MIL-STD-2199A
NOTE: The AFT flanges of controllable pitch propeller (CPP) shafts are clad in Inconel by design. Therefore, they do not require the additional preservation as identified in 5.2.3.
5.3 Estimation and preparation of the basic materials required. This section covers the calculation of the amount of primer, elastomeric coating, sealing/fairing compound, fiberglass tape, and laminating resin required for the four-layer shaft covering system and their preparation for application.
5.3.1 First layer - primer. The primer coverage will vary depending on the application method. For estimation purposes, allow 1 gallon for every 60 linear feet of shafting.
5.3.2 Second layer - elastomeric coating. At a thickness of 10 mils (0.010 of an inch), the coverage is approximately 160 ft2/gallon for an approximate shaft diameter of 30 inches. That is, at a 10-mil thickness, one gallon should cover about 25 linear feet of shafting. At a thickness of 20 mils, the coverage is approximately 80 ft2/gallons, meaning one gallon should cover about 12 linear feet of shafting. The amount of elastomeric coating remaining in the hose shall be accounted for when determining the amount of elastomeric coating required.
5.3.3 Third layer - sealing/fairing compound. The sealing/fairing compound is a two-part polysulfide that shall be used to fair the shaft to the sleeve at subject interface. Sealant shall be applied only to the sleeve end and
adjacent shaft in a swath no more than 12 inches wide. The application thickness shall be approximately 20 mils (0.020 of an inch), which corresponds to approximately 1.75 ounces/ft2. Thus, the ounces of sealant required to cover the 1 linear foot of sleeve end (which includes the shaft and sleeve) can be estimated as:
Ounces of sealant/foot = (1.75) x (shaft circumference in inches)/12.
For example, if the shaft is 72 inches in circumference, sealant coverage will require approximately 10.5 ounces per linear foot. However, since sealant is used to fair the shaft to the sleeve, it is thicker at the sleeve end. In addition, a significant amount of the sealant will remain in the mixing container. Therefore, about 1 pound of mixed sealant
will be required to fair each sleeve end. Partial kits can be mixed if necessary by following the instructions in the technical data sheets. This shall require weighing the individual components.
5.3.4 Fourth layer - GRP.
5.3.4.1 Laminating resin. Estimate the total amount of epoxy laminating resin (including hardener) required by using 1 gallon of resin for every 81.5 square feet of tape per layer times five layers (four layers of tape and the finish coat). The 81.5 square feet per gallon is based on resin requirements per layer of fiberglass tape to provide thorough wet-out. The total amount of resin can also be estimated on a mass basis by multiplying the total mass of tape (all four plies, as determined in 5.3.4.2.2) by a factor of 2. Using a factor of 2 will provide a sufficient excess of mixed resin for coating the shaft and thoroughly wetting-out the fiberglass tape.
5.3.4.1.1 Example of epoxy laminating resin calculation based on weight. Four 41-foot lengths of 6-inch tape would have a mass of approximately 5.5 pounds.
Total mass of resin = 5.5 pounds x 2 = 11 pounds.
WARNING: The resin and hardener shall not be mixed together until immediately prior to use, since the mixture will have a limited working life.
5.3.4.1.2 Preparation of epoxy laminating resins. Since epoxy resins have limited pot or working life, especially in warm temperatures, separate batches of resin may need to be prepared for each of the four layers of glass tape. It is recommend that epoxy laminating resins be selected that are available in kits of approximately one gallon. This eliminates the need for weighing out resin-to-hardener ratios, eliminates the potential errors that can occur during weighing of the resin and hardener, eliminates mass-effect on pot life, and provides a convenient batch size.
NOTE: Mass-effect accelerates curing which results in reduced pot life. Resin is a poor heat conductor, so with larger resin volumes, more heat is produced, resulting in higher curing temperatures that further accelerates the chemical reaction.
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