One-Stage Iron Phosphate

Q. We manufacture control housings for the oil industry. The steel housings are zinc phosphated then painted with a durable outdoor finish system, an epoxy primer and a polyurethane topcoat. We also have a small parts line where a five stage iron phosphate is applied. The phosphatizing machine is badly deteriorated. Can we replace it with a parts washer using one of the combination cleaner-phosphates? K. E.

 

A. You probably will not get the same corrosion protection, which may not be adequate for your products, from a one-stage iron phosphate. Obviously, your housings require a high degree of corrosion protection, since you apply a zinc phosphate pretreatment and a long life outdoor finish system. However, your five stage is providing sufficient protection for the small parts finished on the small parts line. Unlike the five stage phosphate, these one stage materials clean and phosphatize using a
single chemical solution and are not designed to give a higher degree of corrosion protection.

Combination products of this type which never seem to do both jobs well, are often used where adequate space and facilities are not available. A parts washer is just that, a parts washer. It’s original use was to remove oil and soil from ferrous and nonferrous parts after machining not as a prepaint treatment machine. On the other hand, parts washers are being used to apply one stage iron phosphates successfully. You must decide whether your parts will be afforded adequate corrosion protection using a one stage iron phosphate. This decision must be based on an evaluation of pretreated and painted parts. A comparison of salt spray, humidity and adhesion tests on painted test panels pretreated with both the present and proposed pretreatments will provide the basis for such a decision.

It is important to note that I am not against parts washers. Instead I am against providing inadequate corrosion to manufactured products.