There are three types of tungsten wire application property: high temperature, room temperature and wire diameter consistency.
1.0 High temperature application property. The working temperature of tungsten filament for incandescent lamp is usually between 2300-2800 Celsius degrees. Generally, the greater the power ratio of bulb is, the higher the working temperature of filament is. It shows that the working temperature of the filament is far higher than the recrystallization temperature. Then due to the self weight effect of the filament, the filament will sag between the two hooks. Seriously the filament can even sag to touch the glass shell of the bulb. In the process of tungsten powder metallurgy, silicon and aluminum are added a few of one million in the final product, and the potassium is added a few parts per million, the sagging degree of doped filament can be greatly improved. It is because the crystal structure of undoped wire has great difference from that of doped wire. The recrystallized crystal of undoped wire is equiaxed crystal, while the recrystallized crystal structure of the doped wire can greatly improve its anti-sag ability at high temperature.
The sagging of incandescent lamp filament has relation with added elements content in the doped tungsten filament and the processing technology, also has relation with the processing technology in the filament producing process. The filament keeps a lot of internal stress when it is drawn into finished filament, and new uneven deformation internal stress come into being on its cross section when winding the filament. These internal stresses must be eliminated before the filament is mounted into the shell, otherwise the filament will be distorted, deformed and sagged at the beginning of the ignition point, and the filament sagging will greatly reduce the luminous efficiency of the bulb.
2.0 Room temperature application property. The tungsten wire mainly shows in winding property. As the producing procedure is long, if the process management is not good, it easily produces a lot of small cracks or local embrittlement, so that it is easy to break during wire winding. The wire wound fracture caused by the crack has a hairy fracture, while the fracture caused by the wire embrittlement appears a flashing crystal surface.
3.0 Application property of wire diameter consistency. The consistent difference of the filament diameter is an important reason for the bad photoelectric parameters of incandescent bulb, and some will affect the life time of the bulb.
