Tips from theTrade
GANA Volunteers Provide Entry-Level Education
at Glass Fabrication Event
by Megan Headley
It all starts with sand. The presentations given during
the Glass Association of North America’s (GANA) Glass Fabrication Educational
Event, which took place in May in Kansas City, Mo., started very much
at the beginning: with silica sand.
The biannual conference is geared toward professionals entering the glass
industry, or those looking for a best practices refresher on various aspects
of fabrication. In that regard, AGC Flat Glass North America’s Ivan Zuniga
helped provide his listeners with the perfect starting point, as he walked
them through the float glass manufacturing process, from charging raw
materials (including silica sand) to melting in the furnace, floating
along the tin bath, to annealing and, finally, cutting. Zuniga related
the process to his audience’s experience, explaining, “For those of you
who contact us and say ‘well I’ve got an architect and he’s got a LEED
project and he wants to know the number of regional materials I have for
this product ...’” Zuniga explained manufacturers are able to look at
the source of each of the products in the glass’ raw batch: silica sand,
cullet, soda ash, dolomite, limestone and other products. “The other thing
you guys ask about is recycled material,” Zuniga continued. “Well, we
do use crushed glass, which is recycled.” However, the way LEED reads,
he explained, recycled content must be from a post-consumer product. “So
according to LEED and according to the ISO definition, cullet does not
comply as a recycled content.”
From Making to Breaking Glass
Following Zuniga’s presentation about making glass, Pilkington North America’s
David Duly took the podium to discuss breaking glass. Duly, too, discussed
raw batch materials, noting that the addition of ingredients such as calcium
and sodium are what gives glass its structure and strength.
Duly went on to explain that there are very high stress concentrations
in glass. For starters, Griffith Flaws are stresses invisible to the eye
but inherent throughout the glass. “When glass is strained, the strain
can be concentrated due to this Griffith Flaw. When the strain exceeds
the strength of the atomic bonds, the glass breaks.” He pointed out, these
are just the flaws existing in glass—then there are the flaws added to
glass, such as scratches, etc.
Next, Duly went on to answer the question of what causes glass to break.
A big concern today, Duly said, is thermal stress. He noted that the prominence
of energy-efficient products absorbing heat can lead to thermal stress
issues. He explained that a classic thermal stress fracture always begins
at the glass edge. It starts at a 90-degree angle before meandering away
from the edge of glass in any direction to escape the stress. “When you
see a single fracture, in most cases the edge is damaged and the stress
at the fracture was low,” he said. More fractures could mean a good edge
simply couldn’t handle the extreme temperature difference between the
center and edge of glass.
Duly ended his presentation by asking what we can do to improve the strength
of glass. “The most common way to improve the strength is to heat-treat
glass,” he said. “When you heat treat glass you’re putting the outer surface
in compression and the inner surface under tension.” The compressive forces
counter the opening of crack tips, he explained.
Chuck Beatty of Edgeworks offered information on properly cutting glass.
He opened his presentation on “Principles and Fundamentals of Glass Cutting”
with an explanation of cutting glass as overcoming the compressive stresses
on the surface. As
Beatty explained, cutting glass means trying to separate the surface without
destroying it. “In the glass cutting process the first rule would be never,
ever destroy the surface of the glass,” he said.
Beatty explained how to release the tension within the glass in a controlled
fashion. He offered his audience a number of tips, emphasizing the importance
of the choice of cutting wheel that’s appropriate for a given thickness
of glass. As Beatty explained, “It wasn’t very long ago everyone was using
one wheel to do everything ... that’s incomprehensible to me now.” Cutting
wheels are dimensioned for each different glass cutting application, with
different finishes available for different results.
The angle and footprint also are important, he added.
“In choosing the right wheel angle it’s important to remember, the less
energy you send into the glass while scoring the cut, the smoother the
resulting edge after the break out,” Beatty said.
He reminded his audience to pay attention to the appropriate psi needed
to make a cut. If an operator opts to turn up the pressure to complete
the cut, the heat also is being turned up. This can lead to more sub-surface
pressures—and potentially destroy the glass. Rather than turning up the
pressure, Beatty advised changing the cutting wheel first, as that should
be done at a regular frequency anyway. He noted that the occasional “shark’s
tooth” flaw on the edge, should be a warning sign to “change something
pretty quick if you don’t want major problems.”
Taking Care with Coated Glass
Dave Cooper of Guardian also had some tips for cutting, specifically when
it comes to high-performance coated glass. He noted the importance of
having the coated side of these glasses facing up during cutting so shards
aren’t scratching that surface, although, he advised, the table surface
should always be kept clean. He also recommended using only as much approved
cutting fluid as needed and moving lites one at a time to prevent scratching.
Cooper reminded his audience of the importance of carefully storing coated
glass prior to cutting. For starters, he said, “These high-performance
glasses reflect solar energy, but they also absorb it, so if it’s stored
in sunlight, it might break.” These high-performance glasses should be
stored out of direct sunlight and away from water, in a stable and well-supported
According to Cooper, though, the most important issue with handling high-performance
glass is washing. “It’s such an important step; it’s repeated throughout
the process often, and having the washer set up and running to the manufacturer’s
specs is critical,” he said. If the glass is not appropriately washed,
any subsequent fabrication is not likely to be successful. He added, “It’s
especially important not to touch the coating as it is being removed from
Bob Lang of Billco had more tips about washing glass of all types in his
presentation on “Understanding and Maintaining a Glass Washing Machine.”
Lang began by explaining how the pre-spray system minimizes the contamination
in the washing zone portion, among other things, as it removes loose debris
from glass before passing through the washer. He also stressed the importance
of using clean water so that minerals—such as those commonly found in
city water—don’t end up contaminating the glass. In addition to using
clean water, regular maintenance of the machine can impact the cleanliness
of the glass. Lang also noted that it’s important to maintain the drying
section rolls so they stay clean and there is no contamination on the
bottom of the glass.
As Lang explained it, “The thing to remember is if the inside of the glass
washer is dirty, the glass can’t get clean.”
Philip Bradbourne of DuPont provided tips on “Troubleshooting Laminating
Glass Manufacturing,” noting as he opened his presentation that producing
good quality laminated glass is “important to have that edge over your
“A number of different things can cause delamination … High moisture can
cause problems with delamination; PVB likes to absorb moisture,” he added.
“The good thing is it sucks it up but you can also recondition it back.”
Other causes of delamination can include rippled or dirty glass, having
the wrong adhesion grade and pinch points in the autoclave, among other
factors. As far as solutions to delamination, Bradbourne advised seeking
lab analysis to know the exact cause.
Bradbourne also reviewed problems such as PVB blocking; where the PVB
interlayer sticks to itself. He noted this can occur when the interlayer
storage temperature is too warm, and that suppliers must be sure the interlayer
is transported in a refrigerated truck on the way to customers. The problem
also can occur if the roll is wound too tightly by the supplier or is
He also discussed causes of bubbles, gas pockets in the interlayer or
between the glass and interlayer. A large number of small bubbles along
the edges could mean the autoclave pressure releases at too high a temperature.
Glass imperfections, such as caliper variations, can cause a large number
of bubbles at the glass-PVB interface.
Bradbourne also stressed the importance of keeping the lay-up or clean
room clean. He suggested using filtered air condition, and making sure
employees use special lint free hats and clothing to prevent static or
contamination—and only allowing authorized personnel entry into the lay-up
To minimize problems, Bradbourne advised having clear written directions,
a troubleshooting model and experienced employees handling the laminating.
Tools for Tempering
Chuck Wencl of Viracon addressed an audience interested in tempering on
the topic of “Roll Wave Distortion.”
He opened by noting there are a number of different definitions for this
problem, but GANA’s Roller Wave Subcommittee offers this one of roller
wave: a repetitive wave-like departure from flatness related to the heat-treated
process, excluding edge effects, distortion influenced by assembly or
Wencl also showed images of glass installations with severe distortion,
including one project that won an award (for energy efficiency he pointedly
added). “If this is what the market will take, this is what the market
gets,” he commented. However, today many fabricators are seeing requests
from the market for thicker lites of glass in an attempt to get flatter
glass. Wencl reviewed a number of tools available today to indicate when
this distortion is present and notify the operator that it’s time to check
the performance of or maintain the rollers or tempering furnace itself.
The Zebra Board
Wencl went through a list beginning with the zebra board, a subjective
test for monitoring roller wave, to the various options available in flat
bottom gauges. He called the 3-point gauge “very effective,” noting for
this particular device, “it doesn’t matter what kind of a surface you
put them on they target that wave only.” In recent years, he noted, digital
grid photography has been introduced. This method uses a grid board and
if “you look at the reflection in a piece of glass you’ll see the variation.”
In addition, a number of automated solutions are available to provide
on-line visual inspection for optical distortion.
Edgetech’s Mike Burk introduced the group to “Triple Glazed Insulating
Glass Units (IGUs)” or, as he suggested calling it, “multiple cavity IGUs.”
As Burk pointed out, it’s not the glass that provides the performance
boost, since more glass means more conductive surfaces—what’s really important
is the extra number of cavities. “It might be better to talk about cavities
rather than the layers of glass,” Burk suggested.
Whatever it’s called, he could safely say of this product segment, “I
think everyone in the industry believes this is going to grow.”
Burk noted that there are people who say triples aren’t the answer to
improving the energy efficiency of window products. He pointed to concerns
about decreased light transmittance, acknowledging that by adding an additional
lite there may be some decrease. He agreed, too, that there could be some
extra weight by adding an extra lite and producing frames that fit (although
products such as suspended film negate that argument). And, he noted that
the concern for a higher risk of glass seal failure on a triple than a
double-lite unit makes some sense, since the product is going from two
to four seals. But that solution, he added, “comes down to workmanship
and training and building good IG.”
Overall, Burk said the three main advantages of triples—thermal performance,
condensation resistance and sound dampening—can outweigh the negatives,
when produced appropriately. He advised his audience to carefully consider
the steps of determining what type of gas to use and in which cavities,
the impact of selecting an appropriate glass type and coatings on light
transmittance, and considering structural components to be sure the frame
can handle the added weight.
For more information on these and other events, visit the Glass Association
of North America at www.glasswebsite.com.
© Copyright 2011 Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.