MIL-STD-1411B
during stripping or drying, PRD limits may be exceeded and contained gas will be released into the paint stripping area.
5.3.6.2.2 Caustic stripping. Paint can be stripped from cylinders in caustic solutions of varying concentrations depending on the working temperature and mechanical agitation.
a. Cold caustic solutions of 25 percent at ambient temperatures 60 to 80 °P will strip paint from submerged cylinders in 4 hours time. Such a slow process does not lend itself to production principles and saturated flanges will drain for extended periods of time over newly painted surfaces.
b. Hot caustic solutions of 25 percent heated to 150 °P ± 20 °P will strip old paint from a submerged cylinder in 10 to 12 minutes. Agitation of the solution will increase the general effectiveness of the stripping procedure more than it will decrease the stripping time. A long narrow tank of depth equal to cylinder height will lend itself to continuous monorail application.
c. Hot caustic solutions of 15 percent heated to 150 °P ± 20 °P, circulated through a coarse filter, screen, or a settling process and directed uniformly in pressure spray against the cylinder wall will strip old paint to the base metal in 10 to 12 minutes. Cylinders hanging from a monorail that will rotate as they pass through an enclosed spray cabinet for the allotted time would constitute an efficient production system.
5.3.6.2.3 Water rinsing of caustic solutions. Cold water rinsing is possible but the caustic solutions will require volumes of fresh water for flooding and must then be forced-air dried to control surface oxidation. When the caustic solution is rinsed away by hot water with a temperature of 150 °P ± 20 °P, it will leave a residual heat in the cylinder that will allow the cylinder surface to evaporate to dryness in the ambient air. Ambient drying can be controlled by circulating room air about the cylinders and exhausting a portion to control the relative humidity.
5.3.6.3 Metal surface pretreatment. The reduced metal surface shall be treated and passivated if the best adhesion and refinishing is to be achieved. The surface of a cylinder recently cleared of old paint and rust displaying the reduced metal condition will oxidize very quickly if it is not immediately protected. The metal cylinder surface should be sealed with an impervious deoxidizing prime coat, or coated with either type I zinc phosphate or type II iron phosphate chemical agents conforming to TT-C-490. Surfaces may be prepared by wash primers conforming to DOD-P-15328 or MIL-C-8514.
5.3.6.4 Prime coating. A prime coat shall be applied over treated metal surfaces as soon as possible in normal processing. Only primed cylinders are to be held in storage. After extended storage, the surfaces must be freed of oil, grease, dust, and stains before finishing. The prime coat shall be compatible with the proposed finish coat. The paint must dry hard, creating an impervious moisture seal over the base metal with a thickness of 1.0 to 1.5 mil. Por continuous operations where a minimum of time elapses (less than one hour), a deoxidizing primer such as a combination of basic zinc chromate and phenolic vinyl butyral may be used to combine the metal surface preparation and the prime coating in one operation. If such a
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