Growing of irregular shape sapphire products
Notwithstanding the obvious advantages of the single crystal sapphire to be used as a material for guidance system domes, the constraining factor for replacement of the previously used materials consists in high cost of production cycle. The most popular technology of production consists of three successive steps:
The most heavy operation is cutting of blank for the future product due to extreme hardness of sapphire. EZAN has developed a technology of blank production for the sapphire semi-spherical domes with the shape close to that of the finished product. The technology is based on the method of dynamic shaping. According to this method, the crystal growth takes place layer-by-layer from the shaper the working surface of which is created by the shape element of the crystal cross-section. By making the relative movements of the upper rod and shaper in the course of growth it is possible to obtain hollow crystals with the programmable shape of the side surface, which significantly reduces machining costs. This method also provides the extremely high crystal growth rates. To perform the dome blanks the installation of crystal growth "Crystallization center" providing 5 degrees of crystal and shaper movement freedom was created. The unique software-hardware complex of the installation ensures coordination of drives operation in order to obtain the product with the preset profile and automatically supports the optimum parameters of the crystallization process. At the present moment the technology allows growing the hollow crystals out of melt with the preset shape of the side surface with cross-dimension up to 130 mm and height up to 200 mm. In order to produce the dome out of the obtained blank it is sufficient to remove mechanically a layer not more than 1 mm in thickness from the external and internal sides and carry out fine polishing, which significantly reduces the product cost. The domes have successfully passed the tests at AOMZ (Azov optico-mechanical plant) for mechanical properties and transmission in the infrared band (3-5 mm) and millimeter band (3 mm).  The installation “Crystallization center”, semi-spherical sapphire crystals grown directly from the melt for seed (samples base diameter – 110-115 mm, outer surface curvature – 53 mm, product wall thickness in radial direction – 3-4 mm) and the ready-made domes with base diameter of 100 mm with different surface curvatures |
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