issue: May 2003 APPLIANCE Magazine International Appliance Technical Conference 2003 Dana Chase, Sr. Memorial Award-Winning Paper New Glass Ceramic Material for Cooking Surfaces Allows for Reduction of Boil-Up Times by up to 20 Percent	Share  Printable format  Email this Article  Search
by Christiane Baum, applications manager, Schott HomeTech North America This is an edited version of a paper delivered at the 54th Annual International Appliance Technical Conference (IATC), March 10-12, 2003, West Lafayette, IN, U.S. The author was awarded the Dana Chase, Sr. Memorial Award for the best paper presented at the conference.

A new generation of glass ceramic has been developed by Schott Glas (Mainz, Germany) that is proven to reduce boil times.

The new glass ceramic cooktop panel, CERAN¨ SUPREMAª, has a higher IR-transmission and withstands higher temperatures, enabling more powerful heating elements to be used to reduce boil time by 15-20 percent. This new generation of cooktop panels prepares customers for the future and provides faster cooking.

A New Generation of Glass Ceramic

To address the desire for faster cooking, several concepts have already been developed and brought to the market (i.e., induction cooking, SiN cooking disks, and halogen heating elements).

Induction cooking is great if one looks for quick responses in combination with easy-to-clean surfaces. However, the relatively high costs and the need for special cookware have slowed the market penetration of induction.

The concept of using SiN cooking disks requires special cookware and is very expensive. Dual heating elements are not available, and the advantage of the easy-to-clean, full, smooth glass ceramic surface is not there.

The perception of halogen heating elements is a quicker reaction time. However, a real performance advantage is not realized when compared to common ribbon heating elements.

Considering these results, the most cost-effective solution might be to optimize the performance of the current system.

The normal operating temperature of current heating elements is to be set at 560¼C (1,040¼F) to comply with U.S. and European safety standards. However, special circumstances (cooking with an empty pot, the use of poor cookware, off-set pots, or pots with uneven bottoms) can lead to temperatures higher than 750¼C (1,382¼F) and should be prevented. The micro-crystals in glass ceramics have a tendency to start growing as the temperature gets too high.

The result is a structural change that influences the properties of the material.
If the transmission in the IR wavelength range used for cooking were to be improved, the emitted energy could be used more efficiently to cook food. Another improvement would be if the glass ceramic panel could accommodate higher temperature settings. This approach has been realized with a new generation of glass ceramic panels for cooking surfaces. The new ceramic withstands approximately 40K higher temperatures, resulting in a recommended adjustment temperature of 600¼C (1,112¼F). The higher temperature settings, improved temperature/time load, and the higher IR transmission allow for a reduction of boiling times of up to 15 percent, depending on cookware. The usage of more powerful heating elements calibrated at higher temperature settings along with intelligent control systems can result in gains of an additional 5 percent, resulting in a final performance improvement of up to 20 percent, depending on cookware.

Table 1. Comparison of loading temperature.

Table 1 shows the adjustment temperatures currently recommended for common black glass ceramic compared with the improved settings possible for the new generation of glass ceramic for cooking surfaces.

Figure 1. Load cases according to draft DIN VDE 0700 part 6 A8, April 1989.

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Safety Requirements

Extensive tests have been carried out to comply with U.S. and European safety standards. If higher temperature settings are utilized, the two most important tests facing a new material are the VDE Load Case Test (according to draft DIN VDE 0700 part 6A8) and the black wall test.

Figure 1 shows the different load cases along with the load parameters that are requested for the VDE Load Case Test. The adjustment temperature applied to the new glass ceramic cooktop panels was in all cases 40K higher than traditional settings. The new ceramic material withstood all load cases and is approved in accordance with the VDE test requirements (according to draft DIN VDE 0700 part 6A8).

For the black wall test, the following parameters were applied in accordance with EN60335-1 and/or EN60335-2-6:

• Usage of 1.24 times of rated wattage
• Cooking zone without heat transfer (free radiation)
• Only one cooking zone in action (most critical condition)
• Usage as long as a constant condition is reached
• Maximum allowed temperature increase of surrounding area DTmax = 150K

As a result of the 40K higher adjustment temperature allowed for the new ceramic material, the free radiation temperature showed increases. The easiest and most cost-efficient option to fulfill the black wall test would be a slightly longer distance between the cooktop panel and the wall.

Figure 2. Maximum free radiation adjustment at minimum wall distance

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If the countertop width does not allow increasing the distance to the wall, an alternative would be to increase the distance between the rear heating elements and the outer edge of the burner box. (Figures 2 and 3 show the maximum free radiation adjustment at minimum wall distance.) If a larger distance to the side walls (left and right) can be arranged, the front burners can be adjusted to higher temperature settings without any problems.

Certainly, the most sophisticated solution would be intelligent control systems. Since the energy used for boiling only needs to be applied during the first few minutes until the food comes to a boil, a system that would control the temperature depending on time can be considered. Another way could be a temperature sensing system that measures the temperature directly on the glass ceramic, the pot, or at the wall to prevent higher than allowed temperatures.

Figure 3. Maximum free radiation adjustment at minimum wall distance (standard radiant heaters).

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A system that has been evaluated in combination with the new ceramic material allowed adjusting the temperature depending on time. In the case of the black wall test, the controller would, for instance, decrease the temperature setting after a boost cycle. This means that higher temperatures are only applied when neededÑduring the boil-up time. If the food comes to a boil, the temperature will be reduced to a normal setting or, if desired, to a simmer setting.

The combination of intelligent controls and the new glass ceramic allows even higher power heating elements for a given heated area than would be normally acceptable for conventional glass ceramic types with non-intelligent controls, without compromising the life of the glass ceramic.

Boil-Up Performance

Comprehensive tests have been carried out to evaluate the performance of the new ceramic cooktop panels. Figures 4 and 5 show the differences in boiling performance between the traditional and the new glass ceramic (40K higher temperature settings were applied to the new material).

The new glass ceramic type has been proven as a material that allows for significant performance advantages and complies with international safety standards. It can replace the current black glass ceramic materials without any disadvantages. Decoration colors are approved and fulfill the same high quality standards as the current materials. Heating element suppliers should be contacted to confirm the lifetime resistance of the heating elements and limiters if higher temperature adjustments are to be used.

Figure 4. Comparison of boiling performance between traditional glass ceramic and new glass ceramic material (halogen heating elements).

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Figure 5. Comparison of boiling performance between traditional glass ceramic and new glass ceramic material (ribbon heating elements) .

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Conclusion

A new standard of glass ceramic cooktop panels has been developed. Its capability to withstand higher temperature settings along with the higher IR transmission enables the use of more powerful heating elements. Using those improved settings allows for a reduction of boil-up time by 15-20 percent, depending on cookware.

About the Author

Ms. Christiane Baum received her masterÕs degree in Engineering from University RWTH Aachen, Germany. She began her business career in 1996 as a development engineer with SCHOTT JENAer Glas, Germany. She was named manager, Customer Service & Order Logistics for Fire Resistant Glazings in 1998. Ms. Baum joined Schott HomeTech North America in January 2001 as applications manager for CERAN cooking surfaces.