Patent Application
20220386445
The invention relates to a consumables holder assembly for a plasma arc torch. The plasma arc torch which is also known as plasma arc, plasma gun or plasma cutter which is a device for generating a directed flow of plasma. The high energy plasma jet is generated by ionization of plasma gases and is directed via the plasma torch to a workpiece to be treated. The plasma jet can be used for applications including plasma arc welding, plasma spraying and plasma gasification for waste disposal. Thermal plasmas are generated in plasma torches by direct current, alternating current, radio-frequency and other discharges.
The plasma arc welding (PAW) process which is carried out by the plasma arc torch is similar to the gas tungsten arc welding (GTAW). The difference from GTAW is that in PAW, by positioning the electrode within the body of torch, the plasma arc can be separated from the shielding gas envelope. The plasma is then forced through a nozzle which constricts the arc and plasma exits the orifice at high velocities which approaches the speed of sound and a temperature approaching 28000° C. or higher.
A typical plasma arc torch comprises a torch main body, an electrode and a nozzle at the distal end of the torch. The torch main body comprises an anode element which is electrical communication with the positive side of a power supply, and a cathode body that is electrical communication with the negative side of the power supply. The torch main body further comprise coolant supply tube, plasma gas supply tube, shielding gas supply tube by which the coolant and gas are directed to the distal end of the torch, where the electrode and nozzle are positioned. The electrode carries negative potential and operates as a cathode, whereas the nozzle constitutes a positive potential and operates as an anode. In operation, the plasma gas will be delivered from the proximal end of the torch to the chamber formed between the electrode and the nozzle. The plasma gas is ionized in the chamber and results in a pilot arc. As the torch is moved to a position close to the workpiece, the arc jumps from the torch nozzle to the workpiece to form an electric arc between the electrode and the workpiece. Accordingly, the workpiece serves as the anode and the plasma arc torch is operated in a transferred arc mode.
The energy of the plasma jet and thus the temperature is dependent upon the electrical power employed to create arc plasma. A typical value of the temperature obtained in a plasma arc torch may be of the order of 28000° C. against about 5500° C. in ordinary electric welding arc. Due to the high temperature torch components must be properly cooled in order to prevent damage or malfunction to increase the operating life and maintain the accuracy of the operation.
The plasma arc torch is operated with high current levels and high temperature under which the components of the torch, especially the electrode and nozzle, will be damaged or wearied after a certain period of operation even with the cooling. Therefore, these components, which are commonly known as consumable components, need to be replaced frequently. In addition, the arrangement of the consumable components requires an alignment of high concentricity to ensure the welding accuracy. Hence, every replacement of the components must fulfill the requirement of the concentricity over the life of the plasma arc torch.
However, the existing systems available on the market are difficult to use and difficult to assemble and present a steep learning curve for the operator. Existing system are strongly dependent on the operator and if the arc torch is assembled correctly, the results of the torch performance changes from one consumable set to another set if the replacement is not carefully checked and verified by a qualified welder.
Most torches are not easy to use. That means they are prone to errors and the assembling procedure is very time consuming. E.g. threads are used to assemble the single parts.
In most cases the electrode is clamped with radially with a chuck. The contact surface is therefore very limited and thus the electrical and especially the thermal contact is bad.
Torches with a changeable consumable holder compensate this with direct cooled electrodes. The disadvantage is an open water circuit. Furthermore, the friction between electrode and conductive element on the torch creates friction.
The present invention provides a consumables holder assembly for a plasma arc torch according to claim 1 which solves the aforementioned problem.
The plasma arc torch comprises a torch main body having a torch head and the consumables holder assembly in the distal direction of the torch. The consumables holder assembly comprises a main body, a shielding cup which engages the main body to hold the consumable components within the space formed between the cup and the main body. Further, the assembly comprises at least one consumable component selected from an electrode, a nozzle, a plasma gas distributor (PGD), a shielding gas distributor (SGD) which are all placed inside the shielding cup.
The torch main body is in connection with a power supply. It comprises an anode element which is in electrical communication with the positive side of a power supply, and a cathode body that is electrical communication with the negative side of the power supply. The torch main body further comprise coolant supply tube, plasma gas supply tube, shielding gas supply tube and optional focus gas supply tube by which the coolant and gas are directed to the distal end of the torch, where the electrode and nozzle are positioned.
The electrode carries negative potential and operates as a cathode, whereas the nozzle constitutes a positive potential and operates as an anode. The nozzle comprises a central exit orifice by which the plasma arc is constricted and then exits out of the torch towards the workpiece to be treated. The nozzle is electrically isolated from the electrode by the plasma gas distributor. There is an arc chamber formed between the electrode and the nozzle in which the plasma gas is ionized.
Advantageously, the nozzle comprises two focus gas passageways which extend axially to the distal end of the torch to lead a focus gas from the proximal end to outside of the torch via two focus gas holes. The focus gas is used for injection on two sides of the arc. It influences the shape of the arc and changes it from a circular/symmetric arc to oval shape by cooling the fringes of the arc. In so doing, the focus gas also decreases the arc pressure. These two focus holes are positioned perpendicular to the welding direction in operation which helps to further shape the arc in a desirable way. In addition, it is preferably to have visual signs on the outside of the torch indicating the orientation of the focus holes so that the operator can easily recognize the position of the arc torch. By doing so, it is not necessary for the operator to check the downside of the nozzle every time to determine the correct operation direction of the arc torch
Preferably, the plasma gas distributor is cylinder-shaped and comprises multiple circumferential holes about its axis through which the plasma gas goes through. The electrode is preferably stick-shaped without any hollow spaces or holes therein and preferably made of tungsten.
The shielding gas distributor (SGD) is cup-shaped and preferably made of plastic and metallic material as like polyether ether ketone (PEEK) and brass or copper. Any other thermosoftening plastic are also possible. The proximal plastic part of the SGD ensures the insulation of the shielding cup to the electrical signals within the torch and the distal metallic part of the SGD with high heat resistance prevent the SGD from being damaged easily by the high temperature of the arc and thus prolong the lifetime of the shielding gas distributor. The shielding gas distributor delivers shielding gas via the gap between the shielding cup and the shielding gas distributor to provide shielding of the weld pool.
The shielding gas cup holds all the consumable components inside and is engaged to the main body by connection means as like thread means.
In operation, a direct current power source having a current up to 550 amps is preferably applied. The shielding gas is delivered from the shielding gas supply at the proximal end of the torch to the distal end of the torch via the gas shielding distributor to prevent the weld poos from contacting the atmosphere and thus provide a shielding environment. The plasma gas is delivered from plasma gas supply at the proximal end of the torch via the plasma gas distributer to the arc chamber. The plasma gas is ionized in the arc chamber and results in a pilot arc. As the torch is moved to a position close to the workpiece, the arc jumps from the torch nozzle to the workpiece to form an electric arc between the electrode and the workpiece. The arc is constricted with the help of the small diameter nozzle which squeezes the arc, increases its pressure, temperature and heat intensely. Accordingly, the workpiece serves as the anode and the plasma arc torch is operated in a transferred arc mode. A non-transferred arc process with the present invention is also possible.
The distal direction refers to the axial direction along the arc torch from the torch head towards the nozzle and the proximal direction refers to an axial direction along the arc troch from the nozzle to the torch head.
The electrode, PGD, nozzle and SGD are assembled by a drop-in mount with the different geometry of these components. Preferably, the stick-shaped electrode comes through the ring-shaped PGD, wherein the electrode comprises a bottom seat at its proximal end which is preferably made of copper. The seat encloses the bottom of the electrode and prevent the PGD from falling out when it is assembled with the electrode. These two parts drop into the nozzle which holds them in position and forms the arc chamber with the electrode. The assembled parts are then attached to the main body and then placed inside the SGD. Preferably, the SGD has an indirect contact with the main body via an O-ring. Preferably, all these parts are assembled only by their different geometric diameters fitting in with each other without any fixing or locking means as like thread. The parts are then attached onto the main body by a connection means as like thread or bayonet mount. Finally, the shielding cup is screwed onto the proximal portion of the main body.
This assembled part, which is also the consumables holder assembly, can be attached to or detached from the torch head as one unit so that this unit can be replaced as a whole. A such designed consumables holder assembly eases the process of replacement of the consumable components which ensures a good repeatability of the assembly and welding outcome so that no highly qualified operator or complicated check is necessary.
Preferably, among the mentioned consumable components only the nozzle is in direct connection with the distal portion of the main body.
A mechanical attachment mechanism is provided in the connection means which make the connection means engageable with the torch head. It could be a thread or a bayonet mount which allows the connection means move proximally towards the torch head and prevent a rotation after the engagement. The preferred bayonet mount comprises at least two pins at the connection means which correspond to the grooves situated in the torch head. The consumables holder assembly attaches to the torch head via the bayonet mount which prevents a rotational movement between the whole consumables holder assembly and the torch head, and thus ensure a high concentric alignment therebetween. Consequently, all the supplies for coolant, plasma gas, focus gas and shielding gas in the torch main body and the consumable holder assembly can be accurately aligned to allow fluid connection from the proximal end to the distal end of the arc torch.
A compression member, preferably a spring, is provided between the connection means and the main body which exerts a force onto the connection means and allows it keep moving upwards to have its bayonet pins inserted into the corresponding grooves of the torch head. In operation, when the whole consumables holder assembly is attached to the torch main body, the electrode engages the torch head and initiate the contact. The inner component comprising main body, electrode, PGD, nozzle, shielding cup and SGD then stay axially in place, while the connection means keeps moving up proximally via the compression means and the mechanical attachment mechanism and activating a force on the electrode. Through a proper design the axial movement for engagement compresses the compression means through a pre-determined distance which results a pre-defined force on the contact area between the electrode and torch head. It ensures the correct contact for both electrical connection and thermal heat transfer from the electrode to the torch main body.
In one preferred embodiment the main body is made of a metallic material and an insulative material. The metallic material is preferably brass or copper and the insulative material is thermoplastic, preferably polyether ether ketone (PEEK). Advantageously, the metallic material is used in the distal portion of the main body which is in direct connection with the hot nozzle in the operation so as to improve the heat resistance of the main body. The insulative material is used in the proximal end of the main body to prevent the electric communication between the cathodic parts and anodic parts. More preferably, the referred distal portion made of metallic material is ring shaped and amounts 10% to 30% of the axial length of the main body and the proximal portion made of insulative material amounts 70% to 90% of the axial length of the main body.
Preferably, the middle section of the main body comprises at least two circumferential grooves having the same axis, wherein the first groove comprises a first radial passageway and the second groove comprises a second radial passageway which both extend through the main body and allow a fluid communication between the exterior and the interior of the main body. Preferably, there is only one radial passageway on each circular groove. More preferably the two passageways are axially in line with each other.
In addition, an essentially axial groove is provided between the at least two grooves which allows a fluid communication from the first groove to the second groove, especially from the first radial passageway to the second radial passageway. Preferably, the axial groove is positioned in the opposite of the two passageways, which has an angle of 180° to the passageways, so that the cooling fluid can cool the both whole grooves. In operation, a cooling fluid, preferable water, flows from the interior of the main body outwards via the first radial passageway in the first groove and then flows to the second groove via the axial groove and then flows to the interior of the main body via the second radial passageway in the second groove. Preferably, the first and second grooves comprises only one such radial passageway respectively and preferably the main body contains only two such passageways for circulating a cooling fluid. With a such configurated middle section a more efficient cooling effect is achieved with minimal space within the torch which simplifies the torch structure and improves the torch robustness at the same time.
Furthermore, the main body, especially the middle section of the main body, comprises multiple axial passageways for passing the shielding gas from the interior to the exterior of the main body. The shielding gas flows through the main body to the shielding gas distributor and exits at the distal end of the torch via the gap between the shielding gas distributor and the shielding cup.
Preferably, there is no passageway in the main body through which the plasma gas flows and neither electrical power or signals are passed through the main body.
Preferably, there are three alignments between the torch head, main body and the connection means.
The connection means is preferably aligned with the torch by the mechanical attachment mechanism as like thread, but preferably a bayonet mount. The bayonet mount comprises at least two pins which correspond to the grooves situated in the torch head. The consumables holder assembly attaches to the torch head via the bayonet mount which prevents a rotational movement between the whole consumables holder assembly and the torch head, and thus ensure a high concentric alignment therebetween. Consequently, all the supplies for coolant, plasma gas, focus gas and shielding gas in the torch main body and the consumable holder assembly can be accurately aligned to allow fluid connection from the proximal end to the distal end of the arc torch.
The connection means is preferably aligned with the main body by multiple locking pins which prevents a rotation between the connection means and the main body when they are engaged.
The main body is preferably aligned with the nozzle by at least one main body pin which is positioned in the distal end of the main body. More preferably, there are two main body pins sitting opposite to each other at the distal end of the main body which correspond to the recesses in the nozzle. The nozzle is assembled to the main body by inserting these two pins into the corresponding recesses of the nozzle and thus prevent any rotation between the nozzle and the main body.
In use of these three alignments, it ensures that for every replacement of the consumables holder assembly, the supply of the cooling medium, shielding gas, plasma gas and focus gas are accurately aligned with the torch head without any complicated assembly and without careful check by a qualified operator.
Preferably, the consumables holder assembly comprises orientation means providing angular localization between the consumable holder assembly and the main torch. More preferred, these orientation means has a 180-degree symmetry allowing assembly of the consumable holder in one of two orientations.
In a preferred embodiment there is an external visual feature between the connection means and the torch head which indicates the orientation of the focus holes at the nozzle. By having this feature the operator does not have to look down at the focus hole every time for replacement to determine the orientation of the arc torch in respect of the travelling direction of welding. It makes the replacement of the consumables holder assembly easier and more efficient.
In the plasma arc torch, at least three gas supply tubes are provided for plasma gas, shielding gas and focus gas respectively and at least one supply tube is provided for coolant medium to prevent overheat of the torch. Each gas flow is preferably separately controlled in terms of the gas composition, gas flow etc.
The shielding gas comprises preferably pure argon. The focus gas comprises preferably up to 70 vol. % argon and the rest could be H2, He, O2, N2 or mixture thereof. The plasma gas comprises preferably also up to 70 vol. % argon and the rest could be H2, H2, N2 or mixture thereof. The coolant medium is preferably liquid, more preferably water or glycol.
The present invention will be further discussed with the detailed description and the accompanying drawings.
A torch head 2 is provided at the distal end of the torch main body 1 and is further adjoined with a coolant supply tube, a plasma gas supply tube and a shielding gas supply tube. The plasma gas and shielding gas are supplied from the proximal end of the plasma arc torch via the torch head to the consumables holder assembly at the distal end and released to the atmosphere to benefit the welding process, while the coolant is supplied also from the proximal end to the consumables holder assembly and then return back to the proximal end of the plasma arc torch during operation.
The torch main body 1 is engaged with the consumables holder assembly 3 by connection means which ensures an accurate alignment of the supply passageways of the fluid in both torch main body 1 and the consumables holder assembly 3. The consumables holder assembly 3 holds all the consumable components in its housing which needs to be replaced regularly. By such a construction in accordance with the present invention all the consumable components can be attached to or detached from the torch head as one unit. This unit, which is the consumables holder assembly 3, provides a quick and reliable replacement of the consumable components which ensures an accurate alignment of the torch and a good repeatability of the welding outcome.
In addition, the referred proximal end and distal end are indicated as A and B respectively in
The main body 4 is a cylinder-like shaped component which holds the electrode 6, PGD 8, nozzle 7 within its housing and can be connected and disconnected with the torch head. The main body 4 comprises coolant passageways allowing coolant to flow through, and it comprises also shielding gas passageways allowing shielding gas to flow through the main body 4. By “flow through” it means that the coolant or the shielding gas flows from interior to exterior of the main body 4 or vice versa. The main body 4 comprises however no passageway through which the plasma gas flows. Furthermore, there is no electrical power or signals are passed through the main body 4. The main body 4 is made of metallic and plastic material, preferably made of brass and polyether ether ketone.
After the electrode 6 is engaged to the torch head, the electrode 6 carries negative potential and operates as a cathode, whereas the nozzle 7 carries positive potential and operates as an anode. The electrode 6 is stick shaped without hollow space inside and is made of tungsten. There is an arc chamber 10 formed between the electrode 6 and the nozzle 7 in which a pilot arc is generated by ionization of the plasma gas.
The plasma gas is flowed into the arc chamber 10 through the PGD 8 which surrounds the electrode 6. The PGD 8 has multiple circumferential plasma gas holes 12 about its axis through which the plasma gas flows radially inwards into the arc chamber 10. The PGD 8 is assembled with the electrode 6 by sitting on a seat of the electrode 11 which encloses the electrode 6 on its proximal end.
The electrode 6 and the surrounding PGD 8 are engaged to the nozzle 7 by dropping them into the central recess of the nozzle 7. The central recess has a shoulder 16 which has a diameter smaller than it of the PGD 8 but bigger than it of the electrode 6 which holds the PGD 8 sitting on the shoulder and render the electrode 6 go through to form the arc chamber 10. By having these components constituted as such, the anodic nozzle 7 is electrically isolated from the cathodic electrode 6 by the PGD 8. The nozzle 7 further comprises a central exit orifice 15 by which the arc is constricted. In operation, when the torch is moved to a position close to the workpiece to be treated, the pilot arc jumps from the torch nozzle 7 to the workpiece through the orifice 15 which constricts the arc to form a plasma arc between the electrode 6 and the workpiece. Accordingly, the workpiece serves as the anode and the plasma arc torch is operated in a transferred arc mode.
Furthermore, the nozzle 7 comprises two focus gas passageways 22 which extends axially to the distal end of the torch to lead a focus gas from the proximal end to outside of the torch via two focus gas holes 23 as shown in
The SGD 9 is cup-shaped and made of insulative and metallic material, preferably PEEK and brass. The SGD 9 comprises a shoulder at its distal end which holds the nozzle 6 in a drop-in way when they are assembled. Furthermore, the SGD 9 comprises passageways for shielding gas to flow through it. After the shielding gas goes through the SGD 9, it flows into a shielding gas passageway 14 which is formed between the shielding cup 5 and the SGD 9, and then flows out of the torch to provide a shielding atmosphere surrounding the plasma arc which is generated through the exit orifice 15 in the middle.
The shielding cup 5 is the outermost cup which holds all the other consumable components within its internal space. It is engaged on the proximal portion of the main body 4 by a thread means.
Preferably, the connection means comprises two pins which lock grooves provided at the torch main body 1 to form a bayonet mount to engages the whole consumables holder assembly 3 to the torch main body 1. The bayonet mount ensures a high concentric alignment between the consumable holder assembly 3 and the torch main body 1 which prevents any undesirable rotation therebetween, so that all the supplies for coolant, plasma gas, focus gas and shielding gas in the torch main body 1 and the consumables holder assembly 3 can be accurately aligned to each other to allow fluid connection from the proximal end to the distal end of the arc torch.
Preferably, there is a visual feature (not shown) on the connection means 12 and the outside of the torch head 2 which indicates the orientation of the focus holes 23 at the nozzle 7. When the consumables holder assembly 3 is engaged with the torch head 2 correctly, the visual feature on the connection means 12 and the torch head 2 matches together and shows the direction of the focus holes 23 so that the operator does not have to look down at the focus hole 23 in nozzle 7 to determine the orientation of the arc torch in respect of the travelling direction of welding which makes the replacement of the consumables holder assembly 3 easier and more efficient.
Moreover, there is an essentially axial groove 24 provided between the first groove 18 and the second groove 19 which allows a fluid communication from the first groove to the second groove, especially from the first radial passageway 20 to the second radial passageway 21. The axial groove 24 is positioned in the opposite of the both radial passageways which enable an efficient cooling of the both grooves (18, 19). In operation, the coolant, e.g. water, flows from the interior of the main body towards the first groove 18 via the first radial passageway 20 and then flows to the second groove 19 via the essentially axial groove 24 and then flows again in the interior of the main body 4 via the second radial passageway 21 in the second groove 19.
Furthermore, the middle section 17 comprises multiple axial passageways at its circumference (not shown) for passing the shielding gas axially from the interior to the exterior of the main body 4 and then through the shielding gas passageway 14 to exit the arc torch. There is no passageway in the main body 4 to pass plasma gas and the electrical power or signals are also not passed through the main body 4. Moreover, the main body 4 comprises two main body pins (29) sitting opposite to each other which correspond to the recesses in the nozzle (7) to engage it to the nozzle (7) to prevent rotational movement between the nozzle (7) and the main body (4).
The main body 4 is made of metallic and plastic material. It is shown in the
When the assembled consumable holder assembly 3 is attached to the torch main body 1, the electrode 6 engages the cathode of the torch main body 1 and initiate the contact. As the consumable holder assembly 3 is engaged with the torch main body 1, the inner component comprising main body 4, electrode 6, PGD 8, nozzle 7, shielding cup, SGD stay axially in place, which the connection means keeps moving up through the bayonet mount of the connection means 12 engaging the spring 27 activating a force on the electrode 6. Through the proper design the axial movement compresses the spring 27 through a pre-determined distance which results a pre-defined force on the contact area between the electrode 6 and torch head 2. It ensures the correct contact for both electrical connection and thermal heat transfer from the electrode 6 to the torch main body 1.
The engagement of the consumables holder assembly 3 and the torch main body 1 allows all the fluid communication of the coolant, plasma gas, shielding gas, focus gas to flow from the proximal end to the distal end of the torch.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19020626.8 | Nov 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/025493 | 11/5/2020 | WO |
