After the Negative Cylindrical Len is finely ground by the grinding liquid, the surface of the optical lens has a crack layer of about 2–3 m thick, and the method for eliminating the crack layer is polishing. Polishing and grinding are the same as the polishing tool. The material used for polishing is different from polishing. The materials used for polishing are cloth, polyurethane and pitch, which are usually polished with high precision. The most commonly used material is advanced polished asphalt.
The use of asphalt for polishing is based on the fine surface of the asphalt, which drives the polishing liquid to grind the surface of the lens to heat, so that the glass melts and flows, melts the rough apex and fills the bottom of the crack, and gradually removes the crack layer. At present, the polishing powder used for polishing glass lenses is mainly cerium oxide (CeO2), and the proportion of the polishing liquid is different depending on the polishing period of the lens. Generally, the polishing liquid is used at the initial stage of polishing and when the mold is closed with the polishing mold. After the surface of the lens is bright, use a thinner polishing solution to avoid fogging of the mirror surface.
Polishing is the same as the motion mechanism used for grinding. Except that the polishing tool is different from the working fluid, the environmental conditions required for polishing are more severe than those for grinding. Generally, the matters to be noted when polishing are as follows: There should be no impurities in the surface of the polished asphalt and the polishing liquid, otherwise the mirror surface will be scratched. The surface of the polished asphalt should conform to the surface of the Negative Meniscus Lens, otherwise it will bounce during polishing, thus biting the polishing powder and scratching the surface of the lens.