Diffuser shape vent slots in a hand torch shield castellation

A torch tip for a plasma arc torch includes a body having a first end, configured to attach to the torch, and a second end, where an end wall is disposed. A plasma exit orifice is formed in the end wall. At least two castellations are formed in the end wall. At least one slot is disposed between two castellations. Each slot is defined by a first and second castellation wall, and a slot floor. The first castellation wall is opposite the second castellation wall. The torch tip has at least one of the following characteristics: a slope of the slot floor within the at least one slot tapers in an outward radial direction relative to the plasma exit orifice toward the first end of the body, or a distance between the first and second castellation walls along the slot floor increases with distance away from the exit orifice.

TECHNICAL FIELD

The present invention relates generally to plasma arc cutting torches, and more particularly, to diffuser shape vent slots in a hand torch shield consumable.

BACKGROUND

Welding and plasma arc torches are widely used in the welding, cutting, and marking of materials. A plasma torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, passages for arc control fluids (e.g., plasma gas), and a power supply. Optionally, a swirl ring is employed to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle. The torch produces a plasma arc, 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). In 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 contact starting methods.

In some torches, a shield is used to prevent molten spatter from damaging the other components of the torch, for example, the electrode, nozzle, or swirl ring. Often, the molten spatter builds up on the shield causing double arcing or melting of the shield. The build-up typically increases as the cutting time increases.

To decrease the amount of molten spatter that builds up on the shield, prior torches have used shields with vent slots added to the end face of the shield. The vent slots act as channels for melted metal, for example, slag, to leave the end face of the shield. These shields employ four slots that are arranged in a symmetrical pattern about the end face surrounding a plasma exit orifice. The slots retain the same dimensions as a function of distance from the plasma exit orifice.

Prior art shields with vent slots do not adequately remove slag for certain applications. Instead, the slag builds up on the shield and within the vent slots. The slag can block all or a portion of the vent slots resulting in a double arc or melting of the shield. Cleaning slag build-up is difficult. Operators often replace the shield once build-up has occurred instead of performing the time-consuming task of cleaning the shield. The slag build-up can also lead to premature failure of the shield and, sometimes, the premature failure of other consumables. In addition, slag build-up can increase the down time of the torch because the operator is required to stop the system to either clean or replace the shield when too much build-up occurs. Increased down time and premature consumable failure result in increased operating costs.

SUMMARY OF THE INVENTION

What is needed is a shield that reduces the molten spatter buildup during operation of the torch. Several variables can be altered to address the problem, for example, shield slot size and shape and shield castellation mass and shape. Altering the shield slot size and shape affects the molten spatter buildup. For example, increasing the size of the shield slot increases the amount of molten spatter that can be removed from the shield. Altering the shield castellation mass and shape affects the heat transfer properties of the shield (e.g., how quickly the shield melts). For example, increasing the castellation mass increases the amount of heat the shield can absorb.

However, simply reducing the number and/or size of the shield slots to increase the number and/or size of the castellations or vice-versa is insufficient. First, altering the properties of the vent slots to maximize molten spatter removal adversely affects the castellation mass and heat transfer properties of the shield. Second, altering the properties of the castellation mass to increase the heat transfer properties of the shield adversely affects the vent slot openings and shape resulting in molten spatter buildup. Therefore, the number, size, and shape (or geometry) of both the shield slots and castellations should be balanced or optimized to avoid slag build-up and premature melting, respectively. The appropriate balance of these factors can increase the performance and life of the shield.

In one aspect, the invention features a torch tip for a plasma arc torch for reducing molten spatter buildup during operation of the plasma arc torch. The torch tip includes a body having a first end and a second end. The first end of the body is configured to attach to the plasma arc torch. The torch tip also includes an end wall disposed at the second end of the body. A plasma exit orifice is formed in the end wall at the second end of the body. At least two castellations are formed in the end wall. At least one slot is disposed between two castellations. The at least one slot is defined by a first castellation wall, a second castellation wall, and a slot floor. The first castellation wall is opposite the second castellation wall. The torch tip having at least one of the following characteristics: (a) a slope of the slot floor within the at least one slot tapers in an outward radial direction relative to the plasma exit orifice toward the first end of the body, or (b) a distance between the first and second castellation walls along the slot floor increases with distance away from the plasma exit orifice.

In another aspect, the invention features a shield for a plasma arc torch. The shield includes a body having a first end and a second end. The first end of the body is configured to attach to the plasma arc torch. The shield also includes an end wall disposed at the second end of the body. A plasma exit orifice is formed in the end wall at the second end of the body. The shield also includes no more than three slots disposed between the at least two castellations. Each slot has a generally semi-frustoconical geometry. Each slot is defined by a first castellation wall, a second castellation wall, and a slot floor. The first castellation wall is opposite the second castellation wall.

In yet another aspect, the invention features a torch tip for a plasma arc torch for reducing molten spatter buildup during operation of the plasma arc torch. The torch tip includes a body having a first end and a second end. The first end of the body configured to attach to the plasma arc torch. An end wall is disposed at the second end of the body. A plasma exit orifice is formed in the end wall at the second end of the body. Three castellations are formed in the end wall. The torch tip includes three slots disposed between the castellations. Each slot is defined by a first castellation wall, a second castellation wall, and a slot floor. The first castellation wall is opposite the second castellation wall.

In another aspect the invention features a plasma arc torch system. The system includes a torch body defining a plasma gas flow path for directing a plasma gas to a plasma chamber in which a plasma arc is formed. The system also includes an electrode disposed within the torch body. The system further includes a nozzle disposed relative to the electrode at a distal end of the torch body to define the plasma chamber. A shield is disposed relative to an exterior surface of the nozzle at the distal end of the torch body. The shield includes a shield body having a first end configured to attach to the torch body and a second end. An end wall is disposed at the second end of the body. The shield also includes a plasma exit orifice formed in the end wall at the second end of the shield body. At least two castellations are formed in the end wall. The shield also includes at least one slot disposed between two castellations. The at least one slot is defined by a first castellation wall, a second castellation wall, and a slot floor. The first castellation wall is opposite the second castellation wall. The shield has at least one of the following characteristics: (a) a slope of the slot floor within the at least one slot tapers in an outward radial direction relative to the plasma exit orifice toward the first end of the body, or (b) a distance between the first and second castellation walls along the slot floor increases with distance away from the plasma exit orifice.

In some embodiments, the torch tip or shield includes three slots. The torch tip or shield can include three slots and three castellations separating each of the slots. In some embodiments, each castellation has a substantially planar top surface.

The at least one slot can have a rounded, generally semi-cylindrical, or generally semi-frustoconical geometry.

The torch tip can be a shield. In some embodiments, the torch tip or shield is made from a material having a high thermal conductivity. The torch tip or shield can be formed of copper.

In some embodiments, the first castellation wall and the second castellation wall are angled from about 45 arc degrees to about 75 arc degrees about the end wall.

In some embodiments, the height of the first and second castellation walls increases with distance from the exit orifice.

The torch tip or shield can have at least one of the following characteristics: (a) a slope of the slot floor within the at least one slot tapers in an outward radial direction relative to the plasma exit orifice toward the first end of the body, or (b) a distance between the first and second castellation walls along the slot floor increases with distance away from the plasma exit orifice. In some embodiments, the slots can extend radially from the plasma exit orifice.

DETAILED DESCRIPTION

FIG. 1shows a cross-sectional view of a plasma arc torch100. A plasma torch tip is comprised of a variety of different consumables, for example, an electrode105, a nozzle110, a retaining cap115, a swirl ring120, or a shield125. The nozzle110has a central exit orifice mounted within a torch body. The torch and torch tip can include electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). The shield125is used to prevent molten spatter from damaging the other components of the torch, for example, the electrode105, nozzle110, retaining cap115, or swirl ring120. Often, the molten spatter builds up on the shield125causing double arcing or melting of the shield125. The build-up typically increases as the cutting time increases.

To decrease the amount of molten spatter buildup on the shield, slots can be added to the shield to create a channel for the molten spatter to exit the shield.FIG. 2shows a prior art torch tip150having four symmetrical vent slots155. The vent slots155are arranged in a symmetrical pattern around the plasma exit orifice160. The vent slots155retain the same profile dimensions as a function of distance from the plasma exit orifice160. For example, the width w of the slot floor156at the plasma exit orifice160is the same as the width w of the slot floor156at a distance away from the plasma exit orifice160. In addition, the width of the slots155is the same at the plasma exit orifice160as the width of the slots155at a distance from the plasma exit orifice160. In other words, the slot walls157,158do not taper and are parallel to each other. These vent slots155create a channel that allows the molten spatter to exit the shield. However, these prior art torch tips or shields are inadequate for certain applications and often have substantial molten spatter buildup, which can occupy some or all of the regions of the slots, effectively blocking the channels.

The torch tip150also has four castellations165that separate each of the slots155. The castellations165absorb the heat generated by the plasma arc torch. Another heat source of the shield is located at the vent surface, where heat can be transferred from the molten spatter to the shield. The more solid mass that is distributed in the castellations the more heat the shield can absorb from the surrounding environment. In addition, the heat capacitance of the material used to make the shield is related to how much heat the shield can absorb from the surrounding environment. A higher heat capacitance can result in better shield performance, because the shield can absorb more heat while remaining at a lower temperature than a shield with a lower heat capacitance. A shield that has a low castellation mass and/or a low heat capacitance can melt prematurely.

To reduce the amount of molten spatter buildup and prevent the torch tip or shield from melting prematurely, a shield can be designed that balances the need to reduce the amount of molten spatter buildup with the mass of the shield castellations to prevent premature melting of the consumable.

FIG. 3shows a perspective view of a torch tip200having three slots205, according to an illustrative embodiment of the invention.FIG. 4Ashows a perspective view of a torch tip200′ having three slots205′ with a generally semi-frustoconical geometry, according to an illustrative embodiment of the invention.FIG. 4Bshows a side view of the torch tip200′ shown inFIG. 4A, e.g., a torch tip having three slots205′ with a generally semi-frustoconical geometry, according to an illustrative embodiment of the invention. Referring toFIG. 3, the torch tip200includes a body210, having a first end215and a second end220. The torch tip also includes an end wall230disposed at the second end220of the body210. A plasma exit orifice225is formed in the end wall230at the second end220of the body210. The first end215of the body210is configured to attach to a plasma arc torch (such as the torch shown inFIG. 1). The torch tip200can attach to a plasma arc torch using any fastening mechanism, for example, threads, friction fit, press fit, etc.

The torch tip200also includes at least two castellations240formed in the end wall230. The castellations can be generally rectangular in nature or the castellations can be curved, e.g., crenulations. In some embodiments, the castellations can be crenulations or a standoff. At least one slot205is disposed between two castellations240. Each slot is defined by three sides, a first castellation wall235, a second castellation wall236and a slot floor237. The first castellation wall235and the second castellation wall236are opposite each other. Referring toFIG. 4B, when the slot205′ has a curved, rounded, generally semi-cylindrical, or generally semi-frustoconical geometry, the slot floor can be located in the lower portion of the slot, for example, in region X, and the first and second castellation walls can be located in the upper regions of the slot, for example, in regions Y1and Y2.

The torch tip200, and more particularly the slots205, can have at least one of two characteristics. The first characteristic is that a slope of the slot floor237within the at least one slot205tapers in an outward radial direction relative to the plasma exit orifice225toward the first end215of the body210. For example, the slot floor237tapers toward the first end215of the body210as a function of distance away from the plasma exit orifice225such that a first location on an outer edge of the slot floor237(e.g., the edge of the slot floor237that is farthest away from the plasma exit orifice225) is closer to the first end215of the torch tip200than a second location on an inner edge of the slot floor237(e.g., the edge of the slot floor that is closest to the plasma exit orifice225). Referring toFIG. 4A, a first location P2, P3, P4on an outer edge of the slot floor237′ is closer to the first end215′ of the torch tip200′ than a second location P5, P6, P7on an inner edge of the slot floor237′. The first P2, P3, P4and second P5, P6, P7locations can be axially aligned relative to an axis A1, A2, A3extending from a center P1of the plasma exit orifice225′. For example, axis A1contains first location P2on the outer edge of the slot floor237′, second location P5on the inner edge of the slot floor237′, and a center P1of the plasma exit orifice225′. Axis A2contains first location P3on the outer edge of the slot floor237′, second location P6on the inner edge of the slot floor237′, and a center P1of the plasma exit orifice225′. Axis A3contains first location P4on the outer edge of the slot floor237′, second location P7on the inner edge of the slot floor237′, and a center P1of the plasma exit orifice225′. In other words, referring toFIG. 4B, the slot floor tapers in a downward direction toward the first end215′ of the body210′, tapering away from the plane A-A (e.g., the plane A-A is perpendicular to the sheet of paper) that contains the inner edge239of the slot floor. The outer edge238of the slot floor is in a different plane B-B (e.g., the plane B-B is perpendicular to the sheet of paper) than the plane A-A that contains the inner edge239of the slot floor. For example, referring toFIG. 3, the slot floor237located in the end wall230can be shaped like a bowl or a turtle shell, with its highest point in the region of the plasma exit orifice225.

Still referring toFIG. 3, the second characteristic is that a distance between the first castellation wall235and the second castellation wall236along the slot floor237increases with distance away from the plasma exit orifice225. For example, distance d1(e.g., the distance between the first castellation wall235and the second castellation wall236as measured at the slot floor237near the plasma exit orifice225) is less than distance d2(e.g., the distance between the first castellation wall235and the second castellation wall236as measured at the slot floor237farthest away from the plasma exit orifice225).

In one embodiment, the torch tip200can have the first characteristic. In another embodiment, the torch can have the second characteristic. In another embodiment, the torch tip200can have both the first characteristic and the second characteristic.

In yet another embodiment, the torch tip200can have a third characteristic. The distance between the first castellation wall235and the second castellation wall236can increase with distance away from the slot floor237. For example, the first castellation wall235and the second castellation wall236can taper such that the distance w1between the first castellation wall235and the second castellation wall236at the slot floor237is less than the distance w2between the first castellation wall235and the second castellation wall236at a location away from the slot floor237.

In some embodiments, the torch tip200can include all three characteristics or any combination thereof. For example, the torch tip can have the first and third characteristic or the second and third characteristic.

In some embodiments, the height of the first and second castellation walls235,236increases with distance from the exit orifice. For example, the height h1of the first castellation wall235and the second castellation wall236at a location close to the plasma exit orifice225is shorter than the height h2of the first castellation wall235and the second castellation wall236at a location farther away from the plasma exit orifice225.

In some embodiments, the torch tip200,200′ is a shield. The torch tip200,200′ or shield can be made from a material having a high thermal conductivity, for example, copper.

As shown inFIGS. 3 and 4A, the torch tip200,200′ can have three slots,205,205′, respectively. In this embodiment, the torch tip200,200′ has three slots205,205′ and three castellations240,240′, respectively. Each castellation240,240′ can separate two of the three slots205,205′. In some embodiments, each castellation240,240′ has a substantially planar top surface. The slots205,205′ and castellations240,240′ can be arranged in a symmetrical pattern around the plasma exit orifice225,225′, respectively.

The slots205,205′ can have a rounded, generally semi-cylindrical, or generally semi-frustoconical geometry. For example, the slots205′ have a generally semi-frustoconical geometry as shown inFIGS. 4A and 4B. In general, the slots205,205′ can have any other type of geometry that is conducive to reducing the amount of molten spatter buildup during operation of a plasma arc torch.

In some embodiments, the shield has no more than three slots each having a generally semi-frustoconical geometry. In some embodiments, the torch tip or shield has exactly three slots and three castellations. In some embodiments, the slots205,205′ extend radially from the plasma exit orifice225,225′, respectively.

FIGS. 5A-5Care schematic illustrations, including side views and a top view, of the torch tip ofFIG. 2.FIGS. 6A-6Care a schematic illustrations, including side views and a top view, of the torch tip ofFIG. 3, according to an illustrative embodiment of the invention.FIG. 7A-7Care schematic illustrations, including side views and a top view, of torch tip ofFIG. 4, according to an illustrative embodiment of the invention.

FIGS. 5A-5C,6A-6C, and7A-7C provide additional details about the shields inFIGS. 2,3, and4, respectively. As shown inFIGS. 5A-5C, the prior art shield has four slots305that are arranged symmetrically around the plasma exit orifice310. The slots305are not curved or tapered. The slots305are instead generally semi-rectangular and the castellation walls315,316form right angles with the slot floor317. The slot floor317of the shield is generally flat. This slot geometry is not optimal because molten spatter can easily build up in the slot, particularly, the molten spatter can build up where the castellation walls315,316meet the slot floor317.

Still referring toFIGS. 5A-5C, the slot geometry does not change based on the distance from the plasma exit orifice310.FIG. 5Arepresents the cross-section of the torch tip labeled5A inFIG. 5CandFIG. 5Brepresents the cross-section of the torch tip labeled5B inFIG. 5C. Section5B is slightly closer to the central exit orifice310than section5A. Comparing section5B to section5A, the geometry does not change. For example, the depth of the slot is 0.060 in both sections5A and5B. In addition, the distance between the first and second castellation walls315,316is 0.100 inches in both sections5A and5B.

As shown inFIGS. 6A-6Cand7A-7C, the number of slots and the slot geometry has been modified to optimize the performance and life of the shield. As shown, the shields have three slots320and three castellations325. ComparingFIGS. 6A-6CwithFIG. 5A-5C, the castellation walls326,327of the shield ofFIGS. 6A-6Care tapered such that a distance between the first and second castellation walls326,327along the slot floor328increases with distance away from the plasma exit orifice330(e.g., the distance d1is less than the distance d2). The castellation walls326,327are also tapered such that the distance between the castellation walls326,327increases with distance away from the slot floor328(e.g., the width w1is less than the width w2).

Referring toFIGS. 6A-6C, the first and second castellation walls236,327and the slot floor328have an angle θ from about 45 arc degrees to about 75 arc degrees about the end wall. In some embodiments, the first and second castellation walls236,327and the slot floor328have an angle θ of about 60 arc degrees about the end wall.

As shown inFIGS. 6A-6C, the slot geometry changes based on the distance from the plasma exit orifice330.FIG. 6Arepresents the cross-section of the torch tip labeled6A inFIG. 6CandFIG. 6Brepresents the cross-section of the torch tip labeled6B inFIG. 6C. Section6B is slightly closer to the plasma exit orifice330than Section6A. The distance between the castellation walls326,327increases with distance from the plasma exit orifice330. The distance between the castellation walls326,327at the slot floor328in section6B is 0.110 and that distance increases to 0.118 in section6A. In addition, the distance between the castellation walls326,327at a distance away from the slot floor328also increases with distance from the plasma exit orifice330, for example, the distance increases from 0.185 in section6B to 0.193 in section6A. The depth of the slot remains constant in this embodiment, at 0.060 inches in both sections6A and6B.

FIGS. 7A-7Cshows another embodiment of the invention. The slot350is generally semi-frustoconical in geometry. Similar toFIGS. 6A-6C, the distance between the castellation walls355,356increases at both the slot floor357and at a distance away from the slot floor357with distance away from the plasma exit orifice360.FIG. 7Arepresents the cross-section of the torch tip labeled7A inFIG. 7CandFIG. 7Brepresents the cross-section of the torch tip labeled7B inFIG. 7C. For example, section7B is slightly closer to the plasma exit orifice360than section7A. The radius of the generally semi-frustoconsical slot increases with distance from the plasma exit orifice, for example, the radius is 0.090 in section7B and the radius increases to 0.092 in section7A. In addition, the distance between the castellation walls355,356at a distance away from the slot floor357also increases with distance from the plasma exit orifice360, for example, the distance increases from 0.174 in section7B to 0.180 in section7A. In addition, the height of the slot350also increases with distance from the plasma exit orifice360(e.g., the height h1is less than the height h2). For example, in section7B, the distance from the slot floor357to the top of the castellation365is about 0.068. In section7A, this distance increases to 0.070. This indicates that the slot floor is tapered toward the shield body370with distance away from the plasma exit orifice360. Another indication that the slot floor tapers with distance away from the plasma exit orifice is shown in4B. The slot floor tapers in an outward radial direction relative to the plasma exit orifice toward the first end215′ of the body210′. Thus, the slot floor tapers away from the plane A-A that contains the inner edge239of the slot floor. The outer edge238of the slot floor is in a different plane B-B than the plane A-A that contains the inner edge239of the slot floor.

The invention in another aspect features a plasma arc torch system.FIG. 8is a schematic illustration of a plasma arc torch system400, according to an illustrative embodiment of the invention. The torch system includes a torch body405that defines a plasma gas flow path for directing a plasma gas to a plasma chamber in which a plasma arc is formed. An electrode (not shown) is disposed within the torch body405. The electrode can be, for example, the electrode105ofFIG. 1. A nozzle (not shown) is disposed relative to the electrode at a distal end410of the torch body405. The nozzle can be, for example, nozzle110ofFIG. 1. The torch system400also includes a shield415disposed relative to an exterior surface of the nozzle at the distal end410of the torch body405. The shield can be, for example, any of the embodiments of the shield or torch tip described above with reference toFIG. 3,4A,4B,6A-6C, or7A-7C.

A torch tip or shield as described with reference toFIG. 3,4A,4B,6A-6C, or7A-7C reduces molten spatter buildup during operation of the plasma arc torch. In addition, the torch tip or shield is easier to clean than the torch tip or shield described with reference toFIG. 2or5A-5C. Furthermore, the torch tip or shield as described with reference toFIG. 3,4A,4B,6A-6C, or7A-7C does not melt as easily or quickly as the torch tip or shield described with reference toFIG. 2or5A-5C. These benefits can be achieved by the balance between the number of the slots, the slot shape and geometry and the number of castellations and the mass of the castellations.

Improved performance of the shields illustrated inFIGS. 3,4A and4B over the shield illustrated inFIG. 2can be shown by comparing the amount of molten spatter each shield accumulates under set conditions. For example, the shields illustrated inFIGS. 2,3, and4A and B were tested using a robot to pierce perpendicular to the work piece while directly contacting the material during cutting (e.g., 0″ standoff), with each shield repeated 30 times. After each pierce cut, the shields were weighed to monitor the weight gain of the present slag.

FIG. 9is a graph700of molten spatter buildup on each of the three torch tips shown inFIGS. 2,3, and4A and B, showing the results of the example described above. The shield illustrated inFIG. 2, labeled “4 Para Vents” onFIG. 9, with four vent slots, showed the most slag buildup. The average slag buildup for the shield illustrated inFIG. 2was about 0.25 grams. In contrast, the average slag buildup for the shields illustrated inFIG. 3, labeled “3 Vents No. 1”, and the shield illustrated inFIGS. 4Aand B, labeled “3 Vents No. 2”, was about 0.05 grams. The shields ofFIGS. 3,4A and4B reduced about 80% of the slag buildup of the shield ofFIG. 2.

Although various aspects of the disclosed method have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.