Iron Phosphate Coating Process

A. Hi Patrick,

It is true. Phosphate coatings have high specific surface area. Phosphate coatings tend to absorb water and other organic compounds from atmospheric environments in terms of capillary effect with time, particularly in the humid areas and industrial fields. Both water and other organic contaminants are harmful to paint adhesion. Baking at an adequate temperature is able to eliminate water and the organic contaminants absorbed over time.

Regards,

A. Sir ji,

Apply the drying or non drying rust preventive oil after phosphating it will give you 1000 hours salt spray life. You can get parker dw 36 or parker 20t from Chemetall Oakite .

Regards,

A. Absolutely should have a seal. Chrome good, have to treat for chrome rinse water. Non-chrome sealers equivalent to chrome protection just as good. If you are buying proprietary phosphate, that supplier should have a seal.

A. Hi Sally,

Your question is somewhat lacking in details, but I can try to answer anyway.

I assume that you want a suggestion for a pretreatment operation that utilizes iron phosphating. How many stages does your system contain? Is it spray or immersion?

The best phosphating scenario would be clean in Stage 1 (sounds like you're already doing this), water rinse in Stage 2, iron phosphate in Stage 3, water rinse in Stage 4, post-treatment in Stage 5.

How you set this up depends on the end use of your parts. You say that the parts rust after a short period of storage. This is not unusual because an iron phosphated surface does not have a great deal of corrosion resistance in and of itself. Iron phosphating is a widely used pre-paint treatment. Ideally, you would paint the parts right after applying the phosphate coating. If the parts are not going to be painted, then you can apply some kind of rust inhibitor that can act as a barrier to corrosion.

As far as handling the iron phosphate, these are strong acid products; rubber gloves ⇦ this on eBay or Amazon [affil links] and eye protection (goggles ⇦ this on eBay or Amazon [affil links] ) are the minimum equipment. Check your chemical supplier's MSDS for details.

A. Sorry, John, I don't understand the question. Are you suggesting that the phosphatizing that you are presently providing is not corrosion resistant on cast iron, but you have seen phosphatizing done that was corrosion resistant, and you are wondering what chemical you saw someone add to their tank to adjust theirs and tailor it to cast iron?

Two possible solutions are:
- to order a phosphatizing process from a reputable supplier, which will include technical data sheets (you will find a number of suppliers listed in our directory of Chemicals and Consumables, or
- to study phosphatizing in more detail from one of the books previously mentioned. Best of luck.

A. Hi Nilesh,

You can increase coating weight by increasing contact time, temperature and concentration. But increasing the coating weight will not necessarily improve corrosion protection. Corrosion resistance is related to the composition of the coating, and not the amount.

A. Dear Nilesh Baraskar,

If corrosion resistance is your only concern then try zinc phosphating.

A. Hi, James. That would be an "iron phosphating solution". Although the best of these are patented or trade secret, yes, you can formulate your own. Please try to get hold of a few expired patents on the iron phosphating processes (it's so easy today), and also look into the principles behind the process in Preparation of Metal for Painting ⇦[this on Amazon affil links] or "Phosphating of Metals" ⇦[this on Amazon or AbeBooks affil links] by Werner Rausch.

Just remember that oils & soils are best removed in hot alkalies, so it's not ideal to try to remove them with the cooler, acidic iron phosphatizing solution; and an iron phosphatizing solution won't work its best when oils & soils are floating around in it. You can toss the apple pie into the chicken soup to save a bowl and a step, but no matter how well you do it, it's just not going to work as well as keeping the soup and the desert separate. Good luck.

Regards,

A. Hi, Nader. I feel you should be eliminating Cr6 passivation, because of its toxicity, rather than trying to reinforce it. I'm not familiar with TETA as an additive to Cr6 passivation, but I think you probably need to improve the iron phosphating itself or move to zinc phosphating rather than look for a magic final rinse additive to fix it. Good luck.

Regards,

A. Hi Srini,

A zinc phosphated surface with no supplementary treatment is going to have a very short life before corrosion starts.

I don't know how easy this would be for you to do, but you could consider vacuum bagging parts, so removing the air that would cause the problem, or maybe you could bag and inert gas charge the bags (e.g., nitrogen or argon). These methods will stop the onset of corrosion.