News Analysis: Curved Glass

Getting Ahead of the Curve: The Growing Trend Toward Large Bent Glass

By Jordan Scott

The demand for glass is growing from traditional architectural glazing to jumbo glass sizes. Innovation will likely continue to push the envelope, and oversized curved glass could be the next darling of architects’ designs.

What’s the largest size glass that can currently be bent? The answer depends on who you ask.

“Our largest glass size with heat-treated glass (heat strengthened or fully tempered) is 96 inches by 130 inches. Glass thickness can range from 3/16 of an inch to ¾ of an inch,” says Jake Bowser, architectural sales manager at Standard Bent Glass Corp. based in East Butler, Pa.

His company educates customers about what to expect prior to the ordering process.

“With increasing demands pushing the limits of our bending ovens, providing job-specific mock-ups becomes essential. Keep in mind, those mock-ups are not only beneficial to our customers but to SBG as well. Mock-ups are duplicated to not only send to our customers and beyond, but also for SBG to keep and monitor the quality of parts shipping for that project,” says Bowser.

Size Limitations

At Cristacurva, of Guadalajara, Mexico, the glass size limits depend on whether the curved glass is annealed or tempered. The company has a general guideline of 126 inches by 196 inches for tempered glass and 130 inches by 240 inches for annealed and laminated glass.

“The maximum size is also dependent on thickness, glass type, radius and other items. It is always a very good idea to check…regarding the specific requirements for a project. We can help select the best solution,” says Javier Sánchez-Gil, company CEO. “We are capable of making oversized products that are both flat and curved. When going above certain sizes, it is import-ant that we understand glass make-up, thickness, fabrication process, radius, wind loads and other factors so that we can advise as to feasibility. In general, however, we are capable of making very large flat and curved units.”

Bowser says one of the biggest challenges he’s come across is the difference between customer expectations and industry standards, specifically those regarding aesthetic.

“Even at that, the industry standards do not address all aesthetic possibilities for curved glass,” he says. “A common theme would be to address oversized glass through the industry-wide standards, and to educate the masses (architects, general contractors, etc.) as to what can be expected from oversized curved glass. That could determine the success or lack thereof. Manufacturing equipment specific to curving the glass is only one cog in the wheel. Oversized fabrication starts with oversized cut-ting equipment, edging equipment capable of handling the large sizes and so on down the line. Simply transporting the glass from department to department inside a fabrication facility becomes tedious.”

Sánchez-Gil finds meeting tight tolerances, especially with low-E products, one of the biggest challenges of bending oversized glass. Others include supply and availability of glass, time to ship larger, special glass products from the main manufacturers to the fabricators, and handling throughout the fabrication and shipping processes.

“Sputter-coated, low-E glass offers the highest performance. Some of them, like Guardian’s SunGuard coated glass product line, are durable enough to be bent, and Cristacurva has used them in many projects throughout North America,” he says.

According to Sánchez-Gil, changes needed to meet requests for oversized curved glass include getting glass in larger formats more easily, with more frequency to accommodate the over-sized machinery already in place.

Following the Trends

The trend toward increased curved glass sizes is impacting Glasshape Ltd., as well. The New Zealand-based company produces curved glass panels at a girth of 96 inches.

“Increasing glass panel sizes creates challenges for any manufacturer. It’s not only the ability to curve larger pieces of glass, it’s all of the supporting processes that have to be considered too—being able to handle larger sheet sizes, having larger CNC edge-working equipment, having larger laminating ovens, etc. It means that everything becomes more challenging when having to accommodate larger sizes,” says Andrew Bissett, strategic business development and de-sign manager at Glasshape.

The overall size of railings is also a growing trend, but Bissett has seen the biggest growth in glass performance.

“With thicker glass laminates being specified in order to create structural panels with minimal supporting hard-ware and structures, creating a cleaner design aesthetic with safety is also a major consideration and advantage,” he says.

Budgets can also be an obstacle for the industry in its work to accommodate requests for larger curved glass.

“The cost increase between standard-size bends and oversize bends often dictates a client’s decision to run with an oversized panel of glass,” says Bissett. “However, anything is possible at a price.”

Tighter bends, multiple bends and different types of glass are also considerations when curving oversized glass.

According to Bowser, tighter bends don’t necessarily become more difficult if glass is oversized.

“Small glass sizes with tight radius requirements can be equally as challenging as oversized glass with tighter radius dimensions,” he says. “Our bending ovens can only curve glass to a quarter circle of any given radius inside the capability range. For example, if the de-sired radius is 32 inches, the largest arc dimension (around the curve) would be 50.25 inches. As that radius dimension rises, so does the arc, until it reaches our maximum size capability.” He adds that multiple bends are not an option with Standard Bent’s heat-strengthened or tempered bent products.

Sánchez-Gil would ask a customer several follow-up questions to establish if tighter bends are difficult to achieve with oversized glass.

The glass’ thickness coupled with whether the glass is tempered or annealed and whether it is clear, tinted textured or coated all factor into the answer.

“A 90-degree angle with certain radii, thickness and sizes can be accomplished with curved tempered glass,” says Sánchez-Gil about achieving 90-degree bends with oversized glass.

“Curved annealed allows us to go as far as 180 degrees. However, it is necessary to understand the radius, thickness and size required before fully answering the question. Multiple bends are possible with curved annealed, and with certain selected glass types,” he adds.

He adds that Cristacurva can bend any glass type, but limitations exist when considering thickness, size, angles and radii.

“The range of possibilities are also affected by whether the glass is curved, annealed or curved tempered. Coated glass that is durable enough to be heat-treated is required for bent applications. Guardian SunGuard coated glass is a great example of a high-performance soft-coat low-E glass that can be bent. [This includes] the newest SunGuard SNX triple-silver coating,” says Sánchez-Gil.

Curved Glass Considerations

Machine limitations are a major challenge to making advancements in the length and radius of oversized glass.

“We are ‘capped’ if you will at 96 inches in regard to the curved edge. That is a function of our bending equipment we have purchased. In order to produce larger glass, SBG would need to purchase bending ovens capable of such. Not only would the bending equipment need to be upgraded larger, so would the other fabrication equipment (i.e. cut-ting, polishing, etc.),” says Bowser.

According to Glasshape’s curved glass specifications, tighter curves re-quire thinner and small glass sizes. To achieve a 160-degree angle, the glass must be 2 mm thick, with a minimum radius of 50 mm and between 50 to 1,200 mm in length. Bends up to 145 degrees can be achieved with glass 19 mm thick and a 450-mm radius.

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