Why are two rinses often recommended after passivation?

When parts are passivated with citric or nitric acid, the parts themselves, as well as the basket they are in, carry some of the acid  into the rinse tank. This “drag out” means that the rinse solution has to be constantly replaced or will simply become more and more acidic over time. The biggest issue is not that the parts will be rinsed off, but that when the parts are withdrawn from the rinse tank, they may have soil redeposited on them. Once the parts are dried this soil can cause spotting on the surface of the otherwise clean parts. A second rinse bath produces a much cleaner final product by rinsing off the soil that is redeposited during the first rinse.

Often times, the second rinse tank includes a heated facility water inlet which constantly overflows the second rinse tank with small amounts of water to ensure water cleanliness.  The second rinse tank overflow is sent to rinse tank 1 and then rinse tank 1 overflows to drain.  This cascade overflow process ensures constant water quality over time no matter the amount of drag out on the parts and baskets.

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