CA1205545A - Infrared sensor for the control of plasma-jet spray coating processes - Google Patents
Infrared sensor for the control of plasma-jet spray coating processesInfo
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- CA1205545A CA1205545A CA000425403A CA425403A CA1205545A CA 1205545 A CA1205545 A CA 1205545A CA 000425403 A CA000425403 A CA 000425403A CA 425403 A CA425403 A CA 425403A CA 1205545 A CA1205545 A CA 1205545A
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- infrared
- plasma spray
- jet
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Abstract
INFRARED SENSOR FOR THE CONTROL
OF PLASMA-JET SPRAY COATING PROCESSES
Abstract of the Disclosure A multi-purpose optical sensor operates in the medium-to-far infrared wavelength spectral region to sense the surface temperature of plasma-jet spray coating materials. The plasma itself emits little or no radiation in the region and, accordingly, the output signal from the sensor is used to adjust electrical input and other variables associated with the plasma spray torch to insure that particles arriving at the substrate surface to be coated are, in fact, in a molten state. The sensor employs infrared interference filters and, additionally, the sensor may be used to monitor not only coating temperature but also plasma beam divergence and particle seeding density to provide other control functions.
OF PLASMA-JET SPRAY COATING PROCESSES
Abstract of the Disclosure A multi-purpose optical sensor operates in the medium-to-far infrared wavelength spectral region to sense the surface temperature of plasma-jet spray coating materials. The plasma itself emits little or no radiation in the region and, accordingly, the output signal from the sensor is used to adjust electrical input and other variables associated with the plasma spray torch to insure that particles arriving at the substrate surface to be coated are, in fact, in a molten state. The sensor employs infrared interference filters and, additionally, the sensor may be used to monitor not only coating temperature but also plasma beam divergence and particle seeding density to provide other control functions.
Description
5S~5 RD-14,149 ~NFRARED SENSOR FOR THE CONTROL
OF PLASMA-JET SPRAY COATING PROCESSES
, _ Background of the Disclosure This invention relates to sensors for use in plasma spray jet processes. More particularly, the present invention relates to infrared sensors and plasma spray jet torches controlled with the assistance of such sensors so as to insure that particles arriving at the substrate to be coated are in a molten state. Other variables are also monitored and controlled.
In plasma spray processes for coating various substrate materials with protective coatings, particulate matter is iniected into a plasma-jet which is directed at the substrate. The substrate and particulate matter is typically metal with the particulate matter forming a complex protective coating on the substrate. The protective coating often exhibits superior properties of wear resistance or resistance to corrosion, for example. The structure and properties of the particlllate coating are complex functions of plasma torch operating conditions such as the nature and the flow rate of the gases employed, the powder particles size and particle size distribution, the torch-to-substrate distance, electrical power supplied to the torch, and powder injection position, velocity and direction. Because of the large nu~ber of interrelated variables, the problem of controlling .., .. , . . . ,~
ss~s RD-14,149 such a process is exceedingly difficult but for one observation: namely, that the particles must arrive at the substrate in a molten condition. Solid particles reaching the substrate can form, in effect, a defect in the coating. The minimum particle temperature in the plasma is perhaps the singlemost important parameter determining the integrity of the coating but until now, there was no effective means to monitor this parameter.
This is due to the overwhelming infrared radiation levels emitted by the plasma as opposed to the particulate matter entrained in the plasma flow.
In short, the plasma spray process has been developed from flame spraying processes largely by empirical methods.
The control of such processes is often accomplished through the sole use of empirical methods to ensure that the particles arrive at the substrate in a molten condition.
However, because of the large number of variables occurring in such processes, automatic control has hitherto not been employed to control plasma spray jet processes.
Remote temperature measurements of particle tempera~
tures in a plasma-jet have been attempted in research investigations by A. ~ardelle and co-workers at the University of Limo~es, France, using near-infrared photomultiplier-based optical pyrometers to deduce particle temperature distributions. However, visible and near infrared measurements are affected by the radiation emitted by the plasma itself ~hich is several thousand degrees (in any conventional temperature units) than the particle temperature. Other experimenters have employed videcon-type cameras for investigations of plasma arcs in arctorch welding. However, prior experimenters in the plasma spray jet processes have not appreciated the fact that the plasma of ionized noble gases emits little or no radiation in the far-infrared wavelengths. Only the continuous Planckian radiation from the entrained particles, that is the coating material, falls within this far-infrared range.
RD-14,1~9 ~ 3 --Other work in a related field has been reported in a progress report titled "Improvement of Reliability of Welding by In-Process Sensing and Control (Development of Smart Welding Machines For Girth Welding of Pipes)"
submitted to the Department of Energy in June, 1981 by Jose Converti et al. This report describes initial experiments conducted using contact sensors (thermo-couples) to probe the temperature distribution near weld puddles and seams. Attempts to use nearinfrared photo-diodes, described therein, for remote temperature sensingwere not successful due to significant optical inter-ference from plasma radiation reflected from the metal surface~ In particular, Converti et al. propose using a simple optical filter to reduce the radiation from the plasma arc through use of materials similar to conventional welders' goggles.
Summary of the Invention In accordance with a preferred er~odim~nt of the present invention, an infrared sensor for monitoring plasma spray jet processes comprises focussing means for receiving inErared radiation from the vicinity of a plasma spray jet together with infrared detection means for providing electrical signals in response to the intensity of the infrared radiation impinging upon the detection means; furthermore, filter means are disposed in the optical path between the detection means and the disposed in the optical path between the detection means and the focussing means, the filter selectively passing infrared radiation having a waYelength greater than about 3 microns.
In a preferred embodiment of the sensor of the present invention, the infrared detection means comprises either indiumantimonide or mercury-cadmium telluride detectors in contact with a cooling medium such as liquid nitrogen to provide the desired sensitivity in response to particu-late thermal conditions. The present invention alsopreferably includes an iris diaphragm to narrow the angle ~2(:~;S~
RD-14,149 of view.
In another embodiment of the present invention, the infrared sensor described above is configured with a plasma spray jet apparatus for coating a specimen. This apparatus further includes a plasma spray gun with a nozzle which is disposed at least partially within an evacuable housing.
Furthermore, there are provided means to control the spray gun in response to electrical signals provided by the above-described sensors. Depending upon the parameters of interest, one or more sensors may be employed and these may be directed at one or more regions of the plasma spray jet or at the substrate itself near to where the plasma spray jet impinges upon it.
Accordingly, it is an object of the present invention to provide a sensor for monitoring the temperature of particulate matter entrained within a plasma spray jet stream.
It is also an object o~ the present invention to provide a means for more accurately controlling the temperature of particulate matter in plasma spray jets and, in particular, to ensure that the particles arrive at the substrate to be coated in a molten condition.
Lastly, it is an object of the present invention to provide a sensor and plasma spray gun apparatus to carry out the above-described objectives.
Descrip_ion of the Figures The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by refexenceto the following descript;on taken in connection with the accompanying drawings in which:
Figure 1 is a schematic diagram illustrating a RD-14,149 preferred embodiment for the sensor of the present invention;
Figure 2 is a schematic diagram illustrating another preferred embodiment of the present invention in which one or more of the sensors shown in Figure 1 are configured with a plasma spray gun and control circuit for monitoring and controlling the plasma spray process;
Figure 3 is a graph of detector output voltage as a function of wavelength for a welding process employing argon gas and a thoriated tungsten electrode; and Figure 4 is a graph similar to that shown in Figure 3 for a welding process employing helium gas and a tungsten electrode.
~etailed Description of the Invention Figure l illustrates a preferred embodiment of a sensor 10 in accordance with the present invention. In particular, within one end of housing 13, infrared detector 18 is disposed within dewar 17 which preferably holds a cooling fluid such as liquid nitrogen. In general, it is desired that infrared detector 18 be cooled to provide the desired degree of sensitivity and response time for the present invention. For example, in contrast to applications of devices similar to the instant sensor for use in arc welding operations, the level of irradiated infrared ~5 ener~y in the 3-14 microns wavelength spectral region is relative].y low for particulate matter entrained within a plasma-jet stream, which is the application contemplated in the invention disclosed herein. Hence, liquid nitro~en or other cooling means is preferred to i.ncrease the desired detector sensitivity and dynamic range.
An important aspect of the present inventi.on is the inclusion of long-pass infrared filter 16 disposed in optical path prior to detector 13. As discussed below with reference to Figures 3 and 4, it has been observed by the instant inventor that the intensity of infrared JSS~5 RD-14,149 radiation generated by the plasma itself is relatively low for the band of infrared wavelengths yreater than appxoxi-mately 3 microns. Accordingly, filter 16 acts to eliminate infrared noise signals from the plasma gases which would otherwise overwhelm the desired infrared signal from the entrained particulate matter. Thus, infrared long-pass interference filter 16 is provided to reduce -this noise component.
With respect to detector 18 itself, it preferably comprises a liquid nitrogen-cooled material comprising either indium antimonide (InSb~ or mercury-cadmium telluride (HgCdTe~ infrared detector ma-terial. Such materials are conventionally employed in infrared radiometry carried out in this particular region of the infrared spectrum. While detector 18 may comprise a single element generating electrical signals in response to the intensity of infrared radiation impinging thereon, it is also possible to employ a linear array of infrared detectors for detector 18, particularly in the case that temperature profile measurements of particulate matter in the plasma spray jet are desired.
Additionally, sensor 10 in Figure 1 also preferably includes an adjusta~le iris aperture 15 which characteristi-cally exhibits a plurality of field stops, and functions to restrict the sensor's view to a narrow angle so as to prohibit backgro~md radiation from other solid body surfaces from reachin~ the detector. In particular, the view angle may be narrowed to prohihit background radiation from the substrate itself from interfering with measurements of the plasma-jet particulate matter taken in close proximity to the substrate being coated. Additionally, it is also preferably desired to include focussing means to provide proper sensor resolution. Focussing means are particularly important when detector 18 comprises a linear array of detector elements. While Figure 1 illustrates a focussing system including a pair of lenses 12 and 14, it is well 1~(3SS~
RD-14,149 appreciated by those familiar with optics that the focussing system may, in fact, comprise a plurality of yariously-configured lenses, or even a single lens by itself. In the instant diagram, lens 1~ is a fixed lens disposed in housing 13; lens 12 is a movable lens disposed within lens barrel 11 which, for example, may be screw mounted onto housing 13. The principally-required characteristic of the lenses employed in the present invention is that they be transmissive to infrared radiation having a wavelength of 3 microns or greater. In particular, lens material comprising sapphire ~ay be employed. However, since this is a relatively expensive lens material, alternate lens material includes KRS-5 which is a lens material comprising a mixture of thalium iodide and thalium bromide in crystalline formO
The electrical output signal from infrared detector 18 is preferably supplied to preamplifier 21 which operates to amplify the signal. The resulting signal from the preamplifier is then supplied to signal conditioner 20 which may be employed to provide one or more significant statistical indicators relating to the intensity of the infrared signal in the infrared band having a wavelength of 3 microns or higher. For example, signal conditioner 20 may operate to produce an output electrical signal S~II which is indicative of the peak infrared signal over a specified period of time. Similarly, signal conditioner 20 may also operate to produce an electrical signal SLOW which is indicative of a minimal level of infrared radiation in the appropriate band over a specified period of time. Additionally, signal conditioner 20 may also operate as an integrator thereby producing an output signal SMEAN which is indicative of the average value of infrared radiation impinging upon the det-ector over a given period of time~ For use in the control of plasma spray jet processes, the period of time over which the samples are taken in generally between about 10 and 1,000 milliseconds in duration, although other durations may also be employed.
lZC3SS9~i RD-14,149 Figure 2 illustrates an embodiment of the present invention in which sensor lO of Figure l is positioned in various locations in a plasma spray torch apparatus. The positioning of the various sensors is significant since each position shown in Figure 2 is operative to measure a different parameter of the plasma spray process. For example, sensor lOa is best suited to monitor in-fli.ght particle temperature.
This sensor is also capable of monitoring particle number, particle density and beam divergenceO For these reasons, sensor lOa is preferably implemented as a linear array of infrared detector elements. Such a linear array provides a preferred method and apparatus for measuring plasma-jet divergence. For these reasons, sensor lOa is preferably implemented as a linear array of infrared detector elements.
Such a linear array provides a preferred method and apparatus for mea-suring plasma-jet divergence. In contrast~. sensor lOb positioned and directed as shown in Figure 2, is particularly suited for measuring particle temperature immediately prior to impact of the particle on substrate 35 which is to be pro-vided with the desired coating 36. Sensor lOb is the mostdesirable sensor to employ for the purpose of inserting that the particles entrained in the plasma-jet are molten just prior to impact upon substrate 35. However, if it is desired to measure the temperature of coating 36 itself, then a sensor such as lOc is preferably employed.
Figure 2 illustrates a conventional plasma spray jet apparatus in which the sensors of the present .invention are deployed to monitor various aspects of the spray coating process. In particular, plasma spray torch 30 having nozzle 34 is disposed within vacuum chamber 31~ Plasma spray torch 30 operates to direct plasma-jet 33 toward substrate 35 so that particles 32 ent.rained within the plasma jet are heated to molten temperatures prior to the.ir impact on substrate 35.
Sensors lOaf lOb and lOc are variously disposed to monitor certain aspects of the pl.asma sp~ay jet process.
S
RD-14,149 g _ Electrical output of each of these sensors is supplied to plasma spray gun control 40. This control operates to vary certain parameters (such as electrical power input) associated with plasma spray torch 30 in response to electrical signals provided by sensors lOa, lOb and lOc.
It should be noted, however, that while Figure 2 illustrates a plasma spray torch apparatus Utilizing three infrared sensors, a yreater or lesser number of sensors may be employed as desired to monitor various aspects of the process. It is also noted that plasma spray gun control 40 typically operates to control the electrical power supplied to torch 30.
The sensor and plasma torch apparatus of the present invention is an outgrowth of experimental investigations of the infrared spectral characteristics of welding arcs.
Pursuant to a hypothesis advanced by the instant invention that electronic transistions in the arc plasma are re-sponsible for the bulk of radiation emitted by the welding arc, it was reasoned that in the infrared spectral regions above 3 microns, no significant radiation would be emitted by the plasma. Experiments have confirmed this hypothesis with respect to electric arc plasma. Accordingly, it is also found that plasma in a plasma spray torch operates in the same fashion to produce a similar infrared spectrum.
In particular, Figures 3 and 4 illustrate such a spectrum for arc welding torches. In particular, Figure 3 illustrates a plot of detector output voltage in millivolts as a function of wavelength for a tungsten inert gas (TIG) arc.
The inert gas employed was argon and the electrode material employed was thoriated tungsten. A similar plot is shown in Figure 4 which illustrates the near-infrared spectral distribution of a tungsten inert gas arc in which the inert gas employed was helium and the electrode material substantially comprised only tungsten itself. Again, it is seen that the infrared radiation from the arc itself ~L;~OS5~5 RD-14,149 is somewhat band limited centering around a wavelength of about 2 microns and extending from about 1-1~2 to about
OF PLASMA-JET SPRAY COATING PROCESSES
, _ Background of the Disclosure This invention relates to sensors for use in plasma spray jet processes. More particularly, the present invention relates to infrared sensors and plasma spray jet torches controlled with the assistance of such sensors so as to insure that particles arriving at the substrate to be coated are in a molten state. Other variables are also monitored and controlled.
In plasma spray processes for coating various substrate materials with protective coatings, particulate matter is iniected into a plasma-jet which is directed at the substrate. The substrate and particulate matter is typically metal with the particulate matter forming a complex protective coating on the substrate. The protective coating often exhibits superior properties of wear resistance or resistance to corrosion, for example. The structure and properties of the particlllate coating are complex functions of plasma torch operating conditions such as the nature and the flow rate of the gases employed, the powder particles size and particle size distribution, the torch-to-substrate distance, electrical power supplied to the torch, and powder injection position, velocity and direction. Because of the large nu~ber of interrelated variables, the problem of controlling .., .. , . . . ,~
ss~s RD-14,149 such a process is exceedingly difficult but for one observation: namely, that the particles must arrive at the substrate in a molten condition. Solid particles reaching the substrate can form, in effect, a defect in the coating. The minimum particle temperature in the plasma is perhaps the singlemost important parameter determining the integrity of the coating but until now, there was no effective means to monitor this parameter.
This is due to the overwhelming infrared radiation levels emitted by the plasma as opposed to the particulate matter entrained in the plasma flow.
In short, the plasma spray process has been developed from flame spraying processes largely by empirical methods.
The control of such processes is often accomplished through the sole use of empirical methods to ensure that the particles arrive at the substrate in a molten condition.
However, because of the large number of variables occurring in such processes, automatic control has hitherto not been employed to control plasma spray jet processes.
Remote temperature measurements of particle tempera~
tures in a plasma-jet have been attempted in research investigations by A. ~ardelle and co-workers at the University of Limo~es, France, using near-infrared photomultiplier-based optical pyrometers to deduce particle temperature distributions. However, visible and near infrared measurements are affected by the radiation emitted by the plasma itself ~hich is several thousand degrees (in any conventional temperature units) than the particle temperature. Other experimenters have employed videcon-type cameras for investigations of plasma arcs in arctorch welding. However, prior experimenters in the plasma spray jet processes have not appreciated the fact that the plasma of ionized noble gases emits little or no radiation in the far-infrared wavelengths. Only the continuous Planckian radiation from the entrained particles, that is the coating material, falls within this far-infrared range.
RD-14,1~9 ~ 3 --Other work in a related field has been reported in a progress report titled "Improvement of Reliability of Welding by In-Process Sensing and Control (Development of Smart Welding Machines For Girth Welding of Pipes)"
submitted to the Department of Energy in June, 1981 by Jose Converti et al. This report describes initial experiments conducted using contact sensors (thermo-couples) to probe the temperature distribution near weld puddles and seams. Attempts to use nearinfrared photo-diodes, described therein, for remote temperature sensingwere not successful due to significant optical inter-ference from plasma radiation reflected from the metal surface~ In particular, Converti et al. propose using a simple optical filter to reduce the radiation from the plasma arc through use of materials similar to conventional welders' goggles.
Summary of the Invention In accordance with a preferred er~odim~nt of the present invention, an infrared sensor for monitoring plasma spray jet processes comprises focussing means for receiving inErared radiation from the vicinity of a plasma spray jet together with infrared detection means for providing electrical signals in response to the intensity of the infrared radiation impinging upon the detection means; furthermore, filter means are disposed in the optical path between the detection means and the disposed in the optical path between the detection means and the focussing means, the filter selectively passing infrared radiation having a waYelength greater than about 3 microns.
In a preferred embodiment of the sensor of the present invention, the infrared detection means comprises either indiumantimonide or mercury-cadmium telluride detectors in contact with a cooling medium such as liquid nitrogen to provide the desired sensitivity in response to particu-late thermal conditions. The present invention alsopreferably includes an iris diaphragm to narrow the angle ~2(:~;S~
RD-14,149 of view.
In another embodiment of the present invention, the infrared sensor described above is configured with a plasma spray jet apparatus for coating a specimen. This apparatus further includes a plasma spray gun with a nozzle which is disposed at least partially within an evacuable housing.
Furthermore, there are provided means to control the spray gun in response to electrical signals provided by the above-described sensors. Depending upon the parameters of interest, one or more sensors may be employed and these may be directed at one or more regions of the plasma spray jet or at the substrate itself near to where the plasma spray jet impinges upon it.
Accordingly, it is an object of the present invention to provide a sensor for monitoring the temperature of particulate matter entrained within a plasma spray jet stream.
It is also an object o~ the present invention to provide a means for more accurately controlling the temperature of particulate matter in plasma spray jets and, in particular, to ensure that the particles arrive at the substrate to be coated in a molten condition.
Lastly, it is an object of the present invention to provide a sensor and plasma spray gun apparatus to carry out the above-described objectives.
Descrip_ion of the Figures The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by refexenceto the following descript;on taken in connection with the accompanying drawings in which:
Figure 1 is a schematic diagram illustrating a RD-14,149 preferred embodiment for the sensor of the present invention;
Figure 2 is a schematic diagram illustrating another preferred embodiment of the present invention in which one or more of the sensors shown in Figure 1 are configured with a plasma spray gun and control circuit for monitoring and controlling the plasma spray process;
Figure 3 is a graph of detector output voltage as a function of wavelength for a welding process employing argon gas and a thoriated tungsten electrode; and Figure 4 is a graph similar to that shown in Figure 3 for a welding process employing helium gas and a tungsten electrode.
~etailed Description of the Invention Figure l illustrates a preferred embodiment of a sensor 10 in accordance with the present invention. In particular, within one end of housing 13, infrared detector 18 is disposed within dewar 17 which preferably holds a cooling fluid such as liquid nitrogen. In general, it is desired that infrared detector 18 be cooled to provide the desired degree of sensitivity and response time for the present invention. For example, in contrast to applications of devices similar to the instant sensor for use in arc welding operations, the level of irradiated infrared ~5 ener~y in the 3-14 microns wavelength spectral region is relative].y low for particulate matter entrained within a plasma-jet stream, which is the application contemplated in the invention disclosed herein. Hence, liquid nitro~en or other cooling means is preferred to i.ncrease the desired detector sensitivity and dynamic range.
An important aspect of the present inventi.on is the inclusion of long-pass infrared filter 16 disposed in optical path prior to detector 13. As discussed below with reference to Figures 3 and 4, it has been observed by the instant inventor that the intensity of infrared JSS~5 RD-14,149 radiation generated by the plasma itself is relatively low for the band of infrared wavelengths yreater than appxoxi-mately 3 microns. Accordingly, filter 16 acts to eliminate infrared noise signals from the plasma gases which would otherwise overwhelm the desired infrared signal from the entrained particulate matter. Thus, infrared long-pass interference filter 16 is provided to reduce -this noise component.
With respect to detector 18 itself, it preferably comprises a liquid nitrogen-cooled material comprising either indium antimonide (InSb~ or mercury-cadmium telluride (HgCdTe~ infrared detector ma-terial. Such materials are conventionally employed in infrared radiometry carried out in this particular region of the infrared spectrum. While detector 18 may comprise a single element generating electrical signals in response to the intensity of infrared radiation impinging thereon, it is also possible to employ a linear array of infrared detectors for detector 18, particularly in the case that temperature profile measurements of particulate matter in the plasma spray jet are desired.
Additionally, sensor 10 in Figure 1 also preferably includes an adjusta~le iris aperture 15 which characteristi-cally exhibits a plurality of field stops, and functions to restrict the sensor's view to a narrow angle so as to prohibit backgro~md radiation from other solid body surfaces from reachin~ the detector. In particular, the view angle may be narrowed to prohihit background radiation from the substrate itself from interfering with measurements of the plasma-jet particulate matter taken in close proximity to the substrate being coated. Additionally, it is also preferably desired to include focussing means to provide proper sensor resolution. Focussing means are particularly important when detector 18 comprises a linear array of detector elements. While Figure 1 illustrates a focussing system including a pair of lenses 12 and 14, it is well 1~(3SS~
RD-14,149 appreciated by those familiar with optics that the focussing system may, in fact, comprise a plurality of yariously-configured lenses, or even a single lens by itself. In the instant diagram, lens 1~ is a fixed lens disposed in housing 13; lens 12 is a movable lens disposed within lens barrel 11 which, for example, may be screw mounted onto housing 13. The principally-required characteristic of the lenses employed in the present invention is that they be transmissive to infrared radiation having a wavelength of 3 microns or greater. In particular, lens material comprising sapphire ~ay be employed. However, since this is a relatively expensive lens material, alternate lens material includes KRS-5 which is a lens material comprising a mixture of thalium iodide and thalium bromide in crystalline formO
The electrical output signal from infrared detector 18 is preferably supplied to preamplifier 21 which operates to amplify the signal. The resulting signal from the preamplifier is then supplied to signal conditioner 20 which may be employed to provide one or more significant statistical indicators relating to the intensity of the infrared signal in the infrared band having a wavelength of 3 microns or higher. For example, signal conditioner 20 may operate to produce an output electrical signal S~II which is indicative of the peak infrared signal over a specified period of time. Similarly, signal conditioner 20 may also operate to produce an electrical signal SLOW which is indicative of a minimal level of infrared radiation in the appropriate band over a specified period of time. Additionally, signal conditioner 20 may also operate as an integrator thereby producing an output signal SMEAN which is indicative of the average value of infrared radiation impinging upon the det-ector over a given period of time~ For use in the control of plasma spray jet processes, the period of time over which the samples are taken in generally between about 10 and 1,000 milliseconds in duration, although other durations may also be employed.
lZC3SS9~i RD-14,149 Figure 2 illustrates an embodiment of the present invention in which sensor lO of Figure l is positioned in various locations in a plasma spray torch apparatus. The positioning of the various sensors is significant since each position shown in Figure 2 is operative to measure a different parameter of the plasma spray process. For example, sensor lOa is best suited to monitor in-fli.ght particle temperature.
This sensor is also capable of monitoring particle number, particle density and beam divergenceO For these reasons, sensor lOa is preferably implemented as a linear array of infrared detector elements. Such a linear array provides a preferred method and apparatus for measuring plasma-jet divergence. For these reasons, sensor lOa is preferably implemented as a linear array of infrared detector elements.
Such a linear array provides a preferred method and apparatus for mea-suring plasma-jet divergence. In contrast~. sensor lOb positioned and directed as shown in Figure 2, is particularly suited for measuring particle temperature immediately prior to impact of the particle on substrate 35 which is to be pro-vided with the desired coating 36. Sensor lOb is the mostdesirable sensor to employ for the purpose of inserting that the particles entrained in the plasma-jet are molten just prior to impact upon substrate 35. However, if it is desired to measure the temperature of coating 36 itself, then a sensor such as lOc is preferably employed.
Figure 2 illustrates a conventional plasma spray jet apparatus in which the sensors of the present .invention are deployed to monitor various aspects of the spray coating process. In particular, plasma spray torch 30 having nozzle 34 is disposed within vacuum chamber 31~ Plasma spray torch 30 operates to direct plasma-jet 33 toward substrate 35 so that particles 32 ent.rained within the plasma jet are heated to molten temperatures prior to the.ir impact on substrate 35.
Sensors lOaf lOb and lOc are variously disposed to monitor certain aspects of the pl.asma sp~ay jet process.
S
RD-14,149 g _ Electrical output of each of these sensors is supplied to plasma spray gun control 40. This control operates to vary certain parameters (such as electrical power input) associated with plasma spray torch 30 in response to electrical signals provided by sensors lOa, lOb and lOc.
It should be noted, however, that while Figure 2 illustrates a plasma spray torch apparatus Utilizing three infrared sensors, a yreater or lesser number of sensors may be employed as desired to monitor various aspects of the process. It is also noted that plasma spray gun control 40 typically operates to control the electrical power supplied to torch 30.
The sensor and plasma torch apparatus of the present invention is an outgrowth of experimental investigations of the infrared spectral characteristics of welding arcs.
Pursuant to a hypothesis advanced by the instant invention that electronic transistions in the arc plasma are re-sponsible for the bulk of radiation emitted by the welding arc, it was reasoned that in the infrared spectral regions above 3 microns, no significant radiation would be emitted by the plasma. Experiments have confirmed this hypothesis with respect to electric arc plasma. Accordingly, it is also found that plasma in a plasma spray torch operates in the same fashion to produce a similar infrared spectrum.
In particular, Figures 3 and 4 illustrate such a spectrum for arc welding torches. In particular, Figure 3 illustrates a plot of detector output voltage in millivolts as a function of wavelength for a tungsten inert gas (TIG) arc.
The inert gas employed was argon and the electrode material employed was thoriated tungsten. A similar plot is shown in Figure 4 which illustrates the near-infrared spectral distribution of a tungsten inert gas arc in which the inert gas employed was helium and the electrode material substantially comprised only tungsten itself. Again, it is seen that the infrared radiation from the arc itself ~L;~OS5~5 RD-14,149 is somewhat band limited centering around a wavelength of about 2 microns and extending from about 1-1~2 to about
2-1/2 microns. Thus, an optical filter having a cut-on wavelength of about 3 or 3.5 microns placed in the optical path ahead of the detector 18 opexates to effectively shield the detector from the infrared radiation produced by the plasma gases. Although the amplitudes shown in Figures 3 and 4 are somewhat distorted at either wavelength limit (a feature commmon to all grating spectrographs), the radiation signature of the arc ciearly changes beyond
3 microns wavelength fro-m the intense line spectra typical of electronic transitions to faint continuous spectra. It is further seen that the observed line spectra originates entirely from the gas used. Workpiece or electrode material combinations showed no discrenable effect on the arc radiation spectral line locations. Because these carrier gases are also used in plasma spray coating processes, and since plasma and arc welding temperatures are of the same order o~ magnitude, similar results are obtainable from spectral measurements of plasma-jet radiation.
From the above, it should be appreciated that the sensor of the present invention provides an effective means for measuring various plasma spray jet coating processes.
It should also be apparent from the above that the infrared sensor of the present invention provides a means for controlling the plasma torch so that particles en-trained in the plasma are made to impact upon the sub-strate in a molten condition. Furthermore, it is seen that this control may be affected using a feedback control loop and involving only one measured parameter, namely, the electrical power being supplied to the torch. This eliminates the necessity for controlling a large number of inter-related plasma torch parameters. However, it should be realized that more complex control functions are also made possible by the present sensor.
~'05S~5 ~ RD-14,149 While the invention has been described in detail herein in accord with certain preferred embodiments there-of, many modifications and changes therein may be affected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.
From the above, it should be appreciated that the sensor of the present invention provides an effective means for measuring various plasma spray jet coating processes.
It should also be apparent from the above that the infrared sensor of the present invention provides a means for controlling the plasma torch so that particles en-trained in the plasma are made to impact upon the sub-strate in a molten condition. Furthermore, it is seen that this control may be affected using a feedback control loop and involving only one measured parameter, namely, the electrical power being supplied to the torch. This eliminates the necessity for controlling a large number of inter-related plasma torch parameters. However, it should be realized that more complex control functions are also made possible by the present sensor.
~'05S~5 ~ RD-14,149 While the invention has been described in detail herein in accord with certain preferred embodiments there-of, many modifications and changes therein may be affected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.
Claims (4)
1. A plasma spray jet apparatus for coating a specimen, said apparatus comprising:
a plasma spray gun having a nozzle through which particles and gas are ejected;
a vaccum housing in which said specimen and at least said spray gun nozzle are disposed;
focussing means for receiving infrared radiation from the vicinity of said plasma spray jet;
infrared detection means for producing electrical signals in response to the intensity of infrared radiation impinging upon said detection means;
filter means disposed in the optical path between said detection means and said focussing means, said filter selectively passing infrared radiation having a wavelength greater than about 3 microns; and means to control said spray gun in response to said electrical signals from said infrared detection means.
a plasma spray gun having a nozzle through which particles and gas are ejected;
a vaccum housing in which said specimen and at least said spray gun nozzle are disposed;
focussing means for receiving infrared radiation from the vicinity of said plasma spray jet;
infrared detection means for producing electrical signals in response to the intensity of infrared radiation impinging upon said detection means;
filter means disposed in the optical path between said detection means and said focussing means, said filter selectively passing infrared radiation having a wavelength greater than about 3 microns; and means to control said spray gun in response to said electrical signals from said infrared detection means.
2. The plasma spray jet apparatus of claim 1 in which at least one sensor is aimed at a mid-stream portion of said plasma spray jet.
3. The apparatus of claim 1 in which at least one sensor is aimed at said plasma spray jet just prior to its impact upon said specimen.
4. The apparatus of claim 1 in which at least one sensor is aimed at said substrate in the vicinity of impact by the plasma spray jet on said specimen.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/371,704 US4484059A (en) | 1982-04-26 | 1982-04-26 | Infrared sensor for arc welding |
| US371,704 | 1982-04-26 | ||
| US44254282A | 1982-11-18 | 1982-11-18 | |
| US442,542 | 1982-11-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1205545A true CA1205545A (en) | 1986-06-03 |
Family
ID=27005488
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000425403A Expired CA1205545A (en) | 1982-04-26 | 1983-04-07 | Infrared sensor for the control of plasma-jet spray coating processes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1205545A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7063747B2 (en) | 2002-05-29 | 2006-06-20 | Acushnet Company | Coating control system for use on a spherical object |
-
1983
- 1983-04-07 CA CA000425403A patent/CA1205545A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7063747B2 (en) | 2002-05-29 | 2006-06-20 | Acushnet Company | Coating control system for use on a spherical object |
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