereof, and a body of dehydrated silicate laterally surrounding and contacting with said electrode.

Signed by me, this 24 day of September,

STANLEY J. JOHNSON.

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