Water and the Plating Process : Part 2

In the first part of this three-part series, we discussed water and the integral part it plays in the plating process. We are talking about how the different types of water impact the plating process in different ways. In this post, we will talk about soft water and how it affects different process tanks.

Soft Water

Soft water, much like hard water, contains cations. However, these cations are different from hard water cations. Soft water typically contains Na⁺ (Sodium) and K⁺ (Potassium) rather than Ca²⁺ (Calcium) and Mg²⁺ (Magnesium). Let’s take a look at how these different cations affect the cleaning process. Sodium and Potassium will not prevent saponification. This is an important part of the cleaning bath, because as you might recall, saponification is the process by which the cleaner reacts with the soil on the surface of the part and allows it to be pulled off the part into the cleaner solution, thus cleaning the part. And unlike hard water, which is softened by the cleaner, soft water will generally not produce as much sludge in the bottom of the tank.

Total Dissolved Solids

So soft water is better than hard for the cleaning tank, that’s excellent. But how does it work in the rinse tanks? Well, soft water, much like hard water, still has a fair amount of “stuff” in solution. This can lead to difficulties in getting everything off the surface of a part, which can spell trouble later down the line. In an effort to avoid discussing rinsing and water in nebulous terms, let’s discuss what we mean by “stuff”. This “stuff” is better defined as Total Dissolved Solids (TDS). TDS can be measured by conductivity, ask your Asterion rep for more information on how to equate TDS and conductivity. By measuring the TDS, we can get a good idea of how dirty our water is. Ideally, the TDS in a rinse tank would be low.

The big reason we would want low TDS in our rinse tanks is that it would be less likely for large amount of soils/chemistry to end up in the plating process tank. Because of a chemical phenomenon known as the Common Ion Effect, we don’t want a lot of TDS in the water that makes up the plating process tank. This means that soft water, while probably better than hard water, is still not ideal for making up a plating tank. There are other issues associated with making up a plating tank with soft water, such as “salting out”. Salting out is when a more soluble ion kicks a less soluble ion out of solution. This will follow the Hoffmeister series. The upside of soft water in the plating tank is that you generally will not run into issues with the deposit. This means that as long as you don’t run into the above issues, then you should have no problem with using soft water to make up a plating tank.

To wrap things up, soft water is generally a better option than hard water. It will not cause nearly as much sludge in the tanks or mineral build up on pipes. However, it still has a lot of cations in solution, which can lead to some issues. Because of the above, soft water is likely not the best option, but is likely the best balance of economics and quality.

In the third part of this series, as we will talk about purified water and the plating process. For a much more in-depth discussion on water and the plating process, please contact either the Asterion main office or your friendly Asterion rep.