T.O. 33B-1-12-62SECTION VIDEVELOPERS2.6 DEVELOPERS.2.6.1 Summary.This section covers the development process. Development follows penetrant application, dwell, and removal of excesssurface penetrant. The section contains basic, intermediate, and advanced information on the process theory, materials,and application procedures. The first portion is introductory in nature, discussing the functions and required propertiesof developers. The second portion is devoted to the mechanisms and theory of developers. The third portion coversdrying of the part after surface penetrant removal or application of a water base, aqueous, developer. The fourthportion describes the materials and application procedures for dry, aqueous and nonaqueous developers. The sectionconcludes with a comparison of the various types of developers.2.6.2 Fundamentals.2.6.2.1 FunctionsOfADeveloper.The basic function of all developers is to improve the visibility of the entrapped penetrant indication. The improvementin visibility is achieved through a number of mechanisms that include the following:a. Assist in extracting the entrapped penetrant from discontinuities.b. Spread or disperse the extracted penetrant laterally on the surface, thus increasing the apparent size ofthe indication.c. Improve the contrast between the indication and the background.2.6.2.2 SelfDevelopment.CAUTIONSelf-development SHALL NOT be used in aircraft and engine maintenanceinspection where service-induced flaws must be detected.Self-development is the formation of an indication without the application of a developer material. All penetrants arecapable of some degree of self-development since they will exude from a discontinuity and spread over the surface. Thecritical factors are the size and volume of the discontinuities that must be detected. A relatively large volume ofentrapped penetrant is required, and self-development is not reliable in detecting small tight flaws.2.6.2.3 MechanismsofDeveloperAction.2.6.2.3.1 CapillaryAction.Just as capillary action draws penetrant into a crack, it draws penetrant back out of a crack into the small spacesbetween developer particles.2.6.2.3.2 AdsorptionversusAbsorption.Developer action involves adsorption and absorption. Adsorption refers to the collection of a liquid on the outer surfaceof a particle due to adhesive forces. This action contributes to the developer particle build-up at a crack as the particlesadhere to the exuded penetrant. Absorption refers to the blotting action that occurs when a liquid merges into an
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