Plasma arc torch and method for cutting a workpiece

• US 6,337,460 B2
• Filed: 01/29/2001
• Issued: 01/08/2002
• Est. Priority Date: 02/08/2000
• Status: Expired due to Term

• Current Assignee: Victor Equipment Co. (Enovis Corp.)
• Original Assignee: Thermal Dynamics Corporation (Enovis Corp.)
• Inventors: Roberts, Jesse A., Kelkar, Milind G., Putnam, Geoffrey H., Small, David A., Horner-Richardson, Kevin D.
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US09/772,260
• Publication Number:
  US 20010025833A1
• Time in Patent Office: 344 Days
• Field of Search: 219/121.48, 219/121.36, 219/121.5, 219/121.51, 219/121.59, 219/74, 219/75, 313/231.41, 313/231.51
• US Class Current: 219/121.5
• CPC Class Codes: H05H 1/34 Details, e.g. electrodes, nozzles
• CPC Class Codes: H05H 1/3405 Arrangements for stabilising or constricting the arc, e.g. by an additional gas flow
• CPC Class Codes: H05H 1/3436 Hollow cathodes with internal coolant flow
• CPC Class Codes: H05H 1/3442 Cathodes with inserted tip
• CPC Class Codes: H05H 1/3457 Nozzle protection devices
• CPC Class Codes: H05H 1/3478 Geometrical details

Abstract

A plasma arc torch and method for cutting a workpiece in which the torch has a primary gas flow path for receiving a primary working gas and directing it through the torch to a central exit opening of the torch for exhaustion from the torch onto the workpiece in the form of an ionized plasma. A secondary gas flow path in the torch receives a secondary gas separate from the primary working gas and directs it through the torch. The primary gas flow path is in fluid communication with the secondary gas flow path substantially upstream of the central exit opening of the torch to bleed primary working gas in the primary gas flow path into the secondary gas flow path for admixture therewith to form a secondary gas mixture to be exhausted from the torch.

Claims

1. A plasma torch comprising:

a primary gas flow path in the torch for receiving a primary working gas and directing it through the torch to a central exit opening of the torch for exhaustion from the torch onto a workpiece in the form of an ionized plasma;

a secondary gas flow path in the torch separate from the primary gas flow path for receiving a secondary gas and directing it through the torch,

the primary gas flow path being in fluid communication with the secondary gas flow path substantially upstream of the central exit opening of the torch to bleed primary working gas in the primary gas flow path into the secondary gas flow path for admixture therewith to form a secondary gas mixture to be exhausted from the torch.

2. A plasma torch as set forth in claim 1 further comprising a secondary exit opening in the torch separate from the central exit opening and in spaced relationship therewith for exhausting the secondary gas mixture from the torch.

3. A plasma torch as set forth in claim 2 wherein the secondary gas flow path is sealed from the primary gas flow path generally downstream of said fluid communication between the primary gas flow path and the secondary gas flow path to prevent secondary gas mixture in the secondary gas flow path from impinging on the primary working gas as the primary working gas exits the central exit opening of the torch.

4. A plasma torch as set forth in claim 3 further comprising:

a cathode;

an electrode electrically connected to the cathode;

a tip surrounding the electrode in spaced relationship therewith to define a primary gas passage forming at least part of the primary gas flow path, the tip having a central exit orifice in fluid communication with the gas passage;

a shield cap surrounding the tip and having a central opening in fluid communication with the central exit orifice of the tip to define the central exit opening of the torch through which primary gas is directed onto the workpiece in the form of an ionized plasma, the shield cap further having at least one secondary opening in spaced relationship with the central opening of the shield cap to define the secondary opening of the torch for exhausting the secondary gas mixture from the torch;

the tip having at least one bleed hole in fluid communication with the primary gas passage upstream of the central exit orifice of the tip, the bleed hole also being in fluid communication with the secondary gas flow path to bleed a portion of the primary gas in the primary gas passage into the secondary gas flow path for admixture with the secondary gas in the torch to form the secondary gas mixture whereby the secondary gas mixture is exhausted from the torch through the at least one secondary opening in the shield cap.

5. A plasma torch as set forth in claim 4 further comprising a sealing member for sealingly engaging the tip and shield cap intermediate the central opening of the shield cap and the at least one secondary opening of the shield cap to seal the secondary gas flow path from the primary gas flow path for preventing the secondary gas mixture in the secondary gas flow path from impinging on the primary gas as the primary gas exits the central exit orifice of the tip and the central opening of the shield cap.

6. A plasma torch as set forth in claim 1 wherein the primary gas is oxygen.

7. A plasma torch as set forth in claim 6 wherein the secondary gas is air.

8. A plasma torch as set forth in claim 1 wherein the fluid communication of the primary gas flow path with the secondary gas flow path allows an amount of primary working gas in the primary gas flow path to bleed into the secondary gas flow path in accordance with a current level at which the torch operates.

9. A plasma torch as set forth in claim 8 wherein the torch is operable at a current level of approximately 15 amperes, the fluid communication of the primary gas flow path with the secondary gas flow path allowing approximately 78 percent of the primary working gas in the primary gas flow path to bleed into the secondary gas flow path for admixture with the secondary gas in the secondary gas flow path.

10. A tip for use in a plasma arc torch of the type having a primary gas flow path for directing a primary working gas through the torch and a secondary gas flow path for directing a secondary gas through the torch, the tip having an inner surface at least partially defining the primary gas flow path and an outer surface, the tip further having at least one bleed hole extending from the inner surface to the outer surface for bleeding gas in the primary gas flow path into the secondary gas flow path for admixture with the secondary gas to form a secondary gas mixture, the at least one bleed hole being located in the tip such that admixture of the primary and secondary gases occurs generally within the torch.

11. A tip as set forth in claim 10 wherein the outer surface of the tip at least partially defines the secondary gas flow path of the torch.

12. A tip as set forth in claim 10 wherein the at least one bleed hole angles generally downward and outward from the inner surface of the tip to the outer surface of the tip.

13. A combination tip and shield cap for use in a plasma arc torch of the type having a primary gas flow path for directing a primary working gas through the torch and a secondary gas flow path for directing a secondary gas through the torch, the tip having a central exit orifice through which primary gas from the primary gas flow path exits in the form of an ionized plasma, the shield cap substantially surrounding the tip and having a central opening in generally coaxial relationship with the central exit orifice of the tip, said shield cap further having at least one secondary opening in spaced relationship with the central opening of the shield cap and in fluid communication with the secondary gas flow path for exhausting secondary gas in the secondary gas flow path from the torch, at least one of the tip and shield cap being configured for sealing the secondary gas flow path against fluid communication with the primary gas flow path intermediate the secondary opening and the central opening of the shield cap to prevent secondary gas in the secondary gas flow path from impinging on the primary gas as the primary gas exits the torch.

14. A combination tip and shield cap as set forth in claim 13 wherein the tip and shield cap have opposing surfaces in closely spaced relationship with each other when the shield cap surrounds the tip, at least one of the opposing surfaces of the tip and shield cap having a groove therein for seating a sealing member, the sealing member being sized for protruding outward from the at least one opposing surface for sealing engagement with the other of said opposing tip and shield cap surfaces.

15. A combination tip and shield cap as set forth in claim 14 wherein the opposing tip and shield cap surfaces are generally cylindric and are concentric with the central exit orifice of the tip.

16. A combination tip and shield cap as set forth in claim 14 wherein said groove is formed in the tip surface, the groove being sized for seating an O-ring defining the sealing member for sealing engagement with the opposing shield cap surface.

17. A combination tip and shield cap as set forth in claim 13 wherein the central opening of the shield cap defines a central exit opening of the torch through which primary working gas exits the torch in the form of an ionized plasma.

18. A gas mixture system for a plasma torch, the torch being of the type having a primary gas flow path for directing a primary working gas through the torch and a secondary gas flow path for directing a secondary gas through the torch, the system comprising a plurality of tips each adapted for use in the plasma torch, each tip having an inner surface at least partially defining the primary gas flow path and an outer surface, each tip further having at least one bleed hole extending from the inner surface to the outer surface for bleeding gas in the primary gas flow path into the secondary gas flow path for admixture with the secondary gas to form a secondary gas mixture, the at least one bleed hole being located in the tip such that admixture of the primary and secondary gases occurs generally within the torch, the at least one bleed hole of each tip being sized such that the amount of primary gas bled from the primary gas flow path through the at least one bleed hole of each tip is different for each tip and corresponds to a current level at which the torch operates.

19. A gas mixture system as set forth in claim 18 wherein the outer surface of each tip at least partially defines the secondary gas flow path.

20. A gas mixture system as set forth in claim 18 wherein the size of the at least one bleed hole of each tip is sized as a function of the current level at which the torch operates.

21. A gas mixture system as set forth in claim 18 wherein the number of bleed holes in each tip is a function of the current level at which the torch operates.

22. A shield cap for use with a plasma torch of the type having a primary gas flow path for directing a primary working gas through the torch and a secondary gas flow path for directing a secondary gas through the torch, the shield cap comprising a hollow body having a central longitudinal axis, an upper end adapted for connection to the torch, a lower end having a central opening on said central longitudinal axis, at least one secondary opening spaced radially outward from the central opening and in fluid communication with the secondary gas flow path for exhausting gas in the secondary gas flow path from the torch, and an annular sealing surface on the shield cap for sealing engagement with the torch to seal the secondary gas flow path against fluid communication with the primary gas flow path downstream of the fluid communication of the secondary opening with the secondary gas flow path to prevent gas in the secondary gas flow path from impinging on the primary gas as the primary gas exits the torch.

23. A shield cap as set forth in claim 22 wherein said sealing surface is engageable by an O-ring seal disposed on the torch.

24. A shield cap as set forth in claim 23 wherein said sealing surface comprises a generally cylindric surface engageable by said O-ring seal disposed on the torch.

25. A shield cap as set forth in claim 22 wherein said sealing surface comprises a generally cylindric surface, said cylindric surface having a circular groove therein receiving an O-ring seal for sealingly engaging the torch.

26. A method of operating a torch of the type having a primary gas flow path for directing a primary working gas through the torch and a secondary gas flow path for directing a secondary gas through the torch for cutting a workpiece, the method comprising the steps of:

directing primary gas to flow through the primary gas flow path to a central exit opening of the torch for exhaustion from the torch onto the workpiece in the form of an ionized plasma;

directing secondary gas to flow through the secondary gas flow path of the torch;

bleeding primary working gas in the primary gas flow path into the secondary gas flow path substantially upstream of the central exit opening of the torch for admixture with the secondary gas to form a secondary gas mixture to be exhausted from the torch generally toward the workpiece.

27. The method of claim 26 further comprising the step of sealing the secondary gas flow path from the primary gas flow path generally downstream of the bleeding of primary working gas into the secondary gas flow path to prevent secondary gas mixture in the secondary gas flow path from impinging on the primary working gas as the primary working gas exits the central exit opening of the torch in the form of an ionized plasma.

28. The method as set forth in claim 26 further comprising the step of adjusting the amount of primary working gas in the primary gas flow path bled into the secondary gas flow path in accordance with a current level at which the torch operates.