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The high-performance microporous insulation products used by today's technology-driven aircraft manufacturers are the most efficient high-temperature systems currently available and are also widely accepted in industrial applications.
Microporous engineering systems range from soft manufacturing using a variety of textiles to partial encapsulation using metal foil. Design considerations for efficient thermal insulation systems used in the aerospace industry prompted researchers to define the best theoretical thermal insulation.
This is based on minimizing the main heat transfer modes, including gas conduction, solid conduction, and the simultaneous effects of radiation and convection. A product model is required to meet specific standards, including:
This research produced a product consisting of a microporous fumed silica powder insulation material quilted between two layers of glass fiber cloth. It combines special material additives, fine particle filling and precise production methods to make microporous insulation with excellent thermal properties.
Compared with traditional thermal insulation products, the advantage of microporous thermal insulation products is that their thermal conductivity at a given thickness is much lower. For example, at 1000 °F (538 °C), the thermal conductivity of microporous thermal insulation materials is 1/3 of that of ceramic fiber blankets, and 1/4 of that of 2300 °F (1260 °C)-class insulating refractory bricks.
Therefore, 1 inch (25 mm) thick microporous insulating materials, such as Thermal Ceramics' BTU-Block(tm), are available at 1000 °F with 3 inches (75 mm) thick ceramic fiber blankets or 4 inches thick ceramic fibers The heat transfer result of the blanket is almost the same (100 mm) and the thickness of the equivalent grade IFB (insulated refractory brick).
In addition to their very low heat storage and thermal conductivity, some other advantages of microporous insulation products are very low shrinkage and resistance to excessive compression. These materials can resist a wide range of compression under heavy loads, and their thermal conductivity is hardly degraded.
Unlike typical rigid insulation systems, its uniformity and thermal performance are actually improved by compressing the insulation material when it is slightly deformed, and the microporous insulation product does not reach the critical load/deformation point.
When used as backup insulation materials at temperatures up to 1800 °F (982 °C), they have extremely low shrinkage. In most applications, the insulating layer is also easy to install. Usually fiber cement or sodium silicate is used to fix them.
Image source: Morgan Advanced Materials
The forms of thermal ceramic microporous insulation systems such as BTU-BLOCK™ and Min-K® include plate and shape, flexibility, face plate, ladle lining and moldability.
Plates and shapes are available in a variety of sizes and configurations. They are rigid and microporous products with maximum structural integrity and highest density. The flexible product consists of a microporous core encapsulated between high-temperature cloth layers and quilted into a 1 inch (25 mm) square.
The panel is a low-density product encapsulated in fiberglass fabric. It provides flexural strength, mechanical protection, and substrate for bonding to walls or other insulating materials. The material has good rigidity, high strength, low cost and the ability to be made into a variety of shapes and sizes.
The quilting maintains the core distribution in a high-vibration environment and allows the insulating material to bend or wrap during installation to conform to a unique shape.
The lining of the ladle is very similar to the flexible product, but uses parallel stitching to allow it to be wound on round or cylindrical containers, such as crucibles and ladle.
The moldable product can be placed by hand or wiped with a towel to areas where other insulation systems cannot be installed, and it is a wet microporous form of insulation. It is ideal for use in on-site manufacturing work or custom applications that lack engineering design support.
Certain applications have special considerations that require the selection of non-standard materials. For example, in some applications, BTU-BLOCK products use a special hydrophobic core material, so that wet products such as refractory castables can be directly placed on the microporous insulating material without damaging the product structure.
Thin foil coatings can be used to increase the strength of fabric-coated microporous products. Various material densities from 14 to 25 lb/ft3 (224 to 400 kg/m3) enable selection to meet specific compression resistance requirements or cost constraints.
A new composite product combines a quilted microporous insulating core with the company's K-Shield® Felt AG. The composite product is lighter than conventional microporous insulating materials-11 lb/ft3 vs. 16 lb/ft3-without sacrificing insulation performance.
By using a 2300 °F felt material on the hot side, the composite material can be used at a higher temperature than the rated use temperature of the microporous core.
Image source: Morgan Advanced Materials
The aerospace industry often requires high-performance thermal management systems to maintain a consistent operating temperature or provide a fire barrier in addition to achieving its traditional thermal control goals.
These challenges may be combined with space constraints, high vibration environments, and weight constraints. Flexible and molded microporous insulating materials provide the durability, physical properties, and dimensional configurations required for aerospace applications.
The manufactured products or standard sizes meet the requirements of customers for immediate installation. Flexible insulation is a composite system consisting of a microporous core contained between high-temperature textile finishes.
In order to maintain core distribution while creating a flexible blanket, the system is then quilted with one-inch square high-temperature threads. The thickness ranges from 0.125 to 0.500 inches (3 to 13 mm), and the core density is 8, 10 and 16 pcf.
Quilted composite materials can be cut and manufactured into unique geometries and used to replace traditional fiber insulators, typically reducing the required thickness by 50% to 75%. The highest standard temperature ratings (500, 1200 and 1832 °F) are usually determined by the outer textile fabric.
In order to prevent engine heat loss, flexible microporous thermal insulation materials are widely used in many applications in the aerospace industry, including thermal insulation of engine nacelles or shells. This enhances the consistency of the internal working temperature, improves the working efficiency and protects the shell.
The product has also passed the standard 2000 °F/15-minute performance test appraisal and is used as a fire barrier for auxiliary power unit enclosures. It is also used to isolate the landing gear struts.
Molded microporous insulation materials are also used in many aerospace applications, most commonly as fire protection for flight data recorders (FDR) (called "black boxes"). It can be pressed into a metal casing and then machined into shape, or the parts can be machined from a standard molded plate into a free-standing casing.
The extremely low thermal conductivity of the material keeps the contents of the box low, especially the data collection system, to ensure that the data can be recovered after a simulated fire.
The test procedure exposes the system to 2000 °F (1095 °C) for one hour and utilizes the maximum internal temperature requirements based on the recoverability of the data collected after the test.
Although molded insulating materials provide extremely low thermal conductivity, the need for smaller FDR devices and devices that can withstand longer fire tests requires the development of improved systems. Molded Min-K formulations containing endothermic ingredients will react at higher temperatures to absorb heat.
Although the endothermic material does not change the final steady-state heat flux through the insulator, it takes longer for the system to reach steady-state, thereby improving the overall performance of the system. In addition to the fire test, the Min-K in the FDR application has also passed a number of rigorous durability tests designed to simulate aircraft failures.
Image source: Morgan Advanced Materials
Traditional refractory materials, such as castables and refractory bricks, have long been the main force in high-temperature lining construction. Due to the energy-intensive nature of typical processing industries such as steel and non-ferrous metals and rising fuel costs, heat treatment equipment requires consistent and efficient backup insulation systems.
High-performance products such as microporous insulation are beginning to gain widespread acceptance because they now meet the stringent thermal insulation requirements of industrial applications.
By using products such as BTU-BLOCK insulation materials, huge energy-saving benefits can be obtained by reducing the thermal conductivity of the lining structure. For example, many types of ladle, such as plant transfer and road ladle, are ideal applications for microporous insulation.
Ladles usually use thermal insulation refractory bricks, lightweight castables or thin fiber thermal insulation materials behind the hot surface refractories.
As a backup product, the microporous insulating material can ensure that the molten metal will not solidify when the metal stays in the ladle for a long time, thereby reducing heat loss and helping to reduce the overall lining thickness, thereby making the volume in the ladle larger.
The following example shows how to use microporous insulating materials in the ladle to minimize the degradation of expensive ladle shells due to hot spots and high shell temperatures, which is beneficial for large steel mills and improves the bottom of the ladle Safety of pouring operation.
In order to replace the previously failed fiberboard system, the company also needed a durable material. By installing a 0.375 inch (9 mm) thick BTU-BLOCK board as a backup in a 200-ton ladle, the case temperature was reduced by 15%.
In addition, the reduced heat loss enables the ladle to be completely emptied before the metal solidifies. In addition, due to the faster cooling rate of the heating ladle, the flexibility of the process flow has been enhanced. Due to better molten metal uniformity, product quality is improved.
In another example, a primary aluminum manufacturer wanted to reduce the thickness of the wall of its carbon oven in order to increase the size of the pit to add a larger anode to the electrolytic tank.
The new design combined with the BTU-BLOCK insulation material reduces the overall tube wall thickness by 6 inches (152 mm), and at the same time reduces the theoretical heat loss by 30% compared with the current tube wall design.
Continuous steel casting facilities and aluminum castings also use a large number of microporous insulating materials in the long runner section to help prevent the solidification of molten metal. They are also used in filter boxes and tundishes to keep the metal hot.
This also helps save energy costs by eliminating the need to overheat the molten metal. Other industrial applications of microporous insulation include aluminum melting furnaces, ceramic tunnel kilns, chemical processing ethylene plants, and back-up ceramic feed bowls.
The use of lightweight, ultra-low thermal conductivity microporous insulation materials in composite insulation systems, such as BTU-BLOCK and Min-K products, has many advantages, including:
This information is derived from materials provided by Morgan Advanced Materials-Thermal Ceramics and has been reviewed and adapted.
For more information on this source, please visit Morgan Advanced Materials-Thermal Ceramics.
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