Plasma torch condition monitoring

• US 5,717,187 A
• Filed: 09/24/1996
• Issued: 02/10/1998
• Est. Priority Date: 03/25/1994
• Status: Expired due to Term

• Current Assignee: Commonwealth Scientific & Industrial Research Organisation (Commonwealth Of Australia As Represented By Department Of Industry, Innovation, Climate Change, Science, Research And Tertiary Education)
• Original Assignee: Commonwealth Scientific & Industrial Research Organisation (Commonwealth Of Australia As Represented By Department Of Industry, Innovation, Climate Change, Science, Research And Tertiary Education)
• Inventors: Rogozinski, Maciej Wlodzimierz, Ramakrishnan, Subramania, Doolette, Ashley Grant, Couch, Richard W. Jr., Sanders, Nicholas A.
• Primary Examiner(s): Paschall, Mark H.
• Application Number:
  US08/716,264
• Time in Patent Office: 504 Days
• Field of Search: 219/121.56, 219/121.55, 219/121.54, 219/121.48, 219/121.51, 219/74, 219/75, 219/121.59
• US Class Current: 219/121.54
• CPC Class Codes: B05B 15/18 for improving resistance to wear, e.g. inserts or coatings; for indicating wear; for handling or replacing worn parts
• CPC Class Codes: H05H 1/3494 Means for controlling discharge parameters
• CPC Class Codes: H05H 1/36 Circuit arrangements H05H1/38, H05H1/40 take precedence

Abstract

A method and apparatus for monitoring the condition of a plasma arc torch determines whether the nozzle (13) of the torch and an electrode (11) of the torch have suffered any erosion and distinguishes the two. The pressure of a plasma forming gas that is supplied for the torch (p₁ or p_n) is monitored while the torch is operating to detect erosion of the orifice (12) of the nozzle (13), and the voltage U_ne between the electrode (11) and nozzle (13) is monitored, also while the torch is operating, to detect erosion of the electrode (11). A pressure, p₁ or p_n below a reference pressure indicative of a good (un-eroded) nozzle indicates erosion of the orifice (12), and a voltage U_ne above a reference voltage indicative of a good (un-eroded) electrode indicates erosion of the electrode. The pressure measurement and U_ne are compared with appropriate reference values to logically discriminate between wear of the nozzle and wear of the electrode (given that an increase in U_ne due to electrode wear is opposed by a decrease in U_ne due to nozzle wear). The apparatus and method may provide a binary "good" or "bad" output for the nozzle and electrode, respectively, or may allow for the degree of wear of each to be determined.

Claims

1. A method for detecting erosion of a nozzle of a plasma arc torch while a plasma jet is being generated by the torch including measuring the pressure of a plasma forming gas supplied to the torch at a location upstream of the nozzle orifice, comparing the measured pressure with a reference pressure value representative of a non-eroded nozzle, wherein a measured pressure value which is less than said reference value indicates the presence of erosion of the nozzle orifice, and additionally measuring an electrical parameter associated with the plasma jet and comparing the measured electrical parameter with a reference value for detecting a change in length of an arc forming the said plasma, wherein the pressure measurement and comparison with a reference value, and the electrical parameter measurement and comparison with a reference value, are used to distinguish between erosion of the nozzle of the torch and erosion of the electrode of the torch.

2. A method as claimed in claim 1 wherein the pressure of a plasma forming gas within the nozzle of the plasma arc torch is measured.

3. A method as claimed in claim 1 wherein the pressure of a plasma forming gas is measured in a supply line downstream of a pressure regulator associated with a supply of the plasma forming gas.

4. A method as claimed in claim 1 wherein the electrical parameter is a voltage.

5. A method as claimed in claim 4 wherein the voltage between an electrode and the nozzle of the plasma arc torch is measured.

6. A method as claimed in claim 1 wherein the measured electrical parameter is compared with an upper and a lower reference value, an unacceptably eroded nozzle and a good relatively un-eroded electrode being indicated if the measured pressure is lower than the reference pressure value while the measured electrical parameter is below the lower of its reference values whereas an unacceptably eroded electrode is indicated if the electrical parameter is above the said lower reference value, a good relatively un-eroded nozzle and a good relatively un-eroded electrode being indicated if the measured pressure is higher than the reference pressure value while the measured electrical parameter is between the said upper and lower reference values whereas an unacceptably eroded electrode is indicated if the measured electrical parameter is above said upper reference value.

7. A method as claimed in claim 1 including determining the degree of wear of the nozzle using the measured pressure value.

8. A method as claimed in claim 1 including determining the degree of wear of the torch electrode using the measured pressure value and the measured electrical parameter.

9. Apparatus for detecting erosion of a nozzle of a plasma arc torch while a plasma jet is being generated by the torch including means for measuring the pressure of a plasma forming gas supplied to the torch at a location upstream of the nozzle orifice and means for comparing a measured pressure value determined by said first mentioned means with a reference pressure value representative of a non-eroded nozzle, wherein a measured pressure value which is less than said reference value indicates the presence of erosion of the nozzle office, and means for measuring an electrical parameter associated with the plasma jet and for comparing said measured electrical parameter with a reference value for determining a change in length of an arc forming the plasma, said electrical parameter measuring means including means for measuring voltage between an electrode and the nozzle of the plasma arc torch, wherein the pressure measuring means, pressure comparing means, electrical parameter measuring means and electrical parameter comparing means functionally distinguish between erosion of the nozzle of the torch and erosion of the electrode of the torch.

10. Apparatus as claimed in claim 9 wherein the pressure measuring means includes a sensor located within the nozzle of the torch.

11. Apparatus as claimed in claim 9 wherein the pressure measuring means includes a sensor located within a gas supply line downstream of a pressure regulator associated with a plasma forming gas supply.

12. Apparatus as claimed in claim 10 or claim 11 wherein the sensor is a strain gauge bridge pressure sensor.

13. Apparatus as claimed in claim 9 wherein the means for comparing a measured pressure value with a reference pressure value provides a binary "1" or "0" output, a "1" output being provided if the measured pressure is higher than the reference value to thereby indicate a good relatively un-eroded nozzle, and a "0" output being provided if the measured pressure is lower than the reference value to thereby indicate a worn unacceptably eroded nozzle.

14. Apparatus as claimed in claim 9 wherein the electrical parameter comparing means provides for comparison of the measured electrical parameter with an upper and a lower reference value.

15. Apparatus as claimed in claim 14 wherein the electrical parameter comparing means provides an output that indicates a good relatively un-eroded electrode if the measured pressure value is lower than the reference pressure value and the measured electrical parameter is below the lower of its reference values;

an output that indicates a worn unacceptably eroded electrode if the measured pressure value is lower than the reference pressure value and the measured electrical parameter is above the lower of its reference values;

an output that indicates a worn unacceptably eroded electrode if the measured pressure value is higher than the reference pressure value and the measured electrical parameter is above the upper of its reference values; and

an output that indicates a good relatively un-eroded electrode if the measured pressure value is higher than the reference pressure value and the measured electrical parameter is between the upper and lower of its reference values.

16. Apparatus as claimed in claim 9 wherein the pressure comparing means and the electrical parameter comparing means provide outputs for indicating, respectively, the degree of wear of the nozzle and the degree of wear of the electrode.