Tag Archives: Toughened Glass

Toughening/Tempering Process of Glass Explained

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Source: berlinerglas.com

Glass is a naturally fragile material. To boost its functional properties and enhance its operational safety, it undergoes the process of tempering.

Tempering or toughening is a process where the glass is heated at high temperatures to make it stronger and more resistant to breakage. This process creates a balance in the product’s internal stresses, so that when the glass is broken, it would crumble into tiny granular chunks instead of breaking into sharp, jagged pieces.

Because of its increased strength and safety, builders and architects utilise them in a multitude of demanding applications. This includes showers, vehicle windows, refrigerator trays, glass tables, diving masks, glassware, cookware, fireplace grates, bulletproof windows, architectural glass doors and virtually anywhere else that needs safe and strong glass.

The Tempered Glass Manufacturing Process

Tempered glass goes through a process similar to that of a tempered steel. Below, we take you through its sophisticated manufacturing process.

Stage 1: All toughened glass begins life as a float glass. Before it undergoes tempering, the glass is examined for imperfections. Bubbles, inclusions, and cracks may cause the float glass to break during toughening. So if any signs of such flaws are found, the glass can’t be tempered.

Stage 2: Prior to toughening, it must first be cut to the desired shape as it won’t be possible to cut or etch the finished product in its toughened state. Once cut, the edges are smoothed and any burrs produced during etching or cutting are removed.

Stage 3: To completely remove the grains of glass that were deposited during sanding, the float glass is thoroughly washed. This also ensures that dirt and any other tiny debris won’t interfere with the tempering.

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Source: breakglass.org

Stage 4: In the tempering process, the surface of the float glass is heated at over 600 degrees Celsius as it travels through a furnace. Some manufacturers heat the glass above its annealing point of approximately 720 degrees Celsius.

Stage 5: The scorching glass is then rapidly cooled through quenching by a high-pressure blast of air for a period of three to 10 seconds at various angles. As it cools and begins to shrink, tensile stresses temporarily build-up in the interior zone of the glass while its surface consequently develops surface stresses. These compressive stresses eventually enhance the strength of the glass, making it tougher to break.

A properly tempered glass should be able to withstand pressures of a minimum of 10,000 pounds per square inch (psi) and can be expected to break at about 24,000 psi.

Beyond the added tensile strength and safety, tempered glass has a greater resistance to thermal shock and thermal stresses. Essentially, it can withstand constant exposure to temperatures as high as 243 degrees Celsius.

Despite these property enhancements, the characteristics of tempered glass are that of clarity, chemical transmission, colour, expansion coefficient, and chemical composition (which remains unaltered).

If tempered glass is the right product for you contact Economy Glass with the details.

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How Do I Know If My Glass is Toughened/Tempered Safety Glass?

Tempered or toughened glass could save lives.

Produced using a slower cooling process, this type of safety glass is much stronger and safer as compared to standard glass. Because of its high resistance to heat and breakage, tempered glass is widely preferred for building and establishment windows. It is also usually used for aquariums and table tops as well as a protective eyewear for divers and machinists.

glass table top

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To the untrained eye, tempered glass may seem to look the same as any type of glass. In order to identify it, many people would joke around and say, “Whack it! If it shatters into tiny, bite-size pieces, then it’s definitely tempered.” But, in all seriousness, how do you tell if a glass is tempered (without a hammer involved)?

Below, we give you less destructive ways to identify whether or not your glass is toughened.

Examine Its Edges

Normally, tempered glass has completely smooth edges due to the extra processing it goes through, while other types of glass usually have scuffed or ridged edges.

If the edges of the glass are exposed, run your fingers along them. Provided that the roughness is not the result of abrasion, any impression of roughness likely means that the glass isn’t tempered.

Keep an Eye for the Bug

We don’t mean the insect. In the construction trades, a bug is a tiny label etched or sandblasted in the glass’s corner. Along with the manufacturer name and the CPSC (Consumer Product Safety Commission) standards, this stamp indicates whether the glass is tempered or not.

If you got the glass directly from the manufacturer, you’ll easily see the marking. But that isn’t always the case, especially when the glass has frames concealing the stamp. So you have to watch out for other clues.

Look for Imperfections

If you notice any warping, bending, or dimples on the glass, then it is most likely toughened glass. These imperfections typically occur during the heating process. Because the glass undergoes extreme heat, the tongs used to handle it often leave a slight impression on the surface that you may be able to identify if you look closely enough.

Some tempered glass may also have surface scratches that are typically caused by the small particles from the machine rollers that melted and fused to its surface. This leftover debris gets dragged around during normal cleaning, producing light scratches.

View the Glass Through Polarized Lenses

If you try to view tempered glass in sunlight with a polarized pair of sunglasses, you will see dark, shady spots or lines stretching across its surface–a prime indicator that the glass is toughened. These lines were formed by the machine rollers during the tempering process.

Score a Line (Only If You Plan on Cutting It Away)

If all else fail, consider scoring a line on the glass surface using a window-cutting tool. If it creates an uneven and flaky line, it’s tempered. If you plan to cut the glass, take it to a specialist so that it can be cut without causing cracks or chips.

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