MIL-HDBK-1165
to travel through the membrane pores. Diffusion dialysis is used
to separate clean acid from metal contaminants in acid baths.
Diffusion dialysis can operate continuously without regeneration
and only requires an electrical source to drive the peristaltic
pump. Relatively low flow rates must be used to ensure proper
separation making diffusion dialysis a slow recovery process.
i) Filtration. During the plating process, impurities
are introduced into the plate bath solution from several sources:
the workpiece, the water or chemicals used to make the plating
solution, and from drag out of the previous tank. Additionally,
in the rinse-water recovery process, along with the desired
plating chemicals, some undesirable impurities will also be
separated from the rinse-water and returned to the plate bath.
This accelerates the level of impurities already present in the
bath. Consequently, plate bath solutions must periodically be
purified. Filtration combined with electrolytic migration is a
technology that can be employed for this and involves
electromotively forcing positively charged impurities through a
filter and collecting them on a cathode.
5.3.3
Metal Cleaning Facilities. Metal cleaning is an
operation employed in a variety of military facilities to prepare
metals and metal parts to perform satisfactorily in their
intended applications. Examples of military facilities that
require metal cleaning include aircraft repair facilities,
electroplating facilities, machine shops, paint shops, and ship-
fitting facilities. Metal cleaning involves using chemicals to
remove dirt, oil, grease, rust, or other contaminants from the
metal's surface.
Just as for plating processes, the rinse stage of the
metal cleaning process uses the majority of the required water.
Rinsing is either conducted by spraying the metal piece or by
dipping it into a rinse tank. Generally the rinse tank method
consumes significantly more water than spraying. Used rinse-
water will contain the chemical(s) used to clean the metal, as
dipping it into a rinse tank. Generally the rinse tank method
consumes significantly more water than spraying. Used rinse-
water will contain the chemical(s) used to clean the metal, as
well as the metal contaminants themselves. Chemicals typically
used for metal cleaning are solvents, acids, detergents, or
alkaline substances. The rinse-water must be of sufficient
quality so that the metal parts are not contaminated when sprayed
or dipped. Check the process specifications for the tolerable
contamination levels for metal cleaning rinse-water.
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