US3277685A - Electrical heaters - Google Patents

Description

Original Filed March 11, 1960 Oct. 11, 1966 H. F. DICKSON, JR., ET AL 3,277,685

ELECTRICAL HEATERS 5 Sheets-Sheet l U 56 /ZZ :51 g. E l 36 I 4/ 3.9 39 INVENTORS 4 HERBERT E D/c/rso/v Jv.

PAUL rv /ms ATTORNEY Oct. 11, 1966 DICKSON, JR" ETAL 3,277,685

ELECTRICAL HEATERS Original Filed March 11, 1960 3 Sheets-Sheet 2 fly;- 7

IN VENTORS HERBERT i. D/cnso/v JR.

7nuL Hans ATTORNEY Oct. 11, 1965 o c so JR" ETAL 3,277,685

ELECTRICAL HEATERS Original Filed March 11, 1960 5 Sheets-Sheet 5 PAUL Hxms ATTORNEY United States Patent 3,277,685 ELECTRICAL HEATERS Herbert F. Dickson, Jr., and Paul Haas, Seneca Falls,

N.Y., assignors to Sylvania Electric Products Inc., a corporation of Delaware Original application Mar. 11, 1960, Ser. No. 14,471, now Patent No. 3,160,946, dated Dec. 15, 1964. Divided and this application June 12, 1963, Ser. No. 287,401 Claims. (Cl. 72-146) This application is a division of Serial No. 14,471, filed March 11, 1960, entitled Electrical Heaters, now Patent No. 3,160,946, issued on December 15, 1964, and assigned to the same assignee as the present invention.

This invention relates to heaters for electrical devices and more particularly to heaters adapted for use with thermionic cathodes of the type employed in electron tubes.

It has been proposed that a low heater power type of cathode assembly may be used in electron tubes. One form of such a heater-cathode assembly employs an insulated heater wire embedded in the cathode base. In this structure the cathode base metal material in powdered form is deposited about the heater wire and subsequently the powder is pressed into a pellet and sintered.

It is difiicult to make a satisfactory heater embedded cathode assembly. The pellet itself is small and the requirements for electron emission at low heater power are such that a considerable length of the heater wire must be packed within the pellet. In order to achieve the proper uniform temperature of the cathode pellet, the heater should physically be uniformly and symmetrically placed, there should be no shorted sections of the heater, and the heater-cathode leakage should be a minimum.

The fabrication of the heater itself is an important factor in achieving the requirements enumerated above. For instance, the heater wire should be formed into a configuration to provide a relatively large amount of wire Within the pellet, and the configuration should be symmetrical with uniform sectional spacings. In addition, the insulating coating should be of uniform thickness over the enitre embedded heater portion.

Accordingly, it is an object of this invention to fabricate a heater adapted for use in heater embedded cathode assemblies.

It is a further object to form a substantially fiat heater coil with uniform coil wraps, uniform spiral turn spacings, and a uniform coating.

The foregoing objects are achieved in one aspect of the invention by the provision of a process and apparatus for forming a spiral reverse coil wound heater. The resistance heater wire is spiral wound upon a mandrel and this wire spiral and mandrel assembly are subsequently twisted into a reverse wound flat coil with substantially uniformly spaced wraps. The mandrel is then removed and the heater wire spiral is coated with insulating material. In the coil winding operation, the mandrel is placed in a chuck and twisted with the ends of the mandrel arrested from rotational movement by stop pins.

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 a length of heater wire spiral wound upon a mandrel;

FIG. 2 shows the heater coil winding device;

FIG. 3 is an enlarged top view of the heater winding chuck employed with the device of FIG. 2;

FIG. 4 illustrates a cross-sectional view of the heater winding device;

FIGS. 5, 6, and 7 illustrate the manner reverse heater coil;

of forming the 3,277,685 Patented Oct. 11, 1966 method of annealing the formed FIG. 8 illustrates the heater coil;

FIG. 9 shows the manner of removing the mandrel from the heater spiral;

FIG. 10 illustrates the heater coating operation; and

FIG. 11 is a plan view of a finished spiral reverse coil wound flat heater.

Referring to the drawings, a spiral reverse wound substantially fiat coiled heater 13 is shown in FIG. 11. The heater resistance wire 15 is formed into a spiral which is in turn twisted as a reverse wound coil. Each turn of the spiral is coated with an electrical insulating material 17 except the last several turns. The straight wire ends 19 are left uncoated to allow for welding to the heater power supply leads when employed in an electron tube.

Heater 13 is uniquely adapted to provide maximum heat for a given area with minimum power. Due to its relatively small size, compactness and uniform spacing and symmetry, the heater is suitable for use in an indirectly heated cathode assembly wherein the heater is embedded in the cathode base material. This type of cathode assembly is shown and described in co-pending application S.N. 14,472, now Patent No. 3,097,419, issued on July 16, l963,'entitled Heater-Cathode Assemblies, filed concurrently herewith by the common assignee.

FIG. 1 illustrates a spiral length of heater wire 15 which has been selected to provide the heat necessary for a given application at a given power rating. The wire, which may be tungsten, is wound upon a mandrel 21 made of, for instance, molybdenum. The diameter of thewire, turns per inch of the spiral, and length of the heater can be varied in order to produce the desired electrical characteristics. In the spiral winding operation, the wire 15 is preferably stretched beyond the elastic limit so that the initial spiral shape will be substantially maintained after mandrel 21 has been removed as will be hereafter described.

The mandrel and wire spiral assembly 22 are subsequently formed or twisted into a substantially fiat reverse wound coil. A winding device 23 is provided for the purpose of accomplishing this reverse winding operation. Referring to FIGS. 2-7, device 23 comprises a cylindrical block 25 having an aperture 27 extending longitudinally therethrough. The upper heater supporting surface 29 may be tapered a slight amount, e.g., several degrees, radially symmetrically downward from aperture 27 toward the periphery of the block 25 to prevent the wire spiral from climbing over itself during the twisting operation.

Mounted upon surface 29 are two frusto-conical shaped arresting pins 31. The small diameters of the pins lie adjacent surface 29 so that the pins are beveled outwardly to prevent the ends of mandrel 21 from riding upwardly and to provide a drag on the mandrel during the coil wrapping operation. Pins 31 preferably exceed the height of the spiral of wire and are oppositely disposed from and equally radially spaced from the center of aperture 27. For simple reverse wound coils, the pins may be permanently located as shown. However, for larger or more intricate coil configurations, it may -be desirable to either move the pins radially during the winding operation or to raise and lower a plurality of pins sequentially from surface 29.

Block 25 rests upon a cylindrical base 33 having a rod 35 passing through aperture 27. The upper end of the rod has a chuck 36 formed with a spiral and mandrel assembly receiving slot 37 defined by laterally spaced slot walls 39. The opposed outside edges 41 of the walls are recessed from the rod periphery and are curved to meet a portion of the rod periphery to provide the initial coil wrap configuration. The height of the walls preferably exceed the diameter of the wire spiral. Since block 25 merely rests upon base 33, these parts may be rotated relative to one another. The amount of rotation of, for instance, base 33 or chuck 36 relative to block 25 may be ascertained from pointer 43 and markings 45. Also, base 33 and block 25 may reciprocate longitudinally relative to one another so that chuck 36 can be retracted to a mandrel assembly release position.

In the reverse coil winding operation, assembly 22 is first placed within slot 37 as shown in FIG. 2. When a symmetrical reverse coil such as is illustrated in FIGS. 7 and 11 is desired, the center of assembly 22 is positioned at the center of the slot. The initial partial Wrap of the coil is achieved by applying tension to the mandrel and rotating base 33 to provide rotation of chuck 36, FIG. 5. The tension may be applied by holding the ends of mandrel 21 to provide drag and therefore bending around the edges 41 of walls 39, or it may be accomplished by pressing downwardly against the spiral and mandrel to achieve the same results. After the partial first wrap is made, chuck 36 is further rotated until assembly 22 contacts arresting pins 31. Continued rotation of the chuck wraps the spiral wire and mandrel assembly as shown in FIG. 6. Due to the beveled sides of arresting pins 31, assembly 22 tends to become trapped between the pins and the upper block surface 29. This trapping action creates a drag on the mandrel and thereby provides relatively tight Wrapping. During this latter rotational movement, some overwrappin-g is desired. The amount of overwrapping depends upon the spacing re quired between sections of the coil 13.

After the spiral wire and mandrel assembly 22 have been wound as a reverse coil as shown in FIG. 6, chuck 36 is then rotated in the opposite direction. During this rotation, assembly 22 contacts pins 31 on the opposite sides thereof, which causes the coil to unwrap an amount sufiicient to provide the coil spacing desired, see FIG. 7. The ends of the coil thereby extend tangentially from the curvature of the outside turns. Rod 35 with its chuck 36 is then retracted into aperture 27 to release the substantially flat reverse coil formed from assembly 22. The releasing operation is achieved by moving base 33 or block 25 longitudinally away from one another.

After assembly 22 has been wound into a reverse coil, it is placed in an oven (not shown) and fired between flat tungsten plates 47, see FIG. 8. The firing operation may be performed in a wet hydrogen reducing atmosphere in accordance with the temperature-time relationship required for annealing wire 15 and mandrel 21. The substantially fiat coil is then immersed in a solution 49 which removes the mandrel by selective etching, see FIG. 9. A suitable solution such as one consisting of 50 percent nitric acid, 30 percent sulfuric acid, and 20 percent water by Weight is capable of etching a .002 inch diameter molybdenum mandrel in a relatively short time without attacking the tungsten wire 15.

The reverse wound coil of wire may be subsequently rinsed in deionized water and subsequently electrophoretically coated in tank 50 with the insulating material 17. During the coating operation, the coil of wire 15 is held in electrode 51, FIG. so that the area to be coated is exposed to coating bath 53, which may consist of a dispersion of aluminum oxide in a partially hydrolized aluminum nitrate and alcohol solution. Electrode 51 shields the last several turns of wire and the ends 19 so that no coating is deposited thereon. The uncoated portions of the wire are utilized for a welding connection during ultimate assembly in an electron tube. An anode 55 is also disposed in bath 53, and positive and negative potentials are applied to anode 55 and electrode 51 respectively to electrophoretically coat wire 15 in a manner well understood in the art. Due to the uniformity of spacing between the spiral turns and coil wraps, the insulating coating is uniformrly deposited over the desired area.

After coating, wire 15 is subsequently fired between flat plates of the type shown in FIG. 8. Here again, a wet hydrogen atmosphere may be used during this operation. Firing of the wire assures flatness of the coil, it removes any distortion in the reverse coil wraps, and it sinters the insulating coating 17 to produce the reverse coil wound spiral heater 13, shown in FIG. 11.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What is claimed is:

1. A device for winding turns of heater wire comprising a block having a heater supporting upper surface and an aperture extending longitudinally therethrough, a lurality of heater movement arresting pins mounted upon said surface and radially spaced from said aperture, and a rod rotatably mounted in said aperture having a heater chuck formed at the end thereof to twist the heater wire during rod rotation into a substantially flat reverse wound coil having uniform spacing and symmetry While the ends of said Wire are arrested from rotational movement.

2. A device for winding turns of heater wire comprising a block having a heater supporting upper surface and an aperture extending longitudinally therethrough, and a plurality of outwardly beveled heater arresting pins mounted upon said upper surface, the pins being radially spaced equally from said aperture, in combination with a rod rotatably mounted in said aperture formed to provide a chuck at the end thereof having a heater wire receiving slot therein to provide upon the rotation of said rod a substantially flat reverse wound coil having uniform spacing and symmetry.

3. A device for winding turns of heater Wire comprising a block having a heater supporting upper surface and an aperture extending longitudinally therethrough, said upper surface being tapered radially symmetrically downward from the aperture toward the periphery of said block, and two outwardly beveled heater arresting pins mounted upon said upper surface, the pins being oppositely disposed from and radially spawd equally from said aperture; in combination with a rod rotatably mounted in said aperture formed to provide a chuck at the end thereof with a heater receiving slot formed by laterally spaced Walls.

4. A device for Winding turns of heater wire comprising a block having a heater supporting upper surface and an aperture extending longitudinally therethrough, said upper surface being tapered radially symmetrically downward from the aperture toward the periphery of said block, and two frustro-conical shaped heater arresting pins mounted with the smaller diameters thereof upon said upper surface, the pins being oppositely disposed from and radially spaced equally from said aperture; in combination with a rod rotatably mounted in said aperture formed to provide a chuck at the end thereof with a heater receiving slot formed by laterally spaced walls, the opposed outside edges of said walls each being recessed from the rod periphery and having a curvature to meet a portion of the rod periphery to provide a substantially symmetrical initial coil wrap configuration.

5. A device for winding turns of heater wire comprising a block having a heater supporting upper surface and an aperture extending longitudinally therethrough, said upper surface being tapered radially symmetrically downward from the aperture toward the periphery of said block, and two frustro-conical shaped heater arresting pins mounted with the smaller diameters thereof upon said upper surface, the pins being oppositely disposed from and radially spaced equally from said aperture; in combination with a rod rotatably mounted in said aperture formed to provide a chuck at the end thereof with 5 6 a heater receiving slot formed by laterally spaced walls, References Cited by the Examiner the opposed outside edges of said Walls each being UNITED STATES PATENTS recessed from the rod periphery and havmg a curvature formed to meet a portion of the rod periphery to provide 1,841,784 1/1932 Brown 72-456 a substantially symmetrical initial coil Wrap configura- 5 FOREIGN PATENTS tion, said chuck being reciprocatingly mounted in the 1178 741 12/1958 France block aperture for movement between an extended heater Winding position disposed above said upper surface and CHARLES LANHAM Primm'y Examine" a retracted heater release position. R. D. GREFE, Assistant Examiner.

Claims (1)

1. A DEVICE FOR WINDING TURNS A HEATER WIRE COMPRISING A BLOCK HAVING A HEATER SUPPORTING UPPER SURFACE AND AN APERTURE EXTENDING LONGITUDINALLY THERETRHOUGH, A PLURALITY OF HEATER MOVEMENT ARRESTING PINS MOUNTED UPON SAID SURFACE AND RADIALLY SPACED FROM SAID APERTURE, AND A ROD ROTATABLY MOUNTED IN SAID APERTURE HAVING A HEATER CHUCK FORMED AT THE END THEREOF TO TWIST THE HEATER WIRE DURING ROD ROTATION INTO A SUBSTANTIALLY FLAT REVERSE WOUND COIL HAVING UNIFORM SPACING AND SYMMETRY WHILE THE ENDS OF SAID WIRE ARE ARRESTED FROM ROTATIONAL MOVEMENT.

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