Microporous insulation offers superior thermal properties and results in much higher thermal efficiency than conventional materials with substantially thinner layer thicknesses. Excelfrax® is a microporous inorganic thermal insulating material, supplied by Unifrax, for the nonferrous industry. It has extremely low thermal conductivity, which results in saving space, weight and energy. In addition, the product is easy to install and environmentally compatible.

Fig. 1. Excelfrax microporous insulation family of products

Fig. 2. Excelfrax microporous insulation used as backup insulation in a melting furnace

Based on micro-porous-insulation technology, the Excelfrax® product line is a family of products that all exhibit superior insulating characteristics. This microporous insulation is composed of inorganic oxides, primarily fumed silica. Silicates and opacifiers are added to improve the material performance.

Microporous materials are very efficient insulation products. These products actually have thermal-conductivity values lower than still air. This performance is based on the ability of microporous insulation to block the three modes of heat transfer – conduction, convection and radiation.

Due to the product’s low density and the porous structure on the microscopic level, heat transfer due to conduction is reduced. This microporous structure minimizes the contact points between the molecules, which results in reduced energy transfer from one molecule to another.

Since solid materials have a much higher thermal conductivity than still air, typical insulation materials are designed to trap air in small spaces, reducing heat transfer. Movement of the air, due to convection currents within insulation, transmits heat through the material. In microporous insulation, the structure of the material results in trapped air pockets smaller than the mean free path of air. Due to this material structure, molecular “collisions” that transfer heat from one surface to another are avoided.

Excelfrax microporous insulation incorporates opacifiers, which are specifically designed to reduce the heat transfer due to radiation.

The nonferrous industry demands a high measure of thermal efficiency and flexibility from the high-temperature insulation suppliers, while at the same time expecting ways to reduce operating costs. Increased energy costs and reduced lead times directly affect customer costs. One measure to reduce overall production cost is utilizing a thermally efficient insulating lining for the production process.

Fig. 3. Backup insulation in a melting furnace

Melting-Furnace Applications

In the aluminum industry, the melting furnace is an important component in the processing of primary or secondary aluminum. It is essential that an optimal temperature distribution be provided inside the furnace around the melt line in all ranges in order to keep a homogeneous liquid. The Excelfrax 1800 has been used very successfully in this application.

By the use of the thermal-insulation properties of these microporous inorganic products and the optimization of the proper insulating lining, additional positive effects are identifiable:
  • The clear reduction of the cold-side temperature leads to a lowering of the operating cost by improvement of the energy balance together with increase of the utilizable volume.
  • The lower cold-side temperature allows improvements in industrial safety.
  • The health risks before, during and after the installation are eliminated in contrast to the use of other standard insulation material.
  • The use of these products allows for an increase in the lifetime of the furnace since adhering aluminum due to premature freezing at the fireproof lining can be avoided, therefore increasing the working reliability.
As an example, the use of the product’s board or flexliner as backup insulation resulted in a 50% reduction in the insulation thickness versus standard RCF board with a 30% heat-loss reduction. The result was increased energy savings, extended furnace life and improved product quality.

Fig. 4. Excelfrax used in an aluminum-transport ladle

Applications for Aluminum-Transport Systems

Aluminum-transport systems for the secondary aluminum industry transfer molten aluminum between plants and require efficient delivery of the aluminum at consistent elevated temperatures. The application of this microporous heat-insulating material permits a significant lower loss of temperature per time unit in comparison to conventional insulating superstructures. This effect allows aluminum suppliers to increase safety time to freezing of the liquid aluminum and supply more customers at a greater distance.

By increasing the heat-insulating properties of the transport ladle, the preheating and reheating times are noticeably reduced, which saves operating cost. Also, with larger distances to the final customer, the gas consumption necessary for reheating the ladle will be reduced noticeably, thereby lowering the operating cost. The resulting thinner lining allows for an increase of the utilizable volume of a transportation ladle, which affects direct operating cost of the supplier and end-use customer costs. For example, a 2-inch-thick Excelfrax 1800 board lining provides the same cold-face and heat-loss benefits as a 7-inch-thick mineral-wool board. The working-lining reliability is also increased, and therein the service life is extended.

Use in Aluminum Launders

Aluminum launders move molten aluminum from the melting area to the casting operation area. This application requires a material that will minimize heat loss and reduce the requirement for superheating aluminum during the casting process. Microporous insulation is an excellent choice for this application, as it utilizes its superior thermal conductivity to reduce heat loss and decrease lining thickness to allow for increased launder capacity. As an example, the use of Excelfrax 1800 board or flexliner as backup insulation resulted in a 1.5-inch-thick reduction in the insulation thickness versus standard calcium-silicate board with a 65% heat-loss reduction. The result was increased launder capacity, energy savings, extended furnace life and improved product quality.

Fig. 5. Installation of Excelfrax 1800 Flexliner

Product Features and Benefits

The microporous-insulation product line offers users a number of important advantages.
  • Saves space, weight and energy as a result of extremely low thermal conductivity.
  • Increases capacity of ladles, kilns, industrial ovens and commercial appliances while maintaining thermal performance.
  • Reduces weight while maintaining thermal performance. This weight reduction can reduce structural requirements for furnaces and other high-temperature vessels.
  • Saves energy and reduces operating costs by reducing heat loss in conventional refractory linings.
  • Thermal stability – Designed to withstand continuous operating temperatures up to 1832°F (1000°C).
  • Consistent operating temperatures – Due to the superior insulating characteristics of this product, processes may be easier to regulate and control, which often results in a more consistent final product.
  • Easy to fabricate – Can be fabricated with commonly available tools.
  • Resistance to thermal shock – Products are resistant to thermal shock caused by both low and high temperatures.
  • Noncombustibility – Products are completely noncombustible per German standard DIN 4102 Class A1.
  • Wetting – Wetting agents such as water, liquid detergents, oil, petroleum, alcohol, etc. can have an adverse effect on the insulation since these liquids can destroy the microporous structure of the product. This can be greatly reduced or eliminated by encapsulating Excelfrax in a barrier material such as polyethylene or aluminum foil.
  • Storage – The product can be stored indefinitely and should be handled and stored in liquid-free conditions. Moist air or steam does not adversely affect the stability of the microporous insulation.
Excelfrax microporous-insulation products are available in several product forms and are used to solve a range of thermal-insulation problems.
  • Excelfrax 1800 Board – A rigid material with comparatively high density, compression resistance and strength. It is available in thicknesses up to 50 mm (2 inches).
  • Excelfrax 1800 Flexliner – A thin material with good compression resistance that is vacuum sealed in a laminated PA/PE film to allow maximum flexibility. It is available in thicknesses up to 10 mm (0.4 inches).
Overall, microporous insulation can improve energy efficiency while continuing to provide a number of thermal-insulating solutions in the nonferrous industry.IH

For additional information on Excelfrax® Microporous Insulation, contact Unifrax I LLC, 2351 Whirlpool Street, Niagara Falls, NY 14305; tel: 716-278-3800; fax:716-278-3900; e-mail:info@unifrax.com; web: www.unifrax.com. Excelfrax® is a registered trademark of Unifrax. Jim Smith is the global market manager – process industry.

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