This video from Ohara Inc., Japan's first exclusive optical glass manufacturer, provides a detailed look into the production processes for two of its specialized glass products. The first half of the video documents the creation of i-line high-homogeneity optical glass, a critical component in semiconductor manufacturing and high-precision instruments. The process is shown from the initial blending of raw materials through a double-melting procedure to refine the refractive index, followed by a weeks-long annealing process, precise grinding, polishing, and a rigorous final inspection. The second part showcases the manufacturing of CLEARCERAM™-Z, an ultra-low expansion glass ceramic used for large telescope mirrors. This process involves casting multi-ton blocks of molten glass, followed by a crucial heat treatment to induce nano-crystallization, which gives the material its near-zero thermal expansion properties.
The Manufacturing of High-Performance Optical Glass at Ohara Inc.
00:00:05 Introduction to Ohara Inc.: The video profiles Ohara Inc., a world-leading Japanese manufacturer that was the first in the country to specialize exclusively in optical glass.
00:01:01 High-Homogeneity Optical Glass: The first process detailed is for i-line high-homogeneity optical glass, valued for its uniform refractive index and used in lenses for semiconductor exposure equipment.
00:01:07 Raw Material Blending: The process begins by weighing and mixing hundreds of kilograms of powdered raw materials, including silica sand, borax, and soda ash.
00:02:52 Primary Melting and Casting: The raw material mix is melted at over 1000°C and poured into a crucible. This molten glass is then "cast" onto a tray to cool and solidify.
00:05:12 Creating "Cullet" for Refinement: The solidified glass is intentionally crushed into pieces known as "cullet." This step is essential for the next stage, where the glass is re-melted to achieve a highly uniform refractive index.
00:06:33 Secondary Melting and Annealing: The cullet is melted a second time to precisely homogenize the glass. The resulting sheets are then placed in an electric furnace for annealing—a slow cooling process that takes several weeks to finely tune and lock in the exact refractive index.
00:09:53 Grinding and Polishing: After annealing, the glass is mechanically shaped. The surfaces are ground to the specified thickness, the outer edge is shaped, and both faces are polished to achieve high flatness and accuracy.
00:12:56 Meticulous Final Inspection: Before shipping, every piece of glass is subjected to a final quality check, including measurements for refractive index uniformity and a one-by-one visual inspection for internal bubbles, foreign materials, or surface scratches.
00:14:45 Ultra-Low Expansion Glass Ceramic (CLEARCERAM™-Z): The video then transitions to the manufacturing of CLEARCERAM™-Z, a glass ceramic with near-zero thermal expansion used for massive telescope mirrors and semiconductor equipment.
00:15:08 Large-Scale Casting: Unlike the previous process, this involves melting and pouring several tons of molten glass into a single large mold.
00:17:07 Gradual Cooling: The massive, hot glass block is moved to an annealing furnace where the temperature is lowered very gradually to prevent cracks, fractures, or internal distortion.
00:18:14 The Crucial Crystallization Step: The most important part of the process is crystallization. The glass is heat-treated in an electric furnace, which causes nano-crystals to precipitate within the material. These crystals are what counteract thermal expansion, giving the ceramic its defining property.