Patent Description:
The invention relates generally to the field of plasma arc cutting systems and processes. More specifically, the invention relates to improved consumable components (e.g., swirl rings including contact elements) for operating a plasma arc torch.

Plasma arc torches are widely used in the cutting and marking of materials. A plasma arc torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). The torch produces a plasma arc, i.e., a constricted ionized jet of a 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). During operation, a pilot arc is first generated between the electrode (part of the cathode) and the nozzle (part of the anode). Generation of the pilot arc can be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or by means of any of a variety of starting methods. Plasma arc torches can utilize cartridges including one or more consumable components (e.g., a nozzle, electrode, and/or a swirl ring) for ease of installation and operation.

<FIG> show a cartridge for a prior art plasma arc torch <NUM> having a nozzle <NUM>, a shield <NUM>, an electrode <NUM>, a retaining cap <NUM>, a swirl ring <NUM>, and a fixed "crown" or contact element <NUM> disposed about the swirl ring <NUM>. This contact element <NUM> does not move relative to the swirl ring <NUM>, e.g., is fixed in an axial direction relative to the swirl ring <NUM>. The contact element <NUM> passes a cutting current from a plunger <NUM> of the plasma arc torch <NUM> to the electrode <NUM>. Because plasma cutting requires a high cutting current, a solid electrical connection must be maintained between the plasma arc torch <NUM> and the electrode <NUM> to ensure proper operation and to limit or eliminate arcing, which can damage equipment and shorten component life.

This "fixed crown" design has a failure mode when the contact element <NUM> is not in full contact with the plunger <NUM> (e.g., because the cartridge is not fully tightened within the plasma arc torch <NUM>). In this failure mode, a gap <NUM> can be created between the contact element <NUM> and the plunger <NUM>, as shown in <FIG>. This gap <NUM> results in a poor electrical connection, and can cause poor performance and component failure. In addition, the poor connection can lead to arcing between the cathode (e.g., the plunger <NUM>) and the contact element <NUM>, which can destroy the entire torch instead of just one or more consumable components. What is needed is a consumable cartridge that avoids this failure mode and ensures proper and complete contact between the plunger <NUM> and the contact element <NUM>, even if the cartridge is not fully screwed on or is otherwise loose. Other examples of the known prior art are disclosed in <CIT>, <CIT> and <CIT>.

The present invention relates to improved consumables (e.g., plasma arc torch cartridges and swirl rings including contact elements) for plasma arc torches and associated methods of operation. Specifically, the design shown and described above in <FIG> is modified such that the "fixed crown" above is replaced by a "floating" contact element, which is a separate piece within the cartridge that is allowed to translate a predetermined distance (e.g., an axial length) within the torch during installation and/or operation in the torch. The contact element can be snap fitted or dropped within a swirl ring or cartridge and confined to a certain region within which there is enough space (or "play") for the contact element to slide freely. In such a configuration, proper and complete contact with the torch cathode can be maintained even if the cartridge is not fully screwed onto the torch (with the torch cathode biasing the contact element axially forward). This configuration protects the torch and ensures that proper electrical contact is maintained within the torch.

For example, one embodiment includes a "snap fit" design that allows the contact element to travel in an axial direction at the fault region during installation in the torch. Thus, instead of being rigidly fixed to the swirl ring, the contact element is located within a track or set of tracks within the swirl ring and is biased by a spring that pushes the contact element toward the torch if there is a gap (e.g., because of an untightened thread). During proper assembly the cathode will push the contact element forward slightly toward the electrode but still maintain a gap for piloting. The gap and the spring being compressed during cutting and arc ignition are a result of gas force in the swirl ring and plenum. This freedom of movement of the contact element ensures proper mating with the cathode through several stages of cartridge turning and installation.

In one aspect, the invention features a consumable cartridge for a plasma arc torch as defined in claim <NUM>.

In another aspect, the invention features a method of assembling a plasma arc torch cartridge according to claim <NUM>.

The foregoing discussion will be understood more readily from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

<FIG> is a cross-sectional view of a plasma arc torch <NUM> with a cartridge <NUM> including a "floating crown" or electrically conductive contact element <NUM> installed therein, according to an illustrative embodiment not covered by the invention. The plasma arc torch <NUM> has a nozzle <NUM>, a shield <NUM>, an electrode <NUM>, a retaining cap <NUM>, and a swirl ring <NUM>. The contact element <NUM> installed in the plasma arc torch <NUM> includes a spring <NUM> of the electrode <NUM> configured to bias the contact element <NUM> axially backward toward the plunger (cathode) <NUM>. During proper assembly, the cathode <NUM> will push the contact element <NUM> slightly forward toward the electrode <NUM> but still maintain a gap between the electrode <NUM> and the contact element <NUM> for piloting and arc generation during a beginning of operation. During cutting and/or arc ignition, this gap and the spring will be fully compressed as a result of gas forces within the swirl ring <NUM> (and/or plenum). In contrast to the prior art embodiment shown in <FIG>, this freedom of movement of the contact element <NUM> ensures proper mating with the cathode <NUM> through several stages of cartridge turning and installation.

<FIG> is a cross-sectional view of the swirl ring <NUM> (i.e., a consumable cartridge for a plasma arc torch) having a "floating crown" or electrically conductive contact element <NUM> installed therein, according to an illustrative embodiment of the invention, and <FIG> is a side view of the swirl ring of <FIG> rotated <NUM> degrees about a longitudinal axis <NUM> of the swirl ring <NUM>. The swirl ring <NUM> has a body <NUM> (e.g., a cartridge frame) having a first end <NUM> and a second end <NUM> opposite the first end <NUM>, the first and second ends defining a longitudinal axis <NUM>. The second end <NUM> includes a plurality of discrete retaining features 420A, 420B. The discrete retaining features 420A, 420B are protuberances that take the shape of projections, distensions or longitudinal extensions at the second end <NUM>. In this embodiment, there are two retaining features 420A, 420B that are diametrically opposed, but in other embodiments there are another number of discrete retaining features, including three, four, or a different number.

The contact element <NUM> is secured to the body <NUM> by the plurality of discrete retaining features 420A, 420B. The contact element <NUM> has a core <NUM>, a proximal surface <NUM>, and a distal surface <NUM>. The proximal surface <NUM> is shaped to contact a torch plunger (e.g., the cathode <NUM> shown and described in <FIG>) of the plasma arc torch upon installation into the plasma arc torch. The distal surface <NUM> is shaped to contact an electrode (e.g., the electrode <NUM> shown and described in <FIG>) of the plasma arc torch during an operation of the plasma arc torch. The contact element <NUM> is physically separate from the electrode <NUM> and is removed from direct physical contact with the electrode <NUM> when the plasma arc torch <NUM> is not in operation. The contact element <NUM> is translatable up to a predetermined distance <NUM> within the body <NUM> along the longitudinal axis <NUM> at the second end <NUM>. The contact element <NUM> can be manufactured from brass, copper, and/or another conductive material.

At least one discrete retaining feature (or protuberance) in the plurality of discrete retaining features 420A, 420B can include a means for engaging a consumable sense feature of the plasma arc torch (e.g., a switch <NUM>) during operation of the plasma arc torch. The consumable sense feature can be for sensing a presence of a consumable (e.g., the retaining cap <NUM>) secured to a torch body of the plasma arc torch, as shown in <FIG>. In addition, at least one discrete retaining feature in the plurality of discrete retaining features 420A, 420B (as shown, each discrete retaining feature) includes a guide track <NUM> for interfacing with the contact element <NUM>. The contact element <NUM> includes at least one complementary guide channel <NUM> for interfacing with the at least one discrete retaining feature in the plurality of discrete retaining features 420A, 420B. In some embodiments, the plurality of discrete retaining features 420A, 420B can include one or more axial stops 448A, 448B (or "lip" features) that serve, e.g., as a means for locking the contact element <NUM> into the cartridge. The plurality of discrete retaining features 420A, 420B is shaped to matingly engage the contact element <NUM> and to define a translation path of the contact element <NUM> within the body (e.g., corresponding to the predetermined distance <NUM>). The translation path has two or more radial interface surfaces between the contact element <NUM> and the body <NUM>.

The body <NUM> forms a swirl ring or, in other embodiments not covered by the present invention as claimed, swirl feature of the plasma arc torch. The first end of the body <NUM> includes a set of passages (e.g., passages 452A, 452B, 452C, etc.) fluidly connecting an internal surface <NUM> of the body <NUM> and an external surface <NUM> of the body <NUM>. The contact element <NUM> can include a snap fit feature <NUM> for coupling to the body <NUM>. The contact element <NUM> can be configured to slide along the longitudinal axis <NUM> during installation in the plasma arc torch upon contact with the torch plunger <NUM>. The plurality of discrete retaining features 420A, 420B and the contact element <NUM> define a set of vent passages 468A, 468B. In some embodiments, the contact element includes a "cap" feature integrally formed with the core (e.g., as shown below in <FIG>). In some embodiments, the contact element <NUM> includes scalloped edges (e.g., as shown below in <FIG>). In some embodiments, the body <NUM> is formed of a thermoplastic and/or is molded.

The embodiment of the invention shown in <FIG> has been tested in comparison to the "fixed crown" cartridge design of <FIG>. During testing, the cartridge thread for each setup was left slightly untightened to generate a gap of roughly <NUM> inches (<NUM>). Each system was run in gouging mode, which provides a lower gas pressure and a higher risk of arcing. For the "fixed crown" cartridge design of <FIG>, two test cases out of twelve failed, and in one of those two test cases, the torch was completely burned or destroyed. By comparison, when the same tests were run with the "floating crown" embodiment shown in <FIG>, the torch passed the test every time without any damage, showing that the embodiment of <FIG> provides a more robust torch and consumable design.

<FIG> show various views of another consumable cartridge <NUM> for a plasma arc torch having a contact element <NUM> installed therein, according to another illustrative embodiment of the invention (<FIG> shows a side view; <FIG> shows a top view; <FIG> shows a sectional view; <FIG> shows an exploded view). Elements of this consumable cartridge <NUM> can be substantially similar to those shown and described above in <FIG>. The consumable cartridge <NUM> includes a swirl ring <NUM> having a body <NUM>. The body includes a first end <NUM> and a second end <NUM> opposite the first end <NUM>, the first and second ends <NUM>, <NUM> defining a longitudinal axis <NUM>. The body <NUM> is shaped to matingly engage an electrode <NUM> of the plasma arc torch. The body <NUM> includes a set of protuberances 532A, 532B extending from the second end <NUM> in a direction of the longitudinal axis <NUM>. At least one protuberance 532A, 532B includes an interior guide track 536A, 536B. The swirl ring <NUM> also includes an electrically conductive contact element <NUM> confined by the set of protuberances 532A, 532B. The contact element <NUM> includes at least one guide channel 544A, 544B complementary to the at least one guide track 536A, 536B. Alignment of the contact element <NUM> with the swirl ring <NUM> is facilitated by an interaction of the at least one guide channel 544A, 544B with the at least one guide track 536A, 536B.

At least one protuberance 532A, 532B defines a region <NUM> that the contact element <NUM> can occupy during normal operation of the plasma arc torch. The first end <NUM> includes a set of passages (e.g., 552A, 552B, 552C, and similar passages) fluildly connecting an internal surface <NUM> of the swirl ring <NUM> and an external surface <NUM> of the swirl ring <NUM>. The contact element <NUM> can include a snap fit feature for coupling to the body of the swirl ring <NUM> (e.g., it can snap within the protuberances and be retained within the consumable cartridge <NUM> by the same). The electrode <NUM> includes a spring <NUM> configured to bias the contact element <NUM> toward a cathode of the plasma arc torch. The contact element <NUM> is configured to slide along the longitudinal axis <NUM> during installation in the plasma arc torch upon contact with a plunger of the plasma arc torch. The set of protuberances 532A, 532B defines a translation path (e.g., within and confined to the region <NUM>) for the contact element <NUM>. The set of protuberances 532A, 532B and the contact element <NUM> define a set of vent passages 568A, 568B. The translation path has two or more radial interface surfaces 572A, 572B between the contact element <NUM> and the swirl ring <NUM>. In some embodiments, one or more protuberances in the set of protuberances 532A, 532B can have one or more of the following linear dimensions: a height (e.g., in a direction of the longitudinal axis) of approximately <NUM> millimeters, or optionally between approximately <NUM> and <NUM> millimeters, or optionally between approximately <NUM> and <NUM> millimeters; a width (e.g., in a direction of a radius of the consumable cartridge) of approximately <NUM> millimeters, or optionally between approximately <NUM> and <NUM> millimeters, or optionally between approximately <NUM> and <NUM> millimeters; and/or a length (e.g., in a direction perpendicular to both the width and the height) of approximately <NUM> millimeters, or optionally between approximately <NUM> and <NUM> millimeters, or optionally between approximately <NUM> and <NUM> millimeters.

<FIG> is a perspective view of the contact element <NUM> for a plasma arc torch cartridge shown in <FIG>, according to an illustrative embodiment of the invention. This contact element <NUM> is electrically conductive. The contact element <NUM> has a core <NUM> (e.g., a solid core or a hollow core) and a cap <NUM>. The cap <NUM> includes one or more locating surfaces 612A, 612B for aligning with a swirl ring (e.g., swirl ring <NUM>) of a plasma arc torch cartridge and one or more channels <NUM> for interlocking with complementary protuberances of a swirl ring. The contact element <NUM> has one or more further channels <NUM> for defining a set of vent passages when engaged with one or more protuberances of a swirl ring. The contact element <NUM> can have a similar set of features on an opposing end (e.g., <NUM> degrees away from) of the contact element <NUM> for each of the one or more channels <NUM> and the further channel <NUM> (both not shown). <FIG> shows a similar contact element <NUM> with some differences. One notable difference is that the channels 654A, 654B for forming the vent passages have scalloped edges, rather than square or angular edges. One of ordinary skill in the art will readily appreciate that other shapes and configurations are also possible.

<FIG> is a flow diagram illustrating a method <NUM>, not covered by the present invention, of operation of a plasma arc torch, according to an illustrative embodiment of the invention. In a first step <NUM>, a consumable cartridge is provided for the plasma arc torch, the consumable cartridge having a cartridge frame with a first end and a second end that define a longitudinal axis, the consumable cartridge including an electrically conductive contact element confined by the cartridge frame. In a second step <NUM>, the consumable cartridge is installed in the plasma arc torch, the contact element translated in a first direction along the longitudinal axis toward the first end once contact is made with a torch plunger of the plasma arc torch. In a third step <NUM>, an electrode of the plasma arc torch is translated in a second direction opposite the first direction along the longitudinal axis, the electrode contacting the contact element during a cutting operation of the plasma arc torch. The contact element is separated from the electrode when the plasma arc torch is not performing the cutting operation.

<FIG> is a flow diagram illustrating a method <NUM> of assembling a plasma arc torch cartridge, according to an illustrative embodiment of the invention. In a first step <NUM>, a swirl ring is provided that has a body shaped to matingly engage an electrode of a plasma arc torch, the body including a first end and a second end that define a longitudinal axis, and a set of protuberances extending from the second end along a direction of the longitudinal axis, the set of protuberances including a set of guide tracks. In a second step <NUM>, an electrically conductive contact element is provided that has a set of guide channels complementary to the set of guide tracks of the swirl ring. In a third step <NUM>, the contact element is installed in the swirl ring, the guide channels of the contact element matingly engaging the set of guide tracks of the swirl ring. During installation of the contact element into the swirl ring the contact element translates a fixed distance along the longitudinal axis within the swirl ring, and wherein after installation the contact element is held securely within the plasma arc torch cartridge. In some embodiments, after installation the contact element is able to translate a fixed distance within the plasma arc torch cartridge along the longitudinal axis. In some embodiments, the translation of the contact element in a direction of the second end is limited by at least one retaining feature disposed on an interior surface of at least one of the protuberances.

Claim 1:
A consumable cartridge (<NUM>) for a plasma arc torch, the consumable cartridge comprising a swirl ring (<NUM>, <NUM>) and an electrically conductive element (<NUM>, <NUM>), the swirl ring comprising:
a body (<NUM>, <NUM>) having a first end (<NUM>, <NUM>) and a second end (<NUM>, <NUM>) opposite the first end, the first and second ends defining a longitudinal axis (<NUM>, <NUM>), the second end (<NUM>, <NUM>) including a plurality of discrete retaining features (420A, 420B, 532A, 532B), wherein the discrete retaining features are protuberances taking the shape of projections, distensions or longitudinal extensions at the second end; and
wherein the electrically conductive contact element (<NUM>, <NUM>) is secured to the body (<NUM>, <NUM>) by the plurality of discrete retaining features (420A, 420B, 532A, 532B) and freely translatable up to a predetermined distance within body (<NUM>, <NUM>) along the longitudinal axis at the second end, the contact element (<NUM>, <NUM>) having a core (<NUM>), a proximal surface (<NUM>), and a distal surface (<NUM>),
wherein the plurality of discrete retaining features (420A, 420B, 532A, 532B) are shaped to matingly engage the electrically conductive contact element (<NUM>, <NUM>),
wherein the proximal surface (<NUM>) is shaped to contact a torch plunger of the plasma arc torch upon installation into the plasma arc torch and the distal surface (<NUM>) is shaped to contact an electrode of the plasma arc torch during an operation of the plasma arc torch.