- Email: [email protected]
Waste treatment of soak cleaners
Heardon the Hotline by Ted Mooney, P.E.
Join us at http://www.finishing.com/Letters
A
presumably reliable statistic from May claimed that the percentage of business people in the U.S. who have Internet access and regularly use E-mail had reached the 40% mark and was still climbing rapidly. If you are already signed up we’ll see you on line. If not, by the time you are reading this, the percentage of connected business people will probably be hovering right around the magic 50% divide. Since such figures always have a margin of error it’s possible for you to sign on right now and still arguably claim to yourself that you were in the forefront. But that won’t be possible just a couple of months from now; so this is your very last chance to avoid being a foot dragger. The Internet, E-mail, the web, and electronic file transfers are not going away, and those who don’t get on board are choosing to consign themselves to the business backwaters. It’s later than you think.
GALVANIC CHASSIS
CORROSION
AND COMPUTER
We manufacture equipment used in the computer industry. The question that I have relates to plating sheet metal parts with electroless nickel versus using a zinc (ASTM B 633 Type 3) plating. In some cases the plating is then covered with paint. We have a chassis with complex bends and are concerned that the process used to plate zinc does not yield acceptable coverage (special electrodes would be required). Because of a concern about galvanic corrosion, parts that come in contact with the above part would also be specified as electroless nickel rather than zinc. Some vendors seem to prefer to work with zinc. Where can I find more information on galvanic corrosion and its relative importance in our market? (1 can understand the concern about equipment that has a long life cycle exposed to the weather, but I need help assessing the issue as it relates to computer assemblies.) Is galvanic corrosion a concern when designing a computer chassis (typical office environment) using parts in contact with each other that have been plated with electroless nickel and zinc? Is there any reason to specify that all of the parts be either one or the other type of plating? Phillip Hogland, Rimage Corp., [email protected] Zinc plating is the usual approach, and I am not familiar with any computer chassis being electroless nickel plated, although I can’t say it isn’t done. The zinc plating solution should be alkaline, and preferably cyanide, due to its far greater throwing power. Acid zinc is probably inappropriate METAL FINISHING
. SEPTEMBER
1997
for chassis work. Yes, auxiliary anodes are beneficial and sometimes mandatory for good coverage; but so what? It will still probably be significantly less expensive to zinc plate the chassis than to electroless nickel plate them. There are some environments where electroless nickel exhibits superior corrosion resistance to zinc, and some where it doesn’t. It is important to recognize that nickel is cathodic to steel and accelerates its corrosion if the coating is breached. Zinc is anodic and protects steel even if there are scratches or pores. Consider the screws. They are small in surface area, and thus will corrode rapidly if anodic to the chassis. Will they also be electroless nickel plated? I don’t know your full story, but my first thought is that switching from zinc to electroless nickel, in an application where it isn’t necessary and may be detrimental, to avoid the use of auxiliary anodes, which aren’t that big a deal, isn’t the right approach. Ted Mooney, Finishing Technology, [email protected] Ted is absolutely correct about using internal anodes. Properly designed, zinc plating coverage can be quite uniform. especially when using a cyanide electrolyte. Even with the extra tooling costs it will be much less than electroless nickel plating. Have you considered using precoated sheet steel? Coverage is guaranteed and you can avoid plating costs entirely. Galvanneal and electrogalvanized sheet stock work well in many cases for computer frames and chassis. Many computer manufacturers are now using precoated steels for some or all of their sheet metal parts. Pop the top on your PC and have a look inside. Chances are it’s precoated steel inside. In a benign office atmosphere, precoated steels can provide adequate corrosion protection, even on cut edges. It may not work for everyone, but it’s well worth considering. Gary Krech, [email protected]
WASTE TREATMENT
OF SOAK CLEANERS
I am working on a student project (for completion of a MS Environmental Engineering degree) for a metal plating and finishing shop. This small shop currently disposes of their soak cleaners as hazardous waste. The local POTW will let them dispose of the cleaners to the POTW but the metal concentrations are too high. They also have a wastewater treatment system with precipitation and clarification for their rinses. The chelating agents in the soak cleaner interfere with the current treatment system. I think they should treat this cleaner separately for metals, maybe emul-
0 Copyright Elsevier Science Inc.
69
CHEMICAL COMPANY Our success is built on quality and service while providing total chemical processing capabilities. Coral Chemical manufactures over 1800 proprietary, industrial chemical products. From the press room to the paint room, Coral can help. ??
Metalworking
Fluids
Coolants Drawing/Forming
?? ??
Compounds
Stamping ??Rust Inhibitors
??
??
Metal
Finishing
Cleaners ??Iron/Zinc ??
??
Phosphates
Process
Water
Treatments
Conditioners ??Flocculants ??
??
System
Controllers
??
Anodizing
??
Customized
Products
Call today for a brochure on how Coral Chemical Company can assist you.
CHEMICAL COMPANY
U.S. OWNED AND OPERATED FOR OVER 40 YEARS WAUKEGAN, ILLINOIS (647) 336-8100 (800) 228-4646 FAX: (847) 336-8518 LITHONIA, GEORGIA (770) 593-8000 (800) 228-4646 FAX: (770) 593-4260 PARAMOUNT, CALIFORNIA (562) 531-6363 (800) 899-6364 FAX: (562) 531-6405
Circle 029 on reader information card 70
sion breaking followed by precipitation, or look into different cleaners, which have chelating agents that will not interfere with treatment. (1) How do most smaller facilities dispose of soak cleaners? (2) What should I be looking for in a more treatable cleaner? (3) What options have worked for treatment of these cleaners? I would appreciate any input on this. Kim Cook, ERG, [email protected] I can answer question (2) for you. One method, which is successful in choosing a cleaner to fit in with your waste treatment procedures is to take a sample of the cleaner from your supplier and make up a 3% solution. Next, add a copper containing solution such as a used nickel stripper, and waste treat it in your lab. If, upon analysis, you have less than 2 ppm of copper you’re in pretty good shape. Many modern cleaner manufacturers make nonchelating cleaners, and you need to make your supplier aware of your needs from the start. He may handle all the preliminary lab work for you. Hope this helps. Mike McDonald, Mack Products, [email protected] The first thing I would suggest is to switch to a nonchelated cleaner. I have experience treating both, and I believe not only will they be easier to deal with as waste, but they will also outperform the chelated cleaners. You did not specify if your system is running continuous flow or batch treating. My preferred method is continuous flowing rinse waters, with concentrates routed to a separate dump tank for treatment. After neutralization and the addition of polymer, the concentrates should be pumped through the filter press. Effluent from the filter press should be routed to the waste rinse water tank for a second treatment as well as the dilution effect of any possible remaining residuals. As far as treatment, I have tried several methods of treating waste cleaners. My best luck has been with ferric sulfate and industrial grade hydrogen peroxide. Sulfuric acid should be used to drop the pH until all cleaner is reacted. This may not happen until you reach 2.5 to 3.0 pH. From this point the pH should be raised to about 4.5 to 5.0 pH. For a 300-gal tank add approximately 4 gallons of ferric sulfate. Follow this with 10 gallons of hydrogen peroxide. After letting the treated cleaner react with the iron and peroxide for about an hour, gradually add caustic soda to raise the pH to 7.0 to 7.5. With the addition of the caustic, the mixture will foam up so be sure not to overdue it. This works very well with nonchelated cleaners. Phil Pace, [email protected] We were faced with a similar problem of treating a highly chelated cleaner in our batch treatment facility. Having tested and rejected ferric chloride, we had some success with calcium chloride but were not able to reduce the concentration of nickel to our discharge limit (2.4 ppm). Then we finally started working with magnesium hydroxide and this stuff works. Not by itself, in combination with sodium hydroxide, but we are treating now a highly chelated room temperature cleaner at, sometimes, a 30% concentration in our wastewater with, at times 100 to 200 ppm nickel. After months of trial-and-error and with some help from a supplier, we have a magnesium hydroxide/sodium hydroxMETAL FINISHING
??
SEPTEMBER
1997
ide cycle that breaks up chelates batch treat the effluent:
PUTA
and lets us consistently
1. Reduce pH to below 2 with sulfuric acid. 2. Add about 1 lb/100 gal of magnesium hydroxide (we buy it dry and prepare a slurry right before use). Allow to mix for 15 to 30 min. This brings the pH up to above 5.0. Add sodium hydroxide to raise pH to above 11.0. Mix for 30 min. Add flocculent. Let precipitate. It usually takes anywhere from 1 to 6 hours in our 500-gal treatment tank. Transfer supernatant into pH reduction tank, lower the pH, and discharge. This cycle reduces the concentration of nickel to less than 1.5 ppm. 7. Dewater the sludge with a filter press. We like this cycle for its simplicity, low expense, and high tolerance to cleaners, nickel sludge dumps from anode bags, and just about anything. No upsets so far in over 6 months of using it. Try this stuff-it is good. Knowing how reluctant production people could be to switch cleaners (or, for that matter, change anything in a cycle that works), finding a treatment method that does not require any process changes in plating may be a blessing. Berl Stein, Reflexite PTC, [email protected]
Base mounted, in-tank, space-maker & bag filtration systems ??Stock or custom designed systems 0 Large selection for filtration, carbon treatment & precious metal recovery ??
Berl: Several years ago I read of people who preferred magnesium sulfate to calcium chloride or ferric chloride for handling spent cleaners. So I suspect that the benefit of magnesium hydroxide in treating cleaners has to do with the superiority of magnesium as a chelate breaker, more than the long reaction time of magnesium hydroxide slurry compared to caustic. If an occasion suggests, you might try the sulfate. Phil: In 1997 I don’t believe in continuous treatment of anything. When the settlement agreements between NAMF and EPA were reached 16 years ago and 40 CFR said that platers had to be in “consistent compliance,” I thought “consistent” held an accepted meeting of “the great majority pressure, of the time.” Under unceasing environmental “consistent” seems to have in practice come to mean “absolutely flawless.” I think batch treatment, with the ability to test every batch released, is the only safe approach anymore. Mike: I’m not so sure that nonchelated cleaners are always necessary. I have recently become a convert to the proprietary organometallic coagulants. While powerful precipitants like dithiocarbamate (DTC) have been around for a while, they didn’t seem to live up to their promise because they tended to produce a thin cloud of essentially unsettleable precipitate; the organometallic coagulants seem to turn this cloud into a fairly settleable floe. Ted Mooney, Finishing Technology, [email protected] The data we obtained developing our cycle seems to indicate that you are right and the main benefit of magnesium is its chelate-breaking “power”; however, there might be other factors such as the adsorptive properties of magnesium hydroxide sludge that may coprecipitate and, therefore, more fully remove the other heavy metals in the mix. Help me understand why you are suggesting we try mag-
FILTER
PUMP INDUSTRIES 7932 Ajay Drive, Sun Valley CA 91352 (818)504-2391FAX (818) 768-7590 Circle 042 on reader information card
METAL FINISHING
??
SEPTEMBER
1997
71
nesium sulfate instead of magnesium hydroxide. Magnesium hydroxide is so inexpensive, easy to work with, and serves the multiple purpose of raising the pH, breaking up the chelates, and (maybe) coprecipitating the sludge without contributing additional ions (sulfate) in the treated water that I think it is the right substance to use. Berl Stein, Reflexite PTC, [email protected]
acting sodium hydroxide does. Sorry for the confusion, I wasn’t proposing a change to a proven system, but discussing another weapon for other situations. Ted Mooney, Finishing Technology, [email protected] HUMIDITY PLASTIC
FAILURE
IN WATERBORNE
PAINT ON
We are currently having problems with condensing humidity failures with waterborne paints over ABS and polycarbonate. It appears that the infrared oven is annealing the top surface of the film, entrapping the water in the film. The failure mode is streaking or whitening. Has anyone seen failures like this? Any insight on fixes? Longer bake? Slower or faster solvent blend? Resin problems? Kris Pierce, [email protected]
You’ve developed a treatment cycle that works fine, and you are right about its advantages; there is no reason to change it. My point was only that, if magnesium hydroxide is great stuff but has the one big disadvantage of long reaction time, it might be possible to eliminate that disadvantage-should the need arise-by using a soluble salt in place of the slurry. But your suspicion that magnesium hydroxide may also tie up metals by adsorption could be correct; I don’t know. While magnesium sulfate might break the chelate, and quickly, it cannot be expected to contribute to filterability the way magnesium hydroxide does, because this is not a function of the magnesium ion but the fact that the sparingly soluble hydroxide does not rapidly precipitate the metals into a hydrated gelatinous mass the way rapidly
Is this occurring straight from the oven? If not then it is likely to be a general humidity failure of the resin, which would cause “chalking” of the surface, i.e., streaking. Sounds like a resin problem to me. Paul Lindley, [email protected] Ted Mooney is an independent consulting engineer based MF in Kinnelon, N.J.
WANT TO WRITE FOR METAL FINISHING? write to request a copy of our guidelines for authors, or simply contact the editor at METAL FINISHING 660 White Plains Rd., Tarrytown, NY 10591,Phone 914-333-2571?? Fax 914-333-2570
Call or
With Forty-Five Years of Ultrasonic Experience...
1960's
ComDact Sire: Only 4 9/l 6” high-ideal for limited space installations. Low Cost: Excellent for systems requiring quickopening/quick-closing solenoid valves. . Hlah Pressures: Back pressures to 90 PSI, inlet to I 140 PSI. ?? Unique: Teflon Bellows barrier type dynamic seal prevents leaking of fugitive emissions. ?? Versatile: Used with virtually all solutions: acids, caustics, solvents and ultra-pure liquids. Der or Performaw: 2,000,OOO cycle design. ??slzas: 114”& i/2” pipe size - 3/l 6” orifice. ?? _Materialg: PVC, Polypro & PVDF.
cleaning problem, we’ve probably had some experience cleaninnm-- a similar oart or material. Since 1951 &e Wave has been applying the power of ultrasonic cavitation to cleaning aluminum, brass, ceramics, copper, glass, iron, nickel, plastics, printed circuit boards, steel, zinc and others. If you have a new or ongoing cleaning problem, let Blue Wave make it a thing of the past Call us at 1-800-573-0144.
For further information request Catalog EAST
Blwwave-ka
960 S. RoHfStreet Davenport,IA 52802
Phone:l-319-322-0144 Fax:l-319-322-7180 I
Circle 087 on reader information card
72
Circle 127 on reader information card Mt
IAL t-~NIYHINU
??
5tr
I imt5en
IYY/
Join us at http://www.finishing.com/Letters
A
presumably reliable statistic from May claimed that the percentage of business people in the U.S. who have Internet access and regularly use E-mail had reached the 40% mark and was still climbing rapidly. If you are already signed up we’ll see you on line. If not, by the time you are reading this, the percentage of connected business people will probably be hovering right around the magic 50% divide. Since such figures always have a margin of error it’s possible for you to sign on right now and still arguably claim to yourself that you were in the forefront. But that won’t be possible just a couple of months from now; so this is your very last chance to avoid being a foot dragger. The Internet, E-mail, the web, and electronic file transfers are not going away, and those who don’t get on board are choosing to consign themselves to the business backwaters. It’s later than you think.
GALVANIC CHASSIS
CORROSION
AND COMPUTER
We manufacture equipment used in the computer industry. The question that I have relates to plating sheet metal parts with electroless nickel versus using a zinc (ASTM B 633 Type 3) plating. In some cases the plating is then covered with paint. We have a chassis with complex bends and are concerned that the process used to plate zinc does not yield acceptable coverage (special electrodes would be required). Because of a concern about galvanic corrosion, parts that come in contact with the above part would also be specified as electroless nickel rather than zinc. Some vendors seem to prefer to work with zinc. Where can I find more information on galvanic corrosion and its relative importance in our market? (1 can understand the concern about equipment that has a long life cycle exposed to the weather, but I need help assessing the issue as it relates to computer assemblies.) Is galvanic corrosion a concern when designing a computer chassis (typical office environment) using parts in contact with each other that have been plated with electroless nickel and zinc? Is there any reason to specify that all of the parts be either one or the other type of plating? Phillip Hogland, Rimage Corp., [email protected] Zinc plating is the usual approach, and I am not familiar with any computer chassis being electroless nickel plated, although I can’t say it isn’t done. The zinc plating solution should be alkaline, and preferably cyanide, due to its far greater throwing power. Acid zinc is probably inappropriate METAL FINISHING
. SEPTEMBER
1997
for chassis work. Yes, auxiliary anodes are beneficial and sometimes mandatory for good coverage; but so what? It will still probably be significantly less expensive to zinc plate the chassis than to electroless nickel plate them. There are some environments where electroless nickel exhibits superior corrosion resistance to zinc, and some where it doesn’t. It is important to recognize that nickel is cathodic to steel and accelerates its corrosion if the coating is breached. Zinc is anodic and protects steel even if there are scratches or pores. Consider the screws. They are small in surface area, and thus will corrode rapidly if anodic to the chassis. Will they also be electroless nickel plated? I don’t know your full story, but my first thought is that switching from zinc to electroless nickel, in an application where it isn’t necessary and may be detrimental, to avoid the use of auxiliary anodes, which aren’t that big a deal, isn’t the right approach. Ted Mooney, Finishing Technology, [email protected] Ted is absolutely correct about using internal anodes. Properly designed, zinc plating coverage can be quite uniform. especially when using a cyanide electrolyte. Even with the extra tooling costs it will be much less than electroless nickel plating. Have you considered using precoated sheet steel? Coverage is guaranteed and you can avoid plating costs entirely. Galvanneal and electrogalvanized sheet stock work well in many cases for computer frames and chassis. Many computer manufacturers are now using precoated steels for some or all of their sheet metal parts. Pop the top on your PC and have a look inside. Chances are it’s precoated steel inside. In a benign office atmosphere, precoated steels can provide adequate corrosion protection, even on cut edges. It may not work for everyone, but it’s well worth considering. Gary Krech, [email protected]
WASTE TREATMENT
OF SOAK CLEANERS
I am working on a student project (for completion of a MS Environmental Engineering degree) for a metal plating and finishing shop. This small shop currently disposes of their soak cleaners as hazardous waste. The local POTW will let them dispose of the cleaners to the POTW but the metal concentrations are too high. They also have a wastewater treatment system with precipitation and clarification for their rinses. The chelating agents in the soak cleaner interfere with the current treatment system. I think they should treat this cleaner separately for metals, maybe emul-
0 Copyright Elsevier Science Inc.
69
CHEMICAL COMPANY Our success is built on quality and service while providing total chemical processing capabilities. Coral Chemical manufactures over 1800 proprietary, industrial chemical products. From the press room to the paint room, Coral can help. ??
Metalworking
Fluids
Coolants Drawing/Forming
?? ??
Compounds
Stamping ??Rust Inhibitors
??
??
Metal
Finishing
Cleaners ??Iron/Zinc ??
??
Phosphates
Process
Water
Treatments
Conditioners ??Flocculants ??
??
System
Controllers
??
Anodizing
??
Customized
Products
Call today for a brochure on how Coral Chemical Company can assist you.
CHEMICAL COMPANY
U.S. OWNED AND OPERATED FOR OVER 40 YEARS WAUKEGAN, ILLINOIS (647) 336-8100 (800) 228-4646 FAX: (847) 336-8518 LITHONIA, GEORGIA (770) 593-8000 (800) 228-4646 FAX: (770) 593-4260 PARAMOUNT, CALIFORNIA (562) 531-6363 (800) 899-6364 FAX: (562) 531-6405
Circle 029 on reader information card 70
sion breaking followed by precipitation, or look into different cleaners, which have chelating agents that will not interfere with treatment. (1) How do most smaller facilities dispose of soak cleaners? (2) What should I be looking for in a more treatable cleaner? (3) What options have worked for treatment of these cleaners? I would appreciate any input on this. Kim Cook, ERG, [email protected] I can answer question (2) for you. One method, which is successful in choosing a cleaner to fit in with your waste treatment procedures is to take a sample of the cleaner from your supplier and make up a 3% solution. Next, add a copper containing solution such as a used nickel stripper, and waste treat it in your lab. If, upon analysis, you have less than 2 ppm of copper you’re in pretty good shape. Many modern cleaner manufacturers make nonchelating cleaners, and you need to make your supplier aware of your needs from the start. He may handle all the preliminary lab work for you. Hope this helps. Mike McDonald, Mack Products, [email protected] The first thing I would suggest is to switch to a nonchelated cleaner. I have experience treating both, and I believe not only will they be easier to deal with as waste, but they will also outperform the chelated cleaners. You did not specify if your system is running continuous flow or batch treating. My preferred method is continuous flowing rinse waters, with concentrates routed to a separate dump tank for treatment. After neutralization and the addition of polymer, the concentrates should be pumped through the filter press. Effluent from the filter press should be routed to the waste rinse water tank for a second treatment as well as the dilution effect of any possible remaining residuals. As far as treatment, I have tried several methods of treating waste cleaners. My best luck has been with ferric sulfate and industrial grade hydrogen peroxide. Sulfuric acid should be used to drop the pH until all cleaner is reacted. This may not happen until you reach 2.5 to 3.0 pH. From this point the pH should be raised to about 4.5 to 5.0 pH. For a 300-gal tank add approximately 4 gallons of ferric sulfate. Follow this with 10 gallons of hydrogen peroxide. After letting the treated cleaner react with the iron and peroxide for about an hour, gradually add caustic soda to raise the pH to 7.0 to 7.5. With the addition of the caustic, the mixture will foam up so be sure not to overdue it. This works very well with nonchelated cleaners. Phil Pace, [email protected] We were faced with a similar problem of treating a highly chelated cleaner in our batch treatment facility. Having tested and rejected ferric chloride, we had some success with calcium chloride but were not able to reduce the concentration of nickel to our discharge limit (2.4 ppm). Then we finally started working with magnesium hydroxide and this stuff works. Not by itself, in combination with sodium hydroxide, but we are treating now a highly chelated room temperature cleaner at, sometimes, a 30% concentration in our wastewater with, at times 100 to 200 ppm nickel. After months of trial-and-error and with some help from a supplier, we have a magnesium hydroxide/sodium hydroxMETAL FINISHING
??
SEPTEMBER
1997
ide cycle that breaks up chelates batch treat the effluent:
PUTA
and lets us consistently
1. Reduce pH to below 2 with sulfuric acid. 2. Add about 1 lb/100 gal of magnesium hydroxide (we buy it dry and prepare a slurry right before use). Allow to mix for 15 to 30 min. This brings the pH up to above 5.0. Add sodium hydroxide to raise pH to above 11.0. Mix for 30 min. Add flocculent. Let precipitate. It usually takes anywhere from 1 to 6 hours in our 500-gal treatment tank. Transfer supernatant into pH reduction tank, lower the pH, and discharge. This cycle reduces the concentration of nickel to less than 1.5 ppm. 7. Dewater the sludge with a filter press. We like this cycle for its simplicity, low expense, and high tolerance to cleaners, nickel sludge dumps from anode bags, and just about anything. No upsets so far in over 6 months of using it. Try this stuff-it is good. Knowing how reluctant production people could be to switch cleaners (or, for that matter, change anything in a cycle that works), finding a treatment method that does not require any process changes in plating may be a blessing. Berl Stein, Reflexite PTC, [email protected]
Base mounted, in-tank, space-maker & bag filtration systems ??Stock or custom designed systems 0 Large selection for filtration, carbon treatment & precious metal recovery ??
Berl: Several years ago I read of people who preferred magnesium sulfate to calcium chloride or ferric chloride for handling spent cleaners. So I suspect that the benefit of magnesium hydroxide in treating cleaners has to do with the superiority of magnesium as a chelate breaker, more than the long reaction time of magnesium hydroxide slurry compared to caustic. If an occasion suggests, you might try the sulfate. Phil: In 1997 I don’t believe in continuous treatment of anything. When the settlement agreements between NAMF and EPA were reached 16 years ago and 40 CFR said that platers had to be in “consistent compliance,” I thought “consistent” held an accepted meeting of “the great majority pressure, of the time.” Under unceasing environmental “consistent” seems to have in practice come to mean “absolutely flawless.” I think batch treatment, with the ability to test every batch released, is the only safe approach anymore. Mike: I’m not so sure that nonchelated cleaners are always necessary. I have recently become a convert to the proprietary organometallic coagulants. While powerful precipitants like dithiocarbamate (DTC) have been around for a while, they didn’t seem to live up to their promise because they tended to produce a thin cloud of essentially unsettleable precipitate; the organometallic coagulants seem to turn this cloud into a fairly settleable floe. Ted Mooney, Finishing Technology, [email protected] The data we obtained developing our cycle seems to indicate that you are right and the main benefit of magnesium is its chelate-breaking “power”; however, there might be other factors such as the adsorptive properties of magnesium hydroxide sludge that may coprecipitate and, therefore, more fully remove the other heavy metals in the mix. Help me understand why you are suggesting we try mag-
FILTER
PUMP INDUSTRIES 7932 Ajay Drive, Sun Valley CA 91352 (818)504-2391FAX (818) 768-7590 Circle 042 on reader information card
METAL FINISHING
??
SEPTEMBER
1997
71
nesium sulfate instead of magnesium hydroxide. Magnesium hydroxide is so inexpensive, easy to work with, and serves the multiple purpose of raising the pH, breaking up the chelates, and (maybe) coprecipitating the sludge without contributing additional ions (sulfate) in the treated water that I think it is the right substance to use. Berl Stein, Reflexite PTC, [email protected]
acting sodium hydroxide does. Sorry for the confusion, I wasn’t proposing a change to a proven system, but discussing another weapon for other situations. Ted Mooney, Finishing Technology, [email protected] HUMIDITY PLASTIC
FAILURE
IN WATERBORNE
PAINT ON
We are currently having problems with condensing humidity failures with waterborne paints over ABS and polycarbonate. It appears that the infrared oven is annealing the top surface of the film, entrapping the water in the film. The failure mode is streaking or whitening. Has anyone seen failures like this? Any insight on fixes? Longer bake? Slower or faster solvent blend? Resin problems? Kris Pierce, [email protected]
You’ve developed a treatment cycle that works fine, and you are right about its advantages; there is no reason to change it. My point was only that, if magnesium hydroxide is great stuff but has the one big disadvantage of long reaction time, it might be possible to eliminate that disadvantage-should the need arise-by using a soluble salt in place of the slurry. But your suspicion that magnesium hydroxide may also tie up metals by adsorption could be correct; I don’t know. While magnesium sulfate might break the chelate, and quickly, it cannot be expected to contribute to filterability the way magnesium hydroxide does, because this is not a function of the magnesium ion but the fact that the sparingly soluble hydroxide does not rapidly precipitate the metals into a hydrated gelatinous mass the way rapidly
Is this occurring straight from the oven? If not then it is likely to be a general humidity failure of the resin, which would cause “chalking” of the surface, i.e., streaking. Sounds like a resin problem to me. Paul Lindley, [email protected] Ted Mooney is an independent consulting engineer based MF in Kinnelon, N.J.
WANT TO WRITE FOR METAL FINISHING? write to request a copy of our guidelines for authors, or simply contact the editor at METAL FINISHING 660 White Plains Rd., Tarrytown, NY 10591,Phone 914-333-2571?? Fax 914-333-2570
Call or
With Forty-Five Years of Ultrasonic Experience...
1960's
ComDact Sire: Only 4 9/l 6” high-ideal for limited space installations. Low Cost: Excellent for systems requiring quickopening/quick-closing solenoid valves. . Hlah Pressures: Back pressures to 90 PSI, inlet to I 140 PSI. ?? Unique: Teflon Bellows barrier type dynamic seal prevents leaking of fugitive emissions. ?? Versatile: Used with virtually all solutions: acids, caustics, solvents and ultra-pure liquids. Der or Performaw: 2,000,OOO cycle design. ??slzas: 114”& i/2” pipe size - 3/l 6” orifice. ?? _Materialg: PVC, Polypro & PVDF.
cleaning problem, we’ve probably had some experience cleaninnm-- a similar oart or material. Since 1951 &e Wave has been applying the power of ultrasonic cavitation to cleaning aluminum, brass, ceramics, copper, glass, iron, nickel, plastics, printed circuit boards, steel, zinc and others. If you have a new or ongoing cleaning problem, let Blue Wave make it a thing of the past Call us at 1-800-573-0144.
For further information request Catalog EAST
Blwwave-ka
960 S. RoHfStreet Davenport,IA 52802
Phone:l-319-322-0144 Fax:l-319-322-7180 I
Circle 087 on reader information card
72
Circle 127 on reader information card Mt
IAL t-~NIYHINU
??
5tr
I imt5en
IYY/