NOZZLE FOR A LIQUID-COOLED PLASMA CUTTING TORCH WITH GROOVES

Abstract

This application relates to a nozzle (3) for a liquid-cooled plasma cutting torch, having at least one groove (6a) which is arranged on an outer wall (4) of the nozzle (3) with which the liquid makes contact, is oriented with the direction of its longitudinal axis (18) approximately perpendicular to the nozzle mid-axis (17) of the nozzle (3) and reduces the wall thickness (15) of the nozzle (3), at least in this region, and has a groove base (12, 13) that reaches into the wall thickness (15), wherein the groove base (12, 13) of the groove (6a) is formed so as to be approximately parallel to the contour of the inner wall (5) of the nozzle (3).

Description

FIELD OF THE INVENTION

The subject matter of the invention is a nozzle for a liquid-cooled plasma cutting torch with improved cooling.

PRIOR ART

Plasma cutting is a thermal cutting procedure, in which the material is melted by the plasma jet, and is blown out of the kerf.

Plasma arc cutting is particularly suited for cutting alloyed steels and nonferrous metals. With these materials, the melting temperatures of the resulting oxides are higher than that of the metal itself. For this reason, autogenic torch cutting is not possible.

With plasma cutting torches a pilot light arc is ignited between the tungsten electrode and the torch nozzle. The gas flowing through the nozzle is ionized thereby, i.e. it becomes electroconductive (plasma gas). By activating the plasma flow, the arc between the electrode and the workpiece then bums. The thin plasma jet generated in this manner exits the cooled tapered nozzle with a high energy density.

The molten liquid material is then blown from the kerf by the high exit speed of the plasma gas resulting from the uniform advancement of the cutting torch. The cutting rates, depending on the thickness of the material, range between 1 m/min. to 8 m/min.

In order to minimize the resulting environmental impacts such as, e.g. smoke, dust, noise and UV radiation during plasma cutting, a water shielding is implemented during the cutting process.

This may be formed either through a water curtain surrounding the torch, or by cutting in a water bath.

Plasma cutting is distinguished by a good cutting quality and a high cutting speed at comparably low costs. As a result, it is already a permanent production fixture in many industrial fields.

Plasma cutting torches are subdivided into two categories:

• • Direct plasma generators: The arc is transferred directly to the substrate that is to be processed. The anode is located outside of the plasma generator.
  • Indirect plasma generators: The arc exists only in the plasma generator—the anode is a component of the plasma generator.

With the use of nitrogen, preferably a tungsten electrode is used. In contrast to this, when compressed air is used, an electrode having a zirconium or hafnium coating is used, as said coating results in a formation of a more stable arc spot.

The nozzle of the plasma cutter is exposed to a high thermal load, and for this reason it is preferably made of a metallic material having a high degree of thermal conductivity and electric conductivity as well. In order to obtain greater durability with regard to the nozzle, said nozzle is cooled with a liquid, such as water, for example. The cooling agent flows through the coolant space formed by the nozzle and the nozzle hood. In order to efficiently exploit the cooling effect of the liquid, according to the prior art, the nozzle has projections extending from the nozzle wall, which are supposed to cause a turbulence in the cooling fluid. This enables a better heat transfer from the nozzle wall to the cooling fluid.

DE 1 565 638 shows a nozzle configuration for a plasma torch. The torch head has a particularly slender shape and is preferably used for plasma cutting or for the preparation of welding edges. A coolant space is formed between the nozzle hood and the cutting nozzle, designed as a straight, uniform annular channel. The feeding and drainage of the cooling fluid is carried out in the upper region of the torch nozzle.

A nozzle for a liquid cooled plasma torch is described in DE 10 2008 018 530 A1. The nozzle features at least one cone-shaped projection on the exterior wall of the nozzle, expanding toward the tip of the nozzle, which forms a flow resistance, or a turbulence, respectively, in the cooling fluid. The projections extend, in all of the embodiment examples presented therein, away from the exterior wall of the nozzle, and are at a certain angle with respect to the tip of the nozzle.

A plasma torch is described in WO 92/00658 having a nozzle exterior wall with grooves directed inwards. The incisions are rectangular, and have a straight groove base. The groove base runs parallel to the central axis of the nozzle as a result. In the sloped section of the exterior wall of the nozzle, the straight groove base depicts either a cross-section reduction of the wall thickness, wherein the wall thickness in the upper region of the groove base is disadvantageously thin. Or the spacing between the interior wall and the straight groove base is so great that no effective heat transfer from the nozzle wall to the cooling fluid can take place.

All of the aforementioned embodiments have either a straight coolant space, or a coolant space having extending projections, respectively, or they have grooves directed inward having a straight groove base. Both embodiments present a disadvantage with respect to an efficient heat transfer from the nozzle wall to the cooling fluid.

SUBJECT MATTER OF THE INVENTION

The invention therefore assumes the objective of obtaining a nozzle for a liquid cooled plasma torch having an improved cooling effect.

To attain the assumed objective, the invention is characterized by the technical teachings of Claim 1.

The substantial characteristic of the invention is that the groove base of the groove is designed to be substantially parallel to the shape of the interior wall of the nozzle.

In a first embodiment, the nozzle has individual grooves, designed as inward oriented incisions in the exterior wall of the nozzle. The grooves have preferably a rectangular profile, whereby they have a sloped groove base. The sloped groove base is designed such that it runs parallel to the contour of the interior wall of the nozzle. This represents a substantial advantage over the prior art, because as a result, a more effective heat transfer from the interior wall to the cooling fluid flowing over the exterior wall can be achieved. In another design, the grooves can have a trapezoidal profile. In this case, the grooves become wider in the form of a wedge from the groove base outward.

Another advantage is the uniform wall thickness obtained in the region of the sloped groove base. By this means, not only is a certain minimum wall thickness provided, but at the same time, a good heat transfer is also ensured.

The number of grooves on the exterior wall of the nozzle should not be restricted to one—numerous grooves in both the straight region as well as in the sloped region of the nozzle may be present. A symmetrical configuration, however, of the annular grooves is preferred.

In a second embodiment the groove is designed as an annular groove, and has a sloped groove base running parallel to the contour of the interior wall. A more effective heat transfer over the entire exterior circumference of the nozzle takes place by means of the annular groove.

Another advantage is that the sloped groove base enables a minimal wall thickness. Moreover, as a result of the existing minimal wall thickness, an embodiment having numerous annular grooves on the exterior wall of the nozzle can be realized.

In another preferred embodiment the groove is designed as a longitudinal groove, and runs in the direction of the longitudinal central axis of the nozzle. By this means, it is possible to allow the cooling fluid to run along the nozzle. The longitudinal groove is preferably rectangular in shape, whereby the groove base is adapted to the contour of the interior wall. As a result, a good heat transfer is made possible with a uniform wall thickness. The embodiment is not limited to one longitudinal groove thereby; it may also have numerous longitudinal grooves in an arbitrary configuration on the exterior circumference.

In the following, the invention shall be explained in greater detail, based on drawings depicting only one means of execution. Other characteristics and advantages substantial to the invention can be derived from the drawings and the descriptions thereof.

They show:

FIG. 1 a: shows the prior art

FIG. 1: is a schematic depiction of a nozzle having grooves and a sloped groove base

FIG. 2: is a cut through FIG. 1 having a groove and a sloped groove base

FIG. 3: is a schematic depiction of a nozzle having annular grooves

FIG. 4: is a cut through FIG. 2 having an annular groove and a sloped groove base

FIG. 5: is a schematic depiction of a nozzle with longitudinal grooves

FIG. 6: is a cut through FIG. 5, with a depiction of the longitudinal grooves

FIG. 7: is another cut through FIG. 5, with a depiction of the longitudinal grooves

FIG. 1 a shows the prior art for plasma cutting torch nozzles. The nozzle device of the plasma torch head 1 consists substantially of a nozzle hood 2 and a nozzle 3. A coolant space 10 is formed between the nozzle hood 2 and the exterior wall 4 of the nozzle 3. A cooling fluid, such as water, for example, flows through the coolant space 10, whereby the liquid is introduced to the coolant space 10 by means of the coolant feed, and removed by means of the coolant return.

The exterior wall 4 of the nozzle 3 has numerous grooves 6a having rectangular profiles, wherein the groove base 12 is straight. The grooves 6a are each directed inward along the longitudinal axis 18 and are at a right angle 19 to the central axis 17 of the nozzle.

The interior wall 5 of the nozzle 3 forms an annular interior space about the central axis 17 of the nozzle for the plasma gas feed 11.

FIG. 1 shows a schematic depiction of a nozzle 3 having numerous, parallel configured grooves 6a. The grooves 6a have a largely rectangular profile, and are located on the exterior wall 4 of the nozzle 3. For this, the embodiment of the groove should not be limited to a rectangle; any other geometric shape is also possible. The grooves 6a are longitudinal incisions in the exterior wall 4, directed inward toward the central axis 17 of the nozzle, wherein the groove base 13 is sloped. The slope of the groove base 13 is the result of the angle 14. The angle 14 is the angle to the central axis 17 of the nozzle. The sloped groove base 13 represents thereby a parallel to the contour of the interior wall 5 of the nozzle 3.

With this embodiment, a uniform wall thickness 15 in the region of the incisions is ensured by the grooves. The grooves 6a are disposed in the conical section of the nozzle 3. Other, additional grooves 23 can be disposed in the cylindrical section of the nozzle 3, outside of the conical section. These too can exhibit a sloped groove base, as is indicated in FIG. 1. Likewise, this groove base may be designed to be straight, and parallel to the likewise vertical inner contour there.

As a result of the sloped groove base 13, the cooling fluid can more effectively accommodate and discharge heat accumulating on the interior wall 5 of the nozzle, because the wall thickness is effectively minimized and there is no danger that with the creation of the grooves by means of a machining of the tool, the minimized wall will be penetrated in the direction of the interior circumference of the nozzle. The sloped groove base therefore provides for a uniform, consistent wall thickness 15 at this cross-section of the wall. This was previously not possible according to the prior art, because the grooves had a straight groove base 12, and therefore resulted in a varying wall thickness. As a result, in the region of the groove base, there was a greater and a lesser wall thickness, impeding the heat transference.

The embodiment example of FIG. 1 shows a plurality of parallel configured grooves 6a in the conical section of the nozzle 3. These are designed either as encompassing or non-encompassing and recessed annular grooves. Moreover, there is a groove 23 located in the cylindrical, straight section of the nozzle, which can exhibit both a sloped groove base 13, as well as a straight groove base 12.

FIG. 2 shows a cut through the section indicated in FIG. 1. In this case, it concerns a depiction of a nozzle having four recessed grooves 6a, which are evenly distributed on the exterior wall 4 of the nozzle 3, and divided by discontinuation sections 20. In addition, the annular interior wall 5 of the nozzle 3 is depicted, which serves as the plasma gas feed 11.

A nozzle is shown in FIG. 3, having a plurality of annular grooves 6b on the exterior wall 4 of the nozzle 3. The annular grooves 6b have a straight groove base 12 in the upper, cylindrical section 21, and in the lower, conical section 22, they have a sloped groove base. The positions of the respective groove bases (12, 13) are based on the contour of the interior wall, and always run parallel thereto. Moreover, it is visible in this depiction that the wall thickness 15 remains constant in all regions of the grooves 6b. This enables an effective heat transfer from the interior wall 5 of the nozzle 3 to the cooling fluid.

FIG. 4 shows a cut through the region indicated in FIG. 3. This shows a top view of the nozzle 3 with the individual wall thicknesses and the encompassing annular groove 6b. The innermost ring forms the interior wall 5 of the nozzle 3, followed by the encompassing annular groove 6b and the exterior wall 4 of the nozzle 3. In addition, the largest circumference of the exterior wall 4 of the nozzle is depicted schematically. The encompassing annular groove 6b can likewise be divided by differently sized discontinuation regions 20.

A nozzle 3 having longitudinal grooves 16 is depicted in FIG. 5. These preferably have a rectangular cross-section and run along the longitudinal axis in the exterior wall 4 of the nozzle 3. The rectangular cross-section is only to be regarded in this case as exemplary; any other geometric shape is also possible for the groove. Likewise, it is possible that the longitudinal grooves 16 only be present in the upper, cylindrical section 21 or in the lower, conical section 22.

FIG. 6 shows a first cut through the FIG. 5. The longitudinal grooves 16 are located in the exterior wall 4 of the nozzle 3. The wall thickness is, however, reduced to the same degree in all regions of the grooves. The interior wall 5 of the nozzle 3 is designed to be annular in shape, and serves to conduct plasma.

FIG. 7 shows another cut through FIG. 5. The longitudinal groove 16 extends thereby along the body of the nozzle, both over the cylindrical section 21 as well as over the conical section 22, and is located in the exterior wall 4 of the nozzle 3.

The invention also claims a configuration, or combination, respectively, in which both annular grooves 6a, 6b as well as longitudinal grooves 16, 22 are disposed.

KEY TO THE DRAWINGS

1. plasma torch head

2. nozzle hood

3. nozzle

4. exterior wall (nozzle)

5. interior wall (nozzle)

6 a. groove (incision)

6 b. annular groove

7. projection

8. cooling agent feed

9. cooling agent return

10. coolant space

11. plasma gas conductor

12. groove base (straight)

13. groove base (sloped)

14. angle

15. nozzle wall (wall thickness)

16. longitudinal groove

17. central axis of the nozzle

18. longitudinal axis

19. angle

20. discontinuation section

21. region

22. region

23. groove (straight region)

Claims

1. A nozzle for a liquid-cooled plasma cutting torch having numerous, spaced annular grooves disposed on the exterior wall of the nozzle that comes into contact with the liquid, oriented in the direction of the longitudinal axis substantially perpendicular to the central axis of the nozzle, which reduce the wall thickness of the nozzle in at least this region, and in each case have a groove base extending into the wall thickness, wherein the groove bases of the annular grooves are designed to be substantially parallel to the contour of the interior wall of the nozzle, characterized in that numerous spaced longitudinal grooves run in the exterior wall of the nozzle, the groove bases of which are also designed to be substantially parallel to the contour of the interior wall of the nozzle, and the longitudinal grooves have a region having a straight groove base and a region having a sloped groove base at an angle to the central axis of the nozzle, and that the annular grooves, in and of themselves, are closed, and have discontinuation sections.

2. The nozzle according to claim 1, characterized in that the wall thickness is always reduced to the same degree in the region of the groove base.

3. The nozzle according to claim 1, characterized in that the groove is designed as a closed, annular groove miming along the circumference of the nozzle.

4. The nozzle according to claim 1, characterized in that the groove is designed as an annular groove on the circumference of the nozzle, divided by discontinuation sections.

5. The nozzle according to claim 1, characterized in that at least one longitudinal groove runs in the exterior wall of the nozzle.

6. The nozzle according to claim 1, characterized in that the longitudinal groove has a sloped groove base running substantially parallel to the contour of the interior wall of the nozzle.

7. The nozzle according to claim 1, characterized in that the longitudinal groove has a region having a straight groove base and a region having a sloped groove base.

8. The nozzle according to claim 1, characterized in that the wall thickness of the nozzle wall in the region of the groove base is such that the wall thickness of the exterior wall in this region is always reduced to the same degree.

9. The nozzle according to claim 2, characterized in that the groove is designed as a closed, annular groove running along the circumference of the nozzle.

10. The nozzle according to claim 3, characterized in that the groove is designed as an annular groove on the circumference of the nozzle, divided by discontinuation sections.

11. The nozzle according to claim 2, characterized in that at least one longitudinal groove runs in the exterior wall of the nozzle.

12. The nozzle according to claim 3, characterized in that at least one longitudinal groove runs in the exterior wall of the nozzle.

13. The nozzle according to claim 4 characterized in that at least one longitudinal groove runs in the exterior wall of the nozzle.

14. The nozzle according to claim 2, characterized in that the longitudinal groove has a sloped groove base running substantially parallel to the contour of the interior wall of the nozzle.

15. The nozzle according to claim 3, characterized in that the longitudinal groove has a sloped groove base running substantially parallel to the contour of the interior wall of the nozzle.

16. The nozzle according to claim 4, characterized in that the longitudinal groove has a sloped groove base running substantially parallel to the contour of the interior wall of the nozzle.

17. The nozzle according to claim 5, characterized in that the longitudinal groove has a sloped groove base running substantially parallel to the contour of the interior wall of the nozzle.

18. The nozzle according to claim 2, characterized in that the longitudinal groove has a region having a straight groove base and a region having a sloped groove base.

19. The nozzle according to claim 3, characterized in that the longitudinal groove has a region having a straight groove base and a region having a sloped groove base.

20. The nozzle according to claim 4, characterized in that the longitudinal groove has a region having a straight groove base and a region having a sloped groove base.