T.O. 33B-1-1
2-51
2.5.4.5.2
Factors Influencing Effectiveness of Spray Rinse.
2.5.4.5.2.1 Size of Water Droplets.
Removal of excess surface penetrant depends upon the mechanical force of the water impacting the part surface. The
impact force consists of the droplet mass and velocity at impact. The two factors are related, and increasing either will
produce a higher mechanical force. There are limits on both size and velocity; the latter is derived from the water
pressure. 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 a
small area at one time and is actually one large continuous drop.
Figure 2-17. An Improper Washing Procedure.
2.5.4.5.2.2 Water Pressure.
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 10
to 35 psig, is acceptable and is generally used. Water pressures in excess of 40 psig or injection of compressed gases or
air into the water system SHALL NOT be used.
2.5.4.5.2.3 Water Temperature.
The temperature of the rinse water will affect the washability. Some penetrant-emulsifier combinations may form a gel
with water temperatures of 50°F (10°C) or less. This gel can be removed but requires longer wash times. Other
penetrant emulsifier combinations have reduced removability at elevated temperatures, above 110°F (43°C). The effect
of 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) to
100°F (38°C). Hot water, 120°F (49°C) or above SHALL NOT be used.
2.5.4.5.2.4 Spray Angle.
NOTE
Water nozzles that are capable of producing spray patterns such as solid streams or
a fine mist SHALL NOT be used. Rinsing dye penetrant from the surfaces of parts
SHALL 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 is
close to perpendicular (80 to 90 degrees), the droplets will rebound into the on-coming water, diverting the fresh
droplets, which reduces the scrubbing action. The scrubbing action is also reduced when the spray is close to parallel
with the part surface (10 to 20 degrees), since there is little energy transfer at the point of impact. Generally, an angle
of 45 to 70 degrees is most effective.
