US2788081A - Electrostatic gas-treating apparatus - Google Patents

Description

April 9, 1957 E. M. RANSIBURG 2,788,081 smc'rkos'mnc GAS-TREATING APPARATUS 1 Filed SeptLlO, 1952 v 2 Sheets-Sheet 1 INVENTOR.

EDWIN M. RANSBURG BY ATTORNEY April 9, 1957 E. M. RANSBURG 2,788,081

zwcmosmxc GAS-TREATING APPARATUS Filed sept. 1Q, 1952 2 Sheets-Sheet 2 INVENTOR. EDWIN M. RANSEURG ATTORNEY Unite States Patent ELECTROSTATIC GAS-TREATING APPARATUS Edwin M. Ransburg, Indianapolis, ind assignor to Ransburg Electro-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application September 10, 1952, Serial No. 308,746 12' Claims. (Cl. 183- -7) This invention relates to devices for treating a moving stream of gas with liquid particles, and more particularly to apparatus for removing dust and other particles from a gas stream by electrostatic means. More specifically, it relates to means for charging the dust or other particles in the gas, to means: for charging liquid particles downstream for precipitating the dust, to means for dispersing those liquid particles into the gas stream, and to means for readily separating the liquid particles after they have become dust-laden from the gas stream. This application constitutes a continuation-in-part of my co-pendmg application, Serial No. 235,747, filed July 9, 1951, now abandoned.

It is common in effecting dust removal electrostatically to subject charged dust particles to a field of oppositely charged liquid particles. Conveniently, gas cleaning devices operating on this principle are constructed in the form of a short section of gas duct, the cleaning section being installed in the duct as a portion thereof. The overall operation of such gas-cleaning devices is dependent upon the action of at least four inter-related component steps or functions, namely: charging the dust particles to'one polarity, charging the liquid particles downstream to the opposite polarity, causing the charged liquid particles to move into the gas stream to capture the dust, and eliminating the dust-laden liquid from the duct. Each of these component actions, which mutually contribute to the desired gas-cleaning result, I have improved by my invention.

The. first step in electrostatic gas cleaning is that of electrically charging the dust particles. The conventional method of charging or attempting to charge these particles consisted of moving the gas through a grid of metal wires or other structure formed across the gas-carrying ductand maintained at an ionizing potential. Difficulty was often experienced in charging a suificiently high percentage of the particles to make the apparatus efficient due to inability to bring the ionizing zone of the field created by the wires or other conventional structure into etfecttve particle-charging association with the gas-carried particles. When it was sought to provide sufiicient particlecharging structure to gain high particle-charging efficiency, the presence of the structure itself created an ob ectionable resistance to proper flow of the gas through the apparatus; i

The second and third steps in electrostratic cleaning of a gas stream are those of charging liquid particles downstream for dust attraction, and causing those liquid particles to be dispersed into the gas stream to snare or capture the oppositely-charged dust particles. It is apparent that the efficiency of the precipitation process is a function of the number of and dispersion of the precipitationcausing liquid particles in the gasthe greater the number of particles and the more intimate their admixture with the gas, the more likelihood of contact between the gas-borne particles and the precipitation-causing particles. Heretofore, liquid particle dispersion has been attempted by the use of nozzles or orifices, through which liquid is sprayed under gaseous or hydrostatic pressure to form a spray made up of particles which initially possess a velocity component transverse to the gas stream. The charge has been induced in the spray by the use of an ionizing electrode either positioned near the nozzle or made a part of the nozzle, in conjunction with a non-discharging electrode spaced from the ionizing electrode. Pressure atomizing often resulted in the formation of undesirable large, non-uniform drops of liquid.

In many commercial installations portions of the spray would often impinge on the non-discharging electrode, and build up as relatively large drops. These drops upon deposition assume an opposite charge to that of the nearby ionizing electrode and tend to reatomize carrying their new charge, thus partially neutralizing the charge borne by the dust-capturing portion of the spray, thereby limiting the effective charge imparted to the spray. The nozzles often-times become clogged by impurities, rust buildup, etc. Moreover, the liquid particles would in many cases soonjlose their transverse velocity component supplied by the pressure atomizer and hence the particles would then heat in the duct in the direction of the gas stream. The ability of the particles to move transverse to the gas stream increases the likelihood of their contact with dust particles and thus their quick loss of velocity transverse to the gas stream lowers their particle'precipitating efliciency.

The fourth main phase of electrostatic air cleaning is the removal of the dust-laden liquid from the duct. Baftles, water traps and other apparatus for this function have been employed. The advantages of my liquid-eliminating means, in respect to positiveness of liquid elimination, to low gas flow resistance, and to economy of operation and maintenance, will become apparent as the description is understood.

It is therefore one object of my invention to improve the dust-charging means so that less resistance is offered to gas flow, and at the same time increasing the effectiveness of the dust-charging operation.

It is another object to improve gas treatment by providing greater liquid particle dispersion, uniformityand movement in the gas stream.

It is another object to improve the spray-producing and spray-charging means to permit lower liquid pressure and more effective particle-charging.

It is another object to provide more efiective means to remove the dust-laden spray from the gas stream. 1

Further objects and purposes will become apparent as the description is understood.

In carrying out my inventnon as embodied in a gas cleaner, I employ a dust-charging means, preferably comprising an open cone mounted centrally in the gas stream and maintained at a substantial potential difference with respect to the duct. Conveniently, the duct is ground.- ed and the cone insulatedly supported; and a high-voltage potential, applied between the cone and the-duct-wall, causes a stream of ions, formed in the gas adjacent the sharp edge of the cone, to flow away from the cone and towards the duct-wall. The ions, in their travel, collide with dust particles carried in the gas. As a result, these dust particles become charged to the same electrical sign as the cone. I find that this dust-charging means offers less resistance to gas flow than the standard dust-charging grid of rods and fine wires.

The spray-creating apparatus, which is located inside the duct a short distance downstream from the dustcharging means, preferably comprises a device which atomizes the liquid from the extended edge of a thin liquid film. By rotation of a POl'tlOl'lOf the device or other means the liquid is formed into an extended film from the edge of which atomization takes place into an electrostatic field." For use in ducts of circular crosssection, the atomizing head may be disposed centrally of the duct, and arranged to support an annular film of liquid from the peripheral edge of which atomization takes place. For use in ducts of square or rectangular cross-section, the atomizing head is conveniently arranged to support a liquid film which is plane and which has a substantially straight edge from which the atomization takes place. In the latter case, the duct is desirably provided in one wall with a pocket, and the atomizing head is located within such pocket out of the gas stream, the head being so disposed that the film edge from which atomization takes place is substantially parallel to the opposite wall of the duct. When the centrally mounted, circular head is used, the duct is conveniently made of metal and grounded, the head being insulatcdly supported and connected to one terminal of a high voltage source which has its other terminal grounded. In the other arrangement described, the walls of the duct adjacent the atomizing head are made of insulating material except for the wall or wall-portion located opposite the head, such opposite wall or wall-portion being of conductive material and being grounded while the head is connected to the ungrounded terminal of the high voltage source.

In either of the embodiments described, an electrostatic field will exist between the edge of the film supported on the atomizing head and the opposed, spaced duct-wall or duct-wall portion. It has been found that atomization under such conditions as just described will be effected from a number of closely spaced cusps formed along the film-edge and will result in the formation of a great number of uniform, very finely atomized particles. These particles, being highly charged to approximately the same potential, will tend to disperse one from the other and at the same time the particles will move in the direction of the lines of force of the electro-static field into which atomization takes place. Since at least a portion of the walls of the duct opposite the atomizing device are at a potential opposite from the charged liquid particles, it will serve as a highly etficient collecting electrode. Thus, the atomized liquid spray particles can be made to follow a course generally transverse to the path of the gas-borne particles. Such a path for the spray particles combined with the uniformly fine atomization from an,extended edge and the wide dispersion of the spray particles one from another results in an extremely high degre of amalgamation between charged liquid particles and the gas-carried particles. The liquid particles, proceeding under the influence of electrostatic forces transversely of the gas stream in the duct, collect the oppositely charged dust particles in such stream, and impinge on the duct-wall or duct-wall portion.

To remove the dust-bearing liquid, the duct-wall, at the region where the liquid particles impinge upon it, is shaped to collect the liquid particles. Since it is possible to control the path of the particle-collecting, electrically-charged liquid spray to a greater degree than previously realized, the invention also permits control of the area of deposition of the spray particles. Accordingly, there is provided means generally in the form of an offset pocket or section of the duct into which the particlecarrying liquid which has been deposited on the duct walls will flow. Gravity may conveniently be used to carry the deposited liquid from the area of deposition to the otiset pocket or section where the liquids can then be collected into a considerable body and removed from the duct by a conventional drain or other liquid carrying means.

The accompanying drawings illustrate my invention:

Fig. 1 is an elevation, in partial section, showing an embodiment of my invention in a vertical duct;

Fig. 2 is a side elevation, in partial section, showing an embodiment of my invention in a rectangular, horizontal duct; and

Fig. 3 is an end elevation taken on the line 3-3 of Fig. 2.

The embodiment shown in Fig. 1 shows the cleaning apparatus as used in a vertical duct, the direction of gas flow being upward. The gas approaches the cleaner through inlet duct 10 and passes first through association with the dust-charging means. The dust-charging means shown includes a conical-type discharge electrode 12, insulatedly mounted coaxially of the inlet duct 10. To create an electrical potential between the cone 12 and the duct 10, a high-voltage, direct current supply 14 is employed. One terminal of the electrical supply is grounded, and the other terminal, say the negative one, is connected to the cone 12 by insulated wire 15. The duct 10, which is conveniently of metal, is grounded. To adapt the cone 12 as a discharge electrode, it is provided with an attenuated annular discharge portion 16 of extended peripheral length with respect to the inlet duct 10, so that the electrostatic field will be highly concentrated near the ion-emitting portion 16. Conveniently, this portion is made as a part of the cone by converging the inside and outside cone walls near the cone base to form a sharp edge. I find that a slight outward flare 18 near the cone-base assists in concentrating the field. The high potential applied between the cone 12 and the duct 10 causes a stream of ions formed in the gas adjacent the discharge portion 18 to fiow towards the duct 10. In their travel, the ions collide with dust particles carried in the gas. Thereby, the dust particles become charged with the same electrical signas that of the discharge cone 12. For the purposes of describing my invention, I will call that charge negative, though it could be positive if appropriate changes are made in the polarity of elements further downstream.

After passing the dust-charging means, the gas next approaches the spray-forming means, designated generally by reference numeral 20. This means 20 is located relatively near the dust-charging means, and includes a rotating atomizer, conveniently of the general type more fully described in my co-pending application Serial No. 143,994, filed February 13, 1950. This atomizer is insulatedly mounted with respect to the duct on an insulating support 22, and is positioned substantially centrally of the duct 10. The atomizer includes a hollow cone 30, journaled in the atomizer body 31 coaxially with the duct and adapted to discharge atomized particles of the collecting liquid by means now to be described.

Collecting liquid is supplied, through the apex of the cone 30, into the hollow interior of the cone by means of a pump 32 and a non-conducting lead-in pipe 33. The rate of liquid supply is so co-ordinated with the rate of liquid discharge that all the liquid leaving the cone 30 will be in the form of atomized particles. So that the pump does not have to be insulatedly mounted with respect to the ground, the liquid and the pipe 33 are preferably non-conductive. The cone 30 is revolved about its own axis so that centrifugal force distributes the liquid as a film evenly around the inside cone-wall and urges the liquid inthe cone upwardly along the sloping wall to the annular rim 34. For causing rotation of cone 30, I may employ a motor 38, a speed reducer 40 and a flexible shaft 42, arranged to drive an insulated shaft 44 bearinged in and running centrally of the insulator 22. Gearing 46, enclosed in the atomizer body 31, imparts rotation to the cone 30 from the shaft 44.

A high voltage potential, from a direct current source 48, is applied by way of insulated wire 49 between the cone 30 and the wall of discharge duct 50 in order to impress a charge on the atomized liquid particles. The charge on the cone 30 is positive so that the liquid particles discharged therefrom will be of opposite polarity to the charge on the dust particles, so that the dust particles will be electrostatically attracted to and captured by the liquid particles.

The electrostatic charge possessed by the atomized liquid particles will be opposite to that of the duct wall immediately adjacent to the rotating atomizer. The centrifugal force of the rotating atomizing head combined with the electrostatic forces will tend to move these particles from the edge of the atomizing head to the adjacent duct walls, but the particles soon lose any velocity due to centrifugal force while the electrostatic forces continue to act. Thus, the like charge on the particles will cause them to disperse one from another. These dispersed particles moving generally across the gas stream and along the lines of force of the electrostatic field existing between the edge of the atomizing device and the opposite duct walls result in an extremely high efliciency of liquid particle-dust particle amalgamation both by electrical movement of the liquid particles and their resultingextremely wide admixture throughout the moving gas stream and also by electrical attraction between closely adjacent liquid and dust particles. Upon contact between the liquid particles and dust particles, the dust particles will be captured either by forces existing between the two particles or by the dust particle being dissolved in the liquid particle. In any event, the liquid particles and dust particles are usually brought together into an inseparable relationship and as a unit move toward the duct wall.

The dust-laden liquid particles strike the discharge duct 50 and tend to drain downwardly by gravity. To collect and eliminate this dust-carrying liquid, I form the discharge duct-wall into a low-level portion in the form of an annular, upward-opening trough 52, whose smallest diameter is the same as the upstream diameter of the gas duct. The trough 52 is provided with a drain 54 for removing the dust-laden liquid to waste or to a filter either in a re-circulating line or in a dust salvage system. g

It has been observed that the fineness of atomization produced by a rotating atomizing head such as described above depends to a considerable degree upon the thickness of the liquid film distributed along the outer edge of the rotating member-thin films tend to promote fine atomization. In the case of a rotating atomizing head, the velocity with which the liquid approaches the rim of the head varies with the rotational speed of the head. By increasing the speed of the head the thickness of the film edge from which atomization takes place will be decreased and thus fineness of atomization of the liquid material will usually be increased. I have found that if the atomizing heads of the apparatus described in my prior application are rotated at such speeds as to subject the liquid at the fihn-edge to a centripetal force of at least 1000 times the force of gravity the size of the atomized particles is not greatly affected by the strength of the field at the site of atomization. Thus rotational speeds for conventional-sized (eight to three inches) atomizing heads of from about 10,000 R. P. M. to 30,000 R. P. M. have produced particles of satisfactory fineness even without having the periphery of the atomizing head serving as one terminus of an electrostatic field or at least have permitted the intensity of the electrostatic field to be drastically reduced without lowering the quality of atomization. Nevertheless, it has been found desirable to maintain a substantial field at said site in order to promote efiective particle charging.

To cause charged liquid particles to pass through the gas stream in a horizontal duct of rectangular crosssection, I prefer to use the embodiment shown in Figs. 2 and 3. Here the dust particles are charged negatively by passing through an electrostatic field created by a grid of wires 56 and rods 57, held at a potential difference by a high-voltage source 58, and mounted within the inlet duct This particular dust-charging means 56, 57, 58 is not new and forms no part of my invention. A short distance downstream from the dust-charging means 56-58, the conductive inlet duct 10 is provided with a non-conducting duct extension 66, which extends into the discharge duct 68. Upon this extension 66 and at one side of the gas stream emerging therefrom is mounted an atomizer designated generally by reference numeral 70, of the blade type such as is shown in the copending application of W. W. Crouse, Serial No. 141,509, filed January 31, 1950. The .atomizer shown includes a film-supporting blade 74, a revolving roller 76 for feeding liquid to the blade 74, and a liquid-supply chamber 78. The blade 74 is charged positively by means of high voltage source 80 and lead-in wire 82 so as to be of opposite polarityto the charge on the dust particles charged by the means 5658. To insure effective concentration of field-strength at the edgeof the blade 74 and movement of the atomized particles across the gas stream emerging from the duct-extension 66, the portions 84 of the duct in the region of the atomizer 70 are made of non-conductive material, while opposite the atomizer 70, the duct has a wall-portion 85 made of conducting material. The non-conductive duct portion 84 is enlarged near the atomizer 70 to form a pocket housing the atomizer.

The feed roller 76, actuated by motor 86, through insulating shaft 88, dips into the liquid chamber 78 and carries the liquid to the blade 74. Theliquid is supplied to the chamber 78 by a lead-in pipe 90. Preferably the liquid and the lead-in pipe are non-conductive, so that the main fluid supply (not shown) need not beinsulated with respect to the ground. The rate of liquid supply to the chamber 78, and the turning speed of the feed roller 76, are co-ordinated with the rate of liquid dis charge off the blade 74 so that all particles leaving the blade will be in the form of charged, uniformly atomized particles. Since the blade is charged positively, the

liquid particles discharged therefrom will also be posi- 1 tively charged and will attract and ensnare the negatively charged dust particles passing through the dust-precipitating field. The dust-laden liquid particles will then be carried onward to impinge on the conductive duct-wall 85, and the drops will collect on that duct-wall.

For collecting and removing the dust-laden liquid in this horizontal duct embodiment, I form the duct-wall 85 with a low-level portion 96 of funnel-like shape. This low-level portion 96 is drained by a drain 98, which leads to waste or to filter means, not shown. v

In operation of both types of apparatus described, the dust-laden gas first passes through an ionizing electrostatic field whereby a charge of one sign is created on the dust particles, such field being created by a high potential applied between an ionizing electrode anda nondischarging electrode. The charged dust particles next enter the dust-precipitating zone to be capturedby oppositely charged liquid particles passing through the gas stream. The liquid particles are formed by means of atomization from a film-edge and which is affected by a high potential applied between the discharge duct-wall and a liquid-supporting electrode. The lines of force of the electrostatic field existing by virtue of such potential extend transversely of the gas stream, with the result that the charged particles are first dispersed and then accelerated along those lines of force, moving across the stream to the duct-wall. This type of atomization produces a great number of uniformly finely divided liquid particles from the atomizing element which disperse and move toward the opposed duct-wall in the form of an atomized mist, the liquid particles electrostatiscally ensnare the dust particles, and the dust-laden mist is precipitated. Thus the gas is left substantially free of liquid particles. As the liquid particles, now dust-laden, impinge upon the discharge duct wall, they drain to a low level portion, and are then conducted away either to waste or to a filter in a recirculating line or in a dustrecovery system.

It will be noted that the deposited liquid particles tend, immediately upon deposition, to flow under the influence of gravity to regions where the electrostatic field is relatively weak and that the liquid thus collected is promptly and continuously removed. This minimizes the possibility that liquid will be re-atomized from the duct wall.

In describing the apparatus illustrated in the drawings,

. ing action.

I have contemplated that the gas-borne particles to be removed will be charged negatively and the particles of the liquid spray will be charged positively. It will be obvious, however, that those polarities might be reversed, if desired. I have also contemplated that the collecting duct-wall portion will be grounded and the charging electrodes maintained at potentials difierent from ground; but this arrangement is not essential, as all that is necessary in the maintenance at each electrode of an electrostatic field of proper direction to accomplish the desired charg- If the gasstream is not adequately cleaned by the single collecting means shown in each embodiment, one or more additional collecting means, spaced along the duct, may be employed. If dust entrapment by the liquid particles is adequate but some of the dustladen liquid particles escape deposition, the second collecting means may be of the dry type. The atomizing apparatus may be used apart from the dust-charging means where it is desired merely to treat a moving gas stream with a fine liquid spray.

I claim:

1. In an electrostatic precipitator in which a gas stream bearing particles to be precipitated flows through a duct past a particle-charging means which imparts electrical charges of one sign to the gas-borne particles, means for creating a spray of oppositely charged liquid particles moving transversely of such stream, including an atomizer and means for supplying liquid to said atomizer said atomizer having a surface which supports a liquid film with an extended edge for atomizing finely divided liquid particles from the extended edge of said supported film, and means including a high voltage source having one terminal connected to the supported liquid film for creating an electrostatic field capable of charging said particles and of electrostatically dispersing and propelling such charged particles transversely of the gas stream.

2. The invention set forth in claim 1 with the addition of an electrode spaced transversely of the duct from said atomizer, the other terminal of said high voltage source being connected to said electrode whereby liquid spray particles will be urged toward and will impinge on said electrode, and means for promptly removing liquid collecting on said electrode.

3. The invention set forth in claim 2 with the addition that said electrod is a portion of a wall of said duct.

4. The invention set forth in claim 1 with the addition that said duct is of substantially circular cross-section, said liquid-supporting surface is adapted to form the liquid into an annular film having an exposed, circular edge substantially concentric with the duct, and the wall of said duct is of electrically conductive material and is electrically connected to the other terminal of the high voltage source.

5. The invention set forth in claim 4 with the addition that the .film-edge from which atomization takes place is rotated about its axis.

6. The invention set forth in claim 1 with the addition that said duct is of substantially circular cross'section,

" ing liquid collecting on the electrode.

said-atomizer forms the liquid into an annular film having an exposed edge lying in aplane transverse to momrectiop, of gas flow through the duct, an electrode surrounding and radially spaced from said film-edge, and the other terminal of said sqnrce being connected to said electrode whereby the charged liquid particles discharged from the atomiger w'll be electrostatically urged toward and will impinge on, e electrode, and means for remov- 7. In combination with if vertically extending, circular duct adapted to convey stream of gas bearing suspended particles, means for imparting electrical charges of one sign to the gasborne particles, an electrostatic atomizer locuted centrally of said duct posterior to said particlecharging means for creating a spray of liquid particles charged oppositely to the gas-borne particles, the wall of the duct adjacent the atomizer being formed to provide an annular trough opening generally upwardly into the duct, the duct wall immediately above said trough being formed of electrically conductive material, and a highvoltage source having opposite terminals connected to said atomizer and conductive duct-wall whereby charged liquid particles emanating from said atomizer will be electrostatically urged toward the duct-wall to impinge thereon and run downwardly into said trough.

8. In combinaton with a duct adapted to convey a stream of gas bearing suspended particles, means for imparting electrical charges of one sign to the gas-borne particles, said duct having an outwardly offset pocket posterior of said particle-charging means, an elongated electrostatic atomizer located in said pocket and extending in a direction tranverse to the direction of gas fiow through the duct, the wall of said duct opposite said pocket including an electrically conductive portion, and a high-voltage source having its opposite terminals con- .nected respectively to said atomizer and duct-wall portion to create therebetween an electrostatic field for atomizing liquid particles charged oppositely to the gasborne particles from said atomizer and for impelling such charged liquid particles across the gas stream to impinge on said duct-wall portion, said pocket and adjacent portions of the walls of the duct being formed of insulating material.

9. In combination with a duct adapted to convey a stream of gas heating suspended particles, means for imparting electrical charges of one sign to the gasborne particles, at least one wall of said duct posterior of the particle-charging means being oi'r'set outwardly to form a trough in said wall, and means for directing transversely of the duct and toward said trough for collection therein a spray of liquid particles bearing electrical charges opposite in sign to those borne by the gas-borne particles.

10. In apparatus for precipitating gasborne particles, first and second spaced electrodes, said first electrode having a surface terminating in an extended edge, means for supplying liquid to form a film on said first electrode surface, means including a high voltage source for maintaining between the liquid film on said first electrode surface and the second electrode an electrostatic field for electrostatically atomizing discrete charged particles of liquid from the extended edge of said film supported on said first electrode, and means for causing a particlebearing gas stream to pass between said electrodes and the particles therein to be precipitated by said charged liquid particles.

11. In apparatus for precipitating particles suspended in a body of gas, firstand second spaced electrodes, means for supplying liquid atia controlled rate to form an extended liquid film over said first electrode for atomization in the form of finely divided liquid particles into the space between said electrodes, means including a high voltage source for establishing an electrostatic field between the liquid on said first electrode and the second electrode for electrically charging and moving said atomized liquid particles from the vicinity of said electrode toward said second electrode, and means for introducing the body of gas into the space between the electrodes and for causing the particles suspended therein to be precipitated by said charged liquid particles.

12. Apparatus comprising means including a duct to convey a stream of gas-bearing particles suspended therein, an annular discharge electrode coaxial with and within said duct, the wall of said duct opposite said discharge electrode being circular and of electrically conducting material, a first high voltage source whose opposite terminals are connected respectively to said discharge electrode and the opposite duct-wall to create a particle-charging annular region about said discharge electrode which imparts electrical charges of one sign to the gas-borne particle, means downstream of said particle-charging region for creating a spray of oppositely charged liquid particles moving transversely of said stream, said spray creating means comprising an atomizer and a second high voltage source whose opposite terminals are connected respectively to said atomizer and to the duct-wall immediately opposite said atomizer, and liquid-collecting means offset outwardly from said duct-wall to form a low-level portion thereof beneath that portion of said wall spaced opposite from said atomizer.

References Cited in the file of this patent UNITED STATES PATENTS 10 v Elasasser June 17, 1930 Bowman Dec. 5. 1939 Brown July 9, 1940 Penney Sept. 5, 1944 Piquerez May -1, 1945 FOREIGN PATENTS Great Britain July 28,51941

Images