Continuing efforts to develop lightweight, flexible thermal-insulation blankets that withstand high temperatures have led to design and fabrication concepts that effect the following improvements:
- Increase durability while providing adequate thermal protection to structures that would otherwise be subjected to multiple cycles of aeroconvective heating; and
- Provide for closing out the edges of insulating blankets in such a way as to minimize intrusion of water, minimize leakage of heat, provide smooth aerodynamic surfaces at joints between adjacent blankets, and accommodate thermal expansion without buckling of outer blanket surfaces.
Blankets that incorporate these improvements are denoted collectively as "durable advanced flexible reusable surface insulation," and are the latest in a series of similarly named blankets made largely of ceramic fibers.
As shown in Figure 1, a blanket of the present type includes (1) a bulk insulating layer of fibrous ceramic batting sandwiched between inner and outer ceramic fabric layers, (2) a screenlike metal fabric woven from wire, (3) an outer layer of metal foil, and (4) ceramic thread stitching. The metal fabric and foil layers are made of one or two refractory metal(s) — typically, nickel alloy(s).
In fabrication, the metal fabric, ceramic fabric, and batting layers are first stitched together as a first subassembly, using ceramic threads in a lock-stitch pattern. After stitching, the outer ceramic fabric layer is heat-cleaned. A second subassembly is then formed by attaching the metallic fabric layer to the first subassembly, and, in particular, to the ceramic fabric layer by stitching along lines that lie between the first-subassembly stitch lines. Portions of the outer ceramic and metal fabric layers protrude beyond the edges of the stitched area; these portions are stitched together with ceramic thread to form closeout extensions.
The metal-foil layer is then brazed to the metal fabric, thereby providing a relatively impermeable outer layer that helps to protect the ceramic layers against intrusion by water. Unlike in another design, there is no need to braze the metal foil to the ceramic fabric; therefore, a conventional brazing alloy can be used. (Conventional brazing alloys tend not to wet ceramic surfaces.)
After brazing, the blanket is closed out by any of three different methods, only one of which can be described in the space available for this article: A frame of fibrous refractory insulating material is placed around the periphery of the blanket. The frame can be made in sections [typically about 6 in. (≈15 cm) long] and is designed to permit flexing of the blanket on the perimeter without creating any gaps. The frame sections are attached mechanically to the surface of the structure to be protected.
Figure 2 depicts part of a frame that abuts two adjacent blanket sections. The metal-foil layer of each blanket extends onto the outer (top in the figure) surface of the frame. Pairs of rectangular opposed recesses are machined into each frame section, and rectangular openings are made in the metal-foil extensions at the locations of the recesses in the frame. A snap-fitting cover includes pairs of legs that extend through the openings into the recesses. The legs engage the recessed surfaces so as to secure the cover over the edge portions of the foil layers. The blankets are thus sealed on the surface by snapping in the cover.
This work was done by Daniel Rasky, Demetrius A. Kourtides, Daniel L. Dittman, Marc D. Rezin, Clement Hiel, and Wilbur C. Vallotton of Ames Research Center. This invention has been patented by NASA (U.S. Patent No. 5,811,168). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel, Ames Research Center; (415) 604-5104
Refer to ARC-12081.