Lessons Learned In Paint Line Surface Preparation
Any experienced painter will tell you never to paint a dirty surface. The same is true for OEM paint lines. All well-run paint lines begin with sufficient surface preparation. Improper pretreatment will set any line up for failure regardless of applicator experienced or the quality of the coating. Over the 50 years we've been formulating and manufacturing paint, we've come across more than a handful of paint issues that were ultimately traced back to surface preparation.
Lawnmower Coating's Risky Rinse
A lawn care equipment company relied on an Aexcel two component urethane coating for their lawnmowers. The customer sprayed the heavy equipment coating onto their steel frames after a five-stage pretreatment process, including a rinse with local well water. One summer, the manufacturer received several complaints about paint flaking off. At first, the manufacturer scoffed at the complaint, unable to recreate it in their lab. However, when the freshly painted parts were left out overnight, the coating was failing by morning. The manufacturer contacted Aexcel for a solution and to discuss reformulation.
As with all complaints, Aexcel ran a detailed failure analysis. Here, the problem was traced to the customer's pretreatment rinse, specifically their use of well water. The well water left salts behind on the metal parts and the salts were coated over. When the parts were coated, the coating was actually sticking to the salts rather than the metal. When the parts were left out overnight, they were subjected to the morning dew. Unfortunately, the salt on the parts, being water soluble, solubilized when it came into contact with the morning dew. Once that happened, the lawnmower coating lost adhesion.
Armed with this information, Aexcel recommended the lawnmower manufacturer switch from well water to deionized water during its pretreatment process to ensure no salt or other water soluble residue was left behind. After making this adjustment, the manufacturer's failure rate decreased dramatically as their urethane coating no longer peeled in the presence of water. Here, a pretreatment adjustment rather than a formulation overhaul solved the manufacturer's problem.
Brake Coating Breakdown
Another industrial coatings customer was using an Aexcel vinyl chloride coating for their axle and brake drum assemblies. The auto part manufacturer was receiving an inordinate amount of complaints from customers reporting their parts flash rusting. After checking batch retains and ruling out manufacturing errors, Aexcel turned to the customer's pretreatment process.
Prior to coating their parts, the customer was using water with nitrate, followed by a final rinse. Unfortunately, the final rinse was not removing all of the pretreatment, which was basic in pH. The vinyl chloride coating the customer was using on their parts was acidic in pH. When the acidic paint met the basic pretreatment, it neutralized, causing flash rust. After uncovering this issue, the customer implemented a more thorough final rinse process. This adjustment neutralized the flash rusting issue. If your coating line is experiencing problems with flash rusting, keep the pH of your surface preparation and paint in mind during root cause analysis.
Another of Aexcel's customers manufactured parts for tractor engines coated with a high performance urethane coating at the customer's in house paint finishing line. The customer saw adhesion failures in their paint finish shortly after the cure cycle. After performing a failure analysis, Aexcel concluded the paint was failing due to inadequate surface preparation prior to painting. Specifically, the customer's existing pretreatment method using SSPC-SP-3 power tool cleaning was not removing enough soluble substances from their parts. As a result, the urethane was going over a considerable amount of oil and grease from upline manufacturing processes. This caused the coating to lose adhesion over the residue. Aexcel recommended the customer incorporate a solvent cleaning stage to ensure the removal of all manufacturing residue prior to coating their parts. After implementing this solvent wash prior to painting, the customer saw a dramatic decrease in their adhesion issue. Coating a part is usually the final step in its manufacture. This case illustrates the importance of matching your surface preparation process to whatever contaminants may be lurking upstream.
Before ordering your paint supplier to reformulate your industrial OEM coating, consult with them about your surface preparation process. Are you removing all manufacturing contaminants from your substrate before coating your parts? Is your pretreatment wash compatible with your paint from a pH perspective? Are you accounting for what your product will experience in its end use environment? Your industrial coatings manufacturer should act as a partner to walk you through these troubleshooting questions and others when problems arise on your paint line.