In this in-depth article, dive into three types of water and how each of them interact with the plating process.
Let’s state the obvious: water plays an integral role in the plating process. Water is in every bath including the rinse tanks and process tanks. Different types of water will interact with the plating process in different ways. Hard, soft, and purified water all have their own properties and rules for plating interactions.
Hard Water: Water that has a high mineral content, formed when water filters through deposits of limestone, chalk, or gypsum.
Hard water is characterized by its mineral content. These minerals, typically calcium and magnesium, can cause several issues. Hard water, when used in cleaner baths, can prevent saponification. Saponification is the process by which the cleaner reacts with the soil on the surface of the part, allowing it to be pulled from the surface and into the cleaner solution.
The saponification process should be prevented. The cleaner often does the work of softening the water at the expense of the cleaner bath life.
By this softening, hard water will cause a large amount of sludge to be formed in the bottom of the tank, in addition to the normal sludge formation in emulsion-type cleaners.
In the rinse tanks, hard water will affect the rinsing process in a few different ways. First, hard water already has a fair amount of Total Dissolved Solids (TDS) in solution. This means that it will be limited in the amount of soil that it can dissolve off the surface. If it fails to rinse the entirety of soils or chemicals off the surface of the part, the TDS are going to be carried further into the next process tank, leading to issues down the line.
TDS can be measured by 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.
What will hard water do in the plating tank? This is a more difficult question to answer in a very general sense, since different cations (the minerals in the hard water) will affect plating tanks differently.
Generally, you can expect to see one of these options:
Because of these possible headache-inducing issues, it is best to avoid hard water when making up a plating tank. This advice also applies to post-treatment tanks. Because your plating tanks and post-treatment tanks are the last things to touch the parts, as a rule of thumb, they should be kept as clean as possible.
Hard water is less than ideal in all aspects of the plating process due to its high level of reaction cations. These cations can cause sludge buildup in most of the tanks on the line, lead to the formation of lime deposits in pipes, and negatively impact the appearance of the plating deposit. For these reasons, it is recommended that you avoid hard water whenever possible.
Soft Water: Water that has low levels of dissolved calcium and magnesium.
Soft water, much like hard water, contains cations. However, these cations are different from those in hard water. Soft water typically contains Sodium (Na+) and Potassium (K+), rather than Calcium (Ca2+) and Magnesium (Mg2+).
These different cations can have a large effect on the entire cleaning process. Sodium and Potassium will not prevent saponification, making this an important part of the cleaning bath.
Unlike hard water, which is softened by the cleaner, soft water will generally not produce as much sludge in the bottom of the tank.
By now we’ve discovered that soft water is better than hard water for the cleaning tank, but what now? How does it work in the rinse tanks?
Soft water, similar to hard water, still has a fair amount of TDS. This can lead to difficulties in fully cleaning the surface of a part, leading to trouble later down the line.
The big reason we would want low TDS in our rinse tanks is that it would be less likely for significant soils and chemistry to end up in the plating process tank. Because of the Common Ion Effect, the decrease in solubility of a sparingly soluble salt or the reduction of ionization of a weak electrolyte when a common is added to the solution, we don’t want a lot of TDSs 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.
The upside of soft water in the plating tank is that you probably will not run into issues with the deposit. If you do not run into these issues, you can then use soft water to make up a plating tank.
Soft water is generally a better option than hard water in the plating process. 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 the solution, which can lead to issues. Because of this, soft water is likely not the best option for plating but could be the best balance of price and quality.
Purified Water: Water that has undergone a physical purification process to remove dissolved inorganic and organic contaminants, bacterial endotoxins, and microorganisms.
Purified water, such as reverse osmosis and deionized water, will contain few to zero ions. Therefore, it is very different from soft or hard water in how it relates to cleaner baths. Purified water will also not inhibit saponification.
Purified water will also not contribute to the amount of sludge in the bottom of a cleaner. With purified water, you do not need to worry about cleaner being used to soften the water, nor will you run into any extra issues with fully solubility the cleaner.
Sounds like magic, right? Well, purified water does have a downside: its cost. Relatively speaking, purified water is more expensive than hard and soft water.
The cost of purified water is its constant downfall. Were it as cheap as hard water, there would be absolutely no reason to use anything else. Because of this, purified water rinse tanks are often not utilized in plating operations. Purified water is truly ideal in a rinse tank situation. It will not add problems to the process and will accept soil and soaps from the surface of a part.
There are ways to maximize rinsing with non-purified water, such as counterlowing the rinse tanks. The effect of this practice would be amplified in a rinse containing purified water.
As discussed, purified water will cause little to no problems in the plating and post treatment tanks. You will not need to worry about sludge or outside contamination from your water source. You can be sure that whatever you put into the tank is the only thing present. Thus, the only things that you need to monitor.
The three different types of water, hard, soft, and purified, all impact the plating process in unique ways. Hard water, while normally the cheapest water up front, has the potential to cause the most issues. Soft water is likely in the middle of the price range and does not have nearly as many problems as hard water, but is not as high-quality as purified water. While the most expensive of the bunch, purified water should cause almost no issues in a plating line.
Looking to learn more about which water option is right for your plating process?
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