Tempering increases the strength of glass by a factor of four, so that when it breaks it crumbles into granular shards with no sharp edges, which are safe to pick up by hand. Tempering can also increase the functioning temperature range of glass. For this reason, it is often used when strength, thermal resistance and safety are important considerations, and is an essential process for glass used in a range of applications, such as windows, glass partitions, automotive windshields, appliances and cookware.
How it works:
After glass has been formed into flat sheets and annealed, it is ready to start the tempering process. It is sent through a tempering furnace heated to 650°C before being rapidly cooled.
During this process, the cooling of the outside material happens quicker than the center, which causes an opposition of stresses: the outside is in a state of compression while the inside is in tension. This material behavior results in the strengthening of the glass.
Electric heating is the most important step in the process, making the heating element the most important component. This is what delivers the thermal precision required to ensure consistent, high-quality glass.
Choosing the optimal heating solution
There are a number of options when it comes to heating elements such as alloy grade, alloy shape, element design and the specifications. “Selecting the optimal heating element will depend on the specific application and needs to take into account the temperature, atmosphere, operating cycles, mechanical properties and power demands,” says Arthur Moslow, Technical Marketing Manager for North America, Kanthal. “Failure to take these considerations into account can lead to failure issues such as overheating, corrosion (green rot) or sulfur attack.”
Kanthal has extensive experience and wide expertise in providing heating for a variety of industrial processes. Within glass tempering, it offers the full spectrum of different alloy grades, styles and designs.
“Our products can offer a high level of quality and reliability, because we have full control over the entire manufacturing process, from the raw material to the finished product,” says Moslow. “We also have the most experience using our own materials and alloys.”
Because Kanthal has local manufacturing in North America, Europe and Asia, as well as representation and technical support across the world, it can deliver faster services and shorter lead times. Its experts are also on hand to help companies select the best solution to suit their application.
“Our services include element failure analyses and design reviews, where we can help customers overcome element limitations or resolve failure issues,” says Vic Neill, Vice President of Thermaltek, a Kanthal subsidiary with long experience working with glass tempering. “Whether it’s faster throughout, higher temperatures or longer element life, we can help develop a bespoke solution that meets a customer’s specific demands.”
View the on demand webinar: Electric Heating in Glass Tempering
This webinar takes a look at the design considerations when replacing an old heating element or designing a new furnace. Join our experts at Kanthal® who can bring our 90+ years of materials knowledge to you.
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