TECHNICAL FIELD

The present invention generally relates to consumables for a liquid-cooled plasma arc torch, and more specifically, to extended access consumables for a liquid-cooled plasma arc torch.

BACKGROUND

Plasma arc torches are widely used for high temperature processing (e.g., cutting, welding, and marking) of metallic materials. A plasma arc torch generally includes a torch body, an electrode mounted within the body, an emissive insert disposed within a bore of the electrode, a nozzle with a central exit orifice, a shield, electrical connections, passages for cooling and arc control fluids, a swirl ring to control the fluid flow patterns, and a power supply. The plasma arc torch can produce a plasma arc, which is a constricted, ionized jet of 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).

A plasma arc torch can generate a plasma arc using a contact start method. This involves first operating the torch in a pilot arc mode, which includes establishing physical contact and electrical communication between the electrode and the nozzle, e.g., by using a biasing force from, for example, a spring. A current path and a small pilot arc current flow are established between the electrode and the nozzle while they are biased together. A plasma gas is introduced into a plasma chamber between the nozzle and the electrode, such that gas pressure builds up in the plasma chamber to break the physical contact between the electrode and the nozzle to separate the two components. The separation causes an electrical arc to be created in the gap between the electrode and the nozzle in the plasma chamber. The electrical arc ionizes the flowing plasma gas in the plasma chamber to produce a plasma arc (i.e., a pilot arc). The plasma gas can be passed through a swirl ring to impart a tangential motion to the gas as it passes through the torch, thereby improving torch performance. Next, in a transferred arc mode, the torch is moved near a grounded workpiece and the plasma arc makes contact with the workpiece. Upon contact, the current return path transfers from the nozzle to the workpiece, which means that the electrical return path from the nozzle is opened (i.e., electrically disconnected) and the current returns instead from the workpiece back to the power supply. During transferred arc mode, the current flow can be increased to a larger amount such that the arc generated processes (e.g., gouging, piercing or cutting) of the workpiece.

Currently, dimensions of a plasma arc torch are determined by the size and configuration of the consumables discussed above, e.g., the electrode, swirl ring, nozzle, and shield. Design of these consumables is highly technical and has a dramatic impact on torch life and performance. The electrode is generally surrounded by a swirl ring, a nozzle, and in some configurations a shield. All of these components, and the manner in which they are designed and combined, affect the overall torch dimensions, configuration, weight, cost and other parameters.

Furthermore, plasma arc torches are now being used in ever more intricate cutting operations, including those where access to portions of the workpiece can be difficult. Standard torches, due to their dimensions, may not be usable in hard-to-reach areas such as channels, sharp corners and pockets.FIGS.1aand1bshow the positioning of a conventional plasma arc torch100in relation to a vertical flange102to be cut and the resulting cut104made by the conventional plasma arc torch100, respectively. As illustrated, the vertical flange102is perpendicularly located relative to a horizontal base108to create a corner110. Due to the dimensions of the conventional plasma arc torch100, the torch tip106of the plasma arc torch100is unable to be positioned sufficiently close to the corner110between the vertical flange102and the horizontal base108to cut the flange102as close as possible against the base108without damaging the flange102. Instead, as shown from the resulting cut104ofFIG.1b, a diagonal cut is made into the flange102below the base108, thereby unintentionally damaging the flange102.

Another torch design consideration is that standard plasma arc torches, such as the torch100ofFIGS.1aand1b, cannot run at a high percentage duty cycle without melting the torch components and causing other temperature-related problems in the torch. This is because torch consumables (e.g., the electrode, nozzle, swirl ring and shield) are exposed to high temperatures during operation. Torch consumables can be cooled utilizing various techniques, such as water injection cooling to cool the nozzle and/or shield, liquid cooling in the electrode and/or about nozzle, or gas cooled at vent holes to cool the shield as described in U.S. Pat. No. 5,132,512. However, cooling of plasma arc torch consumables can become more difficult when the plasma arc torch is run at high currents (e.g., greater than about 15 Amps) and/or when the plasma arc torch is entirely gas cooled.

FIG.2shows a known liquid cooling path250in a conventional liquid-cool plasma arc torch200. As shown, a liquid coolant is first introduced to the torch tip via a coolant tube216that is inserted into a cavity206the electrode205. The coolant flow250travels distally within the coolant tube116and exits into the cavity206of the electrode205at a distal opening of the coolant tube216. As guided by the wall of the cavity206, the coolant flow250is adapted to reverse direction and travel proximally along the outer surface of the coolant tube116within the cavity206to cool the length of the electrode205. To cool the nozzle210, the coolant flow250exits from the cavity206of the electrode205via a passage207that is disposed in the torch body202connected to the electrode205, and reverses direction to travel distally to reach the nozzle210. To cool the shield225, the same coolant flow250exits from the nozzle210via a passage211of the nozzle210that is in fluid communication with an inner surface of the shield225. Thereafter, this coolant flow250travels proximally to return to the torch body202along the inner surface of an outer retaining cap218that is connected to the shield225. Such zig-zag, back-and-forth pattern of the liquid coolant flow, which comprises the coolant flow alternating several times between distal and proximal flows, is typical of a conventional liquid-cooled plasma arc torch.

SUMMARY

What is needed is a set of consumables in a liquid-cooled plasma arc torch that is designed for plasma cutting in deep channels, tight spaces, and hard-to-reach corners. In some embodiments, the present invention provides an adapter (hereinafter interchangeably referred to as an “extender′) for liquid-cooled plasma arc torches that is configured to operably connect to a set of extended and/or adjustable-length consumables. The use of such an extender and consumable set is advantageous because they minimize overall torch thickness while enabling high-access, long-range plasma cutting. Further, a combination of liquid and gas cooling schemes can be utilized to cool different portions of the plasma arc torch so as to provide adequate cooling for the torch during cutting operations and prevent premature failure of the consumables.

The present invention, in one aspect, features a torch tip for a liquid-cooled plasma arc cutting torch. The torch tip includes an electrode with an elongated electrode body having a distal end and a proximal end extending along a longitudinal axis. The electrode body includes a bore at the distal end for receiving a hafnium insert and at least one interior threaded connection at the proximal end for engaging a liquid-cooled electrode holder. The electrode holder comprises a liquid coolant channel that does not extend into the electrode body. The electrode body has (i) a length extending along the longitudinal axis and (ii) a diameter associated with a widest portion of the electrode body along the longitudinal axis between the proximal and distal ends. A ratio of the length to the diameter of the electrode body is greater than about 5. The torch tip also includes a nozzle having a substantially hollow, elongated nozzle body for receiving the electrode. The nozzle body defines (i) a length extending along the longitudinal axis and (ii) a diameter associated with a widest portion of the nozzle body along the longitudinal axis. A ratio of the length to the diameter of the nozzle body is greater than about 1.75

In some embodiments, the diameter of the electrode is less than about 0.25 inches. In some embodiments, the ratio of the length to the diameter of the electrode body is greater than about 7.

In some embodiments, the at least one threaded connection is configured to engage a complementary threaded connection on an external surface of the electrode holder, such that a distal portion of the electrode holder is disposed in a cavity of the electrode body upon engagement. In some embodiments, the cavity within the electrode body is shaped and sized to substantially surround a protruding boss portion at the distal portion of the electrode holder, thereby axially and radially aligning the electrode relative to the electrode holder.

In some embodiments, the torch tip further comprises a shield coupled to the nozzle via an insulator. In some embodiments, the shield includes a set of radially-oriented passages dispersed around a first circumference of the shield. The radially-oriented passages fluidly connect an exterior surface to an interior surface of the shield and configured to impart a swirling motion on a first portion of a combined gas flow therethrough. The shield can also include a set of axially-oriented passages dispersed around a second circumference of the shield. The axially-oriented passages are configured to axially conduct a second portion of the combined gas flow over an external surface of the shield. In some embodiments, the set of axially-oriented passages of the shield comprises at least one groove disposed on the exterior surface of the shield.

In some embodiments, the combined gas flow at the torch tip comprises a combination of a plasma gas flow and a shield gas flow. In some embodiments, the nozzle comprises a set of radially-oriented passages each connecting an interior surface of the nozzle body to an exterior surface of the nozzle body. The set of radially-oriented passages of the nozzle is configured to fluidly communicate with the radially-oriented and axially-oriented passages of the shield to supply a portion of the plasma gas flow to the shield. In some embodiments, the torch tip, including the electrode, the shield and the nozzle, is substantially cooled by at least one of the plasma gas flow, the shield gas flow or the combined gas flow without being cooled by a liquid coolant in the liquid coolant channel of the electrode holder.

In another aspect, the invention features an extender of a liquid-cooled plasma arc torch for relocating a mounting location of at least one plasma torch consumable within the torch. The extender is located between a torch body and the at least one consumable. The extender includes an elongated body defining a longitudinal axis between a proximal end and a distal end, a liquid cooling passage extending substantially along the longitudinal axis of the elongated body, a proximal interface at the proximal end of the elongated body configured to matingly engage the torch body, and a distal interface at the distal end of the elongated body configured to enable the at least one consumable to mount thereon, such that the mounting location for the at least one consumable is extended in a spaced relationship relative to the proximal interface along the longitudinal axis.

In some embodiments, the at least one consumable comprises the electrode, and the distal interface of the elongated body is configured to engagingly hold the electrode mounted to the distal end of the elongated body. In some embodiments, the at least once consumable further comprises a nozzle coupled to the electrode and a shield coupled to the nozzle via an insulator component.

In some embodiments, a cavity is disposed in the elongated body and configured to receive, via the proximal interface, a liquid coolant tube of the torch body that forms the liquid cooling passage within the elongated body. In some embodiments, the liquid coolant tube extends along a first portion of the elongated body and is absent from a remaining portion of the elongated body. A diameter of the first portion of the elongated body can be less than about 1 inch. In some embodiments, the remaining portion defines a spaced distance along the longitudinal axis between a distal end of the coolant tube and a proximal end of the electrode upon assembly of the plasma arc torch. This spaced distance can be about 1.25 inches.

In some embodiments, a set of radial passages is located within the remaining portion of the extender, where each radial passage is in fluid communication with the coolant tube and configured to fluidly connect an interior surface of the extender to an exterior surface to convey the liquid coolant away from the extender.

In some embodiments, the distal interface of the elongated body comprises a protruding boss portion configured to form a tolerance fit with a complementarily-shaped cavity at a proximal end of the electrode to axially and radially align the electrode upon engagement.

In some embodiments, the elongated body of the extender comprises (i) an electrode holder configured to engage an electrode, (ii) a nozzle holder substantially surrounding an exterior surface of the electrode holder, the nozzle holder configured to engage a nozzle, and (iii) a shield holder substantially surrounding an exterior surface of the nozzle holder, the shield holder configured to engage a shield. In some embodiments, the elongated body of the extender further comprises a swirl ring holder located radially between the exterior surface of the electrode holder and an interior surface of the nozzle holder, where the swirl ring holder is configured to engage a swirl ring.

In yet another aspect, the present invention features a method for liquid cooling a plasma arc cutting torch comprising a torch body, an extender and a torch tip. The torch body is connected to a proximal end of the extender and the torch tip is connected to a distal end of the extender. The extender is elongated such that a length to diameter ratio of the extender is greater than about 5. The method includes conveying a liquid coolant from the torch body to the extender via a coolant tube of the torch body that is inserted into a cavity of the extender upon engagement of the torch body with the proximal end of the extender. The method also includes returning the liquid coolant to the torch body without circulating the liquid coolant to the torch tip. The method further includes conveying one or more gases to the torch tip to cool the torch tip.

In some embodiments, the torch tip comprises an electrode, a nozzle surrounding an exterior surface of the electrode, and a shield surrounding an exterior surface of the nozzle. In some embodiments, the extender comprises an electrode holder to physically engage the electrode to the torch body, a nozzle holder to physically engage the nozzle to the torch body, and a shield holder to physically engage the shield to the torch body, the electrode holder. The nozzle holder and the shield holder are concentrically positioned relative to each other about a longitudinal axis of the torch.

In some embodiments, conveying one or more gases to the torch tip comprises providing a plasma gas flow to travel distally between an exterior surface of the electrode and an interior surface of the nozzle and conducting, by a set of radially-oriented passages in the nozzle, at least a portion of the plasma gas flow from the interior surface of the nozzle to an exterior surface of the nozzle. The method also includes providing a shield gas flow to travel distally over the exterior surface of the nozzle and combining the portion of the plasma gas flow and the shield gas flow at the exterior surface of the nozzle to generate a combined gas flow. The plasma gas flow, the shield gas flow and the combined gas flow are adapted to cooperatively cool the electrode, the nozzle and the shield at the torch tip. The method can further include providing a first portion of the combined gas flow to a channel between the exterior surface of the nozzle and an interior surface of the shield, within which the first portion of the combined gas flow is adapted to travel distally toward a shield exit orifice while cooling both the shield and the nozzle. The method can further include conducting, by a set of axially-oriented grooves disposed on an external surface of the shield, a second portion of the combined gas flow over the external surface of the shield to cool the shield.

In some embodiments, providing a first portion of the combined gas flow to a channel between the nozzle and the shield comprises conducting, by a set of radially-oriented passages disposed in the shield, the first portion of the combined gas flow from an external surface of the shield into the channel. In some embodiments, the set of radially-oriented passages disposed in the shield are configured to impart a swirling motion to the first portion of the combined gas flow therethrough.

In some embodiments, returning the liquid coolant to the torch body without circulating the liquid coolant to the torch tip includes (i) conducting the liquid coolant away from the extender via a set of radially-oriented passages located in a central portion of the extender, each radially-oriented passage connecting an interior surface of the extender to an external coolant channel defined by an exterior surface of the extender and an interior surface of a nozzle holder, and (ii) conveying, by the external coolant channel, the liquid coolant proximally toward the torch body to return the liquid coolant to the torch body.

In yet another aspect, the present invention features a method for liquid cooling a plasma arc cutting torch comprising a torch body, an extender and a torch tip including a plurality of consumable components. The torch body is connected to a proximal end of the extender and the torch tip is connected to a distal end of the extender. The method includes conveying a liquid coolant from the torch body to the extender via a coolant tube of the torch body that is inserted into a cavity of the extender upon engagement of the torch body with the proximal end of the extender. The liquid coolant flows distally from the torch body to the extender within the coolant tube. The method also includes conducting, by a set of liquid passages in the extender, the liquid coolant radially outward from an interior surface of the extender to an external coolant channel defined by an exterior surface of the extender and an interior surface of a nozzle holder. The method further includes conveying, by the external coolant channel, the liquid coolant proximally toward the torch body to return the liquid coolant to the torch body. Both the coolant tube and the external coolant channel are longitudinally spaced from the torch tip such that the liquid coolant is substantially absent from the torch tip. In some embodiments, the method further includes providing one or more gases to cool the plurality of consumable components in the torch tip.

