Strengths Types & Strength of Glass

Saflex main types of glass

There are five main types of glass which are associated with various glass strengths for load and impact. Glass is related to the rate at which it is treated.

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Annealed Glass

Annealed glass is the base glass that is form from the float glass process. As the molten glass begins, under a controlled manner, to cool, it hardens. The slow cooling allows a very limited amount of stress to be retained in the glass and thus the glass can be cut along intentional score marks. Annealed glass typically has excellent optics and minimal optical distortion. Glass can be ultra-clear, clear or colored. It can be smooth, patterned or have wire set into it. Annealed glass can be readily cut to size and shapes as needed, edged, coated with metal coatings, ceramic frit, paint and inks and laminated. Annealed glass is used as the base product to form other fabricated glass.

 

Heat Strengthened Glass

Heat Strengthened Glass is also known as semi-tempered or semi-toughened glass. The heat strengthening process involves first cutting annealed glass to the desired size and shape, edging the glass as indicated, then heating the annealed glass back up to near 650°C (1200⁰F) and then cooling it rapidly. This rapid cooling causes stress in the glass and forms a compressive laver on the glass surfaces and a tension layer in the core. The heat strengthening process increases the mechanical and thermal strength of annealed glass, making it historically twice as strong as annealed glass. Heat-strengthened glass tends to have low levels of glass distortion and bow caused by the strengthening process. Upon breaking, the pattern is similar to annealed glass. Except for cutting after strengthening (with traditional methods) heat-strengthened glass can be fabricated with the same value add coatings and lamination as annealed glass. Heat-strengthened glass is typically used in areas that
 

  •        benefit from low optical distortion,
  •       need to avoid the potential of spontaneous breakage,
  •       need increased mechanical strength versus annealed glass,
  •       are subjected to thermal stress from temperature gradients, and laminated glass applications requiring larger break patterns such as hurricane, balcony (undrilled) and blast and glass shard retention post-breakage.

 

Tempered Glass

Tempered glass is also known as Toughened glass. The tempering process involves first cutting annealed glass to the desired size and shape, edging the glass as indicated, then heating the annealed glass back up to near 650⁰C (1200⁰F) and then very rapidly cooling it. This high speed of cooling causes stress in the glass and forms a compressive laver on the glass surfaces and a tension layer in the core. The delineation of zones in the tempered glass is similar to heat-strengthening but the compressive strength of the surface is significantly higher. The tempering process increases the mechanical and thermal strength of annealed glass, making it historically four times as strong as annealed glass. Tempered glass may to have glass roller wave distortion and bow caused by the strengthening process. Upon breaking, the pattern is unique in that it forms small cube-like pieces which may or may not fall out at the time of impact but have virtually no residual strength as a glass unit when faced with subsequent load. Tempered glass can be fabricated with the same value add coatings and lamination as annealed and heat-strengthened glass. Tempered glass is typically used in areas that
 

  •       need increased mechanical strength versus annealed and heat-strengthened glass,
  •       drilled (prior to tempering) or used in point support systems,
  •       are subjected to thermal stress from temperature gradients, and
  •       locations requiring safety glazing without glass fall-out concerns,
  •       laminated glass applications requiring added glass strength and glass shard retention post breakage.

 

Chemically Strengthened Glass

Chemically Strengthened Glass is annealed glass which is strengthened by a chemical exchange of ions. The chemically strengthening process involves first cutting annealed glass to the desired size and shape, edging the glass as indicated, then submerging the glass in a solution that promotes the ion exchange where the smaller ions are replaced by larger ions. This exchange causes a compressive layer on the glass surfaces and a tension layer in the core. The strengthening process increases the mechanical and thermal strength of the glass, however there is no common value used in the industry to account for the strength enhancement. Chemically strengthened glass tends to have levels of glass distortion and bow similar to the annealed base glass. Upon breaking, the pattern is similar to annealed glass, but in some cases the break pattern can be adjusted to be smaller. Cutting after strengthening (with traditional methods) may weaken the glass. Fabrication of chemically strengthened glass is beginning to be more common in the industry. Lamination of chemically strengthened glass is possible, however compatibility studies should be undertaken prior to use. Chemically-strengthened glass is typically used in areas that
 

  •       benefit from low optical distortion,
  •       need to avoid the potential of spontaneous breakage,
  •       need increased mechanical strength versus annealed glass, and laminated glass applications requiring added strength, low distortion and glass shard retention post-breakage.

 

Laminated Glass

Any of the above types of glass can be laminated. The glass thickness and type is typically specified based on the performance desired for the glazing. Common safety glazing can be produced with thin glass plies (~3mm (0.125 inch) and 0.76 mm (0.030 inch) Saflex or Vanceva polyvinyl butyral (PVB). When laminating products strengthened by heat, a minimum of 1.52 (0.060 inch) should be used.

Laminated glass offers many advantages over monolithic glass types. Safety and security are historically the best-known characteristics of laminated glass as the interlayer tends to retain the broken glass shards and act as a penetration barrier. This aids in reducing the likely-hood of falling glass on pedestrians and can deter entry through the glass for some time depending on the composition of the laminated glass and glazing system. Today, laminated glass can bring more than just safety and impact resistance: noise damping, windborne debris and blast resistance, structural capacity, enhanced UV radiation screening, solar control and an incredible array of over 17,000 color options are all available in laminated glass configurations.