ASTM: new quality standard adopted for chemically strengthened flat glass

3 June 1999: The C 14.08 Flat Glass Subcommittee of the American Society for Testing and Materials (ASTM) recently adopted a new quality standard adopted for chemically strengthened flat glass. The ne…

3 June 1999: The C 14.08 Flat Glass Subcommittee of the American Society for Testing and Materials (ASTM) recently adopted a new quality standard adopted for chemically strengthened flat glass. The new standard is contained in the document C 1422-99, Standard Specification for Chemically Strengthened Flat Glass. The Glass Association of North America, whose Laminating Division coordinated the work of the ASTM, reports that the standard categorizes the process of chemical strengthening according to the case depth and surface compression produced in the glass. Technical consultation for adoption of the standard was provided by Dr. Arun Varshneya of the College of Ceramics at Alfred University, New York. Chemical strengthening is achieved through the process known as ion-exchange. In the case of soda-lime glass, the salt bath consists of potassium nitrate. While the glass is submerged, the large alkali potassium ions exchange places with the smaller alkali sodium ions in the surface of the glass, creating a “strengthened” surface. Because chemically strengthened glass breaks in a pattern similar to annealed glass, it is not used by itself as a safety glazing material. However, it can be laminated for a variety of architectural, security, and transportation applications, and is also used in the optics, aerospace, and laboratory equipment industries. Chemically strengthened glass can be significantly stronger than annealed glass, depending upon the glass composition, strengthening process, level of abrasion, and the application environment. It is said to be an effective way to strengthen glass that is too complex in shape or too small or large to be thermally strengthened. The chemical strengthening process does not affect the colour, clarity, and light transmission of the glass. Optical transmission and surface reflection are the same as the glass from which it was made, thus, reducing the possibility of roller wave distortion. The Glass Association of North America says the C 1422-99 standard will be available in the second half of 1999 from ASTM.