Torch for arc weldinq or cuttinq and method usinq said torch

The invention relates to a torch for plasma processing (welding, cutting, spraying, etc.)· Since the electric arc requires electric energy to be conducted from the energy source towards the electrode, which is positioned in the center of the torch, different components of the torch such as the torch body and the electrode or the torch body and the plasma nozzle need to be connected to each other in an electrically conductive manner while other components need to be electrically isolated from each other in order to prevent short circuits. Conventionally, electrically conductive connections are realized by metal-on-metal contacts.

In such torches different working fluids are used simultaneously, e.g. cooling water or air, inert shielding gases and/or active shielding gases. Therefore, it is necessary to connect different components of the torch in a sealing manner, so that the different fluids cannot mix with or contaminate each other but remain in their respective passageways. Usually such sealing functions are realized through the use of a deformable member such as an O-ring or a gasket.

For maintenance purposes, the torch needs to be disassembled and reassembled regularly, so that the sealing members need to be replaceable. Typical metal sealing components such as copper washers or gaskets can hardly be used due to the need of specialized tools to ensure proper sealing functionality.

The present invention realizes the sealing and electrically conductive connection by using at least one elastically deformable and electrically conductive sealing member. This has the advantage that both functionalities are provided by the same component, offering more freedom of design and the potential to minimize the overall sizing of the torch which is desirable for robotic and manual applications (in welding, cutting, spraying, etc.). A further advantage is that tolerances for fittings can be larger, since the electrically conductive connection does not rely on metal-on-metal contact but is effected by the electrically conductive and elastically deformable sealing member, ensuring electrical conductivity over a wider range of distances. As a consequence, the electrical contact can also occur on a radial surface and therefore no hitting surface, that is in traditionally designed torches the end face surface of a part, is necessary to conduct the current. This drastically reduces the effort for end machining.

Suitable materials for corresponding electrically conductive sealing members are conductive polymers, conductive rubber or non-conductive elastomers, thermoplastic elastomers, neoprene, silicone rubbers, silicone caulks, poly (vinyl chloride) or EPDM with conductive fillers and/or coatings, including but not limited to aluminum, silver, copper, nickel or other metallic material or graphite or other carbon based conductive material like carbon black, fullerenes or carbon nanotubes. The filler and/or coating material can be used in particulate, fibrous or textile form.

"Electrically conductive" material in the terminology of this application is to be understood as a material possessing an electrical resistivity in the range of 0.002 Qcm to 20 Qcm.

Within this application, a "sealing" functionality means that a fluid is prevented from permeating through the respective connection, to such an extent, that a contamination of 20 ppm by volume in the target fluid is not exceeded.

"Elastically deformable" material in the terminology of this application is to be understood as a material with a Young's modulus or similar nonlinear elastic properties in the range of 0,2 MPa to 2 MPa.

The current conducted by the at least one electrically conductive and elastically deformable sealing member according to the invention ranges from 1 A to 1500 A, more preferably from 1 A to 400 A, even more preferably from 1 A to 150 A, while sealing of different fluid passageways is realized with fluid pressures ranging from 0,1 MPa to 2 MPa and more preferably from 0,2 MPa to 1 MPa.

According to the invention, the electrically conductive and elastically deformable sealing member can be used on both the anode and the cathode side of the torch.

In another aspect, the electrically conductive and elastically deformable sealing member may be part of a main conduction path of the torch such as in the connection between the torch body and the plasma nozzle, which is particularly preferred, because these components need to be disassembled frequently for maintenance and replacement.

In another aspect, the electrically conductive and elastically deformable sealing member may be part of a secondary conduction path, such as the pilot circuit.

In another aspect, the electrically conductive and elastically deformable sealing member may be used on a consumable component such as an electrode, particularly a flux-cored feed wire.

Preferably, the at least one electrically conductive and elastically deformable sealing member is in the form of an O-ring. This has the advantage of an easy assembling process and cost effective production.

In one aspect, multiple electrically conductive and elastically deformable sealing members are used. They may be used to connect two components in multiple places, or to join more than two components into one common conduction path.

In one particularly preferred embodiment multiple electrically conductive and elastically deformable sealing members in the form of O-rings connect concentrically cylindrical surfaces of two components in a radial direction. This offers the particular advantage of improved sealing performance in an axial direction while enhancing electrical conductivity in the radial direction. A further advantage of such an embodiment is the retained possibility of movement of the components relative to one another in the axial direction.

In another advantageous embodiment, the electrically conductive and elastically deformable sealing member connects two components in an axial direction, so that it connects two components which have substantially identical lateral dimensions at least in the area where the connection is realized.

Generally, in order to effect a sealing connection, the size of a sealing member should substantially match the geometry of the components which are to be connected. This means, that when more than two torch components are connected with electrically conducting and elastically deformable sealing members according to the invention, it is particularly advantageous to use sealing members of different sizes and/or shapes to match the respective geometry of the connected components.

A torch according to the invention is preferably configured to be used in a welding process like metal inert gas welding, metal active gas welding, tungsten inert gas welding or plasma arc welding or in a plasma cutting, marking or spraying process.

In a preferred embodiment, the fact that, in a torch according to the present invention, poor electrical conductivity means that the seating of the conductive sealing member is imperfect is used to enhance operational security. Before the start of operational use of the torch, the electrical conductivity between different torch components may be measured and compared to calibrated values. If the difference between the measured and the calibrated value exceeds a set threshold, it is very likely that the sealing material failed or that the torch was assembled in an incorrect manner and should not be operated before a thorough revision. Poor electrical conductivity is thus an indicator for possible fluid leaks.

In a similar way, fluid leaks may also indicate poor electrical contact and the detection of fluid leakage can be used as an indicator for incorrect assembly and/or material failure.

In the following, the invention is described in further detail with reference to one preferred embodiment, which is visualized schematically in Figure 1.

Figure 1 shows a schematic cross section of the front part of a torch according to an advantageous embodiment of the invention.

The torch illustrated in Figure 1 comprises an electrode E, a plasma nozzle A, and a torch body B. The nozzle constricts the plasma F generated from the working gas (active gas or inert gas) by the electric current flowing from the electrode E to the nozzle A or the work piece (not shown). The body B and the nozzle are connected by electrically conductive and elastically deformable sealing members D in the form of O- rings. In this case, the O-rings have different diameters, but exhibit the same cross section. These O-rings confine the fluid coolant to the cooling channel C and prevent it from leaking into the flow path of the working gas or plasma F while ensuring the same electric potential in the nozzle and the torch body.