Explanation of Tungsten Heater for Vacuum Plating——Evaporating Coating

Chemical coating was first used in the preparation of the optical element surface protective film. Subsequently, in 1817, Fraunhofe in Germany used concentrated sulfuric acid or nitric acid to corrode glass, occasionally got the first antireflection film. Before 1835, there was someone used wet chemical deposition method to make silver mirror film which was the oldest optical thin-film prepared in the world film. Later, people used chemical solution and steam to plat various optical films. In 1950s, except large windowpane antireflection coating applications, the chemical plating solution was gradually replaced by vacuum coating. Physical vacuum coating process vacuum evaporation and sputtering are by far the two main processes for coating industry. In 1935, it was developed a vacuum vapor deposition of a single layer antireflection coating. Its first application was plating in the spectacle lens after 1945.

Tungsten heater for vacuum plating in evaporation coating process requires following points:
1. Aluminum should be wrapped on tungsten. If previously molten aluminum in plating coated became spherical and covered tungsten, and then it cannot be used, it needs to be replaced a new tungsten wire.
2. The injection mold parts should be pushed into the vacuum chamber buy car, keeping close contact with the electrodes, jaw clucth should be able to rotate.
3. Use a mechanical pump, Roots pump and diffusion pump to exhaust, when the degree of vacuum pointer reaches 5 × 10-4TORR, deposition can be started.
4. The vapor deposition process: the tungsten wire is heated to 650℃, the aluminum would be molten in tungsten, continue to rise to near 1000℃, the molten aluminum atoms is vaporized to its surface, plated products on a vacuum chamber constantly to be rotating with cage which makes plated surface coated with a uniform layer.
5. The average production cycle of coating is about 30 minutes.

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