US2220909A

US2220909A - Cathode sleeve for thermionic valves

Info

Publication number: US2220909A
Application number: US315250A
Authority: US
Inventors: Kershaw Henry
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-01-23
Filing date: 1940-01-23
Publication date: 1940-11-12
Anticipated expiration: 1957-11-12

Description

Nov. 12, 1940. H. KERSHAW 2,220,909

CATHODE SLEEVE FOR THERMIOEIC VALVES v Filed Jan. 23, 1940 '2 Sheets-Sheet 1 Nov. 12, 1940. H. KERSHAW 0, 0

CATHODE SLEEVE FOR THERMIONIC VALVES Filed Jan. 23, 1940 '2 Sheets-Sheet 2 Patented Nov. 12, 1940 UNITED STATES,

CATHODE SLEEVE FOR THERIVIIONIC VALVES Kershaw, Belleville, N. J. 1

Application January 23', 1940, Serial No. 315,250

20 Claims.

My invention relates to a cathode sleeve for thermionic valves or vacuum tubes and to the method of producing the same.

In United States Patent 2,029,482 a cathode 5 sleeve or cylinder is shown, formed from a strip of sheet metal, having its side edges interlocked by providing oppositely facing bent tongues upon the strip. These interlocking edges provide a seam of four layers of metal, and the seam is continued beyond one end of the tube orcylinder to provide a tab, which is to be attached to a post. The tab is formed from spaced tab sections at one end of the sheet and each of these tab sections is folded upon itself to provide a continuation of the interlocking tongues. Considerable difiiculty is experienced in producing this sleeve or cylinder with the tab, as shown in Patent 2,029,482, commercially, and the difficulty resides principally in the formation of the tab integral with the sleeve or cylinder. As a result of this, these sleeves or cylinders ordinarily are produced without'the tabs which are separate from the sleeve or cylinder and are subsequently welded to the sleeve or cylinder. This welding in place of the tab is a separate operation'and increases the cost of producing of the product. It has also been proposed to form the cathode sleeve or cylinder from an integral drawn tube and to provide a separate tab, which is subsequently welded to the drawn tube. This construction is shown in Patent 2,079,057. The drawn tube is expensive.

In accordance with my method, I forin a sleeve having generally radially extending flanges, and portions of these flanges contact but the flanges do not interlock, and these flanges are welded together. The sleeve may be accurately formed in the desired shape, such as circular, square, or other shape in cross-section, and the sleeve will not be distorted by the welding of the flanges. The welding of the flanges Securely unite the side edges of the sleeve, and the welding may be effected rapidly and cheaply. This dispenses with the expensive practice of forming interlocking tongues upon the side edges of the sleeve. In the practice of my method, the tab is formed of tab sections which are preferably in effect continuations of the flanges. Each tab section is singlelayer and portions of their faces contact but have no interlocking engagement and are secured together by welding. The difficulty experienced in shaping tab sections into interlocking tongues is therefore eliminated, and the tab may be readily produced integral with the sleeve orcylinder. I may alsobend over upon the sleeve orcylinder the originally generally radial welded flanges, providing a rib orseam. A portion of the welded flange may be left raised, for providing a shoulder. While it is preferred to bend down the welded flanges, the sleeve may be used without 5 doing this. A further advantage of my construction is that the rib or seam produced by the bent-over welded flanges comprises but two layers of metal, thus effecting the maximum uniform distribution of heat. A further advantage 10 of my construction is that the seam or rib may be arranged wholly upon the exterior of the sleeve, thus permitting of the close arrangement between the electrical heating unit and the sleeve, without liability of these elements con- 15 tacting and scraping oil the-insulation from the heating unit.

The present application is a continuation in part of my original application for Cathode sleeve for thermionic valvesand method of pro- 20 ducing the same, Serial No. 259,908, filedMarch 4,1939, and my application for Cathode sleeve for thermionic valves, Serial No." 281,984, filed June 29, 1939, and which is a division of application 259,908. 25

In the accompanying drawings forming a part of this application and in which like numerals are employed to designate like parts throughout the same:

Figure 1 is a side elevation, principally dia- 30 grammatic, illustrating apparatus used in the practice of the method for producing the cathode sleeve,

Figure 1 is a transverse section, parts broken away, taken on line l -l of Figure 1,

Figure 2 is a perspective view of a portion of the ribbon or strip after being bent in the V- shape,

Figure 3 is a side elevation of the forming rollers which bend the flat strip into the V-shape and produce the row of raised portions at one longitudinal edge of the ribbon or strip,

1 Figure 4 is a perspective view of the V-shaped strip having the tab sections forming opening 45 stamped therein, i

Figure 5 is a transverse section through the stamping punch, in the lowered position, as if taken on line 5-5 of Figure 1,

Figure 6 is a perspective view of the strip transversely cut to provide the section or unit to form the cathode sleeve, v

Figure '7 is a transverse section taken on line 'l| of Figure 1, showing the cutter,

Figure 8 is a central longitudinal vertical secstrip bent about its longitudinal axis to provide upstanding sides,

Figure 12 is an enlarged perspective view of the sleeve, with its flanges and tabs Welded together,

Figure 13 is an end elevation of the welding jaws, in the closed position, illustrating the welding step for producing the sleeve shown in Figure 12,

Figure 12 is an end elevation of the sleeve with the flanges slightly spaced and the raised portions engaging one flange,

. Figure 13 is an end elevation of the sleeve, showing the flanges contacting and welded together and indicating the dimensions of the parts,

Figure 14 is a bottom plan View of the welding J'aws,

Figure 15 is a perspective view of the sleeve,

showing the welded flanges. bent down upon the sleeve and slit to form a stop shoulder,

Figure 16 is a transverse section through the knock-down punch showing the formation of the stop shoulder. the section through the knockdown punch-being taken on line Iii-l 6 of Figure 17,

Figure 17 is a bottom plan view of the knockdown punch,

Figure 18 is a'perspective view, in a vertical position of the completed cathode sleeve, and,

Figure 19 is a side elevation of the cathode sleeve shown in Figure 18, assembled with a grid and associated elemen s.

In Figures 15 and 18 I have shown a cathode sleeve 20, which is cylindrical for the'purpose of illustration. The sleeve 23 has single-layer flanges 2| and 22, whichoverlap, are welded together and bent over or down upon the sleeve, providing a seam of two layers and which serves to stiiien the sleeve.

Tab sections

23 and 74 are formed integral with the sleeve, are in align.- ment with the flanges 2| and 22 and form in ef- .fect continuations of the same. The tab sections are also welded together. The flanges and tab sections have no interlocking engagement andare secured together solely by welding. The flanges 2i and 22 are arranged. upon the outer surface of th sleeve and are transversely slit at 25, affording an outwardly projecting stop shoulder 2.6, which is generally radial.

The cathode sleeve is formed from sheet metal, such as nickel. This sheet metal is thin and ordinarily has a gauge of .0015" (1.5 thousandths of an inch), although the invention is not restricted to this precise gauge. The draw ings show the cathode sleeve in a greatly enlarged diameter. As shown in Figure 13 the internal diameter of the cathode sleeve is .040" (40 thousandths of an inch) and its external diameter is .043 (43 thousandths of an inch). The Width of the flanges and tab sections is .020 (20 thousandths of an inch). These dimensions may vary somewhat either way. Cathode sleeves are mad having an internal diameter as small as .020" (20 thousandths of an inch). The dimensions given are the average dimensions and are recited to show the inherent difficulties encountered in making a cathode sleeve. My invention is not restricted to the precise dimensions given.

I will now proceed to explain the method employed in producing the cathode sleeve 20. In the production of this cathode sleeve I start with a thin metal ribbon, such as nickel, preferably having a gauge of .0015, although the gauge may vary somewhat. This metal ribbon is designated by the numeral 21, Figure 1, and is wound in a roll 28 upon a spool 29, and is unwound from this spool in a step-by-step manner. As the metal ribbon is unwound from the spool it is transversely flat.

The step-by-step feed of the metal ribbon may be efiected by any suitable means, and I contemplate using a block- 30 having a flat recess 3|. Arranged above the block 30 is a top 32 rigidly secured thereto and this top has a vertical opening 33, to receive a friction pin 34, forced down by a spring 35. When the spring acts upon the friction pin 34 this fraction pin engages the ribbon 21 and holds it to the block 30 so that the ribbon will move with the block when the block moves forwardly. When the block moves rearwardly, the intermediate portion of the spring 35 is elevated, relieving the tension from the friction pin 34, and the block may then slideiearwardly with relation tothe ribbon, which is then held against rearward movement. The spring 35 is attached to the top 32 and any suitable means may be employed to operate the spring and any suitable means maybe employed to reciprocate the block 30; The block 30is moved forwardly on each cycle of operation for a distance equal to the combined length of the completed sleeve and tab sections.

The lower block 30 carries a forming roller 33, having a concave periphery which is channeled or V-shaped in cross-section and the roller 36 coacts with an upper forming roller 37, carried by the top 2. The roller 31 is convex and has a periphery which is V-shaped in cross-section, corresponding to the cavity of the roller 35 and adapted to enter the same. The low point 38 of the roller 36 is to one side of the center 39 of this roller. providing a face 40 longer than the face 4|. The high point 42 of the'roller 3'! is to one side of the center 39 providing a face 43 longer than the face 44. The upper roller 3? is provided adjacent to one end of this periphery with an annular groove 45, to receive an annular set of drawing studs 45, carried by the roller 36.

When the block 30 and associated elements are moved from the rear position, Figure 1, to the forward position, it will advance the ribbon 21, as explained. When the ribbon is thus advanced, the forward portion of the ribbon is clamped against rearward movement and the tension of the spring'35 is released from the pin 34 and the block 30 and associated elements are then moved rearwardly and returned to the rear position. The block 30 and the forming

rollers

36 and 31 then travel rearwardly with relation to the then stationary ribbon 21, and the peripheries of the forming rollers 36 and 31'engaging with the ribbon 21 form or bend the same into a V-shape, as shown. In this V-shape one side 41 is wider than the other side 48. At the same time, the drawing studs 46 produce a row of spaced raised portions 49 adjacent to one longitudinal edge of the ribbon. These raised portions or bumps 49 have their convex faces next to the upper face of the side 41, Figure 2. The ribbon is formed or bent into the V-shape and the raised portions 49 are formed when the block 30 and associated elements move rearwardly with respect to the ribbon. When the block 30 and associated elements move forwardly, they feed the ribbon forwardly, and that portion which is V-shaped is rendered thereby stiff so that it is fed forwardly by a pushing action, while that portion of the ribbon at the rear of the block is fed forwardly by a pulling action. If the forward portion of the ribbon were not stiffened by the V-shape, it would not be sufiiciently stiff to be properly pushed forwardly.

When the V-shaped portion of the ribbon is pushed forwardly it is moved to a stamping position and is arranged within a V-shaped recess 50 of a stationary die 5i, having a vertical opening 52, to receivea punch 53, carried by a vertically reciprocatory head 54. The numeral 55 designates a stripper, having an opening 56 to receive the punch.53 and a groove 53 to receive the raised portions 49 and move downwardly by springs 51. The stripper 55 has its lower face V-shaped to conform to the shape of the recess 55. When the V-shaped portion of the ribbon 2! is moved into the recess 50, thehead 54 is shifted downwardly and the stripper 55 moves downwardly and clamps the V-shaped portion of the ribbon within the recess 50, subsequent to which the punch 53 moves down below the stripper 55 and enters the opening 52 of the die and stamps out the opening 51. When the head 54 rises, the punch 53 moves upwardly with respect to the stripper 55 and the V-shaped portion of the ribbon will be separated from the punch by the stripper. When the head 54 is in the uppermost position both the stripper and punch are spaced from the V-shaped portion of the ribbon. When the stripper 55 is clamping the V-shaped portion of the ribbon in the recess 50, the ribbon is held against rearward movementand during this time the block 39 and associated elements are shifted rearwardly. The formation of the opening 51 provides the

tab sections

23 and 24, arranged adjacent to the longitudinal edges of the V-shaped portion of the ribbon'and extending longitudinally of such V-shaped portion be yond one end of the same.

When the block 30 and associated elements are again moved forwardly this V-shaped portion of the ribbon is advanced to the sleeve forming or bending position, and when the head 54 again moves downwardly, the cutter 58 is moved upwardly to sever the

tab sections

23 and 24, at 59, whereby the leading V-shaped ribbon-section is separated from the ribbon. This section is used to form the sleeve and tab of the. cathode sleeve. Particular attention is called to the fact that the raised portions 49 extend throughout the entire length of the V-shaped portion and the entire length of the tab section 24. When the leading section is thus shifted to the bending position it is introduced into a V-shaped recess 60 of a vertically movable forming die 5|, thenin the lowered position. The forming die also has a cyllndrically curved recess 62, receiving the apex of the V-shaped section. The cylindrically curved recess 52 is preferably less than half of a cylinder whereby the sides 41 and 48 of the section, when further bent extend upwardly in a diverging relation. The center of the recess 62 is to one side of the longitudinal center 63 of the die 6|. The numeral 54 designates a horizontal mandrel or core which is cylindrically curved for coaction with the recess 62. The mandrel or core 64 is cylindrical except for an upper flat face 65, as shown. The mandrel 64 is concentric with respect to the recess 62. During the forming of the sleeve, with the V-shaped strip within the recess 60, the mandrel 64 is held stationary above the die BI and the die is first raised sufficiently to clamp the V-shaped section be tween the mandrel and the die and the die is then stopped before the mandrel 64 has reached its lowermost position within the recess 62 and the die BI is held stationary. A knock-down die 66 is now moved downwardly into engagement with the top of the mandrel 64 and forces it to the lowermost position. within the recess 62 and the mandrel 64 and the recess 62 now bend the section to provide a lower cylindrically curved portion 91 carrying the upstanding upwardly diverging sides 41 and 48. The. side 41 extends above the side 48, by virtue of the off-center arrangement of the recess 62 and the mandrel 64 and the wider side 41 carries the raised portions 49. After this operation, the knock-down die 66 is elevated and separated from the mandrel 64. Horizontal reciprocatory electrical

resistance welding jaws

68 and 69 are'moved inwardly and engagethe upstanding sides 41 and 48. and complete the forming or bending of the same about the mandrel 64 and form the flanges 2| and 22. These

jaws

68 and 69 are insulated from parts BI and 64. The welding jaw 68 moves inwardly beyond the center 10 of the mandrel 64 while the welding jaw 69 moves inwardly and terminates short of this center, whereby the flanges 2| and 22 are arranged adjacent to one longitudinal edge of the flat face 65 of the mandrel 64. The

welding jaws

68 and 69 have vertically inclined welding faces H, which are preferably free from notches although notches may be used if desired. The welding jaws extend for the entire combined length of the sleeve and the tab sections.

As' the welding jaws. 68 and 69 move inwardly they first bring the convex ends of the raised portions 49 of the flange 22 and tab section 24 into contact with the flange 2| and tab section 23, and since these raised portions are convex, the minimum area is afforded at the instant of contact between the raised portions and the flange and tab section, thereby producing the maximum resistance at the points of contact. As soon as the jaws move inwardly sufliciently to effect the contact, as described, a welding current is supplied to the

welding jaws

68 and 69, and the raised portions 49 and the contacting portions of the flange and tabsection are rendered plastic, and during this welding period the

jaws

68 and 69 continue to move inwardly until the flanges and tab sections are broughtinto firm contact and the raised portions or bumps are flattened out. The inward pressure of the

welding jaws

68 and 69 follow through during the entire welding period so that there can be no flashing and the flanges and tab sections are brought into firm contact after the raised portions are flattened, and the current is cut off when the jaws still exert the inward lpressure. I use an alternating current of low voltage and high amperage. Satisfactory results are obtained by using an alternating current having a voltage of approximately three (3) volts and an amperage of approximatelyv 2,000 amperes. During the welding period, the current stays on for only a short time, and I have found that satisfactory results are obtained by having the currents turned on for one-half. /2) cycle. The invention is not restricted to the precise voltage and amperage and time recited, as these may be varied. The

welding jaws also weld the

tab sections

23 and 24 sections are arrangedexteriorly of the sleeve, are

inclined and are generally radial with relation to the sleeve and are disposed upon one side of the center of the sleeve. The mandrel or core 64 extends for the entire length of the sleeve and tab section.

During the welding operation the die 6| and the mandrel 64 remain stationary, and they remain stationary during the next step of bending down the welded flanges and tab sections. After the

jaws

68 and 69 are moved to the open position, the knock-down die 66 is again operated. This knock-down die 66 extends throughout the entire length of the sleeve and tab. The knockdown die has a cylindrically curved recess l2, having its center in alignment with the center of the recess 62. The flanges 2| and 22 which are inclined are off-set with respect to the center of the sleeve and the center of the recess 12. It is thus apparent that when the knock-down die '66 again descends it will engage the welded flanges 2| and 22 and the

tab sections

23 and 24 and bend them down over the flattened portion of the sleeve, and this bending down will occur throughout the entire length of the sleeve and the tab except for a short portion which provides the upstanding stop shoulder 26. The shoulder 26 is provided by forming the knock-down die 66, Figure 16, with a transverse slot 13 having a width corresponding to the length of the shoulder 2t. supporting element or hook 14 extends into the slot 13 and is adapted to engage behind the shoulder 26, to prevent the same being bent down. The hook 14 supports the shoulder 26 and the edges of the slot l3 serve to out or shear the flanges'Zl and 22 at the lines 25. The hook element never moves downwardly sufliciently to engage the mandrel or sleeve thereon but does move downwardly sufficiently to engage behind the shoulder 26. The hook may be operated by any suitable means. I have shown a spring l to raise the hook and an adjustable screw 16 carried by the knock-down die 66 to depress the hook. When the die 66 is raised the space between the screw 16 and the hook 14 is such that the face of the recess 12 of the die 66 will engage the sleeve upon the mandrel 64 before the hook M has moved downwardly to engage such sleeve.

After the bending down operation the knockdown die 66 is raised, the hook l4 rises and the forming die 6! is lowered and the mandrel 64 is moved horizontally through a stripper T! which strips the completed sleeve from the mandrel. This completes the cycle of operation of the method. The various instrumentalities employed in. the practice of the method will be moved in properly timed order, and they may be moved manually or automatically.

The sleeve shown in Figure 18 is thereby produced, and the bent-down

flanges

21 and 22 provide a seam of two layers, forming three layers with the adjacent part of the sleeve, and the shoulder 26 is at or in this bent-down seam. In Figure 19 I have shown the cathode sleeve 20 of Figure 18 assembled with a grid 78 and anode T9, in a manner somewhat similar to the arrangement shown in Figure 4 of Patent 2,079,057. In Figure 19 the numeral 89 designates an upper mica disk and Bi designates a lower mica disk,

supported by posts 82. The sleeve 20 contains the usual resistance element or heater including leadin wires 83 and the sleeve is coated at 84 with barium or strontium carbonate, corresponding to the coating I! of Patent 2,079,057. This coating when raised to the proper temperature becomes a good emitter of electrons. The tab 22 formed by the

tab sections

23 and 24 may be'bent slightly so that it can be attached or welded to one of the posts 49. The shoulder 26 rests upon the top of the disk 8|, and supports the sleeve, the ends of which are inserted within openings 85.

It is to be understood that the form of my invention herewith shown and described is to be taken as a preferred example of the same and that various changes in the shape, size, and arrangement of parts may be resorted to without departing from the spirit of my invention or the scope of the subjoined claims.

Having thus described myinvention, what I claim is:

1. A cathode sleeve for a thermionic valve formed from a strip of sheet metal, the longitudinal edge portions of the strip being welded together, the longitudinal edge portions being secured together solely by the welding.

2. A cathode sleeve for a thermionic valve formed from a strip of sheet metal, the longitudinal edge portions of the strip overlapping and Welded together, the longitudinal edge portions being free from interlocking engagement with each other.

3. A cathode sleeve for a thermionic valve, said sleeve being formed from a strip of sheet metal, said strip having spaced tab sections formed integral therewith, said strip having its longitudinal edge portions and the tab sections arranged in overlapping relation and secured together solely by welding.

4. A cathode sleeve for a thermionic valve, said sleeve being formed from a strip of sheet metal, said strip being provided at its longitudinal edges with flanges disposed upon the outer side of the sleeve, the flanges having portions of their side faces contacting with each other and extending beyond one end of the sleeve to produce a tab, the flanges being welded together throughout substantially their entire length, the flanges forming a two-layer seam.

5. A cathode sleeve for a thermionic valve, said sleeve being formed from a strip of sheet metal having tab sections formed integral with one end thereof, said sleeve having flanges integral with the side edge portions thereof, the flanges having portions contacting with each other and being free from interlocking engagement which will prevent the relative displacement between the flanges when they are bent down and the tab sections having portions contacting with each other and being free from interlocking engagement and both the flanges and tab sections being secured togetherby Welding.

6. A cathode sleeve for a thermionic valve, said sleeve being formed of a strip of sheet metal and having its side edges bent to produce flanges which contact without interlocking, said flanges being welded together.

7. A cathode sleeve for a thermionic valve, said sleeve being formed of a strip of sheet metal having its side edges bent outwardly to provide a pair of flanges having portions of their sides contacting without interlocking, the flanges being welded together, the welded flanges forming a seam arranged entirely exteriorly of the sleeve and consisting of two layers of metal.

overlapping relation, the longitudinal edge por- 8. A cathode sleeve for a thermionic valve, said sleeve having a pair of separate tab sections formed integral therewith, the tab sections being assembled with their side faces .i overlapping relation Without interlocking, the tab sections being welded together and forming a tab of two layers of metal.

9. A cathode sleeve for a thermionic valve, said sleeve being provided at its meeting longitudinal edges with a pair of single-layer flanges which are originally flat and have side faces which contact Without interlocking, the flanges being Welded together. v

10. A cathode sleeve for a thermionic valve, said sleeve being formed from astrip of sheet metal, said strip being provided adjacent to its longitudinal edges with outwardly projecting single-layer generally radial flanges having contacting side faces, the flanges being welded together.

11. A cathode sleeve for a thermionic-valve, said sleeve being formed of a strip of bent sheet metal, the sleeve having longitudinal overlapping single-layer flanges at its meeting edges, the flanges being welded together and bent over as a unit, the bent-over flanges constituting a seam arranged upon the outer side of the sleeve.

12. A one-piece electrode for a thermionic tube, said electrode comprising a sheet metal said opening being spaced from the longitudinal edges of the blank to provide tab sections, the marginal longitudinal edge portions of the blank and the tab sections being bent laterally outward- 1y with relation to the blank, the marginal 1011-,

gitudinal edge portions and the tab sections each being of a single layer, one marginal longitudi -1 nal edge portion and one tab section being provided with raised portions, the blank being bent into tubular form and the single-layer marginal edge portions and the single-layer tab sections being welded together.

14. A cathode sleeve for a thermionic valve, said sleeve being formed from a strip of sheet metal, said strip having longitudinal single-layer edge portions which overlap in contacting relation, the contacting edge portions being secured together solely by welding and forming a twolayer seam which stiffens the sleeve.

15. A cathode sleeve for a thermionic valve, said sleeve being formed from a strip of sheet metal, said strip having single-layer longitudinal edge portions which overlap, the overlapping edge portions extending beyond one end of the sleeve to produce single-layer tab sections arranged in.

tions being secured together solely by welding,

a two-layer seam, the welded flanges being bent down upon the sleeve, and a shoulder formed adjacent to the bent-down flanges.

17. A cathode sleeve for a thermionic valve, said cathode sleeve being formed from a strip of sheet metal having tab sections formed integral with one end thereof, said sleeve having flanges I integral with the side edge portions thereof, the

flanges having contacting portions andbeing free .from interlocking engagement which will prevent the relative displacement between the flanges when they are bent down and the tab sections having contacting portions and being free from interlocking engagement, the flanges being welded together and the tab sections being secured together.

18. A cathode sleeve for a thermionic valve, said sleeve being formed of a strip of bent sheet metal, the sleeve having longitudinal overlapping flanges at their meeting edges, at least one of the flanges being a single-layer flange, the flanges being welded together and bent over as a unit, the bent over flanges constituting a seam arranged outwardly of the sleeve, and tab sections formed integral with one end of the strip and extending beyond the sleeve, the tab sections being free from interlocking engagement and secured together and extending from a point adjacent to the assembled flanges.

. 19. A cathode sleeve for a thermionicvalve, said sleeve being formed from a strip of sheet .metal, said strip having edge portions which overlap, at least one edge portion extending beyond the sleeve to produce a tab which is integral with the strip, said tab consisting of two single-layer tab sections which are secured together, the overlapping edge portions being secured together by welding.

20. A cathode sleeve for a thermionic valve, said sleeve being formed from a strip of sheet metal having its side edges arranged in opposed relation and welded together, a two-layer tab formed integral with'the strip and extending beyond the sleeve, said tab consisting of two singlelayer tab sections arranged in overlapping relation and free from interlocking engagement with each other and secured together.

HENRY KERSHAW.