Patent Application
20150329953
Not applicable.
Not applicable.
Nozzles used in thermal spray guns are typically lined with a liner material or sleeve in order to promote longer hardware life. A common liner material is Tungsten (W). Historically, a wall thickness of the Tungsten liner was set arbitrarily, i.e., based upon considerations such as using a common or standard diameter Tungsten blank for a complete family of nozzle bore diameters, with the main concern being ease of manufacture. Thus, there was no attempt to study or optimize characteristics of the lining material such as lining wall thickness. The typical Tungsten material used for the lining material was often chosen to be the same as that used for the plasma gun cathode (i.e., the cathode electrode). This choice was also made for reasons of ease of manufacture since it only requires the sourcing of a single material.
Although Tungsten lined plasma gun nozzles have increased life, when compared to nozzles without such lining materials, they are nevertheless subject to cracking and even failure. The cracking is believed to result from high thermal localized stresses occurring within the Tungsten and worsens over time as the plasma gun is operated. The cracking typically occurs in an area or zone known as the arc attaching zone, as will be described below with reference to
In most cases the cracks align axially with the gun (or Tungsten lining) bore. These axial cracks (see ref. AC in
Since there is no way to predict the potential for the more problematic circumferential cracks and the eventual catastrophic failure of the lining material, personnel operating plasma guns equipped with such nozzles must be extra diligent in checking for signs of potential cracking—which can sometimes be detected by monitoring plasma gun voltage behavior. Based on such signs, the operator will typically stop the coating process and replace the nozzle with a new nozzle. This unpredictability has, at the very least, the effect of reducing the operating lifetime advantage of Tungsten lined nozzles.
Thus, there remains a need to improve the consistency, predictability and operating life of plasma gun hardware as well as the overall gun performance. One way to do this is to reduce the potential for cracking within the nozzle lining or nozzle bore.
In accordance with one non-limiting embodiment, there is provided a thermo or thermal spray gun or system which overcomes one or more of the disadvantages of conventional or existing systems and/or reduces the potential for cracking or crack formation within the nozzle bore, and especially within the lining material lining the nozzle bore.
In accordance with one non-limiting embodiment, there is provided a thermo spray gun comprising an improved lining material having a significantly longer operating life and/or a reduced potential for crack formation.
In accordance with one non-limiting embodiment, there is provided a nozzle for a thermo spray gun comprising a lining material wall thickness (at least along a predetermined axial length of the bore) that has been tailored to the nozzle body so that significant thermal stresses are not created in an area of the arc attachment zone.
In accordance with one non-limiting embodiment, there is provided a nozzle for a thermo spray gun comprising a lining material having at least one mechanical characteristic that is tailored or customized to one or more other portions of the plasma gun or nozzle such that significant thermal stresses are not created (or whose potential is significantly reduced) in the lining material, and especially an area of the bore known as the arc attachment zone.
In accordance with another non-limiting embodiment, there is provided a thermal spray gun comprising a nozzle body and a liner material arranged within the nozzle body. A material of the nozzle body has a lower melting temperature than that of the liner material. A ratio of a total wall thickness of a portion of a nozzle to that of a wall thickness of the liner material has a value determined in relation to or that corresponds to the wall thickness of liner material. The liner material comprises one of a material other than Lanthanated Tungsten and a Lanthanated Tungsten and the ratio being between about 4.75:1 and about 5.75:1.
In embodiments, the ratio is equal to or greater than about 3.5:1.
In embodiments, the ratio is at least one of: between about 3.5:1 and about 7:1; between about 4:1 and about 6:1; around about 5:1. Other exemplary ratios can include; equal to or greater than about 3:1; equal to or greater than about 4:1; equal to or greater than about 5:1; equal to or greater than about 6:1; and equal to or greater than about 7:1.
In embodiments, the liner material is Tungsten.
In embodiments, the nozzle body is made of a copper material.
In embodiments, the wall thickness of the nozzle body and the liner material are each measured in an axial area of an arc attachment zone.
In embodiments, in normal operation, while the liner material experiences more thermal stress in an area of an arc attachment zone than in an area downstream of the arc attachment zone, such stresses are reduced significantly compared to conventional nozzle arrangements so that the area of the arc attachment zone experiences stresses below a level that would cause stress failure, thereby significantly improving the working life of the liner material and nozzle.
In embodiments, the wall thickness of the liner material is at least one of: between about 0.25 mm and about 1.25 mm; between about 0.50 mm and about 1.0 mm; and most preferably between about 0.75 mm and about 1.0 mm.
In embodiments, thermo spray gun further comprises a cathode and an anode body through which cooling fluid circulates.
In accordance with another non-limiting embodiment, there is provided a nozzle for a thermo spray gun comprising a nozzle body and a liner material arranged within the nozzle body. A material of the nozzle body has a lower melting temperature than that of the liner material. A wall thickness of the liner material has a value determined in relation to or that corresponds to a wall thickness of the nozzle body. Alternatively or additionally, a ratio of a total wall thickness of a portion of a nozzle to that of a wall thickness of the liner material has a value determined in relation to or that corresponds to the wall thickness of liner material.
In embodiments, the nozzle is a replaceable nozzle.
In embodiments, a first portion of the liner material has an internal tapered section and a main portion of the liner material is generally cylindrical.
In accordance with another non-limiting embodiment, there is provided a method of making a nozzle of any of the types described above, wherein the method comprises forming the liner material with a wall thickness whose value takes into account at least one of a wall thickness of a portion of the nozzle body and a ratio of a total wall thickness of a portion of the nozzle to that of a wall thickness of a portion of the liner material.
In accordance with another non-limiting embodiment, there is provided a method coating a substrate using a thermo spray gun, comprising installing the nozzle of any of the types described above on the thermo spray gun and spraying a coating material onto a substrate.
In accordance with advantageous aspects of the invention, there is also provided a method making a nozzle that performs optimally with a least amount of thermal stress, whose materials experiences lower operating temperatures, and which reduces the potential to minimize boiling of the cooling fluid.
In accordance with other advantageous aspects of the invention, there is also provided a method making a nozzle which shows no signs of circumferential cracking after prolonged operation, and thus does not experience, among other things, catastrophic failure of the Tungsten lining, melting of the Tungsten lining, and internal melting of the copper nozzle body.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.
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:
a shows a computer model cross-section view of a conventional nozzle and illustrates localized thermal stresses (temperature induced tensile stresses shown in darker regions) which occur in the nozzle when operated at a given test parameter. In
b shows a cross-section view of an actual conventional nozzle operated at the same test parameter as that modeled in
c shows a diagram that illustrates and describes aspects of the catastrophic stress failure shown in
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.
Plasma guns used to spray coatings, like the one encompassed by the invention, have a cathode and an anode. The anode can also be referred to as a nozzle in these plasma guns as it also serves a fluid dynamic function in addition to functioning as the positive side of the electrical circuit forming the plasma arc. The nozzle is fluid cooled, i.e., with water, to prevent melting and is typically constructed of a copper material as it possesses a high thermal conductivity. Nozzles having a lining of Tungsten located in an area of the inside bore facing the plasma arc are produced to provide improved/longer hardware life over those just made of copper. Tungsten possess a relatively high thermal conductivity as well as a very high melting temperature.
Tungsten lined plasma nozzles use Tungsten linings that are typically 1 or more mm in thickness. In some cases the Tungsten may be over 3 mm in thickness. The lining material sleeve is often made of Thoriated Tungsten, which is the same composition used in plasma gun cathodes or electrodes. Both the composition and overall diameter of the Tungsten used to fabricate the nozzle, however, is typically chosen as a matter of convenience. In many cases, the outside diameter of the Tungsten liner used is held constant while its bore diameter varies according to a particular application of gun type. No consideration in the design or configuration of these plasma gun nozzles is given to selecting an optimal wall thickness for the Tungsten lining.
In addition to the thickness of the Tungsten lining, the ratio of the wall thickness of the lining to the overall wall thickness of the nozzle body from the closest distance to the cooling water channel is typically around 1:2. This means the wall thickness of the Tungsten liner is about as thick as the wall thickness of the copper body.
As will be shown below with reference to
The nozzle 20 has a first or cathode receiving end 21 and a second or plasma discharging end 22 having a flange. The cooling fins 24 surround an intermediate portion of the nozzle 20 and function to conduct heat away from an area of the nozzle bore which experiences heating generated by electric arc 40. The arc 40 results when a voltage potential is created between a cathode 50 and an anode 60 whose function is performed by the body 10. The arc 40 can form anywhere in the bore an area referred to as an arc attachment zone 70 (see
With reference to
With reference to
With reference to
a-11c show a comparison between a computer model generated stress failure of the Tungsten lining (
With reference to
In the non-limiting embodiment of
According to one non-limiting example, a plasma gun nozzle of the type shown in
With reference to
In accordance with another non-limiting example of the invention, there is provided a plasma gun nozzle of any of the types shown in
In accordance with still another non-limiting example of the invention, there is provided a plasma gun nozzle having a thin Tungsten lining wall conforming to the following requirements. The ratio between the total wall thickness of copper and Tungsten, i.e., C+D in
Other non-limiting exemplary values and ratios are shown in the table listed below which present various values for two exemplary Sulzer Metco plasma gun types. In the upper part of the table, three old nozzles, i.e., a 6 mm nozzle, a 7 mm nozzle, and an 8 mm nozzle, for a Sulzer Metco F4 plasma gun are compared to new comparable size nozzles for the same F4 plasma gun. In the lower part of the table, six old nozzles, i.e., a G-W nozzle, a GH-W nozzle, a 930W nozzle, a 931W nozzle, 932W nozzle, and a 933W nozzle for a Sulzer Metco 9 MB plasma gun are compared to new comparable size nozzles for the same 9 MB plasma gun. Extensive testing has shown that nozzles made using the new values have significantly longer operating life and thermal stress profiles closer to that shown in
In the above Table, the value for C+D can be calculated from the equation (E−B)/2 and the value for D can be calculated from the equation (E−A)/2.
In cases where the preferred ratio between the total wall thickness of Copper and Tungsten (C+D/C) and the preferred wall thickness of Tungsten (C) cannot both be met simultaneously, then the total ratio should be given preference. In the above Table, both the preferred values for the ratio and wall thickness cannot be met at the same time for examples 930W through 933W. As a result, preference for these examples is given to having the preferred ratio with the effect being that Tungsten lining is slightly thinner than is preferred.
Experiments have shown that one can improve the hardware life of an old 6 mm F4 nozzle operating at one extreme parameter condition by around 30% on average. Thus, the new 6 mm F4 nozzle can have improved hardware life over the old 6 mm F4 nozzle as follows: a hardware life from about an average of 17 hours (old 6 mm) to about an average of 23 hours (new 6 mm) More importantly, old hardware suffered a 30% catastrophic failure rate whereas no new listed nozzle has failed catastrophically as of the filing date of the instant application. Furthermore, the variation in hardware life as such went from about +/−4 hours to less than +/−1.5 hours. This improved consistency and lack of catastrophic failure associated with the new nozzles represents a very significant improvement over old hardware—at least as it relates to the 6 mm F4 nozzle. Testing of 8 mm F4 nozzles has showed similar results with no catastrophic failures noted and with an improvement in average hardware life of around 25%. Testing of G-W nozzle with a 9 MB plasma gun again showed comparable improvement. Other listed Tungsten lined nozzles have not yet undergone such testing, but it is believed (based on past experience) that they are also likely to experience significant comparable improvement.
Additional experiments with Tungsten linings having a ratio of total thickness of Copper to Tungsten smaller than 3.00 and a Tungsten wall thickness of 2.00 mm demonstrated the benefits of the instant invention to be less dramatic. About 10% of the nozzles tested experienced catastrophic failure of the Tungsten lining versus 30% for conventional nozzles and 0% for the most for the most preferred ratio and wall thickness. Likewise experiments with Tungsten linings with a ratio greater than 7 and a Tungsten wall thickness less than 0.5 mm resulted in a number of nozzles where the Copper beneath the Tungsten lining, in the region of arc attachment, having melted and the Copper bled through the hairline axial cracks. Although this does not result in catastrophic failure of the Tungsten lining, it does have undesirable effects such as Copper spitting and shorter hardware life due to accelerated voltage decay.
Although the various embodiments of the nozzle disclosed herein can be manufactured in a variety of ways, one can, by way of non-limiting example, make the same by first placing a solid Tungsten rod into a casting mold and casting a copper material sleeve around the Tungsten rod. Once removed from the casting mold, the cast assembly can be machined so as to form both the outside profile and the inside profile shown in, e.g.,
In each of the herein disclosed embodiments, the composition of the Tungsten liner can include any doped Tungsten material including but not limited to Thoriated, Lanthanated, Ceriated, etc. Other material considerations include high Tungsten alloys such as CMW 3970, Molybdenum, Silver, and Iridium. As used herein, an alloy is a solid solution of a metal and at least one other element, usually other metals to form a single crystalline phase. Examples Brass, Inconel, stainless steel. In the case of Tungsten alloy, the Tungsten contains small amounts of Nickel and Iron in a solid solution or alloy. Also as used herein, a doped substance is one in which a contaminant or impurity (doping agent) is added to a material, usually a metal or semiconductor. The result is a matrix of a material with an embedded second substance. Typical doping agents are ceramics such as aluminum oxide, thorium oxide, and lanthanum oxide; and elements such as boron, phosphor, and sulfur. In the case of the Thoriated or Lanthanated Tungsten, the Tungsten contains small crystalline impurities of Thorium oxide or Lanthanum oxide. When using materials other than Tungsten, one should adjust the thicknesses and ratios accordingly to take account of the possibilities of melting, stresses, and conductivity properties. Both Moly and CMW 3970 have been tried with some success. Silver and Iridium can be considered but are currently too expensive.
Since Tungsten lining materials have in the past been known to crack or fracture (and thus reduce hardware life), other materials may offer some improvement in this regard. Such materials should preferably have the following properties. They should be more ductile and fracture tolerant than Tungsten especially under high thermal loading and high temperature gradients. They should also have a high melting point similar or close to that of Tungsten. And when lower, they should have a high enough thermal conductivity to compensate for having a lower melting point than Tungsten. Potential materials include pure metals such as Silver, Iridium and Molybdenum as they have many of the above-noted desired properties. Although, as noted above, Silver and Iridium are arguably currently too expensive for practical use, Molybdenum is affordable. Other options include Tungsten alloyed with small amounts of iron or nickel as they have acceptable properties. Preferably, such materials include at least 90% of the primary metal, i.e., Tungsten in the case of a Tungsten alloy. To select the material, one can graph the differential temperature versus thermal conductivity and determine which it is likely to withstand direct contact with the plasma arc. This differential temperature is preferably the difference between the melting point and average plasma temperature (about 9000K) and at least an inverse of the melting temperature. When this is performed for the materials discussed above, i.e., Molybdenum, Iridium, Tungsten, Copper and Silver come closest to having many of the desired properties even while possessing significant differences in regards to ductility, being succeptable to thermal shock and cracking. Preferred materials include Tungsten and Molybdenum and their alloys such as Tungsten containing about 2.1% Nickel and about 0.9% hon. Other Tungsten alloys include those with higher amounts of Nickel and Copper, but with lower melting points and thermal conductivity, but higher ductility as well as those with lower amounts of Nickel and Copper, but with higher melting points and thermal conductivity, but lower ductility. Other materials that can be alloyed with Tungsten include Osmium, Rhodium, Cobalt and Chromium. These metals possess a high-enough melting point and high thermal conductivity such that they can be alloyed with Tungsten and utilized in a nozzle liner material. Commercial grade Molybdenum and a Tungsten alloy having 2.1% Nickel and 0.9% Iron have both been tested and used in nozzle liners by Applicant, and have been compared to a Copper only nozzle.
In addition to the exemplary embodiments discussed above, the invention also encompasses a nozzle utilizing a Lanthanated Tungsten liner having a wall thickness C of between about 0.75 mm and about 1.26 mm, and optionally between about 0.84 and about 1.10 mm or between about 0.75 mm and about 1.10 mm, in combination with a ratio, i.e., (C+D)/C, of between about 4.75 or 4.75:1 and about 5.75 or 5.75:1.
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.
The instant application is an International PCT Application that is based on and claims the benefit of U.S. provisional application No. 61/759,086 filed on Jan. 31, 2013, the disclosure of which is hereby expressly incorporated by reference thereto in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/076610 | 1/31/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61759086 | Jan 2013 | US |
