US3253620A - Making grid-like elements for electron tubes - Google Patents

Description

May 31, 1966 w. R. STUART MAKING GRID-LIKE ELEMENTS FOR ELECTRON TUBES ill! Filed March 20, 1961 INVENTOR. WILLIAM R. STUART ATTORNEY United States Patent 3,253,620 MAKING GRID-LIKE ELEMENTS FOR ELECTRON TUBES William R. Stuart, San Carlos, Califi, assiguor, by mesne assignments, to Varian Associates, a corporation of California Filed Mar. 20, 1961, Ser. No. 96,841 7 Claims. (Cl. 140-715) This invention relates to the art of making grid-like elements for electron tubes and more particularly to a method and apparatus for making extremely accurate grid-like elements.

The term grid-like element as used herein means any element of an electron tube shaped like a grid, whether it be a heater, cathode, grid electrode, or some other element. However, for clarity of description the invention will be explained with particular reference to grid electrodes. The application of the invention to other gridlike elements will be obvious to those skilled in the art.

The grid electrode is an element of electron tubes which is largely responsible for the high cost of manufacture and for the limits on operating capabilities of electron tubes.

The more perfect a grid electrode can be made, the closer is can be placed to adjacent electrodes without shorting, the more advanced can be the electrical charac teristics of the tube such as higher frequency and the more uniform will be the operation of each tube of a given class.

In the past the manufacture of grid electrodes has involved a very large amount of hand labor in manufacturing them and an extremely high degree of skill in mounting them in tubes. This high degree of mounting skill was required because grid electrodes were necessarily imperfect because of the way in which they were made. The high labor content in manufacture and the high skill required for mounting are most pronounced in connection with the manufacture of cylindrical grid electrodes and the mounting of plural cylindrical grid electrodes coaxially in a tube with the grid bars of one of the grid electrodes radially and vertically aligned with the bars of the other grid electrodes. However, it will be obvious that the invention is applicable to the manufacture of other grid electrode shapes, such as planar grid electrodes and to the mounting of single grid electrodes in tubes.

Referring to the pronounced case of the cylindrical grid electrode, the prior method of manufacture has been to wind grid wire on a rod-shaped mandrel so as to form a plurality of parallel wire lengths laying along the length of the mandrel in a cylindrical array. The portions of Wire connecting the lengths together were of course bent over the end of the mandrel. A ring-shaped support for the grid electrode was then slide over the mandrel to a position at a predetermined distance from the end of the mandrel. Next each length of grid wire was individually spot welded to the inside rim of said support ring, a time consum ing and expensive process.

The grid electrodes made by the prior art technique were imperfect. It will be recalled that the lengths of wire had been bent over the end of the mandrel, and'as a result they tend to relieve the stress of these bends by bowing out. To make matters worse, the lengths do not how out uniformly because they pass over the edge of mandrel at different angles to tangents to the periphery of the edge, some at right angles and some at other angles. Those lengths which passed over the end at rightangles tend to bow straight out while those at other angles tend to bow toward or away from each other. In addition, the lengths tended to bend as a result of the curved shape they have developed from the shipping spool. In any event the lengths of wire on grid electrodes made prior to this invention were neither perfectly straight nor perfectly parallel, and these imperfections were of a magnitude visible to the naked eye.

Some of the grid electrodes were of course better than others, and considerable time and skill was wasted rejecting those which were unusable. Moreover endless hours were spent by extremely skillful technicians trying to match grid electrodes for use in tubes having plural grid electrodes, and then orient the plural grid electrodes in a manner of best compromise to obtain as nearly as possi ble a condition where each length of wire in each grid electrode is parallel with and radially in line with the corresponding bar in the one or more additional grid elec trodes.

It is an object of this invention to provide improved electron tubes by providing improved grid-like elements for them.

Another object of the invention is to make grid-like ele ments less expensive to manufacture and install in elec tron tubes, a further object being to make more accurate grid-like elements.

An additional object of the invention is to provide a new method of manufacturing grid-like elements which results in much more accurate structures.

Another object is to provide a new method of manu facturing grid-like elements which permits an accurate structure to be made by brazing.

A further object is to provide eflicient apparatus for making grid-like elements according to the invention.

These and other objects, features and advantages will become apparent from the following description when read in conjunction with the accompanying drawings in which FIGURE 1 is an elevational view of a mandrel without any grid wire on it; 7

FIGURE 2 is an elevational view of the mandrel after grid wire has been wound on it;

FIGURE 3 is an elevational View of the wound mandrel associated with jigging and other elements required for forming a finished grid electrode according to the invention; and

FIGURE 4 is an elevational view of a finished grid elec trode made according to the invention.

Referring in more detail to the drawings, FIGURE 1 shows a mandrel or forming member 5, having a plurality of parallel grooves 6, a notched rim 7, and a tying pin 8 projecting from a shaft portion 9. The upper end of the mandrel is preferably slightly recessed so that the lands between grooves 6 project above the end as shown in FIGURE 1.

FIGURE 2 shows the mandrel of FIGURE 1 after grid wire has been wound on it. The Wire is wound by tying one end on pin 8, laying the wire in one of the notches in rim 7 and along one of the grooves 6, over the end of the mandrel, down along the mandrel in another groove, through another notch in rim 7, across the bottom of rim 7, up through still another notch, and so on until all of the grooves 6 are filled. The wire is then tied on pin 8 and finally cut from the spool. This winding technique results in a plurality of lengths of wire 12 running along the mandrel and a plurality of connection portions 13 passing over the top of the mandrel. Various patterns are available for the connecting portions depending on the sequence in which the grooves 6 are filled. The invention is not dependent upon selection of any particular pattern for connecting portions 13.

The apparatus and procedures thus far described are well known in the art. Past practice next involved sliding a supporting member or ring 15 over the loaded mandrel. The supporting member or ring 15 is also part of the present invention, and, as in the prior practice, has a collar portion 16 which fits snugly around the grid C; Wire lengths 12. According to the prior technique, each wire length 12 was individually spot welded to collar'16 and the lower portions of lengths 12 were broken off at the welds to make a finished grid electrode.

According to the invention the loaded mandrel is inserted in a jig 17 consisting of a base 18 and four upwardly extending legs 19. The two legs in the foreground are cut away in FIGURE 3 for clarity. The base has a central bore 20 through which the shaft portion 9 of the mandrel passes. In practice the base is placed on a flat surface and the loaded mandrel is dropped into place so that the bottom of shaft portion 9 also rests on the flat surface, and then ring 15 is pushed down into contact with the upper ends of legs 19. In this manner the position of support ring 15 is accurately determined relative to the top of the mandrel and the proper length grid electrode is obtained.

The preferred practice of the invention involves brazing the wire lengths 12 to the collar 16. This is accomplished by painting a brazing paint on wire lengths 12 just above collar 16; or the paint can be applied to the inner surface of collar 16 before it is placed on the mandrel. Another possibility is-to plate the wire or rim 16 with a material such as gold which will form a brazing alloy with the base metals involved, such as copper. In any case it is beneficial to cut away the lower portions of the lengths 12, as shown in FIGURE 3,.prior to heating the assembly to brazing temperature. In this way the lower ends of the wire lengths are free to expand and contract Without causing buckling and distortion.

In addition to cutting the lower ends of the wire lengths before brazing, a clamp 22 is placed around the wire lengths before brazing. The clamp is made of several segments, preferably four, provided with grooves 23, around which wires 24 are tightened to hold the segments pressed against the wire lengths 12. The tension of wires 24 is not critical but is preferably suflicient to hold the clamp by friction from sliding down the mandrel by gravity before the brazing step. It should be understood that the grooves 6 are shallow enough relative to the thickness of wire lengths 12 that clamp 22 contacts the wire lengths rather than the lands between the grooves 6. After the wires have been cut and the clamp 22 has been put in place, the entire apparatus shown in FIGURE 3 is placed in a brazing furnace and collar 16 is brazed to wire lengths 12. Next the apparatus is removed from the furnace; the clamp is taken off; the ring 15 and attached wires are removed from the mandrel; and finally the lower ends of wires 12 are broken oif' at the bottom edge of collar 16 to form the finished grid.

When materials for the various parts are chosen with the proper coetficients of expansion relative to each other, the clamp 22 will hold wire lengths 12 firmly in place against the mandrel in grooves 6 during brazing. The result is that when the assembly is placed in a furnace and heated to brazing temperature, the wire lengths 12 are forced to remain in the perfect shapes provided by the grooves 6, and then when the wire lengths are stress relieved by being heated they are stress relieved in perfect position rather than in the distorted shapes they would tend to assume without clamp 22. The term stress relieved signifies the result of the process called stress relieving, defined by Metals Handbook, published by the American Society of Metals, as a process of reducing residual stresses in a metal object by heating the object to a suitable temperature and holding for a sulficient time.

'There are at least two reasons why a grid electrode formed by the invention is so superior in shape to those made by the prior art. One is that according to the prior art, even if each wire length 12 remained in its groove during spot welding, it was not stress relieved because welding provides only a very local heating. Thus as soon as the mandrel is removed after spot welding, the wire lengths bowed out of shape as a result of the internal stresses caused by bending the Wire onto the mandrel and the stresses caused by bending the wire onto the carrying spool. Another reason for the relatively poor results of the prior practice is that not only did it not relieve stresses, it created them due to the extremely localized heating effect of spot welding. An incidental but extremely important benefit of the invention is that the brazed connection between wire lengths 12 and collar 16 has such an improved thermal efiiciency over the prior spot welds that in tubes in which the prior grid electrodes operated so hot that'they had to be gold coated to prevent electron emission, the new grid electrodes run so cool that the expensive gold coating can be eliminated.

Various materials and temperatures will now be described in more detail. A preferred material for the mandrel '5 is stainless steel having a high chrome content, such as No. .304 stain-less steel made by the International Nickel Company. One of the problems with the new process was the problem of keeping the wire lengths from be coming brazed to the mandrel as well as to the support ring 15. This problem was solved by providing a stable oxide coating on .the mandrel, which in the case of No'. 304 steel is chrome oxide obtained by firing in wet hydrogen. In one application of the principles of the invention the support ring 15 is made of copper; the clamp 22 is made of No. 304 steel; the tension wire 24 is .020 inch diameter molybdenum; the grid wire is .0108 inch diameter molybdenum; and the brazing material is coppernickel-gold in paste form. The assembly is heated in an oven to a temperature of about 1045 C. for about 10 minutes or more. Uniformly heating the grid wire (while pressed against the mandrel) to a temperature which results in any stress relieving of the grid wire will result in more perfect grid electrodes than those made by the prior art. However, the optimum result is obtained by heating the grid wire to recrystallization temperature as defined in Metals Handbook, published by the American Society for Metals, in the following words: the lowest temperature at which the distorted grain structure of a cold worked metal is replaced by a new strain-free grain structure during prolonged annealing. Time, purity of the metal, and prior deformation are important factors.

Different materials can be used for the various parts but certain features and relations must [be maintained. For example the mandrel must have a surface which will not braze to the grid. The relative coefiicients of expansion of the mandrel and support ring 15 must be such as to prevent the collar .16 from expanding away from the wire lengths .12 during brazing. The coefiicient of expansion of tension wire 24 must be no greater than the mandrel and preferably less so that firm pressure of the clamp 22 against the wire lengths is assured at high temperature when the grid wire is stress relieved. A different type of clamp could be used; for example, an apertu-red one-piece clamp could be used if its mandrel receiving aperture were machined to close tolerance and if the coefiicients of expansion were in just the right relation to cause pressure between the clamp and the wire lengths during brazing. As previously mentioned the teachings of the invention are applicable to any grid-like element for an electron tube. For example the invention could (be used to make other than cylindrical shapes and have other than all parallel wires simply by changing the shape of the mandrel and the pattern of its grooves. If in some cases it would be desirable or necessary to bond the wire lengths .12 to collar 16 first by some localized heating process a teachmg of the invention could still be applied by thereafter heating :the grid Wire uniformly with the clamp 22 in.

place.

I claim:

1. A method of making a grid-like element for electron tubes comprising the steps of bending wire onto a forming member to make a desired shape, placing a support member in contact with the formed grid Wire, positioning a clamping structure around said forming member in contact with the formed grid wire, said clamping structure having a lower coefiicient of expansion than said forming member, and by the application of heat simultaneously brazing said support member to the formed grid wire and compressing the wire between the forming member and clamping structure.

2. A method of making a grid-like element for electron tubes comprising the steps of placing wire on a forming member, placing a grid support in contact with the wire on the form, bonding said grid support to the wire, heating and cooling said wire uniformly while on said forming member, and holding said wire in place against said forming member during the heating and cooling process, the temperature to which said wire is heated being substantially the recrystallization temperature of the wire.

3. A method of making a grid-like element for electron tubes comprising the steps of bending wire across the top and down the sides of a rod shaped mandrel to provide wire lengths extending along the surface of the mandrel and fastened to the mandrel below the top of the mandrel, sliding a supporting ring over the mandrel to a selected position above the point at which the wires are fastened to the mandrel, cutting said wire lengths between said fastening point and said supporting ring, placing a clamp around said mandrel above said ring, and brazing said Wire lengths to said supporting member.

4. A method of making a grid-like element for electron tubes comprising the steps of placing wire on a forming member to make a desired wire shape, heating and cooling said wire while on said forming member, and holding said wire in place against said forming member during the heating and cooling process, the temperature to which said wire is heated being the recrystallization temperature of the wire.

5. A method of making a grid-like element for electron tubes comprising the steps of bending wire onto a forming member to make a desired shape, heating and cooling said wire while on said forming member, and holding said wire in place against said forming member during the heating and cooling process, the temperature to which said wire is heated being sufficiently high and of sufficient duration to cause said wire to .be substantially stress relieved.

6. Apparatus for making grid-like elements comprising a forming member having a grid forming surface on which grid wire can be placed in a desired shape, a clamping structure surrounding said forming member and having a pressure surface with a shape which matches the shape of said forming surface, said forming member and clamping structure being positionable relative to each other to form a space between said forming and pressure surfaces to accommodate grid wire, and the coefficients of expansion of said forming member and clamping structure being such that said space tends to become smaller as said forming member and clamping structure are heated.

7. Apparatus for making grid-like elements comprising a rod like mandrel having an upper. grooved portion and a lower shaft portion, and a jig having a base portion with a bore slideably receiving said shaft portion of the mandrel, and support means extending up from said base to form a supporting surface around the mandrel.

References (Iited by the Examiner UNITED STATES PATENTS 1,974,312 9/1934 Murphy -715 2,061,759 11/1936 Eitel et a1 140-715 X 2,135,288 11/1938 Koenig 29-25.19 2,359,514 10/1944 Eitel et al. 140-715 2,398,609 4/1946 Werner 140-715 IX 2,438,113 3/1948 Denmark 140-715 2,621,303 12/1952 Law 313-348 2,877,805 3/1959 Van Meurs et a]. 140-715 2,921,363 1/1960 Nielsen 29-2514 2,946,915 7/ 1960 Haase 313-348 FOREIGN PATENTS 392,510 11/1908 France.

CHARLES W. LANHAM, Primary Examiner. RALPH G. NILSON, JAMES D. KALLAM, Examiners.

J. E. BECK, A. S. KATZ, L. A. LARSON,

Assistant Examiners.

Claims (1)

1. A METHOD OF MAKING A GRID-LIKE ELEMENT FOR ELECTRON TUBES COMPRISING THE STEPS OF BENDING WIRE ONTO A FORMING MEMBER TO MAKE A DESIRED SHAPE, PLACING A SUPPORT MEMBER IN CONTACT WITH THE FORMED GRID WIRE, POSITIONING A CLAMPING STRUCTURE AROUND SAID FORMING MEMBER IN CONTACT WITH THE FORMED GRID WIRE, SAID CLAMPING STRUCTURE HAVING A LOWER COEFFICIENT OF EXPANSION THAN SAID FORMING MEMBER, AND BY THE APPLICATION OF HEAT SIMULTANEOUSLY BRAZING SAID SUPPORT MEMBER TO THE FORMED GRID WIRE AND COMPRESSING THE WIRE BETWEEN THE FORMING MEMBER AND CLAMPING STRUCTURE.

Images