US2451847A - Base structure for electron discharge tubes - Google Patents

Description

Oct 19, 1948.

H. D. M ADDEN ETAL BASE STRUCTURE FOR ELECTRON DISCHARGE TUBES Filed April 2, 1943 2 Sheets-Sheet l Oct. 19, 1948. H D MADDEN ETAL 2,451,847

BASE STRUCTURE FOR ELECTRON DISCHARGE TUBES l Filed April 2, 194:' 2 Sheets sheet 2 MWA/v ATTORNEY Patented Oct'. 19, `1948 UNITED STATES PATENT FFICE BASE STRUCTURE FR ELECTRON DISCHARGE TUBES Application April 2, 1943, Serial No. 481,516

22 Claims. 1

This application is a continuation-impart in the nature of a division of an application, Serial No. 234,594, filed October 12, 1938, now Patent No. 2,321,224, dated June 8, 1943, and owned by the assignee of the present application.

This invention relates to electric or electronic tubes and, more particularly, radio tubes and bases for such devices.

One of the objects of the invention, is electric tubes, the stems or bases of which are made from molten glass which is caused to flow around the lead-in and contact devices or conductors comprising prongs or terminal posts and their lead-in wires, while positioned in a suitable mold, after which the mold is opened, the base Withdrawn, electrodes secured thereto, and an envelope sealed thereover.

Another object of the invention is to manufa ture electric tubes in which their external contact members are kept parallel and maintained accurately in their predetermined circular relationship, so that such tubes will nt interchange ably in standard sockets provided therefor.

A further object oi the invention is to provide a stem for an electric tube, such as a radio tube, which may be easily sealed to the envelope in a desirable type of sealing-in machine, and in which cracking is avoided by the construction of the parts and the method of sealing.

A still further object of the invention is to provide a novel stem consisting of a substantially flat disc of glass having a central thickened portion, from one side of which lead-in contacts project, and from the other side of which lead-in conductors extend for connection with electrodes, said thickened portion being suiiiciently strong to stand atmospheric pressure exerted on its lower, generally flat, surface after completion oi the tube.

An additional object of the invention is the provision of a stem for radio and other electric tubes, the body of which is suiciently massive that during the sealing of the stem to the envelope it is not softened to any appreciable extent, an outstanding, relatively thin, peripheral ange being provided for sealing to the corresponding edge of the envelope.

Other objects and advantages of the invention, relating to the particular arrangement and construction of the various parts, will become apparent as the description proceeds.

Referring to the drawings:

Figure l is a perspective view of a radio tube base, embodying our invention.

Figure 2 is an axial sectional View of a base, such as shown in Figure 1, with an envelope for the tube diagrammatically shown.

Figure 3 is a perspective view of the base illustrated in Figure 1, but looking diagonally at the lower surface, or that from which the contact prongs extend, rather than at the upper surface, or that from which the inner leads or electrode supports extend.

Figure 4 is an elevational View, partly in axial section, of a metal ring, which may be formed of Kovar or other material having approximately the same coefficient of expansion as the glass sealed thereto, which is used as a part of the base, illustrated in Figures 1, 2 and 3.

Figure 5 is an elevational view of one of the lead-in conductors, comprising a terminal post with its associated lead-in wire or electrode support extending therefrom.

Figure 6 is a fragmentary vertical sectional view of the mold and associated apparatus, adapted for forming bases such as illustrated in Figures 1, 2 and 3, the upper and lower mold elements being there shown in cooperative relationship, and molten glass being illustrated as filling the mold.

Figure *l is a View of the base and associated electrodes, showing a glass envelope positioned over the electrodes, and its lower edge engaging the metal ring of the base, in the process of being heated and sealed thereto.

Figure 8 is a View corresponding to Figure 7, but showing the position of the parts for forming a modification, in which the envelope is of metal rather than glass, and the lower edge of which is to be welded to the outer peripheral portion of the metal base ring.

Figure 9 is an elevational View showing the position of the parts during the process of sealing the exhaust tube to the base, a portion of said tube and the engaged portion of said base being illustrated in axial section.

Figure i0 is a view corresponding to Figure 9, but showing a subsequent position in which the tube is being tipped on" after having been exhausted.

Figure 11 is a perspective view of a modified form of base in which the use of a metal ring is dispensed with.

Figure 12 is a view corresponding generally t0 Fig. 7, but showing a base or stern and associated electrodes, of the type illustrated in Fig. 1l, with a glass envelope positioned over the electrodes, and its lower edge engaging the corresponding outer edge of the peripheral glass sealing ring or the base, during the process of being heated and sealed thereto.

Figure 13 is a vertical sectional view corresponding generally with Fig. 12, but showing the parts after the engaging edges of the base and envelope have been heated sulciently to effect a sealing therebetween.

Referring to the drawings in detail, and rst considering the embodiment of the invention illustrated in Figures 1 to 5 inclusive, there is shown a base Si for an electric or radio tube 32, the envelope of which is diagrammatically illustrated in dot-and-dash lines and designated by the reference character 33 in Figure 2. The base 3| is formed of glass and has incorporated therewith an annular ring 34, of Kovar or another alloy or metal having a coefficient of expansion closely approximating that of the glass used therewith. For example Kovar may be used with hard glass or nickel-iron with soft glass. The ring 34 comprises a normally unstanding or generally cylindrical flange 35 encircling the periphery thereof, and an outstanding flange 36 forming a surface for attachment to the envelope 33 and, for that purpose, desirably, but not necessarily, provided with a generally circular upwardly pressed corrugation 3l extending therearound. If desired, the cylindrical flange 35 may be provided with one or more corrugations or depressions to lock the ange to the glass base 3|, to prevent endwise relative movement of the flange during withdrawal of base from the mold or from the socket when the device is in use.

The glass base 3| desirably has incorporated therewith, a plurality of metal posts or contact devices 38, shown in detail in Figure 5, and adapted for cooperation with contact members in a corresponding tube socket, as will be understood. Each post is desirably hollow to receive the outer end of a lead-in conductor 39 which passes through the glass base to connect with an associated electrode, not shown, and has a flaring skirt or flange portion 4|, the extreme or upper edge of which is relatively sharp and embedded in the glass base 3|, thereby dening a circumferential groove around the conductor 39, making the terminal post 38 relatively rigid in its relationship with said base. The envelope 33 may be of glass or metal and is desirably secured to the base or metal ring portion 34 in a manner which will be described in detail hereinafter.

The glass base 3| has an exhaust tube stub 42 desirably formed when the parts of the base are consolidated in a mold, said stub 42 having an aperture 43 therethrough terminating in a socket 44 for the reception of an exhaust tube. The stub 42 not only serves for connection with an exhaust tube, but constitutes a guide to fit an aperture of a socket. The stub or guide, for this purpose, is provided with a pin or ridge 42e which enters a slot provided in the wall of the aperture receiving the guide, thus properly locating the Contact pins for entrance into their contact apertures.

Figure 6 illustrates part of a preferred form of apparatus, more fully shown in the parent application referred to, for molding a base such as shown in Figures 1, 2 and 3. A table or support holds an upper mold element 46, which may be relatively xed against vertical movement, but movable horizontally with its associated parts. Said upper mold element 46 is desirably formed of steel or similar material and has a plurality of vertical apertures 41, adapted to snugly receive a corresponding number of terminal posts 38, as shown in Figure 5, with their associated leads or supports 39 extending downwardly therebelow. The apertures 41 desirably allow for the outer ends of the posts 33 to extend above the upper or outer surface of the upper mold element 46, thereby allowing for engagement therewith of a stripping device comprising depending prongs 48 carried by and movable with a reciprocating member, which may be movably carried by the table or support 45, as shown most clearly in Figure 6 of said parent application.

In order to prevent entrapment of air in the` upper mold during molding of glass therein, each hollow terminal post 33 desirably has an aperture 5i which, when the post is in position, communicates with a registering port 52 in the upper mold element 46 in order to allow for the escape of air, as molten glass rises in the mold, submerges the edge of the flange 4|, and desirably fills the groove dened thereby around the conductor 39, as illustrated. rilhe sharpened skirt portion or flange 4| of each terminal post 38 desirably extends into the molding space below the upper inner substantially i'lat and normally horizontal surface of the upper mold 46, in order to become embedded and sealed in the glass base portion during the process of formation.

Associated with said upper mold portion 46 is a lower mold portion 53, also desirably formed of steel or similar material. The mold portion 53 is desirably vertically movable into and out of cooperative relationship with the upper mold element 46, has an annular socket 50 receiving the generally cylindrical portion 35 of the metal ring 34, if such a ring is to be incorporated in a radio base to be formed, the flange 35 of said ring engaging the upper surface of said portion 53, and is provided with apertures 54 registering with the post apertures 4'! and adapted to receive the lower or inner ends of the conductors 39 extending therefrom. The upper inner surface of the lower mold 53 has a contour corresponding with that desired for the normally upper surface of the base or other device to ybe formed therein. In the present instance, while its upper surface is substantially at and normally substantially horizontal, as illustrated, although it may slope slightly to facilitate molding operations, there is an upwardly extending boss 55 provided thereon, for the purpose of forming a corresponding funnel shaped portion 56, communicating with the exhaust aperture 43 in the exhaust stub portion 42 of the base, and an abutment for a cooperating plunger member 5l which makes the aperture 43.

The mold previously described may be used separately or comprise one of a series of molds successively lled by a stream of molten glass under which they move, one by one. If one of a series, the upper mold element 46 is not only apertured, as indicated at 59, to receive the stream of glass 58, but may also have associated therewith a funnel-shaped portion which serves to direct the glass into the aperture 59, from whence it goes to the associated mold elements 46 and 53, and initiates and cuts o the flow of glass into the particular mold under consideration, after the preceding mold and its associated funnel has passed therefrom. Eventually the mold and its funnel will pass from beneath the stream of glass, and the latter will be caught by the subsequent funnel and directed to its associated mold, as will be understood.

In order to accurately predetermine the amount of glass fed to the lower die or mold element 53 through the funnel, we preferably cause the stream of glass to issue from a glass melting furnace, not shown, through an orice provided with a die, not shown, which die, however, is preferably formed of an alloy of platinum and rhodium such as described in Patent #2,031,083, issued February 18, 1936.

The temperature of the stream is desirably maintained uniform by sighting a radiation pyrometer, not shown, thereon, and controlling the heat of the furnace, by means of apparatus such as described and claimed in Patent No. 2,116,450,

dated May 3, 1938, so that an accurately controlled amount of glass, just sufficient to fill the mold to the desired extent, is fed thereto as it passes under the stream.

In order to make the base-forming operation continuous, the mold, comprising the main elements Gil and 53 and associated apparatus, is merely one of a series, and the elements of said series are each caused to move under the stream of glass, one by one, to receive the charge required and then pass on to make way for the next mold, in a manner such as described and claimed in the co-pending application of Richardson et al., Serial No. 205,180, filed April 30, 1938, now Patent No. 2,393,265, and owned by the assignee of the present application. When the glass has filled the lower mold element `53 and risen to the proper level in the upper mold element 4S, after surrounding and wetting intermediate portions of the leads 39, wetting the inner and part of the top surface of and consolidating with the metal ring 35, and wetting and uniting with the depending skirt portions di of the terminal posts 38, it is cut off by moving the mold from thereunder, as previously described, or in any other desired manner, and the plunger 5l then caused to descend thereinto until it engages the boss 55, as shown most clearly in Fig. 6. This forms the exhausting aperture 43 through the `base 3l and causes a corresponding rise in the glass level.

The next operation is illustrated in Fig. 8 of the parent application referred to, where the outer element $2 of the duplex plunger device is shown as having descended, while the inner element 5l remains stationary, to the position shown, thereby forming the socket 44 in the base 3| by the reduced extension 63 on the lower end of the plunger 62,

The next step in the process of making the base, after allowing the molten glass to cool suiiiciently to become rigid, is to cause the stripper device 48 to move downwardly simultaneously with the downward movement of the lower die element 53, and with or without some simultaneous downward movement of the plunger 62, thereby removing the formed base from the upper die element d6, and carrying it down with the lower die element until the outwardly extending flange 36 of the metal ring 34 engages the upper edge of the hollow stripper member E4 into which the lower die element 53 passes, thereby separating the molded base from said lower die element, as illustrated in Fig. 8 of parent case.

Fig. 7 shows how the base 3l, formed as previously described, looks whenv the associated anode 65 has been mounted on the cylindrical flange portion 35 of the metal ring portion 3d of said base, as by means or metal plates 66 riveted to the connected parts, and the leads 35i have been connected to lament, grid, and other associated electrodes which may form part of the complete radio tube.

Referrring now to this Fig. 7, we iind there a glass envelope portion `t3 applied so that its lower edge engages the outer portion or edge of the outstanding flange portion 35 of the metal ring 34, so as to ybe consolidated with it, and the corrugation 3l thereon, if used, as by means of hres (il, while the main portion of the envelope is shielded by a hollow cylindrical member 68 formed of asbestos, metal or other suitable material.

Fig. 8 illustrates an operation corresponding to that shown in Fig. 7, except that the envelope 33a is made of metal and is to be welded to the corrugation 31 of the outstanding iiange portion 36 by being pressed thereagainst and suitable electric current passed into the joint between associated electrodes 69 and 1l, while the latter functions as a support.

Fig. 9 shows a subsequent position, applicable to the radio tube of either Fig. '7 or Fig. 8, in which an exhaust tube 12 has its upper end tted in the socket portion 44 of the exhausting stub 42 for consolidation therewith, as by means of fires 13, while the parts thereabove are protected from undesired heat Iby means of apertured plate 'I4 forming a shield.

Fig. 10 illustrates the final tip-off position where after the tube has been exhausted and the exhaust tube reduced in section, the exhaust aperture is completely closed and the glass restricted by the relatively sharp fires 1G. The dotted position shows what portion of the exhaust tube is removed, and the iire 11, shown dotted, represents one for final shaping and annealing purposes after removing the exhaust tube 12.

Figs. 11 to 13, inclusive, are views corresponding generally with Figs. 1, 'l and 2 except that a modied form of base is illustrated in which the use cf a metal ring 34 is dispensed with, the envelope 33b being united directly with the molded glass -base 3l", provided as indicated in the preceding embodiment Wit'h contact posts 38b having leads 39h, and an exhaust stub 42h. In the present embodiment, as illustrated in Fig. 13, the stub 42b is shown completely sealed after exhaustion, agreeing in this respect generally with Fig. 1D after nal shaping by the fire 11, with the aid of a shaping die, if desired, as disclosed in the parent application referred to.

The manner of connecting the envelope 33lo to the all-glass base or stem 3lb is de'sirably as follows, reference being had iirst to Fig. 12. In said ligure, the glass envelope portion 33b is applied so that its free or lower edge engages the outer portion or edge 0f the outstanding glass flange portion 36h, corresponding with the outstanding ange portion 36 of the metal ring as illustrated in Fig. 7, so as to be consolidated therewith, as by means of fires 61h, while the main portion -of the envelope is desirably shielded from overheating, as by a hollow cylindrical member 68b formed of asbestos, metal, or other suitable material. Drooping of the portion during sealing may obviously be prevented by using a support, such as represented lby the member 1| in Fig. 8.

The fires `Elb act 0n and soften the abutting outer or free edges of the envelope and outstanding base Vor stem flange 36h, eiecting a union between the engaged edges. If the fires (ilb are continued after such an edge union for a still greater length of time, the united edge portions may melt t-o a greater extent and result in a further consolidation, as illustrated in Fig. 13. However, it is not necessary to continue the heating to this extent, as desirable results are obtainable by effecting merely an edge union.

From the foregoing disclosure, it will be seen that we have devised a novel form of glass base for electric tubes which may be molded directly from freely flowing molten glass, thereby avoiding some subsequent steps usually performed. The bases formed may have incorporated therewith, not only contact prongs and lead-in conductors, but also exhaust tube stubs to which exhaust tubes are readily connected and, if desired, also a Kovar (which is a well-known nickel-cobaltiron alloy) or other metal ring having an outstanding ange to which an anode may be conveniently connected and/or a glass or metal envelope, and which has a circular opening in which a mass of fused glass is poured for consolidation therewith. If a metal envelope is connected to such a ring, the use of a separate anode may be dispensed with, as the metal envelope, itself, may serve as an anode.

By virtue of the foregoing invention, one is enabled to -make tubes for radio, andother electrie or electronic devices, which carry leading-in conductors and outer contact elements and keep them parallel and otherwise accurately positioned with respect to one another, so that they t interchangeably into standard sockets. Distortion, which might tend to offset the requisite accuracy of the lead-in conductors and outer contacts therefor, is `avoided by the 4fact that the glass is molten and sealed around rthe conductors, and the embedded portions of the outer contact members, While said elements are maintained in a-'ccurately constructed molds. A glass-filled circumferential groove lof sufficient depth to form a permanent seal, is provided in each lead-in and contact device between its skirt portion 4l and support 39.

Subsequent possible distortion, lduring sealing of the envelope portion to the base or stem, is avoided by retraining from the application of a softening temperature to the relatively thick walled body portion of said base, `which is provided for by having an outstanding relativelythin, peripheral metal or glass flange, 3.6 or 36h, desirably disposed intermediate the upper and lower surfaces of ,the base, to the outer edge of which the corresponding lower or Ifree edge of the envelope 33, 33EL `or 33h is sealed. By Virtue of the construction, it is not even necessary to use a guard shell around the stem of base portion of the tube, especially if a metal ring 4'! is incorporated therewith.

Although preferred embodiments of the invention have been disclosed, it will be understood that modifications may be made, within the spirit and scope of the appended claims.

We claim:

1. A molded glass base having terminal posts extending therefrom andan exhausting stub disposed adjacent said posts, each post comprising a generally cylindrical terminal lportion, a flared skirt extending therefrom and with its free edge embedded in the glass base, a lead extending beyond said skirt and projecting from the opposite surface of said glass base, the extreme end of said exhausting stub having a socket for connection with an exhaust tube.

2. A molded glass base having tubular terminal posts extending therefrom and an open exhausting stub disposed therebetween and terminating in a socket for the reception of an exhaust tube,v

each post having a flared skirt with its free edge embedded in one face -of the base and a lead extending through and beyond said skirt and sealed through and projecting from the opposite -face of the base, and an annular metal element consolidated with the glass Iof said base-and having a flange projecting `outwardly for connection with an enclosing envelope.

3. A molded glass base having tubular terminal posts extending therefrom and an open exhausting stub disposed therebetween and terminating in a socket for the reception of an exhaustg'tube,

each post having one end embedded in one face of the base glass and a lead extending through and 8 beyond said end and projecting from the opposite face of the base.

4. An electric tube comprising a molded glassl base having tubular terminal posts extending therefrom and an open exhausting stub disposed therefrom and an open exhausting stub disposedtherebetween and terminating in a socket for the reception of an exhaust tube, each post having one end embedded in one face of the base and a lead extending through and beyond vsaid end and sealed through and projecting from the opposite surface of the glass base, a metal element consolidated with said glass base and comprising a hollow cylindrical portion having a flange projecting outwardly, electrodes mounted on said leads and the inner surface of said cylindrical portion, and an enclosing envelope with its lower edge secured to said flange.

6. An electric tube comprising a base portion consisting of a relatively-thick-walled body member with lead-in conductors sealed therethrough, a ange with substantially flat and parallel upper and lower surfaces, relatively thin as compared with the body wall thickness, outstanding from the peripheral surface of said body member, and a glass envelope portion closed by having its edge united to the outer edge only of said flange.

'7. An electric tube comprising a base portion consisting of a relatively-thick-walled body member with lead-in conductors sealed therethrough, a flange with substantially nat and parallel upper and lower surfaces outstanding from the peripheral surface of said body member and relatively thin as compared with the body wall thickness, and a glass envelope portion closed by having only its edge united only to the outer edge of said flange.

8. An electric tube comprising a base portion consisting of a relatively-thick-walled body member with substantially flat parallel upper and lower surfaces, lead-in conductors sealed therethrough, a ange with substantially at and parallel upper and lower surfaces outstanding from the peripheral surface of said body member and relatively thin as compared with the body wall thickness, and a glass envelope portion closed by having only its edge united only to the outer edge of said flange.

9. An electric tube comprising a relativelythick-walled generally circular body member with lead-in conductors embedded therein and extendby having its edge united only to the outer edge of said flange.

11. In combination, a stem assembly for electric tubes comprising a relatively thick glass wall member having substantially flat parallel up-per and lower surfaces, a relatively thin sealing edge projecting from said Wall member, a plurality of lead-in conductors sealed into said Wall member, and a glass envelope sealed only to the outer edge of said sealing edge.

12. In combination, a stem assembly for electric tubes comprising a relatively thick glass Wall member having substantially fiat parallel upper and lower surfaces, a, relatively thin lsealing edge projecting from said Wall member, a plurality of lead-in conductors sealed into said Wall member, said conductors being parallel to each other and having their lower ends disposed in a plane, and a glass envelope sealed only to the outer edge of said Isealing edge.

13. In combination, a stem assembly for electric tubes comprising a relatively thick glass Wall member having substantially flat parallel upper and lower surfaces, a sealing edge having a thickness at the point where it join-s said Wall member substantially less than the thickness of said Wall member and projecting from said Wall member a substantial distance With substantially uniform thickness, a plurality of lead-in conductors sealed through said Wall member, and a glass envelope sealed only to the outer edge of said sealing edge.

14. A stem for an electric space discharge device comprising a glass Wall member, a metal lead-in conductor sealed through lsaid glass member, said lead-in conductor having an external section and an annular member formed on said external section and sealed to the outer face of said glass member, the glass of said Wall member extending around the sides of said annular member and being sealed thereto.

15. A stem for an electrical space discharge device comprising a glass wall member, a metal lead-in conductor sealed through said glass member, said lead-in conductor having an external section of suilicient rigidity to serve as an external contact pin and being exposed in the final form of said device te serve as such a contact pin, and an annular member formed on said external section and sealed to the outer face -of said glass member, the glass of said Wall member extending around the sides of lsaid annular member and being sealed thereto.

16. In a vacuum tube, an evacuated envelope having a relatively thick portion formed entirely of a single fusible material, and a plurality of lead-in and contact devices extending from the exterior of said envelope through said portion to the interior of said envelope, and directly engaging said material, the maintenance of the vacuum Within said envelope being dependent upon the establishment and maintenance of a direct seal between said devices and said material, said seal including a circumferential groove on each device lled with said material, said groove being of suiiicient depth so that the material therein forms a permanent seal about the device.

17. In an electrical device which comprises an enclosing metal Wall part having an opening therein, the combination which includes glass fused in the said opening, combined lead-in conductor and terminal post device extending through and sealed to said glass, and a flange formed on the device and fused to the surface of the glass.

18. In an electrical device, an envelope, a body of glass forming a portion of the wall structure of the said envelope, a combined lead-in conductor and terminal post device sealed through the glass, and a flange on said device and sealed to a surface of the glass body in the regi-on of its union with the device.

19. A lead-in arrangement comprising a body of fusible vitreous material, a rigid cylindrical lead-in conductor device sealed through the vitreous material and having a portion extending on one side of said vitreous material to form a contact prong, said device being grooved at the region of its union With the vitreous material, and vitreous material of said body in Asaid groove.

20. A lead-in arrangement comprising a body of glass serving as a sealing-in means, and a rigid cylindrical lead-in conductor sealed through the glass and having a, portion extending on one side of said glass body to form a contact prong, said conductor bearing a flange, only the glass-adjacent-end-portion of which is sealed to said body, leaving uncovered the remainder of said flange.

21. In an electrical device which comprises a sealed container, the combination which includes a body of glass and forming a. part of the Wall structure of the container, and a solid cylindrical lead-in conductor device sealed through the glass and shaped at its outer extremity to serve as a contact prong, said device being grooved at the region at which it passes through the glass.

22. In an electrical device which comprises an enclosing metal Wall part having an opening therein, the combination which includes a mass of glass fused in the said opening, and a solid cylindrical lead-in conductor device sealed through the glass and having a portion extending on one side of said glass to form a contact prong, the said device being grooved at the region of its union with the said glass.

FIDELITY UNION TRUST COMPANY, Eecutor of the Last Will and Testament .of Harry D. Madden, Deceased, By J OHN S. BACI-TELLER,

Assistant Trust O17lcer. JAMES W. GREENBOWE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 21,163 Rose, Jr July 25, 1939 586,055 Olan July 6, 1897 916,844 Colby Mar. 30, 1909 1,813,593 Walton July 7, 1931 1,967,852 Wright July 24, 1934 1,980,840 Wright et al Nov. 13, 1934 2,006,818 Zimber July 2, 1935 2,046,671 Bruijnes July 7, 1936 2,052,542 Thomas Aug. 25, 1936 2,056,621 Roberts Oct. 6, 1936 2,082,848 Rose, Jr June 8, 1937 2,089,044 Thomas Aug. 3, 1937 2,148,314 Wright Feb. 21, 1939 2,171,226 Schoonenberg Aug. 29, 1939 2,195,483 Franke Apr. 2, 1940 2,219,573 Franeckel Oct. 29, 1940 2,219,574 Franeckel Oct. 29, 1940 2,250,183 Miller July 22, 1941 FOREIGN PATENTS Number Country Date 485,665 Great Britain Nov. 24, 1937

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