MIL-STD-2199A
5.1.2 Second layer - elastomeric coating. The second layer of the shaft covering system shall be an elastomeric coating, specifically an epoxy cured with polysulfide, in accordance with A-A-59875, Type II. Two different colors shall be used. The first coat shall be gray in accordance with A-A-59875, Type II, Class 1, and the second coat
shall be black in accordance with A-A-59875, Type II, Class 1.
5.1.3 Third layer - sealing/fairing compound. The third layer of the shaft covering system shall be a polysulfide sealing/fairing compound in accordance with A-A-59875, Type III that shall be applied to the shaft/sleeve interface. Specifically, the sealant shall be applied at the sleeve end to fair the shaft to the sleeve. The sealant shall also be used as a filler material (see 5.2.2) for allowable pitting.
5.1.4 Fourth layer - GRP. The fourth and final layer of the shaft covering system shall be the GRP.
5.1.4.1 Laminating resins. The laminating resins which are used in the GRP are viscous liquids that cure at room temperature into hard, insoluble, plastics. The resin used shall meet the performance requirements of MIL-R-
23461. Although MIL-R-23461 specifies either of two different types of resin systems (i.e., epoxy or polyester), an epoxy resin shall be used for the shaft covering. The reason for this is that epoxy resins adhere strongly to cured
polysulfide. Epoxy resins are mixed as A/B (two-part) kits. The entire kit shall be used to avoid errors in measurement when mixing the epoxy. Pot life of an epoxy resin and associate hardener depends on the ambient
temperature, but it is approximately 45 to 60 minutes (see 5.4).
5.1.4.1.1 Cure. Once the hardener or catalyst has been added and thoroughly mixed with the resin, the epoxy will remain liquid for a limited period of time after which it will begin to gel or thicken and become unworkable. The resin shall cure at room temperature (or according to the manufacturer's instructions). However, optimum properties can be developed in a shorter time by post curing or heating at moderate elevated temperatures (i.e., 120 to 140 °F). Infrared lamps and strip heaters are convenient sources of heat. Post curing shall be used to obtain optimum cure particularly for coverings applied in cold weather or coverings that shall be put in service as soon as possible.
5.1.4.2 Glass reinforcement. Glass reinforcement shall be woven fiberglass tape with a flat selvage on both edges to prevent fraying, in accordance SAE-AMS3824, style 7500, or SAE-AMSC9084, Type XII A. The surface finish, or sizing, shall be epoxy compatible. The width of tape shall depend on the diameter of the shaft. Four-inch wide tape shall be used for shaft diameters 8 inches and less. Six-inch wide tape shall be used for shaft diameters greater than 8 inches.
NOTE: The tape widths outlined above are specified for ease of application. Wider tapes are more difficult to apply and attain a quality finished product. The skill and experience of the laminating team is the limiting factor for the width of tape used.
5.2 Auxiliary materials. Additional material requirements are as follows:
5.2.1 Thixotropic filler (thickening agent). The addition of a small amount (2 to 4 percent) of a thixotropic filler (supplied by resin vendor), or other commercial source, to the epoxy laminating resin shall be used to minimize or eliminate resin drainage from the GRP if applied to a stationary shaft.
5.2.2 Fairing compound for shaft. Irregular surfaces (i.e., allowable pitting and/or approved excavations) shall be filled and smoothed using fairing/sealing compound prior to application of the elastomeric coating, and allowed to cure.
5.2.3 Coating for flange couplings. All waterborne shaft flange assemblies housed within rotating coupling covers shall receive the elastomeric coating (i.e., second layer) described herein. The same shall apply to all new acquisition spare shafting assets. Additionally, all waterborne flange assemblies previously coated with any alternative paint system shall likewise receive the elastomeric coating (i.e., second layer) outlined herein upon renewal/overhaul of the shaft assembly (see Appendix A).
NOTE: Some older ship classes do not possess rotating coupling covers in way of waterborne shaft flange assemblies (i.e., CVN 65 and LPD 7 Class). Instead, their waterborne flange assemblies possess either two (2) coats of an epoxy conforming to MIL-PRF-23236, Class 2 or a resin formulation. For these particular ship classes, upon refurbishment of their respective waterborne shaft sections, the subject flange assemblies shall receive the elastomeric coating (i.e., second layer) specified herein prior to application of either the epoxy or resin formulation.
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