Why Water Quality Matters in Powder Coating

by Marty Korecky

It is easy to take water for granted, especially if it comes out of the tap. We don’t think twice about using it to cook, wash our dishes or our clothes, take a shower, or brush our teeth. For that matter, the older population reading this article might remember when we drank from the garden hose when we were younger. The water source we use at home is often fine for our needs, but that same water can have a negative impact on our powder coating processes.

We might get our water from the local municipality (city water), or we might get our water from a well (well water) and we use it and don’t give it a second thought. Until that is, we have a problem. For example, we find that we have a ring around our bathtub, or maybe the faucet doesn’t work the way it did when it was new. Sometimes as the seasons change, we notice the water tastes a little different, and we think about getting one of those water filter pitchers to put in the refrigerator. For those of us who travel, we find that in some locations we have trouble lathering up in the shower, or conversely, we feel like we can’t rinse the soap off. So, what’s going on?

What’s In Your Water?
The issue at hand is water quality. Chemically speaking, water consists of hydrogen and oxygen (H₂O), but the water we use contains impurities. These impurities include dissolved solids such as calcium, barium, lead, sodium, radon, and zinc, just to name a few. In addition to these dissolved solids, our water can contain runoff from fertilizers, pesticides, manufacturing chemicals, roadway deicing materials, etc.

Other contaminants can find their way into our water as well, such as medications that were flushed down the toilet and have dissolved into our water stream. Many municipalities have been adding fluoride to the water to reduce tooth decay and cavities.
Well water isn’t immune to many of the same contaminants as municipal water. Impurities in well water are different in different parts of the country. The soil is different, the agriculture is different, the climate is different. The one thing that remains consistent is that there are varying types and amounts of contaminants in our water.

The only way to know the true quality of our water is to have a water analysis done. It is recommended to have more than one water analysis done each year. As the seasons change, so do the chemicals we use. Municipalities are required to provide an Annual Drinking Water Quality Report. It should provide information such as radioactive contaminants, inorganic contaminants, disinfectants and disinfection byproducts, and lead and copper levels. They only report what is required by law, so I would still recommend hiring an independent lab to test the water, not just to compare, but to see what other contaminants are found.

Why Does Water Matter?
But how does all of this relate to powder coating and the products we manufacture? Many of the products we manufacture are used outdoors. Often, we list in our specifications the corrosion protection of the product. The quality of our water dictates corrosion protection just as much as the powder we use and other critical factors.

Let’s look at a common part and follow it through production. The mill creates the substrate, and a passivation material is applied so the metal doesn’t begin to corrode before it gets to the manufacturer who is going to use it to make parts or products. In most cases, the substrate is loaded on a truck and driven to the manufacturer.

During transportation the substrate is subjected to various environmental conditions and bound to pick up additional chemicals. The metal is then cut, bent, drilled, machined, etc., into the part we are going to coat. And during that process we may have added cutting oils/lubricants, laser smut, or weldments, all of which we have to remove before we powder coat the part.

Off to the pretreatment system. Let’s assume the process uses a 5-stage system with the first stage being a cleaner, followed by rinses. At some point, we may add a conversion coating or a dry-in-place pretreatment. For the stages that are not water rinses, we add chemicals to the water at a given percentage—which in most cases is less than 7% by volume. That means that 93% of our bath is simply water. That also means that no matter how good the chemicals are, the water quality will dictate the level of corrosion protection you will get on your parts.

The contaminants we discussed earlier are still in the water even after you add chemicals to your pretreatment tanks. Those contaminants dry onto the parts and become the spot where premature corrosion begins. Powder coatings are permeable to air and moisture. That means a powder coating will allow air and moisture to penetrate the coating. As moisture encounters the contaminants, oxidation begins, and part failure will soon follow.

Many years ago, I was giving a presentation and started talking about water quality. One attendee from a very reputable OEM offered a story. She said she was able to get between 600 and 1,200 hours of salt spray on her parts using a 5-stage pretreatment system with a halo at the end. She was using city water. When asked why such a large range, it was due to the incoming city water. Depending on the time of year, the water quality would change so much that it impacted the results that drastically. Her solution was to install a reverse osmosis (RO) water treatment system to remove much of the contamination, providing much more consistent water quality. She said her salt spray results have since improved and they are now able to pass 2,000 hours of salt spray consistently.

Measuring and Improving Water Quality
When I first started my career in the powder coating industry, we measured water by total dissolved solids (TDS). It was a fast and efficient method, and we didn’t need computers (…we didn’t have computers). Automation has driven much of what we do in manufacturing, so measuring water quality by conductivity or resistivity has become the new way to test the quality of water.

The most useful ways to measure water are listed below:

• Conductivity (µS/cm) or Resistivity (MΩ x cm).
• Total dissolved solids (TDS).
• Total organic carbon (TOC).
• Microbial contaminants (CFU/ml).

There are several ways to improve your water quality. Water softeners will remove minerals like calcium, barium, and magnesium that cause hard water. The issue with a water softener is that it uses sodium or potassium (salt) to remove the minerals. Adding salt to your water may not provide the level of corrosion protection you require.

Deionized water is a very common method to increase water quality. It uses filters to remove a wide range of contaminants, including dissolved solids, bacteria, and heavy metals. The system won’t remove everything, but it will remove most of what causes headaches in the finishing industry.

Deionized water systems are available in three versions:

• Type 1 (Ultrapure) – used in critical applications where little to no contaminants are acceptable.
• Type 2 (General or Lab Grade) – suitable for laboratories and places that require a very high level of purity.
• Type 3 (RO Grade) – produces the same high-water quality as a reverse osmosis system.

Reverse osmosis systems push water through membranes to remove a high percentage of dissolved salts and organics, producing very clean water that can help chemistries perform predictably while potentially reducing chemical usage. RO can be scaled to plant-size and, when combined with downstream deionization, offers near-ideal rinse water for high-end finishes.

The level of water quality you require should be dictated by specification. If your current water quality is such that it meets your requirements, consider yourself fortunate. If it does not meet your requirements, you should investigate purchasing a system to improve your water quality. In any case, having your water tested on a regular basis is an inexpensive way to keep tabs on one critical facet of your process.

Before making any changes to your process, always perform testing to benchmark your system. Test changes you make to see if they add value to your operation before finalizing those changes. Always utilize reputable and reproducible test procedures in your decision-making process. And finally, utilize your industry experts as resources. They are a great source of knowledge and insight.

Marty Korecky is owner of MJ Korecky Consulting, LLC.