ELECTRODE FOR PLASMA A GUN

Abstract

A cathode for a plasma gun includes a main body having a first end and a second end, wherein the first end has a protrusion. A method of using the cathode includes mounting the cathode inside a plasma gun and generating an arc discharge via the protrusion.

Claims

1. A cathode for a plasma gun, comprising: a main body having a first end and a second end; and a protrusion extending from the first end, wherein the protrusion has an emission zone diameter that is less than about 4 mm.

2. The cathode of claim 1, wherein the protrusion is one of a reduced diameter or reduced cross-section projection, is a forwardmost portion of the main body and has an axial length less than about 2 mm.

3. The cathode of claim 1, wherein the protrusion has at least one of a smaller diameter or smaller cross-section than any other portion of the main body.

4. The cathode of claim 1, wherein the first end is a first material and the second end is a second material.

5. The cathode of claim 1, wherein the first and second ends are different materials.

6. The cathode of claim 1, wherein the protrusion projects from a flat surface of the first end.

7. The cathode of claim 1, wherein the protrusion projects from a conical surface of the first end.

8. The cathode of claim 1, wherein the protrusion projects from a dome shaped surface of the first end.

9. The cathode of claim 1, wherein the protrusion is between about 0.5 mm and about 2.0 mm in diameter and projects at least 0.5 mm and less than about 2 mm from a surrounding surface of the first end.

10. The cathode of claim 2, wherein the first material is tungsten or doped tungsten.

11. The cathode of claim 1, wherein the first end of the cathode is an emission end.

12. The cathode of claim 4, wherein the second material is copper.

13. The cathode of claim 1, wherein the cathode is water cooled.

14. The cathode of claim 1, wherein the protrusion is coaxially aligned with a center axis of the main body.

15. A method of using the cathode of claim 1, comprising: mounting the cathode inside a plasma gun; and generating an arc discharge via the protrusion.

16. A method of using the cathode of claim 1, wherein the protrusion limits a size of an emission zone or spray area.

17. A method of using the cathode of claim 1, wherein the protrusion increases current density in an emission zone.

18.-40. (canceled)

41. A method of modifying a cathode of a plasma gun, comprising: removing the cathode from the plasma gun; performing metal removing or machining on the cathode in order to shape the forwardmost or arc discharging end so as to have a single centrally disposed and axially oriented protrusion; and reinstalling the cathode on the plasma gun.

42. The method of claim 41, further comprising operating the plasma gun with a power during the application of a coating material, said power being a lower power compared to a power used in operating the plasma gun before the cathode is modified.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Non-limiting embodiments of the invention can be seen from the drawings wherein:

[0066] FIGS. 1 and 2 show front and back views of a prior art plasma gun which can be modified to utilize a cathode of the type described herein;

[0067] FIG. 3 shows a cross-section of the plasma gun shown in FIGS. 1 and 2;

[0068] FIG. 4 shows a cross-section of an internal portion of the plasma gun shown in FIG. 3;

[0069] FIG. 5 shows a cross-section of an internal portion of the portion shown in FIG. 4;

[0070] FIGS. 6-9 show various views of a prior art cathode used in the plasma gun of FIGS. 1 and 2;

[0071] FIG. 10 shows a partial view of a cathode in accordance with one embodiment of the invention which can be used in place of the cathode shown in FIGS. 6-9;

[0072] FIG. 10A shows a front view of the cathode of FIG. 10;

[0073] FIG. 10B shows an enlarged side view of the cathode of FIG. 10;

[0074] FIG. 11 shows a cross-section of the cathode of FIG. 10;

[0075] FIG. 12 shows a partial cross-section view of a cathode in accordance with another embodiment of the invention which can be used in place of the cathode shown in FIGS. 6-9;

[0076] FIG. 13 shows a partial cross-section view of a cathode in accordance with another embodiment of the invention which can be used in place of the cathode shown in FIGS. 6-9;

[0077] FIG. 14 shows a partial cross-section view of a cathode in accordance with another embodiment of the invention which can be used in place of the cathode shown in FIGS. 6-9;

[0078] FIG. 14A shows an enlarged side view of the cathode of FIG. 14;

[0079] FIG. 15 shows a partial cross-section view of a cathode in accordance with another embodiment of the invention which can be used in place of the cathode shown in FIGS. 6-9;

[0080] FIG. 15A shows an enlarged side view of the cathode of FIG. 15;

[0081] FIG. 16 shows a partial cross-section view of a cathode in accordance with another embodiment of the invention which can be used in place of the cathode shown in FIGS. 6-9;

[0082] FIG. 16A shows an enlarged side view of the cathode of FIG. 16;

[0083] FIGS. 17-19 show partial cross-section views of three prior art cathodes;

[0084] FIG. 20 illustrates three profiles of the shaped deposit produced by spraying onto a flat plate; and

[0085] FIGS. 21 and 22 shows TDE on steel rod and DE on flat plate to illustrate a comparison between an invented electrode and a standard (prior art) electrode.

DETAILED DESCRIPTION OF THE INVENTION

[0086] 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.

[0087] Furthermore, in the following description, the various embodiments of the present disclosure will be described with respect to the enclosed drawings. As required, detailed embodiments of the embodiments of the present disclosure are discussed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the embodiments of the disclosure that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure.

[0088] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present disclosure 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 disclosure. In this regard, no attempt is made to show structural details of the present disclosure in more detail than is necessary for the fundamental understanding of the present disclosure, such that the description, taken with the drawings, making apparent to those skilled in the art how the forms of the present disclosure may be embodied in practice.

[0089] As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. For example, reference to “a spray device” would not preclude the use of plural or multiple spray devices unless specifically excluded. For example, as used herein, the indefinite article “a” indicates one as well as more than one and does not necessarily limit its referent noun to the singular.

[0090] Except where otherwise indicated, all numbers expressing quantities used in the specification and claims are to be understood as being modified in all instances by the term “about.” For example, a range of 1 to 5 is intended to encompass or be equivalent to a range of about 1 to about 5. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by embodiments of the present disclosure. At the very least, and not to be considered as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding conventions.

[0091] As used herein, the terms “about” and “approximately” indicate that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the terms “about” and “approximately” denoting a certain value is intended to denote a range within ±5% of the value. As one example, the phrase “about 100” denotes a range of 100±5, i.e. the range from 95 to 105. Generally, when the terms “about” and “approximately” are used, it can be expected that similar results or effects according to the disclosure can be obtained within a range of ±5% of the indicated value.

[0092] Additionally, the recitation of numerical ranges within this specification is considered to be a disclosure of all numerical values and ranges within that range (unless otherwise explicitly indicated). For example, if a range is from about 1 to about 50, it is deemed to include, for example, 1, 7, 34, 46.1, 23.7, or any other value or range within the range.

[0093] As used herein, the term “and/or” indicates that either all or only one of the elements of said group may be present. For example, “A and/or B” shall mean “only A, or only B, or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.

[0094] Terms such as “substantially parallel” can refer to deviating less than 20° from parallel alignment and the term “substantially perpendicular” refers to deviating less than 20° from perpendicular alignment. The term “parallel” refers to deviating less than 5° from mathematically exact parallel alignment. Similarly “perpendicular” refers to deviating less than 5° from mathematically exact perpendicular alignment.

[0095] The term “at least partially” is intended to denote that the following property is fulfilled to a certain extent or completely.

[0096] The terms “substantially” and “essentially” are used to denote that the following feature, property or parameter is either completely (entirely) realized or satisfied or to a major degree that does not adversely affect the intended result.

[0097] The term “comprising” as used herein is intended to be non-exclusive and open-ended. Thus, for instance a composition comprising a compound A may include other compounds besides A. However, the term “comprising” also covers the more restrictive meanings of “consisting essentially of” and “consisting of”, so that for instance “a composition comprising a compound A” may also (essentially) consist of the compound A.

[0098] The various embodiments disclosed herein can be used separately and in various combinations unless specifically stated to the contrary.

[0099] The electrode 10 in accordance with non-limiting aspects of the invention can be used, by way of non-limiting example, to replace the electrode 110 shown in FIGS. 1-9. As can be seen in the example of FIGS. 10, 10A, 10B and 11, the cathode C or electrode 10 includes a protrusion P located on an emission end 11 of a main or elongated body 12 which has one or more generally cylindrical sections. The protrusion P is a projection or extension and has a reduced diameter or reduced-cross-section and forms a tip or portion that constitutes a forwardmost portion of the electrode. The protrusion P can be either integrally formed with the body of the cathode C or a separately formed member mounted thereto. The protrusion P can be centered on the emission zone and/or cathode axis CA and serves to restrict the emission zone to a size or area smaller than would normally be produced by an equivalent cathode without the protrusion. For example, the smaller emission zone can be about 50% smaller in area than one generated by a cathode in a typical plasma gun such as that shown in FIGS. 1-9. The power level used for such a smaller emission zone can be about 28 kW whereas the power level used in the Simplex Pro 90 plasma gun of FIG. 1 is about 42 kW when used to spray a similar coating material.

[0100] In the example shown in FIGS. 10 and 11, the protrusion P has rounded shape and projects from a flat circular ridge having a diameter C of about 3.2 mm. The projection P has a baser diameter B of between about 0.5 mm and about 2 mm and projects a distance A of at least about 0.5 mm. The projection P is sized and configured to create a charge concentration that restricts the emission zone size or area and forms a tighter, more current dense, plasma arc which, in turn, results in a narrower plasma plume with higher energy density.

[0101] Other embodiments are shown in FIGS. 12-16 and in these embodiments the height or length of projection of the protrusion P can range from about 0.2 mm to about 2.0 mm. The bottom or base diameter B of the protrusion can range from about 0.5 mm to about 2.0 mm, whereas the diameter of the main body 12 of the electrode 10 can range from about 5 to about 19 mm. The ratio of height/bottom diameter of the protrusion can range from about 0.5 to about 2.0.

[0102] Exemplary embodiments or shapes of the protrusion P can include mountain shaped protrusions as in the case of FIG. 12, stepped protrusions as in the case of FIGS. 13, 15 and 16, and ringed protrusions as in the case of FIGS. 14 and 16. Other protrusion shapes or combinations thereof may also be used. Still further, the protrusion will generally be centered on the central axis of the main electrode body and may vary from center between about 0 mm and 1 mm with a range of about 0 to about 0.5 mm being most desirable.

[0103] Thus, in the embodiment of FIG. 12, the cathode 10′ has a main body 12′, an emission end 11′ and a pointed or mountain shaped projection P′.

[0104] In the embodiment of FIG. 13, the cathode 10″ has an elongage body 12″, an emission end 11″ and a pointed and stepped shaped projection P″.

[0105] In the embodiment of FIG. 14, the cathode 10′″ has an elongage body 12′″, an emission end 11′″ and a ringed recess shaped projection P′″.

[0106] In the embodiment of FIG. 15, the cathode 10.sup.IV has an elongage body 12.sup.IV, an emission end 11.sup.IV and a pointed and stepped shaped projection P.sup.IV.

[0107] In the embodiment of FIG. 16, the cathode 10.sup.V has an elongage body 12.sup.V, an emission end 11.sup.V and a pointed and stepped shaped projection P.sup.V.

[0108] The operating power of the plasma using an exemplary electrode of the invention can be less than 40 kW, and can preferably be less than 35 kW and more preferably is less than 30 kW for a plasma gun having a normal power limit of 80 kW. In general, the power can be limited to less than 50% of the maximum gun power level for a specific gun, preferably less than 44%, and most preferably less than 38%. The power should be at least about 7.5% of the maximum power or the lowest operating power where the plasma gun can maintain a plasma arc, whichever is less.

[0109] The plasma gun hardware life, most specifically the cathode, can be affected with the affect either to increase hardware life due to lower power operation or decrease hardware life due to increase in plasma arc density. Results will vary depending upon the specific application and parameter sets.

Example

[0110] A cathode C or 10 of the type shown in FIGS. 10 and 11 can be used in a Oerlikon Metco Sinplex-Pro plasma gun (replacing cathode 110 or tip 130 in FIGS. 1-9) and can have a projection P with a bulbous shaped protrusion (such as shown in FIGS. 10 and 11) that is about 0.75 mm in diameter at the base B and about 0.35 mm in height A. A non-limiting power level that can be used such an electrode can be about 28 kW and this example can utilize an emission zone that is about 25% the area which would be generated by the cathode used in the embodiment of FIGS. 1-9.

[0111] In another example or modification of the Examiner above, the plasma gun using the inventive cathode can be operated at about 300 amps and about 92.5 volts for a power level of about 27.8 kW which is significantly lower than a one with a prior art cathode operating at 450 amps and 94 volts and utilizing a power level of about 42.3 kW.

[0112] Tests have been conducted using a test setup to spray and measure both Deposit Efficiency (DE) on flat plate and Target Deposition Efficiency (TDE) on a 5 mm steel bar representing a small diameter part. Weight gain per unit time on the flat plate was used to determine DE while the profile of powder sprayed onto the plate was also used to determine the width of the spray pattern. In a similar fashion, the weight gain on the steel bar was used to determine the TDE. Such tests have successfully demonstrated the operation of one or more embodiments of the invention.

[0113] FIG. 20 shows spray profiles of alumina deposited on a flat plate. The X-axis represents distance in millimeters (mm) spanning the profile cross-section and the Y-axis represents height of the spray deposit. The example labeled “Prior art 1” represents a spray coating applied using an Oerlikon Metco Sinplex Pro plasma gun equipped with a standard electrode. “Prior art 2” was used to spray a coating using an Oerlikon Metco 9 MB gun equipped with a standard electrode. Profile titled “Invented” was used to spray a coating using an Oerlikon Metco Sinplex Pro plasma gun with the cathode depicted in FIGS. 10 and 11. The “Invented” cathode also produced the smallest spray pattern in relative width and the most concentrated in relative height of spray spot. Assuming a target width of a 5 mm steel bar representing a part to be sprayed, it can readily be seen the TDE is significantly higher when using the invented cathode.

[0114] FIGS. 21 and 22 show the resulting measured TDE (top graph) on a steel rod and the resulting measured DE (bottom graph) on a flat plate for the prior art 1 and the invented cathode using an Oerlikon Metco Sinplex Pro plasma gun operated at 28 kW. As should be apparent, there is a significant increase for both values when the plasma gun is equipped with the cathode of the invention. Carrier gas flow was changed to show optimal deposition for both spray conditions.

[0115] Other embodiments include adding or forming any one of the protrusions illustrated in FIGS. 10-16 to any one of the prior art cathodes shown in FIGS. 17-19. Such cathodes have a generally cylindrical main body and either short (FIG. 17) or longer tapered ends (FIGS. 18 and 19). Such modification can include removing the cathode from the plasma gun, performing metal removing or machining on the cathode in order to shape the foremost end so as to have a single centrally disposed and axially oriented protrusion of the type shown or described herein, reinstalling the cathode on the plasma gun. One can then operate the plasma gun with significantly reduced power during the application of a coating material.

[0116] One skilled in the art can discern other ways to measure both DE and TDE as well as TE by itself using different mechanisms currently available in the industry. In addition, those skilled in the art can conceive similar protrusions shapes and combinations thereof within the scope of this invention.

[0117] 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 spirit 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.