Non-sag tungsten wire working temperature is often between 2300 ~ 2800 ℃, generally , the greater the average light bulb power, the higher the wire temperature. It shows that the wire temperature far exceeds the recrystallization temperature of tungsten, at this time, wire is under its own weight, the wire segment between two hooks will produce sagging, and if it is serious, the wire will collide with the glass bulb. In the process of tungsten powder metallurgy, non-sag tungsten wire dope a small amount of potassium oxide and aluminum oxide, although the content of silicon and aluminum is only a few parts per million and the potassium content is tens of parts per million in its final product, non-sag tungsten wire sagging degree has greatly improved. The reason is because the recrystallizing structure of the non-sag tungsten wire is very different from sag tungsten recrystallization structure. Sag tungsten crystal recrystallization essentially is an isometric crystal, while the non-sag tungsten wire crystal structure represent elongated strip whose coarse grains is overlapping each other. From the high-temperature creep theory of metallic materials, the latter kind of crystal structure can greatly enhance the non-sag ability of tungsten at high-temperature.
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