T.O. 33B-1-1
2-66
2.6.4
Water Suspended (Wet-Aqueous) Developer.
2.6.4.1
Description.
NOTE
Developing action in wet suspended developers will not start until all the absorbed
and adsorbed water has been driven off. Developer dwell time SHALL NOT begin
until the part is completely free of moisture.
Water suspended developers consist of inert particles in a water suspension. The particles are insoluble in water and
when dry, are highly adsorptive and absorptive. The developers are supplied as either concentrated liquid or dry, bulk
powder and must be mixed with water prior to using. In addition to the developer particles, they contain chemical
dispersing agents to reduce the tendency of the developer particles to stick together or form clumps. Wetting agents are
added to provide complete and thorough coverage of the parts. Corrosion inhibitors are added to protect the part from
corrosive attack. Finally, biocides are added to provide a reasonable tank life by delaying bacterial growth. When
applied, water suspended developers evaporate very slowly at room temperature and require a hot air oven for proper
drying.
2.6.4.2
Preparation.
Wet suspended developer is always used in stationary systems due to the requirement for a drying oven. Wet developer
concentrates should be mixed with water in the proportions recommended by the manufacturer. The concentrations
vary between types and manufacturers. The measured quantity of powder or liquid concentrate is added to the water
while stirring constantly, until a smoothly mixed suspension is obtained. A newly mixed batch of suspended developer
should stand for 4 or 5 hours before use to allow the developer particles to wet out.
2.6.4.3
Application.
Wet suspended developers are applied by spraying, flowing or immersion. Wet developer, since it has a water base, can
be applied to parts still wet from penetrant removal. When the part has been thoroughly covered with the developer
solution, it is allowed to drain for a short time, (wet suspended developer drain SHALL NOT exceed 30 seconds) and
then placed in a drying oven.
2.6.4.4
Advantages.
Water suspended developers have several attributes which produce greater sensitivity than possible with dry developer:
a. The coating is in more intimate contact with the part surface, and the layer is thicker than that of dry
powder, resulting in increased extraction and the formation of brighter indications.
b. Water suspended developers produce a readily visible coating that shows the extent of coverage.
c. Water suspended developers do not give off any solvent vapors or obnoxious dust and do not require
expensive exhaust and ventilating equipment.
d. Properly applied, water suspended developers can achieve a sensitivity very close to that obtained with
non-aqueous wet developers.
2.6.4.5
Disadvantages.
a. Water suspended developer particles are insoluble and heavier than water, causing them to rapidly settle
to the bottom. Frequent agitation or stirring is required to maintain a uniform concentration.
