Electric heating – Metal heating – By arc
Reexamination Certificate
1998-11-05
2001-03-27
Walberg, Teresa (Department: 3742)
Electric heating
Metal heating
By arc
C219S121480
Reexamination Certificate
active
06207923
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to plasma arc torches, and more particularly to plasma arc torches having a torch tip designed to produce a substantially columnar shield flow that surrounds the plasma arc without substantially interfering with the plasma arc.
BACKGROUND OF THE INVENTION
Plasma arc torches are widely used in the cutting or marking of metallic materials. A plasma torch generally includes an electrode mounted therein, a nozzle with a central exit orifice mounted within a torch body, electrical connections, passages for cooling and arc control fluids, a swirl ring to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle, and a power supply. The torch produces a plasma arc, which is a constricted ionized jet of a plasma gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g. argon or nitrogen), or reactive (e.g. oxygen or air).
In operation, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode). Generation of the pilot arc may be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or any of a variety of contact starting methods.
One known configuration of a plasma arc torch includes an electrode and a nozzle mounted in a special relationship relative to a shield. The nozzle is surrounded by the shield and aligned relative to a longitudinal axis extending through the nozzle and the shield such that the nozzle orifice and shield orifice are concentric relative to one another. A relatively small plasma gas flow passes through the torch and exits through the nozzle orifice. A relatively large shield gas flow passes through the space between the nozzle and the shield. The plasma gas flow passes through the nozzle exit orifice along the axis, while the shield gas flow passes through the gap at an angle relative to the axis. As such the shield flow impinges on the plasma gas flow. After impingement, the plasma arc and shield flows pass through the shield orifice together. This process can disrupt the plasma gas flow, encouraging shield gas entrainment which can result in a degraded cutting performance.
It is therefore the object of the present invention to provide an improved torch tip for a plasma arc torch, which provides a substantially columnar shield flow that does not substantially interfere with the plasma arc.
SUMMARY OF THE INVENTION
In one aspect, the invention features a plasma arc torch for cutting or marking a metallic workpiece. The torch includes a torch body having a nozzle mounted relative to an electrode in the body to define a plasma chamber. The torch body includes a plasma flow path for directing a plasma gas to the plasma chamber. The torch also includes a shield attached to the torch body. The nozzle, electrode and shield are consumable parts that wear out and require periodic replacement.
The nozzle has a hollow body portion and a substantially solid head portion formed integrally with the body portion. In one embodiment, the body portion comprises a conical section and a cylindrical section. The head portion is cylindrically shaped and defines a nozzle exit orifice that extends through the head portion. The shield includes a body portion with a fastening mechanism (e.g., threads or an interference fit) for securing the shield to the torch body in a spaced relationship relative to the nozzle. In one embodiment, the shield body portion comprises a conical section and a cylindrical section. A shield gas passes through the space between the shield body and the body portion of the nozzle. The shield also has a head portion formed integrally with the body portion which defines a shield exit orifice that has an inlet and an outlet. In one embodiment, the shield head portion is cylindrically shaped. The shield exit orifice is dimensioned such that the head portion of the nozzle extends, at least in part, to a position between the inlet and the outlet of the shield exit orifice. The position of the nozzle head portion between the inlet and outlet of the shield exit orifice (1) provides a substantially columnar flow of shield gas that passes through a gap between the inner surface of the shield head portion and the outer surface of the nozzle head portion and passes through the shield exit orifice without substantially interfering with the plasma arc and (2) prevents a substantial portion of splattered molten metal produced during marking or cutting of the workpiece from reaching the nozzle.
In another aspect, the invention features a torch tip for a plasma arc torch for cutting or marking a metallic workpiece. The torch tip includes a nozzle and a shield mounted in a mutually spaced relationship. The nozzle has a hollow body portion and a substantially solid head portion formed integrally with the body portion. In one embodiment, the body portion comprises a conical section and a cylindrical section. The head portion is cylindrically shaped and defines a nozzle exit orifice that extends through the head portion.
The shield includes a body portion with a fastening mechanism for securing the shield in a spaced relationship relative to the nozzle. In one embodiment, the body portion comprises a conical section and a cylindrical section. A shield gas passes through a space between the shield body and a body portion of the nozzle. The shield includes a head portion formed integrally with the body portion and which defines a shield exit orifice having an inlet and an outlet. The shield exit orifice is dimensioned such that the head portion of the nozzle extends, at least in part, to a position between the inlet and the outlet of the shield exit orifice. The position of the nozzle head portion relative to the inlet and outlet of the shield exit orifice (1) results in a substantially columnar flow of shield gas that passes through a gap between the inner surface of the shield head portion and the outer surface of the nozzle head portion and passes through the shield exit orifice without substantially interfering with the plasma arc and (2) prevents a substantial portion of splattered molten metal produced during marking or cutting of the workpiece from reaching the nozzle. In one detailed embodiment, the gap formed between the shield head portion and the nozzle head portion is an annular gap.
In yet another aspect, the invention features a shield for a plasma arc torch for cutting or marking a metallic workpiece. The plasma arc torch includes a nozzle mounted relative to an electrode in the torch body to define the plasma chamber. The torch body includes a plasma flow path for directing a plasma gas to a plasma chamber in which a plasma arc is formed.
The shield includes a body portion with a fastening mechanism for securing the shield to the torch body in a spaced relationship relative to the nozzle. In one embodiment, the body portion comprises a conical section and a cylindrical section. A shield gas passes through a space between the shield body and a body portion of the nozzle. The shield also has a head portion formed integrally with the body portion which defines a shield exit orifice that has an inlet and an outlet. In one embodiment, the shield head portion is cylindrically shaped. The shield exit orifice is dimensioned to receive the head portion of the nozzle so that the nozzle extends, at least in part, to a position between the inlet and the outlet of the shield exit orifice. This configuration produces a substantially columnar flow of shield gas that exits the torch without substantially interfering with the plasma arc and prevents a substantial portion of splattered molten metal produced during marking or cutting of the workpiece from reaching the nozzle.
In one detailed embodiment, the shield exit orifice can have a length to diameter ratio in the range of 0.50 to 1.00. In addition, the shield can have multiple vent holes formed in the shield body.
In yet another aspect, the invention features a nozzle for use in a plasma arc torch for marking or cutting a metallic workpiece. The t
Hypertherm, Inc.
Testa Hurwitz & Thibeault LLP
Van Quang
Walberg Teresa
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