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Technical Information
Float Glass
History of Flat Glass Production
In order to better understand the glass and glazing industry, a
brief history of glass may be helpful.
Glass was discovered over 4000
years ago. It was considered precious and used by royalty and
for religious purposes. During the Roman Empire, glass making
reached a high degree of quality and use, but declined
significantly during the Middle Ages when the main achievement
was “stained glass.” In the 7th century, Syrians developed the
“crown” method for forming flat glass, whereby the molten glass
was taken in lump form and spun on a cylindrical disc to flatten
the glass. Interestingly, this represented the most common
method to produce flat glass for the next 1000 years.
In the early part of the 20th
century, inexpensive sheet glass was formed by drawing the glass
ribbon vertically out of the molten glass pool. Unfortunately,
sheet glass still suffered from distortion because of the
differences in viscosity of the molten glass. In order to obtain
relatively distortion-free glass for use in coach windows or
mirrors, the plate glass process was developed. Plate glass was
made by pouring molten glass onto a table and rolling it until
flattened, then grinding and polishing it into a plate. This
process eventually advanced by feeding the molten glass though
continuous rollers, grinders and polishers. Sheet glass is no
longer commercially produced in the United States.
In 1959, the float glass
process was introduced. This unique glass making process
revolutionized the flat glass industry. In the float process,
molten glass from the furnace flows by gravity and displacement
onto a bath of molten tin where a continuous ribbon is formed.
This glass ribbon is pulled or drawn through the tin bath and
upon exiting is guided on rollers through an annealing lehr
where it is cooled, under controlled conditions, until it
emerges at essentially room temperature. The product is now
flat, fire-finished and has virtually parallel surfaces.
Automatic cutters generally are used to trim the edges and cut
across the width of the moving ribbon. This creates sizes, which
can be shipped or handled for further processing. The float
glass process accounts for almost all of the flat glass
presently produced in the United States.
Commercial float glass is
nearly colorless with a visible light transmittance ranging from
75% to 92% depending on thickness. With the exception of
specialty low-iron glass, a faint green or blue-green color may
be noticeable in glazing applications where the glass thickness
approaches or exceeds 3/8" (10 mm). Specialty low-iron glass has
a higher visible transmittance than commercial float glass of
the same thickness.
Tinted or Heat-Absorbing Glass
is made by adding various colorants to the normal, clear glass
batch to create a desired color. The typical colors produced
domestically include bronze, gray, dark gray, aquamarine, green,
deep green, blue, deep blue and black. Some companies in Europe
produce other colors, for instance rose and emerald green.
Visible light transmittance will vary from 14% to 85%, depending
on color and thickness. The color density is also a function of
thickness. As the thickness increases, visible light
transmittance will decrease.
Tinting reduces the solar
transmittance of glass and increases solar heat absorption.
Because of this heat buildup, heat-treating (heat-strengthening
or tempering) is sometimes required for tinted glass.
Color of tinted/heat-absorbing
glass is a major consideration for either design and aesthetic
reasons or for color matching requirements. Tinted
heat-absorbing glass should be viewed as installed for color
comparison. Colors may vary considerably among different
manufacturers and from run to run. No published color standard
exists; the manufacturer should be consulted for color
information.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Annealed Glass
Upon exiting the tin bath, the float glass
ribbon is guided on rollers through an annealing lehr where it
is cooled, under controlled conditions, until it emerges at
essentially room temperature. The product is now flat,
fire-finished and has virtually parallel surfaces. Automatic
cutters generally are used to trim the edges and cut across the
width of the moving ribbon. This creates sizes that can be
shipped or handled for further processing. This glass is
referred to as annealed glass.
Annealed glass may be used in
its original state or it can be further fabricated by cutting,
heat-treating, coating, laminating, or insulating. Annealed
glass provides the least resistance to mechanical and thermal
stresses when compared with heat-strengthened and fully tempered
glass.
Industry production quality
requirements, product tolerances and test procedures for
annealed glass are defined in the ASTM International (ASTM)
document C 1036 Standard Specification for Flat Glass.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Heat-Treated Glass
In order to provide greater resistance to thermal and mechanical
stresses and achieve specific break patterns for safety glazing
applications, annealed float glass products may be subjected to
a heat-treating process. The most commonly used process for
heat-treating architectural products calls for glass to be cut
to the desired size, transported through a furnace and uniformly
heated to approximately 1150° F (621° C). Upon exiting the
furnace, the glass is rapidly cooled (quenched) by blowing air
uniformly onto both surfaces simultaneously. The cooling process
locks the surfaces of the glass in a state of high compression
and the central core in compensating tension. Heat-treated glass
has two compression layers or zones, one starting at each
surface, plus an interior tension zone centered in the middle of
the glass. Each of the two compression zones is approximately
20% of the glass thickness. The middle 60% of the glass
thickness is the tension zone.
The color,
clarity, chemical composition and light transmission
characteristics of glass remain unchanged after heat-treating.
Likewise, hardness, specific gravity, expansion coefficient,
softening point, thermal conductivity, solar transmittance and
stiffness remain unchanged. The only physical properties that
change are improved flexural and tensile strength and improved
resistance to thermal stresses and thermal shock. Under uniform
loading, heat-treated glass is stronger than annealed glass of
the same size and thickness. Heat-treating glass does not reduce
the deflection of the product for any given load.
Heat-Treated
Glass is separated into two products, heat-strengthened
glass and fully tempered glass, by
definition of the degree of residual surface compression or edge
compression. Most furnaces can produce both. A furnace and its
quench must be adjusted by its operator for one or the other of
a product “run.” The adjustments may include changes in furnace
temperature, exit temperature of the glass, residual time in the
furnace, and volume and pressure of the quench air.
Production
of Heat-Treated Glass
There are two basic methods for producing air-quenched
heat-treated glass. The most commonly used heat-treating
furnace, a horizontal roller hearth, transports glass on
horizontal rollers through the heating and quench processes. A
limited amount of heat-treated glass is produced in vertical
furnaces, which call for the glass to be held in a vertical
position by tongs as it is transported through the heating and
quench processes.
Each method
produces some degree of bow and warp, which is an inherent
characteristic of all heat-treated glass. Tong-held glass, the
vertical process, may exhibit a long arc or “S” curve plus some
minor distortion at the tong points. Horizontally heat-treated
glass will have characteristic waves or corrugations caused by
the transport rollers. Industry fabrication requirements,
product tolerances and testing procedures for heat-treated glass
are defined in the ASTM International (ASTM) document C 1048
Standard Specification for Heat-Treated Flat Glass - Kind HS,
Kind FT Coated and Uncoated Glass.
Heat-Strengthened Glass
Heat-strengthened glass is produced with surface and
edge compression levels less than fully tempered glass, as
specified by ASTM C 1048. The lower compression levels yield a
product that is generally twice as strong as annealed glass of
the same thickness, size and type. The size and shape of the
break pattern of heat-strengthened glass varies with the level
of surface and edge compression achieved in the heat-treating
process. Heat-strengthened glass with low compression levels
will tend to fracture into large fragments, similar to annealed
glass breakage. As the compression levels increase, the size of
the particles of broken glass tend to become smaller.
ASTM C 1048
requires that heat-strengthened glass have a surface compression
level between 3,500 pounds per square inch (psi) to 7,500 psi.
The break pattern of heat-strengthened glass is relatively
large. The glass pieces typically remain engaged in the glazing
pocket, decreasing the probability of fall out. Broken glass
should be removed and the opening boarded up or reglazed as soon
as possible.
Heat-strengthened
glass does not meet the safety glazing requirements of the
American National Standards Institute (ANSI) Z97.1 American
National Standard for Safety Glazing Materials Used in Buildings
- Safety Performance Specifications Method of Test or the
federal safety standard Consumer Products Safety Commission 16
CFR 1201 Safety Standard for Architectural Glazing Materials.
Fully
Tempered Glass
Fully tempered glass is required in ASTM C 1048 to have
either a minimum surface compression of 10,000 psi (69 MPa or an
edge compression of not less than 9,700 psi (67 MPa) or meet
ANSI Z 97.1 or CPSC 16 CFR 1201. The higher compression levels
yield a product that is generally four times stronger than
annealed glass and twice as strong as heat-strengthened glass of
the same thickness, size and type.
When broken by
impact, fully tempered glass immediately disintegrates into
relatively small pieces thereby greatly reducing the likelihood
of serious cutting or piercing injuries in comparison with
ordinary annealed glass. To qualify as a safety glazing material
as defined by ANSI Z97.1 and CPSC 16 CFR 1201, the ten largest
particles taken from a broken fully tempered lite of glass shall
weigh no more than the equivalent weight of 10 square inches (64
sq. cm) of the original specimen when tested according to the
standards. Fully tempered glass that meets ASTM C 1048 does not
automatically qualify as a safety glazing material.
Note: The GANA
Glazing Manual should be consulted for additional
information on Safety Glazing in Hazardous Locations (Section V,
page 33) and Design Considerations (Section II - Fabricated
Architectural Glass Products, page 9) when specifying and using
heat-treated glass.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Chemically Strengthened Glass
Chemical strengthening of glass is
produced through a process known as ion-exchange. One of the
methods used to chemically strengthen glass calls for the lites
to be submersed in a molten salt bath at temperatures below the
strain point of the glass. In the case of soda-lime float or
soda-lime sheet glass, the salt bath consists of potassium
nitrate. During the submersion cycle, the larger alkali
potassium ions exchange places with the smaller alkali sodium
ions in the surface of the glass. The larger alkali potassium
ions “wedge” their way into the voids in the surface created by
the vacating smaller sodium ions.
Chemically strengthened glass
production requirements and test procedures are defined in ASTM
C 1422 Standard Specification for Chemically Strengthened
Flat Glass. The specification covers the requirements for
chemically strengthened glass products, which originate from
flat glass for use in building construction, transportation and
other specialty applications.
Under the specification,
chemically strengthened glass is classified on the basis of
independent levels of surface compression and case depth.
Increasing levels of surface compression permit an increasing
amount of flexure. Greater case depths provide increased
protection from strength reduction caused by abuse and abrasion.
Consumers should consult with chemically strengthened glass
fabricators regarding the recommended surface compression and
case depth levels required for their individual application.
Product classification levels may be confirmed through
laboratory testing in accordance with the specification.
Chemically strengthened glass
can be significantly stronger than annealed glass, depending
upon the glass product, strengthening process, level of
abrasion, and the application. Chemically strengthening glass is
often the alternative to thermal tempering when applications
call for glass that is very thin, small in size, or complex in
shape.
Although chemically
strengthened glass can be cut after treatment, it is not
recommended, as edge strength will be reduced to that of
annealed glass.
When broken by impact,
chemically strengthened glass exhibits a break pattern similar
to annealed glass, and therefore, does not meet safety-glazing
requirements in a monolithic form. When safety-glazing
performance is required, chemically strengthened glass should be
laminated.
While chemically strengthened
glass is often used monolithically, product usage has increased
in laminated constructions for security, detention,
hurricane/cyclic wind-resistant, blast and ballistic-resistant
glazing applications.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Coated Glass
Flat glass products may be coated to
enhance the thermal and optical performance characteristics of
products used in residential and commercial glazing, and
transportation applications. There are two basic types of coated
glass: solar control (reflective) and low-emissivity
(low-e). The major differences are visible light
transmission, UV, visible, and near infrared wavelengths of
energy that are reflected and the directions in which these
wavelengths are usually reflected.
The solar spectrum consists of
ultraviolet light with wavelengths ranging from 300-390 nm,
visible light (390-770 nm) and infrared light (770-2100 nm). The
distribution of energy within the solar spectrum is
approximately 2% ultraviolet (UV), 46% visible and 52% infrared
(IR).
Solar-control glass may have a
variety of metal coating layers that are highly reflective of
solar energy, i.e., those energy wavelengths from 300-2100
nanometers (nm) that constitute the solar spectrum.
The major benefits of
reflective solar control glass include the following:
Aesthetic appeal:
Colors of silver, blue, copper, golden and earth-tone coatings,
applied to the wide range of clear and tinted float glass,
allows the architect considerable flexibility with exterior
design.
Energy savings: through
its ability to reflect, absorb and radiate solar energy, solar
reflective glass substantially reduces interior solar heat gain.
The added cost of the coating will generally be offset by the
reduced size and operating cost of the heating and cooling
systems.
Occupant comfort: is
improved when heat gain is reduced and interior temperatures are
easier to control.
Low-emissivity (low-e)
coated glass may have various combinations of metal, metal oxide
and metal nitride layers of coatings that are nearly invisible
to the eye. Some low-e coatings are highly reflective for the
infrared (IR) part of the solar spectrum and all low-e coatings
reflect long wave IR energy. Long wave IR can be described as
the radiant heat given off by an electric coil-type heater, as
well as the heat that comes from a hot air register. The
re-radiated heat from room furnishings that have absorbed solar
energy is still another form of radiant heat.
While some low-e coatings can
be used in monolithic or laminated glass constructions, the
coatings provide maximum performance when sealed within an
insulating glass unit. The location of the low-e coating within
a unit affects the product performance. A low-e coating on the
second (#2) surface of an insulating glass unit is more
effective at reducing solar heat gain, especially when used in
conjunction with tinted glass. The low-e coating will reflect
re-radiated heat (IR), while the tinted glass reduces the solar
radiation through the glass, resulting in less glare and heat
gain. When using low-e glass in commercial buildings and
residential applications in warm climate regions, this is
generally the most practical way to maintain comfort levels.
In cold climate regions where
building owners and occupants want to maximize solar heat gain
from the sun while minimizing radiant heat loss, insulating
glass units commonly incorporate clear glass with a low-e on the
third (#3) surface. The low-e coating reduces heat loss through
the glass in winter by reflecting interior long wave IR back
into the home or office.
Center of glass U-values in
the range of 0.25 - 0.36 can be achieved with low-e coatings on
the second or third surface of insulating glass units. Low-e
coatings can be combined in an insulating unit with a
solar-control / reflective coating and gas filling to create an
insulating unit having lower U-values and a lower shading
coefficient. Since technology continues to advance and because
the combinations of substrates and coatings are too numerous to
list, it is best to consult the coated glass manufacturers’
published literature for comparisons. A generic listing of
U-values of various glazing products is provided in the GANA
Glazing Manual.
The major benefits of low-e
coated glass are:
Aesthetic Appeal: the
virtually invisible nature of low-e coatings provide a
transparent appearance to the glazing material and building
façade.
Energy Savings: through
its ability to reflect long-wave infrared energy low-e coated
glass reduces winter heat loss and summer heat gain through the
glass, and provides high levels of visible light transmittance
into the building. The combination of thermal control and
reduction in interior lighting requirements reduces energy
consumption for residential, and commercial buildings.
Occupant Comfort: is
improved when heat gain/loss is reduced by keeping the interior
temperature stable regardless of the exterior environment and
when natural daylight is introduced into the building.
Optical and aesthetic quality
requirements for coatings applied to glass are addressed in ASTM
C 1376 Standard Specification for Pyrolytic and Vacuum
Deposition Coatings on Flat Glass.
Note: The GANA Glazing
Manual should be consulted for additional detailed
information on Coating Methods, Specifications and Coating
Imperfections (Section II - Fabricated Architectural Glass
Products, pages 14 & 15) prior to specifying and using coated
glass.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Laminated Glass
Laminated glass is traditionally defined as:
-
Two or more lites of glass
and one or more interlayers of plasticized polyvinyl butyral
(PVB) permanently bonded together under heat and pressure;
-
Two or more lites of glass
and polycarbonate with an aliphatic urethane interlayer
between glass and polycarbonate permanently bonded together
under heat and pressure.
-
Two or more lites of glass
bonded with one or more interlayers of a liquid resin cured
and permanently bonded together by exposure to ultraviolet
light, heat, or chemicals.
-
Two or more lites of glass
with an ionoplast rigid sheet interlayer (similar to a PVB yet
more rigid) permanently bonded together under heat and
pressure.
-
Two or more lites (or
sheets) of polycarbonate (or acrylic) with an aliphatic
urethane interlayer between polycarbonate or acrylic bonded
together under heat and pressure.
-
Two or more lites and
polyester (PET) film with a polyvinyl butyral (PVB) interlayer
between glass and PET permanently bonded together under heat
and pressure.
Annealed, heat-treated,
chemically strengthened, wired, tinted, patterned and coated
glass, as well as one- and two-way mirrors, can be incorporated
into the laminated unit.
This union of materials
provides a variety of performance benefits in architectural,
security and other specialty applications. Its most important
characteristic is the ability of the interlayer to support and
hold the glass when broken and/or plastic sheet when cracked.
This provides for increased protection against fall-out and
penetration of the opening. Most building codes require the use
of laminated glass for overhead glazing as monolithic lites, or
as the lower lite in multiple glazed units. Other applications
include safety, security, detention, seismic-resistant,
blast-resistant, bullet-resistant, burglary-resistant,
hurricane/cyclic wind-resistant and sound reduction
applications. Laminated glazing materials are also used in
specialty applications such as aquariums, animal enclosures,
glass stairs, floors and sports stadiums.
Laminated glass with PVB
interlayers are generally 75% to 100% as strong as annealed
glass of the same thickness depending on exposed temperatures,
aspect ratio, plate size, stiffness and load duration. Laminated
glass, however, can be made with heat-strengthened, fully
tempered or chemically strengthened glass for additional
benefits, such as increased wind-load resistance, impact
resistance, or resistance to thermal stress. The ability of the
interlayer to resist various kinds of penetration may also be
dependent upon thickness, temperature and other variables. Check
with the fabricator for any additional limitations, such as roll
distortion, that may result from this additional processing of
laminated glass. There are several grades of PVB having
different physical properties. Care should be taken to specify
the correct grade for a given application. Consult the
interlayer manufacturer / glass fabricator for full details.
Typical applications for laminated glass with PVB interlayers
and cured resins include locations where safety glazing is
required, such as doors and skylights, shower and bath doors and
enclosures. Other locations where safety glazing may be
specified include operable windows and fixed glazed panels,
balconies, railing systems, elevators, sports stadiums, atriums,
greenhouses, skylights and sloped glazing. Laminated glass
resists glass fall-out from windblown debris in hurricane /
cyclic-windstorm prone areas and provides various levels of
security protection in seismic, blast-resistant,
bullet-resistant and burglary-resistant applications.
Laminated glass with ionoplast
interlayers are similar to PVB laminates; however, the rigid
interlayer provides additional performance in high design
pressure and high security applications where lower deflections
and higher penetration resistance is required after the glass
lites have been broken.
Glass-clad polycarbonate
contains glass layers to the exterior and one or more
polycarbonate layers on the inside. This product combines the
heat, chemical and abrasion resistance of glass with the impact
resistance of polycarbonate. This laminated construction may
also be unbalanced or asymmetrical, where a polycarbonate layer
is exposed to the interior. Although not truly a “glass-clad”
product, the industry recognizes the product under the same
category. Glass-clad polycarbonates provide resistance to forced
entry and ballistics and are commonly used in prisons, detention
centers, jails, psychiatric facilities and other architectural
settings where security is a primary concern.
Organic coated glass-butyral
consist of at least one lite of glass with its interior or
protected surface laminated under heat and pressure to a
composite sheet of PVB with a scratch-resistant polyester (PET)
film. Optionally, the organic coated glass-butyral can be
applied onto multiple-ply laminated glass. The composite organic
coating consists of an abrasion resistant polyester-film
combined with a sheet of PVB for factory lamination to glass.
The PVB is used to adhere the PET film to the glass surface. The
composite must face towards the building’s interior. These
laminates are generally used in security applications where
there is a requirement for zero spalling on the inside of a
building or room following attack from the outside.
Polyester (PET) films can also
be laminated inside the laminated glass using polyvinyl butyral
(PVB) to bond the PET to the glass. This PET film can provide
additional resistance to penetration and cyclic wind pressure.
Quality standards for
laminated glass are defined in ASTM C 1172 Standard
Specification for Laminated Architectural Glass and ASTM C
1349 Standard Specification for Architectural Flat Glass Clad
Polycarbonate. Laminated glass for use as safety glazing is
covered by ANSI Z97.1 and CPSC 16 CFR 1201 Cat. I and II.
Note: The GANA Glazing
Manual and Laminated Glazing Reference Manual should
be consulted for additional detailed information on laminated
glass, burglar-resistant, bullet-resistant, and physical-attack
resistant laminated constructions prior to specifying and using
laminated glass constructions.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Insulating Glass
In order to reduce heat gain or loss through glass, two or more
lites may be sealed together to create an insulating glass
(IG) unit.
The majority of
insulating glass units consist of two lites of glass enclosing a
hermetically sealed air space. The lites are held apart by a
spacer around the entire perimeter. The spacer contains a
moisture-adsorbent material called desiccant that serves to keep
the enclosed air free of visible moisture. The entire perimeter
of the assembly is sealed.
The most commonly
used edge construction contains a metallic spacer of roll-formed
aluminum, stainless steel, coated steel or galvanized steel. It
is sealed with a single seal of polysulfide, polyurethane or
hot-melt butyl, or with a dual seal consisting of a primary seal
of polyisobutylene and a secondary seal of silicone, polysulfide
or polyurethane. The corners of the metallic spacer may be
square-cut and joined with a metal, plastic or nylon corner key,
may be miter-cut and brazed, welded or soldered, or may be bent.
Recent years have seen the introduction of warm edge technology
products as spacer materials. These products include extruded
butyl materials, foam rubber based materials, formed plastics
and metal strip based products, many with desiccant included as
a component.
Improvements in
edge of insulating glass U-values as a result of warm-edge
technologies play a vital role in meeting overall window
performance requirements for state adopted residential
fenestration codes.
Thermal
performance of insulating glass units is enhanced by using solar
control substrates and coated glass (low-emissivity or
reflective), coated polyester suspended films, insulating gases
(such as argon, krypton or xenon) and warm edge technology
products. Initial heating and cooling equipment costs and
ongoing operating costs are reduced.
Insulating glass
units also offer benefits by reducing sound transmission.
Laminated glass constructions and sulfur hexafluoride (SF6) gas
filling further enhance the sound reduction characteristics of
the insulating glass unit.
Industry product
classification, performance requirements and testing procedures
for insulating glass units are defined in the following ASTM
International documents:
E 773 Standard
Test Method Accelerated Weathering of Sealed Insulating Glass
Units
E 774 Standard Specification for Sealed Insulating Glass
Units
E 2188 Standard Test Method for Insulating Glass Unit
Performance
E 2189 Standard Test Method for Testing Resistance to
Fogging in Insulating Glass Units
E 2190 Standard Specification for Insulating Glass Unit
Performance and Evaluation
Most insulating
glass fabricators voluntarily participate in insulating glass
certification programs. The purpose of the certification
programs is to assure the user that the purchased product is a
faithful replica of one that has passed certain prescribed
tests. Therefore, participants in a certification program must
complete the following requirements: 1) submit specimens of
their production product to independent testing laboratories for
the prescribed tests; and 2) agree to periodic, unannounced
inspections of their regular production by an independent agency
to ensure that actual production employs the same materials and
techniques as the tested specimen.
The Insulating
Division of the Glass Association of North America (GANA) and
the Insulating Glass Manufacturers Alliance (IGMA) promote the
highest standards in insulating glass unit production, testing,
certification and business ethics through their memberships. The
industry establishes voluntary quality standards and collects
statistical and other non-proprietary information related to
field performance of insulating glass for dissemination to
manufacturers and consumers.
Note: The GANA
Glazing Manual (Section II - Fabricated Architectural Glass
Products) should be consulted for additional detailed
information on insulating glass design considerations, material
compatibility and glazing guidelines prior to specifying and
using insulating glass constructions.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Spandrel Glass
Spandrel glass is glass that has been
rendered near opaque, i.e., it is non-vision glass. Its major
use is to mask materials or construction from view from the
exterior of a building. Such areas are commonly the hung-ceiling
area above a vision lite or the knee-wall area below a vision
lite. It is sometimes used to hide a column in what is normally
the vision-glass area.
The indoor surface of spandrel
glass is not suitable for use as a finished wall. Additional
suitable material, such as sheet rock, must be installed on the
indoor side when used in quasi-vision areas such as transom
lites, column covers, etc.
In order to reduce the
probability of glass breakage due to thermal stresses, spandrel
glass should be heat-strengthened.
Methods of Fabricating
Spandrel Glass
The most commonly used methods of rendering spandrel areas
opaque are:
Ceramic Frit Opacification
Ceramic frit opacification consists of a coating of durable,
colored ceramic material that is compatible with the base glass
and is fire-fused into one surface of the glass during the
heat-treating process. Since the basic purpose is generally to
render the glass opaque, the ceramic frit is typically applied
to the #2 surface of monolithic glass or the #4 surface of an
insulating unit. The opacity can be improved with thicker or
multiple coats of ceramic frit.
If the application requires
the unit to be visible from both the exterior (#1) and interior
(#4) surfaces, ceramic frit with thicker and/or multiple coats
can be applied in order to provide an architectural finish when
viewed from the inside of the building. Note: In this case, the
exterior lite must have a very low level of light transmittance
because of inherent characteristics (pinholes, uneven appearance
of the coating etc.) in the ceramic frit layer. The
manufacturer/fabricator should be consulted for guidance in
these applications.
Ceramic frit coatings are
available in a wide range of colors. The coating can be applied
to otherwise uncoated glass or, in most cases, to the interior
surface of a pyrolytically coated solar-control reflective
glass, regardless of which surface has the pyrolytic coating.
Light color ceramic frit applications may require a double coat
in order to achieve a more uniform appearance.
Glass with a fired-on ceramic
frit should not be used except with an opaque backup
construction. If it is used where light may be seen through the
glass, consultation with the glass fabricator is mandatory.
Pinholes and uneven appearance of the ceramic coating may be
visible prior to the completion of the opaque backup
construction. These conditions are inherent in the product and
are not reason for rejection.
Film Opacification
Film opacification consists of a factory applied polyester
film adhered to the coated surface of vacuum deposition or
pyrolytic coated glass by means of a solvent based adhesive. The
polyester opacifier was designed to be adhered to a metal
surface and therefore, should not be applied to the float glass
surface of uncoated monolithic glass or the uncoated inboard
lite of an insulating unit. Film opacified glass fabricators
typically recommend against adhering insulation or other
materials to the opacifier surface. The fabricator should be
consulted for guidelines concerning contact of other spandrel
materials with the polyester surface and airspace requirements
behind the polyester surface.
A lite of glass with complete
coverage of polyester film opacifier can be fabricated to meet
the optional fallout resistance test contained in ASTM C 1048
Standard Specification for Heat-Treated Flat Glass - Kind HS,
Kind FT Coated and Uncoated Glass.
For structural silicone
glazing applications, the polyester film opacifier must be cut
back to allow for structural bonding to the coated glass
surface. Glass in this application will not meet the optional
fallout resistance test contained in ASTM C 1048.
Silicone Opacification
Silicone opacification consists of an elastomeric film of
liquid silicone rubber applied to any glass substrate via;
spray, roller coater, or curtain coater. The chemistry utilizes
strong bonding to the similarly composed glass substrate for
adhesion and durability. Silicone opacifiers are applied after
the heat-treating process and may employ a large variety of
color and specialty pigments.
The basic purpose of the
product is to render the glass opaque, thus can be applied to
both monolithic and insulating glass units. For monolithic
applications, the silicone opacification is applied to the #2
surface, and for insulating glass units, to the #2, #3, or #4
surface, depending on application. Edge deletion is required for
all structural applications, as well as the interior surface of
an application of an insulating glass unit. Compatibility
confirmation should be obtained from the spandrel manufacturer
prior to installation.
Standard application thickness
for opacity is 8 mils wet or 3.5 mils dry. Opacity can be
improved with thicker or multiple coats of the silicone
opacifier. To attain fallout certification, the silicone
opacifier must be applied at a thickness of at least 13 mils wet
or 5 mils dry. Silicone spandrels will meet this classification
if proper testing is documented per GANA Tempering Division
Specification No. 89-1-6 – Environmental Durability of Fully
Tempered or Heat-Strengthened Spandrel Glass with Applied
Opacifiers, ASTM C 1048, and CAN/CGSB-12.9-M91 – Spandrel
Glass.
A wide variety of silicone
color coatings can be applied to all glass substrates, including
especially pyrolytic and sputter coated reflective glass
substrates, without harming the reflective coating. As with all
spandrel products, silicone spandrels should not be used except
with an opaque backup construction. If it is used where light
may be seen through the glass, consultation with the glass
fabricator is mandatory.
Water-based silicone
opacification can be used and certified as “green” for the use
in “green” building applications, due to polymer chemistry and
pigment usage.
Silicone opacification product
performance may vary between manufacturers. Consult with the
manufacturer/fabricator to confirm compliance with specification
performance requirements.
Shadow Box Opacification
Shadow box opacification is achieved by enclosing the space
bounded by the vertical and horizontal mullions behind the
glass. This is accomplished by securing a painted metal pan or
dark matte-finished insulation board back from the glass.
Typically, the inner face of the pan or insulation is flush with
the inner plane of the vertical mullions. Shadow box detailing
must also ensure that surfaces of the glazing system and
surrounding materials have a dark surface to prevent
read-through under some lighting conditions.
Note: The GANA Glazing Manual
(Section II - Fabricated Architectural Glass Products, pages
15-17) should be consulted for additional detailed information
on spandrel glass design considerations, spandrel insulation and
spandrel glass inspection and glazing guidelines prior to
specifying and using spandrel glass constructions.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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Bent Glass
Bent glass is fabricated from flat glass,
which has been heated to between 1000°F (538°C) and 1100°F
(593°C), gravity or mechanically formed, and then allowed to
cool to the desired shape. Advances in the technology of bending
glass have enabled glass benders to offer designers and
architects a wide variety of options, including large lites of
glass that can be bent to compound curves or to several radii
with straight legs on one or both ends. Glass can also be bent
to relatively sharp angles. Bent glass is available in various
types including annealed, heat-strengthened and fully tempered.
Bent glass can be laminated or built into insulating glass
units. Check with fabricator for limitations. Pyrolytic solar
control glass can be bent, although the radius of the bend may
be limited by lower bending temperatures to avoid crazing of the
coating. Lites with baked-on ceramic lines or dots, as well as
many patterned glasses, may also be bent.
ASTM document C 1464
Standard Specification for Bent Glass addresses the
requirements for bent glass used in general building
construction, display and various other non-automotive
applications.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
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of Page
Mirrors
Virtually all mirrors for interior use are manufactured by the
conveyor, wet deposition method. Annealed or fully tempered
glass is thoroughly cleaned by the application of cleaners and
passing contact with oscillating scrub brush units. After the
glass is cleaned and rinsed, the surface of the glass is
sensitized with a diluted solution of tin chloride. This surface
treatment allows for the deposition of silver. Silver nitrate is
sprayed onto the sensitized surface of the glass along with
other chemical configurations. The final outcome is the
formation of a uniform silver layer on the glass.
Once the silver
layer is formed on the glass, methods to protect the silver
layer from oxidation are employed. A layer of copper is then
deposited directly onto the silver. Copper can be applied in two
ways: chemically or galvanically. Recent technological advances
have lead to the development of copper free protective films,
which also prevent silver oxidation.
Once the metal
layers are attached to the glass, they are covered by a
protective mirror backing paint. The mirror backing paint
protects the metal layers from corrosion and from mechanical
scratching. The paint can be applied either by passing the glass
through a curtain of paint or by passing glass in contact with a
roller paint coater. There are many mirror backing paint
products available from a number of suppliers. They offer paint
systems that are applied as a single coat or double coat. Both
coating systems are effective.
Tinted mirrors
are produced using the methods described above. The silver
coating is applied to one of the various tinted glass substrates
available on the market. Tinted mirrors are generally used in
decorative applications where color and diminished light
reflection are desirable.
Quality
requirements for silvered annealed monolithic clear and tinted
flat glass mirrors are provided in the ASTM document C 1503
Standard Specification for Silvered Flat Glass Mirror.
Tempered mirrors
are manufactured using fully tempered glass as the substrate.
There are optical characteristics inherent in tempered mirrors,
including roll distortion and the lack of a quality surface for
silvering.
Laminated mirrors are manufactured by combining clear glass,
either annealed, heat-strengthened or fully tempered, and
mirrored glass.
Safety backed
mirrors are known as Organically Coated Mirrors in the CPSC 16
CFR 1201 and ANSI Z97.1 standards. These are manufactured by
applying a sheet of adhesive backed polyethylene material to the
back of annealed mirrors. The backing material does not prevent
breakage of mirrors, but lessens the potential of injury on
impact by retaining the fragments.
Non-Silvered Mirrors
There are two types of non-silvered mirrors: pyrolytic
mirrors and transparent/two-way mirrors.
Pyrolytic mirrors
are highly reflective coated glass products with performance
characteristics approaching that of silvered mirrors. This
product is promoted for use in shower doors and other areas
where moisture can affect the substrate of silvered mirrors.
Transparent/two-way mirrors are composed of reflective glass
products, and as such are not silver mirrors. Transparent
mirrors are manufactured by both the pyrolytic deposition and
vacuum deposition coating processes. Heavy density coatings are
offered on clear and gray tinted glass.
Transparent or
two-way mirrors are designed to permit vision through one
direction while giving the appearance of a standard mirror from
the opposite side. Their major application is to permit
undetected observation for study or surveillance in interior
conditions such as learning centers in schools and universities,
medical and psychiatric clinics, and security stations in
casinos or high-traffic retail stores.
The transparent
mirrors work by reducing the visible light transmittance through
the glass. To ensure proper performance the room lighting design
and surrounding conditions must be carefully planned and
executed. The glass surface in the subject room must appear to
be standard mirror. In order to achieve this condition, the
coated surface should be toward the subject room and the
lighting ratios tightly controlled. For applications utilizing
clear glass, manufacturers recommend a lighting ratio of 10:1
subject’s side to observer’s side. If the lighting ratio drops
to approximately 5:1, the subject may detect movement or
silhouettes through the mirror. If 10:1 lighting ratios cannot
be maintained, a gray transparent mirror should be specified.
Lighting ratios of 5:1 can be successfully used for gray
transparent mirror products.
Design
considerations call for bright contrasting colors in the subject
room and dark, non-contrasting colors in the observer room.
Light color surfaces or objects may be noticeable to the
subject. The design of the observation room should also prevent
sudden light ratio changes. Special care must be taken if
transparent mirrors are used on more than one wall.
The above information is from
the GANA Glazing Manual, 2004 Edition - the most
frequently referenced resource in the architectural glass and
glazing industry. The Glazing Manual is an excellent
addition to any technical library.
Go here to order a
copy of the manual or CD-ROM. For further information on this
and other GANA reference documents visit the
PUBLICATIONS
section of the GANA website.
Top
of Page
Glass Cleaning
The Glass Association of North America (GANA) has published the following Glass Informational Bulletin on the cleaning architectural glass products:
Glass Informational Bulletin GANA 01-0300
Proper Procedures for Cleaning Architectural Glass Products
Architectural
glass products play a major role in the comfort of the living
and working environment of today's homes and commercial office
spaces. By providing natural daylight, views of the
surroundings, thermal comfort and design aesthetics, glass usage
and condition often affect our selection of where we live, work,
shop, play and seek education.
Architectural
glass products must be properly cleaned during construction
activities and as a part of routine maintenance in order to
maintain visual and aesthetic clarity. Since glass products can
be permanently damaged if improperly cleaned, glass producers
and fabricators recommend strict compliance with the following
procedures for properly cleaning glass surfaces.
As dirt and
residue appear interior and exterior glass surfaces should be
thoroughly cleaned. Concrete or mortar slurry that runs down (or
is splashed on) glass can be especially damaging and should be
washed off as soon as possible. Before proceeding with cleaning
determine whether the glass is clear, tinted or reflective.
Surface damage is more noticeable on reflective glass as
compared with other glass products. If the reflective surface is
exposed either on the exterior or interior special care must be
taken when cleaning, as scratches to the reflective glass
surface can result in coating removal and a visible change in
light transmittance. Cleaning tinted and reflective glass
surfaces in direct sunlight should be avoided since the surface
temperature can be excessively hot for optimum cleaning.
Cleaning should begin at the top of the building and continue to
the lower levels to reduce the risk of leaving residue and
cleaning solutions on glass at the lower levels. Cleaning
procedures should also ensure that the wind is not blowing the
cleaning solution and residue onto already cleaned glass.
Cleaning during
construction activities should begin with soaking the glass
surfaces with clean water and soap solution to loosen dirt or
debris. Using a mild non-abrasive commercial window washing
solution, uniformly apply the solution to the glass surfaces
with a brush, strip washer or other non-abrasive applicator.
Immediately following the application of the cleaning solution a
squeegee should be used to remove all of the cleaning solution
from the glass surface. Care should be taken to ensure that no
metal parts of the cleaning equipment touch the glass surface
and that no abrasive particles are trapped between the glass and
the cleaning materials. All water and cleaning solution residue
should be dried from window gaskets, sealants and frames to
avoid the potential for deterioration of these materials as the
result of the cleaning process.
It is strongly
recommended that window washers clean a small area or one window
then stop and examine the surface for any damage to the glass
and/or reflective coating. The ability to detect certain surface
damage, i.e. light scratches can vary greatly with the lighting
conditions. Direct sunlight is needed to properly evaluate a
glass surface for damage. Scratches that are not easily seen
with a dark or gray sky may be very noticeable when the sun is
at a certain angle in the sky or when the sun is low in the sky.
The glass industry takes extreme care to avoid glass scratches by protecting all glass surfaces during glass manufacturing and fabrication as well as during all shipping and handling required to deliver the glass to the end user. A large percentage of damaged glass results from non-glass trades working near glass. This includes painters, spacklers, ironworkers, landscapers, carpenters and others who are part of the construction process. They may inadvertently lean tools against the glass, splash materials onto the glass and/or clean the glass incorrectly, any of which can permanently damage glass.
One of the common
mistakes made by non-glass trades people including glass
cleaning contractors is their use of razor blades or other
scrappers on a large portion of the glass surface. Using two,
three, four, or five inch and larger blades to scrape a window
clean carries a large probability of causing irreparable damage
to glass.
The entire
industry of glass manufacturers, fabricators, distributors, and
installers neither condones nor recommends widespread scraping
of glass surfaces with metal blades or knifes. Such scraping
will often permanently damage or scratch the glass surfaces.
When paint or other construction materials cannot be removed
with normal cleaning procedures a new one-inch razor blade may
need to be used only on non-coated glass surfaces. The razor
blade should be used on small spots only. Scraping should be
done in one direction only. Never scrape in a back and forth
motion as this could trap particles under the blade that could
scratch the glass. This practice can cause hairline concentrated
scratches that are not normally visible when looking through the
glass but are be visible under certain lighting conditions.
Jobsite storage
and construction conditions can lead to stains on the glass
surface. Cleaning and removal of such stains may require the use
of a more aggressive cleaning solution and procedure. If
conditions are found that cannot be cleaned using the above
procedures contact the glass supplier for guidelines on stain
removal.
Members of the
Glass Association of North America (GANA) publish information
relating to jobsite protection and cleaning of architectural
glass products. In order to ensure long-term performance of the
glass in a building GANA encourages glazing contractors, general
contractors, building management and owners to be aware of
conditions that can damage glass and to follow the handling and
cleaning guidelines provided by the glass producer and
fabricator.
Consult the GANA web site
at www.glasswebsite.com for additional information on glass and glazing applications and links to members providing additional technical resources.
The Glass
Association of North America (GANA) has produced this Glass
Information Bulletin solely to provide general information on
basic proper procedures for cleaning architectural glass
products. The Bulletin does not purport to state that any one
particular type of glass cleaning process or procedure should be
used in all applications or even in any specific application.
The user of this Bulletin has the responsibility to ensure the
cleaning instructions from the glass supplier are followed. GANA
disclaims any responsibility for any specific results relating
to the use of this Bulletin, for any errors or omissions
contained in the Bulletin, and for any liability for loss or
damage of any kind arising out of the use of this Bulletin.
Quick-Reference Guide to Cleaning Architectural Glass Products
The following Do's and Do Not's are offered as a supplement to the Glass Association of North America (GANA) Glass Informational Bulletin - Proper Procedures for Cleaning Architectural Glass Products:
The following are things to DO:
-
DO clean glass when dirt and residue appear
-
DO determine if coated glass surfaces are exposed
-
DO exercise special care when cleaning coated glass surfaces
-
DO avoid cleaning tinted and coated glass surfaces in direct sunlight
-
DO start cleaning at the top of the building and continue to lower levels
-
DO soak the glass surface with a clean water and soap solution to loosen dirt and debris
-
DO use a mild, non-abrasive commercial window cleaning solution
-
DO use a squeegee to remove all of the cleaning solution
-
DO dry all cleaning solution from window gaskets, sealants and frames
-
DO clean one small window and check to see if procedures have caused any damage
-
DO be aware of and follow the glass supplier's specific cleaning recommendations
-
DO caution other trades against allowing other materials to contact the glass
-
DO watch for and prevent conditions that can damage the glass
-
DO read the entire GANA bulletin on glass cleaning before starting to clean glass
The following are things to NOT do:
-
DO NOT start cleaning without reading the entire GANA bulletin on glass cleaning
-
DO NOT use scrapers of any size or type for cleaning glass
-
DO NOT allow dirt and residue to remain on glass for an extended period of time
-
DO NOT begin cleaning glass without knowing if a coated surface is exposed
-
DO NOT clean tinted or coated glass in direct sunlight
-
DO NOT allow water or cleaning residue to remain on the glass or adjacent materials
-
DO NOT begin cleaning without rinsing excessive dirt and debris
-
DO NOT use abrasive cleaning solutions or materials
-
DO NOT allow metal parts of cleaning equipment to contact the glass
-
DO NOT trap abrasive particles between the cleaning materials and the glass surface
-
DO NOT allow other trades to lean tools or materials against the glass surface
-
DO NOT allow splashed materials to dry on the glass surface
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