Problems in your phosphate line can lead to issues in your operations. Stop them before they lead to trouble by keeping these three cures in your back pocket.
Spotty Parts
These two dreaded words sum up what happens when issues arise with your phosphate cleaning line; this can become a problem in your shop.
Incomplete coverage, or even worse, no coverage at all, is your tell-tale sign that your phosphate line is negatively impacting your shop’s efficiency and your company’s profitability. Don’t lose hope! There is a cure. Or rather, three cures.
Incomplete surface coverage may indicate that adjustments to the pretreatment process may be necessary, but it may also indicate that there are variations in substrate manufacturing that must be addressed.
Substrate chemistry 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.
It is imperative that you check your cleaners. Keep an eye out for age, soil loading, concentration, temperature.
KEY INSIGHTS: There are many resources out there for troubleshooting cleaners. Make sure to find the one that works best for your purposes to find more details.
If you are certain that the cleaner is not causing issues, 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, HCl baths are hard to understand using titrations alone. When you are in doubt about the diagnosis, contact your supplier or dump the tank to make it up fresh.
KEY INSIGHT: An acid pickle tank is a container that holds acid solutions to remove rust, mill scale, and other impurities from metal surfaces, preparing them for further processing like coating or plating.
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 you are dealing with incomplete zinc phosphate coverage, remember that the zinc phosphate itself is rarely to blame. Why? Because chemistry does not pick and choose when and where to work. If it successfully covers some of the part, it can cover the whole part if the surface is properly prepared.
There is an exception to this rule that occurs 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 the free acid is too high, then the phosphate tank will pickle the parts rather than coat them.
Besides the mentioned exception, no or almost no coverage likely indicates an issue with the zinc phosphate. It is recommended to 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. Check the cleaner and acid baths.
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