T.O. 33B-1-12-512.5.4.5.2 FactorsInfluencingEffectivenessofSprayRinse.2.5.4.5.2.1 SizeofWaterDroplets.Removal of excess surface penetrant depends upon the mechanical force of the water impacting the part surface. Theimpact force consists of the droplet mass and velocity at impact. The two factors are related, and increasing either willproduce a higher mechanical force. There are limits on both size and velocity; the latter is derived from the waterpressure. If the droplet is small or if the pressure is too high, the result will be a fog or mist with little removal ability.On the other hand, a solid stream of water, as shown in Figure 2-17, is not desirable either because it covers only asmall area at one time and is actually one large continuous drop.Figure 2-17. An Improper Washing Procedure.2.5.4.5.2.2 WaterPressure.The effect of water pressure is straight-forward. Increased water pressure increases the speed of removal. However,excessive pressure can atomize the water into a fog that is useless for removal. Normal line pressure, approximately 10to 35 psig, is acceptable and is generally used. Water pressures in excess of 40 psig or injection of compressed gases orair into the water system SHALL NOT be used.2.5.4.5.2.3 WaterTemperature.The temperature of the rinse water will affect the washability. Some penetrant-emulsifier combinations may form a gelwith water temperatures of 50°F (10°C) or less. This gel can be removed but requires longer wash times. Otherpenetrant emulsifier combinations have reduced removability at elevated temperatures, above 110°F (43°C). The effectof temperature on washability depends upon the penetrant formulation, which varies between suppliers. Penetrant-emulsifier combinations meeting specification requirements are washable in the temperature range of 50°F (10°C) to100°F (38°C). Hot water, 120°F (49°C) or above SHALL NOT be used.2.5.4.5.2.4 SprayAngle.NOTEWater nozzles that are capable of producing spray patterns such as solid streams ora fine mist SHALL NOT be used. Rinsing dye penetrant from the surfaces of partsSHALL be accomplished with a fan-shaped, coarse spray.The angle of spray may be varied over a wide range with only slight effects on the removal time. When the angle isclose to perpendicular (80 to 90 degrees), the droplets will rebound into the on-coming water, diverting the freshdroplets, which reduces the scrubbing action. The scrubbing action is also reduced when the spray is close to parallelwith the part surface (10 to 20 degrees), since there is little energy transfer at the point of impact. Generally, an angleof 45 to 70 degrees is most effective.
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