US3097419A

US3097419A - dickson

Info

Publication number: US3097419A
Authority: US
Priority date: 1960-03-11
Publication date: 1963-07-16
Anticipated expiration: 1980-07-16
Also published as: FR1287645A; US3277685A; DE1186559B; US3160946A; GB908096A; NL262042A; US3092748A

Description

H. F. DICKSON, JR HEATER-CATHODE ASSEMBLIES July 16, 1963 Filed March 11, 1960 2 Sheets-Sheet 1 ""---"mi In W llmmmm HN HI E Win &

iiiiiiim INVENTOR Herbs/f ED/ckson Jr:

H. F. DICKSON, JR

2 Sheets-Sheet 2 HEATER-CATHODE ASSEMBLIES July 16, 1963 Filed March 11, 1960 INVENTOR flerberf 7F .D/cksm J: BY

WJM

ATTORNEY United States Patent 3,097,419 HEATER-CATHODE ASSEMBLIES Herbert F. Dickson, Jr., Seneca Falls, N.Y., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Mar. 11, 1960, Ser. No. 14,472 2 Claims. (Cl. 29-155.62)

This invention relates to heater-cathode assemblies of the type adapted to be used in electron discharge devices, and more particularly to methods for fabricating these assemblies wherein the heater is embedded in the thermionic cathode base metal by powder metallurgy techniques.

It is becoming increasingly more important to lower 3,097,419 Patented July 16, 1963 'ice . pacting pressure on the pellet;

the operating power requirements of electron discharge devices such as radio and cathode ray tubes so that they will be better suited for use with, for instance, portable and transistorized electrical equipment. One power requirement which needs to be reduced is that used by the heater to operate the cathode. In order to lower this power requirement, it hasbeen suggested that a length of insulated heater wire be embedded in the cathode base metal so that there is maximum heat energy transfer from the heater to the'cathode base.

Heretofore, it has been ditficult to produce a satisfactory heater embedded cathode assembly. One process that has been proposed suggests aligning two halves of a preformed cathode pellet, with a heater residing there between in formed grooves, and pressing the halves together to temporaliy bond them. The pellet is then sintered to form the cathode-heater base assembly. In such a process, generally the heater does not make adequate and equal intimate contact with the pellet segments and it is seldom centrally located within the pellet. Therefore, the cathode is not adequately and uniformly heated. Also, a number of heater-cathode shorts and heater-cathode leakage rejects occur when the pellet halves are mated and compressed due to the fact that the heater insulating coating is chipped and crushed by the pre-formed contour of the pellet. Generally, the heater is somewhat distorted and willnot lie in an exact pre-formed groove configuration over its entire length. This is especially true where a complex heater form is utilized in order to pack a large length of heater wire into a small cathode base pellet.

Accordingly, it is an object of this invention to produce a heater embedded cathode assembly having uniform heating characteristics.

A further object is to reduce heater-cathode shorts and leakage in heater embedded cathode assemblies.

The foregoing objects are achieved in one aspect of the invention by the provision of a process for fabricating a heater-cathode pellet assembly wherein substantially equal charges of cathode base metal powder are deposited into each half of a segmented pelletizing die. The heater is then placed between the die halves and the powder is compacted under substantially equal pressure from opposite sides of the heater to form a heater embedded cathode pellet assembly. This pellet is subsequently sintered and may then be coated with a materail capable of being rendered electron emissive.

For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates the formation of equal charges of metal powder through the use of reservoirs;

FIG. 2 shows a charge of metal powder being removed from one of the reservoirs;

FIG. 10 illustrates the method of ejecting the pellet from the die half shown in FIG. 3; and

FIG. 11 illustrates the completed heater embedded cathode assembly.

Referring to the drawings, an indirectly heated thermionic cathode assembly 13 is shown with. a heater 15 embedded in a cathode base metal pellet 17. The heater,

9 may be formed as a spiral reverse wound flat coil of the type shown and described in a co-pending application of Herbert F. Dickson, Jr., et al., Serial Number 14,471,

. entitled Electrical Heaters, filed concurrently herewith FIGS. 3 and 4 illustrate two halves of the segmented pelletizing die used in the process;

by the common assignee. Insulating coating '19 covers at least the embedded portion of heater 15 while the ends 21 thereof are left bare to allow electrical connections to be made with the heater power supply. Pellet 17 is coated on one surface with a material 23 capable of being rendered electron emissive after processing. Materials commonly employed for this purpose are carbonates of barium, strmontium and calcium, which convert, upon heating, to oxides of these metals. The oxides in turn combine with the base metal of pellet 17 to produce the electron emissive material'in the finished electron discharge device. A tab 25 is welded to pellet 17 to provide an electrical connection for the cathode.

Assembly 13 is made by powder metallurgy techniques in a manner which produces remarkable results. For instance, the assembly shown in FIG. 11 has been satisfactorily formed with a pellet diameter of .050 inch and a thickness of .011 inch. Such a cathode has an external heating radiating surface of only .0054 square inch compared to the conventional indirectly heated 6.3 volt sleeve radiating surface of .136 square inch or a 25/1 reduction. It is notable that electron emission is achieved with assembly 13 equal to the conventional 6.3 volt 600 milliampere television picture tube assembly while using less than 6 percent of the latters power requirements. Normally, the 600 milliampere heaters use over 4 watts of power while the cathode embodied in the present invention may use less than .2 watt at 1.5 volts. These advantages are brought about by uniformly forming and embedding an insulated heater under uniform pressure centrally in compacted metal powder which is uniformly distributed within and around the heater. When such a structure is achieved, the heat energy transfer from heater 15 to cathode base metalpellet 17 is maximum and uniform, while the radiation losses are minimum.

Referring to FIG. 1, quantities of cathode base metal powder 27 such as nickel or one of many suitable nickel alloys are measured by pouring the powder into reservoirs accurately formed as conical depressions 29 in a nonmagnetic plate 30. The excess powder is removed by brushing or wiping the plate in some manner such as with blade 31. Each reservoir is calculated to hold equal charges of the powdered metal. When forming a pellet 17 having a diameter of .050 inch and thickness of .011 inch, each reservoir 29 holds a charge of .0020 gram of 320 mesh nickel powder. This amount constitutes half of the finished pellet powder.

A charge of powder 27 may be removed from reservoir 29 and transferred to either half of segmented pelletizing die 33 by an electromagnet 35. The die comprises two

halves

37 and 39 formed with

equal diameter chambers

41 and 43 respectively conforming substantially to the desired diameter of the finished pellet 17. Each chamber is closed at one end by the face 45 of a sliding ram 47. When these rams are retracted,

chambers

41 and 43 are open to receive a charge of powder 27. When the rams are thrust forward, the powder is compacted. Lateral grooves 49 are formed in the surface of die half 37 to accept the ends of heater 15 which will protrude from pellet 17.

In order to accomplish the transfer of a charge of powder 27 from reservoir 29 to the

chambers

41 and 43 without appreciable loss, electromagnet'35 and a nonmagnetic funnel 51 are used. The electromagnet 35 is positioned over funnel 51 and the appropriate chamber, and it is then deenergized so that powder charge 27 drops from the end thereof through the funnel and into the chamber. The powder, though it drops away from the electromagnet 35, by reason of gravitational force, still has a slight amount of residual magnetism, sufficient to make the particles cohere but insufficient'to charge the electromagnet. It has been found preferable to tap'the core of magnet 35 with the opposite pole of a permanent magnet to insure release of all of the powder. FIGS. and 6 illustrate the method of filling

chambers

41 and 43 with equal charges of metal powder 27.

Referring to FIG. 7, the reverse coil wound spiral heater 15 is subsequently positioned on the face of die 37 so that the ends thereof reside in grooves 49. These grooves are at least as deep as the coated diameter of the heater coil. Die halves 37 and 39 are then mated with their

chambers

41 and 43 in alignment and held in this position by clamps 53, FIG. 8. The sliding rams 47 are then thrust inwardly by rods 55 driven by any convenient hydraulic, pneumatic or mechanical means (not shown). This compressive force, which may range from 25,000 to 200,000 p.s.i. serves to compact the nickel powder into a smooth pellet.

It is notable that a high degree of uniformity is used during construction of the compressed pellet assembly. For instance, equal quantities of powder 27 are deposited into

equal diameter chambers

41 and 43. Substantially equal pressures are applied simultaneously to opposed rams 47 and the ram faces 45 are moved approximately the same distance toward heater 15. Under these circumstances, .the heater and its coating 19 are relatively undistorted and undisturbed during compaction of the metal powder since substantially equal pressures are being simultaneously applied over the entire heater'area.

It has been found preferable to hold die

halves

37 and 39 horizontally during the compacting operation as shown in FIG. 8. Since the die segments are made of ferromagnetic metal such as steel, there is a tendency for the nickel powder to remain uniformly distributed in

chambers

41 and 43 by virtue of a small amount of residual magnetism. When the ram faces 45 start forward, the powder flows relatively loosely through the heater coil from opposite directions theoretically to the center to completely fill and surround the heater coil. Therefore, when final compaction of the metal powder occurs, the heater coil as a unit and each circular segment thereof is subjected to a uniform compressive force. Accordingly, very little distortion of the heater or cracking or chipping of the insulating coating occurs. Also, the mass of pellet 17 is uniformly distributed about heater 15. These advantageous characteristics are lessened when the ram pressures are not equal or simultaneously applied, or when there is a tendency for powder from one chamber to move faster through the heater coil as may occur if the die halves were mounted vertically during the compacting operation.

It has been found that there is a tendency for the pellet 17 to bind in the chambers and split laterally upon parting of

die halves

37 and 39 if it is not handled properly. Accordingly, to alleviate this condition, it is preferable to part the die halves somewhat while the compacting pressure is still maintained on pellet 17 as shown in FIG. 9. After parting segments 37 and 39 a small amount, the pressure on rods 47 is released and the die segments are completely parted. Pellet 17 is then ejected by moving rod face 45 above the die half which it has adhered to, usually segment 37,'as shown in FIG. 10.

After the heater embedded cathode pellet has been pressure formed, the metal powder is fused in a sintering operation, which may be carried out in a vacuum furnace above 1100 degrees C. for approximately five minutes. The heater 15 is thereby permanently embedded in fused nickel cathode base pellet 17.

In order to complete formation of assembly 13, the cathode tab 25 is welded to pellet 17, and the electron emissive material coating 23 may then be desposited on the top surface thereof in any conventional manner such as by spraying. Alternatively, the emissive coating may be applied after assembly '13 has been mounted upon supports adapted to be used in the finished tube. This assembly produces excellent emission while requiring minimum heater power and is well adapted for use in electron tubes such as the cathode ray tube shown and described in a co-pending application of Herbert F. Dickson, Jr., et al., Serial Number 14,477, entitled Indirectly Heated Cathode, filed concurrently herewith by the common assignee.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is: i

1. In a process of fabricating a heater-cathode pellet assembly of given diameter and thickness adapted for use in an electron discharge device, the steps comprising filling substantially equal volume reservoirs with a charge of cathode metal powder capable of retaining residual magnetism, magnetically transferring a charge of powder from a reservoir into a cylindrical ferromagnetic metal chamber provided in each half of a segmented pelletizing die, each chamber being closed at one end by a sliding ram to provide substantially equal volume chambers, positioning the heater across the open end of one of said chambers, mating the die halves with the parting line of the die halves in a vertical plane and with the heater held therebetween and with said chambers in alignment, the residual magnetism of said powder maintaining the powder form within the chambers applying substantially equal and opposite pressure at an equal rate to the sliding rams to compact the metal powder uniformly about the heater and into a form having substantially said given pellet thickness and diameter, parting at least slightly the die halves in opposite directions while said rams are maintained under pressure, releasing the pressure on said rams and ejecting said pellet assembly, and heating the pellet assembly to cause sintering of the compacted metal powder.

2. The subject matter of claim 1 in which the pressure applied to the rams ranges from 25,000 to 200,000 pounds per square inch and the sintering of the compacted metal powder is at a temperature above 1100 C.

References Cited in the file of this patent UNITED STATES .PATENTS 2,385,386 Stoffel Sept. 25, 1945 2,520,760 Gallet et al. Aug. 29, 1950 2,749,029 Goetzel et al. June 5, 1956

Claims

1. IN A PROCESS OF FABRICATING A HEATER-CATHODE PELLET ASSEMBLY OF GIVEN DIAMETER AND THICKNESS ADAPTED FOR USE IN AN ELECTRON DISCHARGE DEVICE, THE STEPS COMPRISING FILLING SUBSTANTIALLY EQUAL VOLUME RESERVOIRS WITH A CHARGE OF CATHODE METAL POWER CAPABLE OF RETAINING RESIDUAL MAGNETISM, MAGNETICALLY TRANSFERRING A CHARGE OF POWER FROM A RESERVOIR INTO A CYLINDRICAL FERROMAGNETIC METAL CHAMBER PROVIDED IN EACH HALF OF A SEGMENTED PELLETIZING DIE, EACH CHAMBER BEING CLOSED AT ONE END BY A SLIDING RAM TO PROVIDE SUBSTANTIALLY EQUAL VOLUME CHAMBERS, POSITIONING THE HEATER ACROSS THE OPEN END OF ONE OF SAID CHAMBERS, MATING THE DIE HALVES WITH THE PARTING LINE OF THE DIE HALVES IN A VERTICAL PLANE AND WITH THE HEATER HELD THEREBETWEEN AND WITH SAID CHAMBERS IN ALIGNMENT, THE RESIDUAL MAGNETISM OF SAID POWDER MAINTAINING THE POWDER FORM WITHIN THE CHAMBERS APPLYING SUBSTANTIALLY EQUAL AND OPPOSITE PRESSURE AT AN EQUAL RATE TO THE SLIDING RAMS TO COMPACT THE METAL POWDER UNIFORMLY ABOUT THE HEATER AND INTO A FORM HAVING SUBSTANTIALLY SAID GIVEN PELLET THICKNESS AND DIAMETER, PARTING AT LEAST SLIGHTLY THE DIE HALVES IN OPPOSITE DIRECTIONS WHILE SAID RAMS ARE MAINTAINED UNDER PRESSURE, RELEASING THE PRESSURE ON SAID RAMS AND EJECTING SAID PELLET ASSEMBLY, AND HEATING THE PELLET ASSEMBLY TO CAUSE SINTERING OF THE COMPACTED METAL POWDER.