Volume 48, Issue 10- October 2013


Fabricators Find a New Bend in the Latest Insulating Glass Options
As architects push the envelope in their designs, more fabricators are learning to curve that envelope, even in the case of insulating glass units (IGU). The use of bent and curved IGUs is still relatively new in the United States, but it’s a trend that’s growing as changing technologies allow for increased applications.

“This is part of the trend with decorative products,” says Timothy Moore, senior process engineer with Standard Bent Glass (SBG) in Butler, Pa. “Designers, architects and clients are interested in something that is more than just a flat curtainwall or storefront.” He points out that designers are looking for products that truly stand out and adding a curve to combinations of high-performance, low-E and decorative printing is the latest twist to the must-have list of glass traits.

It’s the new coatings that hold the key, says Russell Alder, vice president of Precision Glass Bending in Greenwood, Ark. “The use of bent IG is increasing because of the availability of high-performance low-E coatings that can be bent—for example, the Guardian Sunguard family of coated glass—as well as the advancement of glass bending technology that focuses on quickly heating these coatings with an outstanding level of optical quality. These two changes have expanded commercial and residential use of bent IG by allowing it to conform to the same strict performance parameters of advanced flat IG.”

The most critical aspect of this production process is the product’s fit in assembly and installation, according to Moore. “Flat glazing is typically subjected to glazing pressure at the perimeter to achieve a weatherseal,” he says. “Bent IGU by nature must have critical ‘fit’ of the two bent lites. In turn, the finished IGU must fit the radius of the support structure.”

Joseph Finn, managing director of Bent & Curved Glass in Australia, says distortion is also a big concern when producing an IGU from two laminated bent pieces, “especially in more complex shapes with flat tangents.” In addition, he notes that fabricators are somewhat limited as to which spacers can be used due to the nature of the varying shapes of each job.

Furthermore, he says, “Handling can be an issue as well, due to the weight in a larger panel. This can be especially true on-site as different equipment is needed that is not readily available.”

Moore offers an additional caution to installers. “In reality, there is usually some mismatch by allowed tolerance and installers must be mindful to provide resilience when selecting gaskets and setting blocks to avoid peripheral glazing pressures. Stress in the glass is cumulative from wind, thermal, etc., and the product needs to ‘float’ in the opening to avoid permanent glass stress. Wet glazing or a combination of wet/dry glaze works the best,” he says.

Alder suggests that the main difference between curved versus flat IGUs comes from the equipment being used to produce it—or lack thereof. “The main difference is that flat IG is now fabricated mostly by using automated equipment,” he says. “However, bent glass parts differ along not just two dimensions (length x width) but also a third dimension (x depth) so bent IG is typically assembled using no more than semi-automatic equipment so the insulating seal can be precisely matched to the glass shape as well as size. For this reason, expertise of the bending company as opposed to quality of automated equipment is perhaps more critical in bent IG fabrication when compared to flat IG.”

Finn points out that the lack of automation means these complex panels also may be more subject to human error. In that regard, many fabricators are waiting, and urging, machinery companies to develop new solutions to simplify fabrication of this new product.

Such solutions may need to be customized for each company, if not each job, Finn says. “Every job can be different, so it is difficult to have a machine that can help,” he says. He predicts that it will take a significant increase in the use of curved and bent IGUs before more machinery manufacturers invest in process improvements.

But even with the right tools to do the job, Finn points out that there is one more problem with the growing use of this product line: testing to make sure it’s done correctly. “I also think we need to do more testing to see if there are any particular issues with curved IGUs but, again, this is a question of volume and critical mass,” he says.

At present there are no standards specific to testing curved or bent IGUs. Moore suggests that the standard methodologies used in flat glass work for bent glass, but adds, “It would be great to see the Insulating Glass Manufacturers Alliance (IGMA) or Insulating Glass Certification Council (IGCC) adopt some methodology to incorporate certification of bent glass IGU.

IGMA has a task group on the subject but, being a testing issue, the matter largely has been deferred to IGCC. For the Council’s part, IGCC administrative manager John Kent explains that IGCC adopted guideline G.34 in 2011, clarifying that the ASTM E2190 test method does not provide for testing of bent or curved IGU. The guideline further states: “As such, it is only flat IG units that fall within the IGCC/IGMA Certification Program. This, however, in no way precludes the ultimate use of bent or curved IG units. Labeled spacer may be used in IG units, other than flat glass, but in that case, certification does not apply.” In other words, curved IGUs are tested much in the same way as spandrel, and fabricators must wait for ASTM to step in to develop an overarching standard that dictates testing specific to bent or curved IGUs.

Alder adds, “The key for bent IG going forward is to continue developing fabrication methods that can keep up with the wave of innovation coming in flat IG, namely vacuum evacuated interspaces, clear structural insulating seals, etc.”


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