How is tungsten wire made?

Tungsten wire owns high resistivity and melting point, good strength, and low vapor pressure, which is the best material for making incandescent filaments in all pure metals. However, how is the thin tungsten wire made? As the tungsten is hard, brittle, and difficult to proccess.

The raw material is ammonium para tungstate, which is a white crystal, it is slightly melted in water and is produced in a nearly 700℃ roaster for 40 minutes to produce blue crystal tungsten oxide, at 12 to 19 microns. Raw material used for tungsten powder, doped blue tungsten oxide is a special requirement, and is added with elements such as aluminum and potassium to increase its performance, such as sagging resistance and toughness.

The blue tungsten oxide is reduced to tungsten powder by a hydrogen reduction furnace. The average particle size of the tungsten powder is 2 to 5 micrometers. The tungsten powder is placed in a mold, and the preform is pressed by an isostatic pressing machine. It is sintered in a furnace, and the tungsten bar’s density after sintering is generally 17.7 g/cm³.

When the diameter of the tungsten wire reaches the micron level, it is difficult to accurately determine by conventional caliper. Therefore, it has a diameter of 0.2 mm or less is generally used to indicate thickness by weight of 200 mm in length. For example, the diameter of 15W incandescent filament can be expressed by 0.679 mg/200 mm.

Once it is recrystallized after being used at a high temperature, it becomes very brittle and is easily broken under shock or vibration. To prevent filament breakage, 3 to 5% of yttrium is often added to the doped tungsten, which is called tungsten ruthenium wire, which can reduce brittle transition temperature to room temperature or below.

Tungsten wire owns good acid and alkali resistance at room temperature, but it is easily oxidized in humid air, so it cannot be stored in a humid environment for too long. Besides, tungsten begins to react with carbon at 1200℃ to form carbides. Therefore, we should pay attention to the hydrogen burning of the filament. Otherwise, the filament will become brittle and fracture when it reacts with the graphite lubricant on the surface.

In addition to a small number of tungsten wires used as heating material for high-temperature furnaces, tube thermon, and reinforcing rib of composite materials, most of them are used for making filaments of various incandescent lamps, tungsten halogen lamps, and electrodes for gas discharge lamps.

Nowadays, some people have made the tungsten filament lamp into artwork, which can both illuminate and add an artistic atmosphere. It is made into various complicated shapes. After power is turned on, bulb filament heats up, and the bulb content is like a glow.

With the advancement of science and technology, tungsten wire has been seldom used, but during this time, it has made great contributions to human beings.

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