WO1991012183A1

WO1991012183A1 - Inside diameter arc spray gun

Info

Publication number: WO1991012183A1
Application number: PCT/US1991/000927
Authority: WO
Inventors: Lawrence Nieder; Andrew Ralph; Brian Blades
Original assignee: Tafa Incorporated
Priority date: 1990-02-12
Filing date: 1991-02-12
Publication date: 1991-08-22

Abstract

An inside diameter spray grun is provided which includes an axial gas stream for propelling molten material in an axial direction away from an arc region (37), and a pocket-shaped transverse gas stream (42) which intersects the axial gas stream at a location downstream of the arc region and serves to capture and redirect the molten material at an angle generally perpendicular to the axial direction. The arc spray gun may, therefore, be used to produce a spray coating within tight spaces or inside diameter surfaces of the workpiece intended to be coated. The pocket-shaped gas stream may emanate from a cup-shaped (33), V-shaped (33'), open-box shaped (33'') other pocket shaped orifice located in the arc head of the arc spray gun. The pocket-shaped gas stream serves to capture and redirect the molten material while controlling the dispersion thereof.

Description

Title: INSIDE DIAMETER ARC SPRAY GUN

TECHNICAL FIELD

The present invention relates generally to the art spraying one material onto another material. Mo specifically, the invention relates to an apparatus and met for spraying a stream of material into and/or within ti spaces and onto inside surfaces of small diameter spaces objects. Even more particularly, the invention relates to arc spray apparatus and method for spraying a metal coating tight spaces and so-called inside diameters of objects.

BACKGROUND

Arc spray guns are known in the art. In conventional arc spray gun, an electric arc is utilized to m a metallic material so that the molten metal may be sprayed a steel plate or other object in order to form a coating on surface. Typically, two metal wires serve as consumab electrodes, between which the electric arc is establish Simultaneously, compressed gas is injected into the arc z region. The compressed gas atomizes the molten metal crea by the arc and propels the metal particulate onto the surface.

In a conventional arc spray gun, two metal wires guided through the gun along respective paths. The wires e the gun at a location often referred to as the arc head. arc head includes the gun structure where the wires exit gun and also may include the space near that actual structure. At the arc head the paths of the two wires conve and intersect. An electrical potential difference provi across the two wires causes an electric arc to occur betw the wires at the area at which the wire paths intersect. heat generated by the arc melts the ends of the two wires, a gas nozzle positioned at the arc head directs a stream of which impinges upon and atomizes the molten metal. described above, the gas stream then carries the me particles away from the arc zone, i.e., the area at which arc occurs, and propels them towards the surface of a w piece intended to be coated.

One type of prior electric arc spray gun is referred to as a line-of-sight spray gun. Another type is referred to as a bent direction or bent stream spray gun.

Examples of line-of-sight arc spray guns are described in U.S. Patent Nos. 4,492,337 and 3,546,415, the disclosures of which are hereby incorporated by reference. Examples of bent stream spray guns are described in U.S. Patent Nos. 3,901 ,441 , 4,464,414 and 4,853,513, the disclosures of which are also incorporated by reference.

Line-of-sight arc spray guns typically are used for coating outside surfaces of a work piece or large inside diameters of a work piece where there is adequate space to develop and to direct the spray stream. , The gas nozzle for atomizing the molten metal typically is positioned between the converging wires to direct a gas stream in an axial' direction usually coinciding with or parallel to the longitudinal axis of the spray gun itself and/or generally parallel with the respective wire paths. Because the gas stream directed from the gas nozzle propels the metal spray particulate in such an axial direction, these guns are used to coat surfaces within a so-called line-of-sight of the gun. However, such arc spray guns could not reliably coat the inside surface of a narrow diameter pipe or of a narrow diameter blind hole, for example, due to inadequate space for the gun and/or for the spraying stream uniformly to reach and to coat the desired surface areas at an acceptable impingement angle.

In a bent stream spray gun, a molten metal spray stream initially is developed as it is in a line-of-sight spray gun, and, additionally, a second gas stream is introduced in a generally transverse direction with respect to the axial gas stream. The transverse gas stream serves to "bend" the otherwise axial direction of the metal spray stream. By "bending" the metal spray stream, these type arc spray guns in^" the ideal case were supposedly capable of coating non-line-of-sight surfaces. Unfortunately, such bent stream spray guns encountere several major drawbacks. For example, to provide adequa space to accommodate the second gas nozzle at the arc head, t arc head had to be of such large diameter that it prevented t gun from accessing and spraying surfaces inside narrow diamet spaces, such as inside a narrow pipe.

In prior large diameter arc head bent stream spr guns, the spray angle often was limited to 45 degrees or les for example, due to the limited amount that the wir themselves could be bent, or the improperly designed ai deflection system of other prior metal spray stream deflecti systems. Such restriction on angle made it impossib satisfactorily to project the metal spray stream deep inside narrow opening or at an angle to give satisfactory bo strength. For example, as is described below, the bo strength obtained by a 45 degrees sprayed stream has been fou to be inferior to that obtained by a spray stream projected a larger angle, e.g., on the order of 70 degrees.

Moreover, prior bent stream arc spray guns have be found to produce an undesirably coarse spray pattern resulti in a coarse and inconsistent coating. It is believed this due to lack of control of the transverse gas stream and/or the uncontrolled dispersion of the bent spray stream. appears that this problem may be exacerbated in those cases which the transverse gas stream is focused to impinge direct on the arc in conjunction with the axial gas stream. F example, focusing both the transverse and axial gas strea directly on the arc appears to cause the undesirably wide a relatively uncontrolled dispersion of the metal spray stre and also may tend to cause extinguishing or instability of t arc.

An example of an arc spray gun utilizing a transver gas stream apparently directed through the center of the a zone is described in U.S. Patent No. 4,853,513. The arc spr gun includes an arc spray head which has a primary gas nozz for producing an axial spray stream of molten metal, and replaceable secondary gas nozzle for directing a transverse gas stream laterally through the arc zone.

Other examples of arc spray guns which utilize a transverse gas stream in order to "bend" the metal spray stream are described in U.S. Patent No. 4,464,414 and U.S. Patent No. 3,901,441. Both of the arc spray guns described in these patents include a secondary gas nozzle which directs a transverse gas stream across the path of the axial gas stream at a point slightly downstream of the arc zone. While the positioning of the transverse gas nozzle slightly downstream of the arc zone may alleviate the random dispersion of the metal spray stream to some degree, arc spray guns of the type described in these two patents still would appear to suffer, from a somewhat uncontrolled dispersion of the atomized metal.

Uncontrolled dispersion as it is used in the context of the invention relates to the spreading of the spray stream, or more specifically, the particulate in the spray stream, in various directions away from the initial projection and central axis of flow. In contrast, controlled dispersion relates to the collection or retaining of the stream relatively closer to the central axis during projection of or spraying of the stream in a given direction.

U.S. Patent No. 4,604,306 discloses a high-speed gas jet provided with a quiescent zone into which a spray column of molten or heat-softened particles derived from a plasma spray torch, for example, is injected. The high-speed jet originates from a discharge slot to derive the quiescent zone and to create a jet stream which envelops the particles downstream of the quiescent zone, as the particles tend to be focused and accelerated. Such patent does not address the controlled dispersion which is obtained in the present invention.

A problem associated with previous bent stream arc spray guns has been their inability to compensate for changing size and location of the arc. Bent stream spray guns such as those described above, have utilized a secondary gas stream focused either to impinge directly-on the arc occurring between the converging wires, or at a point slightly downstrea therefrom. However, the exact location at which the wire intersect and the arc occurs may vary due to factors such as change in wire feed speed, a change in applied current o voltage, tip wear, etc. The secondary stream which initiall would be directed at one place relative to the arc, ma therefore become directed at another place due to a variatio in the location of the arc. As a result, both the spra pattern and the spray stream direction of the arc spray gu could dramatically change.

Another problem or disadvantage associated wit previous arc spray guns has been the large diameter siz required for the arc head and"*spray gun housing to accommodat their functions. Such a large diameter size prevents th insertion of the gun into a narrow space, recess, or the like In the past, such a large diameter or size was necessary a least in part in order to provide space for the individua conduits which guide the metal wires and the current supplie to the wires from the one end or portion, e.g., the trigge end, of the gun to the other end, i.e., that at which the ar head is located. Often four separate conduits were needed, wire guide path and current guide for each of the tw respective metal wires. These conduits similarly required considerable amount of space within the housing of the spra gun. In addition to the guide path and current carryin conduits, separate gas carrying conduits were utilized in th past to transfer compressed gas from an external source to th individual primary (axial stream) and secondary (transvers stream) nozzles located at the arc head. These gas conduit also took up additional space in the spray gun housing, furthe increasing the size of the housing and the arc head itself.

Yet another problem associated with previous arc spra guns involved metal buildup at the arc head. Often times phenomenon known as blowback would occur where the metal spra stream would be blown back towards the arc head when sprayin within tight spaces, especially, for example, when sprayin within a blind hole. The turbulence occurring at the bottom of the hole may cause the metal spray to be blown back onto the arc head where it may build up on the edges of the gas nozzles. This buildup could change the size of the nozzles and affect the direction of the gas stream.

Because of blowback and/or other such phenomena, the metal spray could ultimately cover portions of the spray gun and clog the gas nozzles and/or the wire exit ports (such ports sometimes being referred to as the contact tips) at the arc head. Such clogging, etc., therefore, could often result in costly down time, and sometimes necessitated the replacement of the arc head. It would be desirable to reduce the effects of blowback; it has been found that features of the present invention tend to reduce such accumulation of metal at the arc head usually caused in the past by blowback.

Still another problem associated with previous arc spray guns, especially those of the bent spray type, has been the difficulty often encountered, e.g., by manufacturers, in attempting to change the length of the spray gun housing. The length of the spray gun housing often determines the distance that the arc head of the spray gun may be inserted into a narrow recess, for example, into the interior of a long, narro pipe, bore, etc.

Thus, there remains a strong need in the art for a arc spray gun having a relatively small diameter arc head an housing which is capable of coating the inside surfaces an inside diameters of a work piece. In addition, there remains strong need for an arc spray gun for spraying a metal spra stream transverse, e.g., generally perpendicular, to an inside surface being sprayed, while controlling the dispersion of the metal particulate within the spray stream. Still further, there remains a strong need for an arc spray gun which ensures a smooth, tenacious, cohesive, high quality coating. And, furthermore, there remains a strong need for an arc spray gu which is operable over a broad range of wire feed rates, wir current, tip wear, etc. In addition, there remains a strong need in the art for an arc spray gun which avoids the metal buildup at the arc head, such as that caused by blowback of the metal spray stream. There further remains a strong need for an arc spray gun in which the housing length can be changed with a minimum of tools and effort.

One or more of the shortcomings encountered in the prior arc spray guns, especially those of the bent stream type and/or one or more of the various needs mentioned in the previous several paragraphs are addressed by the present invention, which is summarized and is described in detail below.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an arc spray gun is provided which includes means for forming an arc at which material to be" sprayed is melted, first propelling means for propelling the molten material from the arc generally in a first direction, and second propelling means for changing the direction of the propelled molten material, wherein the second propelling means includes means for forming a pocket to capture and redirect at least part of the molten material over a range of variation in the location of the arc.

In accordance with another aspect of the present invention, an arc spray gun is provided which includes means for forming an arc at which material to be sprayed is melted, first propelling means for propelling molten material from the arc generally in a first direction, second propelling means for changing the direction of the propelled molten material, and surface means for reducing unnecessary entrainment of air and dust in the paths of the first and second propelling means.

According to yet another aspect, an arc spray gun is provided which includes a housing, and propelling means that include a compressed gas that is directly contained, at least in part, by the walls of the housing.

In accordance with still another aspect of the present invention, an arc spray gun is provided which includes means for forming an arc at which material to be sprayed is melted, a guidepath for guiding at least one consumable electrode to a location at which the arc occurs, and a current carrying apparatus for providing current to the consumable electrode, the current carrying apparatus being in substantially coaxial relation with the guidepath.

^' The above and other aspects, features, objects and advantages of the present invention will be apparent and fully understood from the following detailed description of the preferred embodiment, taken in connection with the several drawing figures.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail a certain illustrative embodiment of the invention. This embodiment is indicative, however, of but one of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

Fig. 1 is a schematic view of an inside diameter arc spray gun for use in coating the inside surface of a small diameter pipe in accordance with the present invention;

Fig. 2 is a side elevation view, partly in section, looking along the longitudinal axis of an inside diameter arc spray gun in accordance with the present invention;

Fig. 3 is a bottom view partly in section, of the inside diameter arc spray gun looking generally in the direction of arrows 2-2 of Fig. 2;

Fig. 4 is an end view of the arc head of the inside diameter arc spray gun;

Fig. 5 is a bottom view of the arc head;

Fig. 6 is an isometric view of the arc head;

Figs. 7-9 are fragmentary diagrammatic views of the transverse gas nozzle in the arc head showing a V-shaped orifice, open box shaped orifice, and a series configuration o individual orifices, respectively, each of which are differen embodiments of the transverse gas nozzle in accordance with th present invention;

Fig. 10 is a schematic perspective view depicting a exemplary prior art electric arc bent spray process;

Figs. 11 and 12 are schematic perspective view depicting an electric arc bent spray process according to th invention;

Fig. 13 is a cross sectional view of the wire guid and current carrying path of the inside diameter arc spray gu of Fig. 2;

Fig. 14a is a graph showing experimentally obtaine data relating spray angles and bond strength;

Figs. 14b-14d are exemplary cross-sectional views of coated surface relating spray angles to coating surfac uniformity.

Fig. 15 is a fragmentary diagrammatic view of th transverse gas nozzle in the arc head during the arc spra process in accordance with the present invention;

Figs. 16 and 17 are fragmentary diagrammatic views o the arc head and gun housing in open ended and closed ende chambers, respectively, during the arc spray process utilizin exhaust techniques in accordance with the present invention and

Fig. 18 is a fragmentary diagrammatic view of th transverse gas nozzle in the arc head which also includes tw additional side orifices in accordance with the presen invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to Figs. 1 and 2, in accordanc with the present invention, an inside diameter arc spray gun for coating the inside surface of a small diameter pipe, bore recess, etc., designated 6 is illustrated. The arc spray gun produces a controlled dispersion in the form of an atomize metal spray stream, the spreading or dispersing of which i controlled, and which is sprayed at an angle that is non-parallel to and, preferably, is more on the order of generally perpendicular to the inside surface of a pipe 6, which is seen in Fig. 1, or other so-called inside diameter surface desired to be coated. Such surface also includes and alternatively may be a surface in a small space or some other space that is difficult to access for coating, e.g., using a conventional line of sight gun and/or possibly a conventional bent stream gun. It is well known in the art that near perpendicular spray, typically on the order of 90 degrees ± 30 degrees (meaning impingement angle of from 60 degrees in either direction up to 90 degrees), is required to achieve a satisfactory, well-bonded, dense coating. The present- invention provides this capability. The angle, though, is not intended to limit the broad scope of the invention.

The surface to be sprayed should be prepared before spraying. If the spray material is not self-bonding, then preferably the surface is roughened by grit blasting or otherwise pre-treated to assure tenacious adherence of the coating thereto, as is well known. If desired, a bond coat may first be applied before applying the main sprayed coating.

The arc spray gun 5 includes a wire feed assembly 15 which feeds a pair of wires 18 through a generally elongated housing 20 until the wires 18 exit the arc spray gun 5 at a location often referred to as the arc spray head 25. As is explained in more detail below, upon exiting the arc spray head 25 an arc is created between the two wires 18 and the resultant molten metal is atomized and propelled away from the arc head 25 by the combined action of an axial gas stream and transverse gas stream, both of which emanate from the arc head 25.

As is shown in Fig. 1, the arc spray gun 5 further includes a gas hose 26 which provides a supply of compressed gas, pressurized gas, flowing gas, etc., for example, air or some other type of suitable fluid, for use in the axial and transverse gas streams, e.g., as an atomizing, carrying vehicle, etc. In addition, arc spray gun 5 includes an external power supply 27 which provides electrical power to supply a voltage and current to and across wires 18 so that an arc will be created between the wires in the area where their paths tend to converge outside the structure forming the arc head 25. Suction 28a or blower 28b is sometimes utilized in the present invention to provide extraction air and/or gas flow within the pipe 6 in order to reduce the effects of blowback onto the arc head 25, and to sweep overspray dust or other debris away from the metal spray stream and surface to be coated.

In operation, the relatively small cross-sectional diameter of the arc spray head 25 and housing 20 allows the arc spray gun 5 to be inserted a desired distance into the pipe 6. The distance being limited only by the length and cross-sectional diameter of the arc spray gun 5.

Typically, arc spray gun 5 is fixedly mounted- on the mounting assembly 29. The pipe 6 or other object to be coated is typically mounted to a rotary mount (not shown) such as a lathe spindle or other such type rotary device. After it is inserted, arc spray gun 5 sprays a metal spray stream from the arc head 25 onto the inside surface of the pipe 6 as it rotates, thus producing a metal spray coating on an entire inside circumference of the pipe 6.

In addition, mounting assembly 29 may be mounted on a movable track member (not shown), the movable track member allowing the mounting assembly 29 to move along the axis represented by axis A in Fig. 1. The arc spray gun 5 is thereby capable of being moved in and out of the interior of the pipe 6 in order to coat substantially larger portions of the inside surface of pipe 6. As an alternative to having the pipe 6 mounted on a rotary mount, it is well within the scope of the present invention instead to have the arc spray gun 5 or a portion thereof mounted so that it may rotate. In such case, a rotary joint may be used to supply wire, gas and/or electrical power. The pipe 6, then, may remain fixedly mounted while the spray stream is rotated. Referring now to Figs. 2 and 3, an arc spray gun 5 in accordance with the present invention includes the wire feed assembly 15 to feed wires 18, an elongated housing 20, and an arc head 25. The wire feed assembly 15 is located at one end of the housing 20 and functions to feed metal wires 18 at a constant rate or controlled variable rate through the housing 20 towards the arc head 25, which -typically is at or toward the opposite end of the housing 20. As the wires 18 are fed or advanced, they are guided along their respective paths which ultimately converge and intersect at a location just outside the structure of the arc head 25 in the area commonly referred to as the arc zone 30. The leading ends 31 of the wires also would intersect at such location if the arc itself did not first cause the metal to melt off the ends of the wires.

An electric potential difference applied by power supply 27 across wires 18 causes a current to flow and an arc to be created between the ends 31 of the wires 18 at the area where their paths intersect within the arc zone 30. During starting of the arc, the arc generates enough heat to cause the ends of the metal wires 18 to melt back a short distance, and thereafter the wire ends continuously melt off due to the heat generated by the arc, as the wires continue to be fed or supplied to the arc zone 30, as is conventional. An axial gas nozzle 32 and a transverse gas nozzle 33, which are located at the arc head 25, serve to atomize the molten metal and to propel the atomized particles at a predetermined angle onto a surface 34, which is intended to be coated.

In the exemplary embodiment"of the invention described in detail herein, portions of the wires that enter the zone at which the arc exists will be melted, for example, due to the heat in that arc zone. Continued feeding of the wires into the arc zone results in continued melting of the fed wires. The axial gas stream from the axial gas nozzle 32 moves molten material out from the arc zone and propels that material downstream leaving space at the arc zone for subsequently melted material, which may be subsequently, moved out from the arc zone by such axial gas stream.

The molten material referred to may be truly molten or liquid. Alternatively, the molten material may be solid, but somewhat softened to enable disconnecting thereof from the respective wire to be propelled downstream by the axial gas stream. Still further, the molten material may be plural droplets of liquid. The molten material intended to be sprayed also may be or may include a material that converts from a solid to a gas, i.e., sublimes, such as may be the case for carbide particles. The molten material, still further, may be a material that converts from a liquid to a gas. In either of these latter two cases the term molten material would encompass a gas. The molten material also may include a solid material, such as particles that can be sprayed, especially with such particles being included with some other more liquid material being sprayed by the invention. Even further, the molten material may include various combinations of the foregoing. Regardless, reference to melted or molten material herein is intended to encompass the foregoing and variations and equivalents thereof. It will be appreciated, then, that the term molten material envisioned herein means a material that has sufficient fluidic characteristics as to be able to be propelled by the axial gas stream, preferably after such molten material has been heated to a temperature that will enable and/or will facilitate bonding to the surface intended to be coated thereby.

Although the preferred source of the molten material is a pair of wires that are, for example, melted in an electric arc formed therebetween as both wires tend to be melted or otherwise used or consumed, it will be appreciated that other sources of the molten material may be employed in the invention. One example is the use of one non-consume electrode and one consumable electrode between which an arc is established to cause melting of the consumable electrode. Another example is an electric arc gun apparatus that ma employ more than two electrodes among which the arc i established and in which arc one or more of the electrodes is melted, or otherwise used or consumed.

In the preferred embodiment the wires 18 are illustrated as solid wires. Exemplary materials are well known in the art of electric arc spraying. Three such exemplary materials are identified in Table 1 below. Other types of wires also may be used. One example is cored wire, which is formed of a hollow tube of metal in which a second material, such as a powder, for example, may be contained. Other examples are wires formed of aglomerated material, sintered material, extruded material, and so on. Preferably, though, the wires used should have an electrical conduction characteristic enabling it to participate in the dissipating of energy, e.g., by forming an arc, or otherwise contributing to the mechanism by which molten material is provided in the path of the axial gas stream to be propelled thereby. However, if desired, the sprayed material may be other than an electrical conductor, such as a ceramic, for example; in such case other means may be provided preferably to heat such material, e.g., another source of electric arc. Also, such non-conductor may be combined with a conductor. As used herein, then, metal particles may comprehend those materials that are not metals (or conductors). It will be appreciated that the materials that are sprayed may be of the type that are non-self-bonding or are self-bonding. Materials that react or that do not react ^"during the spray process may be used in the invention. Such materials may or may not actually melt or soften in the spraying process.

It also is contemplated, according to the invention, that a further source of material intended to be sprayed may be employed with the source of material described in detail herein, namely, the electric arc and^" wire feed thereto. Such further source may be a spray, a jet, a supply, etc., of such further material that effects or allows injecting or other placement of such further material into the stream to be. sprayed. For example, such further material may be directed into the arc, into the axial gas stream upstream of the ar and/or into the sprayed material relatively downstream of th arc. The further material may or may not actually melt o soften in the spraying process.

Reference to the term atomized herein means th dictionary definition thereof and, even more broadly, th concept of taking material and changing it to particles changing particles to smaller particles, and/or changing th number of particles in a particular group thereof, e.g. increasing that number. Atomization can occur to variou extents, as will be appreciated by those having ordinary skil in" the art. Atomization also includes the concept of partia atomization, e.g., a circumstance in which some particles in group are increased in number and/or are reduced in size whil other particles in that group are not; and/or a circumstanc where it is expected that still further atomization may occu at a later time or in a subsequent process or procedure.

A feature of the invention is the ability for th housing 20 and arc head 25 to be relatively small i cross-sectional diameter, especially compared to conventiona line-of-sight or bent stream electric arc spray guns, thu enabling the invention to be inserted into narrow-spaces narrow diameter passages or openings, etc., as well as large ones, to apply a sprayed coating thereon. Another feature i the use of a transverse stream of fluid, such as air, t capture molten, softened or entrained material, which i developed in the arc and is projected therefrom by an axia flow stream and controllably to redirect the flow of tha material toward a surface or surfaces efficiently an effectively to apply a coating thereto. The apparatus an methods of the invention described in detail below interact t tend to accomplish these and other features of the invention as will become evident to those having ordinary skill in th art.

In the preferred embodiment, then, the housing 20 an arc head 25 of the arc spray gun 5 are of relatively smal diameter to allow both the arc head 25 and at least part of the housing 20 itself to be inserted into small diameter recesses. The gas nozzles 32 and 33 located in the arc head 25 direct respective .axial and transverse fluid streams that propel metal from the arc zone 30 toward a surface at an angle 0 of, for example, approximately 70° to the normal axial direction. As a result, the present invention is capable of reliably coating non-line-of-sight surfaces, for example, the inside diameter of a narrow tube.

. Referring to Fig. 4, an end view of the arc head 25 shows the axial gas nozzle 32 and the exit ports- or contact tips 35 (which normally make the current contact with the wire) from which the wires 18 exit the arc head 25 and housing 20 en. route to the arc zone 30. Wires 18 exit the wire exit ports 35 where their paths then intersect in front of axial gas nozzle 32. Compressed gas, such as air, from within the housing 20 exits the arc head 25 through axial gas nozzle 32 and impinges directly on the arc 37 (Fig. 5) which is created between the ends of wires 18 as described above. The arc 37 may be viewed as a ball of ionized or superheated gases created by the current which arcs between the wire ends 31 and that generates sufficient heat to melt the ends of the wires. The molten metal formed at the arc 37 is atomized by the axial gas stream exiting nozzle 32, and is thereafter propelled in an axial direction (represented by phantom axis line "A") away from the arc head 25. The axis line "A" is seen in Figs. 1, 2 and 3; it comes up out of the plane of the paper in Fig. 4. Further atomization may be effected by the transverse gas stream described in detail below.

Fig. 5 shows a bottom view (relative to the illustration of Fig. 2) of the arc head 25. As is shown, the wires 18 converge toward a location where ultimately their paths intersect preferably at. an included angle of approximately 30°. Although such angle could be larger or smaller, a 30° included angle has been found to provide satisfactory performance. The arc 37 established between the wires 18 is seen in arc zone 30. The transverse gas nozzle 3 is located in the arc head 25 so that the projection of suc nozzle onto the axis A is somewhat downstream of the arc zon 30. Compressed gas from within the spray gun housing 20 exit through the transverse gas nozzle 33 and thereby creates stream of gas traveling transverse to the axial stream (or ou of the page relative to Fig. 5), slightly downstream of the ar zone 30. The actual location of the transverse gas nozzle 3 in the arc head 25 and the direction it points are such tha the location where the transverse gas stream intersects th axial stream will be downstream of the arc zone 30. In th preferred embodiment the transverse gas nozzle 33 is so locate that a projection thereof ontcf the axis A is downstream of th arc zone 30.

In the exemplary embodiment shown in Fig. 5 using 1/1 inch diameter wire 18, the base of the transverse gas nozzle 3 is located approximately 1/16 inch, and may be as much as 1/ inch or possibly even further, downstream of the arc zone 30 Therefore, the location of the arc 37 could vary downstream i an axial direction at least 1/16 inch prior to coming i contact with the transverse gas stream. Accordingly, one o ordinary skill will recognize that the preferred axial distanc between the arc zone 30 and transverse nozzle 33 will var relative to the wire 18 size and transverse nozzle 33 size.

In the preferred embodiment, transverse gas nozzle 3 is a generally cup-shaped orifice which is machined in th generally planar surface 44 of the arc head 25. The cup-shape transverse gas nozzle 33 creates a cup-shaped gas stream i front of the arc zone 30, or slightly downstream from where th molten metal created at the arc 37 was atomized by the axia stream. Fig. 6 shows how the cup-shaped gas stream 42 create what is essentially a cup-shaped gas stream pocket downstrea of the arc 37.

The transverse gas stream projected from th cup-shaped gas nozzle 33 takes the form of a wall-like barrie which collects, redirects and may further reduce the particl size of the metal spray stream from an axial direction (i.e., one generally parallel to axis A) to a direction that is generally transverse to, that is, across, the axial direction. It has been found that the cup-shaped transverse nozzle 33 provides a gas stream having a relatively even velocity profile or gas velocity throughout. As a result, the molten and/or softened and/or solid metal particulates, which initially are atomized by the axial gas stream, are controllably redirected and, importantly, controllably dispersed by the transverse gas stream, so as to provide a generally uniform coating on the surface of the pipe 6 (Fig. 1) or surface 34 (Fig. 2). The sides of the cup-shaped stream serve generally to contain and redirect the metal spray stream produced by the axial stream, allowing for, the controlled dispersion of the metal particulate as it progresses towards the surface 34.

Measured data has shown that the metal spray stream as deflected towards surface 34 has an angle of dispersion of approximately 20°. At a distance of approximately 6 inches from the arc head 25, the spray pattern has been shown to take on a crescent shape whose rounded contour is similar to that of the cup-shaped orifice 33. Thus, it may be seen that the arc spray gun 5 of the present invention offers the relatively controlled dispersion of the metal particulate.

Referring now to Fig. 6, as the molten metal is formed at the ends of the wires 18 by the arcing process in the arc 37, the flow of gas from the axial gas nozzle 32 preferably atomizes the molten metal at least to some extent. The flow of metal coming off the melted wire tips 18 may be visualized as being either a series of of rounded droplets, individual elongated droplets, or large strips of molten metal much like a liquid stream. These partially atomized liquid streams or strips are propelled in an axial direction towards the location where the transverse gas stream from the transverse nozzle 33 intersects the axial gas stream. It is desirable that there be sufficient axial gas flow in order to provide controlled direction and at least some preliminary atomization of the molten metal from the arc 37, and furthermore, to move or propel the molten material into the region where the transverse gas stream intersects the axial stream.

The transverse gas stream serves to capture and redirect the liquid streams or groups of large particles of molten metal which are initially propelled by the axial gas stream as described above, and preferably further atomizes the molten metal or reduces the particle size thereof and accelerates its flow in a direction that is transverse, i.e. across or not parallel, to the axial direction. Therefore, the molten metal after coming off the arc 37 in an axial direction, undergoes a change in direction once impacting upon the cup-shaped gas stream 42. In the preferred embodiment, the molten metal also may encounter an increase in velocity once impacting upon the cup-shaped gas stream 42. The transverse gas stream 42, in addition, further atomizes the molten metal into what is believed to be a fine Gaussian distribution of particles, for example having a mean diameter within the range of ten to eighty microns. The resulting coating produced by such sprayed material is a fine or smooth coating formed on the surface 34, such as that of a narrow pipe or the like, even over a wide range of operation variables, as are discussed in detail below.

Furthermore, while the exact ratio of the axial gas flow to the transverse gas flow will not be critical, it is important, as is stated above, that the axial gas flow be sufficient to move or propel the molten material from the arc 37 into the region where the transverse gas stream intersects the axial gas stream. Any additional gas flow in the axial direction will cause the angle at which the spray strea impinges on the surface 34 to decrease without necessarily affecting the quality of the coating. However, it would not be desirable for the axial gas flow to be so great as to cause the arc 37 to occur at or downstream axially of the location tha the transverse gas stream jet intersects the axial gas stream. In such a case, the metal spray stream may be randoml dispersed or even fail to be redirected by the transverse gas stream. For the embodiment shown in Fig. 5, the axial gas flow rate and the transverse gas flow rate from the axial and transverse nozzles, respectively, preferably differ by less than about 10%. Exemplary flow rates are on the order of 13 cfm and 15 cfm respectively for the axial and transverse streams, and have been found to produce satisfactory results.

The velocities of the axial and transverse gas streams are related to the flow rate and nozzle size as is known. Exemplary velocities for the gas emanating from the axial nozzle 32 and transverse nozzle 33 include those within the range of about Mach 0.2 to about Mach 3.0 for the transverse gas stream 42, and about Mach 0.1 to about Mach 1.2 for the axial gas stream, wherein Mach means one times the speed of sound in the particular medium of interest. These values, of course, are intended to be exemplary and not to limit the scope of the invention in any way.

As is also shown in Fig. 5, the curvature at the base of the cup-shaped orifice^* forming the transverse nozzle 33 generally conforms to the contour of the shape of the arc ball 37. In an exemplary embodiment represented generally in Fig. 5, two wires 18 have a diameter of about 1/16 inch and converge at an included angle of about 30°. One could also use wire 18 having a diameter between, for example, 1/32 and 1/4 inch, these values being exemplary and not intended to limit the invention in any way. The cup-shaped orifice 33 is generally arcuate, i.e., curved, in the preferred embodiment, and the angle between the sides of the arcuate cup-shaped orifice 33 (e.g., where they intersect at the apex of the arc thereof), as well as the length of the sides themselves, may be selected to obtain the desired spray ^• results. If the angle between the sides becomes too narrow, the wires 18 possibly could encounter the force of the transverse stream which emanates from the sides of the cup-shaped orifice 33 before (i.e., upstream) the wires 18 even enter the arc zone 30. In such a situation, the wires 18 could tend to vibrate and therefore result in sporadic spraying, erratic particle sizes, and/or coating of the surfac 34.

In the illustrated exemplary embodiment the width o the orifice 33 between the two arcuate walls thereof i approximately 0.048 inch. The radii of curvature of th respective arcuate walls are 0.092 inch and 0.140 inch. Usin these dimensions, the approximate average arc length of th orifice 33 is about 0.34 inch. Again, these dimensions ar merely exemplary and are not intended to limit the invention.

The axial nozzle 32, on the other hand, consists of a orifice which is primarily the opening between the contact tip 35- as is shown in Fig. 4. For the embodiment shown, thi orifice is approximately 3/16 inch wide, which is the distanc between the inside edges of the contact tips 35. However, i will be apparent that axial nozzle 32 can vary in size an these dimensions are used merely as an example. Also, th axial nozzle 32 need not be the entire space between th contact tips 35, but rather, may be simply an isolated orific in the housing 20 between the contact tips 35.

The distance between the cup-shaped orifice 33 in th generally planar surface 44 of the arc head^' 25 and the arc 3 is typically between 1/16 and 3/8 inches, with a distance o approximately 1/4 inches being preferred. It has been foun that if the cup-shaped orifice 33 is located too close to th wires 18 and arc 37, molten metal droplets can form at the ar 37 and spatter, and can therefore contaminate the surroundin surfaces. For example, it has been found that in the event th orifice 33 is located too close to the arc 37, metal spray ma collect on the surface 44.

While a cup-shaped orifice 33 is utilized in th preferred embodiment, alternate embodiments could utilize othe pocket-shaped orifices for creating a pocket-shaped transvers gas stream for capturing, redirecting and controllin dispersion of the metal spray stream. For example, a V-shape orifice 33' as is shown in Fig. 7, or an open-sided box-shape orifice 33" as is shown in Fig. 8, each serve to create pocket-shaped transverse gas stream which intersects the axial gas stream and is capable of acting as a wall-like barrier which collects, redirects and controls dispersion of the metal spray stream from an axial direction to a generally transverse direction.

In addition, as is shown in Fig. 9 a series of small individual orifices arranged in a pocket-shaped configuration may be utilized, for example, instead of or in addition to the pocket-shaped or cup-shaped orifice 33, to create a pocket-shaped transverse gas stream. The present invention anticipates any number of ways of forming a pocket-shaped transverse gas stream 42. The cup-shaped orifice 33 is preferred, however, because it tends to follow the somewhat blunt contour of the arc ball 37 as is mentioned above.

The present invention utilizes the pocket- shaped transverse gas stream, which is designated 42 in Fig. 6 partially to capture or to collect the metal spray stream while also laterally or transversely redirecting the stream. As was mentioned above, several of the bent stream type arc spray guns in the past utilized a secondary gas stream which was positioned to impinge directly on the arc. This technique le to the undesirable result of the metal spray stream bein widely or randomly dispersed, and furthermore it was intolerant of changes in the location at which the arc occurred. Othe bent stream spray guns simply utilized a secondary orific which focused the transverse gas stream downstream of the arc. This technique often times similarly resulted in the meta spray stream being randomly dispersed. Such random dispersio is undesirable in that as the spray stream becomes mor dispersed, it mixes excessively with the surrounding air, dust, etc., resulting in 'lower velocity of the particles, rando particle size, contamination and possibly the excess oxidatio of the particles, and thereby reducing the quality of th coating. The prior art has failed adequately to address th importance of controlled dispersion of the metal spray stream.

The present invention, by utilizing a pocket-shape secondary gas stream which captures the metal particulate a controls the dispersion of the metal spray stream, offe several distinct advantages over the prior art. For exampl often it is desirable to direct the metal spray stream towar a target which is small in size and yet located within a sma diameter recess, pipe, etc. By using a pocket-shaped seconda gas stream, the present invention produces a metal spray stre which undergoes reduced dispersion, thus allowing for high target efficiency. By controlling the dispersion of the met spray stream, the present invention provides a quality coati having good adhesion to the surface 34 cohesion, smoothne and/or uniformity characteristics.

Another important fe%ture of the present invention , that the pocket-shaped secondary gas stream 42 provides broader operating range for the arc spray gun 5, or mo specifically, reduced sensitivity to movement in the locati of the arc 37. Fig. 10 shows a prior art arc spray process which the gas stream from the transverse nozzle imping directly on the arc occurring at the ends of the wires in ord to atomize and propel the molten metal off the ends of t wires onto the surface to be sprayed. However, as w mentioned above, the transverse gas stream impinging direct on the wires often produces unsatisfactory coating results. has been found that once the converging wires enter direct into or puncture through the transverse gas stream, the wir begin to vibrate and the arc becomes unstable. As a resul the spray pattern becomes erratic.

The arc spray gun 5 is forgiving of movement in t location of the arc 37 due to changes in the wire feed rat voltage, operating current (spray rate), tip wear, et Therefore, the arc spray gun 5 provides for a broader range operation than what is found in previous bent stream type a spray guns. For example, as the contact tips 40 tend natural to wear as is conventional in many arc spray guns, the wires will begin to converge at smaller included angles. As result, the arc 37 will tend to occur at a location which further downstream of the axial nozzle 32. Such a change i location will similarly occur when increasing the wire 18 fee rate. As another example of the arc 37 location changing, whe the voltage supplied to the wires 18 is increased the arc 37 will occur at a location closer upstream to the axial nozzle 32 because the arc then can jump across a larger gap between th wires 18, which, of course, are the electrodes between whic the arc is created. In previous bent stream type spray guns which utilized a transverse gas stream initially focuse directly on the arc 37, such axial movement of the location o the arc 37 tended to cause erratic coating results.

Figs. 11 and 12 show the relationship of the axial ga stream 45 and pocket-shaped transverse gas stream 42 of th present invention, and how the pocket-shaped gas stream 4 extends the operating range of the spray gun 5. Fig. 11 show the axial gas stream 45 atomizing the molten metal at arc 3 and propelling the molten metal spray stream into the pocke found within the cup-shaped transverse stream 42. As the side of the cup-shaped stream 42 collect the metal particulat towards the base of the pocket, the transverse direction of th gas stream 42 redirects the metal downward towards the surfac 34. Fig. 12 shows the arc spray process of spray gun 5 afte the location of the arc 37 has changed, perhaps due to a increase in the wire feed rate or progressive tip wear. I such a situation, the location of the arc 37 simply move further downstream and closer to the base of the transverse ga stream pocket 42. The arc does not, however, move so far as t enter into, or puncture or pierce through the flow of th cup-shaped stream 42 as was often the case with other ben stream type arc spray guns. Instead, the axial gas stream 4 atomizes and propels the molten metal from the arc zone 30 int the pocket-shaped transverse gas stream 42 regardless of th specific arc location. Whether the metal particulate travel in the axial direction a short distance or a somewhat longe distance once the metal particulate hits the "wall" formed b transverse gas stream 42, the metal particulate is furthe atomized and redirected.

Similarly, the pocket-shaped configuration of th transverse gas stream 42 of the present invention also allow for lateral, i.e. perpendicular to the axial direction movement in the location of the arc 37. For example, uneve tip wear in the arc spray gun 5 may result in the arc becomin laterally offset. In prior bent stream spray guns, suc lateral movement of the arc would result in the spray patter changing abruptly. By utilizing the pocket-shaped nozzle 33 the arc spray gun 5 is able to accommodate lateral movement o the arc 37 much in the same manner as it does axial movement thereby providing for a broader range of operation.

Referring again to Fig. 5, transverse gas nozzle o orifice 33 is preferably centrally located in generally plana surface 44. The planar surface 44 makes up a portion of th arc head 25 which extends above and beyond the arc zone 30 Planar surface 44 is generally parallel to the axial gas strea 45 and is offset a predetermined distance from the arc 37 a described above. The surface 44 has a generally rectangula shape whose width is preferably approximately twice it length.

The arc spray gun 5 utilizes the planar surface 44 t somewhat isolate the cup-shaped orifice 33 and to prevent ai and dust from being entrained into the metal spray stream More specifically, the surface 44 tends to block or preven unnecessary entrainmen.t of air and dust from occurring as wel as turbulence along the paths of the axial and transverse ga streams. In the preferred embodiment, the wires 18 intersec at an included angle of 30°, just beneath the planar surfac 44. Utilizing a cup-shaped orifice 33 of the dimension described above with respect to Fig. 5, an arc spray gun having a surface 44 which has a surface area of approximatel 1.75 square inches has been found to provide the desire controlled dispersion of the metal spray stream. Such surfac 44 also may tend to isolate the arc 37, in a sense protectin the metal spray along the axial direction of axis A fro unnecessary entrainment, etc., so that such metal spray then can be gathered and redirected by the cup-shaped transverse gas flow 42. The surface 44 also may provide an isolating effect for the transverse gas stream to tend to minimize turbulence, air entrainment, mixing, jet breakup and/or other relatively uncontrolled fluid flow activity, and to block pick up of at least some blowback waste.

It has been found, however, that when the surface area of the surface 44 is too small, e.g. less than approximately 0.58 square inch area in the exemplary embodiment, the metal spray stream tends to become too dispersed and unsatisfactory coating occurs. Therefore, while the included angle between intersecting wires 18 and the dimensions of nozzle 23 may differ in other embodiments, the preferred surface area is preferably one square inch or larger, the overall objective being to make the surface 44 as large a flat planar area as possible without compromising the diameter of the housing 20 or the arc head 25. As explained above, it is the diameter of the arc head 25 and the housing *20 which may' limit the ability of the spray gun 5 to be inserted into a narrow recess.

As is described above, axial gas nozzle 32 and transverse gas nozzle 33 emit a pressurized gas, such as air, from an external compressed gas supply (not shown) at typically between 40 and 95 PSI. Referring to Fig. 2, shown is the routing of the compressed gas through the arc spray gun 5 from where the gas enters the spray gun 5 at the intake port 50, to where the gas exits the arc head 25 at nozzles 32 and 33. Upon initially entering the intake port 50, the compressed gas is guided through a gas passageway 52 which is machined into what is referred to as the adapter head 54. The gas exits the gas passageway 52 in the adapter head 54 and enters into interior chamber 56 which as a result is filled with the compressed gas. The compressed gas within the interior chamber 56 enters into gas passageways 58 and 60 which are machined into what is referred to as the arc-and-gas transfer head 62. As described above, the mechanical dimensions of the nozzles 32 and 33 as well as that of gas passageways 58 and 60 determine what th ratio is of axial gas flow to transverse gas flow. Therefore a predetermined portion of the compressed gas travels throug passageway 60 between the two wires 18 and out the arc head 2 through axial gas nozzle 32, as shown in Fig. 2. The remainin portion of compressed gas from the interior chamber 56 travel through passageway 58 and arc head 25 where it exits the ar head 25 through the transverse gas nozzle 33.

In the preferred embodiment, both the adapting head 5 and arc-and-gas transfer head 62 are manufactured of non-conductive, easily machinable material such as what i commercially available as Delrin plastic. Both the adaptin head 54 and transfer head 62 are removably insertable int opposing ends of the spray gun housing 20. Each includes a O-ring 63 for forming a gas-tight seal about the edges of th interior chamber 56 as defined by the area within the housin 20 between the adapting head 54 and the transfer head 62. Th inner wall or walls of the housing 20 serve to contain th compressed gas within the interior chamber 56. Thus, th interior chamber 56 formed by the inner walls of the housing 2 provides the passageway through which the gas from the intak port 50 and adapting head 54 travels to the transfer head 6 and ultimately into the arc head 25 and out nozzles 32 and 33 In this manner, the arc spray gun 5 provides for an overal miniaturization or reduction in the diameter of the housing 2 as ^"compared to prior art devices in that it eliminates the nee for additional gas tubing running the length of the housing 2 between the intake port 50 and the axial and transverse ga nozzles 32 and 33 respectively. Furthermore, the tubular-lik structure of the housing 20 offers increased structura rigidity, which is desirable to prevent bowing of the housing especially in situations where the housing 20 is relativel long.

An additional feature offered by the interior chambe 56 is that it may be utilized to provide electrical isolatio of and cooling to the current carrying tubes 70. As th compressed gas travels from the intake port 50 through the interior' chamber 56 and out through the arc head 25, the flow of gas passes directly across the current carrying tubes 70. This relatively constant gas flow acts to cool the current carrying tubes 70 which tend to increase in temperature while providing the necessary current to the wires 18, as is explained in detail below.

In the preferred embodiment of the present invention, both the axial and transverse gas streams originate from the same plenum. Mpre specifically, as shown in Fig. 2, the interior chamber 56 forms a plenum from which passages 58 and 60 provide gas to the nozzles 33 and 32, respectively. Therefore, the ratio of axial to transverse gas flow remains relatively constant since both originate from the compressed gas within the plenum formed by the interior chamber 56. Only the mechanical restrictions of the axial and transverse gas nozzles 32 and 33 can change the proportional gas flow among each. As a result, when the pressure of the compressed gas from the external supply is increased, both the axial and transverse gas flows are proportionally increased, thereby allowing for continued satisfactory operation. Satisfactory results have been obtained operating in the range of 40 to 150 PSI, with a finer spray of metal occurring at the higher end. The higher the pressure, the smaller the particle size and the higher the velocity at which they impinge on the surface 34, therefor typically resulting in a denser, and better adhering coating. However, other pressures outside of this range may also be used within the context of the invention.

Referring again to Fig. 2, the spray gun 5 includes a wire feed assembly 15 which feeds the wire 18 towards the arc head 25 as described above. The wire feed assembly 15 consists of a conventional feed assembly comprising four wire drive rollers 72 (only two of which may be seen in the drawing) . Each wire 18 has two independently driven drive rollers 72 which advance each wire 18 at a constant feed rate through respective wire guide paths 75 (Fig. 13) within the housing 20. The drive rollers 72 are driven by an electric motor (not shown), although in an alternate embodiment an air motor or other drive system may be utilized as is conventional.

As mentioned above, the wire feed assembly 15 feeds the wires 18 through the wire guide paths 75 which guide each wire towards the arc head 25. Fig. 13 shows a cross-sectional view of the wire guide path 75 along its longitudinal axis. Upon exiting the wire feed assembly 15, each wire 18 enters its respective wire transfer tube 77 which is made of nylon tubing such as the commercially available Nylatron GS tubing, or a similar type of non-conductive material. In the preferred embodiment, wire transfer tube 77 is enclosed in a coaxial fashion within the current carrying tube 70, thereby minimizing space required for travel of wires and electrical power in the housing 20. The current carrying tube 70 is made of conductive material such as tellurium copper, although variety of conductive materials may similarly be used in othe embodiments. As a result, as each wire 18 advances through its respective wire transfer tube 77, it remains electricall isolated from current carrying tube 70.

An external power supply 27 (Fig. 1) provides voltage to contact straps 79 by way of power cables 81. Th contact straps 79 are made of brass or a similar conductiv material, and are both mechanically and electrically connecte to the outer surface of current carrying tube 70, typically i a sleeve configuration. In this^" manner, the voltage potentia from the power supply 27 is transferred along the length o current carrying tube 70 while the wire 18 remains electricall isolated within the wire transfer tube 77.

As wire 18 travels towards and eventually exits th opposite end of the wire transfer tube 77, the wire 18 enters contact tube 83 which is threadedly attached to curren carrying tube 70. The contact tube 83 is also made of conductive material, such as tellurium copper, and i electrically coupled to current carrying tube 70 by way of th threaded engagement. In contact tube 83, wire 18 i electrically coupled to the tube 83 by way of physical contact with the inner conductive walls of tube 83 as the wire 18 advances towards the arc head 25. Similarly, wire 18 incurs conductive contact with the inner walls of an electrically conductive contact block 85, which is mechanically and electrically connected to the contact tube 83 at one end, and the contact tip 35, which is mechanically and electrically connected to the other end of the contact block 85. Both the contact block 85 and tip 87 are made of brass or other electrically conductive material. In all, for each wire 18 the respective contact tube 83, contact block 85 and contact tip 35 act to couple the voltage from respective current carrying tube 70 to the appropriate wire 18. The wires 18 are placed on converging paths by the respective angles_^ formed in the guidepaths 75 within the respective contact blocks 85, and therefore the wires 18 exit the contact tips 35 and advance toward each other into the arc zone 30 (Fig. 3).

By coaxially encasing the wire transfer tube 77 within the current carrying tube 70, the present invention reduces the required space necessary within the spray gun housing 20. Rather than a separate conduit for both wire and current as explained above, the coaxial relation of the wire guide 75 with the current carrying tube 70 allows what is in essence a single conduit to perform the function of two. The present invention, therefore, provides increased miniaturization of the spray gun housing 20 and arc head 25 both by using the spray gun housing 20 as part of the interior chamber 56 which serves to transfer gas towards the arc head 25, and by using the wire guide paths 75 in an electrically isolated coaxial configuration with the current carrying conduits 70. As a result of this miniaturization, the cross-sectional diameter of the spray gun 5, in the exemplary embodiment, is 1.75 inches. However, even smaller diameters are possible as will be apparent to one of ordinary skill in the art.

Another feature offered by the present invention is that its configuration permits ease in changing the length of the spray gun 5. By simply changing the length of the housing 20, wire transfer tube 77, and current carrying tube 70, the length of the spray gun, and more importantly, the distance which it may be inserted into a narrow recess may be easily changed. Manufacturers of such spray guns need not keep on hand excessive amounts of inventory in order to accommodate customers with different needs. The standard parts, i.e., those that would remain unmodified regardless of the desired length, could be used to fill any order. Only the housing 20, wire transfer tube 77, and the current carrying tube 70 would need to be stocked in a variety of lengths.

In the preferred embodiment of the arc spray gun 5, the angle at which the transverse gas stream 42 from the transverse nozzle 33 intersects the axial gas stream is slightly forward of 90°, or more specifically, about 75°. The optimum angle of impingement of the metal spray stream onto the surface 34 has been found to be approximately 70°. An angle of 70° has been determined experimentally in at least several operation modes to produce an optimum bond strength as can be seen in the graph of Fig. 14a. As is seen in such graph, bond strength data was obtained using a conventional line of electric arc spray gun, such as Model 8830 of TAFA Incorporated, Concord, NH, using conventional settings and wire material. The wire was sprayed from 4 inches, 6 inches and 8 inches away from a metal substrate at four different angles. The curve plotted from the bond strength and spray angle data indicates optimum bond strength at about 70° spray angle.

Figs. 14b-14d show the effect of the impingement or spray angle on the uniformity of the coating provided to the surface 34. Not only is the bond strength of the coating optimum at a 70° impingement angle. More specifically, at a spray angle of 20°, Fig. 14a shows an exemplary cross section of the coating on surface 34 as having a porous finish with large inclusions. The coating provided with the 20° spray angle tends to resemble a series of waves on the surface 34. The waves include crests behind which inclusions of unmelted particles tend to gather.

Fig. 14b shows an exemplary cross-section view of the coating produced on a surface 34 at an impingement angle of 45°. In this case, the coating tends to have a less pronounced wave effect than that obtained at a 20° spray angle, but the coating still includes somewhat of a rippled finish.

Fig. 14d shows how a spray angle between 70° and 90° produces a smooth, flat, uniform finish which is relatively free from inclusions. As is shown in Fig. 14d, .the exemplary coating provided at a 70° to 90° spray angle has virtually no surface effects, thus providing both a uniform coating along with optimum or nearly optimum bond strength.

While the indicated spray angles are preferred for the reasons noted, it will be appreciataed that other spray angles also may be employed using various features of the invention although the • resulting coating may have less desirable characteristics.

In order to achiev a 70° angle of impingement, the transverse gas stream nozzle 33 or the arc spray gun 5 is directed at a forward 75° angle is as shown in Fig. 15. The gas stream from the axial nozzle 32 atomizes and propels the metal particles in an axial direction into the transverse gas stream pocket 42 which intersects the axial stream at an angle of 75°. The axial momentum of the metal particles results in the metal spray stream being ultimately redirected at approximately optimum 70° angle of impingement. In other embodiments, however, different angles of the transverse nozzle 33 may be used without departing from the scope of the invention.

Table I below shows a comparison of bond strengths obtained using a prior line of sight electric arc spray gun (TAFA Model 8835) and the inside diameter spray gun of the present invention under similar, conventional settings and operating conditions. Three different materials 01SXP and 75 SB/01SXP, which are proprietary wire materials of TAFA Incorporated, and 10T Aluminum Bronze wire. The substrate was 319 cast aluminum. Bond strengths and the nature of the eventual failure (failure mode) for each test are shown. It can be seen that higher bond strengths in general were obtained using the present invention.

TABLE I

COMPARISON OF BOND STRENGTHS OF INSIDE DIAMETER SPRAYER vs. PRIOR ART L NE-OF SIGHT SPRAY GUN

Inside Diameter Spray Gun

Coating Bond Failure

Material Strength Mode

Sprayed^"1" (psi)

01SXP* 3975 A 3925 A 4525 A

75B/01SXP** 5450 F 5225 T 5370 T

1oτ*** 3465 A 3975 A 3885 A

- The substrate onto which coating material was sprayed was 319 cast aluminum in one inch diameter slugs. Conventional ASTM 633-79 test procedures were used to measure bond strength in pounds per square inch needed to cause a failure of the coating, e.g., as an adhesive or cohesive failure or a failure at a bond coat/top coat interface, etc., and to determine failure made, i.e., adhesive or cohesive type, etc. - High silicon/aluminum wire that is sold as a pro¬ prietary material by TAFA Incorporated, Concord, New Hampshire.

** _ A self-bonding coating of 95% nickel, 5% aluminum alloy (material 75B) is first applied to a thickness of 0.005 inch as a bond coat; then a coating of the 01SXP material is applied to a thickness of 0.015 inch to 0.020 inch. *** - Copper, aluminum and iron material sold by TAFA

Incorporated. A - Adhesive failure between coating and substrate C - Cohesive failure within coating F - 75B/Aluminum - Failure at bondcoat/topcoat interface T - Cast Aluminum threads on bond slug stripped before coating failure

Another advantage of the arc spray gun 5 in having the transverse gas stream 42 positioned at a forward angle as is shown in Fig. 15 is that it assists in minimizing blowback of dust and random metal particulate back onto the spray gun 5 apparatus. By directing the metal spray stream at a slightly forward angle, the spray gun 5 remains behind the spray, keeping the housing 20 and arc head 25 less susceptible to contamination with overspray which would otherwise be caused by blowback.

An auxiliary flow of air or another type gas through the pipe 6 or other object whose surface is to be coated is utilized to remove dust and random spray particulate. As is shown in Fig. 16, an auxiliary flow of air 87 (for example, from blower 28b) through the pipe 6 passes over the spray gun 5 and arc head 25, sweeping the dust out of the pipe 6 through the exhaust 89. The auxiliary flow of air provides a cleaner spray environment for the spray gun 5, keeps the housing 20 clean, and results in a more uniform coating along the length of the pipe 6 being coated, with less dust inclusions.

When spraying within a closed region such as a blind hole, the auxiliary flow of air is provided by a concentric tube 90 which surrounds the spray gun housing 20 as shown in Fig. 17. Air is blown through the tube past the arc head 25 region. The auxiliary air is then drawn out of the pipe 6 along a path on the outside of the concentric tube 90 to an evacuation system (not shown) .

In addition, the sloping front faces 92a, 92b (Fig. 6) of the arc head 25 further contribute to a reduction in susceptibility to blowback. The sloping front faces 92a and 92b establish an aerodynamic flow path around the arc head 25 such that any blowback which may occur will tend to flow around the arc head 25 rather than onto its surface. As a result, the effects of blowback are minimized and such blowback may be harmlessly evacuated through the exhaust as is described above.

Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of the specification.

For example, as is shown in Fig. 18 the arc head 25 may also include additional orifices 97 near the pocket-shaped orifice 33 for providing additional gas streams for redirecting and focusing of the axial spray stream as it enters the region of the pocket-shaped transverse stream. These additional jets may serve to change or modify tthe resultant redirection of the metal spray stream, as well as provide further focusing and/or dispersion of the metal spray stream.

In addition, rather than using a pocket-shaped orifice or a series of orifices arranged in the shape of a pocket, the invention may include one or more orifices arranged so as to produce a swirling composite of streams which result in a pocket-shaped composite and/or which otherwise create the desired pocket-shaped flow possibly with particular mixing characteristics.

Furthermore, while the present invention was described above in the context of an arc spray gun 5 utilizing two consumable electrodes (i.e., two wires 18), it is within the scope of the present invention to include or use other type systems which are capable of forming globules or a stream of molten metal or other material to be sprayed. Such a system may include a single wire system in which only one wire acts as a consumable electrode. Alternatively, such a system may utilize three or more wires to produce an arc from which a molten metal may be sprayed within inside diameters.

The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the following claims.

Claims

What is claimed is:

1. An arc spray gun, comprising: means for forming an arc for melting material intended to be sprayed; first propelling means for propelling molten material from the --area of. said arc generally in a first direction; and second propelling means for changing the direction of said propelled molten material, said second propelling means including means for forming a pocket to capture and redirect at least part of said molten material.

2. The arc spray gun of claim 1, wherein said pocket provides controlled dispersion of said molten material in a spray stream.

3. The arc spray gun of claim 2, wherein said molten material is atomized into particles generally between 10 and 80 microns in diameter.

4. The arc spray gun of claim 1, wherein said second propelling means cause said molten material to be redirected at an angle approximately 70° to said first direction.

5. The arc spray gun of claim 4, wherein said second propelling means is directed at an angle approximately 75° to said first direction.

6. The arc spray gun of claim 1 wherein said means for forming a pocket comprises a pocket-shaped orifice from which a propellant emanates.

7. The arc spray gun of claim 6, wherein said pocket-shaped orifice comprises a cup-shaped orifice.

8. The arc spray gun of claim 7, wherein said cup-shaped orifice has a radius of curvature generally equal to the radius of curvature of said arc.

9. The arc spray gun of claim 6, wherein said pocket-shaped orifice comprises a V-shaped orifice.

10. The arc spray gun of claim 6, wherein said means for forming a pocket-shaped orifice comprises an open-ended box shaped orifice.

11. The arc spray gun of claim 1, wherein said means for forming a pocket comprises a plurality of orifices configured in the shape of a pocket from which a propellant emanates.

12. The arc spray gun of claim 1, wherein said second propelling means includes a pocket-shaped orifice and at least one additional focusing orifice from which a propellant emanates.

13. The arc spray gun of claim 1, wherein said arc spray gun has a cross-sectional diameter of approximately 1 3/4 inches in an area at which said arc occurs.

14. The arc spray gun of claim 1, wherein said first propelling means comprises a fluid traveling at a velocity on the order of from about Mach 0.2 to about Mach 3.0.

15. The arc spray gun of claim 1, wherein said second propelling means comprises a fluid traveling at a velocity on the order of from about Mach 0.2 to about Mach 3.0.

16. The arc spray gun of claim 1, wherein said material intended to be sprayed comprises at least one wire.

17. The arc spray gun of claim 16, wherein said wire consists of a cored wire.

18. The arc spray gun of claim 1, wherein said material intended to be sprayed comprises a self-bonding material.

19. An arc spray gun, comprising: means for forming an arc at which material to be sprayed is melted; first propelling means for propelling molten material from said arc generally in a first direction; and second propelling means for changing the direction of said propelled molten material, said second propelling means including a pocket-shaped orifice for forming a pocket-shaped gas stream to capture and redirect at least part of said molten material, said pocket-shaped orifice being located in a generally planar surface which is positioned generally parallel to said first direction.

20. The arc spray gun of claim 19, wherein said generally planar-surface is at least between 1 and 2.5 square inches in surface area.

21. The arc spray gun of claim 19, wherein said planar surface has a generally rectangular shape having a width that is approximately twice its length.

22. The arc spray gun of claim 19, wherein said material to be sprayed comprises at least one wire.

23. The arc spray gun of claim 22, wherein said wire consists of a cored wire.

24. The arc spray gun of claim 19, wherein said material intended to be sprayed comprises a self-bonding material.

25. An arc spray gun, comprising: means for forming an arc by which material to be sprayed is melted; first propelling means for propelling molten material from said arc generally in a first direction; second propelling means for changing the direction of said propelled molten material; and surface means for reducing unnecessary entrainment of air and dust in the path of said first and second propelling means.

26. The arc spray gun of claim 25, wherein said surface substantially isolates said arc and first and second propelling means from external turbulence.

27. The arc spray gun of claim 25, wherein said material to be sprayed comprises at least one wire.

28. The arc spray gun of claim 27, wherein said wire consists of a cored wire.

29. The arc spray gun of claim 25, wherein said material intended to be sprayed comprises a self-bonding material.

30. An arc spray gun, comprising: a housing; means for forming an arc at an end of said housing by which material to be sprayed is melted; and propelling means for propelling molten material from the area of said arc, said propelling means including a compressed gas which is directly contained, at least in part, by the walls of said housing.

31. The arc spray gun of claim 30, wherein said means for forming an arc include current carrying means, and wherein said gas in said housing serves to provide a cooling effect to said current carrying means.

32. An arc spray gun, comprising: means for forming an arc at which material to be sprayed is melted; a guidepath for guiding at least one consumable electrode tσ a location at which said arc occurs; and a current carrying apparatus for providing current to said consumable electrode, said current carrying apparatus being in substantially coaxial relation with said guidepath.

33. The arc spray gun of claim 32, wherein said guidepath is made primarily of an electrically non-conductive material.

34. The arc spray gun of claim 1, said spray gun further including exhaust means for expelling undesirable particulate such as overspray dust while said spray gun is utilized to coat an inside surface of an at least partially enclosed recess, bore, etc.

35. An arc spray gun, comprising: means for forming an arc at which material to be sprayed is melted; first propelling means for propelling molten material from said arc generally in a first direction; and second propelling means for changing the direction of said propelled molten material, said second propelling means including cup-shaped orifice for forming a cup-shaped gas stream to capture and redirect at least part of said molten material over a range of variation in said first direction, said cup-shaped orifice having a radius of curvature approximately equal to the radius of curvature of said arc.

36. An arc spray gun, comprising: a housing; means for forming an arc at which material to be sprayed is melted; propelling means for propelling molten material from said arc generally in a direction, said propelling means including a chamber formed at least in part by said housing, said chamber being utilized to allow passage of a propellant.

37. An arc spray gun, comprising: means for forming an arc at which an end of at least one wire to be sprayed is melted; propelling means for propelling molten material from said arc generally in a direction; wire guide means for guiding said wire to the location of said arc; current carrying means for providing electrical current to said arc, said current carrying means including an electrically isolated conduit which coaxially surrounds a conduit included in said wire guide means.

38. An arc head for an arc spray gun at which at least one wire is melted by an arc and is propelled in an axial direction, said arc head having a body, and propelling means for redirecting such flowing melted wire material from such axial direction to a direction generally transverse to such axial direction to coat at least one of an interior surface or a surface within a relatively confined space, and at least one sloped wall surface on said arc head body for tending to reduce accumulation of material thereon during spraying operation.

39. An arc spray gun, comprising: a housing; means for forming an arc for melting material intended to be sprayed; first propelling means for propelling molten material from the area of said arc generally in a first direction; and second propelling means for changing the direction of said propelled molten material, said first and second propelling means both comprising a gas which emanates from a common plenum within said housing.