The triple-glazing question

Do a growing number of centre pane failures in triple-glazed IGUs represent a ticking time bomb for the UK window and door industry? Glass Times talks to Dave Broxton, managing director of Bohle.

Although double-glazed units represent the vast majority of installation the number of triple-glazed units fitted in the UK is growing. And so are the number of failures of those units, according to Bohle.

This isn’t an issue for the UK alone. Failed triple-glazed units are an issue Europe wide. So, what are the potential causes and what can IGU manufacturers do to insulate themselves – and their customers – from the risks?

“Growth in sales of triple-glazed units has been below expectation, or perhaps in line with it, depending on your take on its potential,” Dave Broxton, managing director of Bohle, said.

“Nonetheless, tens of thousands of units have still been supplied. The problem is that a growing number are failing and there is still no conclusive explanation as to why. Although we do have a theory.”

This, he said, means that installers, fabricators and ultimately IGU manufacturers, could face accumulatively potentially very large liabilities in the future.

The cause of failure in triple-glazed IGUs is currently subject of a European-wide study. The theory is that the use of low-e glass on face three of the unit as part of its thermal make-up, can mean the middle pane in a triple-glazed unit heats up far more than it would do in a standard double-glazed unit. This can cause excessive thermal stress, leading to failure.

Bohle has been a leading contributor to the research, exploring the connection between edge quality and triple-glazed IGU failure.

“We know that edge quality is critical to product performance,” Dave said. “That starts with the way the glass is cut and ultimately the cutting wheel and fluids used in that process.

“We’re looking at how different combinations of both can increase or minimise the risk of triple-glazed unit failure under thermal stress.”

Bohle’s origins are rooted in glass cutting, founded on its Silberschnitt cutting wheel range, which has evolved over almost a century from simple hand-held tools to high-tech automatic cutting wheel designs.

“When you score glass with a cutting wheel you effectively transmit tension into it,” Dave said. “This creates a fault line in the glass, which as you bend it, triggers a break along that line.

“This may seem simple enough in theory but the science that underpins a clean break is complex, defined by multiple factors including: the individual characteristics of the glass; the shape of the cut; the diameter of the cutting wheel; the angle of the cut; cutting force; cutting speed; and the cutting fluid used.

“These factors have a very large impact on how cleanly the glass breaks, the crack depth, lateral cracks, the size of the shatter area and chipping – things that define edge quality and ultimately the stability of that product in life and its response to stress, eg, heat.

“If you’re running hundreds of kilometres of glass a year as part of IGU manufacture, you could be storing up massive problems for the future simply by using a sub-standard cutting wheel or the wrong cutting fluids – things that are cheap as chips to buy,.”

Bohle has developed products in partnership with the leading glass machinery companies including Glaston Bavelloni, Bottero, Bystronic, Benteler, CMS Brembana, Grenzebach, Hegla, Intermac, Macotec and Lisec. With its own research laboratories and a rigorous research and development programme, it’s this partnership approach that has allowed Bohle to deliver a step-change in cutting-wheel technologies, the company said.

This includes the supply of an extensive range of tungsten carbide and PCD (polycrystalline diamond) cutting wheels including Cutmaster Gold. Ideally suited to cutting float line and laminated glass, its service life is around eight to 10 times longer than a standard cutting wheel, and it maintains a consistently high cutting quality.

Cutmaster Platinum uses a specially developed micro-structure that forms a permanently sharp cutting edge but also rather than forming a continuous cut, creates a series of microscopic ‘dots’ along the score line creating a far more precise line.

Bohle also supplies an extensive range of cutting fluids – another critical element in supporting lower stress soft breakout.

This includes Acecut, which includes washable cutting fluids for use in cutting of thick glass (10mm and up), shape cutting and laminate glass cutting. It also supplies a range of evaporating cutting fluids designed for cutting insulated glass and, among others, low-e glass.

“We haven’t got all of the answers but there are two things that are definite,” Dave said. “First, the rate of failure in triple-glazed IGU units is disproportionately higher compared to that in double-glazed units.

“The second is that we know that edge-quality and, particularly the quality of the break-out, can have a massive impact on product stability once installed.

“Given those two factors, surely a little time spent on specifying the right cutting wheel and the right cutting fluid is common sense?”