MIL-STD-866C
damage. Parts shall be stripped if evidence of plate or base metal damage is found during the penetrant inspection. Re-inspect base metal in accordance with 5.3.2 and
5.3.3.
5.3.6 Penetrant inspection. Penetrant materials with SAE-AMS-2644, Level 3 sensitivity shall be used in accordance with ASTM E1417. Penetrant, emulsifier (if used) and developer dwell time shall be used that produce light background fluorescence from the chromium plate micro-cracking. Anodic etching of the chromium plate (0.0001 inch plate removal) is recommended as the preparation of the surface for inspection. Indications of damage include spiraling, chattering and coarse "mud-flat" cracking. The inspection procedures developed shall include photographs for inspection reference of
all rejectable conditions as well as acceptable conditions.
5.3.7 Magnetic particle inspection. Wet, continuous, fluorescent methods in accordance with ASTM E-1444 shall be used. Magnetizing currents and methods shall be used that provide adequate field strength in the part, yet do not cause burning. Because of the poor adherence of particle indications to the smooth chromium surface, the procedures developed shall minimize the chances of indication "wash-off."
5.4 Grinding practices. The grinding practices set forth in these paragraphs are recommended for optimum results under variety of, but not all, conditions. Such practices are not intended to restrict the contractor from developing technology or methodology other that described herein provided the resulting part meets prescribed criteria.
5.4.1 In-house control document. In-house control documents are those documents used by each contractor to control part configuration and quality. They include engineering drawings, engineering process specifications, manufacturing process specifications, inspection procedures and any other documents designed to control manufacturing and inspection techniques. Such documents are to be based upon proven techniques derived from parametric studies, experience, and tests.
5.4.2 Parametric studies. Parametric studies refer to the techniques used by the contractor for the purpose of the initial establishment of grinding practices and inspection procedures that will consistently produce parts within the design criteria. The equipment, grinding wheels, coolant, material, heat treat, and prior processing, feeds, speeds, shall simulate the production techniques used as closely as is reasonably possible. The number of samples used shall be a matter of the contractor's judgment but shall be sufficient to prove the practice and inspection procedure.
5.4.3 Grinding practice guidelines. Grinding practices include control of all the following factors. Lack of control or improper selection of any of these factors can cause decrease in structural integrity.
5.4.3.1 Grinding equipment. The grinding equipment shall be capable of operating in the required wheel speed, feed rate, and work speed ranges, and shall have adequate horsepower to maintain required wheel speed and shall be in good mechanical condition (spindle and bearings).
5.4.3.2 Grinding wheel characteristics. Grinding wheel (normally friable or semi-friable aluminum oxide) in a relatively soft grade normal to open structure, and
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