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Pretreatments

Parts Cleaning articles from Products Finishing are selected and categorized by application for quick reference:

Chlorinated Paraffin/Vacuum Heat Treating   10/01/08
I have a suspicion that the metal stamper is not removing all of the chlorinated paraffin and that the chlorinated paraffin is having an adverse effect on the steel parts during or shortly after the vacuum heat treat. Considering that the heat treatment is being done in a vacuum, I don’t think any paraffin is being decomposed, but rather cracked into smaller alkanes and alkenes. What is confusing me is the apparent rust pattern that develops on these parts. Can you advise me on this?

UV Clear Coat Over Metal   06/01/08
Our company is coating a high polished metal with a UV clear coat. Our precleaning process includes hot alkaline cleaner at 150°F, 80-psi impingement spray, city water rinse and DI water final rinse at 100°F followed by a 120° air blow off. The parts are then sprayed with an electrostatically charged material in a bell. Our question is whether rust sometimes occurs under the UV coating. Can you explain why some may rust quicker than others in a non-humid environment when routine maintenance is performed on all tanks and not all parts rust?

Cleaning Aluminum Castings   04/01/08
Our customer finishes our aluminum lamp surface with powder. We apply dipped degreasing solution with alkali solution and acid treating of the surface and rinsing. We have had a lot of nonconformity reports about adhesion or other covering problems. I’d like to know what cleaning problems result in bad powder coating, or what tests we can do to ensure good cleaning. We apply a heat treatment (250°C, 14 hr) before cleaning to remove trapped gas from aluminum pores.

Etching during stainless passivation   04/01/08
I have a couple of questions about the etching problem finishers run into when they passivate stainless steel. I see many different causes described in the PFOnline archives, but looking at the causes listed I would have trouble convincing a customer that these things take place without published data or studies. I’ve been in the industry for 30 years now, and have to admit that I don’t have the information at hand to give something to a customer that will convince them we simply haven’t strayed from our process travelers. Do you have a list of recommended sources I can buy for that purpose?

Stripping Nickel from Inconel 718   04/01/08
Could you please advise me of the best way to strip sulfamate nickel off of Inconel 718 base material? Is there a risk of damaging the part if it is stripped in 50% nickel due to the high nickel content of the base material? Any advice would be greatly appreciated.

Passivation of 17-4ph Stainless   02/01/08
In response to your Article "Passivation before Heat Treatment" in October 2007: Your second paragraph states "If the atmosphere in the furnace... etc". Stainless steel should never be heat treated in an atmosphere. The only heat treat/anneal that should ever be done to any and all stainless steels should be done in a vacuum environment. If it's done in an atmosphere, any contaminants (steel) will attract to the stainless steel and will cause corrosion.

Phosphating Process   02/01/08
We are in the process of setting up a pretreatment plant, and would like to know which phosphating process will be best, considering quality, investment, and maintenance for: 1) room temperature dicationic process, 2) tricationic process, and 3)high-temperature dicatonic process.

Pretreatments   02/01/08
What is the chemical used to seal after a three-stage cleaning process and higher?

"Fuzzy" Parts   10/01/07
We are chromating impacted parts made from 7075 T6. We are noticing that some of the parts form a "fuzz" where they are machined. This area is white powder and when removed leaves a black spot on the surface of the tube that will not chromate. The issue is sporadic and can occur at any stage of chromating, but is primarily seen immediately upon removal from the soak cleaner. We have tried four proprietary cleaners and still have some of the same issues. We have also determined there are no stray currents. Could this be the blisters that you have written about?

FOLLOW-UP: Passivation Before Heat Treatment   10/01/07
To Readers: I received a very good email from D.H. discussing the August 2007 question regarding the passivation and apparent rust on 17-4PH precipitation hardenable stainless steel. One significant point that I did not mention was that the passivation process may be better done prior to heat treatment. Either that, or an acid cleaning process may be necessary to remove surface contaminants that could be diffused into the surface depending on the time, temperature and atmosphere of the heat treatment.

Pretreatment for Beryllium Copper   10/01/07
I am looking for a pre-treatment/cleaning process (preferably spray, as opposed to a dip method) for beryllium copper parts. What cleaning process would you recommend for this material? In addition, would a bright dip be ideal for a last bath within the process?

Clean Steel Using COR Rinse 404   06/01/07
We have been using cor rinse 404. Could you tell me if there are any issues with adhesion with different paints systems? How do you check if the metal is clean?

Stainless Steel Wash Primers-Which and Where to Get It?   06/01/07
I have a couple of hundred 3/16-inch 304-stainless steel dowels that I need paint to bond too. I am not concerned about corrosion, only concerned about proper bond of paint to the SS. Besides the obvious degreasing and sanding, I keep reading of "Wash Primers." So what brands are there and where I can I get them?

FRP Parts Washer   04/01/07
I am considering the use of a 5 stage part washer constructed from FRP (Fiber Reinforced Plastic). Do you or know anyone who has any experience with a washer constructed from this material? It is intended to wash mild steel sheet metal parts.

Blisters And Creep On Aluminum Castings   02/01/07
We have repeatedly failed a 336-hour salt spray test on an aluminum casting. Our pretreat system and coating have met the same requirement on steel and a shorter salt spray test on aluminum castings.

Removing Rust, Mill Scale And Oils In One Step   02/01/07
We have a small job shop that powder coats. We do parts of varying sizes all the way up to 20 ft in length, made of steel or aluminum, occasional magnesium. The parts we receive, as stated before, are constantly different sizes and shape and some of it is made of HRS steel and has rust and corrosion on it, as well as oil. I always see the typical pretreatment stages to be a cleaner, rinse, phosphate, rinse, sealer, rinse or not. Nowhere do I see anything to deal with the rust and mill scale from the HRS steel. Is there a product that removes the rust, mill scale and oils in one step? Or are there more steps required, I can honestly say most everything I ever read about seems like a perfect world where the only thing the steel has on it is oils. This is not the case in my business. We have a manual spray washing system that we use due to our varied parts, but I can absolutely see the need for a dip tank being a useful tool as well for the smaller parts.

Smut On Titanium Parts   02/01/07
I use a Nitric/HF bath to etch titanium. Afterwards I desmut in 45% by volume nitric acid solution. Recently I have been noticing smut on parts.

Thermal Cleaning   02/01/07
We currently use a phosphate/rinse/non-chrome seal on light gage sheet metal parts. Someone has suggested we consider thermal cleaning instead of chemical cleaning as I'm getting our three-stage wash line quoted for replacement next year.

Plaforization Performance   12/01/06
We are looking to install a Plaforization system for ornamental iron and aluminum fence. Do you know how many hours of salt spray we can get out of that system?

Alodine   08/01/06
We use alodine on 5053 aluminum and use a water based coating. We want to change to powder but we are also having to meet the RoHS requirement that does not allow hexavalent chrome in the alodine. Have you found or know of an alternative to the Alodine that would give good adhesion and good Florida exposure.

June Issue   08/01/06
I am a loyal reader of PRODUCTS FINISHING and just finished reading the June issue. You are always very thorough and descriptive. I observed your response to E.P. regarding the phosphate cleaning systems and have some other suggestions...

Phosphate Cleaning Systems   06/01/06
We currently use an iron phosphate one-step cleaner applied manually through a high-pressure wand. The soap solution is applied at medium pressure and a clean water rinse is applied at high pressure.  Most of the material we are treating is hot-rolled, welded and extremely grimy.
Researching, I noticed we were keeping zero controls on anything we were doing so I started from the ground up.

Hydrogen Embrittlement Problems   04/01/06
We have a problem with hydrogen embitterment.

Iron Phosphate-Rinsing Required?   04/01/06
Must iron phosphate be rinsed before painting? What problems might I have if not rinsed? R.K.

Nanoceramic Pretreatment   04/01/06
I have been informed about nanoceramic pretreatment prior powder painting. Any experience? Is it really good? Where is the catch?

Passivate Using Different Materials   04/01/06
Can I passivate assembled parts with two different materials? One is 304 stainless steel tube and the other is 303 stainless steel solid. I am using epoxy glue made by 3M #2214 regular. I want to know if the acid will create problems to the glue or harm the parts.

USA Made Alternative to Ecophor   04/01/06
I am searching for a U.S.-produced product to take the place of Ecophor A447 product. Do you know of one or can you direct me to someone who may know of one?

Thickener For Nitric Acid   02/01/06
My question is to find one thickener for nitric + HF acid solution for cleaning the stainless steel.

Oxidation Under Paint   12/01/05
We clean our steel parts and use a phosphating process for pretreatment. After this we use chemical to neutralize this. Some weeks later we can find that there is oxidation below the paint and peels off the paint.

Phosphating on Differing Surfaces   12/01/05
Is a smooth surface better for phosphating or a rough one? We are thinking of moving to a steel media in our mass-finishing equipment instead of the ceramic media we are using now. There is no question the steel media provides for a better finish but will it affect the phosphating process negatively?

Changing from Zinc Phosphate to Iron Phosphate   10/01/05
We have been coating for the last 12 years (supply to a major automotive manufacturer). Since then we have been zinc phosphating the steel products. Would a shift to iron phosphate warrant the same qualities in withstanding salt spray tests?

Passivate Stainless Steel   10/01/05
I have been told that it is not necessary to passivate 316 S.S., but that 303 and 304 must be to provide a corrosion resistant surface.

Pretreat for Magnesium AZ91-d   08/01/05
I have some questions around proper pre-treatment of Magnesium AZ-91D. We have suppliers casting our parts in China and are experiencing blistering. Is there a standard pretreatment process and chemical to condition the substrate to accept paint?

Anaerobic Bacteria   06/07/05
We are continually having a reoccurrence of anaerobic bacteria in our system. We dumped the entire system, thoroughly cleaned it with peroxide, and months later, we are there again. One of my arguments is heat in the first stage (phosphate). Range is 90–140°F and it might average 108°F. I am arguing that temperature should be at least 130–135°F. Also, have some dragout issues into the other stages, especially rinse stage. Can you offer any advice on this problem? Am I correct in assuming part of the problem is a temperature issue with the sludge and low temps providing a breeding ground for the bacteria, especially when there is carryover to the rinse stage (ambient temperature)? Any help would be appreciated.

Pickling Stainless Steel Components Revisited   06/07/05
I have had similar problems most notably on 303 and 416 free machining stainless. The pits may be caused by the acid or caustic removing the micro sulfur inclusions that are used to make the material-free machining. Parts made from these materials are better off not having any passivation applied than doing one of these processes. The article in the Feb 2005 Products Finishing magazine did not specify the material. I feel that may be the key to the problem.

Plaforization   06/07/05
I have read some literature on a process for cleaning parts for powder coat called plaforization. Could you clarify the process as well as give your opinion of the process?

Pickling Stainless Steel Components   01/31/05
We are manufacturing SS components which we are pickling in HF/HNO3 soln for approx three mins. After this we are cleaning the components in caustic soda solution (pH 9.4) after which we are passivating in citrisurf at 80°C for 30 mins...

Powder Coating in China   01/31/05
Our company is purchasing powder coated mild steel automotive piece parts from a factory in China. This factory has a zinc phosphate pretreatment process...

Painting Stainless Steel   11/19/04
I built a SS rudder for a 40-ft sailboat after the second fiberglass one broke apart. Then, after I had sanded and faired it out, I warmed it up and painted it with hydrofluoric acid to etch it, rinsed it and painted it with a wash primer. That was coated with a gel coat epoxy primer. Could I have eliminated the acid etch and just used the wash primer, or vice versa?

Passivation of 420 Stainless Steel   06/01/02
I have recently read a very informative article on passivation at www.pfonline.com, however I did not recall seeing anything specific to 420 stainless. Will proper passivation prevent oxidation of this material?

Passivating Stainless Steel   02/01/02
Recently, we had to resurface a small section on a piece of stainless steel equipment. The grinding wheel that was used was made of iron. This was a very small section on a very large part so we would like to know if there is a way of removing any iron contamination without having the whole piece passivated. If it must be passivated, is it possible to do a "spot passivation" and will that be sufficient?

Chromate vs. Phosphate   12/01/01
I know iron phosphate works great on steel, but it is not as effective on aluminum. Chromate is excellent on aluminum, but can it also be used on steel? If so, is it as good as iron phosphate?

Preventing Oxidation and Decarburization   11/01/00
Can I prevent oxidation and decarburization during hardening of 1055 steel at 860C with super-heated steam at 550C using pretreatments? Any better suggestions?

Chlorinated Paraffins in Cutting Oil   09/01/00
I have discovered that our largest customer uses chlorinated paraffins in its cutting oils. My lab tells me that chlorine is present on the surfaces of the parts I am zinc-phosphating (five stages/dip immersion). About 4% of the parts show weak adhesion when they are coated with an air-drying black liquid alkyd. What happens when these paraffins are used? Can they cause this problem? How do I best remove them from the parts?

Determining the Passivation   09/01/00
What test methods are available in determining the passivation of stainless steel? Please give me the "down and dirty" methods. What certified labs are available for performing passivation tests on stainless steel?

Passivating 416 Stainless Steel   09/01/00
I have a customer who wishes to passivate parts made from 416 stainless steel. I have been told that this is not possible. Is this correct or am I being snowed? Also, will this process reduce the size of the part?

Zinc Phosphate Sludge   09/01/00
We run a zinc phosphate spray coating line where mostly mild steel is treated. Since the startup of the line, we have experienced problems with excessive sludge buildup.