Production method:
The raw materials for the production of optical glass are some oxides, hydroxides, nitrates, and carbonates, and phosphates or fluorides are introduced according to the requirements of the formulation. In order to ensure the transparency of glass, the content of colored impurities, such as iron, chromium, copper, manganese, cobalt, and nickel, must be strictly controlled. When ingredients are required, accurate weighing and uniform mixing are required. The main production processes are smelting, forming, annealing and inspection.
- ①Smelting There are single crucible batch smelting methods and tank kiln (see kiln) continuous smelting methods. The single crucible smelting method can be divided into clay crucible smelting method and platinum crucible smelting method. No matter what kind of smelting method is used, it needs to be stirred with a stirrer, and the temperature and stirring are strictly controlled to make the molten glass is highly uniform. The clay crucible can smelt most crown glass and flint glass, at low cost, and is used when the melting temperature of the glass exceeds the service temperature of platinum. The platinum crucible can smelt high-quality glass that has a seriously corrosive effect on the clay crucible, such as a heavy crown, heavy barium flint, rare earth glass, and fluorophosphorous glass. Platinum crucibles are heated by electricity, generally using silicon-carbon rods or silicon-molybdenum rod electric furnaces. However, high-frequency heating can be used to manufacture glass that has a high tendency to crystallize, requires rapid cooling, and has certain requirements on the atmosphere. Since the 1960s, various countries have successively adopted continuous tank smelting lined with platinum, which greatly increased the output and quality of optical glass. This is the main trend in the development of optical glass production technology.
- ②The molding methods for forming optical glass include a classical crushing method, rolling method, and pouring method, but now more and more widely used leakage molding (using a single crucible or continuous melt to flow out the liquid), can directly draw rods or drop materials Pressing or leaking to form large-size blanks improves the utilization rate of gobs and the rate of finished products.
- ③ Annealing In order to eliminate the internal stress of the glass to the greatest extent and improve the optical uniformity, a strict annealing system must be formulated for precision annealing.
- ④ Inspection The indicators measured are optical constants, optical uniformity, stress birefringence, fringes, bubbles, etc.
Cold processing technology:
Cold processing is a method that uses chemical vapor heat treatment and a single piece of soda-lime-silica glass to change its original molecular structure without affecting the original color and light transmittance of the glass so that it can meet the ultra-hardness standard, and meet the fire protection requirements under high-temperature flame impact. Super-hard fire-resistant glass and its manufacturing method and special equipment. It is made of the following weight ratio components: potassium salt vapor (72% ~ 83%), argon (7% ~ 10%), gaseous copper chloride (8% ~ 12%), nitrogen (2 %~6%). It includes the following process flow: cutting with soda-lime-silica glass as the substrate, and cold processing of fine grinding edges → chemical vapor heat treatment of the cold-processed soda-lime-silica glass → coating the surface of the soda-lime-silica glass with a fire protection film → The surface of the soda-lime-silica glass is subjected to special physical tempering treatment. A special thermal decomposition gasification equipment is composed of a cylinder body, a cylinder head fitted with it, and a reaction kettle integrally connected with the cylinder head.
Quality requirements:
- 1. The specific optical constants and the consistency of the optical constants of the same batch of glass
Each type of optical glass has a prescribed standard refractive index value for different wavelengths of light, which serves as the basis for optical designers to design optical systems. Therefore, the optical constants of the optical glass produced by the factory must be within a certain allowable deviation range of these values, otherwise, the actual imaging quality will not match the expected result during the design and the quality of the optical instrument will be affected. At the same time, since the same batch of instruments are often made of the same batch of optical glass, in order to facilitate the unified calibration of the instruments, the allowable deviation of the refractive index of the same batch of glasses is more stringent than their deviation from the standard value.
- 2. High degree of transparency
The image brightness of the optical system is proportional to the transparency of the glass. The transparency of optical glass to the light of a certain wavelength is expressed by the light absorption coefficient Kλ. After a series of light through a prism and a lens, the energy loss at the interface portion of the reflective optical component and another portion of the medium (glass) itself absorbed. The former increases with the increase of the refractive index of the glass. For high-refractive-index glass, this value is very large. For example, the light reflection loss of one surface of counterweight flint glass is about 6%. Therefore, for an optical system containing multiple thin lenses, the main way to increase the transmittance is to reduce the reflection loss on the lens surface, such as coating the surface with an anti-reflection coating. For large-size optical parts such as the objective lens of an astronomical telescope, the transmittance of the optical system is mainly determined by the light absorption coefficient of the glass itself due to its large thickness. By improving the purity of the glass raw materials and preventing any coloring impurities from mixing in the entire process from batching to smelting, the light absorption coefficient of the glass can generally be made less than 0.01 (that is, the light transmittance of the glass with a thickness of 1 cm is greater than 99%).