In our current blog we describe the manufacture of raw glass (lime soda glass). Normally the following raw materials are used for the glass mixture:
The ingredients change according to the type of glass being made. This list therefore only features the most important components. As soon as the batch is made, the melting begins with 3 different phases:
- Phase 1 is the preliminary melting phase. This is when the batch is melted and homogenized
- Phase 2 is refining (removing gas bubbles).
- Phase 3 is cooling down the material in preparation for forming
The glass components slowly begin to melt together at temperatures around 1400 degrees Celcius. The melting is facilitated by injecting air or gas into the process. Refining takes place right after melting where remaining gas bubbles are removed. Since melting can be rough and can reach very high temperatures this process takes a lot of time. Refining is also a determining factor of quality. The forming comes once this process is over. Forming is only possible at lower temperatures. This process varies according to the type of glass being manufactured or the application.
Glass can be formed by extruding, blowing, spinning, rolling, pressing or drawing (see also Finishing techniques):
- Hollow glass is made using several techniques such as pressing, blowing, suction and a combination of these methods
- Fiberglass is produced by, among others, extrusion and drawing techniques
- Flat glass is made using float glass methods, it is drawn, rolled or cast
- Glass tubes are made using drawing techniques
Once the forming process is done, the glass must still be cooled. It is important to watch for stresses that occur during forming. These stresses occur because of the different expansion rates of the materials. These stresses are measurable with an optical stress viewer. Stress sensitivity is dependent upon the expansion coefficient of each type of glass. By constant cooling, or annealing, these stresses are starkly diminished. Depending on the glass type and thickness, the time it takes this process to finish can really vary from a few hours up to several days. Special kilns or industrial cooling paths perform this job.