Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Reexamination Certificate
1999-04-08
2001-10-30
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
C134S022190, C134S026000, C134S029000
Reexamination Certificate
active
06308720
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods for cleaning metallic material surfaces and, more specifically, to a method for precision-cleaning the inner wall surfaces of large containers such as aluminum alloy launch vehicle booster propellant tanks with complex isogrid structured inner wall surfaces.
BACKGROUND OF THE INVENTION
The cleaning of structures having metallic surfaces can often pose various challenges. This is especially the case after fabrication, when complex residues may be found on the surfaces of the structure. Such residues may contain, for example, macroscopic and microscopic metallic particles produced by cutting and smoothing processes during fabrication; organic oils, greases and other lubricants used during fabrication; various fibers from fabrics used in initial cleaning and handling of the structure; and microscopic particles and fibers from the environment. These residues are often a combination of materials. Particulate residues embedded in heavy organic greases usually cannot be removed by washing with water because water will not dissolve or displace the grease. Some solvents that dissolve or displace the residues are generally either too expensive to apply on a large scale or they are a threat to the environment, such as ozone depleting chemicals.
Further, the cleaning of the interior wall surfaces of large container structures can be challenging, especially when it is necessary to precision-clean such surfaces, i.e. to remove not only macroscopic quantities of metal particles, hydrocarbons, and other residues, but also microscopic quantities of such residues. This is the case with the booster tanks of space launch vehicle booster propellant tanks. The inner wall surfaces of such tanks may not to be smooth surfaces. Instead, in some instances, the inner wall surfaces of launch vehicle propellant tanks are complex, having a multiplicity of ridges and test components that extend radially inwardly away from the walls into the internal containment area of the tank, and that may abut or intersect to form corners. Particles and organic residues remaining after the launch vehicle propellant tank fabrication process may adhere to and become lodged against these ridges and components and the corners formed by them, making cleaning difficult. The inner wall surfaces of launch vehicle propellant tanks having an isogrid structure are especially prone to this problem. Such tanks may be fabricated from aluminum panels. Achieving an isogrid structure (e.g., for lightweight and structural strength considerations) on the inner wall surfaces of the panels may involve a process of “hogging out” large quantities of aluminum, leaving numerous large and small aluminum particles on the panels. In addition, the process of hogging out the panels may employ various organic lubricating oils and greases, such that residues of these materials are also left on the inner wall surfaces of the panels making up the launch vehicle propellant tank. Wiping the inner wall surfaces with solvent dampened fabrics removes a significant quantity of these residues. Yet, such physical methods of cleaning are generally not sufficient to precision-clean the surfaces to be substantially free of macroscopic and microscopic residues and are not practical to clean large structures like launch vehicle tanks. In addition, the common practice of physically wiping the inner wall surfaces of launch vehicle propellant tanks may leave behind fibers from the fabric cloth or pad used to wipe the panels. The presence of even small quantities of such residues can cause a fire hazard when the launch vehicle propellant tanks are filled with liquid oxygen. Also, such residues can cause degradation in the performance of the propellants so affecting the efficiency of the launch vehicle's rocket engine.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for precision-cleaning the inner wall metallic material surfaces of large containers (e.g., aluminum alloy launch vehicle propellant tanks).
A further object of the present invention is to provide a method for removing particulates (e.g., particles and fibers, etc.) and organic residue from complex isogrid surfaces comprising a metallic material, such as aluminum alloy.
The present invention achieves one or more of these objectives by providing a method for removing particulate and organic residue from complex surfaces of large structures such as launch vehicle propellant tanks. More specifically, the method of the present invention generally includes the step of applying an aqueous cleaning solution comprising sodium silicate, sodium tetrafluoroborate, and sodium molybdate to the aluminum alloy inner wall surfaces of large structures, such as launch vehicle propellant tanks, to displace and disperse aluminum particles and other particulate and organic residue that may adhere to such surfaces. Utilization of this particular aqueous cleaning solution results in a substantially particulate and residue free inner wall surface. In one embodiment, the method of the present invention includes the steps of applying the aqueous cleaning solution to the aluminum alloy inner wall surface of a launch vehicle propellant tank to remove contaminants by displacement and rinsing the inner wall surface with water to further remove the used cleaning solution with suspended contaminants. For purposes of further enhancing the cleaning process, the method of the present invention may include, prior to the step of applying the aqueous cleaning solution, the step of applying the water to the inner wall surface of the tank to wash the inner wall surface. This step of applying the water wets the inner wall surface, removes gross contaminants such as aluminum particles, and inhibits drying of the cleaning solution during the subsequent applying the aqueous cleaning solution step. In order to enhance the cleaning process, the method may further comprise the step of selecting water to be used in the applying water step having a purity better than the desired cleanliness of the surfaces to be cleaned. Such purity may be achieved by a variety of methods such as filtration or deionization.
In another embodiment, the method of the present invention includes the steps of applying an aqueous cleaning solution comprising sodium silicate, sodium tetrafluoroborate, and sodium molybdate to an aluminum-containing inner wall surface of a tank to wet, loosen, and then displace contaminants, rinsing the inner wall surface with the water to further remove the used cleaning solution with suspended contaminants, and testing the resulting effluent cleaning solution for an indication of hydrocarbon contaminants and testing the resulting effluent rinse water for particulate contaminants, and residual cleaning solution to determine the efficacy of the cleaning process. In one embodiment, the step of testing is conducted after the step of applying the aqueous cleaning solution to determine whether the level of hydrocarbon contaminants in the effluent cleaning solution is excessive (e.g., above a first acceptable level of hydrocarbon contaminants). In another embodiment, the step of testing is conducted after the step of rinsing the inner wall surface with the water to determine whether the level of particulate contaminants and residual cleaning solution in the effluent rinsing solution is excessive (e.g., above a first acceptable level of particulate contaminants and above a first acceptable level of residual cleaning solution). In the event these testing steps indicate the presence of contaminants and/or residual cleaning solution above acceptable levels, then the method of the present invention contemplates repeating the applying and/or rinsing steps.
In a further embodiment of the invention, the method includes the steps of sequentially applying the above-noted cleaning solution and the water rinsing to at least upper and lower sections of the inner wall surface of a vertically oriented tank (e.g., launch vehicle propellant tank). In this embod
Chaudhry Saeed
Gulakowski Randy
Lockheed Martin Corporation
Marsh & Fischmann & Breyfogle LLP
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