Arc torch nozzle shield for plasma

• US 5,132,512 A
• Filed: 06/21/1991
• Issued: 07/21/1992
• Est. Priority Date: 06/07/1988
• Status: Expired due to Term

• Current Assignee: Hypertherm Incorporated
• Original Assignee: Hypertherm Incorporated
• Inventors: Couch, Richard W. Jr., Sanders, Nicholas A.
• Primary Examiner(s): Paschall, Mark H.
• Application Number:
  US07/718,953
• Time in Patent Office: 396 Days
• Field of Search: 219/121.5, 219/121.51, 219/121.55, 219/121.54, 219/121.48, 219/75
• US Class Current: 219/121.5
• CPC Class Codes: B23K 10/006 Control circuits therefor circuits for plasma torches H05H1/36
• CPC Class Codes: H05H 1/28 Cooling arrangements
• CPC Class Codes: H05H 1/30 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/28 takes precedence
• CPC Class Codes: H05H 1/34 Details, e.g. electrodes, nozzles
• CPC Class Codes: H05H 1/341 Arrangements for providing coaxial protecting fluids
• CPC Class Codes: H05H 1/3421 Transferred arc or pilot arc mode
• CPC Class Codes: H05H 1/3442 Cathodes with inserted tip
• CPC Class Codes: H05H 1/3457 Nozzle protection devices
• CPC Class Codes: H05H 1/3468 Vortex generators
• CPC Class Codes: H05H 1/3478 Geometrical details

Abstract

A plasma arc cutting torch, particularly one operating in the 0-200 ampere range, has a shield mounted at its lower end adjacent a workpiece to block splattered molten metal from reaching a nozzle of the torch. The shield is electrically insulated, preferably by mounting it on an insulating ring that is itself secured on a cap screwed onto the torch body. A secondary gas flow through the torch passes through the space between the nozzle and the shield to provide cooling. Bleed ports in the shield allow an enhanced flow rate with the remaining flow being at a rate, in conjunction with the size of an exit orifice in the shield, to stabilize the plasma arc. The bleed ports are outwardly angled away from the arc. Canted ports in the secondary gas flow path, but before the bleed ports, produce a swirling of the gas flow which enhances the quality of the cut. A flow control system, preferably one utilizing parallel branch conduits and control valves, allows the selection of flow rates for the secondary gas depending on the cutting conditions.

Claims

1. In a plasma arc torch having a body, an electrode mounted within the body, a nozzle with an outlet orifice mounted on the body at one end thereof, means for introducing a primary gas fl:

w passing through the body, between the electrode and the nozzle, and exiting through the nozzle outlet orifice, and means for directing an electrical current between said electrode and said nozzle to produce a plasma arc exiting the torch through said nozzle orifice to pierce and then cut a metal workpiece, the imprivement comprising,

a shield mounted on said torch body, said shield generally surrounding said nozzle in a spaced relationship and having an exit orifice aligned with said nozzle orifice,

means for insulating said shield electrically from said body to prevent double arcing, and

means for producing a secondary gas flow through said body, said secondary gas flow passing through the space between said nozzle and said shield at a rate sufficient to cool the shield, said secondary gas flow means including at least one opening in said shield in fluid communication with said space and located before said exit orifice to bleed off a portion of the secondary gas flow, said at least one opening being angled from the vertical at an angle greater than zero degrees.

2. A shield member for a plasma arc torch that pierces and cuts a metallic workpiece and is so piercing and cutting produces a splattering of molten metal directed at the torch, the shield member protecting a nozzle having a central exit port through which a plasma jet exits and attaches to the workpiece, the shield member comprising:

a generally cylindrical sidewall and an end wall extending generally transversely to the plasma jet exiting the nozzle, said sidewall and said end wall being formed of a metallic material with good heat transfer properties;

an exit orifice formed in said end wall generally aligned with said nozzle exit port and having a sufficiently large cross sectional area that it does not interfere with said arc, while being sufficiently small that substantially all of the splattered molten metal strikes the shield member without reaching the nozzle,

at least one bleed port formed in said shield member and sized and located to divert a first portion of a cooling gas flowing toward the exit orifice between said shield member and the nozzle to the exterior of said shield member so that the remaining second portion of the gas flow impinging on the plasma arc does not destabilize it, and

means for securing the shield member to the torch with said end wall and sidewall of the shield in a spaced relationship with the nozzle to define therebetween a flow path for the cooling gas flow.

3. The shield member of claim 2 wherein said securing means comprises a flange portion extending outwardly from the upper end of said cylindrical wall and a further cylindrical portion extending upwardly toward and secured replaceably to said torch.

4. The protected member according to claim 2 wherein said at least one bleed port comprises a plurality of ports which circle said exit orifice.

5. The protected member according to claim 2 wherein said bleed ports are formed in said end wall.