GPD Workshop Addresses Anisotropy Challenges and Concerns

When it comes to what’s important with architectural glass, visual quality is at the top of the list. A workshop that focused on anisotropy, or the visual appearance of glass, took place today as part of Glass Performance Days (GPD). Participants met at Glaston’s headquarters in Tampere, Finland, to discuss the issues and concerns, as well as possible future guidelines.

Glaston hosted a workshop at its headquarters to kick off GPD festivities. The conference opened Wednesday and runs through Friday.

Anisotropy is a fairly new term for describing the appearance of glass. It covers issues such as colors, haze and gray patches in the glass. During the workshop a number of presenters offered perspectives on some of the challenges and issues they’ve experienced.

Graham Dodd of Arup provided a video testimonial on some of his concerns related to anisotropy. He said it’s a problem for customers because it detracts from the quality of glass. While there will most likely always be some level of anisotropy physically, the important thing is getting to a non-discernible level where people don’t see it.

New York-based architect and designer James Carpenter, who will also provide a GPD keynote address Wednesday, shared his experience on one particular project. He explained that the project included chemically strengthened laminated glass. While a mock-up showed no issues, once it was on site there were major visual issues that had to be addressed.

Facade consultant Steve Downey talked about projects in which shipments of glass had to be discarded completely due to anisotropy.

He said he hoped that by attending the workshop, he would be able to answer the architectural question of whether the stress patterns, seen from the outside, affect overall glass strength.

Another thing he said he hoped to address related to roller wave distortion. “I don’t think roller wave has anything to do with anisotropy,” he said. “We typically don’t see those affects in heat-strengthened glass.”

Workshop participants discussed the fact that the industry currently doesn’t have a standard or maximum acceptable value.

One participant commented that the equipment and the process are the reasons for anisotropy. “Processors (fabricators) need to discuss with the customer what is acceptable because there are no levels of standards,” he said

Francis Serruys with Saint-Gobain Building Glass Europe led a session to address the question, “what is anisotropy?”

There are three parameters, he explained:

  • Tempering parameters and the design of the furnace;
  • The proposition of polarized light; and
  • The situation of the glass and where it is installed.

The different types of anisotropy that can occur, he said, can include Kevlar marks, blowing nozzles and stain (color) in the glass.

He also noted that the highly polarized light makes anisotropy marks more visible.

Another concern relates to the thickness of glass, so that the more you combine liters of heat-treated glass the more you increase the risk of anisotropy.

Optimizing a single piece of heat-treated glass increases the possibility of having the best outcome. The thinner the glass, he explained, the lower the risk, but the higher possibility of distortion. The thicker the glass, the flatter it will be, but then there’s a higher risk of anisotropy.

Companies have also developed devices for measuring anisotropy. Rainer Feuster with Viproton and Riku Farm with Glaston each spoke about these developments from their companies.

Feuster addressed the question, “how do we make a real evaluation in the end?” His company offers an online inspection system that interacts right at the exit of the furnace. He said this provides real time anisotropy measurement, as well as detailed visualization of the results; quality/classification; and quality reports

The latest innovation from Glaston is the company’s iLook. This is designed to give more and more information to the operators.

“Tempering is still a lot about the operator,” said Farm. He described the machine as providing anisotropy “scanning because we do not yet have any level of measurement.”

He explained that the system processors to see and correct the problem. Then the next step is analysis of the glass and to correct the problem automatically.

Later in the day, the participants formed individual groups to further discuss some of the challenges and ways these can potentially be addressed in the future.

GPD, which is celebrating its 25th anniversary, officially kicks off later today with the opening ceremonies, and continues through Friday. Stay tuned to USGNN.com™ all this week for our ongoing coverage.

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