Hypertherm, Inc.

Lifeng Luo

Richard W Couch, Jr

Nicholas A Sanders

Zhipeng Lu

John Sobr

Staffan C Stenfelt

Jeffrey L Peterson

Patrik Backander

David J Rhodes

Nichols A Sanders

A plasma arc torch has a secondary gas flow that is extremely large during piercing of a workpiece to keep splattered molten metal away from the torch and thereby prevent 'double arcing'. The secondary flow exits the torch immediately adjacent the transferred plasma arc and is an extremely uniform, swirling flow. A swirl ring is located in the secondary gas flow path at the exit point. A prechamber feeds gas to the swirl ring, which is in turn fed through a flow restricting orifice. For certain applications the secondary gas is a mixture of an oxidizing gas, preferably oxygen, and a non-oxidizing gas, preferably nitrogen, in a flow ratio of oxygen to nitrogen in the range of 2:3 to 9:1. Preferably the flow ratio is about 2:1. A network of conduits and solenoid valves operated under the control of a central microprocessor regulates the flows of plasma gas and secondary gas and mixes the secondary gas. The network includes valved parallel branches that provide a quick charge capability and a set of venting valves, also electrically actuated by the microprocessor, to provide a quick discharge. In a preferred high-definition embodiment, a nozzle with a cut back outer surface and a large, conical head allows a metal seal and enhanced cooling. A two-piece cap protects the nozzle during cutting.

Plasma arc cutting process and apparatus using an oxygen-rich gas shield

Plasma arc or laser cutting uses a mix of reactive and reducing gas flows to cut sheets of stainless steel, aluminum and other non-ferrous metals. The reducing gas flow to the cut varies as a percentage of the total gas flow to maintain a reducing atmosphere down through the cut, but to leave a predominantly oxidizing atmosphere at the intersection of the cut and the bottom surface of the sheet being cut. In plasma arc cutting these flows can also be characterized as either a plasma gas flow, one that forms the arc, or a shield gas flow that surrounds the arc. The reactive gas is preferably a flow of air, oxygen, nitrogen, carbon dioxide or a combination of these gases. The reducing gas is preferably hydrogen, hydrogen 35, methane, or a mixture of these gases. For aluminum, the reactive gas is preferably air or nitrogen and the reducing gas is preferably methane or a mixture of methane and air. In laser cutting the reducing gases such as methane can be used by mixing them with reactive assist gases.

Process for high quality plasma arc and laser cutting of stainless steel

An insert securely disposed in a bottom end of an electrode has an exposed emission surface shaped to define a recess in the insert, wherein the recess is initially dimensioned as a function of the operating current level of the torch, the diameter of the insert, and the plasma gas flow pattern in the torch. The electrode has an elongated body formed of a high thermal conductivity material such as copper, and a bore disposed in the bottom end of the body along a central axis. The insert is formed of a high thermionic emissivity material, such as hafnium, and securely disposed in the bore with the emission surface exposed. The emission surface may be initially shaped by removing a predetermined amount of the high thermionic emissivity material from the insert to define a generally concave recess, a generally cylindrical recess or other shapes. When used in a torch, the electrode provides for reduced deposition of the high thermionic emissivity material on the nozzle, thereby reducing nozzle wear in the torch.

Electrode for a plasma arc torch

Circuitry and methods for reducing nozzle wear during starting of a plasma arc torch, even with a large standoff distance from a workpiece is described. The invention features a method of starting a plasma arc torch for cutting a workpiece using a pilot voltage to ionize a plasma gas and generate a pilot arc between an electrode and a nozzle. The method expedites the transfer of the arc from the nozzle to the workpiece by passing a generally smooth signal through the electrode before, during and after the arc transfers to the workpiece. A high frequency high voltage starting circuit is constructed with a pilot arc circuit isolated from a transfer arc circuit. A signal is generated which has a magnitude sufficient to ionizes a plasma gas to generate a pilot arc between the electrode and the nozzle and has a magnitude which generally increases after the pilot arc has been generated in order to expedite the transfer of the arc. The signal magnitude is, however, low enough to minimize transfer of the arc back to the nozzle.

Plasma arc cutting torch ignition circuit and method providing a forced

A high frequency, high voltage starting circuit for a plasma arc cutting torch is constructed and operated with isolation between a pilot arc circuit and a transfer arc circuit. The duration and value of the energy flow in the pilot arc after initiating the HFHV signal are controlled electronically. The maximum value is sufficient to initiate and support the pilot arc and its transfer. The duration is sufficiently long to allow the pilot arc to transfer, but sufficiently short that nozzle wear is reduced. In the preferred form both circuits have a common D.C. power supply and independent surge injector circuits each formed by a resistor and surge capacitor connected in parallel with the power supply. An L-C loop in the pilot arc circuit maintains a generally constant current output on discharge.

Plasma arc torch ignition circuit and method

A plasma arc torch uses a mix of reactive and reducing gas flows to cut sheets of stainless steel, aluminum and other non-ferrous metals. The reducing gas flow to the cut is varied as a percentage of the total gas flow to maintain a reducing atmosphere down through the cut, but to leave a predominantly oxidizing atmosphere at the intersection of the cut and the bottom surface of the sheet being out. These flows can also be characterized as either a plasma gas flow, one that forms the arc, or a shield gas flow that surrounds the arc. The reactive gas is preferably a flow of air, oxygen, nitrogen, carbon dioxide or a combination of these gases. The reactive gas is usually in the plasma gas flow, whether alone or mixed with other gases. The reducing gas is preferably hydrogen, hydrogen 35, methane, or a mixture of these gases. For aluminum, the reactive gas is preferably air or nitrogen and the reducing gas is preferably methane or a mixture of methane and air.

Process for high quality plasma arc cutting of stainless steel and

In a plasma arc cutting torch a flow of plasma gas is bypassed out of a plasma chamber, preferably at an annular gap between a pre-orifice in an inner nozzle piece and an exit nozzle orifice in an outer nozzle piece. A bypass channel formed between the inner and outer nozzle pieces directs the bypass flow to atmosphere. A metering valve or restricting orifice remote from the gap controls the amount of the bypass flow and delays the response of changes in the flow parameters in the plasma chamber to changes in the bypass flow. The pre-orifice and nozzle orifice are positioned and dimensioned to optimize the mass flow velocity and the strength of a vortex-type flow at the pre-orifice, thereby creating a virtual nozzle immediately below the electrode. The gas flow in the plasma chamber is highly uniform and very steady.

Nozzle and method of operation for a plasma arc torch

The diameter of a hafnium insert press fit into the bottom end of a copper electrode varies as a function of the level of current carried by the electrode. The diameter is the minimum necessary to support emission at that current level while also protecting the copper body against attack by the arc. The insert is generally circular and preferably extends completely through the bottom wall to a circulating flow of cooling water at a hollow interior of the electrode. The bottom wall includes an annular recess in a portion of the copper wall surrounding the insert. A coolant inlet tube extends into the recess in a spaced relationship to provide a high flow velocity of the coolant over the interior rear surface of the electrode.

Electrode for high current density plasma arc torch

A process and apparatus for reducing wear of an electrode in a plasma arc torch involves providing a substantial pressure drop in a flow of plasma gas from the torch to a plasma arc chamber defined by the electrode and a nozzle. The pressure drop is immediately before the plasma arc chamber. There is also a small, localized supply of the plasma gas located between the pressure drop and the plasma chamber. The supply is sufficient to stabilize the arc when the gas flow is cut off upstream of the pressure drop and the arc current is cut off very shortly thereafter. The pressure drop is small enough to permit an adequate flow of plasma gas to the plasma arc chamber during normal operations, but large enough to isolate residual gas in the torch from the plasma arc chamber when the arc current is cut off. The apparatus is preferably a swirl ring with an annular pre-chamber fed by a set of choke holes to feed gas to the chamber and create the pressure drop. A set of swirl holes feed gas from the pre-chamber to the plasma arc chamber.

Swirl ring and flow control process for a plasma arc torch

A process and apparatus for reducing wear of an electrode in a plasma arc torch involves altering the gas flow in a plasma chamber surrounding the electrode immediately before and continuing after cutting of the current that sustains the arc. The altering includes closing off the gas flow upstream of the chamber, switching from a swirling flow to a radial/axial flow through the plasma chamber, reducing the arc current level in conjunction with either of the above, the venting the plasma chamber to rapidly change the gas flow and pressure in the chamber. The interval is sufficient to reduce electrode wear, but short enough that the arc remains stabilized until cut-off. In the flow stop mode, a solenoid valve is placed on an inlet tube for the plasma gas. Flow altering also occurs on start up. A gas preflow is established prior to pilot arc ignition. On transfer, the flow increases to its full operating value in conjunction with an increase in the arc current. The preflow can be axial, or partially axial. Also, the type or composition of the gas used in the preflow and in the operating flow can change during the start up from a less reactive to more reactive gas.

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Lebanon, NH, United States of America

Lifeng Luo