US2657531A - Wall cooling arrangement for combustion devices - Google Patents

Description

L. J..PIERCE 2,657,531 WALL coouuc ARRANGEMENT FOR COMBUSTION DEVICES Nov. 3, 1953 Filed Jan. 22, 1948 2 Sheets-Sheet 1 ooxra 06;; ace 2) o I o 9 O o o o 0 0 o Invent-J01". Lowell J Dierce l-lis Attorney.

, WALL; COOLING ARRANGEMENT FOR COMBUSTION DEVICES Filed Jan. 22, 1948 L. J. PIERCE Nov. 3, 1953 2 Sheets-Sheet 2 Inventor. Lowell-J. Dieboe,

His Attorney Patented Nov. 3, 1953 WALL COOLING ARRANGEMENT FOR COMBUSTION DEVICES Lowell J. Pierce, Saugus, Mass., assignor to General Electric Company, a

York

corporation of New Application January 22, 1948, Serial No. 3,760

11 Claims. 1

This invention relates to apparatus for effecting heat releasing reactions between two fluid reactants and particularly to improved means for cooling the structural walls of such devices.

It has found particular utility in connection with the combustion of fluid fuels in air, as for example, in combustors for gas turbine powerplants. It is this application of the invention which I have elected specifically to illustrate and describe. It is to be understood, however, that the invention is not limited thereto necessarily; and it may be used in various types of rocket motors where many other reactants are employed.

This invention is an improvement in the wall cooling arrangements disclosed in an application of Anthony J. Nerad, Serial No. 750,015, filed May 23, 1947, now Patent No. 2,601,000, and assigned to the same assignee as the present application.

An object of the invention is to provide an improved construction of combustor for fluid fuels which has good performance characteristics wit improved life expectancy.

A further object is toattain improved combustion efliciencies by insuring complete combustion of the fuel before it is discharged from the combustor in an unburned condition together with reaction products, and by preheating the oxidizing fluid.

Another object of the invention is to provide an improved arrangement for passing cooling and insulating fluid strata over surfaces which are exposed to hot reaction products, so as to prolong combustor life by minimizing or preventing the occurrence of localized heating of such surfaces in order to avoid the harmful effect of thermal stresses arising from the existence of an extreme temperature gradient between localized hot regions and the cooler surrounding regions, while permitting operation at extremely high combustion temperatures and with improved uniformity of temperature distribution of the reaction products.

Other objects and advantages will be apparent from the following description taken in connection with the accompanying drawings in which Fig 1 is a view, partly insection, of a thermal reaction chamber in accordance with the invention; Fig. 2 is an enlarged detail view of the arrangement illustrated in Fig. 1 showing the chamber wall and deflectors; Fig. 3 is a sectional view of the deflectors taken on the plane 33 in Fig. 2; Fig. 4 is a view of a portion of the reaction chamber of Fig. 1 adjacent the fuel spray means; Fig. 5 is a partial view looking along the axis of the chamber toward thefuel spray means taken 2 on the plane 55 in Fig. 4; Fig. 6 is a longitudinal section of a reaction chamber embodying a modified arrangement of the invention; and Fig. '7 is an enlarged detail View of the arrangement illustrated in Fig. 6 showing the liner wall and deflectors.

Referring now to Fig. 1, an outer housing or casing is illustrated at l, defining an air supply space or plenum chamber 2, in which a cylindrical inner wall or liner 3 is co-axially supported, as for instance, by a plurality of perforated radially extending fins or bafiles 4. A closure at one end of the chamber is formed by the end dome 5 through which projects a fuel nozzle 6, preferably of a type which produces a hollow conical spray 6a of fuel particles. The fuel spray nozzle may advantageously be of the duplex type, which is more fully disclosed in an application of C. D. Fulton, Serial No. 622,604. filed October 16, 1945, now Patent No. 2,590,853, and assigned to the same assignee as the present application. The means for supplying fuel to the spray nozzle 6 is not essential to an under standing of the present invention and is therefore not shown. For the purpose of illustration, the combustor shown is similar to one disclosed in the above-mentioned application of A. J. Nerad; but it should be noted that the invention may be also applied to other combustion devices of the general type described.

As is more particularly described in the abovementioned Nerad application, air at a pressure appreciably above ambient is conveyed to the air supply space or plenum chamber 2, by means of a conduit from a suitable compressor (not shown). Combustion air is then admitted to the reaction space defined within liner 3 through a plurality of spaced openings i.

To admit cooling air to the inner surfaces of the liner wall 3, I provide a plurality of openings 8 in spaced relation with openings 1. To deflect this cooling air so as to direct it along the inner surface of the liner wall 3, there are a plurality of deflectors 9. Various types of air deflectors in accordance with the invention which have been found to beeffective, are illustrated in Figs. 2, 4, and '7. In Figs. 1 to 3 these deflectors are separate sheet metal plates 9 having a first end portion bent as indicated at 9a to provide two tabs which may conveniently be spot-welded to the inner surface of the liner 3. Approximately at the center of each plate is formed a dimple 9b, which is also welded to the liner, as may be seen in Fig. 3, to form a third point of support for the plate. At the end remote from the tabs 3 9a, plate 9 has a curved end portion to, which is supported in spaced relation to the liner wall and in somewhat overlapping relation to the next adjacent deflector, as clearly shown in Fig. 3.

In operation, cooling and insulating fluid flows through holes 8, as indicated by arrows It in Figs. 2 and 3, and is caused to fan out";later-al"- 1y through the elongated restricted orifices defined between the side edges and curved end portion 90 and the liner Wall. Also, the curved end 90 directs a film of cooling and insulating fluid along the outer surface of the next deflector, as indicated by arrow 16a in Fig. 3.

A sufficient number of cooling "air openings 3 are provided, and they are rnad'e of such a size that a thin substantially continuous envelope of cooling air flows over the inner surface of the liner wall 3, in volume and extent suff cient to cool the liner wall. This film of cooling air also serves to prevent the deposition and adherence of carbonized fuel particles on the inner surface of the wall.

As illustrated in Figs. 4 and 5, to provide adequate cooling of, and to prevent deposit'sof carbon on, the inner surface of the end dorne 5,

there are a plurality of cooling and insulating air adrnission openings Ill spaced in a cireum ferential row around the dome 5, and cooperating with these openings are a series of deflecting plates Ii, each being attached atone end to the inner surface of Wall 5 by welding or other suitable means. It will be observed that these plates are similar to the plates 55 bfFigs. 1-3, but as more particularly shown in Fig. 5, the deflecting plates II are arranged so that each overlaps the adjacent plate by a very substantial amount. Referring to Fig. 5, it will be seen that one end of each deflector H is also arranged in spaced relationship with the inner surface of wall 5 and with the overlapped portion of the next adjacent deflecting plate. The other end of the deflector is riveted to the demo 5, as shdwn in Fig. 5.

It has been found by experiment with cor-m busters of this general Nerad type shown in 1, that because of the high velocities produced around the exterior of the end dorne, the static pressure in this region sometimes is lower than that existing within the dorne. When such conditions exists, there is a tendency for the fluid inside the dome to flow outward through openings iii into the plenum space 2. This is undesirable because it upsets the basic cycle of op eration. To prevent such outward flow and to insure an inward flow of cooling air through the L openings iii, there may be provided an enclosing wall or shroud I'Z which is ordinarily substarn tially hemispherical in shape, although not necessarily so, and in which is located an opening is in co-axial relation with the spray 'no'z zle 6. Opening ii} is made of substantially greater diameter than that of the spray nozzle 6 so as to define therewith an annular air inlet.

Referring now to Fig. 1, the operation of the cornbustor is as follows. Air from the supply means flows in the direction of arrows I4 into the plenum space 2. From this space the major portion of the air flows through the combustion air inlet openings E to form discrete jets, as indicated by arrows it. A second portion of the air flows through the cooling air openings 8 and is deflected by plates 55, as indicated by arrows H5 in Figs. 2 and 3. This flow in the direction of arrows It fans out laterally to form a thin film of comparatively cool fluid which serves to insulate the inner surface of liner 3 from contact with hot reaction products, which may contain unburned fuel particles. If such particles were permitted to contact the surface of liner 3, which is comparatively cool relative to the reaction products, they would be deposited in the ferm of "unburned carbon. Thus, it will be seen that the air flow It serves both to cool liner 3 and to insulate it from contact with unburned carbon particles which might otherwise be deposited thereon; It will be appreciated that excessive carbon deposition necessitates frequent disassembly of the apparatus for cleaning and fother servieing, which is of course undesirable. In Fig. 3, it will be seen that the flow It also serves to insulate, "cool, and prevent the deposition of carbon particles on the surfaces of the adjacent deflectors 9.

previously indicated, it has been found that the static pressure existing within the dome 5 may be less than that within the plenum chambet 2 in the region irnrnediately adjacent the doine. Experience has also shown that in certaincases' the static pressure existing within dome 5 is also less than the total pressure of the air in the plenurn space 2 immediately adjacent the come. As previously stated, opening is is made of substantially greater diameter than that of the fuel nozzle 6 thus forming an annular inlet through which a third portion of the air supply flows fl'OlXlllh space 2 in the direction of arrows I i through opening l3 into the space 12a formed by dome 5 and shroud 12. The resulting dii ference between the total pressure of the air supplied to the space 12a and the static pressure existing within the reaction space has been found to be suflicient to cause a flow of air through openings it. After it enters the dome. this cooling air flows in the direction of arrows H, as more particularly described in a co"p'endirig application of Walter L. Blatz, Serial No. 644,888, filed February 1, 19%, now Patent No. 2,581,999, and assigned to the same assignee as the present application. As illustrated in Fig. 5. this flow ll also forms a thin film of cool air to insulate the inner surfaces of the deflectors H from contact with hot reaction products which also may contain unburned fuel particle's. Thus it will be seen that the air-flow ll serves also to cool the deflecting plates H and to insulate them from contact with unburned carbon particles which might otherwise be deposited thereon.

It is desiredto particularly point out that the quantity of cooling air flow to the interior surface of the liner wall is dependent upon the static pressure difierence existing between the air supply space 2 and the static pressure existing within the reaction space. In order to keep the overall pressure drop across the reaction chamber to a minimum, it is desirable to reduce to a minimum the quantity of cooling air flow; therefore the aggregate area of the cooling air openings 8 should preferably be kept as small as possible. Also, I have found that as the size of the cooling air openings 8 is increased, relative to the size of the combustion air inlet openings l, the wall of the liner 3 tends to run cooler and the temperature distribution of the reaction products issuing from the chamber becomes non-uniform. This imbalance is usually manifested by a net core of gases extending longitudinally down the center of the liner. in practice, any specific design must be made a compromise based on the desired degree of wall cooling, the permissible degree of temperature variation at the exit of the liner, and

5 the permissible overall pressure drop across the reaction chamber.

I have discovered that the optimum aggregate area of the openings 8 should be maintained in the range from .3 to .4 of the aggregate area of all openings in the wall of the liner, that is, the openings 7, 8, and I I]. Also the aggregate area of the cooling openings 8 and It should be kept in the range of .40 to .65 of the aggregate area of the combustion air inlet openings '7.

I have determined by extensive experiments with combustors having a substantially cylindri cal reaction space and substantially round cooling openings 8, that excellent results are obtained if the diameter of the cooling openings 8 is from .05 to .15 of the average diameter of the reaction space. Furthermore, the center-to-center longitudinal spacingof the openings should beoi the order of three times the opening diameter. The optimum circumferential spacing will be somewhat dependent upon the size and capacity of the combustor employed. That is, as the size of the combustor is increased, it will be necessary to employ a greater number of circumferentially spaced openings 8 in order to obtain a continuous film of insulating and cooling air.

It is also desired to point out that the thickness of this protective envelope of insulating and cooling fluid should be minimized in order to avoid disturbing materially the reaction taking place in the chamber. I have discovered that best results are obtained by maintaining the spacing between the deflector wall 9 and the inner surface of the liner 3 from .003 to .03 of the average distance, measured normal to the longitudinal axis of the reaction space, between directly opposed wall portions of the liner.

It will be understood by those skilled in the art, that the liner 3 and the end dome 5 are most subject to deterioration during the operation of the reaction'chamber and therefore require most frequent inspection, servicing, and replacement. My invention provides a mechanically simple yet extremely effective arrangement for cooling the liners of thermal reaction chambers and also for preventing carbon deposition thereon, so that operating temperature limits can be raised and life expectancy increased. 7

Figs. 6 and 7 illustrate a modification of the invention as applied to a combustor shown in the above-identified Nerad application. Here the air supply space or plenum chamber 2 is defined by the wall of liner 3 and the outer housing I. Air under pressure is supplied to the plenum chamber 2 by means of a conduit 30; from a suitable compressor (not shown). Both combustion air and cooling air enter the liner through the spaced holes I8. Here the cooling air deflectors are formed by longitudinal strips l9 secured in spaced relation with the inner surface of liner 3 and in cooperative relation with openings I 8.

It will be obvious that the deflectors I 9 may be constructed in many other different ways. For example, as illustrated in Fig. '7, they may be formed from a single strip of thin sheet metal having a row of suitable spaced holes therein. To provide surfaces for attachment to the inner wall of liner 3 and to maintain desired radial spacing between the deflector and the liner, dimpled portions 2i may be provided at conveniently spaced intervals between the holes 20. These portions may be secured to the wall of liner 3 by welding, riveting, or by any other convenient means of attachment. Deflectors I9 may also consist of a fiat strip of sheet metal having a row of spaced holes 20 therein, and suitable other types of spacer members located at various intervals between the-holes. In some instances it may be desirable to provide flexibility between the points of attachment of the deflector strips to the liner 3. This is necessary in some cases due to the fact that the walls of the liner 3 and the deflector I9 will operate at different temperatures. In such cases, flexibility is required to care for the relative differential thermal expansion between these parts. This flexibility may be provided by the reverse bends 22 in the deflector, but it will be appreciated that other convenient means for accomplishing this result may be employed.

The deflectors I9 are arranged in such relation with openings I8 that openings I8 and 20 are in substantially co-axial alignment. For reasons which will appear later, opening 20 is made of appreciably smaller diameter than opening I8.

Operation of the apparatus illustrated in Fig. 6 is as follows. Air from the plenum chamber 2 flows through openings i 8. The major portion of this air then flows through an opening 28 in strip I9 to form a discrete jet 23 of combustor air. The remaining portion of the air is deflected laterally by walls I9, causing it to form a thin substantially continuous protective envelope of cooling and insulating fluid which flows transversely across the adjacent surfaces of wall 3 as indicated by arrows 24. This flow also serves to cool the walls of deflector I9.

As previously mentioned, it is desirable to minimize the cooling flow and, in practice, a compromise with respect to desired degree of cooling and permissible temperature variation must be made. With reference to these considerations as applied to the embodiment of the invention illustrated in Fig. 6, I have discovered and verified by tests that the appropriate ratio of the aggregate area of openings 20 to the aggregate area of openings I8 is of the order of .5. It is also desirable to minimize the thickness of the protective envelope of cooling and insulating fluid for reasons previously indicated. Here also best results are obtained by maintaining the spac'mg between deflector I9 and the inner surface of the liner from .003 to .03 of the distance between directly opposed wall portions of the liner.

While particular embodiments of the invention have been illustrated and discussed, it is intended that these embodiments shall be considered as illustrative only. It will be apparent to those familiar with the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claims all such changes and modifications as come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a combustor for effecting heat releasing reactions between fluid reactants and having liner walls subject to contact with hot reaction products and defining an elongated reaction space closed at one end and open at the other for the discharge ofreaction products, wall cooling and insulating means comprising liner wall portions defining a plurality of spaced first orifice means arranged to admit fluid reactant into the reaction space, a plurality of second orifice means in said wall in spaced relation with the first orifice means and adapted to admit comparatively cool insulating fluid in a direction substantially normal to said wall into the reaction space, the aggregate area of the second orifice means being "froih 54b "to .65 or the area "or the era orifice means, and a plurality of deflector mantel-s secured in spaced relation to the inner suriace of the liner walls and incoope'r'ative relation with said second orifice means to define restricted openings for discharging a thin substantially continuous film of fluid across the liner wall.

2. In thermal reaction apparatus having a wall defining an elongated reaction space and subject to contact with hot reaction products, cooling and insulating means for said wall including a plurality of circumferentially spaced longitudi- -na1 rows of axially spaced openings in said wall adapted to admit comparatively cool fluid in a direction substantially normal to said wall into the re ction space, and a plurality of separate defies or znernbers each having one end por tion secured to the liner wall and a second end portion in substantially overlapping relation to the surface of the next adjacent deflector -and spaced therefrom, said deflector members being arranged in cooperative relationship with said openings to define restricted openings for dis charging a thin substantially continuous film of cooling and insulating fluid across the inner surface of said wall and on the surface of said adjacent deflector.

3. In a thermal reaction. chamber having a liner defining an elongated substantially cylindrical reaction space and subject to contact with hot reaction products, wall cooling and insulating means comprising liner wall portions deflning a plurality of substantially round openings adapted to admit comparatively cool fluid into the reaction space in a substantially radial dlrection, said openings having a diameter from to .15 of the diameter of the reaction space and being arranged in straight circumferentially spaced longitudinal rows having an axial centerto-center spacing of the order of three times the diameter of the openings, and deflector means comprising a plurality of separate members 'se cured in spaced relation to the inner surface of the liner in cooperative relationship with said openings and with adjacent deflector wall por- Y tions to define restricted openings for discharging a thin substantially continuous film of fluid laterally across the inner surface of said liner and adjacent deflector wall surfaces, the spacing of the deflectors from the wall being from .003 to .03 times the liner diameter.

1. An end dome for the reaction. chain ber compris i ll defining a substantially hemispherical surl having central opening arranged to receive fuel spray means, said dome having a plurality of openings arranged in a circumferen ial row and adapted to admit com paratively cool insulating fluid into the reaction space, a plurality of deflector members secured in spaced relation with the inner surface of the wall and in cooperative relation with said openings, each deflector having a first end portion secured to the dome and a second end portion arranged in substantially overlapping relation with an adjacent clefleotor so as to define -restricted openings for diaoharging a thin substantially continuous fllni of fluid laterally across adjacent portions or the inner doine surface with at least a portion of said fluid flowing radially inward along the inner wall surface and a second portion flowing in a substantially circumferen tial direction across the surface of the adjacent deflector.

5. An end dome for a thermal reaction chamber comprising a wall defining a substantially .8 hemispherical surface with a central openihg adapted to receive fuel spray means, a plurality of spaced openings in the wall arranged in a circumferential row and adapted to admit coolmg and insulating fluid into the reaction space, shroud means surrounding the dome with walls in cooperative relation with the openings and "adapted to receive and conduct fluid uniformly to said openings, a plurality of deflector members each secured in spaced relation to the inner surface of the wall in cooperative relation with at least one of said openings and arranged in substar-ltiall'y overlapping relation with an adjacent deflector so as to define restricted openings for discharging a thin substantially continuous film of fluid across adjacent portions of the inner wall surface with at least a portion of said fluid flowing radially inward alongthe inner wall surface toward the central opening and a second portion flowing substantially tangentially across the surface of the adjacent deflector.

6. In a combustion chamber having 'a wall forming a substantially cylindrical reaction space, an end dome comprising a substantially hernispheric'al wall with a central opening adapted to receive fuel injection means, and cooling and insulating means for the dome including a plurality of substantiallyround openings in said wall arranged in a circumferential row in a common plane normal to the longitudinal axis of the reaction space, shroud means enclosing the dome and in cooperative relation with said openings, said openings having a diameter from .05 to 5 times the diameter of the reaction space, and a plurality of deflector members each secured in spaced relation to the inner surface of the dome and arranged in cooperative relation with at least one of said openings, each deflector being in substantial tangential overlapping relation with an adjacent deflector soas to define restricted openings having a radial width of .003 to .03 times the diameter of the reaction space for discharging a thin substantially continuous film of insulating and cooling fluid across adjacent portions of the hemispherical wall surface with at least a portion of said fluid flowing radially inward along the inner surface of said wall and a secondportion flowing tangentially across the surface of the adjacent deflector.

'7. In a thermal reaction chamber having an inner liner defining a reaction space and subject to contact with hot reaction products, means for forming a protective envelope of cooling and insulating fluid on the inner surface of the liner including a liner wall portion defining a first opening, a deflector member having a second opening and secured in spaced substantially parallel relation to the liner wall with said openings in substantially co-axial relation, the second opening being of substantially smaller cross sectional area than the first, means for supplying a comparatively cool fluid to the first opening whereby a substantial portion of the fluid flows through the first and second openings to form a discrete jet of reactant fluid and the rest of the fluid flows through the second opening only and is deflected laterally to form a thin protective envelope of flowing fluid over adjacent Wall surfaces subject to contact with hot reaction products.

8. In a thermal reaction chamber having walls defining a reaction space and subject to contact with hot reaction products, means for forming a protective envelope of cooling and insulating fluid on the inner surface of said Walls including a wall portion having an opening therein, a deflector member having a second opening with an area of the order of .5 the area of the first opening, the deflector being supported in spaced relation with the first Wall portion with the openings in substantially co-axial relation, and means for supplying a comparatively cool fluid to the first opening whereby a substantial portion of the fluid flows through the first and second openings to form a discrete jet of combustion fluid, and that portion which flows through the first openings only is deflected laterally to form a thin protective envelope of flowing fluid over adjacent wall surfaces subject to contact with hot reaction products.

9. In combustion apparatus for effecting heat releasing reactions between fluid reactants, a combustion chamber having outer walls, other walls defining an inner liner and subject to contact with hot reaction products and defining a substantially cylindrical reaction space, a plurality of spaced openings in the liner walls adapted to admit comparatively cool fluid in a substantially radial direction into the reaction space, deflector means secured in cooperative relation with said openings and in spaced relation to the inner surface of the liner walls and defining therewith restricted lateral openings, a closure at one end of the reaction space comprising a wall defining a substantially hemispherical inner surface with a central opening adapted to receive fuel spray means, a plurality of spaced openings in said end closure wall arranged in a circumferential row and adapted to admit comparatively cool fluid into the reaction space, shroud means including walls in enclosing relation with the end dome and said spaced openings and adapted to receive and conduct cooling and insulating fluid to the openings, a plurality of deflectors secured in spaced relation to the inner surface of the end closure wall and in cooperative relation with the circumferentially spaced openings, said deflectors being arranged with substantial overlapping in a circumferential direction of adjacent deflectors to define restricted lateral openings for discharging a thin fllm of cooling and insulating fluid over adjacent end wall portions and the surfaces of adjacent deflectors.

10. In a combustion apparatus having walls defining a combustion chamber and other walls forming an inner liner and defining a substantially cylindrical combustion space, means for forming a protective envelope of cooling and insulating fluid on the inner surfaces of walls subject to contact with hot reaction products comprising liner wall portions forming a plurality of spaced first orifice means, deflector means secured in spaced relation to the inner surface of the liner and defining second orifice means of substantially smaller area than said first orifice means and in series flow relation with the first orifice means, closure means at one end of the combustion space comprising a wall defining a substantially hemispherical inner surface with a central opening adapted to receive fuel injection means, a plurality of spaced openings arranged in a circumferential row in said closure wall and adapted to admit comparatively cool fluid into the combustion space, shroud means including a wall surrounding the end closure in cooperative relationship with said openings and adapted to receive and conduct fluid to said openings, and deflector means secured in spaced relation to the inner surface of the closure wall in cooperative relation with said openings and arranged with substantial circumferential overlapping of adjacent deflectors to define restricted openings.

11. An end dome for a thermal reaction chamber comprising a wall defining a substantially hemispherical surface having a central opening arranged to receive fuel spray means, said dome having a plurality of openings arranged in a cir cumferential row and adapted to admit comparatively cool insulating fluid into the reaction space, a plurality of deflector members secured in spaced relation with the inner surface of the wall and having an end portion substantially parallel to said inner surface and in cooperative relation with said openings, each deflector having a, first end portion secured to the dome and a second end portion arranged in substantially overlapping relation with an adjacent deflector to define restricted openings for discharging a thin substantially continuous film of fluid laterally across adjacent portions of the inner dome surface with at least a portion of said fluid flowing radially inward along the inner wall surface and a second portion flowing in a substantially circumferential direction across the surface of the adjacent deflector.

LOWELL J. PIERCE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,336,261 Scott Apr. 6, 1920 2,332,866 Muller Oct. 26, 1943 2,398,654 Lubbock Apr. 16, 1946 2,477,584 De Zubay Aug. 2, 1949 2,531,810 Fyife Nov, 28, 1950 2,537,033 Christensen Jan. 9, 1951 2,541,171 McGarry Feb. 13, 1951 2,545,495 Sforzini Mar. 20, 1951 FOREIGN PATENTS Number Country Date 588,086 Great Britain May 14, 1947

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