Spotty parts. These two words pretty much sum it up when issues arise with your phosphate cleaning line. Incomplete coverage —or —no coverage at all is another sign that your phosphate line is negatively impacting your shop’s efficiency and your company’s profitability. There is a cure.
Incomplete Coverage – Substrate: Incomplete surface coverage typically indicates adjustments to the pretreatment process may be necessary or that there are variations in substrate manufacturing that need to be addressed. Substrate issues should be reviewed with the supplier to confirm consistent material is being received. If modifications are made to the substrate’s composition, this could significantly impact surface adhesion and coverage, thereby possibly necessitating adjustments to the pretreatment chemistry.- Incomplete Coverage – Pretreatment Chemistry: Step one is to check the soak cleaner. Age, soil loading, and concentration are the first things I look at. Temperature is another important factor. We have plenty of blog posts about troubleshooting cleaners, so I will skip the specific steps here and encourage you to reference these more detailed postings. If you are certain that the cleaner is not causing any issues, then the next culprit is often the acid pickle tank. Hydrochloric (HCl) acid is the most common acid used as a pickle. When HCl builds iron, it will start turning green. An experienced plater should be able to determine when the HCl is spent based on appearance. Generally speaking, HCl baths are hard to diagnose based on titrations. When in doubt, the best course of action is to contact Asterion; in lieu of that, dump the tank and make it up fresh.
- Special Note – Zinc Phosphates: If incomplete zinc phosphate coverage remains an issue after reviewing the substrate and pretreatment troubleshooting tips detailed above, you most likely have a substrate issue. Typically, this is fixed by running the part through the process a second time. When faced with incomplete zinc phosphate coverage, very rarely is the zinc phosphate itself to blame. This is because chemistry cannot pick and choose when and where to work. If it successfully covers a bit of the part, then it can cover the whole part if the surface is properly prepared. The exception to this rule is when the free acid is too high in the phosphate tank. It is important to test not only the total acidity, but the free acidity. If free acid is too high, then the phosphate tank will pickle the parts rather than coat them.
Counter to that, no coverage (or almost no coverage), likely indicates an issue in the zinc phosphate itself. I recommend you check the strength of the phosphate and the amount of iron contained in the bath. Follow your chemical supplier technical data sheet. If all is within range, then start from the beginning of the line. Check the cleaner and acid baths.
As always, Asterion stands ready to answer your call.