Patent Description:
Plasma arc torches are widely used for high temperature processing (e.g., heating, cutting, gouging and marking) of materials. A plasma arc torch generally includes a torch head, an electrode mounted within the torch head, an emissive insert disposed within a bore of the electrode, a nozzle with a central exit orifice mounted within the torch head, a shield, electrical connections, passages for cooling, passages for arc control fluids (e.g., plasma gas) and a power supply. A swirl ring can be used to control fluid flow patterns in the plasma chamber formed between the electrode and the nozzle. In some torches, a retaining cap is used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal. Gases used in the torch can be non-reactive (e.g., argon or nitrogen), or reactive (e.g., oxygen or air).

Design considerations for a plasma arc torch include features for cooling, since a plasma arc generated can produce temperature in excess of <NUM>,<NUM>, which, if not controlled, can destroy the torch, particularly the nozzle. That is, the erosion rate of a nozzle is affected by the cooling efficiency at the nozzle. Efficient cooling can help to maintain a relatively low temperature, which leads to a lower erosion rate. Prior art nozzles, such as the nozzles described in <CIT>, include a toroidal chamber configured to allow fluid flows through and along the chamber to promote convective cooling of the nozzle. Specifically, a fluid enters the chamber from one side of the nozzle, flows around the nozzle within the chamber to the other side of the nozzle, and exits the nozzle from the opposite side of the nozzle. Such convective cooling tends to promote turbulence in the fluid flow and results in unevenness in cooling as the cooling fluid enters one side of the nozzle and exit from the opposite side at a warmer temperature. There is a need for nozzle cooling features that can provide smooth, laminar fluid flows while enabling uniform cooling around substantially the entire circumference of the nozzle.

<CIT> discloses an example of water cooled nozzle in a plasma arc torch.

It is therefore an objective of the present invention to provide nozzle designs that optimize coolant flow through the nozzles, thereby improving service life of the nozzles and increasing cut quality. In some embodiments, a cooling waist is provided around an external surface of a nozzle to enable laminar coolant flow and uniform nozzle cooling about the perimeter of the nozzle.

In one aspect, a nozzle for a liquid-cooled plasma arc torch according to claim <NUM> is provided.

In some embodiments, the liquid inlet slope comprises an axial alignment flange configured to axially align the nozzle with another component of the plasma arc torch.

In some embodiments, the cooling waist is generally located in a center portion of the body.

In some embodiments, the nozzle further comprises a third sealing member located between the second sealing member and the proximal end of the body. In some embodiments, a vent hole is located between the third sealing member and the second sealing member. The vent hole is configured to connect an interior surface of the body to the exterior surface of the body. A supply hole is located between the third sealing member and the proximal end of the body. The supply hole is configured to connect an exterior surface of the body to the interior surface of the body. A vent hole is located between the first sealing member and the distal end of the body. The vent hole is configured to connect an interior surface of the body to a shield gas supply channel.

In some embodiments, a retaining cap is coupled to the exterior surface of the nozzle body to define a chamber in cooperation with the cooling waist. In some embodiments, the chamber has a volume of about <NUM><NUM> (<NUM> cubic inches).

In another aspect, a method according to claim <NUM> is provided for liquid cooling a plasma-cutting nozzle in a plasma arc torch.

In some embodiments, the method further comprises sealing the nozzle at one or more of a first sealing location between the outlet slope and the distal end of the body, a second sealing location between the proximal end of the body and the inlet slope, and a third sealing location between the second sealing member and the proximal end of the body. In some embodiments, the method further comprises venting at least a portion of a gas flow through at least one of a first vent hole located between the third sealing location and the second sealing location and a second vent hole between the first sealing location and the distal end of the body. In some embodiments, the method further comprises supplying a gas flow into an interior region of the nozzle through a supply hole located between the third sealing location and the proximal end of the body.

In some embodiments, the method includes coupling a retaining cap to the exterior surface of the body to create a chamber in cooperation with the cooling waist. In some embodiments, the chamber has a volume of about <NUM><NUM> (<NUM> cubic inches).

In some embodiments, the method includes axially aligning the nozzle in relation to another component in the plasma arc torch using an axial alignment flange at the inlet slope.

In some embodiments, the method includes operating the plasma arc torch at about <NUM> amps or less.

The advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings.

<FIG> is a cross-sectional view of a liquid-cooled plasma arc torch <NUM> with a nozzle <NUM> having a cooling waist <NUM>, according to an illustrative embodiment of the present invention. The plasma arc torch <NUM> includes a torch body <NUM> having a current ring <NUM> and a torch tip <NUM> having multiple consumables, for example, an electrode <NUM>, the nozzle <NUM>, an inner retaining cap <NUM>, an outer retaining cap <NUM>, a swirl ring <NUM>, and a shield <NUM>. In the torch tip <NUM>, the nozzle <NUM> is spaced from the electrode <NUM> and has a central nozzle exit orifice <NUM>. The swirl ring <NUM> is mounted around the electrode <NUM> and configured to impart a tangential velocity component to a plasma gas flow, thereby causing the plasma gas flow to swirl. The inner retaining cap <NUM> is securely connected (e.g., threaded) to the torch body <NUM> to retain the nozzle <NUM> to the torch body <NUM> and radially and/or axially position the nozzle <NUM> with respect to a longitudinal axis of the torch <NUM>. The shield <NUM>, which includes a shield exit orifice <NUM>, is connected to the outer retaining cap <NUM> that secures the shield <NUM> to the torch body <NUM>. In some embodiments, the nozzle exit orifice <NUM> and optionally, the shield exit orifice <NUM>, define a plasma arc exit orifice through which a plasma arc is delivered to a workpiece during torch operation. The torch <NUM> can additionally include electrical connections, passages for cooling, passages for arc control fluids (e.g., plasma gas). In some embodiments, the liquid-cooled plasma arc torch <NUM> of <FIG> is operated at a current of about <NUM> amperes.

<FIG> are isometric and sectional views, respectively, of the nozzle <NUM> of <FIG>, according to an illustrative embodiment of the present invention. As shown, the nozzle <NUM> has an elongated, thermally conductive body defining a longitudinal axis A extending therethrough and includes a distal end/portion <NUM>, a central portion <NUM>, and a proximal end/portion <NUM> along the longitudinal axis A. The distal end <NUM> of the nozzle body is configured to define the nozzle exit orifice <NUM> through which a plasma jet exits the nozzle <NUM>.

In some embodiments, the central portion <NUM> defines the cooling waist <NUM> located circumferentially about an exterior surface of the nozzle <NUM> for conducting a liquid flow over at least a portion of the nozzle <NUM>. In some embodiments, the cooling waist <NUM> extends at least about <NUM>% of the length of the nozzle <NUM> along the longitudinal axis A. As shown in <FIG>, the cooling waist <NUM> is generally located in the middle of the nozzle <NUM> along the longitudinal axis A.

The cooling waist <NUM> includes a liquid inlet slope <NUM>, a liquid outlet slope <NUM> and a heat exchange region <NUM> between the liquid inlet slope <NUM> and the liquid outlet slope <NUM>. As illustrated, the liquid inlet slope <NUM> is proximal to the heat exchange region <NUM>, which is proximal to the liquid outlet slope <NUM>, such that the liquid inlet slope <NUM> and the liquid outlet slope <NUM> are at different axial locations (with respect to longitudinal axis A) separated by the heat exchange region <NUM>. In some embodiments, the heat exchange region <NUM> extends substantially parallel to the longitudinal axis A, while each of the liquid inlet slope <NUM> and the liquid outlet slope <NUM> is oriented at a non-zero angle relative to the heat exchange region <NUM> (i.e., relative to the longitudinal axis A). In some embodiments, the length of the cooling waist <NUM> along the longitudinal axis A (i.e., extending from the outer edge of the liquid inlet slope <NUM> to the outer edge of the liquid outlet slope <NUM>) is about <NUM> (<NUM> inches). The length of the relatively flat heat exchange region <NUM> along the longitudinal axis A is about <NUM> (<NUM> inches). In some embodiments, the liquid inlet slope <NUM> and the liquid outlet slope <NUM> are oriented generally perpendicular to the longitudinal axis A. In some embodiments, due in part to the axial separation between the inlet slope <NUM> and the outlet slope <NUM>, the cooling waist <NUM> is configured to facilitate an outward radial laminar flow of a liquid coolant therethrough, such that the liquid coolant entering the liquid inlet slope <NUM> does not substantially intermingle with the liquid coolant exiting from the liquid outlet slope <NUM>. Laminar flow of the liquid coolant is desirable because it provides smoother flow of a liquid coolant through the torch <NUM>. Since the liquid coolant is adapted to move from one torch component to another, laminar coolant flow generally results in less pressure drop across the cooling circuit.

In some embodiments, the portion of the nozzle body between the liquid outlet slope <NUM> and the distal end <NUM> defines a groove <NUM> on its exterior surface, where the groove <NUM> is configured to house a first sealing member <NUM>, which may be elastomeric, such as an o-ring. When the nozzle <NUM> is installed into the plasma arc torch <NUM>, surface-to-surface contact between the nozzle <NUM> and the adjacent inner retaining cap <NUM> deforms the first sealing member <NUM> in the groove <NUM> to provide a liquid-tight seal between the nozzle <NUM> and the inner retaining cap <NUM> in that region.

In some embodiments, the portion of the nozzle body between the liquid inlet slope <NUM> and the proximal end <NUM> defines at least one groove <NUM> on its exterior surface, where the groove <NUM> is configured to house a second sealing member <NUM>, which may be elastomeric, such as an o-ring. When the nozzle <NUM> is installed into the plasma arc torch <NUM>, surface-to-surface contact between the nozzle <NUM> and an adjacent torch component, such as the current ring <NUM> of <FIG>, deforms the second sealing member <NUM> in the groove <NUM> to provide a liquid-tight seal between the nozzle <NUM> and the current ring <NUM> in that region. Generally, the sealing members <NUM> and <NUM> are configured to confine the coolant flow to within the cooling waist <NUM>. In some cases, the nozzle <NUM> is provided with a third sealing member <NUM> housed in a grove <NUM> that is located on the exterior surface of the nozzle body between the second sealing member <NUM> and the proximal end <NUM> of the nozzle <NUM>. Thus, the third sealing member <NUM> is axially proximal to the second sealing member <NUM>. The third sealing member <NUM> is configured to provide another liquid-tight seal between the nozzle <NUM> and the current ring <NUM>.

In some embodiments, the liquid inlet slope <NUM> includes an alignment flange <NUM> extending radially from the exterior surface of the nozzle body. The alignment flange <NUM> is configured to axially align the nozzle <NUM> with another component of the plasma arc torch <NUM>, such as the current ring <NUM>, during assembly of the torch <NUM>. Thus, the liquid inlet slope <NUM> is adapted to extend higher in a direction perpendicular to the longitudinal axis A than the liquid outlet slope <NUM>.

In some embodiments, a supply hole <NUM> is positioned between the third sealing member <NUM> and the proximal end <NUM> of the nozzle body. The supply hole <NUM> is configured to connect an exterior surface of the nozzle body to the interior surface of the nozzle body to conduct a supply of plasma gas radially into the interior region of the nozzle <NUM>. The third sealing member <NUM> can be used to direct the plasma gas to flow through the supply hole <NUM> and into the area between the nozzle <NUM> and the swirl ring <NUM>. In some embodiments, a vent hole <NUM> is positioned between the first sealing member <NUM> and the distal end <NUM> of the nozzle body. The vent hole <NUM> is configured to connect an interior surface of the nozzle body to the exterior surface of the nozzle body to conduct a plasma gas flow radially away from the nozzle <NUM>. For example, the vent hole <NUM> is in fluid communication with a shield gas supply channel <NUM> between an exterior surface of the nozzle <NUM> and an interior surface of the shield <NUM>, as shown in <FIG>. In operation, a plasma gas flow from the nozzle <NUM> can be vented to the shield gas supply channel <NUM> via the vent hole <NUM> to supplement the shield gas in the channel <NUM>. The plasma gas vented into the shield gas channel <NUM> is adapted to preheat the shield gas, which adds more heat energy to a cut by the torch <NUM> and allows more assist gas to move the molten metal produced during the cut.

In some embodiments, a vent hole (not shown in <FIG>, but shown as vent hole <NUM> in <FIG>) is positioned between the second sealing member <NUM> and the third sealing member <NUM>. The vent hole is configured to connect an interior surface of the nozzle body to the exterior surface of the nozzle body to conduct a plasma gas flow radially away from the nozzle <NUM>. The vent hole is adapted to be connected to a vent passage, which allows ionized plasma gas from the torch <NUM> to vent to atmosphere.

In some embodiments, the exterior surface of the nozzle <NUM> at the cooling waist <NUM> and an interior surface of the adjacent retaining cap <NUM> cooperatively define a coolant chamber <NUM>, as illustrated in <FIG>. The coolant chamber <NUM> can have a volume of about <NUM><NUM> (<NUM> cubic inches). The coolant chamber <NUM> is configured to facilitate conductive cooling to other sections of the nozzle <NUM>. For example, the relatively wide width of the coolant chamber <NUM> allows the cooling fluid to move quickly therethrough and the resulting high velocity flow promotes cooling.

<FIG> is a cross-sectional view of another plasma arc torch <NUM> with a nozzle <NUM> having a cooling waist <NUM>, according to an illustrative embodiment of the present invention. The plasma arc torch <NUM> can be operated at a current of about <NUM> amperes. <FIG> are isometric and sectional views of the nozzle <NUM> of <FIG>, according to an illustrative embodiment of the present invention. The nozzle <NUM>, including the nozzle waist <NUM>, is substantially similar to the nozzle <NUM> and the nozzle waist <NUM>, respectively, of <FIG>, <FIG>. For example, same as the nozzle <NUM>, the nozzle <NUM> includes a first sealing member <NUM> (corresponding to the sealing member <NUM>), a second sealing member <NUM> (corresponding to the sealing member <NUM>), and a third sealing member <NUM> (corresponding the sealing member <NUM>). A vent hole <NUM> is positioned between the second sealing member <NUM> and the third sealing member <NUM> to conduct a plasma gas flow radially away from the nozzle <NUM> and into the torch body. As shown, the nozzle <NUM> additionally includes a supply hole <NUM>, same as the supply hole <NUM> of the nozzle <NUM>, positioned between the third sealing member <NUM> and the proximal end of the nozzle <NUM> to conduct a supply of plasma gas radially into the interior region of the nozzle <NUM>. Generally, the second sealing member <NUM> is configured to fluidly insulate the vented plasma gas from the cooling fluid in the waist <NUM>, and the third sealing member <NUM> is configured to fluidly insulate the vented plasma gas from the plasma gas supply that flows into the swirl ring <NUM> through the supply hole <NUM>.

In general, a nozzle with a cooling waist, such as the nozzle <NUM> described above with references to <FIG>, <FIG> and the nozzle <NUM> described above with reference to <FIG> can be incorporated into a variety of plasma arc torches that require liquid cooling. For example, the nozzle and the cooling waist described in the present application can be installed in liquid-cooled torches operated at about <NUM> amperes or less, such as at about <NUM> amperes, about <NUM> amperes, and/or about <NUM> amperes.

<FIG> is a diagram illustrating a process <NUM> for liquid cooling a plasma-cutting nozzle in a plasma arc torch, according to an illustrative embodiment of the present invention. The plasma-cutting nozzle comprises a cooling waist, such as the nozzle <NUM> described above with references to <FIG>, <FIG> or the nozzle <NUM> described above with reference to <FIG>. For the purpose of illustration, the process <NUM> is described with reference to the nozzle <NUM>. During cooling, a liquid coolant flow is directed along the inlet slope <NUM> of the cooling waist <NUM> of the nozzle <NUM> at a non-zero angle (step <NUM>), such as at an angle generally perpendicular to the longitudinal axis A. The liquid coolant flow is adapted to be introduced to the inlet slope <NUM> from the torch body <NUM> via a coolant nozzle supply channel <NUM> that is in part formed by an interior surface of the inner retaining cap <NUM>, as shown in <FIG>. The heat exchange region <NUM> of the cooling waist <NUM> then conducts the liquid coolant flow axially in a distal direction toward the outlet slope <NUM> of the nozzle <NUM> (step <NUM>), where the heat exchange region <NUM> is substantially parallel to the longitudinal axis A. The outlet slope <NUM> of the cooling waist <NUM> further directs the liquid coolant flow radially outward away from the nozzle <NUM> at a non-zero angle (step <NUM>), such as a at an angle generally perpendicular to the longitudinal axis A.

In some embodiments, the radial outward flow of the liquid coolant allows the liquid coolant flow to travel along a coolant shield channel <NUM> defined between an exterior surface of the inner retaining cap <NUM> and an interior surface of the shield <NUM>, as illustrated in <FIG>. The coolant shield channel <NUM>, in fluid communication with the outlet slope <NUM> of the nozzle cooling waist <NUM>, conducts the coolant flow proximally toward the torch body <NUM> to further cool the shield <NUM> and the outer retaining cap <NUM>. This coolant flow pattern has the advantage of reducing the space in the torch <NUM> used to redirect the coolant flow from the nozzle <NUM> to the shield <NUM>. Specifically, it allows the coolant to directly flow from the nozzle <NUM> to the shield <NUM> without being routed back into the torch <NUM>.

In some embodiments, the liquid coolant flow through the cooling waist <NUM> forms a substantially laminar flow, such that the liquid coolant entering the inlet slope <NUM> does not substantially intermingle with the liquid coolant exiting from the outlet slope <NUM>. Further, the axial liquid flow from the inlet slope <NUM> to the outlet slope <NUM> is substantially even around a circumference of the nozzle <NUM>. For example, the coolant flow enters the inlet slope <NUM> around substantially the entire circumference of the nozzle <NUM>. The coolant flow then cools the heat exchange region <NUM> uniformly around the circumference of the nozzle <NUM>. The coolant flow is directed away via the outlet slope <NUM> around the circumference of the nozzle <NUM>. The coolant flow does not travel laterally or circumferentially within the cooling waist <NUM>, but travels in a direction parallel to longitudinal axis A. The liquid coolant flow also does not enter from one lateral side of the nozzle <NUM> and exit from the other side. Rather, it is adapted to enter and exit from the same side of the nozzle <NUM> in a straight path generally parallel to the longitudinal axis of the nozzle <NUM>.

In some embodiments, the process <NUM> includes supplying a plasma gas flow into an interior region of the nozzle <NUM> through a supply hole disposed in the nozzle body, such as the supply hole <NUM> located between the third sealing member <NUM> and the proximal end <NUM> of the nozzle <NUM> of <FIG> or the supply hole <NUM> located between the third sealing member <NUM> and the proximal end of the nozzle <NUM> of <FIG>. In some embodiments, the process <NUM> includes venting at least a portion of the gas flow through one or more vent holes, such as the vent hole <NUM> of the nozzle <NUM> located between the third sealing member <NUM> and the second sealing member <NUM> of the nozzle <NUM> and/or the vent hole <NUM> of the nozzle <NUM> located between the first sealing member <NUM> and the distal end <NUM> of the nozzle <NUM>.

It should be understood that various aspects and embodiments of the invention can be combined in various ways. Based on the teachings of this specification, a person of ordinary skill in the art can readily determine how to combine these various embodiments. Modifications may also occur to those skilled in the art upon reading the specification.

Claim 1:
A nozzle (<NUM>) for a liquid-cooled plasma arc torch, the nozzle comprising:
a thermally conductive body having a distal end, a proximal end, and a longitudinal axis extending therethrough;
a plasma arc exit orifice (<NUM>) at the distal end of the thermally conductive body;
a cooling waist (<NUM>) located circumferentially about an exterior surface of the thermally conductive body, the cooling waist including:
a liquid inlet slope (<NUM>) disposed about a circumference of the thermally conductive body for receiving a liquid coolant flow toward the nozzle,
a liquid outlet slope (<NUM>) disposed about a circumference of the thermally conductive body and located at a different axial location along the longitudinal axis from the liquid inlet slope, and
a heat exchange region (<NUM>) between the liquid inlet slope and the liquid outlet slope, wherein the heat exchange region extends substantially parallel to the longitudinal axis and wherein each of the liquid inlet slope and the liquid outlet slope is oriented at a non-zero angle to the longitudinal axis;
the nozzle further comprising:
a first sealing member (<NUM>) located between the liquid outlet slope and the distal end of the thermally conductive body; and
a second sealing member (<NUM>) located between the proximal end of the thermally conductive body and the liquid inlet slope,
characterised in that the cooling waist is configured to facilitate a laminar flow of a liquid coolant through a chamber (<NUM>) defined in part by the cooling waist such that the liquid coolant entering the liquid inlet slope does not substantially intermingle with the liquid coolant exiting from the liquid outlet slope.