Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
1999-10-14
2002-01-22
Beck, Shrive P. (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C427S215000, C427S221000, C427S385500, C427S421100, C106S672000, C106S674000, C106S676000, C524S009000, C524S016000, C524S492000
Reexamination Certificate
active
06340498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to porous materials and more particularly to a porous composition for use in an environment of variable pressure and/or variable temperature.
2. Description of the Related Art
The Payload Fairing (PLF) is the portion of a launch vehicle that encloses the payload, i.e., satellite. One purpose of the PLF is to protect the satellite from the loads and aerodynamic heating associated with launching the satellite into space. Another is that the PLF protects the satellite from contamination, as even the smallest particle of dust or debris could render the satellite useless. The PLF and all parts of the PLF must be designed so that substantially no particles, dust, or any other type of possible contamination would fall onto the payload.
In order to protect the PLF structure from the effects of aerodynamic heating, a thermal protection material is placed over the PLF structure, particularly over the nose on the front of the PLF, which receives the majority of aerodynamic heating. One such thermal protection material is known as MCC-1 (for NASA Marshall Convergent Coating). This material was developed by NASA for use on the Space Shuttle, but is also used by the Air Force on the PLF of the Titan IV launch vehicle. MCC-1 is applied robotically and requires the use of an ancillary material, to repair the MCC-1 and to fix application defects. To repair MCC-1 NASA uses what is known as K5NA, a mixture of epoxy and cork, that serves the NASA application on the solid rocket motors of the Space Shuttle well. But, the solid rocket boosters do not have the same contamination requirement as the Titan IV PLF. Testing showed that the NASA repair material (i.e., K5NA) would not meet the Titan IV PLF contamination-free requirement. It was demonstrated that small pieces of the NASA repair material would break off during flight. Since the portion of the PLF that needed the most thermal protection material was the forward nose cone of the PLF, i.e., directly in front of the payload, any particles coming off the repair material were almost certainly going to contaminate the payload.
It was found that “popped off” small pieces of the repair material were the result of air being entrapped in the material during the process of mixing the ingredients. The aerodynamic heating of the material increased the pressure of the entrapped air, while at the same time the external air pressure was dropping to the vacuum of space. In addition, the heating reduced the strength of the repair material. As a result the repair material failed, leading to the generation of the “pop off” particles. MCC-1 did not suffer this same fate, because MCC-1 was permeable, allowing the entrapped air to escape without doing damage to the material. The inherent permeability of MCC-1 was the result of the fact that the material was sprayed onto the PLF. MCC-1 had air inside of the material, which increased its efficiency as a thermal protection material, but the air was not entrapped. MCC-1 was permeable, allowing any air in the material to escape as the local air pressure dropped, or the air expanded due to the aerodynamic heating. Because of the robotic application of MCC-1, it was not a suitable repair material, particularly at the launch site, located away from the factory at which MCC-1 was applied with special equipment.
It was found that pulling a vacuum on the NASA repair material after mixing the ingredients removed the larger air bubbles, but did not make the material permeable. As a result, when the repair material was used to cover MCC-1, the air entrapped in the MCC-1 pushed pieces of the repair material off. It was clear that a material that could easily be mixed, applied by hand or with a simple spray process, cured at ambient conditions (~50° F. to 90° F.), and was permeable, was required.
U.S. Pat. No. 4,204,899, issued to Walker et al., entitled “Cork-Resin Ablative Insulation for Complex Surfaces and Method of Applying the Same,” discloses a cork-resin ablative insulation material, which may be applied to complex surfaces. The material is intended for broad coverage and is limited to resins that can be B-staged to form the thin, pliable cork sheet that is applied to the surface. It could not be used to fill in nicks, blemishes or other defects. Since it contains 20 to 60 weight percent resin, the cork content would be 40 to 80 weight percent. Such a large concentration of cork would not yield a material that could be worked by hand, or troweled onto a surface. Present applicants' investigations have revealed that if more than 20 weight per cent cork (~90 volume percent due to the differences in density of the resin and cork) is used, the material will not hold together or bond to the substrate to be repaired, e.g., MCC-1.
U.S. Pat. No. 3,844,863, issued to Forsythe, et al., entitled “Repair of Wooden Articles,” discloses a method to repair defects and holes in wood. In a preferred composition, the comminuted cork comprises from 3 to 10 percent by weight of the mixture. Such low weight percentages of cork would not achieve the desired effect of a contamination-free thermal insulator in a variable temperature/variable pressure environment.
U.S. Pat. No. 4,031,059, issued to Strauss, entitled “Low Density Ablator Compositions,” discloses two types of highly filled, elastameric silicone-base ablative compositions whose densities range from about 0.2 g/cc to about 0.3 g/cc. One type is a carbon char-forming, high thermal efficiency ablator containing at least 92% by volume of low-density filler with a total filler-to-resin volumetric ratio of at least 16 to 1. The material's core content is too high to allow its application in a hand-packing mode. It would have to be molded into final shape, obviating its ability to act as a repair material. The second type of material disclosed by Strauss is a silica char-forming, RF-transparent ablator containing at least 90% by volume of low-density filler with a total filler-to-resin volumetric ratio of at least 11 to 1. Again, this material would have to be molded into final shape, obviating its ability to act as a repair material.
U.S. Pat. No. 4,077,921, issued to Sharpe, et al., entitled: “Sprayable Low Density Ablator and Application Process,” discloses a sprayable, low density ablative composition having 100 parts by weight of a mixture of 25-65% by weight of phenolic microballoons, 0-20% by weight of glass microballoons and 4-10% by weight of glass fibers, 25-45% by weight of an epoxy-modified polyurethane resin, 2-4% by weight of a bentonite dispersing aid and 1-2% by weight of an alcohol activator for the bentonite; b) 1-10 parts by weight of an aromatic amine curing agent; and c) 200-400 parts by weight of a solvent. These additives are insufficient to achieve permeability effects required to prevent “pop-off.”
U.S. Pat. Nos. 4,772,495 and 4,837,250, both entitled “Trowelable Ablative Coating Composition and Method of Use,” both issued to Headrick et al. disclose coating compositions which have insufficient quantities of cork particle to prevent pop-off.
U.S. Pat. No. 5,064,868, issued to Simpson et al., entitled “Sprayable Lightweight Ablative Coating,” discloses another composition with insufficient quantity of cork to prevent pop-off in a variable pressure/variable temperature environment.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to meet the contamination-free requirements of the material to be used in a variable temperature and/or variable pressure environment.
Another object is to provide a material that could be either sprayed onto hardware or applied by hand.
Another object is to provide a composition, which can be applied in ambient conditions.
Yet another object is to provide a composition that is thermally insulative.
These and other objects are achieved by the present composition, which in its broadest aspects comprises a mixture of a binder and a particle material. The mixture has 50 to 90 volume percent of the particl
Kirby John Stephen
Watcher John Miles
Beck Shrive P.
Calcagni Jennifer
Ginsberg Lawrence N.
The Boeing Company
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