Ceramic metal halide lamp is made of polycrystalline al […]
Ceramic metal halide lamp is made of polycrystalline alumina ceramics. This kind of ceramic is a translucent material. In fact, its transmittance is as high as 96-98%, which is higher than glass and quartz. But because the linear transmittance is not more than 30%, it becomes translucent. This kind of ceramic material can withstand the high temperature above 200 C higher than quartz. The normal operating temperature after making the arc tube can be as high as 1200 C. The thermal conductivity of the arc tube is higher. The temperature distribution of the arc tube itself is more uniform, even at the cold end, it is above 900 C. Therefore, the metal halide filled in the arc tube can evaporate sufficiently. This is a ceramic metal halide lamp. Reasons for high and stable light efficiency and color rendering index. The thermal and chemical stability of ceramic bulb shell is very high. It does not react with the material filled with arc tube, and there is no sodium leakage problem. Therefore, the lamp has stable performance, low light decay and long life.
After 20 years of research and development and improvement, the basic structure of the lamp has been finalized. Although there are many patents with slightly different structures, it is basically a sleeve with a pair of supporting electrodes symmetrically arranged at the center for a larger arc tube body and two ends (Fig. 1). There are two basic structures in the tube, i.e. cylindrical (a) and spherical (ellipsoid or similar spherical) bubbles (b). The former is patented by Philips and GE. The latter is an integral spherical structure (b). The latter is patented by Everbright Baudick and Osram uses a joint in the middle. Two-piece assembled spherical structure (c), in addition to a variety of cylindrical two-piece and three-piece assembled arc tube (d).
The multi-component assembly of arc tube and shell is made up of the components tightly clamped by the shrinkage rate of the outer sleeve during sintering, and the interlaced growth of grains at the interface. However, if the material, process and sintering temperature are slightly offset, gas lines and bubbles may be generated at the junction. It is difficult to withstand the repeated thermal shock when the lamp is manufactured, resulting in gas leakage or explosion. Although the forming of the integral structure bubble shell is more complicated, it has better quality assurance.
The structure is a finer molybdenum rod with molybdenum helix around the front end of the niobium rod, and a finer thorium-tungsten screw around the front end of the molybdenum rod. The front end of the molybdenum rod is wound with several circles of tungsten wire. The electrode diameter of this structure is thicker and can fill the sleeve of the arc tube, but it is quite flexible, and does not cause excessive stress to the ceramic sleeve due to temperature change to make it crack; this kind of electrode has good enough conductivity, but the thermal resistance is larger, the heat transferred from the tip of the electrode or the lead wire to the ceramic sleeve is less, and does not cause excessive rise. Temperature affects sealing reliability.
Although the electrode structure is ingenious and reliable, its fabrication is complex, and there is a large gap between the electrode and the ceramic sleeve. A large number of metal halides infiltrate and deposit in the electrode during operation, which affects the stability of lamp parameters such as lamp voltage drop, light flux, color temperature and color rendering index.
