continued from page 53
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
quality such as the
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
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-
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”
USGlass, Metal & Glazing | March 2016