Cleaning and deoxidizing agents for Alodine process
Alodine 1200/1200S: The question is; "Using 7175 aluminum, a large dia. (84") rolled ring forging with a cross section of approximately 1" by 4" is coated with Alodine. What are the most popular cleaning and deoxidizing agents? These rings are dipped. It is our understanding that each coating/plating house may use it own particular preference. How much does it vary within the industry? We have to deal with a military spec that nails down the particular cleaning and deoxidizing agents. The particular deoxidizing agent has been discontinued. Our customer (Navy) is hard to convince that we should be allowed to make the spec more flexible to accomodate what the industry is using.
Any help in this area would be appreciated.Jim Hodges
- Magna, Utah
Jim: The Navy's primary concern is that the finished parts they use on their ship or plane or whatever have the properties that they were designed for, and to have assurance for themselves and for the lives of those using the parts, they developed their system of specifications. For the most part most government specifications don't tell how to do the processing, but what properties they expect from a particular process. They do issue qualified products lists for various treatments, and Alodine and other chromate conversion coatings must meet the specification called Mil-QPD-81706 [link is to free spec at Defense Logistics Agency, dla.mil]. To meet the primary procesing specification, Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil], you must use one of the treatments given in the MIL-DTL-81706 qualified products list. I am not aware of any such list of cleaners or deoxidizers, but in order for conversion coated parts to have the properties to meet MIL-C-5541 or similar specifications, the number of cleaning/deoxidizing systems which allow the Alodine coating to meet these specs. is quite limited, particularly when working with high strength alloys. The problems arise, of course because of the alloying elements such as copper and iron.
Basically, the cleaner prior to Alodine is usually a non-etching alkaline cleaner, usually silicated. The idea is that the part must be cleaned of any physical soils without altering the surface. The deoxidizer then finishes the cleaning process by chemically removing any scale or oxides from the surface which might interfere with the chromate conversion coating. The deoxidizer has a minimal, controlled attack on the aluminum surface. Since Alodine was developed in the post- World War II era, the best way to deoxidize the high strength alloys has been to use a blended solution of chromic acid, nitric acid, a small amount of fluoride, and other minor ingredients. The blend must be right, so many processors use proprietary products. The particular spec. you are working to probably was developed for the particular types of parts you are processing, because the products listed allow the Alodine to meet the MIL specs.
- Madison Heights, Michigan
Thanks for your reply to my query. We are still in the process of negotiating with Navy to allow the use of Iridite 14-2 as the chem film of choice along with whatever cleaners and deoxidizers the industry is using. It is our desire to not hold our vendors to our locally created spec but to allow them to use MIL-C-5541 which is much more open ended.
Irridite 14-2 was in the QPL several years ago.
My wife's shop switched from Alodine 1200 to Iridite 14-2 several years ago and found it easier to use (less picky). We had to switch because Parker-Amchem shipped us three pails of off spec material in a row (two different lot numbers) and could not provide a different lot number. Lot numbers are available for those that doubt it.James Watts
- Navarre, Florida
This is turning into a discussion of competitive products, but I'd like to set a few things straight here. First of all, Alodine 1200S, not Alodine 1200, is our direct competitive product for Iridite 14-2. AL 1200S is an improved product over 1200, and we view 1200S as easier to use and less picky. Both products are improvements over Alodine 600, the original chromate conversion coating for aluminum. All of these products have been around since the 50's so why did American Chemical Paint, then Amchem, then Parker Amchem, now Henkel, sell the products side-by-side? Mostly because of the reluctance of the military and aerospace industries to change blueprints and specifications to allow the use of different products, even if new products were improvements. In other words, Jim Hodges' problem has been around for a long time.
This is somewhat proprietary, but I believe interesting: the primary improvements of 1200, 1200S, and 14-2 over products like Alodine 600 were the use of ferricyanide as an accelerator, which also improved bath life. However, after 40 years, some of our larger customers are going back to Alodine 600, because the ferricyanide is much more difficult and expensive to waste treat than hexavalent chromium. As a result, the sales volume of AL 1200 has diminished to the point that it was obsoleted. We will continue to sell AL 1200S for the forseeable future, but we have just recently obtained QPL approval for Alodine 1600, a liquid replacement for Alodine 600 or 1200S. We hope that the industry will see the advantages that we see:
First, our environmental people tell us that the carcinogenic, mutagenic properties of hexavalent chromium come mostly from breathing the dust of chromium oxide or salts, therefore handling liquid chromium products is much safer.
Second, the problem that Jim Watts described relative to Alodine lots out of spec almost surely comes from the difficulty of blending crystalline salts of materials of different crystal size, and having the mixture stay totally uniform is not an easy manufacturing problem. (I used 14-2 for 16 years in two different job shops, and can assure you that Allied, Allied-Kelite, Witco, now Macdermid has had the same problem through the years, as you can see the striations of orange and white salts in any of these products.) The way to get around this problem is to dissolve the salts in water and sell the liquid. There are technical problems involved in making concentrates of these materials, but we got around them by making two packages. We view the necessity of two packages as an advantage, as we can now control bath components separately for increased bath life.
- Madison Heights, Michigan
I appreciate all of the feedback on my original question. Our customer (the Navy) has finally allowed us to proof the use of Iridite 14-2. In fact, we're going to LA next week to witness the operation. In reading the responses, it sounds as though our Navy office is reinventing the wheel. It is more than likely a manifistation of the left-hand/right hand syndrome.
Thanks, again!Jim Hodges
Based on the response about Alodine replacements, I am wondering where I can get information about the Alodine 1600. Does it still contain chromium?Phyllis Brusky
- Columbus, Ohio
Hello, Ms. Brusky. You'd get the info from Henkel - Madison Heights, MI
Ted Mooney, P.E. RET
Pine Beach, New Jersey
I was always used to working with Iridite 14-2 for many years, as I have worked in the Aerospace industry for 10+ years . I always liked the simplicity of using this Aluminum conversion coating. In 1997 the company I worked for, sold the plant to GE Aircraft Engines and we are now a subsidiary of that corporation, located in Middle River Maryland. At this time because of many changes in Mil specs and alot of new technologies with other military manufacturing companies , we switched to using Alodine 600 conversion coating, as it falls under all aspects of Mil-5541 Types I\II\Type II class 3 depending on amount of time immersed in solution. Aerospace manufacturers that we deal with now, preferred the use of this formula and the use of Parker-Amchem 7-17 for deoxidation of material to be coated. I myself am very happy with this conversion coating, its always even and consistent throughout on the materials being coated. It is also much easier to maintain with less titrating and ! PH adjustments, as long as "Dragout" is kept to a minimum. Just thought I would like to share this with you, to give you a perspective on Alodine over Iridite 14-2. In my opinion,either one is great for coating before priming materials, and or for maximum corrosion resistance over all.James C Miller
- Bel Air, Maryland
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