EP0542542B1 - Méthode et appareillage pour surveiller la température et la vitesse des particules au cours de la pulvérisation au plasma - Google Patents

Méthode et appareillage pour surveiller la température et la vitesse des particules au cours de la pulvérisation au plasma Download PDF

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Publication number
EP0542542B1
EP0542542B1 EP19920310333 EP92310333A EP0542542B1 EP 0542542 B1 EP0542542 B1 EP 0542542B1 EP 19920310333 EP19920310333 EP 19920310333 EP 92310333 A EP92310333 A EP 92310333A EP 0542542 B1 EP0542542 B1 EP 0542542B1
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Prior art keywords
radiation
particle
fibre
plasma jet
optical
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Expired - Lifetime
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EP19920310333
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German (de)
English (en)
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EP0542542A1 (fr
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Christian Moreau
Paolo Cielo
Mario Lamontagne
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National Research Council of Canada
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National Research Council of Canada
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/0006—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature
    • H05H1/0012—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry
    • H05H1/0025—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature using electromagnetic or particle radiation, e.g. interferometry by using photoelectric means

Definitions

  • This invention relates to optical sensors for use in thermal spray processes and in particular, in plasma spray processes.
  • Plasma spraying is a powerful technique used widely to produce protective coatings on a large variety of substrates.
  • thermal barrier coatings are plasma sprayed in producing aircraft engines, and ceramic and metal coatings are plasma sprayed for various purposes. Coating properties depend upon many spraying parameters, some of them being related to the spray gun operation. Consequently spraying process control has been implemented by monitoring and regulating such gun input variables as arc current and power, arc gas flow rates, powder feed rate, and powder carrier gas pressure, to keep them at predetermined optimum values.
  • This control approach has been found to be complex because a large number of interrelated input variables must be monitored, and has been found to be incomplete because some variables, such as electrode wear state, cannot be monitored at all.
  • the present invention has been found to be a more powerful structure and method for controlling the plasma spray process.
  • the direct process parameters are monitored rather than (or in addition to) the indirect gun input variables.
  • the most important parameters that control directly the coating microstructure and properties are the temperature and the velocity of the particles immediately before their impact on the substrate.
  • the temperature and velocity are measured on-line, and provide an efficient feedback signal generator performing feedback for the gun input parameters to maintain optimum spraying conditions, and can be used as an efficient diagnostic tool to detect rapidly any problem during the coating operation. Since the temperature and velocity have a direct influence on the coating quality, the present invention at least in its preferred embodiment, facilitates obtaining a closer control of the spraying process, leading to a better reproductibility of the coating properties than in the prior art.
  • the velocity information is obtained from light impinging upon and reflected by the particles, detected by an appropriate sensor.
  • Laser based techniques such as laser Doppler anemometry and laser dual focus velocimetry, are included in this first type of technique. They use intense laser light beams to form interference fringes, or use two focused light beams in the measurement region. When the particle trajectory intercepts the measurement region, the reflected light intensity is modulated as the particle travels through the intensely illuminated zones and the velocity is computed from the modulation period. Periodic light distributions may also be obtained using a high intensity incandescent source and a Ronchi grating. This technique is inappropriate, being bulky and requiring high intensity light sources.
  • the second type of techniques used to perform the velocity measurement takes advantage of the thermal radiation emitted by the particles heated to a high temperature by the plasma.
  • the radiation emitted by individual particles is detected when the particles pass through the detector field of view of known dimensions.
  • the transit time is evaluated and the velocity is computed knowing the travel length. Since the dimensions of the field of view change with the distance from the optical detection assembly, it is necessary to analyse only particles near the assembly focal plane. To do that, a laser beam or a second detection assembly focused in the appropriate region from a different angle must be used in conjunction with a coincidence detection analysis system. Such a system is complex and difficult to keep well aligned under practical operating conditions.
  • velocity measurements can also be performed using high speed cameras.
  • the present invention in its most general embodiment is a method and an apparatus for monitoring the velocity and in its preferred embodiment simultaneously the temperature and its velocity, of sprayed particles without the limitations and problems described above, for previously developed technology. Temperature measurements are performed using a two-colour pyrometry technique, while the velocity measurements are done using a two-slit or a multiple-slit system that collects radiation emitted by the hot particles.
  • the detection assembly permits the simultaneous determination of the temperature and the velocity of each individually-detected particle.
  • the system is comprised of a sensor head attached to the spray gun, an optical fibre transmitting the collected radiation to detection apparatus, and a protective detection cabinet having the detection apparatus that incorporates two detectors.
  • a two-slit or multiple-slit mask is located in the sensor head at the end of the optical fibre.
  • the result is a rugged optical sensor that monitors the temperature and velocity distributions of plasma-sprayed particles simultaneously, immediately before their impact, in which the optical fibres permit the location of the fragile optical and electronic components away from the aggressive environment around the plasma gun.
  • the sensor head is located in the harsh environment close to the plasma, and indeed is preferably attached to the plasma gun for collecting radiation emitted by the hot particles.
  • the particle emitted radiation collected by the sensor head is transmitted to two photodetectors, filtered by interference filters at two adjacent wavelengths.
  • the particle temperature may be computed from the ratio of the detector outputs.
  • the two-slit system collects radiation emitted by the in-flight particles travelling in the sensor field of view, which generates a double peak light pulse transmitted through the optical fibre. The time delay between these two peaks may be evaluated automatically and the particle velocity computed knowing the distance between the two slit images.
  • the velocity measurement can be performed also with a system of three or more slits.
  • the sensor head can also include a linear fibre bundle that provides a continuous monitoring of the position of the sprayed-particle cone.
  • the light collected by the fibre bundle may be detected by a linear CCD camera. This permits the automatic centering of the sensor head field of view relative to the sprayed-particle cone and the detection of any changes in the particle injection conditions.
  • the above-computation is preferably performed by a processor, e.g. a personal computer, which can be programmed to continuously perform statistical computations to obtain the mean and standard deviation of the temperature and velocity distributions.
  • a processor e.g. a personal computer
  • These values and the particle cone position are directly related to the deposition process and are provided to the control apparatus as feedback signals whereby the main spraying variables of arc current, powder feeding gas pressure, etc. as noted above may be controlled.
  • a method of detecting a characteristic of plasma sprayed particles in a plasma jet during flight between a plasma jet gun and a substrate is comprised of the steps of focusing radiation emitted from a particle on a first photodetector through a slit mask formed of at least two parallel slits, and transmitting signals from the photodetector to a processor for determining the velocity of the particle from the delay between two or more peaks which are detected resulting from said radiation.
  • the invention further includes the step of splitting the radiation, filtering the radiation into separate adjacent wavelengths, passing one wavelength to the first photodector, passing the other wavelength to a second photodetector, and transmitting signals from the second photodetector to the processor for integrating the signals from both photodetectors and determining the temperature of the particle from the ratio of the integrated signals.
  • the focusing step includes carrying the radiation via an optical fibre from a position adjacent the plasma jet to a protected location remote from the plasma jet, and locating the photodetectors in the protected location.
  • an optical sensor for plasma sprayed particles in a plasma jet is comprised of a sensor head mounted rigidly adjacent the plasma jet; the head comprising an optical fibre for carrying radiation emitted by a particle in the jet to a protected location remote from the jet, optical apparatus for focusing the radiation on a first end of the fibre, and a slit mask formed of a pair of parallel slits disposed over the end of the fibre through which the radiation may pass; and at the protected location, a pair of photodetectors, apparatus for splitting into two beams the radiation from a second end of the fibre, apparatus for filtering the split radiation into two separate adjacent wavelenghts, and apparatus for passing each of said filtered beams into respective ones of the photodectors.
  • a substrate 1 is given a coating 2 by means of a plasma spray 3 of hot particles, emitted by a plasma spray gun 4.
  • a sensor head 8 is comprised of a lens 9 that images, after reflection on a flat mirror 10, the first end of an optical fibre 11 into the particle jet of hot particles 3 preferably to a single particle.
  • Ray lines 12 illustrate the reciprocal imaging of a particle onto the end of the optical fibre 11.
  • a substrate 1 is given a coating 2 by means of a plasma spray 3 of hot particles, emitted by a plasma spray gun 4.
  • a sensor head 8 is comprised of a lens 9 that images, after reflection on a flat mirror 10, the first end of an optical fibre 11 into the particle jet of hot particles 3 preferably to a single particle.
  • Ray lines 12 illustrate the reciprocal imaging of a particle onto the end of the optical fibre 11.
  • the first end of the fibre is covered by an optical mask 14 as shown in Figure 1A.
  • the optical mask contains two transparent parallel slits 15.
  • the slits are about 25um wide, 50um long and 50um center to center.
  • the slits formed by the lens 9 are about 75um wide, 150um long and 150um center to center.
  • the slit size and arrangement are important for reliable temperature and velocity measurements even when high particle flow rates are used.
  • the radiation collected by the sensor head i.e. at the output (second end) of the optical fibre 11, is sent to a system which is located away and protected from the harsh environment of the plasma spray gun. It should be well shielded electronically and kept in a quiet environment far from the operating spray gun and torch. Radiation from the optical fibre is imaged via a dichroic mirror 17, via a convex lens 18, on two photodetectors, D 1 and D 2 , through respective interference filters 20 and 21. Output signals from detectors D 1 and D 2 are digitised in analog-to-digital converters (not shown) and may be analysed by a computer 24 which computes the temperature and velocity of in-flight particles from the signals, as described below.
  • Figure 3 illustrates the field of view of the two slits 15 of the sensor head. The depth of field is shown by the width between the horizontal arrow heads. A particle 27 of the mass of hot particles travelling through the focal plane will generate a double peak light (radiation) pulse as it moves from the field of view of the first slit to the field of the view of the second slit.
  • FIG 4 Examples of the light (radiation) pulses are illustrated in Figure 4, which show signals output from both detectors D 1 and D 2 drawn as a function of time during the passage of a few particles in the sensor field of view. From the time delay between the two components of each pulse, the particle velocity can be computed, since the distance between the two slit images in the focal plane is known.
  • the particle temperature may be determined from the ratio of the integrated light pulses at both wavelengths, i.e. from detectors D 1 and D 2 .
  • the slit dimensions should be established such that the radiation is collected from the smallest possible volume in the particle jet, to reduce to a minimum the background signal intensity, but the slit images must be larger than the particle diameter in order to collect intense light signals from each single particle.
  • the computer 24 analyses the detector outputs by performing continuously statistical computation to obtain the means and standard deviation of the temperature and velocity distributions. These values are used toprovide continuous feedback to the plasma torch main spraying variables, i.e. arc current, powder feeding gas pressure, etc.
  • the direct particle localization may permit the measurement of temperature and velocity at many points within the particle jet, permitting obtaining a precise characterisation of the spraying process. It may be seen that this has significant advantages over the indirect measurement techniques of monitoring arc current and power, arc gas flow rates, powder feed rates, and powder carrier gas pressure.
  • An advantage of the present invention over active projection particle velocity measurement techniques lies in the fact that the present invention does not require the use of fragile laser devices or intense light sources. Accordingly a more compact and rugged sensor is obtained that does not require any special eye protection for the operator.
  • the present invention may also be used in conjunction with the two-colour pyrometer described earlier, without the use of any additional detectors or electronics.
  • the use of the two-slit mask permits the particles to be measured directly without the use of a laser beam or a second detection assembly focused in the same region within the particle jet.
  • the distance between the axes of the two focused beams is nearly constant through the depth of field, as shown in Figure 3, while the width of a single beam, proportional to the time of flight in a single-slit configuration, changes very quickly. This requires a second coincidence detection to localise the particle, not required in the present invention.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Electromagnetism (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
  • Coating By Spraying Or Casting (AREA)
  • Plasma Technology (AREA)

Claims (14)

  1. Une méthode de détection des caractéristiques relatives aux particules pulvérisées par plasma (27) dans un jet plasma (3) pendant son trajet dans l'air entre un pistolet à jet plasma (4) et un substrat (1), comprenant les étapes de focalisation du rayonnement (12) émis par une particule (17) sur un premier photodétecteur (D1) à travers un masque à fentes (14) constitué de deux fentes parallèles au moins (15) ayant une séparation connue, et de l'acheminement des signaux à partir du photodétecteur (D1) vers un processeur (24) afin de déterminer la vitesse de la particule (27) sur la base de la temporisation entre deux ou plusieurs crêtes qui sont détectées à la suite dudit rayonnement (12).
  2. Une méthode, selon les stipulations de la revendication 1, y compris les étapes de fractionnement dudit rayonnement (12) en deux faisceaux, du filtrage desdits deux faisceaux en longueurs d'ondes adjacentes respectives, de l'attribution d'une longueur d'onde au premier photodétecteur (D1), de l'attribution des autres longueurs d'ondes au deuxième photodétecteur (D2), et de la transmission des signaux du deuxième photodétecteur (D2) audit processeur (24), afin d'intégrer lesdits signaux provenant des deux photodétecteurs (D1, D2) et de déterminer la température de la particule (27) sur la base du taux des signaux intégrés (D1, D2).
  3. Une méthode, selon les stipulations de la revendication 2, dans laquelle l'étape de focalisation comprend l'acheminement dudit rayonnement par l'intermédiaire d'une fibre optique (11) à partir d'une position adjacente audit jet plasma (3) jusqu'à un endroit protégé éloigné dudit jet plasma (3), ainsi que le positionnement desdits photodétecteurs (D1, D2) dans ledit endroit protégé.
  4. Une méthode, selon les stipulations de la revendication 3, dans laquelle l'étape de focalisation comprend l'acheminement du rayonnement à partir de ladite fibre (11) par une lentille convexe (18) et par l'intermédiaire d'un miroir dichroïque (17) et par des filtres séparés (20, 21) jusqu'aux photodétecteurs (D1, D2).
  5. Une méthode, selon les stipulations de la revendication 2, dans laquelle la dimension desdites fentes (15) est suffisamment petite de façon à collecter le rayonnement émis par le plus faible volume possible, mais est suffisamment grande de façon à fournir des images qui sont chacune plus grandes que le diamètre de la particule.
  6. Une méthode, selon les stipulations de la revendication 5, dans laquelle chacune des fentes (15) mesure environ 25 um de large, 50 um de long et 50 um de centre à centre.
  7. Une méthode, selon les stipulations de la revendication 6, dans laquelle l'étape de focalisation comprend l'acheminement dudit rayonnement (12) par l'intermédiaire d'une fibre optique (11) à partir d'une position adjacente audit jet plasma (3) jusqu'à un endroit protégé éloigné dudit jet plasma (3), ainsi que le positionnement desdits photodétecteurs (D1, D2) dans ledit endroit protégé.
  8. Une méthode, selon les stipulations de la revendication 7, dans laquelle l'étape de focalisation comprend l'acheminement du rayonnement (12) à partir de ladite fibre (11) par une lentille convexe (18) et par l'intermédiaire d'un miroir dichroïque (17) et par des filtres séparés (20, 21) jusqu'aux photodétecteurs (D1, D2).
  9. Une méthode, selon les stipulations de la revendication 3, comprenant l'étape de saisie du rayonnement (12) émis par ledit jet plasma (3) à l'une des extrémités d'un ensemble de fibres optiques (11), recevant ledit rayonnement dans une caméra à CCD, et fournissant un signal de ladite caméra pour positionner ledit champ de vision de la tête du capteur par rapport audit jet plasma (3) et/ou pour détecter les changements se produisant dans les caractéristiques d'injection des particules.
  10. Un capteur optique pour les particules pulvérisées par plasma (27) dans un jet plasma (3) comprenant :
    (a) une tête de capteur (8) fixée de façon rigide à côté du jet plasma (3), ladite tête (8) comprenant :
    (i) une fibre optique (11) pour l'acheminement du rayonnement (12) émis par une particule (27) dans ledit jet (3) vers un endroit protégé qui est éloigné dudit jet (3), et
    (ii) un moyen optique (9, 10) permettant de focaliser ledit rayonnement (12) sur la première extrémité de ladite fibre (11) et
    (iii) un masque à fentes (14) constitué d'une paire de fentes parallèles (15) ayant une séparation connue, et positionné au-dessus de ladite extrémité de ladite fibre (11), par laquelle le rayonnement (12) peut être acheminé,
       et dans l'endroit protégé,
    (b) une paire de photodétecteurs (D1, D2),
    (c) un moyen (17) permettant de fractionner le rayonnementprovenant de la deuxième extrémité de ladite fibre (11) en deux faisceaux,
    (d) un moyen (20, 21) permettant de filtrer lesdits deux faisceaux en longueurs d'ondes adjacentes, et
    (e) un moyen permettant de faire passer chacun desdits faisceaux filtrés dans l'un desdits photodétecteurs respectifs (D1, D2).
  11. Un capteur optique, selon les stipulations de la revendication 10, dans lequel ledit moyen de fractionnement (17) est constitué d'un miroir dichroïque (17), comprenant en outre, une lentille convexe (18) pour focaliser ledit rayonnement provenant de la deuxième extrémité de ladite fibre (11) par l'intermédiaire dudit miroir (17) vers lesdits photodétecteurs (D1, D2), et dans lequel ledit moyen de filtrage (20, 21) est constitué d'une paire de filtres optiques (20, 21) chacun étant respectivement positionné entre un photodétecteur correspondant (D1, D2) et ledit miroir (17), afin de faire passer le rayonnement fractionné en longueurs d'ondes séparées vers l'un desdits photodétecteurs respectifs (D1, D2).
  12. Un capteur optique, selon les stipulations de la revendication 11, dans lequel ledit moyen optique (9, 10) est constitué d'un miroir (10) permettant de réfléchir le rayonnement émis par ladite particule, et d'une lentille convexe (9) permettant de recevoir ledit rayonnement réfléchi et de le focaliser sur l'extrémité de ladite fibre (11).
  13. Un capteur optique, selon les stipulations de la revendication 11, dans lequel lesdites fentes parallèles (15) mesurent environ 25 um de large, 50 um de long et 50 um de centre à centre.
  14. Un capteur optique, selon les stipulations de la revendication 10, comprenant en outre un ensemble de fibres optiques (11) dont l'une des extrémités est disposée dans ladite tête du capteur (8) pour détecter le rayonnement émis par ledit jet plasma (3), une caméra à CCD pour détecter ledit rayonnement émis par l'autre extrémité dudit ensemble (11), et un moyen pour recevoir un signal émis par ladite caméra afin de positionner ledit champ de vision de la tête du capteur par rapport audit jet plasma (3) et/ou de détecter les changements se produisant dans les conditions d'injection des particules.
EP19920310333 1991-11-12 1992-11-12 Méthode et appareillage pour surveiller la température et la vitesse des particules au cours de la pulvérisation au plasma Expired - Lifetime EP0542542B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA 2055267 CA2055267C (fr) 1991-11-12 1991-11-12 Appareil servant a controler la temperature et la vitesse des particules projetees par plasma et methode connexe
CA2055267 1991-11-12

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EP0542542A1 EP0542542A1 (fr) 1993-05-19
EP0542542B1 true EP0542542B1 (fr) 1997-05-07

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10140299A1 (de) * 2001-08-16 2003-03-13 Mtu Aero Engines Gmbh Verfahren zur Überwachung von Plasma- oder Flammspritzverfahren
US7688441B2 (en) 2005-04-08 2010-03-30 Mtu Aero Engines Gmbh Arrangement for monitoring thermal spray processes

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7070835B2 (en) * 2003-06-09 2006-07-04 Siemens Power Generation, Inc. Method for applying a coating to a substrate
EP1978790B1 (fr) * 2007-03-23 2010-05-19 Siemens Aktiengesellschaft Dispositif et procédé destinés au revêtement d'un composant doté d'un dispositif d'ajustement
GB0819359D0 (en) * 2008-10-22 2008-11-26 Intrinsiq Materials Ltd Plasma torch
CN111006704B (zh) * 2019-11-29 2021-11-23 江苏智冷物联技术有限公司 一种传感器数据处理方法、管理平台及传感器表头

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4122351A (en) * 1977-08-30 1978-10-24 The United States Of America As Represented By The United States Department Of Energy Automatic targeting of plasma spray gun

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10140299A1 (de) * 2001-08-16 2003-03-13 Mtu Aero Engines Gmbh Verfahren zur Überwachung von Plasma- oder Flammspritzverfahren
US6797939B2 (en) 2001-08-16 2004-09-28 Mtu Aero Engines Gmbh Method for monitoring plasma or flame-spray processes
DE10140299B4 (de) * 2001-08-16 2004-10-28 Mtu Aero Engines Gmbh Verfahren zur Überwachung und online-Diagnose eines thermischen Spritzprozesses
US7688441B2 (en) 2005-04-08 2010-03-30 Mtu Aero Engines Gmbh Arrangement for monitoring thermal spray processes

Also Published As

Publication number Publication date
DE69219560T2 (de) 1997-11-13
EP0542542A1 (fr) 1993-05-19
DE69219560D1 (de) 1997-06-12
CA2055267C (fr) 1999-01-12
CA2055267A1 (fr) 1993-05-13

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