Patent Grant
7397013
Not Applicable.
The present invention generally relates to plasma spraying and, in particular, relates to plasma spray methods and apparatus for improved plasma spraying of coating material.
Plasma spraying is a process in which a coating material is sprayed by a plasma spray device onto a target surface to provide a desired coating. In a conventional plasma spray device, the induced swirling of gas around the cathode centrifugally ejects any injected coating material away from the plasma stream after it exits the anode, reducing the amount of coating material applied to the target surface. In some plasma spray devices, the plasma stream exiting the anode may have an overall particle pattern angle of greater than 90°. The resulting depositional efficiency of the spraying process may be as low as 25% in such an arrangement. Such a low depositional efficiency results in increased costs arising from longer processing times and wasted coating materials.
Moreover, a conventional plasma spray device may experience high consumable wear, requiring the frequent replacement of parts worn down by constant contact with the high energy DC arc which ignites the plasma.
What is needed is a plasma spraying process and apparatus with an increased depositional efficiency and a longer consumable life. The present invention satisfies these needs and provides other advantages as well.
In accordance with the present invention, an anode for a plasma spray device has an axial bore with a non-circular cross-sectional shape for lineating the flow of a plasma stream within the anode. The lineation of the flow of the plasma stream reduces the angle of the overall particle pattern of the plasma stream after it exits the anode, resulting in a plasma spray device with a higher depositional efficiency and lower processing times. The turbulence of the plasma stream caused by the transition from a cyclonic flow to a lineated flow reduces the wear on the anode caused by the high energy DC arc used to form the plasma, resulting in a longer consumable life for the anode.
According to one embodiment, the present invention is a plasma spray device including a plasma chamber region for having a plasma formed and a throat region coupled to the plasma chamber region. The throat region includes an end surface and an axial bore. The axial bore is formed in a direction substantially along a longitudinal axis of the throat region, and has a non-circular cross-sectional shape. The axial bore at the end surface is for ejecting a plasma stream.
According to another embodiment, a plasma spray device of the present invention includes a throat region having an end surface and an axial bore. The axial bore is formed within the throat region in a direction substantially along a longitudinal axis of the throat region. The axial bore has a plurality of grooves, at least a portion of which are formed in a direction substantially along the longitudinal axis of the throat region. The axial bore at the end surface is for ejecting a plasma stream.
According to yet another embodiment, an electrode for a plasma spray device according to the present invention includes a plasma chamber region and a throat region coupled to the plasma chamber region. The throat region has an end surface and an axial bore. The axial bore is formed substantially along a longitudinal axis of the throat region. The axial bore is for ejecting a plasma stream. The axial bore has at least a cross-sectional shape for lineating a flow of the plasma stream before the plasma stream exits the axial bore.
Additional features and advantages of the invention will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:
In the following detailed description, numerous specific details are set forth to provide a full understanding of the present invention. It will be obvious, however, to one ordinarily skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the present invention.
Referring to
Because of the lineating design of anode 101, the induced swirling of inert gas 103 which occurs within plasma spray device 100 is substantially reduced as plasma stream 104 passes through axial bore 110 of anode 101. Lineation of the flow of plasma stream 107 confines the injected coating material 106 to a denser pattern, reducing the centrifugal ejection as it leaves anode 101 in plasma stream 107, such that the overall particle pattern angle θ 120 is substantially smaller than in conventional plasma spray devices. This smaller overall particle pattern angle θ 120 increases the concentration of coating material 106 in plasma stream 107 and thereby increases the depositional efficiency of the plasma spray device.
According to one aspect of the present invention, overall particle pattern angle θ for plasma stream 107 is less than about 90°. According to another aspect of the present invention, overall particle pattern angle θ for plasma stream 107 is less than about 50°. According to one embodiment, an overall particle pattern angle may be any number between 0 and 90°.
In another embodiment, the labels cathode and anode as described with respect to
Referring now to
Throat region 202 has an outer wall 280, an end surface 203 and an axial bore 204. Outer wall 280 is cylindrical in this example, but it may be any shape (e.g., rectangular, polygonal, elliptical, irregular). Axial bore 204 having a first end 230 and a second end 240 is formed within throat region 202 substantially along a longitudinal axis 210 of throat region 202, and has a non-circular cross-sectional shape. In this example, first end 230 of axial bore 204 is second end 296 of plasma chamber region 201. Second end 240 of axial bore 204 is at end surface 203 of throat region 202. Axial bore 204 at second end 240 (or at end surface 203) ejects a plasma stream. According to one embodiment of the present invention, an axial bore can be a hole, an opening, or a passage.
In this example, the longitudinal axis 210 is located substantially along the center line of throat region 202. In another embodiment, a longitudinal axis may be away from the center line. In yet another embodiment, a longitudinal axis may be substantially perpendicular or substantially not perpendicular to end surface 203. According to another embodiment, a throat region may be non-integrally coupled to a plasma chamber region, and a throat region may be directly or indirectly coupled to a plasma chamber region.
According to another aspect of the present invention, axial bore 204 includes a plurality of grooves 206 formed substantially along the longitudinal axis of throat region 202. Grooves 206 may extend throughout the entire length of axial bore 204 as shown in
According to another embodiment of the present invention, axial bore 204 has a cross sectional shape for lineating the flow of the plasma stream before the plasma stream exits axial bore 204 at second end 240. The lineation of the flow of the plasma stream reduces the induced swirling of gas within the plasma spray device, improving the depositional efficiency of the plasma spray device as explained more fully below.
According to one embodiment, anode 101 includes copper (Cu) or tungsten (W). According to another embodiment, anode 101 may have a length L of about 2.5 inches and have an outside diameter D of about 1.6 inches.
With reference to
As can be seen with reference to
Referring now to
According to one aspect of the present invention, electrode 303 may be cooled by the flow of a liquid coolant (not shown) in and/or around electrode 303. The liquid coolant may be water, a mixture of ethylene glycol and water, or another suitable liquid coolant.
According to another aspect of the present invention, axial bore 404 has a non-circular cross-sectional shape 313 defined by a plurality of overlapping substantially circular lobes 406 for lineating the flow of the plasma stream before the plasma stream exits axial bore 404.
Now referring to
According to one embodiment, the diameter of axial bore 510 at first end 530 may be about 1 inch, the diameter of axial bore 510 at cylindrical section 514 may be about 5/16 inches, and the diameter of axial bore at second end 540 may be about ¾ inches. The length of axial bore 510 may be about 2.5 inches.
Now referring to
The present invention is not limited to the shapes of an axial bore shown in
Turning now to
Similarly, to add a circumferential coating of 6 mm along the length of another cylindrical target tube, a plasma spray device with a conventional, non-lineated anode requires, on average, 8.5 hours and consumes about 75,000 grams of powdered coating material. In contrast, a plasma spray device with a lineated anode according to one embodiment of the present invention with a 35.8% depositional efficiency would require only 6.23 hours and would consume only 48,150 grams of coating powder to accomplish the same task.
According to one embodiment of the present invention, because of the increased turbulence at the intersection of lineating axial bore and the plasma chamber region of the lineated anode, the wear on the lineated anode is substantially less than the wear evident on the conventional, non-lineated anode. This turbulence, caused by the transition of the plasma from a cyclonic flow to a linear flow, acts to prevent the high energy DC arc formed between the lineated anode and the cathode from adhering to one particular region or area of the lineated anode, such that the lineated anode experiences significantly less wear than a conventional non-lineated anode, thereby substantially extending the usable life of the lineated anode. In a lineated anode according to one aspect of the present invention, the wear evident after spraying 79,370 g of coating material using the lineated anode was about 25%-50% of the wear evident on a conventional anode used in the plasma spraying of 119,789 g.
While the present invention has been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the invention. There may be many other ways to implement the invention. Many changes and modifications may be made to the invention, by one having ordinary skill in the art, without departing from the spirit and scope of the invention.
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| Number | Date | Country | |
|---|---|---|---|
| 20070114212 A1 | May 2007 | US |
