glass and glazing Flashcards
• Tempered Glass
- Tempered Glass: produced by cutting annealed glass to required size, reheating to 1200 degrees’ and cooling both its surfaces rapidly with blast of air while core cools more slowly
- Glass is about 4 times as strong in bending and much more resistant to thermal stress and impact.
- If it breaks, the sudden release of internal stresses causes it to break into small granules rather than long,sharp edged shards
- Used in exterior doors, floor to ceiling sheet glass, doors that have no frames, squash/handball courts, hockey rink enclosures, basketball hoop backboards • More expensive than annealed glass
• Heat Strengthened Glass:
This glass type falls between annealed and tempered glass. Tempered glass is twice as strong as HS glass however HS glass is more preferred due to spontaneous breakage being less of an issue compared to tempered glass. When it breaks, HS glass stays in the opening where tempered glass tends to leave the opening. When it breaks HS glass doesn’t turn into small cubicle pieces like tempered glass so it cannot be considered as safety glass. When there is thermal stress concern available, HS glass is preferred such as: spandrel are of an all-glass curtain wall. Also HS glass has less optical distortion compared to tempered glass.
- Heat Strengthened Glass: process is similar to tempering but the induced compressive stresses in the surfaces and edges are about 1/3 as high
- About 2 times as strong in bending and more resistant to thermal stresses and impact compared to annealed
- Breakage is more like annealed glass than tempered glass
• Laminated Glass
- Laminated Glass: made by sandwiching a transparent polyvinyl layer between sheets of glass and bonding the three together under heat and pressure
- Not quite as strong as annealed glass of the same thickness
- When it breaks the interlayer holds the shards of glass in place
- Used in skylights and overhead glazing
- A better barrier to the transmission of sound than solid glass
- Used to glaze windows of residences, classrooms, hospital rooms, etc., that must be kept quiet in otherwise noisy environments
- Security Glass used at drive up bank tellers and other secure locations is basically beefed up laminated glass and can stop any caliber of bullet
• Fire Rated Glass:
- Fire Rated Glass: • Glass in fire doors/separation walls must maintain its integrity as a barrier to the passage of smoke, heat, and flames even after exposure
- Specially tempered glass is rated at 20 minutes of fire protection
- Wired Glass is produced by rolling a mesh of small wires into a sheet of hot glass
- When wired glass breaks from thermal stresses, the wires hold the sheets of glass together to act as a fire barrier
- Holds a fire resistance rating of 45 minutes
• Fritted Glass:
- Fritted Glass: surface of glass is imprinted with silk screened patterns of ceramic based paints, which are made of pigmented glass particles called frit
- After it’s been printed, the glass is dried and fried, turning the firt into hard, permanent ceramic coatings in a variety of color
• Insulating Glass:
- Insulating Glass: glass is an extremely poor thermal insulator
- It conducts heat about 5x faster than polystyrene foam insulation
- Double Glazing: a second sheet o glass applied to a window with an air gap between cuts heat loss in half
- Practice of doubling (or tripling) layers has been used in cold climates • The thickness of an airspace is less critical to the insulating value than the mere presence of it
- A standard overall thickness is 1” with 2, 1/4” glass sheets and a 1/2” air gap
- Thermal performance can be improved by low-e coating on one or both of the sheets of glass. It’s a thin metallic coating that reflects selected wavelengths of light and heat radiation
Heat-soaked tempered glass
Heat-soaked tempered glass: Is the most expensive of all heat treated glasses. When the risk of breakage is required to lowered more, this type of glass is used. However, since it is very expensive, the use should be justified carefully.
Low-E Glazing: which side does film go?
Low-E Glazing:
double glazing with a thin film in the glazing cavity that allows visible and near infrared to be transmitted
In cold climates: apply to the inside pane of glass
In warm climates: apply to the outside pane of glass
As objects in the room are heated and emit long wave radiation, the film prevents the loss of this heat by reflecting it back into the room
When used with argon gas the system is very efficient
Spectrally Selective Glazing
Spectrally Selective Glazing:
coatings that help block solar heat gain from entering the building
- Used with Low-E and double glazed systems can achieve a SHGC of .25
- For buildings that have a long cooling season and require high light levels
Super Windows:
Super Windows:
- Two low-E coatings with gas filled cavities between three layers of glass
- Units can actually gain more thermal energy than they loose over 24 hour
period in the winte
Electromagnetic glazing:
Electromagnetic:
• Multilayered thin film applied to glass that changes continuously from dark to clear as low voltage electrical current is applied
Photochromic glazing:
Photochromic:
- Glazing that darkens under direct action of sunlight
- As light intensity increases, window becomes darker
- An automatic action…doesn’t have user control like electromagnetic glazing
Thermochromic glazing:
Thermochromic:
- Changes darkness of glass in response to temperature
- An automatic action
Transition Metal Hydride Electrochromics glazing:
Transition Metal Hydride Electrochromics:
- Changes from transparent to reflective
- Coatings of nickel magnesium
