Smooth Radius Nozzle for use in a Plasma Cutting device with sub-sonic nozzle flow rate

Abstract

A nozzle for use with a plasma arc torch is provided. The nozzle has a nozzle body having a length that extends from a proximal end to a distal end, a central bore disposed within the nozzle body along a central axis having a feed orifice at the proximal end of the nozzle body, and a discharge orifice at the distal end of the nozzle body. The central bore has a series of internal sections that transition with one or more radial edges between the feed orifice and the discharge orifice. The series of internal sections have a first section beginning at the feed orifice transitioning to a converging section transitioning at a throat to a diverging section ending at the discharge orifice. The length of the converging section is longer than a length of the diverging section. A Venturi effect is created by the converging and diverging sections of the nozzle.

Claims

1. A nozzle for use with a plasma arc torch, comprising: a nozzle body having a length that extends from a proximal end to a distal end; a central bore disposed within the nozzle body along a central axis having a feed orifice at the proximal end of the nozzle body and a discharge orifice at the distal end of the nozzle body; wherein the central bore comprises a series of internal sections that transition with one or more radial intersections between the feed orifice and the discharge orifice; wherein the series of internal sections comprise a first section beginning at the feed orifice that transitions to a converging section that transitions at a throat to a diverging section ending at the discharge orifice; and wherein a length of the converging section is longer than a length of the diverging section.

2. The nozzle of claim 1, wherein the first section comprises a cylindrical bore adapted to receive an axial electrode.

3. The nozzle of claim 2, wherein the first section comprises a substantially uniform diameter and extends for substantially half of the length of the nozzle body.

4. The nozzle of claim 1, wherein the diverging section is configured as a bore bounded by a wall, wherein the shape of the bore comprises a region bounded by a curve and revolved about the central axis, wherein the curve is continuously increasing toward the discharge orifice.

5. The nozzle of claim 4, wherein the curve comprises one or more curve sections defined by a continuous smooth mathematical function.

6. The nozzle of claim 1, wherein the diverging section is conical or parabolic and has an upward slope toward the discharge orifice of between 0-15 relative to the central axis.

7. The nozzle of claim 1, wherein the converging section is configured as a bore bounded by a wall, wherein the shape of the bore comprises a region bounded by a curve and revolved about the central axis, wherein the curve is continuously decreasing toward the discharge orifice.

8. The nozzle of claim 7, wherein the curve comprises one or more curve sections defined by a continuous smooth mathematical function.

9. The nozzle of claim 1, wherein at least a portion of the converging section is conical or parabolic and has a downward slope toward the discharge orifice of between 30-60 relative to the central axis.

10. The nozzle of claim 7, wherein the converging section comprises a combination of one or more of an ellipsoid section, a conical section, and a parabolic section.

11. The nozzle of claim 10, wherein transitions between the sections are substantially smooth sharing a common tangent direction at the transitions.

12. The nozzle of claim 1, wherein the throat that connects the converging section and the diverging section is substantially smooth sharing a common tangent direction at the transition.

13. The nozzle of claim 1, wherein the throat comprises a minimum diameter for the central bore.

14. The nozzle of claim 1, wherein at least one of the one or more radial intersections is located distal to an initiation point generated at a gap between the nozzle body and an electrode disposed within the central bore of the nozzle body.

15. The nozzle of claim 1, wherein the nozzle is adapted to increase the velocity of a plasma gas to at least 250 m/s by reducing the amount of turbulence and the recirculation zones.

16. The nozzle of claim 1, wherein the nozzle is adapted to maintain a plasma gas velocity at the throat within a range of 200 m/s to 343 m/s.

17. The nozzle of claim 1, wherein the nozzle is adapted to maintain a plasma gas velocity at the throat to substantially 278 m/s.

18. The nozzle of claim 1, wherein the nozzle is configured such that a ratio of the throat diameter to the exit velocity is substantially 7.40e-6 seconds.

19. The nozzle of claim 1, wherein the nozzle is configured such that a ratio of the throat diameter to the exit velocity is within a range of 1.0287e-5 seconds to 5.998e-6 seconds.

20. The nozzle of claim 1, wherein the nozzle is configured such that the pressure ratio of the nozzle intake pressure to nozzle exhaust pressure is 1.16941.

21. The nozzle of claim 1, wherein the nozzle is configured such that the pressure ratio of the nozzle intake pressure to nozzle exhaust pressure is within a range of 1.1 to 1.5.

22. A nozzle for use with a plasma arc torch, comprising: a nozzle body having a length that extends from a proximal end to a distal end, wherein the nozzle body is formed from a single piece of material; a central bore disposed within the nozzle body along a central axis having a feed orifice at the proximal end of the nozzle body and a discharge orifice at the distal end of the nozzle body; wherein the central bore has at least one radial intersection.

23. The nozzle of claim 22, wherein a pressure drop between a nozzle intake pressure and a nozzle exhaust pressure is between 68.94 kpa (10 psi) and 137.89 kpa (20 psi).

24. The nozzle of claim 23, where in the pressure drop is substantially 15 psi.

25. The nozzle of claim 24, wherein the nozzle body has a throat diameter of 0.0020574 m (0.081 in).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figures are not drawn to scale.

[0011] FIG. 1 is a cross section of a prior art plasma torch assembly;

[0012] FIG. 2 is a partial cross section detailing the central axial bore and exit orifice of a prior art plasma torch nozzle;

[0013] FIG. 3 is a cross section of one embodiment illustrating aspects of the present invention;

[0014] FIG. 4 is a cross section of a second embodiment illustrating aspects of the present invention;

[0015] FIG. 5 is a cross section of a third embodiment illustrating aspects of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the invention shown. The present invention is a plasma torch nozzle having a configuration adapted to address the undesirable turbulence and recirculation zones.

[0017] Generally speaking, as illustrated in FIGS. 3-5, the nozzle 20 is adapted for use with a plasma arc torch (not shown), and includes a nozzle body 22 having a length L that extends from a proximal end to a distal end and a central bore 30 disposed within the nozzle body 22 along a central axis 25. The central bore 30 has a feed orifice 32 at the proximal end of the nozzle body 22 and a discharge orifice 39 at the distal end of the nozzle body 22. The nozzle 20 is manufactured from one piece of material and only has one flow path defined by the central bore 30.

[0018] The central bore 30 comprises a series of internal sections L.sub.1, L.sub.2, L.sub.3 that transition with one or more radial intersections between the feed orifice 32 and the discharge orifice 39 along its length L. The radial intersections generally exhibit geometric continuity between the faces of the internal sections L.sub.1, L.sub.2, L.sub.3. This geometric continuity provides for smooth transitions. The series of successive internal sections comprise a first section L.sub.1 beginning at or around the feed orifice 32, transitioning to a converging section L.sub.2 wherein the cross-sectional area decreases, transitioning to a diverging section L.sub.3 wherein the cross-sectional area increases ending at the discharge orifice 39.

[0019] The first section L.sub.1 is generally shaped as a cylindrical bore adapted to receive an axial electrode (not shown). The converging section L.sub.2 and the diverging section L.sub.3 may be configured in a variety of bore configurations, geometrically speaking, such that each section forms one or more solids of revolution. The solids of revolution seen in the prior art are generally defined by combinations of cones and cylinders that have angular intersections. Unlike the prior art configurations, the solids of revolution provided for herein can be defined by curves (i.e., continuous smooth functions) other than those that strictly form cylinders or cones, including shapes resulting from curves represented by algebraic functions (e.g., quadratic, rational, root), transcendental functions (exponential, hyperbolic, logarithmic, power, trigonometric), and the like.

[0020] Three different embodiments are shown in FIGS. 3-5, wherein like reference numeral designate the same or substantially corresponding parts. As correspondingly shown in these three embodiments of FIGS. 3-5, the first section L.sub.1 is generally shaped as a cylindrical bore and adapted to receive an electrode (not shown). The first section L.sub.1 transitions at intersection I.sub.1 to the converging section L.sub.2, which is generally configured as a smoothly converging bore. The configuration of the walls forming the bore defined by the converging section L.sub.2 is bounded by one or more continuous joined curves decreasing toward the exit orifice revolved about the central axis 25. Thereafter, the converging section L.sub.2 transitions at intersection I.sub.2 to the diverging section L.sub.3. The intersection between converging section L.sub.2 and diverging section L.sub.3 forms a throat 34, which serves as the minimum diameter of the central bore 30. The configuration of the walls forming the portion of the central bore 30 defined by the diverging section L.sub.3 is bounded by a continuous curve revolved about the central axis 25. As correspondingly shown in these three embodiments of FIGS. 3-5, this continuous curve of diverging section L.sub.3 may be a sloped line forming a conical shape or a parabolic curve forming a paraboloid that resembles a trumpet or funnel shape (hereinafter referred to as a parabolic section).

[0021] Turning now to the distinctions between the embodiments shown in FIGS. 3-5, the following discussion mainly focuses on different configurations of converging section L.sub.2 and intersection I.sub.1. In the first embodiment shown in FIG. 3, a smooth/radial intersection I.sub.1 connects the sections with a radius/arc or similar smooth transition or curve rather than a sharp corner as often seen in the prior art. In this manner, sections L.sub.1 and L.sub.2 share a common tangent direction at the join point I.sub.1. The radial intersection I.sub.1 transitions into a series of three continuous curves forming sub-sections of L.sub.2, namely, L.sub.2A, L.sub.2B, and L.sub.2C. Looking at each of these continuous curves in detail and their corresponding solids of revolution, L.sub.2A substantially comprises a radial curve or circular curve that generally resembles an ellipsoid section, L.sub.2B substantially comprises a sloped line that generally forms a conical section, and L.sub.2C substantially comprises a parabolic curve that generally forms a parabolic section. The intersections between each of these sub-sections of L.sub.2, namely, L.sub.2A, L.sub.2B, L.sub.2C, substantially share a common tangent direction at the intersection point to allow for a smooth transition and avoiding sharp corners or edges.

[0022] In a second embodiment shown in FIG. 4, the configuration is essentially the same as that of FIG. 3 except converging section L.sub.2 comprises two sub-sections, L.sub.2A and L.sub.2C. A smooth/radial intersection I.sub.1 connects sections L.sub.1 and L.sub.2 with a radius/arc or similar smooth transition or curve rather than a sharp corner so that sections L.sub.1 and L.sub.2 share a common tangent direction at the join point I.sub.1. The radial intersection I.sub.1 transitions into a series of two continuous curves forming sub-sections of L.sub.2, namely, L.sub.2A and L.sub.2C. Looking at each of these continuous curves in detail and their corresponding solids of revolution, L.sub.2A substantially comprises a radial curve or circular curve that generally resembles an ellipsoid section and L.sub.2C substantially comprises a parabolic curve that generally forms a parabolic section. The intersections between each of these sub-sections of L.sub.2, namely, L.sub.2A, and L.sub.2C, substantially share a common tangent direction at the intersection point to allow for a smooth transition and avoiding sharp corners or edges.

[0023] In a third embodiment shown in FIG. 5, again the configuration is essentially the same as that of FIG. 3 except the initial intersection I.sub.1 is not radiused and sub-section L.sub.2A is not provided. In this embodiment, a sharp/angular intersection I.sub.1 connects sections L.sub.1 and L.sub.2. Thereafter, a series of two continuous curves form sub-sections of L.sub.2, namely, L.sub.2B and L.sub.2C. Looking at each of these continuous curves in detail and their corresponding solids of revolution, L.sub.2B substantially comprises a sloped line that generally forms a conical section and L.sub.2C substantially comprises a parabolic curve that generally forms a parabolic section. The intersections between each of these sub-sections of L.sub.2, namely, L.sub.2B and L.sub.2C, substantially share a common tangent direction at the intersection point to allow for a smooth transition and avoiding sharp corners or edges.

[0024] In each of these embodiments, except where noted otherwise, the walls forming the sections of the central bore 30 and the transitions between the sections are specifically configured to substantially incorporate smooth transitions and avoid sharp corners or edges. This can be accomplished by including radius edges or by connecting the sections with a radius/arc or similar smooth transition or curve. In computer-aided design, this can be accomplished using the tangent or tangent arc function to connect a line to an arc, circle, parabola, and other similar intersections. Such a feature is available in CAD programs such as SolidWorks, Inventor or ProEngineer. In this manner, at the intersections, the curves share a common tangent direction at the join point. Because much of the turbulence occurs after the initiation point, a focus is to at least have the radial or smooth edges for the sections and curves located distal to the initiation point generated at a gap between the nozzle body and an electrode disposed within the central bore of the nozzle body.

[0025] In addition to the specifically illustrated shapes of the sections in FIGS. 3-5, any number of shapes or functions defining curves that form the bore sections and sub-sections to avoid sharp corners or edges are contemplated herein. By configuring a central bore with these smooth transitions and curves, such a nozzle can achieve cut quality that is equal to or superior to prior art nozzles that do not incorporate smooth transitions or even prior art nozzles that include a secondary flow path within a two-piece nozzle. Without a smooth transition between the cylindrical and conical sections, especially after an initiation point as you approach a throat and discharge orifice, turbulent flow or recirculation zones can occur at these intersections resulting in a decrease in the portion of the plasma jet that is in laminar flow. Through the use of smooth transitions in a central bore, the exit velocity of the plasma jet can be increased over similar designs that do not incorporate smooth transitions. The increased plasma jet velocity can facilitate increased perpendicularity of cut surfaces, sharper corners on the edges of cuts, and smoother or more uniform surface finish of cuts made with a nozzle in accordance with the invention. The net effect being reduced secondary machining of parts cut by a nozzle manufactured in accordance with the present invention.

[0026] Moreover, another advantage of the configuration herein is the combined shape of the converging and diverging sections L.sub.2 and L.sub.3 being generally similar to that of a de Laval style rocket nozzle where the intersection of the converging section L.sub.2 and the diverging section L.sub.3 comprises a throat where the cross-sectional area is at a minimum and produces a laminar flow stream when optimally sized and a turbulent or choked flow stream when improperly sized. In a typical de Laval style rocket nozzle the length of the diverging section is longer than the converging section of the nozzle. In contrast, the length of converging section L.sub.2 is longer than the length of the diverging section L.sub.3 in a nozzle made in accordance with the present invention. The specifically configured converging and diverging sections herein increase the velocity of the plasma jet produced by the nozzle through the use of a Venturi effect, similar to the de Laval nozzle, but without the use of a diverging outlet section that is significantly longer than the converging inlet section. In this manner, the configuration herein improves upon the de Laval style plasma torch nozzles of the prior art.

[0027] The following examples illustrate specific embodiments and example dimensions of the invention.

[0028] Referring to the embodiment of the present invention illustrated in FIG. 3, the following detailed dimensions illustrate a specific example of the invention. In this specific example, the conical section L.sub.2B and the central axis 25 forms an angle/slope within a range of 30-60. The throat 34 constitutes a minimum inner diameter of the nozzle 20 and is within a range of 0.001905 m (0.075 in) to 0.00254 m (0.100 in). The diverging section L.sub.3 can be defined as a conical or parabolic section with an angle/slope between 0-15 relative to the central axis 25 of the nozzle 20. The curve of the diverging section L.sub.3 is connected tangent to the curve of the converging section L.sub.2 at the throat 34.

[0029] Referring now to the embodiment of the present invention illustrated in FIG. 5, the following detailed dimensions illustrate a specific example of the invention. In this specific example, the conical section L.sub.2B forms a fixed angle/slope of 43 relative to the central axis 25, but this angle can be between 30 and 60. In this case, the throat 34 constitutes a minimum inner diameter of the nozzle 20 and is 0.0020574 m (0.081 in), but can be within a range of 0.001905 m (0.075 in) to 0.00254 m (0.100 in), for a plasma torch that has a plasma gas mass flow rate of substantially 80 L/min. It should be noted that the throat 34 will have to be resized for a plasma torch that uses a different mass flow rate for the plasma gas, such as a plasma torch with a different current rating. The diverging section L.sub.3 is defined by a conical section that has an angle/slope of 5 relative to the central axis 25, but can be between 0-15. The curve of the diverging section L.sub.3 is connected tangent to the curve of the converging section L.sub.2 at the throat 34.

[0030] Testing has revealed that the exit velocity of nozzle 20 manufactured in accordance with the present invention is preferably kept at or below supersonic to prevent separation of plasma jet, rather Mach number less than or equal to 1. Maintaining an exit velocity between 200 m/s and 343 m/s when compressed air is used as the plasma gas has yielded favorable results, in particular 278 m/s, for nozzle 20 with a throat 34 diameter between 0.001905 m (0.075 in) and 0.00254 m (0.100 in). The pressure and mass flow rate of the plasma gas are accounted for when sizing nozzle 20 in accordance with the invention. Testing has determined that a feed orifice 32 to discharge orifice 39 pressure ratio between 1.40 and 1.15 produces beneficial results. Additional testing with compressed air as the plasma gas has determined that the ratio of exit velocity to throat 34 diameter should be between 1.0287e-5 seconds to 5.998e-6 seconds.

[0031] The pressure drop produced by a nozzle 20 manufactured in accordance with the present invention has been found to be within a range of 62.05 kpa (9 psi) and 137.89 kpa (20 psi) depending on the mass flow rate and the geometry of the diverging and converging sections. In one embodiment, the pressure drop was found to be substantially 103.42 kpa (15 psi.). The pressure drop in a nozzle 20 designed in accordance with the present invention will be lower than a prior art design that does not have smoother radial transitions. Additionally, prior art nozzles that have a secondary flow path to reduce turbulence and recirculation zones will inherently have a reduced mass flow rate at the nozzle orifice that translates to a lower exit velocity when compared to a nozzle with a single flow path with similar geometries, like the present invention.