Abstract:
Plume shield shroud ( 10 ) for a plasma gun ( 30 ) includes a substantially tubular member ( 14 ) comprising an axial length, a plume entry end ( 11 ), and a plume exit end ( 13 ). The shroud ( 10 ) is adapted to be mounted to a plasma gun ( 30 ). A method of protecting, confining or shielding of a gas plume of a plasma gun ( 30 ) includes mounting ( 20 ) a gas plume shroud ( 10 ) on the plasma gun ( 30 ) such that the shroud ( 10 ) is sized and configured to substantially surround at least a portion of the gas plume

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The instant application is an International Application based on U.S. provisional application No. 61/298,366, filed Jan. 26, 2010, the disclosure of which is hereby expressly incorporated by reference hereto in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO A COMPACT DISK APPENDIX 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    Plasma spray is perhaps the most flexible of all of the thermal spray processes as it can develop sufficient energy to melt any material. Plasma spray guns use powder as the coating feedstock, and the number of coating materials that can be used in the plasma spray process is almost unlimited. In a plasma spray gun, a high frequency arc is ignited between an anode (nozzle) and a cathode (electrode). Process gases, generally mixtures of argon, nitrogen, hydrogen and helium, flowing between the anode and the cathode is ionized to become a plume of hot plasma gas, reaching temperatures of 6,600° C. to 16,600° C. (12,000° F. to 30,000° F.). When the coating feedstock material is injected into the gas plume, it is melted and propelled towards a target substrate. 
         [0005]    The plasma plumes produced by atmospheric thermal spray guns that are laminar are sensitive to the surrounding environment. These plumes can be easily disrupted by air currents. As the thermal spray gun is moved or traversed over a substrate, air currents impinge upon the plume. Compounding this is the need to have a forced flow of air through a spray booth during operation of the plasma gun. Disturbing the plasma plume can cause several undesirable effects. 
         [0006]    In a first undesirable effect, the plume can be shifted in a direction relative to powder injection resulting in poor energy transfer to the powder particles and subsequent poor coating results. 
         [0007]    In another undesirable effect, the laminar tube of the plume can collapse and result in increased interaction with the environment. Laminar plumes are considered very effective for spraying as the energy is contained within the laminar tube and thus transfers more heat energy to the powder particles. 
         [0008]    In another undesirable effect of extreme cases, for example with the external arc plumes, the arc position can be affected resulting in damage to the cathode, anode, and/or the surrounding components from misplaced arc energy. 
         [0009]    Accordingly, what is needed is an apparatus that protects a laminar plasma plume from being disturbed from the ambient air currents and/or which overcome one or more of the above-noted deficiencies. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In accordance with a non-limiting aspect of the invention there is provided a plume shield shroud comprising a substantially tubular or cylindrical member having an axial length, a plume entry end, and a plume exit end, wherein said shroud is adapted to be mounted to a plasma gun. 
         [0011]    In embodiments, the substantially cylindrical member comprises a perforated metal member. 
         [0012]    In embodiments, the substantially tubular or cylindrical member comprises at least one of a side opening adapted to receive therein a member of the plasma gun and a side opening allowing powder to be injected into a gas plume. 
         [0013]    In embodiments, the substantially tubular or cylindrical member comprises a mounting member for mounting the shroud to the plasma gun. 
         [0014]    In embodiments, the substantially tubular or cylindrical member comprises a mounting member for mounting the shroud to a mounting assembly. 
         [0015]    In embodiments, the mounting assembly is structured and arranged to mount said shroud to the plasma gun. 
         [0016]    In embodiments, the plume shroud further comprises a mounting assembly for mounting the shroud to the plasma gun. 
         [0017]    In embodiments, the plume shroud further comprises a mounting assembly for movably mounting the shroud to the plasma gun. 
         [0018]    In embodiments, the shroud is at least one of movably mounted to the plasma gun, pivotally mounted to the plasma gun, and removably mounted to the plasma gun. 
         [0019]    In embodiments, the axial length is at least one of greater than a diameter of the substantially cylindrical member and sized to shield a gas plume starting approximately at a point where the gas plume leaves the plasma gun to a predetermined distance past a location of powder injection into the gas plume. 
         [0020]    According to another non-limiting aspect of the invention, there is provided a plasma gun plume shield shroud comprising a member sized and configured to substantially surround at least a portion of a gas plume, wherein the member is sized and configured to prevent at least partial disruption of the gas plume by an air current. 
         [0021]    In embodiments, the member is at least one of a substantially cylindrical member and a perforated metal member. 
         [0022]    In embodiments, the member comprises at least one of a side opening adapted to receive therein a member of a plasma gun and a side opening allowing powder to be injected into the gas plume. 
         [0023]    In embodiments, the member comprises at least one of a mounting member for mounting the shroud to a plasma gun and a mounting member for mounting the shroud to a mounting assembly. 
         [0024]    In embodiments, the shroud further comprises a mounting assembly structured and arranged to mount said shroud to a plasma gun. 
         [0025]    In embodiments, the shroud is at least one of movably mounted to a plasma gun, pivotally mounted to a plasma gun, and removably attached to a plasma gun. 
         [0026]    According to another non-limiting aspect of the invention, there is provided a method of protecting, confining or shielding a gas plume of a plasma gun, wherein the method comprises mounting a gas plume shroud in an area of the gas plume, wherein the shroud sized and configured to substantially surround at least a portion of the gas plume. 
         [0027]    In embodiments, the gas plume shroud is at least one of a substantially cylindrical member and a perforated metal member. 
         [0028]    In embodiments, the gas plume shroud comprises a side opening adapted to receive therein a portion of the plasma gun. 
         [0029]    In embodiments, the mounting comprises at least one of movably mounting the gas plume shroud to the plasma gun, removably movably mounting the gas plume shroud to the plasma gun, and pivotally mounting the gas plume shroud to the plasma gun. 
         [0030]    Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The present invention is further described in the detailed description which follows, in reference to the noted drawings by way of a non-limiting example embodiment of the present invention, and wherein: 
           [0032]      FIG. 1  is a perspective view of an embodiment of the plume shield shroud; 
           [0033]      FIG. 2  is a side planar view of the shroud shown in  FIG. 1 ; 
           [0034]      FIG. 3  is a first end view of the shroud shown in  FIG. 1 ; 
           [0035]      FIG. 4  is a second end view of the shroud shown in  FIG. 1 ; 
           [0036]      FIG. 5  is a top rear side perspective view of the plume shield shroud mounted to a mounting assembly; 
           [0037]      FIG. 6  is a top front side perspective view of the plume shield shroud and mounting assembly of  FIG. 5 ; and 
           [0038]      FIG. 7  is a top and right side perspective view of a plume shield shroud and mounting assembly attached to a plasma gun. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice. 
         [0040]    Development of laminar plasma plumes in atmospheric thermal spray applications is relatively recent, and the problems with adverse effects to these plumes is a new revelation. Laminar plasma plumes have existed for some time in low pressure and reactor chambers, however the problems with ambient gas was not encountered in these situations. 
         [0041]    One aspect of the invention relates to a shroud for the laminar plasma plume. This shroud minimizes any potential forced interaction with air currents. The air currents might be caused, for example, by exhaust flow or gun motion. The shroud shields the plume starting approximately at the point the plume leaves the gun body to a predetermined distance past the location of powder injection into the plume. In a preferred embodiment, this distance is approximately one third the spray distance. In another embodiment, this distance is one half the spray distance. In still another embodiment, this distance is approximately one third to approximately one half the spray distance. 
         [0042]    In an embodiment, the shroud is arranged as generally cylindrical. The length of the generally cylindrical shroud is similar to the lengths discussed above as the length of the shroud. The diameter of the generally cylindrical shroud is suitable to protect the plume. In an embodiment, the diameter of the generally cylindrical shroud is approximately 7 cm to approximately 10 cm. 
         [0043]    In another embodiment, the shroud is made of any suitable material. For example, in an embodiment, the shroud is made of a metal, more preferably a high temperature metal that can withstand the heat of the plasma plume. Non-limiting examples of such materials are described below. 
         [0044]    In another embodiment, the shroud is made of an open frame or perforated metal. This allows the plume to be viewed through the shroud. The shroud may have approximately one third to one half of the surface area open with holes. The holes or openings may range from approximately 15 mm to approximately 50 mm in diameter. Larger holes may also be used but with reduced effectiveness. Use of a metal or wire mesh may also be used. 
         [0045]    In another embodiment, the shroud has a thermal barrier material or coating applied to the inside facing surface, i.e., the surface surrounding the gas plume. This thermal barrier contains the radiated heat and improves the thermal efficiency of the process. 
         [0046]    In another embodiment, the shroud is mountable on a plasma gun. Additionally, the shroud, when mounted on a plasma gun, may also be pivotal and/or rotatable to allow full view of the plume or plume area when the gun is not in motion. This allows, for example, the taking of diagnostic measurements that would otherwise be blocked or interfered with by the shroud. 
         [0047]    In another embodiment, the shroud may use a two-layer shroud. For example, an outer layer having a finer inner mesh inner layer. This multi-layer shroud may be used for additional resistance to penetration by air currents. In embodiments, an outer layer of the shroud is a perforated member and an inner layer of the shroud is a metal or wire mesh. In embodiments, an outer layer of the shroud is a wire or metal mesh and an inner layer of the shroud is a perforated member. In embodiments, both the outer and inner layers of the shroud are a perforated member. In embodiments, both the outer and inner layers of the shroud are a metal or wire mesh. 
         [0048]    Referring now to the figures which show non-limiting aspects of the invention, there is shown in  FIGS. 1-4  a shroud  10  in accordance with the invention, while  FIGS. 5 and 6  show a non-limiting mounting assembly  20  to which the shroud  10  can be mounted and  FIG. 7  shows a non-limiting way in which the assembly  10 / 20  can be mounted to a plasma gun  30 . 
         [0049]      FIGS. 1-4  show details of the plume shield shroud  10  in accordance with the invention. The shroud  10  has a first end  11  and a second end  13 . The first end  11  is open and includes a shroud ring member  12  secured thereto. In embodiments, the ring  12  is secured to the first end  11  via welding. Other joining techniques may also be utilized. The ring  12  has an annular portion whose inner edge  12   b  is sized to be smaller than an inside diameter of a main section  14  of the shroud  10  and a circumferential portion  12   a  sized and configured to receive therein or slide over the first end  11 . The section or main body  14  is made of an open frame or a perforated metal. In accordance with a non-limiting embodiment, the outside diameter of the generally cylindrical body  14  is between approximately 7 cm and approximately 10 cm. 
         [0050]    The body  14  is a tubular member and can be made of any suitable material. In embodiments, the body  14  is made of a metal and more preferably a high temperature metal that can withstand the heat of a plasma plume. The body  14  material may be or include any of the following materials; steel; stainless steel; copper; inconel; high temperature nickel, chromium and/or cobalt based alloys; other metal families and alloys that can withstand tempts of up to 1500 degrees C. or more. Ceramics may also be used, for example, aluminum oxide. In embodiments, the body  14  utilizes or includes a thermal barrier material or coating applied to the inside facing surface, i.e., the surface surrounding the gas plume. 
         [0051]    In embodiments, the body  14  is perforated with the perforations  15  being of any size and/or shape. As described above, in embodiments, the holes or openings  15  may range from approximately 15 mm to approximately 50 mm in diameter. The shape may be, for example, circular, partially circular, polygons, partially polygonal, irregular in shape, as well as any shape that includes curved or linear sections or mixtures thereof. Additionally, artistic designs may be incorporated in the perforations and/or may result from their particular arrangement. In embodiments, the void to solid ratio of the body  14  may be between about 5% and about 90%. 
         [0052]    In embodiments, the body  14  is formed of a bent perforated sheet metal member which is bent into a generally tubular shape and which includes a main opening  16  which is sized and configured to receive therein a portion of the plasma gun such as a powder injection member. The opening  16  allows the shroud  10  to pivot into and out of the gas plume shielding position shown in  FIG. 7 . A seam  17  (which can be connected by, e.g., welding) is utilized to join ends of the bent member so that section or body  14  retains its tubular shape. In order to facilitate mounting the shroud  10  to a plasma gun, the shroud  10  includes a mounting bar  18  which is fixed or secured to the body  14  via connections  19 . In embodiments, the connections  19  are formed by welding. Member  18  (as well as member  12 ) can be made of the same or similar materials as those used in making the body  14 . 
         [0053]    While a cylindrical shape of the shroud  10  is preferred, other tubular shapes may be used, for example, generally oval in cross section, square or rectangular in cross section, as well as having triangular cross section, n-sided polygonal cross section, irregular cross section, a clover leaf cross section, and the like. 
         [0054]    In embodiments, the body  14  may also be a weave of metal strands or metal fibers (not shown). Such a woven shroud  10  may have a predetermined void to solid ratio of between about 5% to about 75%. This mesh may be regular or irregular or combinations thereof. 
         [0055]    Referring now to  FIGS. 5 and 6 , there is shown a non-limiting mounting assembly  20  to which the shroud  10  can be mounted. In this regard, the mounting assembly  20  includes a mounting plate  21  which includes plural mounting openings and which can be mounted to a plasma gun  30  using, e.g., fasteners such as screw fasteners. Other mechanisms may also be utilized whether they allow for a non-removable mounting or a removable mounting. The mounting assembly  20  also includes a mounting member  23  which includes plural mounting openings and which can be connected to the mounting bar  18  using, e.g., fasteners such as screw fasteners. Other mechanisms may also be utilized whether they allow for a non-removable mounting or a removable mounting. The mounting assembly  20  additionally includes a pivoting shaft  22  which connects the mounting member  23  to a lever  24  which can be moved by a user from a use position, i.e., shown in  FIG. 7 , to a downward position wherein the shroud  10  no longer surrounds the gas plume (not shown) or a gas plume area. In embodiments, an arrangement is utilized to non-movably retain the shroud  10  in each of these two positions. Such an arrangement can include the spring shown in  FIGS. 5 and 6 . In embodiments, members  21 - 24  can be made of the same or similar materials as those used in making the member  18 . 
         [0056]      FIG. 7  illustrates an embodiment for mounting the mounting assembly  20 , and thereby the shroud  10 , to a plasma gun  30 . In this regard, the mounting assembly  20  is secured to a bottom surface of the plasma gun  30  so that the shroud  10  can assume the use position shown in  FIG. 7  when a central axis of the shroud  10  is oriented generally parallel to the bottom surface. In this position, a majority of the gas plume (not shown) is confined within the shroud  10 . Moreover, when a user desires to move the shroud  10  out of the use position, the lever  24  (see  FIGS. 5 and 6 ) can be moved downwards to cause the shroud  10  to rotate about an axis of shaft  22  so as to move to a position that does not surround the gas plume. This movement can occur while the powder injector (which in the use position shown in  FIG. 7  has a portion extending through opening  16  and into a space within body  14 ) remains stationary. The advantage of this arrangement is that it allows the plasma gun  30  to be used without the shroud  10  (if desired) and also allows for servicing, replacing or changing-out of the shroud  10 . 
         [0057]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and sprit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.