Glass-to-metal and glass-to-glass sealing involves the softening or melting of glass and subsequent wetting to glass or metal surfaces to form a seal that is hermetic and electrically insulated.
Glass-to-metal seal may be either matched seal or compression seal. Creating these seals requires careful control of surface oxides, together with thermal sealing and annealing profiles with temperatures as high as 1000°C.
Crown corks are used for sealing glass bottles containing carbonated or non-carbonated drinks. The cap is pre-formed during the manufacturing process and clinched onto the top of the bottle manually or automatically after the bottle has been filled.
Most foods that are packaged in glass are either liquids, such as drinks and syrups or thicker pastes such as sauces, chutneys etc. Many foods that are packaged in glass are then heat processed and for these it is usual to hot-fill the containers (fill at 80°C or above).
Glass has to be heated and cooled carefully to avoid the risk of breakage and therefore it is usual to pre-sterilise containers before hot filling. This can be done by placing bottles/jars in a large pan of warm water and heating it to boiling. The containers are boiled for 10 minutes and then removed for immediate filling and sealing.
Glass sealing
