Glazing – Technology and Surface Treatments

Warm Edge Spacers

The lites of multi-pane units are held apart at the preferred distance by spacers. In addition to keeping the glazing lites separated, the spacer must serve many functions:

• accommodate stress induced by thermal expansion and pressure differences
• provide a moisture barrier that prevents the passage of water or water vapour that would fog the unit
• provide a gas-tight seal that prevents the loss of any special low-conductance gas in the air space
• create an insulating barrier that reduces the formation of interior condensation at the edge

A warm-edge spacer is a type of spacer bar used in double-glazed or triple-glazed window products, separating the lites and seals off air cavities.

Typically, spacers are made of high conductivity aluminium, while modern, warm edge spacers generally made from vinyl (uPVC) or high-grade steel which have improved thermal insulation properties.

As a result, the term ‘warm edge’ is given, as heat loss is reduced both at the edge of the glazing and within the frame, the glazing product is installed in. Typically included in glazing products where other insulative measures have already been undertaken, warm edge spacers are often required in higher performance glazing systems to reduce condensation risk.

Frit

To use colour and patterns on glazing, we often use surface treatments such as ceramic fritting combined with clear or tinted substrates on tempered or heat strengthened glazing.

Comprised of tiny glazing particles, pigment, and a medium to mix the glazing and pigment together, frits are applied to one side of the glazing and fired in a tempering furnace to create a permanent, durable coating.

For a double-glazed unit, the frit pattern is ideally located within the sealed cavity for protection and can also be applied to laminated glazing units. To reduce solar transmittance, the fritted layer is positioned on the interior surface of the exterior pane of a double-glazed unit, where a low-E coating can also be placed on top if required.

In practice, the SHGC of a frit coating is affected by its colour, distribution and location in the glazing system. This impacts the Total SHGC of the installed product but also the light transmittance. While frits are useful for reducing solar transmittance, they are not a replacement for shading or better quality, spectrally selective glazing.

Acid-etching and Sandblasting

Acid etching is another surface treatment that gives a matte finish to glazing, with the degree of finish being determined by the length of time the acid is in contact with the surface. By masking, patterns and pictures can be etched into the glazing and provide design flexibility. An intense etching process roughens the glazing surface, which diminishes transparency while light passing through the glazing is scattered to obscure view and diffuse light.

Glazing can also be sandblasted to give a similar matte finish. It should be noted that diffusing glazing can sometimes increase glare since surface brightness is increased.