Processing Magazine

Fused glass/metal windows offer sight and light in sanitary applications

October 10, 2006

Now available in a wide variety of sanitary-application designs, Metaglas® mechanically prestressed borosilicate glass windows deliver service well beyond the limits of conventional windows or of prestressed windows using soda-lime glass.

The unique Metaglas concept lends itself to sight ports, light ports and flow indicators. In all they offer strict compliance with sanitary codes while also providing benefits in ease of maintenance and reliability.

Metaglas prestressed windows are formed by fusing borosilicate glass inside a precisely formed stainless steel ring. Since steel has a much higher coefficient of thermal expansion than borosilicate glass it imposes radial compression as it cools around the solidifying glass. As a result the two materials fuse under pressure to present a continuous transition to the process flow, free of voids where bacteria might build up. Equally significant, due to the radial stress the resulting window is more uniformly elastic than standard glass, tempered glass or even similarly prestressed soda-lime glass, since soda-lime glass has a higher coefficient of thermal expansion than borosilicate glass.

In service, potential cracks that could otherwise lead to failure are absorbed by the homogeneous compression stress that is imposed across the full section of the glass. Significantly, Windows based on this concept have been in service for nearly thirty years without a single in-service failure.

An additional benefit of Metaglas windows is that when a vessel or a pipeline must be opened for maintenance or repair they can be removed and reinstalled. Conventional windows must be discarded and replaced if they have been removed. Metaglas windows are also highly resistant to damage from accidental impact, from wide temperature variations and bending moments.