Glass forming is somewhat reminiscent of the ancient art of glassblowing. Until the end of the 19th Century, glass production relied on the traditional method of production glassblowing to produce glass products. Though a tried and true process, blowing into a tube to form glass products was time consuming and labor intensive. As the demand for glass products increased, manufacturers searched for methods to produce the same quality of products using advanced production techniques. The result was the mechanization of glass production. Though the innovations of the 19th Century have been updated and improved, they are essential the same ones used by producers today.
There are three distinct parts associated with the glass forming process – raw material processing, molten glass forming or hot end, and cooling or cold end. Each step requires the efficient completion of the previous one to effectively produce well formed glass products.
Glass forming starts with molten soda lime glass or borosilicate glass mixed as raw material in the processing section or batch housing. In most glass production plants, there is enough raw material for up to five days of production. The amount that is distributed to the forming process is carefully measured and mixed. The color, quality, and purity of the final product is determined by the specifications from this section.
Once the mixture is released from the batch housing, it is sent to the production center or forming section. Here, the molten glass is cut into small carefully measure portions called gobs, cut to the specific weight for placement in the mold for the forming of the final product. The gob is formed into a parison prior to being placed in the mold. The parison is moved to the mold where compressed air is blown into it forcing the molten glass against the sides of the mold. For certain products, compressed air may be blown a couple of times to ensure equal distribution of the molten glass.
After being removed from the mold, the completely formed product is coated with a thin layer of a metal as the first stage of the coating process. At this stage, the product looks as though it is completed and ready for shipment. In the molding process, the outside of the product cools faster than the inside creating an unevenness causing stresses in the glass.
To address he stresses and unequal temperature of the inner and outer side of the product, it is put through a process called annealing where it is cooled and heated until the inner and outer layer have the same temperature. This portion of the production process takes the most time lasting from an hour to an hour and a half depending on the type of product.
The final step is the treatment of the skin of the product by coating it with a polymer finish. It is applied to the exterior of the container to form a scratch resistant shield, which provides durability and extra strength to the glass.
Glass products are easily recycled and reused. The bottles that are collected by supermarkets and collection centers are shipped to glass processing plants where they are crushed into pieces, have their impurities removed, and formed into a cullet that is melted and used to produce new glass products.