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Optical Windows
Manufacturing principle of optical glass pressure type
Sep 21, 2018
The forming process of optical blank is directly related to optical glass melting technology and optical processing technology.So you have to think about them as a system in general.

Since the development of optical glass, glass parts blank (lens, prism) production is generally will be melted good chunk glass material, to soften, loading metal mold pressing into the shape of the roughly, and then through the coarse grinding, fine grinding, polishing and make out.This method was used as an auxiliary method after the appearance of optical glass continuous melting technology in the 1970s

Since the 1970s, the main factories in Japan with developed optical glass have adopted the most advanced production technology in optical glass production.Three straight (3 D) production technology, namely direct electric melting, molding, precision directly annealing directly, including direct forming continuous melting or crucible leakage drops of material forming method, abroad to be called "pressed" at a time.This kind of advanced forming technology is the glass directly compressed into optical blank, so that greatly simplify the production technology of secondary molding, saves the manpower, equipment, reduce energy consumption, improve the utilization rate of raw materials.Japan's valley company three straight line optical glass, the clay crucible furnace classical method need to 170 days, with platinum crucible pouring method need to shorten the production cycle of 34 days to 3 production cycle.The yield increased from the highest 40% in classical law to more than 90%.

The optical glass pressing type is also called non-abrasive pressing type, which means that the optical elements produced by the pressing type do not need grinding, polishing, grinding edge, center and other optical processing, and are directly assembled to the optical instrument.The optical glass molding pieces of surface finish and dimensional accuracy requirements quite high, usually with optical gauge block on the optical element surface finish and dimensional accuracy measure, measure its quality to produce the number of interference fringes, for lens for the camera systems usually require through the lens radius of Newton ring number should be less than 6, through the two mutually perpendicular radius of the number of Newton ring sent to less than three, two kinds of Newton ring number is less, the higher the quality of the lens.

Precision pressing involves placing heated and softened glass into a mold protected by an inert gas, such as nitrogen 2, which has a high surface finish and dimension precision on its inner surface.Attached to the inner surface of the material should have high hardness, good oxidation resistance, good thermal conductivity, not bonded with glass at high temperature, good impact strength and analysis strength, not through the gas, water vapor and liquid.The materials that meet the above requirements are glass carbon, silicon carbide and silicon nitride.However, compared with the latter two, the glass carbon is loose and easy to oxidize, easy to scratch and small elastic modulus.Low impact and analysis strength, poor thermal conductivity.According to foreign patent reports, glass carbon was used on the inner surface of the moulding mould in the early 1970s, while silicon carbide or silicon nitride was used in patents issued in the mid-1970s.The methods to attach the two materials to the inner surface of the mold include (1) hot pressure, (2) ion splash lining and (3) gas deposition.The thickness of its fixation layer is at least lOptm.The structure of this kind of mould is quite complex. After the glass pressing is finished, the mould cannot be removed immediately, and the glass temperature needs to be lowered below the transition temperature before it can be removed.Precision pressing can suppress the optical parts of the sphere, aspheric surface and other complex shapes.In the mid 80 s to the production of optical glass is made of moulded a forming two precision lens of glass surface machining precision of Y / 10, 10 um thickness and diameter tolerance, wedge Angle is less than 10-3 mil., birefringence per CM less than 10, Y/refractive index evenness of 10-6, a precision molding precision lens in Japan, Germany and other countries have adopted.

The production of optical glass has gone through the development process of lump material and secondary pressing material and direct liquid pressing material.At present, the main supply form of optical glass production in China is still lump material.Considering the economic benefit of the whole optical industry, it is urgent to develop the production of type materials.Based on China's current optical glass production technology level and the actual needs of the market, we should first do a good job of secondary pressure production, in the improvement of secondary pressure production to pay attention to the solution of good material preparation.Mold release agent, non-stick glass over porcelain box materials and mechanical f {2 son main technology problems, such as automation, direct liquid pressure type a secondary pressure type for obvious technical and economic effect, is the only way for optical glass production in the future.But starting from the actual needs of the current optical industry in China and at the same time refer to the international development trend of the optical glass production technology, the developing direct liquid pressure type it is important to pay special attention to the development of our country many varieties, small batch of many specifications of pressed directly, and to solve the good small batch direct optical glass molding must first solve the small batch optical glass melting technology, development of the corresponding optical glass melting tank furnace.While developing and improving the secondary pressure type and direct liquid pressure type, the research and test of precision pressure type should be carried out actively so that China's optical glass pressure type technology can catch up with the world advanced level as soon as possible.

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