Multiple Rare Earth Tungsten Electrodes Preparation by SPS Sintering Method

Tungsten electrodes are the key materials used in inert gas shielded welding and plasma welding, cutting, spraying and other equipment. At present, thorium and tungsten electrodes (including ThO₂) and cerium tungsten electrodes (including CeO₂) are used more. In addition, a small amount of lanthanum tungsten electrodes and yttrium tungsten electrodes are used.

Several rare earth tungsten electrode materials have their own advantages and disadvantages: thorium is a radioactive element, and the processing performance of cerium tungsten electrode is good, but it is difficult to lead arc in use, it is easy to break arc in welding process, and the lanthanum tungsten electrode is stable when working in small and medium current, but the burning loss is serious with the increase of current. Yttrium tungsten electrode has good burning resistance when working at high current, but the arc is unstable and the machining performance is poor when small current is used.

At present, the traditional vertical melting and sintering process is commonly used in the production process of rare earth tungsten electrodes. During this process, more than 90% of the energy converted by electric energy is lost by the flow of hydrogen and heat radiation, and the temperature of the two ends of the tungsten strip is low during the vertical melting and sintering, and the density requirement of the subsequent plastic processing is not reached after the sintering. It needs to be processed before the plastic processing. About 3% of the material is removed, resulting in double waste of rare earth and tungsten resources and energy.

A new type of high consumption multielement rare earth tungsten electrode has been innovated. The use of a variety of rare earth elements instead of radioactive thorium and the new technology of Re₂O₃ and SPS to improve the plastic processing properties have not only made the welding performance of the electrode material reach or exceed the thorium tungsten electrode, but also solved the high content of the rare earth tungsten material. It is difficult to work hard and the rate of timber is low.

The new high energy consumption multi rare earth tungsten electrode contains four rare earth oxides of Re₂O₃, La₂O₃, Ceo₂ and Y₂O₃, and the rest is W. The total content of rare earth oxides is 1 ~ 3% with weight percentage, and the weight ratio of the oxide components is Re₂O₃: La₂O₃: Ceo₂: Y₂O₃ = 1: 2: 2: 6.

The rare earth nitrate and deionized water are mixed into a solution, and the tungsten powder is prepared in the form of APT powder in the form of fog. After two hydrogen reduction at 600~650°C and 850~1000°C, the tungsten powder is obtained. A four tube furnace is used for one reduction. The maximum temperature in the furnace is 650°C, the flow rate of hydrogen is 5.0m3/h, the speed of the boat is 30, the loading of the boat is 2000g, two times reduction using 13 tube furnace, the hydrogen flow rate is 1.4m3/h, the speed of pushing boat is 40 points / boat, the loading capacity is 2000g, the maximum temperature in the reduction zone is 880°C.

Tungsten powder is sintered through SPS and then formed various kinds of electrodes through rotary forging and drawing, of which the temperature is 1600~1650°C, the intermediate is annealed at one time. No pressing and pre firing is needed. During the sintering process, the sintering pressure is 20MPa, the weight is 1.0Kg, the sintering density is 17.8 to 18.2G /cm2, SPS equipment is 3000 KWh. The time is 3 minutes, the energy consumption per unit product is 18KWh.

SPS sintering is an isoelectric ion sintering technology, which has been developed in recent years. It is a rapid, low temperature, homogeneous, high density, using the direct current of sintering process. Then polishing and testing.

The combination of rare earth elements in the rare earth tungsten electrode instead of thorium completely solves the pollution and harm to the environment and human health after the thorium tungsten electrode is produced, used and abandoned. With the addition of Re₂O₃ to improve the plastic processing properties, not only the welding performance of the electrode material reached or exceeded the thorium tungsten electrode, but the addition of Re₂O₃ and the adoption of the SPS sintering process have solved the difficult problem of the high content of the rare earth tungsten material and the low yield of the material. The production rate of the traditional production electrode is 86.1%, SPS The sintering process reached 93.73%, much higher than the current thorium tungsten level. Compared with the same type tungsten electrode, the working energy of the composite tungsten electrode made by this process is lower than the thorium tungsten electrode. The arc stability is stable, the arc resistance is good, the consumption resistance is increased by 28%, and the same type of thorium tungsten welding electrode can be replaced completely. 

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