GB2407050A - Rotary ring cathode for plasma spraying - Google Patents

Rotary ring cathode for plasma spraying Download PDF

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Publication number
GB2407050A
GB2407050A GB0322964A GB0322964A GB2407050A GB 2407050 A GB2407050 A GB 2407050A GB 0322964 A GB0322964 A GB 0322964A GB 0322964 A GB0322964 A GB 0322964A GB 2407050 A GB2407050 A GB 2407050A
Authority
GB
United Kingdom
Prior art keywords
powder
plasma
electrodes
particles
method
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0322964A
Other versions
GB0322964D0 (en
Inventor
Peter Edmond Chandler
T Lester
Michael Bernard Coupla Quigley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
C A Technology Ltd
Quiguley Associates
Metallisation Ltd
Original Assignee
C A TECHNOLOGY LTD
Metallisation Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by C A TECHNOLOGY LTD, Metallisation Ltd filed Critical C A TECHNOLOGY LTD
Priority to GB0322964A priority Critical patent/GB2407050A/en
Publication of GB0322964D0 publication Critical patent/GB0322964D0/en
Publication of GB2407050A publication Critical patent/GB2407050A/en
Application status is Withdrawn legal-status Critical

Links

Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05HPLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00Generating plasma; Handling plasma
    • H05H1/24Generating plasma
    • H05H1/26Plasma torches
    • H05H1/32Plasma torches using an arc
    • H05H1/34Details, e.g. electrodes, nozzles
    • H05H1/40Details, e.g. electrodes, nozzles using applied magnetic fields, e.g. for focusing or rotating the arc
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05HPLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00Generating plasma; Handling plasma
    • H05H1/24Generating plasma
    • H05H1/26Plasma torches
    • H05H1/32Plasma torches using an arc
    • H05H1/44Plasma torches using an arc using more than one torch

Abstract

A number of electrodes 3 are used to provide arcs which are then rotated at a chosen speed to cause a plasma 8 to be formed through which powder can be fed axially 10. In this way the heating effect on the powder is far more uniform that the conventional side injection of powder into the plasma jet. The rotation can be caused by the application of magnetic fields 5 or by the use of special power supplies that switch the power between the electrodes at high frequency.

Description

Novel Plasma Torch Using a Ring Cathode and a Magnetically Rotated Arc For

Axial Injection of Powders and Wires This invention relates to thermal spraying processes and is most particularly concerned with the control of the injection of the powder particles into the plasma.

In plasma spraying powder is injected into a plasma which then heats and accelerates the particles. When wire is used as the feed material the wire is injected into the plasma where it melts and form particles which are then heated and accelerated towards the substrate. These particles then impact on the surface and form a specialized coating that will protect the substrate from corrosion, erosion or both or to impart special properties such as low friction. In most plasma spraying equipment powder is injected into the plasma from a side port. It is thus imperative to arrange that the powder particles are injected into the jet at a speed such that they reach the centre of the jet and are carried along axially towards the substrate.

The combination of the heating and acceleration ensures that at impact the temperature of the particles has been raised to a level that is such that the particles can bond to the substrate to be coated. Ultimately the objective is to produce a coating that imparts specific properties to the coating such as corrosion or wear resistance. Such coatings are widely used in engineering plant for a very wide range of applications but aerospace is the best known application whereby such coatings are used in gas turbines to enable the turbines to operate at high temperatures thus improving efficiency and offer environmental advantages.

As the particles typically have a range of sizes of 3:1 the mass of the individual particles will vary by a factor of 27:1. As the particles are injected into the jet the lighter particles will tend to bounce off the jet whereas the heavier ones will tend to penetrate through the jet. In both cases the particles will not be propelled axially through the plasma; the lighter ones will be overheated, oxidise and tend to form a "fog" above the jet and will create oxide on the substrate and in the coating.

The heavier particles will not be heated sufficiently to enable melting to take place and will result in a number of unfused (i.e. loose) particles being present in the coating. Current "older type" spray systems have this type of powder injection and are renowned for their "spray droop" problems. With this phenomenon the spray pattern tends to be below that of the aiming point. In practical terms the spray stream does not go where it is aimed resulting in a loss of efficiency and productivity and an increase in environmental issues such as powder recovery and handling. Many of the powders involved in these processes are hazardous and it is essential that both the fume and the powder residue are kept to a minimum.

This invention describes a method of improving the plasma spraying process by arranging to have an axial feed system. Axial feeding of powder means that all the particles flow through the centre of the torch and the plasma and represent the best way of ensuring that the maximum heating and accelerating forces are applied to the particles. To ensure that an axial powder feed is obtained in a plasma system it is clearly necessary to arrange for the plasma arc/jet to, initially, surround the injected powder.

In the proprietary Mettech system this is achieved by having 3 cathodes, 3 arcs and 3 power supplies. This does have the desired effect up to a point but is expensive and bulky, especially with the power supplies.

The ideal system would have only a single power supply and would be capable of being retro-fitted to existing plasma spray systems. This is a critical point in order ensure wide and rapid adoption of any new technology.

There are two main embodiments in this patent.

The first is to provide a 'ring' cathode with the arc/plasma being forced to rotate by means of an applied magnetic field. The 'ring' would typically be made up of a number of simple gas cooled tungsten electrodes (such as cheap 100A welding electrodes) positioned in a ring. The powder would then be fed through the centre of this assembly.

The main problem is to ensure that the arc moves from electrode to electrode around the circle and so produce a stable and uniform plasma jet to surround the injected powder. This can be done by means of an appropriately designed magnetic field that applies a rotational force to the arc. The circulating arc would also mean that all of the electrodes act as the cathode in turn thus averaging out the currents taken from each electrode.

This cathode system can then be retro fitted to existing standard plasma torches. No modifications will be needed to the anode or to the gas supplies to the torch. The external non-axial powder feed system would need to be replaced by an axial powder feed arrangement.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings (Figures 1 and 2).

In Figures 1 and 2 can be seen the plasma torch assembly, comprising the anode 1, the cathode assembly 2 comprising a number of electrodes 3 which may or may not have additives in them and the exit from the torch 4. The applied external magnetic field is generated from coils 5 with the electrical power feeding the coils 5 being supplied from a power supply 6 which has a control 7 that causes the frequency of rotation of the arc/plasma 8 to be changed to form the axi-symmetrical plasma. The powder particles 9 are supplied through a powder feeder pipe 10 at the back of the cathode assembly 2 and insulated from it by an insulator 11. Electrical power from the main power supply 12 is connected to the cathode assembly 2 to which all of the individual cathode electrodes 3 are connected.

The second embodiment is where a plurality of electrodes each electrically insulated from the other is arranged in a ring similar to that in the first embodiment. The electrodes are connected to a high frequency polyphase power supply, for example three phases if three electrodes are used. An arc is struck to initiate the process and as in any three phase system current flows from the more positive to the more negative electrode at any time. The frequency of the power supply phase rotation is relatively high (several kHz) so that at any instant the arc is moving from one electrode to another following the phase rotation as in a high frequency induction motor. As the frequency is high the heating effect upon the gas is such as to maintain the gas in an ionised condition so that, unlike mains frequency arcs, the arc does not have to be re-initiated as the current curve passes through zero. If desired the tubular nozzle referred to as an anode in he first embodiment may be at some potential other than the neutral potential of the three phase system but otherwise it serves no purpose other than as a guide for the hot gases and the entrained particles as the arc is maintained solely between tips of each of the previously mentioned ring of separate electrodes. If the "anode" voltage is shifted away from the neutral value then some portion of the current and therefore the arc will be transferred between the ring electrodes and the "anode" causing a change in shape of the ionised stream.

In Figure 3 the electrodes 13 are arranged in a ring similar to that in the first embodiment and insulated from each other by the insulator 14. The plasma forming gas is supplied through the port15 and the powder is fed through the powder feed tube 16. The resulting plasma issues through the nozzle 17. The power supply 18 has a variable frequency to maintain the gas in an ionised condition. The powder being sprayed is shown as 19 and the plasma jet containing the powder being sprayed is shown as 20. A switch 21 is provided so that the nozzle potential can be made neutral or connected to earth or other potential as desired.

Claims (6)

  1. What we claim is 1. A method for the improvement of powder injection in
    plasma spraying apparatus.
  2. 2. A method as claimed in claim 1 in which the arcs from a number of electrodes are magnetically rotated to provide a uniform heating for the particles being sprayed.
  3. 3. A method as claimed in claim 1 and 2 in which axial injection of powder is used.
  4. 4. A method for the improvement of plasma spraying by having a plurality of electrodes and a power supply that arranges that the resulting plasma effectively rotates by the use of special power supplies that switch the power between the electrodes at high frequency.
  5. 5. A method as in claim 4 in which powder is injected through the centre of the rotating plasma to be heated and accelerated and to form a coating on the target.
  6. 6. A method as in claims 1, 2, 3, 4 and 5 in which the arcs from a number of electrodes are formed and then rotated to provide a uniform plasma through which particles are passed axially to be heated and accelerated and to form a coating on the target.
    _
GB0322964A 2003-10-01 2003-10-01 Rotary ring cathode for plasma spraying Withdrawn GB2407050A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0322964A GB2407050A (en) 2003-10-01 2003-10-01 Rotary ring cathode for plasma spraying

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0322964A GB2407050A (en) 2003-10-01 2003-10-01 Rotary ring cathode for plasma spraying

Publications (2)

Publication Number Publication Date
GB0322964D0 GB0322964D0 (en) 2003-11-05
GB2407050A true GB2407050A (en) 2005-04-20

Family

ID=29415290

Family Applications (1)

Application Number Title Priority Date Filing Date
GB0322964A Withdrawn GB2407050A (en) 2003-10-01 2003-10-01 Rotary ring cathode for plasma spraying

Country Status (1)

Country Link
GB (1) GB2407050A (en)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009018838A1 (en) * 2007-08-06 2009-02-12 Plasma Surgical Investments Limited Cathode assembly and method for pulsed plasma generation
AT505812B1 (en) * 2007-10-10 2009-06-15 Qasar Technologieentwicklung G Method for operating a plasma brainer and plasma burner
DE102009005078A1 (en) * 2009-01-16 2010-02-18 Daimler Ag Plasma spray assembly for automotive crankshaft bearing has a circular non-sacrificial electrode surrounded by electromagnetic coils
US7928338B2 (en) 2007-02-02 2011-04-19 Plasma Surgical Investments Ltd. Plasma spraying device and method
US8030849B2 (en) 2007-08-06 2011-10-04 Plasma Surgical Investments Limited Pulsed plasma device and method for generating pulsed plasma
US8105325B2 (en) 2005-07-08 2012-01-31 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device, use of a plasma-generating device and method of generating a plasma
US8109928B2 (en) 2005-07-08 2012-02-07 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device and use of plasma surgical device
US8613742B2 (en) 2010-01-29 2013-12-24 Plasma Surgical Investments Limited Methods of sealing vessels using plasma
US8735766B2 (en) 2007-08-06 2014-05-27 Plasma Surgical Investments Limited Cathode assembly and method for pulsed plasma generation
US9089319B2 (en) 2010-07-22 2015-07-28 Plasma Surgical Investments Limited Volumetrically oscillating plasma flows
US9913358B2 (en) 2005-07-08 2018-03-06 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device and use of a plasma surgical device

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06183886A (en) * 1992-10-20 1994-07-05 Fujitsu Ltd Production of diamond and apparatus therefor
RU2066515C1 (en) * 1994-01-05 1996-09-10 Акционерное общество Научно-исследовательский институт стали Plasma centrifuge
US5565249A (en) * 1992-05-07 1996-10-15 Fujitsu Limited Method for producing diamond by a DC plasma jet

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5565249A (en) * 1992-05-07 1996-10-15 Fujitsu Limited Method for producing diamond by a DC plasma jet
JPH06183886A (en) * 1992-10-20 1994-07-05 Fujitsu Ltd Production of diamond and apparatus therefor
RU2066515C1 (en) * 1994-01-05 1996-09-10 Акционерное общество Научно-исследовательский институт стали Plasma centrifuge

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
WPI ABSTRACT, Acc. No. 1994-252643; & JP 06 183886 A (FUJITSU LTD) (05-07-1994) *
WPI ABSTRACT, Acc. No. 1997-200890; & RU 2066515 C1 (AKTSIONERNOE OBSHCHESTVO) (10-09-1996) *

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8109928B2 (en) 2005-07-08 2012-02-07 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device and use of plasma surgical device
US10201067B2 (en) 2005-07-08 2019-02-05 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device and use of a plasma surgical device
US9913358B2 (en) 2005-07-08 2018-03-06 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device and use of a plasma surgical device
US8105325B2 (en) 2005-07-08 2012-01-31 Plasma Surgical Investments Limited Plasma-generating device, plasma surgical device, use of a plasma-generating device and method of generating a plasma
US8337494B2 (en) 2005-07-08 2012-12-25 Plasma Surgical Investments Limited Plasma-generating device having a plasma chamber
US8465487B2 (en) 2005-07-08 2013-06-18 Plasma Surgical Investments Limited Plasma-generating device having a throttling portion
US7928338B2 (en) 2007-02-02 2011-04-19 Plasma Surgical Investments Ltd. Plasma spraying device and method
US8030849B2 (en) 2007-08-06 2011-10-04 Plasma Surgical Investments Limited Pulsed plasma device and method for generating pulsed plasma
US8735766B2 (en) 2007-08-06 2014-05-27 Plasma Surgical Investments Limited Cathode assembly and method for pulsed plasma generation
EP2557902A3 (en) * 2007-08-06 2014-10-29 Plasma Surgical Investments Limited Cathode assembly and method for pulsed plasma generation
WO2009018838A1 (en) * 2007-08-06 2009-02-12 Plasma Surgical Investments Limited Cathode assembly and method for pulsed plasma generation
AT505812B1 (en) * 2007-10-10 2009-06-15 Qasar Technologieentwicklung G Method for operating a plasma brainer and plasma burner
DE102009005078A1 (en) * 2009-01-16 2010-02-18 Daimler Ag Plasma spray assembly for automotive crankshaft bearing has a circular non-sacrificial electrode surrounded by electromagnetic coils
US8613742B2 (en) 2010-01-29 2013-12-24 Plasma Surgical Investments Limited Methods of sealing vessels using plasma
US9089319B2 (en) 2010-07-22 2015-07-28 Plasma Surgical Investments Limited Volumetrically oscillating plasma flows
US10463418B2 (en) 2010-07-22 2019-11-05 Plasma Surgical Investments Limited Volumetrically oscillating plasma flows
US10492845B2 (en) 2010-07-22 2019-12-03 Plasma Surgical Investments Limited Volumetrically oscillating plasma flows

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Publication number Publication date
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