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"Finishing Technology Hotline BBS" Postings by Topic

Ed. note: before the internet existed, there was a time when "Sysops" (system operators) ran publics forums via dial-up modems and "BBS" (Bulletin Board System) software. Here is one such discussion from 1992.


Process control

And I thought muriatic acid was pretty much cut and dried. Yikes! Msg. #2955 in ** Ask Plater B**
Posted on 10/27/92 at 21:03:50
To: ALL From: KEN ROSENBLUM - MURIATIC ACID We use muriatic acid on a number of different plating lines to 1) pickle oxide off of steel and 2) strip zinc and cad from rack tips on those lines. I would like to find an analytical test to determine when the acid becomes weak enough to dump (we would set this point). Presently, we test for free acidity, and metal content. Unfortunately, none of these consistently correlates with the strength of the acid as seen on the plating line. Sometimes, the free acidity is high, with little metal content, but the acid does not pickle well. Sometimes, the opposite occurs. Does anyone have any ideas to help better regulate acid life? The production personnel always claim that the acid is weaker than it actually is and the waste treatment people always claim that the acid should not have to be dumped so soon. I'm sure that most every job shop that runs miscellaneous work wrestles with this problem. Thanks, Ken

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Msg. #2958 in ** Ask Plater B**
Posted on 10/28/92 at 08:19:17
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'MURIATIC ACID'
Ken, is the temperature of your acid always constant? What I mean is, of course, that the acid will act slower when cold and *much* faster at elevated temperatures. That may help explain the discrepancy between the analytical data and the acid apparent strength. Regards, Plater B

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Msg. #2962 in ** Ask Plater B**
Posted on 10/28/92 at 10:01:06
To: KEN ROSENBLUM From: TED MOONEY - Reply To 'Process Control'
My suggestion would be to start by requiring the platers to log the voltage and amperage, without you declaring in advance what the values ought to be. Eventually, as they are forced to observe the values, the pattern will become clear to them. They will see the significance, and may also volunteer information regarding what their real world experience has taught them about required V-A for different parts and load sizes. Things like hole size in the barrels, broken danglers, dirty joints in the bussing of a particular station will begin to surface as variables that must be corrected.

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Msg. #2964 in ** Ask Plater B**
Posted on 10/28/92 at 23:54:09
To: BERL STEIN From: KEN ROSENBLUM - Reply To 'MURIATIC ACID'
Berl, the acid temperature is fairly constant -- at least over the time period of the life of a typical acid bath- 1 to 2 weeks. It is probably 15 degrees F colder in the winter than in the middle of the summer, but this doesn't explain the discrepencies I see. Also, it seems that acid strength correlates more closely with the acid's ability to strip zinc than the ability to strip chrome. As a correlary, it seems that chrome metal will kill the aggressiveness of muriatic acid more rapidly than a similar amount of dissolved zinc. Ken

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Msg. #2966 in ** Ask Plater B**
Posted on 10/29/92 at 00:00:19
To: TED MOONEY From: KEN ROSENBLUM - Reply To 'Process Control'
Ted, thanks for the idea. Although, I'll have to prepare myself for the chorus of "Well, just don't expect me to keep up with the production you want if I have to do all this paperwork". Or does this only happen in Union shops?

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Msg. #2969 in ** Ask Plater B**
Posted on 10/29/92 at 09:21:26
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'MURIATIC ACID'
Ken, one other thing that might explain the apparent loss of acid activity would be organic contamination
- starting from plain old oily films floating on the surface ( look at the acid dip tank walls right above the solution level for oily stuff) and all the way down to dissolved organics coming from the stripped metal, dragin, etc. The metals themselves might act a s inhibitors, too. I don't think dissolved zinc does, but am not so sure about chromium
- will have to check some books. Good luck Plater B

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Msg. #2977 in ** Ask Plater B**
Posted on 10/30/92 at 08:55:39
To: BERL STEIN From: TED MOONEY - Reply To 'MURIATIC ACID and CHROME'
I don't think they'll be an awful lot of chromium in the muriatic acid, Berl, because it is very readily stripped in most electrocleaners.

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Msg. #2981 in ** Ask Plater B**
Posted on 10/30/92 at 18:42:34
To: BERL STEIN From: KEN ROSENBLUM - Reply To 'MURIATIC ACID'
Berl, We also thought about oils inhibiting the acid activity, so we installed flo-king in tank skimmers. Now, the acids look pristine, but the activity differences we see still exist. Ken

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Msg. #2990 in ** Ask Plater B**
Posted on 11/03/92 at 08:07:09
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'MURIATIC ACID'
Are you using carbon or regular filters on your acid tanks? There might be some dissolved organics that will not be removed readily, except through carbon treating. Berl

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Msg. #2994 in ** Ask Plater B**
Posted on 11/03/92 at 21:51:57
To: BERL STEIN From: KEN ROSENBLUM - Reply To 'MURIATIC ACID'
Berl, we are using regular 100 um cotton spun filters. We could try carbon filters. I know, though that there are a lot of oils because the regular filters are coated with oil. In fact, there is so much oil, that I think that regular filters do just as much as carbon filters would. My feeling, though, is that there is some basic stoichemetric (chemical) reason why free acidity does not correlated with agggressiveness of pickling as we see it on the plating line. I just wish I knew what it is. I think that we're either not measuring the right parameters or we are not looking at them correctly.

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Msg. #2995 in ** Ask Plater B**
Posted on 11/04/92 at 07:22:49
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'MURIATIC ACID'
Ken, I don't think that chemistry itself is to blame: if you are using the right titration methods and appropriate indicators, your measured concentration is what you have. From what you're telling me ( filter cartridges covered with oil), you need a skimmer that'll remove the oil without letting it get onto the filter cartridges and filtration through a carbon pack or cartridge in the least to get rid of the dissolved organics. Again, some ingredients of machining and other oils are water/acid soluble and will inhibit your reaction either through true inhibition or simply by adsorption. Try it. Good luck, Plater B

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Msg. #3162 in ** Ask Plater B**
Posted on 12/07/92 at 19:50:02
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'Muriatic acid strength'
Ken, I have been thinking about your HCl problem and I think I'm a little confused. You have tested how much the presence of zinc slows down the stripping action of the acid, in other words, you have a chart or plot that tells you that at, say 5g/l zinc the same concentration of HCl will strip Zn slower than at 1g/l, is that correct? And with time the acid apparently loses strength more than what it should be if you went by your zinc concentration? Is that correct? Cheers, Plater B

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Msg. #3163 in ** Ask Plater B**
Posted on 12/07/92 at 22:19:40
To: BERL STEIN From: KEN ROSENBLUM - Reply To 'Muriatic acid strength'
This is what we are trying to do. Unfortunately, I have baths where I find no correlation between stripping rate and zinc concentration, iron concentration, free acidity, or a combination of these. This is the confusing part. Ken

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Msg. #3179 in ** Ask Plater B**
Posted on 12/09/92 at 07:44:06
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'Muriatic acid strength'
OK, you have metal concentrations in your acid along with the free acidity, and you can measure the stripping rate. Now, when the acid is old and contains a lot of various ions your stripping rate is lower than what the free acidity would suggest, is that what you are experiencing? Berl

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Msg. #3186 in ** Ask Plater B**
Posted on 12/10/92 at 00:05:00
To: BERL STEIN From: KEN ROSENBLUM - Reply To 'Muriatic acid strength'
Most of the time, as the acidity decreases and the metal ions increase our stripping rate decreases as you would expect. About 25% of the time, the stripping rate decreases with high acidity and low metal ion concentrations. This is the confusing part. Ken

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Msg. #3188 in ** Ask Plater B**
Posted on 12/10/92 at 07:46:25
To: KEN ROSENBLUM From: BERL STEIN - Reply To 'Muriatic acid strength'
My question still is: do you know how much of a decrease to expect? In other words, did you ever dissolve on purpose, say 5g/l Zn and measured the stripping rate, then did the same for 7g/l, etc. That is the only way to test how much the metal ions themselves would slow down the stripping rate. If you did this and then found that in practice that relationship does not hold, you would go for other contributors (Fe, Cr, organic inhibitors,etc.). Cheers, Plater B

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Msg. #3190 in ** Ask Plater B**
Posted on 12/10/92 at 08:34:33
To: BERL STEIN From: TED MOONEY - Reply To 'Muriatic acid strength'
I wouldn't expect this to be a factor in muriatic acid pickling, since it's rather dilute, but I know that in the steel industry they carefully control the water content in the sulfuric for controlled attack. When the attack rate starts slowing down, they ADD water to bring it back up. In other words, there isn't enough water for maximum activity while the acid is still strong--and this allows them to maintain a constant rate as metal builds up, by adding water.

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Msg. #3197 in ** Ask Plater B**
Posted on 12/11/92 at 23:18:16
To: BERL STEIN From: KEN ROSENBLUM - Reply To 'Muriatic acid strength'
I think we did this, but don't remember the results. I'll check with my chemist on Monday. thanks, Ken

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Msg. #3932 in ** Ask Plater B**
Posted on 06/14/93 at 07:50:26
To: BERL STEIN From: STEVE RUDY - Non destructive thickness determination. Dear Berl, Is it possible to measure thickness of brass electroplate over copper substrate, non destructively? I would assume X Ray with a known alloy deposit as the standard, measure radiation of the zinc. What do you think? What else to consider? S. Rudy

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Msg. #3936 in ** Ask Plater B**
Posted on 06/14/93 at 20:18:48
To: STEVE RUDY From: BERL STEIN - Reply To 'Non destructive thickness determination.'
Steve, give me a couple of days to look into the problem
- nothing comes to mind off-hand (not that I am a non-destructive testing expert). Get back to you soon, Plater B

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Msg. #3937 in ** Ask Plater B**
Posted on 06/16/93 at 07:43:08
To: BERL STEIN From: STEVE RUDY - Reply To 'Non destructive thickness determination.'
Thanks...SFR

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Msg. #3939 in ** Ask Plater B**
Posted on 06/17/93 at 21:26:46
To: STEVE RUDY From: BERL STEIN - Reply To 'Brass over copper non-destructively?'
Steve, it looks like the approach you suggested, X-ray fluorescence is the only viable one (unless, of course, you can physically measure the parts before and after deposition and use the dimensional difference to calculate plate thickness). You may want to call VEECO/UPI at 516-349-8300. By choosing ext.477 you'll get to speak to Mr. Frank Ferrandino who is an expert in the method. Cheers, Plater B

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Msg. #3941 in ** Ask Plater B**
Posted on 06/19/93 at 22:50:51
To: STEVE RUDY From: BERL STEIN - Reply To 'Non destructive thickness determination.' ØĚSteve, here is some additional information on your problem which I just received from my brother in Montreal. "The letter I was trying to send you reads: Mr Brad (Kevin) Krompart from TCI is saying they do not have problems measuring copper over brass, while he does not know if brass on copper indeed is a problem, it should be expected. He suggests to call Serge Joffe
- Twin City President, at 716-692-8855 or 716-692-3265, who may have some info on the matter. In any case, they may work out an alternative non-destructive method." Hope this helps. Regards, Plater B

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Msg. #5082 in ** Ask Plater B**
Posted on 04/28/94 at 21:32:31
To: ALL From: JOEL TOMASETTI - Chrome in Nickel Baths What is the best way to remove chrome from a nickel sulfamate plating bath. We barrel plate stainless steel parts and the chrome must be leaching from these parts. But I've gotten different answers as to how to dummy it out. Is it better to use low ASF or high ASF dummying to get rid of the chrome. Appreciate any help on this matter.

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Msg. #5083 in ** Ask Plater B**
Posted on 04/28/94 at 22:49:32
To: JOEL TOMASETTI From: TED MOONEY - Reply To 'Chrome in Nickel Baths'
Neither. I don't think you will find it possible to dummy chrome out of a nickel bath at any current density, high OR low. There are procedures for using ferrous sulphate, raising the pH, and filtering--and they may work for you. You probably should go into this bath electrically "hot" so the chromium does not dissolve this way.

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Msg. #5085 in ** Ask Plater B**
Posted on 04/29/94 at 19:22:16
To: JOEL TOMASETTI From: BERL STEIN - Reply To 'Chrome in Nickel Baths'
Joel: Whatever advice you get, you'll have to test it yourself to make sure it works, and I can't think of a better and easier way to do it then in a Hull cell. Simply take your contaminated solution, run a standard test for your baseline, say at 1 A for 5 min. Then, treat the solution, say, with hydrogen peroxide, and start dummy plating at a low current density (.5-1 ASF), watch the cathode appearance, then go higher in amperage, etc. After dummying for what you think would be enough (2-4 hours, I once did it for 12), run another Hull cel under standard conditions and see if if helped. Trial and error, but it always works. Good luck, Plater b

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Msg. #5087 in ** Ask Plater B**
Posted on 04/29/94 at 19:43:29
To: BERL STEIN From: TED MOONEY - Reply To 'Chrome in Nickel Baths'
I agree on hull cell testing, Berl. And I'll agree that dummying can remove tramp metals. But it took one of plating's greatest inventions to just get chrome to plate _at_all_, with the sulfate ratio just right. I don't think there's any possibility of plating chrome out from a nickel sulfamate bath.

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Msg. #5089 in ** Ask Plater B**
Posted on 04/30/94 at 20:41:45
To: TED MOONEY From: BERL STEIN - Reply To 'Chrome in Nickel Baths'
It may not be possible to dummy hexavalent chromium out directly, but some combination of oxidation/reduction along with pH manipulation might get it out
- remember, we are not trying to make it plate bright and shiny, or coherent at all, for that matter
- we just want to get rid of it. People who plate Cr on top of Ni must be doing it routinely..., since cross-contamination is almost unavoidable with mass-production techniques. Plater B

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Msg. #5091 in ** Ask Plater B**
Posted on 05/01/94 at 15:15:25
To: BERL STEIN From: TED MOONEY - Reply To 'Chrome in Nickel Baths'
People who plate chrome on top of nickel _are_ routinely removing impurities from the nicklel. They are dummying to remove copper and other stuff; but I think they are using ferrous sulphate to precipitate the chrome, and filtering it out.

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Msg. #5096 in ** Ask Plater B**
Posted on 05/01/94 at 23:09:39
To: ALL From: TOM PULLIZZI - chrome in nickel use bisulphite to reduce chrome, then hi pH treat to remove trivalent if the person who wnterested would call me at 609-361-2272 i would't mid mind sharing my reference material with him

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Msg. #5103 in ** Ask Plater B**
Posted on 05/04/94 at 08:11:10
To: BERL STEIN From: STEVE RUDY - Reply To 'Chrome in Nickel Baths'
Generally cross contamination, or chrome backwards into the nickel bath is almost nil in occurence. That's chefly due to the specific arrangement of process tanks and rinses. But there is one typical source of chrome contamination into the nickel bath. This is poor condition of rack coatings (tears, rips, pinholes, etc...). Chrome solution may not totally drain out as the racks return and some chrome seeps in the nickel bath. Another chance, although remote is the drag in of chrome contaminated electrocleaner. It's got to pass the post cleaner rinse and acid plus post rinse. As Tom mentioned the best purification procedure for hexavalent chrome in nickel is sodium metabisulfite reduction to the trivalent state followed by precipitation as the hydroxide, above pH 5.0. Another older practice was to add a lead salt to precipitate the lead chromate, but the status of lead prohibits this procedure. SFR

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Msg. #5104 in ** Ask Plater B**
Posted on 05/04/94 at 08:23:23
To: TED MOONEY From: STEVE RUDY - Reply To 'Chrome in Nickel Baths'
Yes, quite correct. And what a curious position regarding chromium. It cannot be dummy plated out of a contaminated plating bath. Just as metallic contaminants cannot be dummy plated out of hexavalent chromium plating bath. Berl, if you thing the bath may contain hex chrome, immerse a brass panel in the solution dead for about 30 seconds, then plate. Splotchiness or blistered plate will likely verify the presence of hexavalent chromium. You can also employ the dephenylcarbazide spot test,as a color test confirmation. Another neat test is to reduce pH of a test tube sample of plating solution to 2 with sulfuric acid. Add a few granules of potassium iodide or 10% potassium iodide solution. Next add a few mls of a non polar or weakly polar solvent (methylene chloride, tec...) if hex chrome positive, the bottom layer in test tube (solvent) will be pink to red colored. This is result of hex chrome oxidizing iodide to elemental iodine. It's a sensitive test down to 25 ppm of hex chrome. SFR

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Msg. #5107 in ** Ask Plater B**
Posted on 05/06/94 at 22:17:42
To: STEVE RUDY From: BERL STEIN - Reply To 'Chrome in Nickel Baths'
Looks like I missed a couple of messages 'round here when they appeared- thanks to all who contributed with good advice and experience in this murky business. Plater B

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Msg. #5149 in ** Ask Plater B**
Posted on 05/12/94 at 12:10:29
To: BERL STEIN From: STEVE RUDY - Reply To 'Chrome in Nickel Baths'
No problem, I hope the information helped. SFR

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