Glass molding, also known as precision glass pressing, is used for the manufacture of lenses for cameras and glasses. Designed as a replicative process, glass molding uses blanks to produce flawless glass products in pressurized molds. The blanks, or floated glass, are reshaped and configured by being pressed between the side of a mold.
Floating produces blanks of uniform thickness with a flat clean surface, an essential part of glass molding. To create a blank, hot molten glass is poured over molten tin or lead and allowed to slowly cool to achieve the appropriate thickness. Floating was invented because of the inefficiency of the Bessemer method that produced sheets of glass that were flawed and required polishing, which etched imperfections into the glass. Sir Alastair Pilkington noted this deficiency in the Bessemer process and designed floating, used in the creation of modern windows. Additionally, floated glass blanks are ideal for glass molding since they do not have imperfections or flaws.
Glass molding involves multiple steps using technical equipment that monitors and controls each aspect of the process. In the glass industry, it is considered to be a very efficient and cost-effective way to produce high quality products that require minimal labor or finishing. The various precision details of each step guarantee its success.
The first step of glass molding is the insertion of a blank into the bottom of a precast mold. For the best results, the blank should be smooth and clean. As an extra precaution, the mold should be inspected for any miscellaneous materials as well. Small minute imperfections or bits of foreign matter can ruin the process.
With the blank and bottom of the mold properly set, the top of the mold is placed closely over the bottom of the mold and the blank without touching either of them. Once all three pieces are in place, they are heated. As the temperature rises, the blank will become pliable enough to be shaped and cast. To ensure the successful completion of the process, the heating must be carefully monitor so that the blank reaches the proper softening point without being overheated.
At the malleable temperature, the upper portion of the mold is slowly lowered onto the blank and bottom of the mold. As it moves downward, the blank is very slowly pressed against the bottom of the mold by the top to achieve the proper thickness and shape. The downward movement ceases when the correct thickness is achieved.
The new part and mold are set aside to cool until the part can be safely removed. The cooling time will vary depending on the type of part and the requirements established for the production process.
Glass molding relies on the use of specially designed molds that are durable enough to withstand the controlled temperatures and pressure of the molding process. Flawless blanks ensure that the final product will meet the highest standards.
Most glass molding is done with borosilicate or soda lime glass to produce high quality low cost products. Glass molding production happens quickly and efficiently since the product does not require polishing or buffing. Once a part is removed from the mold, it can be easily coated or finished.