he desire for optical glass ciency and glass quality. These include  
quality has evolved tremen- products such as the Osprey from Lite-  
dously over the past several sentry and the recently developed  
decades. It has been driven in iLook, available on Glaston furnaces.  
large part by the evolution of Chuck Wencl, process engineer with  
the glass coatings.If you look Viracon and chair of the Glass Associa-  
at the tempering industry tion of North America’s (GANA) Tem-  
three decades ago, fabri- pering Division Optical Distortion  
cators primarily oper- Committee,says his company uses such  
ated radiant heating devices, which has helped them target  
systems, so the indus- issues immediately during the temper-  
try did not necessarily ing process. He says being able to see  
demand better quality everything as it happens is a huge ben-  
and the products did not nec- efit. “With the old way, you took ran-  
essarily require higher technology for dom samples. Today, you can see  
heating. This changed, however, as glass immediately as it happens and can  
T
coatings evolved.  
One side of coated glass is reflect- you can see if something changed in the  
ing heat while the other is absorbing it, heat-treating process.”  
make adjustments; from piece to piece  
which caused uneven heating in tradi-  
Doug Sampsel,general manager with  
tional radiant heated furnaces,” says Trulite Glass and Aluminum Solutions  
Ren Bartoe, director, glass and indus- in Atlanta, has a similar perspective.  
trial technologies with Vesuvius plc in  
“The advantage to us as a fabricator  
Beaver Falls, Pa.“At the same time, the is it’s a very simple, easy system high-  
market demand for higher optical qual- lighted by different colorations. When  
ity became a challenge. This drove ad- we go by the screens on the furnace,  
vances in furnace technology (i.e. each piece of glass is measured and if it  
convection heating).”  
deviates from the standard you put in,  
As the demands for optical quality that line item will be shown in red.This  
increase,so do the means and methods way we know if we’re meeting our tar-  
to ensure aesthetics. These include get quality specs.”  
measurement tools and equipment, as  
well as discussions about the develop- ing to Joe Santelli,who has many years of  
ment of an industry standard. tempering equipment sales experience.  
It protects the fabricators because  
Consistency is another benefit,accord-  
HoWwhilieteqsuDipmonenet for measuring op- they can produce a document that  
proves they made a product within  
tical quality has been available for their standards. It costs the fabricator  
decades,the tempering industry money up front,because more glass can  
today has seen increased inter- be rejected at the factory,but saves him  
est in the use of on-line inspec- money because the lower-quality prod-  
tion systems. These allow uct does not get into the marketplace  
operators to measure flatness and and into the buildings,” he says. “Re-  
visual quality in real time and control moving/replacing the glass [in the  
the equipment, ensuring furnace effi- field] can be very expensive.”  
52  
USGlass, Metal & Glazing | March 2016  
www.usglassmag.com  
As Demands for Optical  
Quality Increase, So, Too,  
Do Assurance Means and  
Methods  
b y E l l e n R o g e r s  
According to Mark Abbott, owner  
and president of LiteSentry Corp. in  
Northfield,Minn.,while the systems do  
provide a means to reject poor quality  
glass before it leaves the plant, the true  
benefit is process control.  
Use of a zebra  
board provides  
visual indication of  
how any distortion  
looks on the  
tempered glass.  
“Measure it and it will improve,” he  
says.“‘It’s any important attribute of the  
product, particularly those that can  
cause failures in downstream processes  
and/or those that the customer finds  
most critical. Any process can be im-  
proved with proper monitoring, quan-  
tifiable measurements and proper  
reaction to the data.”  
According to Wencl, much of the de-  
mand is coming from architects.  
“I think that the fact the equipment  
is available and architects know the  
technology is out there has spurred the  
demand,” says Wencl.“People realize if  
you can [check something] digitally  
rather than relying on humans, you get  
[
better] accuracy.”  
Abbott agrees the main reason for  
growinginterestinonlineinspectionisthe  
needs of the end customer.  
“Poor quality leads to complaints  
from customers.As customers become  
ever more sophisticated in managing  
materials, suppliers and quality, the  
glass fabricator is faced with direct and  
increasing feedback and is forced to re-  
spond,” says Abbott, pointing out that  
profit is another reason. “Improved  
quality control and, by extension, im-  
proved process control always leads to  
improved profitability.”  
Santelli says the use and develop-  
ment of on-line inspection systems is  
growing because standards set by the  
industry are not good enough to give  
the architect or building owner a  
Developments  
such as the iLook  
from Glaston  
provide an  
integrated online  
glass quality  
measuring system  
for issues such as  
roller wave and  
edge kink.  
continued on page 54  
www.usglassmag.com  
March 2016 | USGlass, Metal & Glazing  
53  
continued from page 53  
consistent product.  
The deviations in roller wave and  
overall look once the glass is put into a  
building varies greatly,” says Santelli.  
The increase now is a result of previ-  
ous companies’ use of the inspection  
stations and architects seeing what  
kind of glass the furnaces and temper-  
ing companies can produce when held  
to a higher standard—and they like it.”  
On-line equipment for  
measuring optical  
quality such as the  
StOavnerdthaerydeaDrse,tvheeGloApNmA Teemntpering  
Division discussed development of an  
industry standard for an acceptable  
level of optical distortion. But this re-  
mains to be seen. (Editor’s note: while  
there currently is not an industry-wide  
Osprey from LiteSentry,  
provides fabricators with  
a way to immediately  
address issues that  
could occur during the  
tempering process.  
standard to specify acceptable values for Santelli.“The technology is available for good glass, but don’t have the money or  
optical distortion, ASTM C1651, Stan- the tempering community to put a ability to buy sophisticated measuring  
dard Test Method for Measurement of much better product into the market- equipment. But there is always another  
Roll Wave Optical Distortion in Heat- place. There are several companies that way,”Sampsel says.“Anyone with a zebra  
Treated Glass, is available.)  
Nothing has changed in the stan- logical upgrades because they realize will get an acute ability to judge product  
dards for 25 years,and our industry re- what is required to produce the higher- quality without sophisticated means.”  
have recently invested in these techno- board at the end of the tempering line  
fuses to step up and make the difficult quality product. Unfortunately, it is not  
decisions to make these changes,” says yet an industry standard.”  
Bartoe also points out that it’s not likely  
every tempering company would need to  
Should one be developed,Wencl says make an investment in this type of equip-  
this would provide the industry with a ment. For example, companies focusing  
specified number to rely on when read- on uncoated glass substrates,certain res-  
idential products,interior glass products,  
Sampsel adds, “I think it would be bath enclosures and painted or patterned  
good for all of us, and it’s something glass may not have the same processing  
that from the 1980s on we’ve discussed challenges or optical quality demands as  
in tempering meetings.As the industry those producing glass for a storefront.  
is getting better at developing newer Glass thickness,he explains,regardless if  
equipment, a standard would allow us clear or coated,will also play a role in se-  
to explain to any of the architects/own- lecting the type of furnace technology.  
What to Know  
When it comes to measuring opti-  
cal quality, here are a few terms to  
keep in mind:  
ing architectural specifications.  
Roll Wave: A repetitive wave-like  
departure from flatness in glass that  
results from heat treating glass in a  
horizontal roller hearth furnace. Roll  
wave excludes edge effects such as  
edge kink and distortion influenced  
by assembly or installation.  
ers that [if something] doesn’t meet  
“Companies have to decide‘fitness-for-  
specification, you have a standard to use’when selecting furnace systems often  
Millidiopter (mdpt): The diopter  
D or dpt) is the unit of measure-  
judge that product on.”  
But it wouldn’t be perfect.  
based on the type of glass substrate,  
where their products are going to be in-  
(
ment for distortion (lens power) in a  
curved surface equal to the recipro-  
cal of the focal length (1/f). A millid-  
iopter equals 1/1000 of a diopter  
and is the accepted unit for quanti-  
fying the magnitude of roll-wave dis-  
tortion in flat glass.  
Optical Distortion: Alteration of  
viewed images caused by variations  
in glass flatness or inhomogeneous  
portions within the glass.  
“The downside is, if you put a num- stalled, production efficiencies and what  
ber out there, you hold a lot of compa- they need to achieve in quality,”he says.  
nies accountable to those tolerances,”  
There are also other products available  
says Wencl.“Different companies have at what may be a more reasonable price.  
different requirements. I don’t think These include surface gauges,which can  
one optical number fits all. Maybe be used to measure roll wave distortion.  
someday we can create categories for These devices generally are used off-line  
different processes, etc., but now it’s a and move across the glass surface per-  
huge undertaking.”  
pendicular to the rollers in the furnace,  
And on-line measuring equipment according to GANA’s glass informational  
isn’t cheap. Many come at a price point bulletin,“Methods of Measuring Optical  
Source: GANA’s glass informational bulletin,  
that not every temperer can afford.  
Distortion in Heat-Treated FlatArchitec-  
Methods of Measuring Optical Distortion in Heat-  
“There are small shops that can make tural Glass.” They then measure out-of-  
Treated Flat Architectural Glass”  
5
4
USGlass, Metal & Glazing | March 2016  
www.usglassmag.com  
plane deformation of the glass surface newer furnaces have much better con- processes such as lamination, rejects  
i.e., roll wave peak-to-valley depth). trols and abilities to regulate the heat- will occur at an increasing rate.”  
(
This measurement, in inches or mil- ing process compared to some of the  
limeters, can then be converted to opti- older furnaces.”  
On-line inspection systems could be  
an advantage.As Wencl points out,“we  
cal power and expressed in millidiopters  
Abbott adds that the misperception have multiple systems from the same  
of quality labels and the large down- manufacturer,and I can take glass from  
stream cost of poor flatness are also one to the next to the next to the next  
(see box on page 64).  
LoInotkhiendgecaAdhesetao dcome, the industry challenges.You have to also consider all and they all read so close together. If  
types of distortion that can be caused they are all set the same, everything is  
can expect glass performance technolo- by the tempering process.  
accurate and reliable … I’m just not  
gies to continue to advance.How will this  
impact the tempering industry?  
“Optical distortion is often simplified sure everyone understands how they  
to roller wave. In this mistake, one work, so more education [is needed].”  
And as for another plus,he adds,“the  
develop advanced, sophisticated coat- control—it’s not just roller wave,” Ab- equipment is very consistent and does  
ings, it requires an astute ability for fur- bott says. “Distortion comes in an al- not vary from shift-to-shift and opera-  
nace operators to understand and find most infinite variety.With sophisticated tor-to-operator.” s  
the correct recipe to keep glass as flat as glass products and complex  
“As our glass suppliers continue to misses the benefits of improved process  
possible [to] minimize distortion,”says tempering furnaces, controlling  
Sampsel.“As superior coatings [are de- the process becomes even more  
E l l e n R o g e r s is the  
veloped], it will be a challenge to heat- challenging. If you conquer  
editor of USGlass magazine.  
treat those products. Fabricators that roller wave but ship tempered  
Follow her on Twitter  
temper glass have to purchase coated product with edge lift, picture  
@
USGlass and like USGlass  
glass from suppliers and then process framing, pocket distortion or  
through heat-treating trying to keep cross-conveyor kink to the cus-  
glass as flat as possible. Some of the tomer or to downstream  
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March 2016 | USGlass, Metal & Glazing  
55