Testing Water Suspended Developer

T.O. 33B-1-1 1-39 a. Performing a check of the touch-up, spray hydrophilic remover concentration SHALL be accomplished by one of the methods explained in paragraph 1.5.5.4.1. The concentration of the spray remover is much lower than immersion baths, and the results of the check must reflect this change. Important items to remember are: (1) If the touch-up, spray hydrophilic remover is not of the same batch as the remover in the immersion tank, a new graph SHALL be plotted for the touch-up material. (2) Make sure that the temperature of the touch-up remover is within the parameters of the instrument/graph being used or compensated for. b. The penetrant-material system concept SHALL apply to the hydrophilic remover use in the touch-up step of the penetrant inspection. The material being used in the immersion remover tank and as touch- up spray SHALL be of the same manufacturer. 1.5.5.5 Testing Water Suspended Developer. NOTE When taking a specific gravity reading to determine the concentration of in-use suspendible or soluble developer, the following SHALL apply: suspendible developers SHALL be thoroughly agitated immediately prior to taking the specific gravity reading; whereas, soluble developer SHALL NOT be stirred or agitated after its initial mixing. There are a number of service factors that affect the performance of water suspended developer. Most significant are concentration changes, closely followed by contamination problems. Concentration may vary for a number of reasons. Evaporation of the water will increase the concentration, causing excessive coating thickness. Prior to using a new solution, a working level should be established by measuring the distance from the top of the tank to the solution. This working level should be maintained by the addition of water to replace evaporation losses. As parts are processed, developer is removed due to the film adhering to the surface, plus some developer is entrapped in recesses. This loss of developer is termed drag-out and, unless concentrate is added, will reduce the concentration of the developer. Reduced concentration results in thin coatings that decrease the sensitivity of the system. Inadequate agitation will allow some of the developer particles to settle out which also reduces concentration. It is also possible for the developer particles to cake on the bottom or in the corners of the tank preventing them from being suspended. The wetting agents in the developer can remove some of the entrapped penetrant causing fluorescent dye contamination. Developer solutions SHALL be periodically tested to assure acceptable performance (see paragraph 1.5.1.5 for frequency). Suspended developer baths SHALL be tested for concentration using a hydrometer. The hydrometer indicates specific gravity that is proportional to the amount of developer particles in suspension. Prior to obtaining the hydrometer reading, the working solution SHALL be filled to the proper working level, thoroughly agitated, and the tank checked for caked particles on the bottom or in the corners. Newly prepared solutions SHALL NOT be used or checked for concentration until 4 hours after mixing. This aging period is to allow the developer particles to become wetted or saturated. The solution must be stirred after the aging period. The hydrometer may be placed directly in the tank, and when floating free and not touching the tank sides, the specific gravity can be read from the scale. It may be more convenient to take a sample from the tank using a long, narrow glass container such as a graduated cylinder, which is deep enough to float the hydrometer. Figure 1-7 is a graph of specific gravity versus concentration for two water suspended developers illustrating the variation that can occur in the specific gravity’s of different water suspended developers, even from the same manufacturer. The supplier can provide an accurate conversion chart for the specific developer, which SHALL be used when checking the developer concentration.