Optical glass production method

The primary production steps include melting, forming, annealing, and testing. The melting process can be carried out using either a single-batch method or a continuous kiln system. In the single-batch approach, two common techniques are the clay crucible method and the platinum crucible method. Regardless of the method used, the molten glass must be thoroughly stirred, with strict control over temperature and mixing to achieve a highly homogeneous liquid. Clay crucibles are often used for melting most types of bismuth and flint glass due to their cost-effectiveness, especially when the melting temperature exceeds the limits of platinum. Platinum-rhodium crucibles, on the other hand, are preferred for high-quality glasses that are highly corrosive to clay, such as heavy lead, strontium, rare earth, and fluorophosphate glasses. These crucibles are typically heated using silicon carbide or silicon molybdenum rods. However, high-frequency heating is sometimes employed for glasses prone to devitrification, which require rapid cooling or specific atmospheric conditions.

Since the 1960s, many countries have adopted continuous kiln systems lined with platinum, significantly increasing the output and improving the quality of optical glass. This advancement has become a key trend in the development of optical glass manufacturing processes.

For the forming stage, traditional methods like the breaking, rolling, and casting techniques are still used, but modern approaches such as leakage molding—where liquid glass is drawn directly into rods or dripped into molds—are becoming more common. These methods allow for the production of large blanks with higher material utilization and yield.

Annealing is a crucial step to reduce internal stresses and enhance the optical uniformity of the glass. A precise annealing schedule is required to ensure the glass meets the necessary quality standards.

Finally, during testing, several key parameters are measured, including optical constants, optical uniformity, stress birefringence, streaks, bubbles, and other visual imperfections. These tests help ensure that the finished product meets the high standards required for optical applications.