What are the uses of tungsten electrodes?

    Tungsten electrode is a rod-shaped non-consumable electrode material with metal tungsten as the substrate, rare earth oxides such as lanthanum oxide, cerium oxide or zirconia added, and formed by powder metallurgy technology. Tungsten electrode has good conductivity, high temperature stability and low electron work function. Based on these characteristics, it can be used as a conductive, discharge or electron emission component at high temperature, high current density or strong electric field, covering welding manufacturing, vacuum electronics, energy equipment and special processing and other fields.

I. Application of tungsten electrode in argon arc welding

    Tungsten argon arc welding is one of the welding processes with the widest coverage of tungsten electrodes. Tungsten electrodes provide stable arc light, argon as a shielding gas to isolate air, and obvious weld oxidation, slag inclusion and other defects. Different tungsten electrode products correspond to different current outputs and base metal types.

    Pure tungsten electrode is suitable for AC welding, mainly used for aluminum, magnesium alloy profile and plate processing. The cathode cleaning effect of AC arc can effectively peel off the oxide film on the surface of aluminum-magnesium materials, and the probability of blowhole formation in welds is large. It is widely used in aluminum alloy chassis, lightweight decorative aluminum components and other production fields. The current-carrying capacity of the electrode is narrow (generally no more than 150A), and it is easy to lose rapidly due to melting in high-current AC operations, so it is not suitable for long-term high-power conditions.

    The zirconium-tungsten electrode is suitable for high-current AC aluminum-magnesium alloy welding conditions. The electrode tip has good resistance to molten pool pollution. It is suitable for thick aluminum alloy plates and large and medium-sized aluminum structural parts. It can be used with high-power AC and DC welding machines. The uniformity of weld forming is stable.

    The cerium oxide doping ratio of cerium-tungsten electrode is generally 1.8% ~ 2.2%, and there is no radioactivity. The arc starting voltage in the low current range is maintained at 20 ~ 30V, which is suitable for DC thin plate welding scenarios. It is mostly used in stainless steel with a thickness of less than 1.6 mm, low-carbon steel components, small instrument hardware and thin-walled chemical pipelines, and there is a large demand for automatic short-line welding equipment.

    The lanthanum-tungsten electrode has a range of 0.8% ~ 2.2% lanthanum oxide doping content, which is compatible with both AC and DC welding, and has no radioactivity. It can be used in various base materials such as carbon steel, stainless steel, copper alloy, titanium alloy, aluminum-magnesium alloy, etc., and is suitable for low-current micro-precision welding and large-to-medium-current long weld continuous processing scenarios.

II. Application of tungsten electrode in plasma processing

    In plasma equipment, tungsten electrodes are used as emitters to excite and maintain the arc under the action of an electric field. Using the arc energy to ionize the shielding gas into a plasma state, the plasma arc is compressed, and plasma arc welding, plasma spraying and inert plasma cutting are derived into three processes.

    Plasma arc welding: The energy density of compression plasma arc is significantly higher than that of conventional argon arc welding, and the penetration performance is better. Tungsten electrode is used as cathode to maintain the stability of arc beam, which is suitable for single-side welding and double-side forming of stainless steel thick-walled chemical pipes and titanium alloy heat transfer components. The CNC automatic plasma welding platform mostly uses lanthanum-tungsten or cerium-tungsten electrodes, and the deformation range of the electrode tip is small during the long-term continuous processing.

    Plasma spraying: Tungsten electrodes are placed in an inert airtight cavity to excite a high-temperature plasma heat source, and metal or ceramic powders are sprayed on the surface of the work-piece after melting, so as to realize the preparation of wear-resistant and corrosion-resistant coatings. Widely used in hydraulic parts, mechanical transmission accessories surface modification treatment. Inert operation can effectively oxidize the tungsten electrode and prolong the continuous operation time of the equipment.

    Inert plasma cutting: The application scenarios are different from those of air plasma hafnium electrodes. Tungsten electrodes are suitable for oxygen-free cutting of nitrogen, argon-hydrogen mixture, etc., and are mostly used for blanking special metal plates that are easy to oxidize such as titanium and nickel-based alloys.

III. Application of tungsten electrodes in the field of high temperature and vacuum electronics

    Tungsten electrodes, with their ultra-high melting point and low evaporation rate, exhibit stable and reliable performance in high temperature vacuum, and are often used as hot electron emitters or structural supports.

    Thermal electron emission source: In vacuum electron tubes, X-ray tubes, microwave tubes and some high-end spectral analysis instruments, tungsten wires or tungsten electrodes are used as cathodes to generate a large number of hot electrons through resistance heating and provide a stable electron flow. Typical applications include electron beam evaporation coating equipment, scanning electron microscope guns, etc. After polishing, the uniformity of ion current distribution on the surface of high-purity tungsten electrode is significantly improved, and the error of arc discharge is controlled in a small range.

    High-intensity gas discharge lamps: Tungsten electrodes are widely used in xenon lamps, mercury lamps and high-pressure gas discharge lamps due to their extremely low evaporation rate at high temperatures. They are used as electrode materials to maintain stable arc output high-intensity beams, and are often used in projectors, optical amplifiers and other high-end lighting scenes.

    Special metallurgy and crystal growth: In the electron beam melting furnace, tungsten electrodes can be used to prepare high-purity titanium, molybdenum and other refractory metals. When the Czochralski method is used for the growth of monocrystalline silicon, pure tungsten electrodes are used as heating sources to carry a large current, ensuring a uniform and stable melt temperature and ensuring the stability and purity of the crystal growth process.

IV. Application of tungsten electrodes in new energy industry

    The new energy industry has formulated clear management and control standards for weld cleanliness and heat input range, and tungsten electrodes have become the choice for lightweight material sealing and connection processes.

    Processing of power battery parts: square aluminum battery shell sealed weld, battery copper-aluminum adapter pole, water-cooled heat dissipation stainless steel flow channel, mostly using AC and DC dual-purpose lanthanum-tungsten electrodes for TIG welding, which can narrow the width of the heat-affected zone, Thin-walled shell deformation probability.

    Lightweight components for rail transit: aluminum alloy profiles for the car body, stainless steel pipelines inside energy storage equipment, and conductive support components, zirconium-tungsten and lanthanum-tungsten electrodes are used to complete segmented weld processing; AC working condition is used to eliminate the oxide layer on the surface of aluminum profiles, and DC working condition is used to complete the welding of stainless steel load-bearing parts.

    Manufacturing of hydrogen energy equipment parts: fuel cell stainless steel bipolar plates and titanium alloy sealed pipelines are micro-welded with fine-diameter cerium-tungsten electrodes, with less oxidation in the weld interlayer, and air-tight performance testing standards.

V. Application of tungsten electrodes in the processing of medical devices and precision sensing elements

    The processing of medical devices and miniature sensing elements has strict restrictions on weld impurities and radioactive residues, and radioactive-free rare earth tungsten electrodes have become the mainstream selection in this field.

    Welding of medical metal instruments: titanium alloy surgical instruments, stainless steel minimally invasive accessories, and nickel-titanium alloy small implanted components are welded with low-current cerium-tungsten or lanthanum-tungsten electrodes, and inert gas is inserted throughout the process for protection, and harmful impurities are generated inside the welds.

    Packaging of detection and sensing equipment: temperature and pressure micro-stainless steel sensor shell, optical instrument metal bracket, sealed and packaged with tungsten electrode micro-arc spot welding, arc heat input is within a controllable range, effective internal precision electronic components heat damage probability.

VI. Precautions for tungsten electrode selection

    For the selection of tungsten electrodes in different processing scenarios, it can be matched and referenced according to three basic conditions: base metal material, welder current and production operation conditions.

    Processing base material material: Pure tungsten or zirconium-tungsten electrodes with cathode cleaning effect are preferred in aluminum-magnesium alloy processing scenarios; For base materials requiring DC welding such as carbon steel, stainless steel, and titanium alloy, cerium-tungsten or lanthanum-tungsten electrodes are preferred to achieve a balance between weld cleanliness and forming stability.

    Output current of welding machine: Under AC working condition, the electrode with natural spheroidization and suitable for cathode cleaning should be preferred; Under DC conditions, emphasis should be placed on cerium-tungsten or lanthanum-tungsten electrodes with stable electron emission performance after doping with rare earth elements to ensure the stability of arc light and the accuracy of low-current arc initiation.

    Production and operation conditions: cerium-tungsten electrodes can be used for short-term small-batch precision welding; The long-term continuous processing of automated production lines gives priority to the use of lanthanum-tungsten electrodes, which not only takes into account environmental protection requirements, but also achieves overall efficiency improvement by balancing the electrode replacement cycle and welds.