Operating Manual

91
10.5 Automatic film processing
NDT-U (universal) film processor
Over the last few years there has been a vast increase in the use of automatic processors for
handling industrial X-ray films. Not only is it a faster and more efficient process, the
uniform process also leads to improved image quality. The total processing time may be
between 1.5 and 12 minutes (nominally 8 minutes), significantly shorter than in manual
processing. Of these 8 minutes, the film will be in the developer solution for only 100
seconds, the so-called “immersion time”. These shorter processing times have been made
possible by the use of special chemicals (G135 and G335), and by a higher temperature of
the solutions: 28°C instead of 20°C.
The shortest processing time of 1.5 minute is essential for the development of the special
films used on board lay-barges, where the results must be available quickly.
The chemicals used are more active at higher temperatures. The higher temperature of the
solutions makes the emulsion layers swell, resulting in a faster diffusion of the liquid
through the layers and, consequently, more rapid action of the chemicals.
Swollen emulsion coatings do, however, have the disadvantage of being softer and hence
more vulnerable to damage; a compromise between the advantages and drawbacks is rea-
ched by adding a carefully determined proportion of hardening ingredients to the fixer.
Chemicals for use in automatic processors also have additives to inhibit oxidation of the
solutions and formation of fog in the emulsions.
Automatic film processing not only makes the results available sooner, it also standardises
(improved reproducibility/uniformity) the development process and, consequently, the
exposure technique. This increases the quality and reliability of radiography as a method
of non-destructive testing.
GE Inspection Technologies supplies integrated Agfa-systems in which X-ray films, chemi-
cals and processing equipment are all adapted to each other. Through the uniform charac-
teristics of its films, carefully formulated chemicals, continuous agitation, automatic reple-
nishment and accurate temperature control of the solutions in the processors, Agfa systems
ensure top-quality results.
The Agfa NDT-U processor is equipped with an infrared film drier while its functions are
controlled by a microprocessor. Its throughput depends on the required cycle time (adjus-
table between 1.5 and 12 minutes) and film size. All normal film sizes, including roll film,
can be processed. When set for an 8-minute cycle (100 seconds immersion time) for exam-
ple, approximately 100 films of size 10 x 48 cm can be processed per hour.
90
10.3 Recommendations for the darkroom
Cleaning of tanks
Whenever the processing solution is renewed the tank must be cleaned, preferably with
hot water and soap. If this proves inadequate, polyester tanks can be cleaned using a
bleach solution (100-200 ml/litre of water), hydrochloric acid (10 ml/litre of water) or
acetic acid (50 ml/litre of water). Stainless steel tanks may be cleaned with a solution
of nitric acid (10 ml/litre of water) or acetic acid (50 ml/litre of water). Hydrochloric
acid must never be used for stainless steel tanks.
There are industrial cleaning agents on the market (for example Devclean and the, envi-
ronment-friendly, Fixclean), specially developed for cleaning of darkrooms.
Stained fingers
Brown stains on the fingers can be avoided by rinsing the hands in water whenever they
come into contact with developer. If fingers do become stained, they should be immersed
in a solution of:
a. 1 litre of water
b. 2 gr of Potassium-permanganate
c. 10 ml of concentrated sulphuric acid
d. Next the hands should be rinsed in an acid fixer solution, and finally washed
with soap and water.
Chalky water
If hard, chalky water is used for mixing the solutions, troublesome processing faults
may occur. Calcium salts may, in the presence of carbonates and sulphites, result in a
whitish deposit on the films which is insoluble in water. To prevent this, the diluant can
be softened by using a special filter, or by boiling it first and letting it cool down before
making up the chemical solutions.
To remove chalk deposit from films, they may be soaked in a solution of 7 ml glacial
acetic acid to a litre of water.
10.4 Silver recovery
The silver halides in the emulsion which were not reduced during development, are
dissolved in the fixer. Silver can be recovered from the fixer in order to keep the silver
content of the fixer solution as low as possible so that the fixer lasts two to four times
longer, and sell the silver.
Silver recovery can, for example, be done by electrolysis. In addition to electrolysis
equipment, there are other silver recovery systems commercially available.
It is worthwhile considering subcontracting this work to a specialised firm in view of
secondary aspects such as organisation, logistics, storage and environmental requirements.