US3136484A - Angular blast gas cap - Google Patents

Description

June 9, 1964 F. J. DlTTRlcH ANGULAR BLAST GAS CAP Filed June 22, 1960 INVENTOR United States Patent O 3,136,484 ANGULAR BLAST GAS CAP Ferdinand J. Dittrich, ellmore, NX., assigner to Meteo Inc., a corporation of New `lersey Filed June 22, 1960, Ser. No. 38,031 5 Claims. (Cl. 23S-79) This invention relates to an angular blast gas cap for a heat-fusible material spray gun. Heat-fusible material spray guns are devices in which a heat-fusible material is fed into a heating zone, where the same is melted or at least heat-softened, and then propelled in finely divided form, as for example, against a surface to be coated. The heat-fusible material may be fed to the heating zone in a finely divided or powdered form, in which case the gun is generally referred to as a powder type gun, or in the form of a rod or wire (the term wire being used generically to define both of these elements), in which case the gun may generally be referred to as a Wire type gun.

In heat-fusible material spray guns of the Wire type the Wire is fed into the heating zone, in which the tip of the wire is melted or at least heat-softened, and a blast gas, such as air, is directed against the tip of the wire thus heated in order to atomize ne particles from the Wire and propel the same in the form of a spray. The blast gas is generally directed against the tip of the wire by means of a blast gas cap, often referred to as an air cap, as air is usually used as the blast gas.

The most common commercially utilized heat-fusible material spray guns utilize a combustion flame for heating, and frequently an additional blast gas for atomizing and propelling is used. Thus, for example, the heat in the heating zone may be generated by the burning of a fuel gas, such as acetylene or propane, with air or oxygen, and the blasting where a separate blast gas is provided, may be effected with air, nitrogen or the like. A typical heat-fusible material spray gun of the wire type is, for example, described in U.S. Patent 2,340,903.

Less common types of spray guns do not provide for blast gas but utilize the expanding combustion gases as a blast gas by allowing the same to expand from a confined combustion zone through a throttle nozzle or to expand through an elongated nozzle or the like.

In accordance with newer constructions, the heat for the melting or heat-softening of the heat-fusible material is produced by a plasma flame, i.e., a flame in the energy state above the gas state, with electrons being actually stripped from the atoms of the material forming the gas. The plasma is most commonly generated utilizing an electric arc and most usually a constricted arc. The plasma flame may be used for spraying in a manner similar to the combustion llame, and a separate blast gas may be used for atomizing and propelling the material being sprayed, if desired.

Other modes have been known or proposed for generatin g the heat for heat-fusible material spray guns. These include electric heating, as for example electric resistance heating or induction heating or ordinary arc heating. With the use of an ordinary electric arc two separate heatfusible material wires may be fed forward at a converging angle and an electric arc struck therebetween. A blast gas may then be propelled against the arc, atomizing the wires as they are consumed and melted in the arc, and propelling the atomized material away from the arc in the form of a spray. Alternatively the wire or powder may be, for example, fed through an electric arc formed from separate electrodes,

In heat-fusible material spray guns of the powder type the powdered heat-fusible material is generally fed, entrained in a small stream of carrier gas, into a flame where the same is heated to heat-softened or molten con- 3,136,44 Patented June 9, 1964 ICC dition and propelled by the velocity of the combustion gases from the flame or by means of a separate blast gas to the surface being sprayed.

For certain applications it is necessary to change the direction of the heat-fusible material spray. Thus, when spraying in confined spaces, such as interior surfaces, as for example when spraying the interior of tubes or cylinders, it is necessary to deflect the spray at an angle to its normal direction so that the spray gun nozzle, as such, or at the end of an extension may be inserted in the tube or cylinder, in'the general direction of its axis, and effect the spraying of a sprayed coating on the Walls of the tube or cylinder. For this purpose the spray was generally directed against a solid deflector surface which would deflect the spray and project the same against the tube or cylinder side wall. The solid deflector surface was generally formed as part of a special blast gas or air cap, known as an angular blast gas or air cap. This angular aircap would have the construction of a conventional blast gas or air cap except that its outlet opening was ollset to one side at an angle to its normal axis, and the interior adjacent its outlet opening was in the form of a rounded and smooth deflector surface. Thus, in effect, the outlet opening was, for example, directed at an angle of 45 from the normal axis, and the interior of the cap was constructed as a rounded deflector surface in order to deflect the spray stream and direct the same out through the outlet opening at this angle. The cap and the portion forming the deflector were generally constructed of metal.

These angular caps presented various difficulties in operation and were very sensitive to flame conditions, wire speed and air pressure adjustments. In order for the same to function properly, it was necessary that the molten tip of the wire be precisely positioned at a fixed spot with respect to the deflector surface. If this tip would be too close to the deflector surface, sprayed heatfusible material, such as the metal, would deposit on the surface, causing sticking, spattering and the like. If the tip were too far away from the deflector surface, the angle of spray would change and the work would not be evenly coated. The difliculty of maintaining the tip at this exact required position may be readily appreciated when considering the dynamic conditions encountered during operation, with the wire constantly being moved and with metal being constantly melted and atomized off from the tip at a fairly rapid rate. A very slight change in the flame characteristics, the air flow or even the metallurgy or crystal structure of the Wire will affect the position of the wire tip and thus can cause difficulties as mentioned above.

Even when the wire tip is precisely maintained at the desired position with respect to the deflector surface of the cap, the caps still have a tendency to loading with spray metal, which of course changes the flow characteristics around the deflector section, causing difilculties. A frequent interruption of operation, with cleaning and polishing of the caps, is thus generally required in operation. Furthermore the caps, particularly with respect to the deflector section, must be manufactured with precision and maintained in this condition, for if the same contains burrs, pits or roughnesses, turbulent flow may be caused which in turn will permit the sprayed metal to deposit on the cap. This in turn will result in disturbance of the flame, flickering, and spattering of the spray, and ultimately back-firing or sticking of the wire in the nozzle. In spite of these many disadvantages of long standing in the art, a more satisfactory solution for the deflection of the spray was not found. Attempts to effect the deflection of the sprayed stream by the use of an additional blast gas or gas curtain in place of the solid deflector surface, did not prove practical. The spray stream from the heat-fusible material spray gun is not homogeneous and there is a higher percentage of larger particles in the center of the stream, with most of the finer particles being concentrated at the outside of the stream. These fine particles in turn contain a higher percentage of oxides, which are deleterious to the coatings. In normal spraying procedures these fine particles are blown away by deflection vof the gas stream as it strikes the Work, and thus are not deposited in harmful quantities on the work surface. When attempts were made, however, to deflect the normalY direction of the spray stream with the use of an auxiliary blast gas stream or curtain of gas, the original distribution of the particles is disrupted, so that the finer particles with the deleterious oxides are no longer deflected from the surface, but will be deposited, producing an inferior coating. Furthermore, the larger particles are given an asymmetrical distribution pattern, which results in an uneven coating when, for example, spraying is effected in the conventional manner, i.e., the surface is sprayed with overlapping stripes.

Gne object of this invention is to overcome these dii culties. A further objectV of this inventiony isa novel angular blast gas cap which overcomes these difficulties. These and still further objects will become apparent from the following description read in conjunction with the Vdrawings in which:

FIG. l is a vertical section of an embodiment of an angular blast gas cap in accordance with the invention;

FlG. 2 is a cross-section of the embodiment shown in FlG. l; Y

FlG. 3 is a partial vertical section showing the air cap of FlG. l as positioned on a metal flame spray gun;

FIG. 4 is a plan view of the embodiment shown in FIG. 3;

FiG. 5 is a plan view of a portion of a further embodiment of an angular cap in accordance with the invention;

FIG. 6 is a plan View of a portion of a still further embodiment of an angular cap in accordance with the invention; and

FIG. 7 diagrammatically shows a vertical, cross-sectional view of a portion of a powder gun in accordance `With the invention.

The invention is particularly applicable to flame spra guns of the wire type, but as hereinafter described is also applicable to other types of heat-fusible material spray guns.

In accordance With the invention it has been surprisingly discovered that the deflection of the stream of heatfusible material being sprayed may be effected by a separate blast gas stream without the disadvantages previously encountered if this separate blast gas stream is of a cross-sectional shape approximating that of a trough, with the plane of the base of the trough bisecting the axis of the normal spray direction at an anglebetween about 60 and 90 and preferably at about 90. If the side walls of the trough-shaped blast gas stream extend in the normal spray direction, the shape of the stream will not be appreciably distorted. If these side walls, however, extend opposite the normal spray direction, i.e., point upstream of the normal spray direction, then the deflected spray stream will be distorted into a fan shape but will still produce an excellent quality coating, and this dis` torted shape may be useful in certain instances.

rl`he defiecting trough-shaped blast gas stream is preferably generated by passing a blast gas through a multiple number of jets having a corresponding trough-shaped configuration, but may be generated in any other known or desired manner. A preferred embodiment'of the invention comprises an angular blast gas or air cap which,

in contra-distinction to the conventional angular air cap,

does not have an offset outlet opening or nozzle, but an outlet or nozzle extending in the normal axial direction and is provided with means, such as a multiple number of jets of the proper configuration off to one side thereof, for directing a trough-shaped blast of gas transversely across the outlet opening, with the plane of the base of the trough bisecting the axis of the blast gas flow passage through the cap at an angle between about 60 and 90.

Referring to the embodiment shown in FIGS. 1 4 of the drawing, the angular blast gas cap in accordance with the invention comprises a housing 1, of metal or other suitable material conventionally used for the construction of air caps, defining Va blast gas flow passage 2 extending substantially axially therein and terminating at a forwardly directed outlet opening or nozzle 3 and an inlet opening 4 at its rear end portion. This portion of the construction as thus far defined is substantially identical to that of a conventional blast gas or air cap, ie., as contrasted to an angular cap. In accordance with the :invention the cap has an extending lip S on one side,

this lip extending past the outlet opening 3. A multiple number of blast gas jets 6 extend through this lip in a direction substantially normal to the axis of the blast gas flow passage 2. These jets are in a trough-shaped configuration, as may best be seen from FlG. 4. The underside of the extending lip 5 is shaped to define the hollow air chamber 7 provided with an open bottom which in 'turn is sealed by the closure plate 8. A multiple number of gas flow passages 9 extend coaxially with the bore of the passage 2 into this chamber '7'.

The cap is positioned on a heat-fusible material spray gun, as for example a llame spray gun of the wire type, in the conventional manner as shown in FIG. 3. The cap is thussecured in the gun housing 10 in the conventional manner. The nozzle body 11 of the gun extends into the passage Y2. This nozzle body 11 is provided with a central axial wire feeding orifice 12, a wire guide bushing 13, and a multiple number of converging burner jets 14. An annular groove 15 is cut in the rear face of the nozzle body so that the same intersects the burner jets 14. The rear face of the nozzle body 11 is machined flat and pressed against a corresponding fiat surface of the gun head 16 by means of the nut 17. The gun head 16 has an annular groove 18 which corresponds to and mates with the groove 15, in the nozzle body. A gas feed passage 19 leads into the groove 1S. The head 16 also has an axial bore or orifice 20 which corresponds to Vand mates with the wire feeding orifice 12. In operation a wire 21 of heat-fusible material, as for example a conventional metallizing rod or wire of metal, is fed through the gun, through the orifice 20, the wire feeding orifice 12 and the guide bushing 13, through the passage 2 to the position shown. The feeding of the Wire may be effected in any known or conventional manner, as for example by feed rolls driven by any known or conventional drive means, such as a gas turbine actuated by blast gas, an electric motor or the like, or even manually pushed through. A combustible gas mixture of, for example, acetylene and oxygen, acetylene and air, propane and air, propane and oxygen, or the like, is fed, for example, through a mixing chamber through the fuel gas passage 19 and passes into the annular groove 18 to the annular groove 15 through the burner jets 14, where the same is ignited in front of the nozzle body lLforming a heating zone. The flame from the jets 14 impinges on the tip of the wire 21, melting the same. A blast gas, such as compressed air, is fed through the space 22, passes through the openings 23 in the nut 17, through the inlet opening 14 of the cap and through the blast gas flow passage 2 of the cap -out through the outlet opening or nozzle 3:, where the same impinges on the tip of the i'od 21, atomizing material from this melting tip and propelling the same in the form of a fine spray away from the gun in the conventional manner, in a direction coaxial with the passage 2 and direction of feed of the wire 21. A portion of the blast gas passing through the space 22 will pass through the gas passages 9 into the chamber '7. From the chamber '7 the gas will flow out of the jets 6 in the form of a trough-shaped blast of gas corresponding in cross-sectional shape to the trough-shaped configuration of the jets 6, as may be seen from FIG. 4. This trough-shaped blast of gas will pass transversely across the outlet opening or nozzle 3. The direction of this blast is such that it would normally bisect the axis of the blast gas ow passage 2 at an angle of about 90 though the jets 6 could be so constructed that the plane of the base of this trough-shaped blast of gas would bisect the axis of the passage 2 at any angle between about 60 and 90. This trough-shaped blast of gas will deect the spray so that the same will change its direction to pass at an angle to the axis of the passage 2 and wire 21, as for example at a 45 angle, thus enabling the spraying of a surface extending in the direction of the wire 21. In this manner, for example, the interior of tubes or cylinders may be sprayed in the conventional manner, as when using conventional prior art angular air caps.

While the blast gas from the jets 6 is normally directed so that the same will bisect the axis of the blast gas ow passage 2 at an angle between about 70 and 90, the component ow, due to the deflection of the spray, will of course be at a different angle. When reference, however, is made herein and in the claims to the angle of 60-90, the same is meant to deiine the normal angle if the blast of gas would extend from the jets unimpeded, i.e., the angle at which the same is directed, rather than the angle that the same actually crosses the outlet opening. Very surprisingly the deflected spray will produce a homogeneous, high quality coating, and for some unexplained reason the deposit efficiency is increased even in comparison with the undeflected spray. None of the disadvantages previously encountered when attempting to deflect the spray with a gas stream or curtain occur, and of course none of the disadvantages which were encountered when using a solid deflecting surface, as for example in a conventional angular air cap occur, there being of course no solid deiecting surface on which sprayed metal could deposit or on which surface imperfections could occur, causing difliculties. The jets 6 are preferably in the trough configuration as shown in FIG. 4, with two rows of staggered jets and two outermost jets forming the walls of the trough, which extend in the normal spraying direction, i.e., with the base of the trough directed toward or facing the spray.

In place of having the jets 6 in a trough-shaped configuration, the same may be directed so as to form the trough-shaped blast of gas. Thus, for example, the jets may be in an even row, with the outer jets inclined slightly forward so as to form the trough walls.

In place of individual jets any other means for forming the trough-shaped blast gas may be used, as for example the slot-shaped opening as shown in FIG. 5.

With the side walls of the trough directed in thenormal direction of spray, the spray pattern as deposited on the sprayed surface will not be materially changed as compared with an undeected spray. If, however, the walls of the trough are directed inwardly toward the spray, using for example an array of jets as shown in FIG. 6, then the spray pattern will be flattened out into a fan shape, so that the spray will be deposited in narrower bands of a greater length which may be desirable in certain instances. The exact shape of the troughshaped blast gas is not critical as long as the same has this over-all cross-sectional shape. Preferably the height of the side walls of this trough-shaped blast above the inside trough base when initially formed, should be at least and preferably at least 30% of the width of the trough. Thus, in the embodiment shown in FIG. 4, the distance of the outermost row of the jets 6, i.e., the two outermost jets which form the wall of the trough from the next adjacent row, should be at least 15% and preferably 30% of the average length of the other rows of jets.

The following is a practical example of operation given by way of illustration and not limitation:

Example In this example a metallizing flame spray gun having the construction corresponding to that shown in FIG. 3 and commercially sold by the Metallizing Engineering Co. Inc. of lWestbury, Long Island, as a Model K gun, was used. The air cap 1 had an over-all length of 1.17", the diameter of the outlet opening 3 was .305 and of the opening 4 .573. The lip 5 was positioned .285l from the central axis of the cap and had a length of Vs. The jets 6 were .0315 in diameter, with each row being spaced .078" apart. The centers of the individual jets of each row were spaced .0625 apart and the distance between the outermost jets forming the wall of the trough-shaped blast was .375. The innermost row of jets was positioned .125" from the face of the cap. The passages 9 were 1/16 in diameter, with their centers 3732" apart. The gun was operated with air at an air pressure of between and 100 p.s.i. as the blast gas, and with acetylene as the combustion gas and oxygen as the oxidizing gas, the oxygen being maintained at 40 p.s.i. and the acetylene at 15 p.s.i. The wire feed speed was maintained at 8 lbs. per hr., the air at a ow rate of 37 cu. ft. per min., oxygen at a ow rate of 97 cu. ft. per min., and the acetylene at a ow rate of 35 cu. ft. per min. With these values the spray was deected at an angle of about 45 from the axis of the passage 2. The interiors of engine cylinders were successfully sprayed with steel, bronze, aluminum, zinc and molybdenum, with this set-up.l The wire size used for the spraying was Ms" and in all cases an excellent, homogeneous coating was obtained with a higher deposit efficiency than would be indicated for the spray without the deflection, and a deposit eiciency substantially higher than that which could be obtained with a conventional angular air cap having a solid metal defiecting surface. Even after continuous operation there was no deposit build-up on the cap and no conditions occurred which would interfere with continuous operation.

While, as mentioned, the invention is particularly suitable for use in connection with wire type flame spray guns, and in particular as a novel blast gas or air cap construction therefor, the invention is also applicable for deecting heat-fusible material sprays in general, including all of the various types as previously mentioned herein. For this purpose the spray is effected in the conventional manner and the trough-shaped blast of gas is passed transversely across the normal spray pattern at an angle of between about 60-90 with respect to the axis thereof for the deflection.

FIG. 7 diagrammatically shows an embodiment of the invention in connection with a powder spray gun. The gun has a conventional spray nozzle 24 provided with an outlet passage 25 for the powdered material, and an annular ring of combustion gas jets 26. Heat-fusible material in powdered form, such as powdered metal or the like, is fed through the conduit 27 from a hopper or container or the like, and a stream of a carrier gas, such as air, is passed through the passage 28. This gas passes through the outlet orifice 29 and entrains a small quantity of the powder, carrying the same out through the passage 25. Combustion gas and combustion supporting gas, such as acetylene and oxygen, or propane and oxygen, are passed through the jets 26 and ignited at the face of the nozzle. The heat-fusible powder entrained in the carrier gas passes into the llame and is heat-softened and propelled in the form of a spray by the expanding cornbustion gases. A lip 5 of the construction previously described is positioned on one side of the nozzle and provided with jets 6 of the configuration previously described, the chamber 7, and the passages 9. A blast gas is passed through the passages 9 from the tube 30 and ilows from the jets 6 in the form of the troughshaped blast of gas, deiiecting the spray at an angle to the axis of the passage 2 and the normal spray direction. The jets 6 may have any desired shape or coniiguration, as previously described, capable of producing this troughshaped blast. The required velocity of the blast may be very easily empirically determined for the particular angle of deilection desired.

While the invention has been described in detail with reference to certain specic embodiments, various changes and modications which fall within the spirit of the invention and scope of the appended claims will become apparent to the skilled artisan. The invention is therefore only intended to be limited by the appended claims or their equivalents, wherein I have endeavored to claim v all inherent novelty.

I claim:

1. An angular blast gas cap for a flame spray gun comprising a housing deiining a blast gas flow passage extending substantially axially therein, terminating as a forwardly directed outlet opening at its forward end and an inlet opening at its rear portion, and means for directing a trough-shaped blast of gas transversely across said outlet opening, with the plane of the base of said trough bisecting the axis of said blast gas passage at an angle between about 60 and 90, said means for directing a troughshaped blast of gas compris-ing a multiple number of jets in trough-shaped configuration, with means for passing a blast gas therethrough, said jets being dened through a at surface positioned on one side of the outlet opening VVof said blast gas iiow passage, said fiat surface extending in a plane substantially parallel to the axis of said gas iiow passage, said jets being parallel jets positioned in three substantially equally spaced-apart rows, said irst and second rows in the direction away from said outlet opening containing a multiple number of equi-distantly spacedapart jets, with the jets of each row being staggered with respect to the jets of the other row in a zig-zag pattern, and said third row comprising two jets spaced apart from each other at a distance greater than the distance between the outermost jets of the other rows.

2. An angular blast gas cap according to claim 1 in which said first mentioned row contains tive jets and said second mentioned row six jets.

3. An angular blast gas cap for a iiame spray gun cornprising a housing deiining a blast gas ow passage extending substantially axially therein, terminating as a forwardly directed outlet opening at its forward end and an inlet opening at its rear portion, and means for directing a trough-shaped blast of gas transversely across said outlet opening, with the plane of the base of said trough bisecting the axis of said blast gas passage at an angle between about 60 and 90, said means for directing a troughshaped blast of gas comprising a multiple number of jets in trough-shaped configuration, said jets being parallel vjets positioned in three substantially equally spaced-apart rows, said iirst and second rows in the direction away from said outlet opening containing a multiple number of lequi-distantly spaced-apart jets, with the jets of each row being staggered with respect to the jets of the other row in a zigzag pattern, and said third row comprising two jets spaced apart front each other at a distance greater than the distance between the outermost jets of the other rows.

4. In a heat-fusible material spray gun having a spray nozzle, the improvement which comprises means for directing a trough-shaped blast of'gas transversely-across said nozzle, with the plane of the base of said trough bisecting the axis of said nozzle at an angle between about 60"V and 90, said means for directing a trough-shaped blast of gas comprising a multiple number of jets in troughshaped configuration, and means for passing a blast gas therethrough, said jets being defined through a flat surface positioned on one side of said nozzle, said hat surface extending in a plane substantially parallel to the axis of said nozzle, said jets being parallel jets positioned in three substantially equally spaced-apart rows, said iirst and second rows in the direction away from said nozzle containing a multiple number of equi-distantly spaced-apart jets, withV the jets of each row being staggered with respect to the jets of the other row in a zig-zag pattern, and said third row comprising two jets spaced apart from each other at a distange greater than the distance between the outermost jets of the other row.

5. In a heat-fusible material spray gun having a spray nozzle, the improvement which comprises means for directing a trough-shaped blast of gas transversely across said nozzle, with the plane of the base of said trough bisecting the axis of said nozzle at an angle between about 60 and 90, said means for directing a trough-shaped blast of gas comprising a multiple number of jets in trough-shaped configuration, said jets being parallel jets positioned in a mulitple .number of substantially equally spaced-apart rows, including a iirst row adjacent said nozzle and a last row remote from said nozzle in the direction of spray, theV jets of said rows other than said last row being substantially equi-distantly spaced-apart, with the jets of each row staggered with respect to the jets of the other row, said third row comprising two jets spaced apart from each other at a distance at least substantially equal to the length of said other rows.

References Cited in the tile of this patent UNITED STATES PATENTS 2,610,092 Thompson Sept. 9, 1952 2,707,847 Anliker May 10, 1955 2,769,663 Jensen et al. Nov. 6, 1956 FOREIGN PATENTS 9,793 Australia Oct. l0, 1927

Claims (1)

1. AN ANGULAR BLAST GAS CAP FOR A FLAME SPRAY GUN COMPRISING A HOUSING DEFINING A BLAST GAS FLOW PASSAGE EXTENDING SUBSTANTIALLY AXIALLY THEREIN, TERMINATING AS A FORWARDLY DIRECTED OUTLET OPENING AT ITS FORWARD END AND AN INLET OPENING AT ITS REAR PORTION, AND MEANS FOR DIRECTING A TROUGH-SHAPED BLAST OF GAS TRANSVERSELY ACROSS SAID OUTLET OPENING, WITH THE PLANE OF THE BASE OF SAID TROUGH BISECTING THE AXIS OF SAID BLAST GAS PASSAGE AT AN ANGLE BETWEEN ABOUT 60* AND 90*, SAID MEANS FOR DIRECTING A TROUGHSHAPED BLAST OF GAS COMPRISING A MULTIPLE NUMBER OF JETS IN TROUGH-SHAPED CONFIGURATION, WITH MEANS FOR PASSING A BLAST GAS THERETHROUGH, SAID JETS BEING DEFINED THROUGH A FLAT SURFACE POSITIONED ON ONE SIDE OF THE OUTLET OPENING OF SAID BLAST GAS FLOW PASSAGE, SAID FLAT SURFACE EXTENDING IN A PLANE SUBSTANTIALLY PARALLEL TO THE AXIS OF SAID GAS FLOW PASSAGE, SAID JETS BEING PARALLEL JETS POSITIONED IN THREE SUBSTANTIALLY EQUALLY SPACED-APART ROWS, SAID FIRST AND SECOND ROWS IN THE DIRECTION AWAY FROM SAID OUTLET OPENING CONTAINING A MULTIPLE NUMBER OF EQUI-DISTANTLY SPACEDAPART JETS, WITH THE JETS OF EACH ROW BEING STAGGERED WITH RESPECT TO THE JETS OF THE OTHER ROW IN A ZIG-ZAG PATTERN, AND SAID THIRD ROW COMPRISING TWO JETS SPACED APART FROM EACH OTHER AT A DISTANCE GREATER THAN THE DISTANCE BETWEEN THE OUTERMOST JEST OF THE OTHER ROWS.

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