US3395300A - Electron discharge device envelope having heat transfer element - Google Patents

Description

D. E. ELECTRON DISCH HAVING HEAT July 30. 1968 2 Sheets-Sheet 1 Filed Oct. 14, 1965 I I I 3 B W F w I m a w w I/ 75 5: w. m 5 wMm ::v w E m i A. |-.l I n .iMU n 3 Q 3 I M 8 Q N. a a- H 2 4 w 6 p 8 H 3 2 July 30. 1968 o. E. MARSHALL ELECTRON DISCHARGE DEVICE ENVELOPE HAVING HEAT TRANSFER ELEMENT 2 Sheets-Sheet 2 Filed Oct. 1.4, 1965 FIG.4.

E V R U C G W A l R l W l R W n R N U G C a m m A 8 A T RR 1 A O N E M H R n l. N m 0 0 0 00 000000 0 0 0 0 0 0 0 00 000000 0 0 0 0 O 0 O 40 098765 4 3 2 l 5 4 3 2 I 20 3O 4O 6O 80 I00 I40 200 AVERAGE CURRENT PER IGNITRON -AMPERES United States Patent 3,395,300 ELECTRON DISCHARGE DEVICE ENVELOPE HAVING HEAT TRANSFER ELEMENT Donald E. Marshall, Beaver Dams, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 14, 1965, Ser. No. 496,077 4 Claims. (Cl. 313-22) ABSTRACT OF THE DISCLOSURE This invention relates to a pool-type rectifier in which a portion of the envelope surrounding the discharge region between the anode and cathode includes a thick section of material of high thermal conductivity and storage capacity. By this structure, heat generated within the envelope may be quickly removed from the inner surface of the envelope to provide increased operating capabilities of the pool-type rectifier.

This invention relates to electron discharge devices and more particularly to those in which a gaseous vapor is utilized.

A particular application of this invention is within a gaseous discharge device utilizing a pool-type cathode such as an ignitron. This invention is particularly directed to ignitrons for applications wherein there is intermittent service demanded of the device.

During conducting periods, the ignitron provides relatively unlimited electron emission from the mercury pool cathode. The ignitron is therefore utilized in those applications where intermittent high current demands are found such as in welding systems. It is found that during these conduction periods that the heat generated within the ignitron results in a substantial temperature rise in the envelope of the ignitron. This in turn results in a rise in the mercury vapor pressure within the envelope. It is found within this high temperature enviroment that frequent arc-back occurrences result. These arc-backs result in uneven heat control of the welds made and in some cases the unbalanced voltages resulting therefrom cause transformer saturation to occur which result in complete operation failure. This adverse feature has been accepted by the industry and has been lived with mainly because most applications of the ignitron do not require the full rated capabilities of the tubes. However, often when attempts were made to use the full capability of the ignitron, trouble with too frequent arc-backs occurred.

It is accordingly an object of this invention to provide an improved electron discharge device.

It is another object to provide an improved electron discharge device employing a pool-type cathode.

It is still another object to provide an improved ignitron providing an improved cooling system for providing an increase in peak demand current capability and an increase in maximum average current capability.

It is still a further object to provide an improved igni tron in which the arc-back rate is greatly reduced.

Briefly, the present invention accomplishes the above cited objects by providing a pool-type rectifier in which 'a portion of the envelope includes a thick section of high thermal conductivity material is good thermal transfer relationship with the interior of the envelope. A cooling medium is associated with the thick section. The thick section provided between the anode and the pool-type cathode is of high thermal conductivity material for providing heat storage capability and good conductivity of the heat from the interior of the envelope to the cooling medium which may be circulating water.

Further objects and advantages of the invention will be- 3,395,300 Patented July 30, 1968 come apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

FIGURE 1 illustrates a mercury pool tube of an ignitron type which incorporates teachings of this invention;

FIG. 2 illustrates a modification of a portion of the envelope shown in FIG. 1 illustrating another embodiment of this invention;

FIG. 3 illustrates another modification of a portion of the envelope shown in FIG. 1 and illustrating another embodiment of this invention; and

FIG. 4 are curves illustrating the properties of an ignitron according to this invention in comparsion with the properties of a prior art ignitron.

Referring in detail to FIG. 1, there is shown a gaseous electrical discharge device. The electrical discharge device comprises an inner tubular member or casing 11 of a suitable material such as stainless steel. The cylindrical casing 11 is closed at the lower end by a plate member 13. The plate member 13 has a downwardly turned flange 15 around the periphery of the plate 13. The plate 13 may be of a suitable material such as steel. The downwardly turned flange 15 of the member 13 is seam welded to the lower portion of the casing 11. The end portion 14 of the cylindrical casing 11 below the plate member 13 is flared out about its periphery as illustrated. This flared end portion 14 is welded to the inner surface of an outer tubular casing 17 at the lower end and the outer casing 17. The outer casing 17 may also be of stainless steel of a thickness of about .060 inch.

The upper portion of the inner casing 11 also has a flared out portion 12 and the external surface thereof is fitted against the inner surface of the upper portion of the outer casing 17 and is seam welded thereto. An annular space or region 19 is thereby defined between the two tubular casings 11 and 17.

An opening 21 is provided in the outer casing 17 near the lower portion of the space 19 to permit the introduction of a cooling medium such as water, or the like, into the space 19. Another opening 23 is provided near the upper portion of the space 19 in the outer casing 17 to provide an outlet for the cooling medium introduced into the space 19. In this manner, a cooling medium may be introduced into the space 19 and may be circulated throughout the space 19 from a source of cooling medium (not shown) for the purpose of reducing the temperature of the inner casing 11. In the specific device shown, water guides 18 are also provided within the annular region 19 to increase the eifective cooling action of the circulating water. A heat conductive element 16 may also be provided between the inner casing 11 and the outer casing 17 of a suitable heat conductive material such as copper. The element 16 is in intimate thermal contact with the inner and outer casings 11 and 17. A thermostat 20 may be provided on the outer surface of the casing 17 for sensing the temperature of the interior surface of the inner casing 11. This thermostat 20 may be used for controlling the flow of cooling medium. A circular lining 22 of a material such as copper is positioned within the inner casing 11 and is metallurgically bonded to the inner surface of the inner casing 11 by a suitable braze material. A suitable braze material is a stainless steel braze or a braze known under the tradename Nicro-Braze which is a nickel chrome alloy with boron, silicon or phosphor therein. This material may be obtained from the Colmonoy Corp. The liner 22 must be in good thermal contact with the inner casing 11 and of a suitable high heat conductivity material such as copper. Other suitable materials are aluminum, iron or brass. It is necessary to provide a coating 24 over the copper member 22 of a material such as iron plate to protect the copper from attack by the mercury. This coating 24 may be electroplated onto the copper to a thickness of about .002 inch to .010 inch. The thickness of the liner 22 is about .250 inch, and extends down and makes contact with the plate 13. The upper portion of the member 22 is tapered as illustrated to be substantially parallel with the outer surface of an anode 46.

The plate member 13 which serves as a closure member for the bottom portion of the inner tubular member 11 also provided the bottom surface of a container for a mercury pool cathode 29. The pool cathode 29 is retained within the lower portion of the envelope formed by the plate 13 and the adjacent wall of the liner member 22. A cathode terminal and support member 9 is welded or brazed to the under surface of the plate member 13.

An igniter electrode 31 is inserted into the mercury pool cathode 29 in a suitable manner. The igniter electrode 31 consists of a body of high resistance material such as boron carbide. The igniter 31 is supported by an arm 33 which is in turn supported by rod 35 of insulating material such as ceramic. The rod 35 passes through an aper ture provided in the plate 13. A terminal 38 is provided exterior of the envelope for application of potential to the igniter 31.

The anode 46 is of a suitable material, such as graphite, and is positioned in the upper portion of the envelope. The anode 46 is provided with a supporting conductive rod 48 which extends above the upper portion of the casings 11 and 17 to provide an external terminal 40 for the anode 46. A plate or disc member 43 is provided having a downwardly turned flange 45 about its periphery. An aperture 26 is provided in the center of the plate member 43 providing an opening through which the anode rod 40 passes. The disc 43 is welded to the rod 40 about the aperture 26 to provide a vacuum tight seal. The plate member 43 is of any suitable material such as Kovar alloy (Westinghouse Electric Corporation trademark for an alloy of nickel, iron and cobalt). The annular edge of the downwardly turned flange 45 on the plate 43 is sealed to the upper edge of a cylindrical member 28. The member 28 is of a suitable insulating material, such as borosilicate glass. The lower edge of the glass cylinder 28 is sealed to the inner upwardly turned flange 32 of an annular trough-shaped member 30. The outer surface of an outer upwardly turned flange 34 of the member 30 is welded or brazed to the inner surface of the casing 11 below the flared out portion 12. The inner flange 32 of the member 30 is of a similar material as plate member 43, while the remainder of the member 30 may be of steel. The inner flange portion 32 is resistance welded to the remainder of the member 30. A shield member may be provided between the cathode 29 and the anode 46 to further reduce possibility of arc-back in a well-known manner.

In FIG. 2, there is illustrated a modification of the invention shown in FIG. 1. The structure shown in FIG. 2 is modified in that a portion of the inner casing 11 is removed and the copper liner 22 is in direct contact with the cooling fluid. The liner or thick region 22 is provided with a series of water guides 52 on the outer surface for improving the cooling of the member 22.

In FIG. 3, there is shown a liner 54 in which the inner surface is provided with circumferential grooves 56 to increase the heat transfer area. This permits the use of a material such as iron. Iron is less expensive than copper and does not require a corrosion resistant coating. Iron has a lower thermal conductivity than copper.

In the application of the ignitron, an alternating potential is impressed between the anode 46 and the pool cathode 29. A discharge is initiated between the cathode 29 and the anode 46 by means of the igniter assembly 31. By proper circuitry and associated controls, the periods of conductivity of the ignitron can be controlled by the igniter 31. In the specific application of resistance welding,

the ignitron is called upon to carry in some applications heavy current for the welding operation. This is normally an intermittent operation and therefore it is normal procedure that the tube be able to carry for brief intervals current much in excess of that it could carry in continuous operation. During the conducting period, the heat generated in the tube must be removed or the increase in temperature will increase the mercury vapor pressure. The likelihood of arc-back when the anode 46 is negative with respect to the cathode 29 is greatly intensified. The cooling system provided by the flow of the water between the inner wall 11 and the outer wall 17 of the ignitron provides continuous cooling and of course would perform the function of cooling where the tube is in continuous operation. However, in the case of the intermittent operation wherein the device is called upon to supply a current larger than that normally permitted in continuous operation, it is found that water cooling does not adequately provide the necessary protection of the tube from arcback. By providing the relatively thick section 22 of high thermal conductivity material a vastly improved ignitron is provided. In addition to the fact that the arc-back rate is greatly reduced over the prior art devices, it is also found that the ignitron provides a 60 percent increase in peak demand current capabilities and a 60 percent increase in the maximum average current capabilities for resistance welding application. It is believed that this vast improvement is obtained by the heat storage capability of the thick wall portion 22. During the conductivity periods, the heat generated in the tube is absorbed into the thick wall region 22. This reduces the amount of temperature rise of the mercury condensing surfaces and therefore reduces rise of mercury vapor pressure in the tube. The lower vapor pressure results in much less tendency for arc-back thus improving the reliability of the tube. It is important that the thick wall section 22 or 54 be made of a high heat conductivity material so that the heat that is generated at the inner surface of the tube envelope can diffuse rapidly from the inner surface into the depths of the thick wall 22 or 54. It is important therefore that the corrosion resistive coating 24 used with liner 22 also be of a high conductivity material or very thin in order to permit the dilfusion of the heat rapidly from the inner surface of the ignitron into the thick region 22. The water guides 18 and 52 provided on the outer surface of the inner wall 14 provide a high velocity water flow in this thick region and provide more efficient cooling. The thick wall 22 or 54 is used around the discharge region of tube in order to conserve the amount of the expensive high conductivity material in comparison with stainless steel. It is also important that the low temperature cooling be provided near the mercury pool cathode 29. It is found that less eflicient cooling in the region of the anode 46 is advisable to provide for reduction of mercury condensation in the anode region which of course causes the arcback due to the mercury particles striking the anode. In addition, the bafiie 50 which is provided between the pool cathode 29 and the anode 46 also provides a feature within the tube which reduces the frequency of arc-back. The baflle assembly 50 is to prevent mercury thrown by mechanical action of the arc on the cathode 29 from striking the anode 46. The tapered anode 46 promotes the collection of electrons on the side of the anode 46 thus reducing current density at the anode face and thereby reducing the anode face temperature and the arc-back rate.

In FIG. 4, two curves are shown to illustrate the improved capabilities of this invention over the prior art type of ignitron. The vertical scale represents the demand current during the weld and the horizontal scale shows a corresponding maximum on time plus off time average current rating of the ignitron. Any points to the left of the curves represents permissible operating condition for the tube. The area between the curves represents additional operating conditions permissible 'for this invention described herein in contrast to the prior art.

The theory of water cooling teaches that white the water itself can absorb large quantities of heat it does not make a perfect thermal contact with the surface of the water jacket. In fact, the temperature of the tube envelope under load is always greater than the water temperature. This difference in temperature is directly proportional to the energy density flowing from the water jacket surface to the water. If a tube is operated at about a 16 to 1 duty ratio, this temperature difference during conduction could be 16 times the value which would be found under continuous operations at the same long time average current. For comparable operation, the cooling surface would have to be 16 times greater in area for the on/off operation than for continuous operation at the average current. However, if the heat generated in the ignitron during the on time can be stored in a mass of metal and then be cooled during the off time, the 16 to 1 ratio of temperature rise can be materially reduced. Previous ignitrons were designed without consideration of the transient temperature rise of the envelope walls. To prevent corrosion caused by the Water cooling alloy steel were used. These materials are generally of low thermal conductivity. The diffusion of heat into the material is slow and the surface temperatures therefore during the on times rose to comparatively high values, resulting in frequent occurrence of arc-back.

Ignitrons according to the invention described herein exhibit arc-back frequency many times lower than the prior art type of device. In fact, the improvement is so great that an increase in rating of these tubes is possible to the degree shown in FIG. 4.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will occur readily to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. An electron discharge device comprising an envelope, said envelope having a pool-type cathode provided at one end thereof, an anode supported above the cathode and defining the discharge region therebetween, said envelope comprising an outer cylindrical member of stainles steel, an inner cylindrical member of stainless steel and a liner of a material having higher thermal capacity than stainless steel surrounding said discharge region and being metallurgically bonded to the inner surface of said inner member, said liner having a corrosion resistive coating thereon of less than .010 inch in thickness.

2. An electron discharge device comprising an envelope having a pool-type cathode therein, an anode supported within said envelope and insulated from said cathode and defining the discharge region therebetween, said envelope comprising a cylindrical portion and end plates for each end thereof, said cylindrical portion including an inner cylindrical member and an outer cylindrical member, means provided between said inner and outer cylindrical member for conducting a cooling medium to provide cooling of said inner member, a liner member thicker than said inner cylindrical member bonded to the inner surface of said inner cylindrical member, said liner of a material of higher thermal capacity and thermal conductivity than said inner cylindrical member and positioned so as to surround substantially said electron discharge region to provide heat storage and high conductivity of heat generated within said envelope to said cooling medium.

3. An electron discharge device comprising an envelope, said envelope having a pool-type cathode provided at one end thereof, an anode supported above the cathode and defining the discharge region therebetween, said envelope comprising an outer cylindrical member of stainless steel, an inner cylindrical member of stainless steel and said inner member including a portion of a material having higher thermal capacity than said stainless steel surrounding said discharge region, said portion thicker than the remaining portion of said inner member to provide heat storage and having a serrated inner surface to provide a large area heat conducting surface.

4. An electron discharge device comprising an envelope having a pool-type cathode therein, an anode supported within said envelope and insulated from said cathode and defining the discharge region therebetween, said envelope comprising a cylindrical portion and end plates for each end thereof, said cylindrical portion including an inner cylindrical member and an outer cylindrical member, means provided between said inner and outer cylindrical member of conducting a cooling medium to provide cooling of said inner member, a liner member bonded to the inner surface of said inner cylindrical wall member, said liner member of a material of high thermal capacity and thermal conductivity and positioned to surround at least said electron discharge region to provide storage and high conductivity of heat generated within said envelope to said cooling means, said liner member being thicker than said inner cylindrical member having an irregular surface to provide a large area to increase removal ratio of heat from said discharge region.

References Cited UNITED STATES PATENTS 2,121,579 6/1938 Bahls 313-20X 2,224,750 12/1940 Slepian et al. 31318 X 2,433,181 12/1947 White 313-18 X 3,045,138 7/1962 Pohl 313-21 DAVID J. GALVIN, Primary Examiner.

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