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Safety glass can now be cut to any shape

23 October 2012

Shock-resistance is the great benefit of safety glass. However, difficulties arise when the pane is cut; using conventional processes, only straight cuts are possible.

Photo courtesy of Fraunhofer IWM
Photo courtesy of Fraunhofer IWM

With safety glass, a tear-proof film is inserted between two panes of glass, which makes the lamination shock resistant. If glass fragments arise, they stay attached to the film. Safety glass panes are produced in panels measuring 6 x 3.20m, which are subsequently cut-to-size as required.  Since the inserted film is tear-proof, cutting the pane is not at all straightforward.

First, both glass panes encasing the film are carved and fractured. Then, the break line is heated with an infrared heating element. The heat softens the film, and the halves are forcibly pulled apart until a knife can be guided through the gap. But this method has a drawback - it only allows for straight-line cuts.

If architects want extravagantly shaped windows, like round ones, the standard practice is for the safety glass panes to be carved and detached by hand. However, the resulting gap is too small to allow enough space for a knife, which could also inadvertently sever the film.

To widen the gap, and ultimately to be able to cut the desired form, the film is softened with heat by applying alcohol and setting it alight.

A new method will soon be able to circumvent this dangerous procedure. Researchers at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, working jointly with Hegla, have engineered a new process.

“We cut the interior film before the glass is scored and broken apart,” explains Tobias Rist, a scientist at Fraunhofer IWM. We use a laser beam that can be guided over the pane as desired. This is why we are also able to cut unusual geometries.” 

The laser beam penetrates the glass and releases its energy primarily in the film. The film gets hot enough for it to melt and vaporise. With this method a channel is produced in the film, and the film is separated locally. When the film is 'cut' the glass is carved and fractured parallel to the resulting film channel. “The process can be readily automated and applied on an industrial scale,” says Rist.

Helga will integrate the laser process into a new laminated safety-glass pattern cutting system. The company has  been granted a German and a European patent for the process of carving contours; meanwhile the researchers are working on another step that will make the process even faster.

A undulating-cut pane of safety glass will be shown at the Glasstec trade fair from 23 to 26 October 23-26, Düsseldorf (Hall 15, Booth E25).

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