Toughening/Tempering Process of Glass Explained

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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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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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