The consumption of chemicals in processes of surface treatment is mainly caused by the drag-out of bath solution. Knowing the amount of the drag-out helps to maintain the process stable and is necessary for minimizing waste water and dosage of additives. Mostly, the values of the drag-out only are estimated - sometimes they are unknown. However, it is very easy to find out how much bath solution is dragged out. This Technical Letter shows how to determine the drag-out using two examples taken from the electroplating technique.
In the running process of trivalent bluepassivations, the zinc and the iron content are rising nearly linear. The limiting factor of the service life of a blue passivation normally is the iron content. In rack processes without steps to increase the service life (see Technical Letter No. 4), the blue passivations usually do not get so old that zinc is accumulated too much, causing problems. Only well controled rack baths or barrel processes can reach long service lifes and zinc contents up to 20 g/l. Trivalent blue passivations as SurTec 660, 661, 662 and 664 can be used without any loss of quality up to very high zinc contents, which is described in this Technical Letter.
The service life of trivalent blue passivations for zinc is limited mainly by the increase of dissolved iron during operation. The normally sky-blue passive layers get an increasing yellowish colour with increasing content of iron in the passivation bath. Depending on the desired quality of the zinc-plated and passivated parts, the upper limit of tolerable iron lies within 300 and 800 ppm. Efficient control of the dissolution of iron and its effects will prolong the service life of blue passivations by several times. This Technical Letter presents actions which were proved in practice to extend the durability of passivation baths.
In the new modular cleaning systems the builder component and the surfactants are formulated as individual products. This allows a separate and adapted dosing according to the real need in the cleaning bath. For good cleaning quality and recycling as well as a good handling the individual componets should be highly concentrated, demulsifying and liquid.