Functions and gestion of surfaces

In modern plants, rinsing operations are designed, organized and operated in the same way as unit operations in chemical engineering, and can thus be referred to as "rinsing functions" (FR). In a wet processing line, when these rinsing functions are installed between two "sequences" of unit operations (surface preparation sequence and electrolytic coating sequence, for example), they act as a barrier to pollution of the downstream sequence by entrainments from the upstream sequence, and are typically governed by dilution processes between two liquids of different kinematic viscosity. On the other hand, when a rinsing function is implemented at the line outlet, its role is mainly anti-corrosion, or even adhesion-promoting; its effect is either immediate (cathodic polarization rinsing) or delayed (passivating rinsing). Rinsing operations can therefore be divided into two categories: i) "dilution" rinses with an immediate effect, as an anti-pollution barrier between two sequences, and ii) "reaction" rinses with a functional character, whose activity is electrochemical in origin.

Good rinse management is a response to two main constraints: one administrative, the other economic.

The administrative constraint aims to reduce, as far as possible, the consumption of rinse water to comply with the ministerial decree of June 30, 2006, which limits, in the majority of cases, to 8 L.m ^-2 the maximum quantity of water discharged as effluent in a rinsing function. As we shall see later, one of the practical consequences of this administrative constraint is to offer original solutions in terms of rinsing structures on TSVH lines.

The economic constraint is linked to i) compliance with environmental standards through pollution abatement by optimizing rinsing structures, and ii) improving the economic performance of TSVHs through financial gains generated by judicious coupling between rinsing structures and recycling, recovery or regeneration processes, or even reclamation of electrolytes previously considered as waste effluents.

In this article, using concrete industrial examples, we show that a rinsing operation is not as trivial as it seems, and that mastering it requires a scientific approach based on process engineering.

A glossary of terms and a table of acronyms and symbols are provided at the end of the article.