Firebricks have been used to line furnaces and kilns for many years. These bricks are durable but usually have poor thermal insulating properties. Firebricks are also very dense. As a result, the weight of firebricks produces extra costs and complications during distribution and inconvenient limitations and burdens during installation. Also, since the thermal insulating properties of firebrick are poor, lining thicknesses must often be extensive.
More recently, blankets made from ceramic fibers have been substituted for firebricks. These blankets are light weight, possess strong thermal insulating and acoustic dampening properties, and have been a successful substitution in many applications. Ceramic fiber blankets, however, are not durable or rigid. Rather, the blankets have a felt or wool-like texture and flexibility. It is this flexibility that gives blankets good resistance to thermal and bending stresses that occur in many high temperature applications.
In some instances, the flexibility of these ceramic fiber blankets may not be desired. For example, blankets can be cumbersome and difficult to hang in the interior of a furnace shell, a typical application of thermal insulation. In other instances, blankets are prone to sagging or tearing and a gradual breakdown of the thermal insulation. As combustion liners for boilers and heaters, blankets must be held in place with special fixtures or attachment systems.
Ceramic fiber boards and other shapes have been developed to provide rigid, yet highly thermal insulating products. Numerous formulations are commercially available, creating products for a wide range of temperatures and uses. These products have a uniform composition throughout the thickness. For high temperature applications, a suitable high temperature ceramic fiber formulation would be selected. As temperatures drop through the thickness of the insulation, however, lower temperature/lower cost materials could be used. This can be accomplished by using multiple materials, but complexity and construction costs may increase. Being more rigid than blanket reduces the noise suppression characteristics of these board products as well and makes it more difficult to eliminate gaps and joints in a typical construction. Also, while ceramic fiber boards have excellent thermal shock resistance, ceramic fiber blankets have even better resistance to thermal shock.
Ceramic fiber blankets can be glued to ceramic fiber board to obtain the advantages of both product forms. However, high temperature glues or cements must be used to withstand the temperatures. Additional labor and material costs are necessary. Surface preparation is critical in permanently attaching the blanket. Catastrophic failure can result from debonding or peeling of the blanket.
Therefore, there exists a need in the thermal insulating art for rigid, light weight, self-supporting materials with flexible, heat resistant, and noise reduction characteristics. Further, there remains a need to optimize such materials by minimizing the amount of high temperature/high cost materials which end up being used at temperatures far below their capability, decreasing installed cost and maximizing thermal performance. There is lastly a need for a commercially feasible system of fabricating such materials without secondary steps of gluing or anchoring boards and blankets together.