In the manufacture of cooking appliances, thermal insulation has long been a key element to ensure energy efficiency and safety to both commercial and domestic customers.
Fiberglass is the conventional material of choice for thermal insulation in appliances such as range cookers, ovens, and dual fuel cooking tops, but a shift change in favor of higher performance alternatives is now shaking up what has been, until recently, a relatively steady marketplace.
In this article, Morgan Advanced Materials’ Engineering Services Manager Richard Ellenberger discusses why high temperature Alkaline Earth Silicate (AES) fibers have become an integral specification choice for manufacturers seeking to benefit from increased design flexibility, better performance, and improved safety.
In cooking appliances such as range cookers and ovens, thermal insulation is predominantly used to prevent heat loss through conduction in electric, gas, and dual fuel models. In some electric and dual fuel cooking tops, thermal insulation is used to avoid heat transfer to the surrounding work surfaces.
Like many other industries, the cooking appliance sector is following new scientific and computer based technology developments. Driven by a food-loving society that requires speed and convenience, ovens are not only getting hotter, but they are coming with more highly technical cooking features than ever before.
Particularly, commercial oven manufacturers are under pressure to offer products that feature a larger cooking chamber, smart controls, multiple cooking techniques, and the all-important pyrolytic (self-cleaning) cycle, without increasing the size of the external footprint.
Satisfying these design, safety, and performance demands requires the specification of materials that are capable of performing under higher temperatures, in smaller or more complex cavities, which is where conventional fiberglass thermal insulation fails to deliver.
Fiberglass, an Outdated Choice for Modern Appliances
Fiberglass delivers better performance in less demanding cooking environments, providing acceptable levels of energy efficiency and safety at temperatures below 1000 °F (538 °C). This performance is more than adequate for conventional cooking temperatures of 300 °F - 500 °F (149 °C - 260 °C).
However, fiberglass is no longer the material of choice for manufacturers of mid-to-high end cooking appliances, including highly technical commercial ovens.
For ovens featuring integrated cooking sensors, electronic, touch-sensitive controls, and other highly sensitive electrical parts, fiberglass cannot provide protection to the modern additions from becoming damaged from heat.
Conversely, AES fibers, such as Superwool® Plus™, are capable of withstanding temperatures of around 1800°F (982°C) and offering between 5% and 20% lower thermal conductivity. As a result, these fibers can be employed in reduced thicknesses, making it suitable for bending around small electrical components to provide complete protection.
With a temperature limit of 1000 °F (538 °C), fiberglass is not an efficient, effective or safe insulation solution when it comes to the sought-after integrated self-cleaning function. To eliminate organic matter from within the oven chamber without using chemicals or detergents, a temperature range of 900 - 950 °F (482 - 510 °C) is used by pyrolytic ovens to burn away unwanted combustibles.
The temperature is even higher for some parts of the oven for periods of many hours, creating a highly challenging environment for any insulation material. Sustained heat of this nature exceeds the thermal performance limits of fiberglass and other e-glass needle mats, resulting in irreversible damage, shrinkage, and distortion, which can change the oven profile over time.
In addition to increased functionality, another factor driving the evolution of commercial and domestic cooking appliances is aesthetic style. Smaller footprints, bigger oven capacity, slimmer profiles, and touch-screen operation are all key design factors that both commercial kitchens and homeowners desire, without sacrificing energy efficiency, performance, and safety.
As a stiff material, fiberglass poses real restrictions when it comes to thermally insulating compact or intricate appliance designs. Conversely, AES fibers are versatile and flexible when bending or wrapping around electronic parts.
For small footprint and slim profile cooking tops or footprint ovens, engineers and designers can use AES fibers in smaller quantities to achieve the same thermal conductivity and ensure correct insulation. Compared to the thickness range of 1” - 3” (2.5 - 7.6 cm) of standard fiberglass, AES fibers have a thickness range of 0.25” - 2” (0.6 - 5 cm), making them crucial in the creation of larger cooking spaces, within a small oven footprint.
AES – Advanced Performance for a Global Market
AES fiber is a man-made, vitreous (amorphous) fiber (MMVF) similar to fiberglass, and AES and fiberglass together represent around 95% of the market for fiber insulation. For many years, fiberglass has dominated the market, providing a highly cost-effective solution for traditional cooking demands.
However, AES materials are now gaining interest due to the ever-increasing demand for mid-to-high end domestic appliances, in addition to highly technical commercial models. Customers now have a greater appreciation for high quality products and an interest to invest in return for better energy efficiency, safety, and product longevity.
For manufacturers at the forefront of technologically more advanced cooking appliance design, this means implementing crucial specification changes in favor of materials that offer optimized performance credentials. For thermal insulation, this means AES fiber, which offers significant benefits in high temperature insulation applications, including low linear shrinkage and thermal conductivity.
AES fibers have a maximum performance temperature of around 1800 °F (982 °C), offering superior insulation in the most demanding cooking environments as the temperature shifts from the convective to radiant heat transfer range. This delivers improved safety, far better energy efficiency, and consistent cooking performance.
Manufacturers looking to maximize the selling potential of their new or future product ranges also have to take into account the global movement of their goods and any regulations that may restrict the sale or component parts. AES fibers or AES wool are beneficial for any appliance manufacturer seeking to globalize sales because they are ideal for unrestricted global use due to their low bio-persistence.
Significantly Lower Thermal Conductivity at Higher Temperatures
The lower a materials thermal conductivity, the better it is at restricting the flow of energy from hot to cold. When choosing materials for an application that requires a set thickness of insulation, the material with a lower conductivity will offer a greater temperature difference between the cold and hot faces, and therefore provide the lowest energy loss.
Some market-leading AES materials, such as Superwool Plus insulating fiber, consist of a higher fiber concentration per unit, making them a more efficient thermal insulating material without the need for increasing thickness or density. The use of advanced manufacturing technology can make molten glass for Superwool Plus fiberize more completely, improving the ratio of shot to fiber and minimizing the size of the pieces of shot.
This carefully managed process offers about 30% more fibers and improves the thermal conductivity up to 20%, making it more effective in restricting thermal energy transfer.
As a result, design engineers now have the flexibility to use less material density while maintaining the same thermal profile, or less thickness and the same density to create a larger cooking chamber within the same external footprint.
The Future of Cooking Appliance Design and Manufacture
As the cooking appliance market continues to be driven by design and technological advancements, as well as improved customer awareness around product performance, energy efficiency and lifespan of appliances, more manufacturers will shift in favor of AES fibers over conventional fiberglass insulation.
Being able to improve product lifespan, optimize cooking performance, minimize carbon consumption, and effectively insulate aesthetically pleasing, compact, slim-line and electronically operated modern appliances are all attractive benefits which will further drive a market shift that shows no signs of slowing.
This information has been sourced, reviewed and adapted from materials provided by Morgan Advanced Materials.
For more information on this source please visit Morgan Advanced Materials.