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Safety Glass

Technical FAQs

Technical specifiers and manufacturers of laminated glass often ask similar questions relating to their needs. The following is a representative sampling of typical questions and answers.

 

What are the thicknesses of DuPont interlayers?
DuPont™ SentryGlas® ionoplast interlayers start at 0.035 in. (0.90 mm) for general safety glass and hurricane-rated glass; 0.060 in. (1.56 mm) for architectural glazing such as canopies, railings and facades; and up to .090 in. (2.28 mm) and above for large missile impact an high security bomb blast systems. The typical thicknesses of Butacite® PVB are 0.030 in. (0.78 mm) for general-purpose safety glazing, .060 in. (1.56 mm) for burglar resistance, bomb blast resistance, and overhead glazing laminates made with heat-treated glasses; and .090 in. (2.28 mm) for hurricane-rated systems.

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Which interlayer is best for acoustics?
DuPont does not manufacture a specially formulated acoustical interlayer. Softer interlayers made with PVB, such as DuPont? Butacite®, tend to reduce sound transmission more than stiffer SentryGlas® interlayers.

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What does DuPont offer for bomb blast protection?
Blast-resistant designs rely on the combined performance of safety glass and related structural elements of the building envelope. Energy-absorbing PVB interlayers can be used in low- to medium-level bomb blast applications. SentryGlas® ionoplast interlayers provide stiffer resistance to blast-produced deflections, and can be used in low- to high-level blast-resistant applications, especially in embassy windows designed to mitigate maximum threats.

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What is ceramic frit and how is it applied?
Ceramic frit is a paint comprised of minute glass particles and pigment. The enamel is fired onto the glass using a silkscreen process, creating a permanent coating. The application of ceramic frit is often helpful in controlling glare, and can be combined with products such as SentryGlas® in laminated safety glass.

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What are the maximum sizes of glass? Laminated glass?
Maximum sizes of glass vary depending on thickness and type. To get the maximum size of a particular glass product, consult the primary glass manufacturer's catalog.

Maximum size of laminated glass is often dependent on the size of the laminating line and the autoclave. Typical laminating lines vary in width from 84 in. to 130 in.

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What are glass-clad polycarbonates?
Glass-clad polycarbonate laminates combine outside plies of glass, with inner plies of polycarbonate. Standard PVB interlayers are not compatible with polycarbonate so a different adhesive interlayer that is compatible with both glass and polycarbonate is used.

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When would you use heat-strengthened glass instead of annealed?
Heat-strengthened glass is used to resist higher mechanical loads and when there is a concern for thermal stress breakage. Heat-strengthened glass offers 2x the strength of annealed glass.

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How does heat-treating glass make it stronger?
Heat-treating, either heat strengthening or tempering, requires reheating the annealed glass to 1100-1500 F. and rapid cooling it so that a compression envelope develops around the glass surfaces and edges and a balanced tension stress within the glass itself. The equilibrium of stresses causes the strength of glass to increase 2x or 4x that of the original glass. Heat strengthened glass has a surface compression between 3500-7500 psi (2x strength increase). Tempered glass has a minimum surface compression of 10,000 psi (4x strength increase).

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Is laminated glass fire-rated?
Laminated glass with Butacite® PVB or SentryGlas® is not fire-rated. Products that pass the 45-minute fire test are wired glass and other special fire-rated glasses.

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What are low-e coatings?
Low-emissivity (low-e) coatings applied to glass reflect invisible long-wave infrared (IR) energy, or heat. They reduce heat gain or loss in a building by redirecting the heat.

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Can low-e coatings be laminated to the inside of the laminate?
Pyrolytic low-e coatings are typically placed on the outside surface of the laminate; however, sputter coatings face inward and directly touch the interlayer.

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How do you know when to use annealed, heat strengthened or tempered glass in overhead glazing?
Overhead glazing only requires laminated glass. The choice of annealed or heat-treated glass is based on uniform equivalent load requirements (principally wind and/or snow loads), size of glass panels, residential or commercial applications. Typical commercial glass configuration is outboard tempered glass, 1/2-inch air space, inboard 9/16-inch heat strengthened laminated glass.

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Can laminated glass be reduced in thickness vs. tempered glass to negate some of the added cost of laminated glass?
The determination of glass thickness is based on the ability of the glass to meet specified loads. The load resistance of tempered or laminated glass should be analyzed independently of one another to be sure the proper glass thickness has been specified.

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How is it determined that laminated glass passes the shot bag impact test in CPSC 16 CFR 1201?
Laminated glass passes if no tear or shear of the opening occurs through which a 3-inch-diameter sphere can pass freely.

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How is laminated glass marked to show safety glazing compliance?
Glass or interlayer carries a mark indicating the manufacturer or installer, type of glass (laminated or tempered), safety glazing standard (CPSC 16CFR 1201), Category I or II.

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What are the conditions in which glazed panels are considered safety glazing?
Glass must meet all of these conditions: Individual exposed area of the glass pane must be greater than 9 sq. ft. Exposed bottom edge is less than 36 in. above the floor Exposed top edge is greater than 36 in. above the floor Within 36 in. of walking surface.

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Can laminated glass be used everywhere that tempered glass can be used for safety and security glass minimum requirements?
Yes, both laminated and tempered glasses are suitable for use in safety glazing applications. When glass retention or a persistent weather barrier is desired, such as in burglar- or storm-resistant applications, only laminated glass offers the added security of maintaining protection after glass fracture.

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What does Category II mean in safety glazing?
The Category II designation is for safety glazing that has passed the 400 foot-lb impact test. Category II compliance is required for glazing going into most of the hazardous locations specified by the building code. The Cat. II will appear on the ?bug? that appears in the corner of safety glazing.

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What is the UV filtration of PVB and SentryGlas®?
Both interlayers filter up to 99 percent of ultraviolet radiation, a major cause of fading of fabrics and fibers.

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What makes a spectrally selective glass different than normal float glass?
Spectrally selective glass permits some portions of the solar spectrum to enter a building while blocking others.

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How do you know if tempered glass has the proper surface compression (greater than 10,000 psi according to ASTM C1048)?
The glass fabricator can use an instrument to measure surface compression. The Grazing Angle Surface Polarimeter (GASP) is an instrument used to measure surface stress in the glass. Another test instrument is called a DSR (differential surface refractomer). Alternately, the glass fabricator can break the glass and examine the fragments to see that they meet the criteria in ANSI Z97.1 or CPSC 16 CFR 1201. If the glass does not break after the shot bag impact, it can be broken with a center punch.

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How thin can laminated glass be made and still meet the ANSI and UL 972 standard acceptance criteria?
Laminated glass with a 30-mil PVB interlayer is typically used for safety glazing (meeting either ANSI or CPSC standards). Laminated glass with a 60-mil PVB interlayer will meet the UL standard.

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What is the wavelength range of UV?
The wavelength range of UV is 300 to 380 nanometers (nm). UV light is invisible to the human eye. Long-term UV exposure can result in fading and deterioration of fabrics and furnishings. Infrared light is also invisible to the human eye. It falls between approx. 790-3000 nm and has a penetrating heat effect. The only portion of the solar spectrum that is visible to the human eye is the visible light range, 380-720 nm.

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What is the maximum use temperature for laminated glass made with a SentryGlas® interlayer?
DuPont temperature cycle testing has shown that the maximum use temperature for laminated glass made with a SentryGlas® interlayer is 82°C (180°F). Exposure to temperatures above 82°C (180°F) can lead to changes in optical properties.

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Can SentryGlas® be used in constant contact with water?
No. Exposed edges of laminated glass made with a SentryGlas® interlayer can withstand occasional, brief contact with liquid water but the edges should not be immersed continually in liquid water. Because SentryGlas® ionoplast interlayers resist moisture ingress more strongly than similarly exposed polyvinyl butyral (PVB) interlayers, SentryGlas® is generally considered more weather-durable than PVB and other interlayers in open-edged laminate applications.

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