METHOD FOR STARTING A MULTI-GAS PLASMA ARC TORCH

• US 20120261392A1
• Filed: 04/13/2012
• Published: 10/18/2012
• Est. Priority Date: 04/14/2011
• Status: Active Grant

• Current Assignee: Victor Equipment Co. (Enovis Corp.)
• Original Assignee: Thermal Dynamics Corporation (Enovis Corp.)
• Inventors: Barnett, Daniel Wayne, Hussary, Nakhleh
• Granted Patent: US 9,024,230 B2
• Time in Patent Office: Days
• US Class Current: 219/121.59
• CPC Class Codes: B23K 10/006 Control circuits therefor circuits for plasma torches H05H1/36
• CPC Class Codes: B23K 9/0678 Ionization of the arc gap by means of an auxiliary arc
• CPC Class Codes: H05H 1/3405 Arrangements for stabilising or constricting the arc, e.g. by an additional gas flow
• CPC Class Codes: H05H 1/3421 Transferred arc or pilot arc mode
• CPC Class Codes: H05H 1/3436 Hollow cathodes with internal coolant flow
• CPC Class Codes: H05H 1/3457 Nozzle protection devices

Abstract

A method of starting a multi-gas plasma arc torch for cutting a workpiece is provided that includes directing a pre-flow gas within the plasma arc torch and switching the pre-flow gas to a plasma gas before a pilot arc is transferred to the workpiece. The plasma gas is supplied initially at a first gas pressure when the pre-flow gas is switched to the plasma gas. The gas pressure is switched to a second gas pressure that is different than the first gas pressure after the pilot arc is transferred. The method provides a smooth transition from the pre-flow gas to the plasma gas and reduces the time delay in replacing the pre-flow gas with the plasma gas in the plasma arc torch, thereby improving cut or marking quality.

Claims

1. A method of starting a plasma arc torch for operating on a workpiece, the method comprising:

directing a pre-flow gas supply within the plasma arc torch;

switching to a plasma gas supply that is different from the pre-flow gas supply;

transferring a pilot arc to the workpiece after the pre-flow gas is switched to the plasma gas; and

adjusting the pressure of the plasma gas after the pilot arc is transferred to the workpiece.

2. The method according to claim 1, wherein the pressure is increased after the pilot arc is transferred to the workpiece.

3. The method according to claim 1, wherein the pressure is decreased after the pilot arc is transferred to the workpiece.

4. The method according to claim 1, wherein the pilot arc is generated within the plasma arc torch after switching from the pre-flow gas supply to the plasma gas supply.

5. The method according to claim 1, wherein the pilot arc is generated within the plasma arc torch before switching from the pre-flow gas supply to the plasma gas supply.

6. The method according to claim 1 further comprising directing the pre-flow gas at a first pressure and directing the plasma gas at the first pressure when the pre-flow gas is switched to the plasma gas.

7. The method according to claim 6 further comprising switching the plasma gas from the first pressure to a second pressure after the pilot arc is transferred to the workpiece.

8. The method according to claim 7 wherein the second pressure is higher than the first pressure.

9. The method according to claim 1 further comprising increasing an arc current to a first set value to transfer the pilot arc to the workpiece.

10. The method according to claim 9 further comprising ramping up the arc current from the first set value.

11. The method according to claim 10 further comprising switching the plasma gas from a first pressure to a second pressure when the arc current reaches a second set value that is higher than the first set value.

12. The method according to claim 1, wherein the pre-flow gas is switched to the plasma gas approximately 10 ms-1000 ms before the pilot arc is transferred to the workpiece.

13. The method according to claim 1, wherein the plasma arc torch has a tip orifice smaller than about 0.040 inches.

14. The method according to claim 1, wherein the pre-flow gas is directed at a pressure greater than about 50 psi.

15. The method according to claim 1, further comprising operating the plasma arc torch at a value of between about 4 amps to about 150 amps.

16. The method according to claim 1, wherein the pre-flow gas is selected from a group consisting of argon, nitrogen and air.

17. The method according to claim 1, wherein the plasma gas is oxygen.

18. A method of starting a plasma arc torch for cutting a workpiece, the method comprising:

directing a pre-flow gas;

switching from the pre-flow gas to a plasma gas;

supplying the plasma gas at a first gas pressure;

transferring the pilot arc to the workpiece after the pre-flow gas is switched to the plasma gas; and

switching the plasma gas from the first gas pressure to a second gas pressure that is higher than the first gas pressure after the pilot arc is transferred to the workpiece.