MIL-STD-2199A APPENDIX A
GRP
FIGURE A-15. Schematic showing the GRP.
NOTE: The application steps described above represent the basic method of application and the one most likely to produce good results under all conditions. Variations on this method are possible and permissible provided the end result is not degraded. For example, it has been reported that the covering layers can be applied faster if two layers are applied at the same time, starting at opposite ends of the shaft. However, there are some cautions that shall be kept in mind. The second layer shall not be applied over the first layer until the resin has had time to wet out the first layer. Otherwise, there is a risk of trapping dry fiber and air bubbles in the underlayer. The amount of time the wet out requires depends on the particular resin system used as well as the temperature of both the shaft and the air.
If wraps are being applied from opposite ends, it may be necessary to end one wrap before the other approaches it in order to allow sufficient time for wet out to occur before the one layer overlaps the other. When wet out has
occurred, the passing layer can proceed over the stopped layer and after wet out at the junction, the stopped layer
can be continued over the passing layer. The junction of the stopped layer shall be made with an overlap wrap as would be used when making a joint at the end of a roll of glass tape. When two layers are applied at the same time, after they cross, additional resin shall be applied to the bottom layer to provide wet out up through the next or passing layer. This is the same as if the layers were being applied one at a time. However, as noted above, the resin shall not be applied to the under layer until wet out has occurred so as not to trap air bubbles in the underlayer. It is always better to have the resin wet its way up through the glass tape, pushing out the air, rather than to put the resin on the dry tape and have it wet down into the glass tape, whereby the air has to work its way out through the resin. Modifications to the basic method may be possible but it is the end product that counts. There shall be no loss of quality in the finished covering.
A.3.2.5 Cure. The shaft shall continue to rotate during the curing period until the resin has gelled, preventing the resin from draining and forming runs or globules on the lower part of the shaft. If the shaft cannot be rotated continuously, even periodic 120-degree turns will be helpful to prevent runs and drainage. If the shaft cannot be rotated at all, any globules of resin on the underside of the shaft shall be removed periodically, until the resin has gelled. Just before the resin gels during the curing reaction, the resin will heat up (exotherm) and the viscosity will be reduced. This will cause accelerated draining from the glass wrap and resin may need to be added to the top
until it gels in order to obtain a quality laminate. Cure time for some resins will be approximately 24 hours at 73 °F but the resin manufacturer shall be consulted for a specific resin's cure characteristics. A longer cure time shall be required at 60 °F. Cure time may be shortened appreciably by raising the temperature of shaft and environment up
to 100 to 125 °F. Temperature shall not exceed 125 °F in order to avoid an overly rapid cure or excessive thermal
expansions. The cured covering shall be smooth, hard, and tack free. After hardening, if the shaft is to be moved, it shall be wrapped in plastic and heavy paper or canvas to protect the GRP coating from being scratched or scored.
A.3.2.6 Painting. The covered shaft body area(s) and sleeve ends shall be painted by the shaft installation activity in accordance with S9086-VD-STM-010/631. Surfaces in way of bearings shall not be painted. Refer to S9086-VD-STM-010/631 for specific details on paint formulas, their application, and the type and number of coats of anti-fouling paint to be used.
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