Tungsten and molybdenum are commonly used refractory metals. They are used as electrode materials in spot welding machines because they have higher melting points, higher hardness and anti-adhesion characteristics. The electrical conductivity of tungsten and molybdenum is higher than that of iron. And other metals.

Tungsten lacks plasticity at room temperature and is easy to be brittle. The whole electrode made of tungsten rod is only suitable for welding under low current and low pressure, such as welding small copper alloy parts in electronic products, when welding under high current and high pressure. Tungsten rods or tungsten sheets are often embedded in the head of the copper alloy electrode to form a composite electrode. On the one hand, it can improve the conductivity of the electrode and improve the heat dissipation effect of the tungsten electrode. On the other hand, it can prevent the tungsten electrode from being impacted during welding. And broken.

Molybdenum has a lower melting point than tungsten, and its thermal conductivity, thermal expansion and electrical conductivity are similar to tungsten. Molybdenum has lower hardness than tungsten, has excellent toughness, and is easy to process. Molybdenum is the same as tungsten when used as an electrode. The copper alloy is made into inlaid composite electrodes together.

The use of pure tungsten or pure molybdenum as the electrode inlay is limited by the size of the material, generally not too large, and the form of the electrode is also limited. Therefore, more powder sintered materials such as copper-tungsten and silver-tungsten are used.

Using copper or silver powder, mixed with a certain proportion of tungsten powder, after pressing and sintering, a series of powder sintered materials with different hardness and different electrical conductivity can be made. The softening temperature of these materials is close to the melting point of copper or silver. Hardness and conductivity depend on the content of tungsten powder, particle size and its distribution.

As the electrode material of spot welding machine, copper-tungsten usually contains more than 60% tungsten by weight. Commonly used varieties are Cu-W70 and Cu-W80.

The performance of silver-tungsten is similar to that of copper-tungsten, but its conductivity and oxidation resistance are not as good as copper-tungsten due to its electrical conductivity and oxidation resistance, and it is more expensive.

Copper-tungsten carbide is a sintered electrode material with strong oxidation resistance at high temperatures. The contact resistance of copper-tungsten carbide electrode is stable and the anti-adhesion performance is good. However, tungsten carbide has higher hardness and poor processing performance.

Powder sintered materials can be processed into electrodes of different shapes and sizes. For example, cylindrical electrodes have a diameter of 10-85mm and a height of 10-50mm, while the diameter of a tungsten rod is only 10mm.