Patent Description:
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 (cathode) and the nozzle (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.

In many prior art plasma arc torches, coolant travels along a circuitous path within the torch (e.g., forward to the nozzle, then back to the torch head, then forward to the shield, then back to the torch head), requiring a significant driving force to propel the coolant within the torch. An example of such a prior art torch is shown and described in <CIT>, entitled "Apparatus and method for a liquid cooled shield for improved piercing performance. " In this arrangement, coolant flows from a source through the plasma arc torch to a surface of the shield and back through the plasma arc torch, requiring multiple trips for the coolant to contact both the shield and the nozzle. <CIT> discloses a plasma arc torch that comprises a set of torch consumable components secured to a torch head, wherein a supply of cooling fluid flows coaxially through the torch to cool torch components and a supply of plasma gas and secondary gas flows through the torch to generate and stabilize a plasma stream for operations such as cutting workpieces. The torch consumable components, in part, comprise an electrode and a tip that include a variety of configurations for improved cooling, electrical contact, and attachment to adjacent torch components. Further, a consumables cartridge is provided for ease of use and replacement of the torch consumable components. <CIT> describes a plasma burner has an annular passage extending along an insulated tube defining the outer wall of the electrode lance and located between the electrode lance and the multi wall burner shell to deliver the auxiliary gas outwardly of the plasma gas. The nozzle forming end of the electrode lance has a coolant circulation as has the burner shell and the annular passage extends substantially to the coolant inlets and outlets of the burner. The construction avoids the formation of parasitic arcs. Still some other prior art torches have substantial deadspots in the coolant flow and/or unidirectional coolant flow which does not provide even cooling to the nozzle, shield, and other consumables in the torch tip. What is needed is a configuration in which the coolant is routed directly to the consumables, such that a minimal driving force is required to move coolant through the plasma arc torch in a substantially uniform and symmetrical manner.

The present invention relates to improved consumables such as inner caps for plasma arc torches. An interleaved series of apertures or slots, some of which carry liquid coolant and some of which carry shield gas, is arranged in an inner cap to produce a cross-flow of liquid and gas within and/or through the inner cap. An axially oriented set of holes permits the shield gas to pass to the shield, and a radially oriented set of holes permits a liquid coolant to pass from the nozzle to the shield, both within an annular portion (or "neck") of the inner cap near the plenum.

The present invention enables coolant to be moved directly through the consumables via a direct coolant pathway, minimizing the required driving force needed to propel coolant through the torch. In addition, the invention uses space more efficiently in the annular portion of the inner cap, so that certain features can be removed from the torch itself. In some embodiments, this reorganization allows the "pointiness" of the torch to be increased, which can be beneficial for robotics applications and can make it easier for the torch to fit into tight spaces.

In addition, the present invention reorganizes the inlet and the outlet to be essentially radially symmetrical, with the consumables fed from <NUM> degrees. This stands in contrast to previous designs that fed from <NUM> degrees (i.e., there was an "in" flow side and an "out" flow side), in which the inlet and outlet needed to be oriented with respect to each other, and in which dead spots and uneven cooling in the torch tip were common. A key feature is to push some of the more complex torch features into the retaining cap, allowing the complex machining processes to be done less frequently. In addition, the shield cap is allowed to be manufactured as a single piece (rather than in two pieces), which results in a savings of cost and weight. In particular, the shield cap now needs to direct coolant only in one direction. In previous technologies, the shield cap included two pieces because the coolant traveled back into the torch after cooling the nozzle. The coolant then had to be directed forward to the shield and then rearward back to the power supply by the shield cap. Because the coolant had to go both to and from the shield, it required two pieces. The direct path from the nozzle to the shield enables the present invention to use a single piece shield cap.

In one aspect, the invention features an inner cap for a liquid-cooled plasma arc torch. The inner cap includes an inner component having an interior surface and an exterior surface, the inner component defining a longitudinal axis of the inner cap. The inner cap also includes an outer component circumferentially disposed around the inner component, the outer component having an interior surface, an exterior surface, and an annular region. The annular region extends beyond the inner component along the longitudinal axis toward a torch end of the inner cap. The inner cap also includes a set of radial liquid passageways formed in the annular region of the outer component and oriented perpendicularly to the longitudinal direction. The set of liquid passageways is configured to pass a liquid coolant from a nozzle of the plasma arc torch to a shield of the plasma arc torch. The inner cap also includes a gas channel formed within the inner cap. The gas channel includes a first portion defined, at least in part, by a portion of the exterior surface of the inner component and a portion of the interior surface of the outer component. The gas channel also includes a second portion defined within the annular region of the outer component. The second portion includes a set of axial gas passageways configured to pass the gas to the shield of the plasma arc torch. In the annular region, subsets of passageways in the set of liquid passageways and the set of gas passageways alternate in a rotational direction about the longitudinal axis to create a cross-flow of liquid and gas during operation of the plasma arc torch.

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 perspective view of an inner cap <NUM> for a liquid-cooled plasma arc torch, according to an illustrative embodiment of the invention, and <FIG> is a half-sectional perspective view of the inner cap <NUM> shown in <FIG>. The inner cap <NUM> includes a substantially hollow body <NUM> having a longitudinal axis <NUM>, a first end <NUM>, and a second end <NUM>. The first end <NUM> includes an annular portion <NUM> configured to be disposed proximate a torch tip of the plasma arc torch. The inner cap <NUM> includes a liquid passage <NUM> (e.g., having a first set of ports 114A-114F in the annular portion <NUM>) that is formed within the body <NUM> and shaped to convey a liquid therethrough. The inner cap <NUM> also includes a gas passage <NUM> (e.g., having a second set of ports 118A-118C formed in the annular portion <NUM>) that is formed within the body <NUM> and shaped to convey a gas therethrough. The gas passage is configured to transport a shield gas and the liquid passage is configured to transport a consumable coolant.

As shown in the embodiment of <FIG>, subsets of ports in the first set of ports 114A-114F direct the liquid in a radial direction with respect to the longitudinal axis <NUM> and alternate, in a rotational direction about the longitudinal axis <NUM>, with subsets of ports in the second sets of ports 118A-118C that direct the gas in a direction substantially parallel with the longitudinal axis <NUM>. For example, in <FIG>, subsets of ports alternate as follows in a radial direction about the longitudinal axis <NUM>: 114A-114C; 118A; 114D-F; 118B; and so on, such that the alternation pattern is three liquid ports followed by one gas port. In this way, the first set of ports can be interleaved with the second set of ports to create alternating cross-flow regions of liquid and gas through the tip of the inner retaining cap during operation of the plasma torch. In such arrangements, the inner cap <NUM> can create a full radial "showerhead" effect, with liquid passing radially in multiple streams through the first set of ports, and gas passing perpendicularly or substantially perpendicularly through the second set of ports. This arrangement promotes, for example, more even cooling (e.g. uniform cooling around all <NUM> degrees) and gas flow.

Generally, subsets of ports can include one or more ports each. In some embodiments, subsets of ports alternate in a regular pattern, e.g., one gas port, followed by two liquid ports, followed by one gas port, followed by two liquid ports. In some embodiments, subsets of ports alternate in an irregular pattern, e.g., one liquid port, two gas ports, three liquid ports, two gas ports. In some embodiments, only one liquid port and/or one gas port is used. In some embodiments, the sets of ports are oriented perpendicular or substantially perpendicular to each other, e.g., each port in the first set of ports is perpendicular or substantially perpendicular to a corresponding port in the second set of ports. In the invention, the first set of ports is oriented perpendicular to the longitudinal axis, and the second set of ports is oriented parallel to the longitudinal axis. In some embodiments, the first set of holes includes between five and nine holes and the second set of holes includes between six and eighteen holes. In some embodiments, the axially oriented gas flow holes (e.g., including but not limited to 118A-C) have a total cross-sectional area of at least <NUM> mm2 (. <NUM> square inches). In some embodiments, the radially oriented coolant holes (e.g., including but not limited to 114A-F) have a total cross-sectional area of at least about <NUM> mm2 (<NUM> square inches), or optionally about <NUM> mm2 (<NUM> square inches). In other embodiments, the total cross-sectional area of the radially oriented coolant holes is as large as the other constraints on the plasma arc torch will permit. In some embodiments, holes are uniformly distributed around the circumference to provide even cooling to the shield.

The inner cap <NUM> includes an outer portion (or outer component) <NUM> and an inner portion (or inner component) <NUM>. The outer portion <NUM> has an exterior surface 122A and an interior surface 122B, and the inner portion <NUM> has an exterior surface 123A and an interior surface 123B. The outer portion <NUM> at least substantially encloses the inner portion <NUM>. The outer portion <NUM> can be formed of plastic, and the inner portion <NUM> can be formed of a metal or metal alloy, such as brass. In some embodiments, the inner cap <NUM> includes a snap feature <NUM> configured to secure the outer portion <NUM> to the inner portion <NUM>. In some embodiments, the snap feature <NUM> includes a ridge or a notch in the outer portion <NUM> and a corresponding protrusion in the inner portion <NUM>, the protrusion fitting snugly into the ridge or notch to secure the inner portion <NUM> to the outer portion <NUM>. In some embodiments, the inner cap <NUM> is electrically insulative. In some embodiments, the first end <NUM> includes a tapered portion <NUM> adjacent to the annular portion <NUM>. In some embodiments, the tapered portion <NUM> and the annular portion <NUM> form a neck portion.

As shown in <FIG>, a first portion <NUM> of the gas channel is defined, at least in part, by a portion of the exterior surface 123A of the inner component <NUM> and a portion of the interior surface 122B of the outer component <NUM>. A second portion <NUM> of the gas channel is defined within the annular region <NUM> of the outer component <NUM>. In some embodiments, at least one of the first and second sets of ports can include slots in the body <NUM>. Slots can be desirable as they are easier to manufacture than holes, which can be more expensive to drill. Slots can also be desirable because they permit more coolant flow area than some alternative geometries, and in some embodiments create less of a pressure drop as a result of drag forces from the walls of the slots. In some embodiments, the inner cap <NUM> includes a third set of ports <NUM> (e.g., 130A, 130B, 130C) aligned with the first set of ports <NUM> to form a set of liquid passageways through the inner cap.

The second portion <NUM> includes a set of axial gas passageways configured to pass the gas to the shield of the plasma arc torch (shown and described below in <FIG>). The second portion <NUM> can include a set (e.g., of six) of holes drilled in the axial direction. The axial holes can be "pass through" only, e.g., they do not have a swirl impact (as opposed to in past designs, in which they imparted some directionality to the fluid flow). Generally, there should be a sufficient number and/or cross-sectional area of axial holes so that the holes are not a choke point in the system. In addition, a ratio of flow area between the second set of holes and a set of metering holes (e.g., in the swirling insulator <NUM> shown and described below in <FIG>) in the first end of the inner cap can be at least <NUM>:<NUM>. In one exemplary configuration, the ratio is about <NUM>:<NUM>. In some embodiments, the inner cap <NUM> includes a plenum region <NUM> formed at least partially within the body <NUM>.

<FIG> is a cross-sectional view of an inner cap <NUM> for a liquid-cooled plasma arc torch installed in a plasma arc torch <NUM>, according to an illustrative embodiment of the invention. In this view, the features of the inner cap <NUM> shown and described above correspond to the numerals in <FIG>. When installed in the plasma arch torch <NUM>, the inner cap <NUM> surrounds (e.g., at least partially surrounds) the nozzle <NUM>. Shield gas flows through the passageway <NUM> along flow path <NUM> within the inner cap <NUM> and impinges on an interior surface 204A of the shield <NUM>. Shield gas then continues through an orifice 212A in the swirling insulator <NUM> of the plasma arc torch <NUM>. Shield gas then continues down passageway <NUM> and out the front orifice <NUM> of the plasma arc torch <NUM>. Meanwhile, liquid coolant flows from the nozzle <NUM> through passageway <NUM> of the inner cap <NUM> along flow path <NUM>. Liquid coolant then passes from the nozzle <NUM> side of the inner cap <NUM> to the shield <NUM> side of the inner cap <NUM> into passageway <NUM> (e.g., impinging on contact point <NUM>), up back to the torch head. In this way, the total distance traveled by the liquid coolant is reduced over past designs, as the liquid coolant is able to pass directly from the nozzle to the shield, using the shortest path between these two consumables.

Claim 1:
An inner cap (<NUM>) for a liquid-cooled plasma arc torch, the inner cap comprising:
an inner component (<NUM>) having an interior surface (123B) and an exterior surface (123A), the inner component defining a longitudinal axis of the inner cap;
an outer component (<NUM>) circumferentially disposed around the inner component, the outer component having an interior surface (122B), an exterior surface (122A), and an annular region (<NUM>),
the annular region extending beyond the inner component along the longitudinal axis toward a torch end;
a set of radial liquid passageways (114A-F) formed in the annular region of the outer component and oriented perpendicularly to the longitudinal direction, the set of liquid passageways configured to pass a liquid coolant from a nozzle of the plasma arc torch to a shield of the plasma arc torch; and
a gas channel formed within the inner cap, the gas channel comprising:
a first portion (<NUM>) of the gas channel defined, at least in part, by a portion of the exterior surface of the inner component and a portion of the interior surface of the outer component; and
a second portion (<NUM>) of the gas channel defined within the annular region of the outer component, the second portion including a set of axial gas passageways (118A-C) configured to pass the gas to the shield of the plasma arc torch,
wherein, in the annular region, subsets of passageways in the set of liquid passageways and the set of gas passageways alternate in a rotational direction about the longitudinal axis to create a cross-flow of liquid and gas during operation of the plasma arc torch.