T.O. 33B-1-12-582.5.5.4.4 ApplicationofRemover.The removal of excess surface penetrant using hydrophilic removers can be accomplished through the use of eitherimmersion or spray technique, or a combination of both. Each technique offers certain advantages along withdisadvantages that are discussed in the following paragraphs.2.5.5.4.4.1 ImmersionTechnique.a. Procedure. The primary advantage of the hydrophilic immersion technique compared to the spraytechnique, is its effectiveness on hollow or complex geometry parts where the configuration interfereswith the spray impinging on the part surface. In use, the part or parts are immersed in the remover tankwhile still wet from the pre-rinse. The principal mode of action is a detergent mechanism. A slightagitation is necessary to bring fresh solution in contact with the surface. Agitation can be movement ofthe part through the solution, but is most usually produced by an air manifold in the bottom of the tank.Excessive agitation that is evidenced by foaming SHALL be avoided. Time of immersion depends on alarge number of factors and will vary between 30 seconds and 2 minutes. The maximum time of 2minutes is seldom necessary, except on very rough surfaces or when remover is depleted.b. RemoverConcentration. Each penetrant manufacturer has its own formulation that varies inaggressiveness. The concentrations of hydrophilic emulsifier (in water) used for qualification areidentified in the Qualified Products List (QPL) and should not be exceeded without approval from thecognizant engineering authority. Caution must be exercised when changes in suppliers are involvedbecause the required concentration may change. Penetrant and remover are qualified as a system (seeparagraph 2.2.5.3) and SHALL NOT be interchanged.c. PenetrantTolerance. One of the disadvantages of the hydrophilic immersion technique is the remover'slimited tolerance to penetrant contamination. As parts are processed, the amount of penetrant in theremover gradually increases. If the removal process is closely timed, penetrant contamination willreach a point where a distinct performance change occurs. The amount of penetrant causing thisperformance change is called the remover's penetrant tolerance point or level. The amount of penetrantthat can be tolerated is directly related to the concentration of the remover and sensitivity level of thepenetrant. Typical tolerance levels for a remover concentration of 33% is 5% to 6% for a SensitivityLevel 3 penetrant and 3% to 4% for a Sensitivity Level 2 penetrant.d. BathAppearance. A freshly mixed remover bath is a transparent or clear, pink solution. During use,as penetrant is removed from the parts and retained, the bath becomes turbid or cloudy with distinctcolor change. As additional parts are processed and the penetrant tolerance point is approached,globules of penetrant will rise to the surface, and then slowly disperse back into the mixture. This effectis not usually noticed in an agitated bath, but is visible when the agitation is shut off. When thepenetrant tolerance point is reached, the penetrant will remain floating on the surface. A characteristicof the bath is that the excess penetrant does not spread across the surface, but collects at the sides. Theremover will continue to function in this condition, but at a very reduced rate. A problem with usingthe remover after the penetrant tolerance point is reached, in addition to the longer removal time, is thetendency of the floating penetrant to deposit on the part as it is withdrawn from the solution. Thisresults in an objectionable background. If the bath is to be used after the tolerance point is reached, themajority of the floating penetrant should be removed. This can be done by wiping the tank edges withabsorbent newspaper, paper towels, or rags.2.5.5.4.4.2 HydrophilicSprayTechnique.a. Procedure. Hydrophilic remover can be applied by spraying the part with a mixture of water andremover. This method of application has several advantages: it does not require a separate tank; itworks well on simple contoured parts; and it can be easily automated. The procedures and equipmentare identical with those used in spray rinsing, (see paragraph 2.5.4.5). The usual concentration range is
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