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How is Glass Tempered?

How is Glass Tempered?

Tempered glass, also known as safety glazing, is about four times stronger than ordinary, annealed glass. Tempered glass fractures into small, relatively harmless pieces when broken, unlike annealed glass that shatters into jagged shards. That's why tempered glass is used whenever there is potential for broken glass that could harm people.

Tempered glass is used in various applications, such as car windows, entrance doors, microwave ovens, skylights, patio furniture, and of course as phone screen protectors.

Tempered glass usually has a surface compression of around 10,000 psi, and breaks not until typically over 20,000 psi. If you’ve ever wondered how tempered glass is made, here’s a look at the basic steps:

  • Cutting – Before glass is tempered, it should be cut into the desired shape. The tempering process will weaken the glass, increasing the likelihood of breakage if you try to cut it afterward.
  • Inspection – The cut glass is then inspected for any imperfections such as cracks or bubbles, which may cause the glass to break during the tempering process. The glass will be rejected if there are any signs of imperfection.
  • Sanding the edges – The edges of the cut glass should be sanded for smoothness. Sanding removes any burrs that may have been created during the cutting or etching stages.
  • Washing – The cut glass should be thoroughly washed to remove dirt or dust particles or the tiny grains of glass that might have accumulated during sanding. Debris can interfere with the tempering process.
  • Heating – Cut glass may be fed continuously or in batches into the tempering oven. The oven’s temperature could reach over 600 degrees Celsius or 1,112 degrees Fahrenheit. The industry standard is 620 degrees Celsius or 1,148 degrees Fahrenheit.
  • Quenching – The heated glass is then subjected to blasts of high-pressure air at various angles. The blasts provide rapid cooling to the outer surfaces of the glass, causing them to contract faster than the center. This gives the tempered glass its strength.