MIL-STD-869D
5.1.4 Preheat. Preheat before spraying to remove all moisture and provide expansion. Manufacturer's bulletin should be followed regarding substances and material to be sprayed. Temperature control may be accomplished using temp stick or pyrometers.
5.1.5 Spraying. Spray the area to be coated using the gun to work distance recommended by the equipment manufacturer's for the material being sprayed. The direction of the metal spray should be as close to 90°F as possible with the surface being coated and never less than 45°F. The coating shall be allied in multiple passes. Complete area coverage must be made with each pass before the next pass is started. Spraying will continue until the coating thickness plus finishing allowance has been completed.
5.1.6 Remove Masking. Remove masking material.
5.1.7 Sealing Sprayed Coatings. All flame sprayed parts should be sealed unless intended as a bearing surface or as otherwise specified by engineering. Only, quality commercial sealers shall be used. Type of sealer used depends on the type of environment parts will be subjected to.
5.1.8 Finish Machining and Grinding. Remove the overspray and flash spray material build-up to prevent cracks form extending into the main coating immediately
after spraying. Finish machine or grind in accordance with MIL-STD-866 and/or updated manufacturer's bulletins to the dimension specified or as shown on the blueprint.
5.2 Quality Control
5.2.1 Workmanship. The sprayed coating shall present a uniform appearance with a fine-to-medium granular finish. Surface defects of the coating shall be limited to nodules not exceed 0.045 inches in diameter and shall not exceed 0.025 inches above the surrounding sprayed surface. The following shall be cause for rejection:
a. Blisters b. Cracks
c. Chips or loosely adhering particles
coating.
d. Oil or other internal contaminations that bleed out through the finished
e. Fits that expose the undercoating or base metal.
f. Chips, cracks or tears of the coating after final machining
5.2.2 Testing. The most reliable test for any flame-sprayed coating is satisfactory performance in service and/or simulated service testing. Whenever service testing cannot be performed, the following tests shall be used as a method of controlling the quality of the flame-spray coatings.
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