US3298769A

US3298769A - Method and apparatus for making electron discharge devices

Info

Publication number: US3298769A
Application number: US422753A
Authority: US
Inventors: Charles L Toomey
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1964-12-31
Filing date: 1964-12-31
Publication date: 1967-01-17
Anticipated expiration: 1984-01-17
Also published as: GB1134639A

Description

i-uv T a 6 73 11a 1 11 w EZECTKOZZE l6 'VOZTHGE 2/0000 G/IUS-QV 1,2 q 1o B2 (2500 6/21/55) v I Jan. 17, 1967 TOOMEY A 3,298,769

METHOD AND APPARATUS FOR MAKING ELECTRON DISCHARGE DEVICES Filed Dec. 51, 1964 INVENTOR.

United States Patent Oil-ice 3,298,769 Patented Jan. 17, 1967 3,298,769 METHQD AND APPARATUS FOR MAKING ELECTRON DISCHARGE DEVICES Charles L. Tourney, Danvers, Mass., assignor to Sylvania Electric Products, Inc., a corporation of Delaware Filed Dec. 31, 1964, Ser. No. 422,753 7 Claims. (Cl. 316-15) This invention rel-ates to the manufacture of electron discharge devices, and particularly to discharge devices having an electrode within an envelope containing gas, even in residual quantities, at a stage of manufacture when the electrode and its coating, if any, are resistively heated to release gases therefrom. a

One example of such devices is the fluorescent lamp comprising a glass envelope with an internal fluorescent coating, enclosing afill of-mercur-y and inert gas, and including spaced emissively coated electrodes for supporting an arc discharge by thermionic electronemission and ion counterflow. In the process of manufacturing a fluorescent lamp gaseous impurities are removed by exhausting atmosphere from the lamp and flushing it with an inert gas, either simultaneously or sequentially. -Then, prior to adding the mercury and inert gas and. sealing the envelope, each electrode is processed by passing a current through it to heat it resistively and dispel gases. Generallythese steps are performed in many discharge devices whether mercury filled or not, or whether the electrode is coated or not. In fluorescent lamps the electrode, prior to processing is coated with a mixture of alkaline earth carbonates which are subsequently decomposed to emissive oxides by the above mentioned resistive heating with the release of carbon dioxide. Also, gases entrapped in the electrode metal are driven out by the heating. At the time the electrode is resistively heated other residual gases in various quantities will be present. And at the low pressure of the exhaust they will have a determinable ionizationpotential.

To bring the electrode to the desired temperature, typically in the order of 1450 C'., it is necessary to pass current through the electrode at a volt-age above the ionization potential of the residual gases. Hitherto the residual gases, including those dispelled from the electrode, have ionized well below the voltage required to produce the desired electrode temperature. When ionized, the residual gases form a conductive path shunting the current intended to heat the electrode and preventing adequate outgassing of the electrode and its coating. An inadequately outgassed electrode produces a lamp which is diflicult or impossible to start, which quickly develops discoloration, and which has a short life.

Thus, the object of the present invention is to provide a Way in which an electrode of a discharge device may be resistively heated to a desired temperature despite the presence of ionizable gases.

According to the invention the process of making an electron discharge device having an electrode within an envelope containing gas comprises heating the electrode by passing a current therethrough at a voltage above the ionization potential of the gas, and simultaneously apply ing a magnetic field to the electrode thereby to inhibit ionization of said gas adjacent the electrode and shunting of electrode current through ionized gas.

Further according to the invention apparatus for outgassing the electrode within the envelope of an electron discharge device containing a gas ionized at a predetermined potential comprises means to supply current through said electrode at a voltage in excess of said potential resistively to heat said electrode to outgassing temperature, and means to apply to said electrode a magnetic field of strength to suppress ionization of the gas and prevent shunting of said current through ionized gas.

For the purpose of illustration typical embodiments of the invention are shown in the drawing in which:

FIG. 1 is a schematic diagram showing one way of processing a fluorescent lamp electrode;

FIG. 2 is a graph of electrode current versus electrode potential for diiferent values of applied magnetic field; and

FIG. 3 is a schematic diagram showing another Way of processing an electrode.

. Shown fragmentarily in FIG. lis a typical fluorescent lamp under manufacture comprising a tubular envelope 1 whose inner surface 2 carries a phosphor coating. At each end of the envelope 1 is an electrode structure and mount including a glass stem 3 sealing the end of the envelope and having an exhaust tube 4 communicating through the stem with the interior of the envelope. Two

lead wires 6 extend through a press portion 7 of the stem. Across the inner ends of the leads wires 6 is a coated electrode 8 which may be of the coiled-coil or triple-coiled type.

At the stage of manufacture shown the lamp has been heated, flushed with inert gas and exhausted by a pump P to about 100 microns to 10 millimeters pressure leaving some residual gases within the envelope. At this point the alkaline earth carbonates are decomposed to active oxides by heating the electrode, which heating also drives off the produced carbon dioxide. In fluorescent lamps, as well as other discharge devices having uncoated electrodes, it is also highly advantageous to remove gases en trapped in the wires forming the electrode 8. To heat the electrode a voltage is applied from a suitable alternating current source E to the lead wires 6 causing the electrode to be heated resistively by current through it.

To reduce the carbonate and to release entrapped gases the electrode must be heated as high as 1450 C. To reach such temperatures voltages Well in excess of operating voltage must be applied to the electrode to draw suflicient current.

. 2 at and above this voltage the residual gases in the envelope i-onize and shunt current around the electrode so that further increase in the voltage across and the current through the electrode is not possible.

According to the invention the shunting effect of the residual gases is suppressed by applying an external magnetic field B through the envelope 1 and the electrode 8 at the same time that the heating current is applied. As shown in FIG. 1 the field is produced by coils 9 wound on cores 11 and supplied by a battery E or any other suitable direct current source. Typically the field B of the magnet is in the order of 500 to 2500 gauss, and many more turns 9 than are shown will be required. A permanent magnet of such strength may be used instead of the electromagnet shown in FIG. 1. And, as shown in FIG. 3, an electromagnet supplied with alternating current may be used.

On FIG. 3 the primary T1 of a transformer is connected to alternating current lines A, C. One transformer secondary T2 is connected to the coils 9a of an electromagnet wound on cores 11a. The filament 8 of the lamp to be processed is connected to a transformer secondary T3 such that current through the electrode is substantially in phase with current through the electromagnet coils 9a.

By applying a magnetic field to the electrode 8 or 8:: at the same time the electrode is heated resistively, the high voltages necessary to heat the electrode to decom- For example, a typical VHO lamp electrode requires a current of 2.7 amperesv for proper posing and outgassing temperature may be applied across the electrode, even though the voltage exceeds the normal ionization potential of the residual gases present, without causing the gases to ionize and shunt the electrode current.

In FIG. 2, two examples of relation between electrode voltage and current and the external field are shown. Curve Bl shows the values of electrode current versus electrode current with an applied field of 1000 gauss. With such a field a voltage of nearly 16, well above the normal ionization potential of about 9 volts on curve B0, will produce an electrode current of about 2.8 amperes, more than needed to produce the desired processing temperature. With a field of 2500 gauss electrode voltages over 18 and currents over 3.2 amperes may be obtained as shown by curve B2.

The values given are typical for a VHO lamp when a direct current field B is directed at the preferred angle of 45 to the axis 801 of the electrode as shown in FIG. 1. However, the relative angle of the field B may be as shown in FIG. 3, or any other value between 0 and 90 with only slightly reduced effectiveness.

Thus it should be understood that the present invention is not limited by the illustrative examples but comprises all modifications and equivalents falling within the scope of the appended claims.

I claim:

1. In the process of making an electron discharge device having an electrode within an envelope containing gas, the steps comprising heating the electrode by passing a current therethrough at a voltage above the ionization potential of the gas, and simultaneously applying a magnetic field to the electrode thereby to inhibit ionization of said gas adjacent the electrode and shunting of electrode current through ionized gas.

2. The process according to claim 1 wherein said current and magnetic field are alternating and in phase at the same frequency.

3. The process according to claim 1 wherein the magnetic axis of said field is at an angle of 45 to the axis of the electrode.

4. In the process of making an electron discharge device including an envelope and an electrode therein for treatment above a predetermined temperature, the steps comprising exhausting the envelope to leave a residue of gas normally ionizable at a predetermined potential, passing a current through the electrode at a voltage above said normal ionization potential and effective to heat the electrode resistively to said predetermined temperature, and simultaneously applying to the electrode an external magnetic field of strength to inhibit ionization of said gas adjacent said electrode, thereby to prevent said gas from shunting said current around the electrodes and preventing heating of the electrode to said predetermined treatment temperature.

5. In the process of making a fluorescent lamp including an envelope and an electrode therein with a coating decomposable to emissive state above a predetermined temperature, the steps of exhausting the envelope to leave a residue of gas, passing a current through the electrode at a voltage above the normal ionization potential of the gas to heat the electrode resistively to said predetermined temperature and thereby decompose said coating to emissive state, and simultaneously applying to the electrode an external magnetic field of strength to inhibit ionization of said gas adjacent the electrode, thereby to prevent said gas from shunting said current and preventing heating of the electrode to said predetermined temperature.

6. Apparatus for outgassing the electrode within the envelope of an electron discharge device containing a gas ionizable at a predetermined potential, comprising means to supply current through said electrode at a voltage in excess of said potential resistively to heat said electrode to outgassing temperature, and means to apply to said electrode a magnetic field of strength to suppress ionization of the gas and prevent shunting of said current through ionized gas.

7. An apparatus for outgassing the electrode of a fluorescent lamp having an envelope around the electrode, said electrode having a coating decomposable to emissive state above a predetermined temperature, comprising means to exhaust and maintain the envelope at a pressure of residual gas normally ionizable at a predetermined potential, an electnomagnet for applying a magnetic field through the envelope to the electrode, and a transformer having a primary for connection to an alternating current source, a first secondary for supplying alternating current through the electrode at a voltage above the normal ionization potential of said residual gas, thereby to heat the electrode resistively to said predetermined temperature and decompose said coating to emissive state, and said transformer having another secondary for supplying alternating current to said electromagnet substantially in phase with the current through said electrode, whereby said electromagnet field inhibits ionization of said gas adjacent the electrode and permits heating of the electrode to said predetermined temperature.

No references cited. RICHARD HQEANES, ]R., Primary Examiner.