US1680272A - Raymond r - Google Patents

Description

Aug. 7,1928. 1 4 1,680,272

R. R. MACHLETT LIUMINOUS'TUBE AND PROCESS OF muumc'runme THE SAME Filed Nov. 17, 1927 IN VENTOR ia. M m

I in con unction Patented Aug. 7, 1928.

UNITED STATES PATENT OFFICE.

RAYMOND R. NIACHLETT OF NEW YORK, N. Y., ASSIGNOR TO RAINBOW LIGHT, INQ, OF

LONG ISLAND CITY, NEW YORK, A CORPORATION OF NEW YORK.

LUMINOUS TUBE AND PROCESS OF MANUFACTURING THE SAME.

Application filed November 17, 1927. Serial N0. 233,772.

My present invention relates to an improved luminous discharge tube and to an improved process of manufacturing the same. The improved tube is of the type in which interior electrodes are used and which contains a rarefied atmosphere comprising .an inert gas, such as neon. Argon, helium or other so-callcd noble gas may be used either alone or in combination, and mercury vapor in minute quantity may be employed therewith in order to increase the range' of colors.

' The pressure of will become luminous under the effect of an "electrical discharge. Vith neon, for example, although the pressure at which maximum conduction occurs is in the neighborhood of l m. m'. of mercury. absolute, yet initial pressures in the neighborhood of 8 to 10 iii. In. are preferred, since in this way the life of the tube may be enormously increased without necessitating the employment of prohibitively long tubes.

\Vith my improved possible to employ electrodes which are of cry small size, and hence can be more cheaply manufactured and installed. These small electrodes also enable the tube to be made with end portions which are not unduly large and cumbersome. This feature of the invention is particularly valuable in connection with tubes of large size, such as a neon beacon, in which very heavy currents are employed.

When ordinary interior electrodes are used it is important that the current density should be such as not to increase the normal cathode drop of potential, and this means that the negative glow should not extend further than to just encompass the electrode surface. If the current density is increased beyond this normal value, a very great rise in the cathode drop takes place accompanied by heating, and the phenomenon of sputtering or vaporization becomes much more pronounced with an accompanying depletion of the conducting atmosphere, a reduction in the pressure, and eventually in the failure of the tube to conduct. The life of the tube is thus shortened.

I have found that with ordinary interior electrodes the critical area at which the normal cathode drop tends to become abnormal is between 10 and 1.4 sq. deeimeters per amthe gas is such that it luminous tube it ispere of current with neon gas at a pressure of 7 in. m. of mercury. As the pressure of gas is diminished the cr tical electrode area becomes larger and, therefore, it is the practice to make'the electrodes substantially larger than the critical value at the pressure of gas employed, in order that,'as the pressure is reduced. the normal cathode drop may still he maintained. It would not be commercially practicable to make the electrodes sufliciently large to maintain the normality of the cathode drop with the gas at the minimum pressure when conduction has ceased, because to do that would involve the use of electrodes of enormous size.

Commercial practice, therefore, is in the nature of a compromise,the electrodes being substantially larger than the critical area referred to, in order to take care of a substantial reduction of pressure representing the greater part of the life of the tube Then, as the pressure tends to still further decrease, there will be a gradual increase in the cathode drop representing further useful life. The final hours of the tube Will be those in which the sputtering becomes very violent, since this phenomenon is greatest at low pressures.

By means of my invention I am enabled to make a luminous tube in which the electrode area is many times smaller than that required by the class' :al rules of current density, so that a neon beacon, for example, can be made and operated with currents of from 5 to 10 amperes or more and yet the electrodes will be of relatively small size. This is an extremely important consideration in the commercial manufacture of very large luminous tubes where the employment of ordinary interior electrodes might involve the use of glass chambers several feet long and a foot or more in diameter.

The method which I have developed for making these tubes is a specific improvement on the process disclosed in my Patent, No.- .1.618,767, dated February 22, 1927. With the patented process I am enabled to obtain a luminous tube in its complete final state of puritymlirectly from the pumping apparatus and without the necessity of further aging or seasoning, thereby securing a substantial saving of time of manufacture. \Vith my present method I employ the same fundamental idea disclosed in said patent,

, a great saving of time will be effected.

\Vhile the improved process is especially intended for use in the manufacture ofluminous tubes having interior electrodes and finds its greatest value in this field, yet it may be employed in the manufacture of tubes having exterior electrodes.

My objects generally are to provide an im )rovcd luminous tube of high efiiciency and long life and employing electrodes of relatively small size and to provide a process by which such tubes may be economically manufactured, all, as 1 will hereafter described and claim.

In order that the invention may be better understood attention is directed to the accompanying drawing, in which Figure 1 is a perpesctive view of a suitable oven for processing the tubes, showing three tubes therein, the front of the oven being elevated to disclose its interior; and

Figure 2 a side elevation. on a somewhat larger scale, showing a single tube in process of manufacture.

In both of these views corresponding parts are represented by the same numerals.

1 represents the improved luminous tube which is shown as having a straight central portion and enlarged ends 2-2, made'preferably of boro-silica glass having a high melting point, as disclosed in said patent. It will be understood, of course, that the shape of the tube is unimportant.

The enlarged chambers 2-2 of the tube are formed with inwardly-extending necks 3, in which are sealed the conductors 44 leading to the electrodes 5-5. Each electrode is supported upon a neck or tube 6 made prefcrablyof quartz.

The electrodes 55 are made of a conducting material having the property of occluding or absorbing substantial amounts of 'the alkali vapor admitted to the tube, as I will hereafter describe. I have found that graphite or other forms of carbon are admirably suited for the purpose.

The surface area of the electrodes is rela-' tively small, and I have in practice made use of. graphite electrodes having a surface area as low as .6 decimeters per ampere of current with neon gas at a pressure of 7.

m. m. of mercury. Electrodes of this size give excellent results and remain cool in operation, at least for most of the life of the tube, which may be several thousand hours. In processing the improved tubes a number of them are mounted side by side and secured together by tubulations 7 leading to a common tube 8 and supported by .hangers 9 within a suitable oven 10. For the purpose of illustration I show three of these tubes 1 in the oven 10, although the number may be 'more or less. By thus simultaneously processing a plurality of tubes, I very greatly extend the capacity of the ovens and reduce the time required to perform the necessary operations. \Vith the method disclosed specifically in my patent above referred to, one tube at a time is processed and the operationfurther involved the carrying out of the steps which I am now able to dispense with, as I will describe.

The oven 10 is heated in any suitable way, such as by means of gas jets 11 located below a perforated partition 12. It is also provided with a door 13 capable of being lifted up and down or otherwise opened and closed, and said door is provided with one or more sight openings 14 therein covered with mica, in order to permit the tubes within the oven to be observed.

A tubulation 15 depends from each tube preferably near its centre and contains a small quantity 16 of an alkali metal, the vapor of which is to be employed as the purging agent.

The tube 18 extends through one of the I side walls of the oven. and leads to suitable pumping apparatus as indicated. This may be of any suitable and approved type. In my patent I have indicated more specifically a desirable arrangement.

The tube .8 is also provided with *a branch tube 15 leading to a suitable gas supply, such as neon. Valves 16and' to cut oil the tubes which are being processed from the pumping apparatus or gas supply as may be needed.

The conductors 4 are shown in Figure 2 as being connected to the secondary 18 of a transformer, the primary 19 of which is in circuit with a suitable source of alternab ing current 20. All of the tubes have similar electrical connections and their conductors 4 may be connected in multiple with, a single secondary 18, as will be obvious.

Assuming that the tubes are supported within the oven. as shown in Figure 1 and that the" door 13 is closed, the process is carried out as follows:

The pumping apparatus being started, air will be exhausted simultaneously from all the tubes. Vhen the pressure has been sufficiently reduced all the electrodes in the tubes are strongly heated by the passage of a heavy current through the same. The ef-- fect of thus heating the electrodes is to drive off gases occluded therein and to activate the carbon ofwhich they are composed, so as to make it strongly susceptible to the occlusion of the alkali metal vapor when this is provided. The current which is employed for thus activating the'electrodes is substantially greater than the normal value of the current with which the tube is 17 are shown. 1

metal '16 ives. 11 tubes; The tern nature to which the aesegm pends eeaa e m lill to 1): ttiv l em a at ee s a [invariant Pa te Sti e ape a 1 aePQa-a a or h as been thhs through the tubes the heating is dis'cbii' .lfiued and the' tgnbeszarre a-lloyfir fiqfi The pas sage ot the cufrnt is also discontinued. As soon as the oven temperature has dropped sufficiently low, the several tubulations 15 are sealed'ofi so as to arrest the supply of alkali metal vapor and the pumping continues thereafter until substantially all traces of the vapor have been dI'HWILOfi from the tubes, Any residual vapor remaining in the tubes will be too slight to have any efi'ect on the color or electrical characteristics of the tube.

The valve 16 is now closed to cut oil the pump and the valve 17 is opened to permit the introduction into all the tubes of neon or other rare gas at the desired pressure,

'ious 1m purities ab lbentv e a Jpe a are. l-lL ther in automatically,

, mer hea, in wthe-utube 2. An improved luminous tube, comprising a transparent tubular container-having therein a rare gas of the atmosphere under reduced pressure, and interior electrodes within the tube of carbon having an alkali metal vapor occluded therein, "substantially as set forth.

3. An improved luminous tube, comprising a transparent tubular container having therein a rare gas of the atmosphere under reduced pressure, and interior electrodes within the tube of graphite having an alkali inga.

reduced ,pressure, .within the tube of vapor occluded therein, substanti y as set occluded therein, substantially forth. 5. An improved luminous tube, comprismg a transparent tubular container havingneon therein under reduced pressure, and mterior electrodes within the tube of carbon having an alkali metal vapor occluded therein, substantially as set forth.

6. An improved luminous tube, compristransparent tubular container having neon therein under reduced pressure, and interior electrodes within the tube of carbon vmg carsium vapor occluded therein, substantially as set forth- 7. An improved luminous tube, comprising a transparent tubular container having therem a rare gas of the atmosphere under reduced presure, and interior electrodes w thin the tube of carbon having an alkali metalvapor occluded therein, the area of each of said electrodes being less than one square decimeter per ampere of normal curing a transparent neon therein under reduced a tubular rent at a gas pressure of 7 A; m. m. of mer cury, substantiall as set forth.

8. An lmprov luminous tube, compristubular container having pressure, and interior electrodes within the tube of carbon having an alkali metal vapor occluded therein, the area of each of said electrodes being 1cm than one square decimeter per ampere of normal current at a gaspressu're of 7 in. m. of mercury, substantially as set forth.

9. An improved luminous tube, compriscontainer having neon therein under reduced pressure, and interior electrodes within the tube of carbon having caasium-va r occluded therein, the area ofeach of said electrodes being less than one square decimeter per ampere of normal current at a gas pressure of 7% m. m. of mercury, substantially as set forth.

10. The method of processing luminous forth.

11. The method of processing luminous tu having interior carbon electrodes and provided with a tubulation containing caesium, which consists in passing a heavy rent between the electrodes to activate them, in creating a partial vacuum within the tube and tubulation, in subjecting both the tube and tubulation to a heated atmosphere, whereby under the reduced pressure caesium vapors will be evolved and will be diffused through the tube and become occluded in the electrodes, and in passing a current of substantially normal value between the electrodes before sealing off the tubulation until under the spectroscope the spectrum of caesium. is alone visible, substantially as set forth.

12. The method of processing" luminous tu containing interior electrodes of carbon and provided with a tabulation containing caesium, which consists in creating a partial vacuum Within the tube and tubulation, in then activating the electrodes-in then subjecting the tube and tabulation to the eflect of heat, whereby under thereduced pressure caesium vapor will be evolved and will be difi'used through the tube so as to be occluded in the electrodes, in maintaining a current of substantially normal value within the tube, before sealing oil the tubulation, said current being maintained until the pure caesium spectrum is alone visible, in then redu the temperature of the tube and continuing the exhaustion so as to remove substantially all of the free vapor within the tube and in finally admitting the desired rare gas withinthe .tube, substantially as set forth.

RAYMoNn R. MACH'LETT.

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