Patent Application
20090155477
The embodiments described herein generally relate to foam insulation used in connection with spacecraft fuel tanks and the like, and more particularly relate to automated spray-on foam insulation (SOFI) systems.
It is often desirable to coat various spacecraft components with an insulating coating to protect the component from very high and/or low temperatures. This is particularly the case with spacecraft fuel tanks and the like. One often-used form of coating is spray-on foam insulation (SOFI). In the SOFI process, two materials—a resin component and an isocyanate component—are mixed together and sprayed using a spray gun, resulting in an exothermal reaction that forms a tough polymeric, cellular (foam) coating on the workpiece surface.
Despite the popularity and wide use of such SOFI coatings, there is substantial room for improvement in the processes used for their formation. For example, the resulting SOFI coating often exhibits uneven thickness as well as localized bumps on its surface. For this reason, it is customary to utilize a robotic system to “shave” off a small amount of the as-deposited SOFI surface to remove any such nonuniformities. This rework increases the cost and time associated with the coating process.
Furthermore, the resin and isocyanate components are provided with a “blowing agent” that assists in movement of the materials through the gun and various hoses used in the process. As the Environmental Protection Agency (EPA) has banned certain ozone-depleting materials—many of which have traditionally been used for blowing agents—challenges remain for developing SOFI processes that utilize EPA-compliant blowing agents while at the same time maintaining or improving the quality of the resulting SOFI coating.
Accordingly, it is desirable to provide methods and systems for depositing uniform spray-on foam insulation layers on surfaces in a way that reduces rework (e.g., shaving of resulting insulation layer) and which uses desirable blowing agents in connection with the spray components (e.g., EPA-compliant blowing agents). Other desirable features and characteristics of the various embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
Methods and apparatus are provided for producing improved spray-on foam insulation layers. In one embodiment, systems and methods for forming a spray-on insulation (SOFI) coating on a structure include providing a resin material and an isocyanate material, both maintained at a temperature of between approximately 95 and 105° F., and mixing the resin material and the isocyanate material to produce a mixed material (e.g., using a spray gun having a mixing module). Using a repeated overlapping pattern having a periodicity of between approximately 5 to 10 inches, the mixed material on the structure is sprayed using a spray profile that is substantially flat and is produced at a predetermined spray distance between approximately 25-35 inches. A non-ozone-depleting blowing agent may be used.
Various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
In general, what is described are improved methods and systems for applying polymeric spray-on foam insulation (SOFI). In this regard, the following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
For simplicity and clarity of illustration, the drawing figures depict the general structure and/or manner of construction of the various embodiments. Descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring other features. Elements in the drawings figures are not necessarily drawn to scale: the dimensions of some features may be exaggerated relative to other elements to assist improve understanding of the example embodiments.
Terms of enumeration such as “first,” “second,” “third,” and the like may be used for distinguishing between similar elements and not necessarily for describing a particular spatial or chronological order. These terms, so used, are interchangeable under appropriate circumstances. The embodiments described herein are, for example, capable of use in sequences other than those illustrated or otherwise described herein. Unless expressly stated otherwise, “connected” means that one element/node/feature is directly joined to (or directly communicates with) another element/node/feature, but not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, but not necessarily mechanically.
The terms “comprise,” “include,” “have” and any variations thereof are used synonymously to denote non-exclusive inclusion. The terms “left,” right,” “in,” “out,” “front,” “back,” “up,” “down,” and other such directional terms are used to describe relative positions, not necessarily absolute positions in space. The term “exemplary” is used in the sense of “example,” rather than “ideal.” In the interest of conciseness, conventional techniques, structures, and principles known by those skilled in the art may not be described herein, including, for example, conventional SOFI processes, polymeric coatings, robotic manipulators, and the like.
Spray gun 120 is mechanically coupled to a manipulator or “robotic system” 128 that effects translation and/or rotation of gun 120 in three dimensions relative to surface 104. The speed of robotic system 128 will vary depending upon the application, but in one embodiment is between 4-25 mm/sec. Robotic system 128 maintains the desired distance 140 (d) from gun 120 to surface 104 of structure 102. Spray gun 120 includes a mixing module 122 for mixing material 130 with material 132, and a pattern control disc (PCD) configured to produce a particular spray pattern, as described in further detail below.
A variety of known spray guns 120 may be used in connection with the illustrated embodiment. In one embodiment, for example, as illustrated in
In one embodiment, spray gun 120 is fitted with a relatively “flat” PCD 124. That is, PCD 124 preferably has a relatively flat elliptical or diamond-shape aperture—e.g., one in which its width is less than or equal to approximately one fourth of its length. In one embodiment, PCD 124 is a model no. 203 PCD manufactured by Graco/Gusmer Corp. and has a 0.050″×0.010″×0.102″ aperture (respectively indicating depth, width, length). In another, PCD 124 is diamond shape and has a 30 degree, 0.020″×0.082″ mil aperture.
One of the several factors that can affect the quality of coating 106 is the size of the mix module 122 port holes with respect to the output rate (grams per second) of the spray 126. Diameter selection for the A and B port holes in mixing module 122 is preferably performed to match the respective components hose pressure settings, thus ensuring optimum mixing of the two components in the mixing chamber of the mixing module, In accordance with one embodiment, the size of these holes and the output rate for both A and B components are adjusted such that the pressure drop at hoses 131 and 133 is within an acceptable range of 200 psi or less during the spray process. This also ensures that the optimum mixing of the two materials inside the chamber of mixing module 122 is maintained. The A and B components port holes of the mixing module are sized by carefully boring the existing holes with pre-selected drill bit sizes. In one embodiment, there are four port holes in mixing module 122—two for the A component and two for the B component. The geometry of the mixing module holes are, in one embodiment, 0.042″ for A and 0.026″ for B (barrel spray) and 0.055″ for A and 0.035″ for B (dome spray). It will be appreciated that the range of embodiments are not limited to the illustrated type of spray gun and PCD.
Material 130 is generally an isocyanate material, and source 132 is generally a resin material. As mentioned above, material 130 is also often referred to in the art as the “A” component, the “ISO” component, or “the activator.” Similarly, material 132 may be referred to as the “B” component, the “RES” component, or the “Polyol” component. These terms will be used as synonyms herein. When the two materials are mixed (i.e., in mixing module 122), they react, and the resulting exothermic reaction causes polymerization, thus forming spray-on coating 160.
A variety of SOFI materials 130 and 132 are suitable for the present invention. In various embodiments, for example, NCFI 28-134 materials manufactured by North Carolina Foam Industries (NCFI) are used. Each material 130 and 120 also includes a suitable “blowing agent” mixed in to assist in pressurizing the material for transfer within hoses 131 and 133. Because of their ozone-depleting characteristics, many traditional blowing agents have been banned for use by the Environmental Protection Agency (EPA). Thus, it desirable to utilize an EPA-approved blowing agent (e.g., HFC-245fa) in the SOFI process. The NCFI materials cited above are satisfactory in this respect.
The SOFI is robotically sprayed using a robotic system 128 onto a horizontal cylindrical tank rotating in a heated and humidity-controlled booth. The tank is also heated internally during the SOFI spray. As shown in
In addition to the ambient temperature and relative humidity, the temperatures of materials A and B (T1 and T2, preferably about 95-105° F.), as well as the temperature Ts of surface 104 (preferably about 120-135° F.), are maintained at predetermined target values. Furthermore, the pressures of the materials 130 and 132 are also maintained at predetermined values. In one embodiment, the temperature of both materials 130 and 132 are maintained at approximately 100° F. (e.g., +/−5°), and the preferred pressure of A and B components is between 1000 to 1200 psi. Further in accordance with one embodiment, the surface 104 of structure 102 is maintained at a temperature of approximately 130° F. (e.g., +/−5°). In an exemplary embodiment, the ambient relative humidity is maintained at approximately 20%.
The present inventors have determined that certain selections of parameters and geometries described above lead to synergistic and/or unexpectedly favorable results with respect to the uniformity of the resulting SOFI coating. That is, coatings that are sufficiently uniform that they do not require any trimming of waves and or bumps as is common in prior art systems. In a particular embodiment, for example, a highly satisfactory coating is produced using materials 130 and 132 having the properties of NCFI 28-134 describe above and maintained at temperature of about 100° F. The materials are sprayed on using a PCD having a relatively flat geometry, wherein the spray distance 140 is substantially equal to 30″ to 40″, the temperature Ts of surface 104 is maintained at about 130° F., and the overlap between layers (i.e., the periodicity of adjacent layers) is reduced to between 5″ and 10″.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the described embodiments in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope as set forth in the appended claims and the legal equivalents thereof.
