Hold the refractometer close to a light source so that the light illuminates and enters the prism.
A bright light is necessary. Overhead fluorescent lamps may not furnish sufficient illumination.
With the cover plate contacting the prism, look through the eyepiece. Read the Brix value
(refractive index units) where the bright and dark areas meet. A clearer meeting line may be
created by adjusting the angle between the light source and the prism face or holding the prism
face closer to the light source. Record the refractive index units. Using the manufacturers
literature, determine the concentration of the test sample from the refractive index value.
(5) When the test has been completed, clean the refractometer cover plate and prism face with a soft
lint-free cloth. Place the refractometer in its own protective pouch, and return it to the penetrant
test kit carrying case.
c. When using the hydrometer, perform a water content test in accordance with the following procedure:
Mix a test sample of the new hydrophilic remover as recommended by the manufacturer in a
500-ml graduated cylinder or similar container.
Using the hydrometer, check the concentration of the test sample by noting its specific gravity
and recording this reading.
Mix the working bath to the same concentration as the test sample within 5%.
A quick test to determine if penetrant is present in the remover in a large enough quantity to become a possible
contaminant can be accomplished by passing a blacklight over the surface of the remover in the tank and visually
examining it for signs of fluorescence.
The immersion removal time cited is typical. Actual time will depend upon type of
penetrant, type of remover, agitation and remover concentration. Actual time must
be determined at each depot or base for each system involved. Trials must be
accomplished using fresh or uncontaminated remover. The objective is to use the
minimum time necessary to produce a background-free surface on the immersion
panel when the remover is uncontaminated.
Penetrant materials used in open tanks are continuously undergoing evaporation
that may increase the viscosity and also affect removability. Therefore, before
changing the remover bath, perform the procedures in paragraph 188.8.131.52.1c.
A performance check to verify the concentration of used immersion hydrophilic remover baths is required. The
penetrant from parts disperses in the remover, causing turbidity and a change in the refractive index. The turbidity
makes a color comparison invalid and the change in refractive index is no longer a true indicator of concentration. The
shift in refractive index requires developing a compensation curve for variation with penetrant concentration.
Performance testing is the easiest and most practical way of determining the adequacy of a remover bath. The test
involves processing two roughened panels with different removal contact times and comparing the results using the
a. Performance Check. Use two oxide blasted, stainless steel panels as described in paragraph 184.108.40.206.2. A
typical processing procedure is as follows: