• Topic #41906 "Dummying" an electroplating bath?"

A. Hello...

That's interesting. Because you think zinc contamination, but then in your part's low current density area would be dark not white. So I couldn't say zinc contamination. So we must think different reasons. I think it must be white Wash or rinse contaminant (stains). And your transfer time from copper to nickel must be short. And also I offer to you very important advice: You must use separate nickel baths for zinc die casting and ferrous bath. And you must use hot water for final rinse.

Good luck.

A. Sergio,

I plate a lot of zinc in my nickel tanks so I am very familiar with the contamination problem. I would recommend grabbing a bath sample when it is good and one when the spots show up and have it analyzed for trace metals. It is a ten minute test on an AA. Your chemical supplier ought to do this for you for free.

From my experience zinc doesn't cause white spots. I see darkness in the very low current density areas of my parts. I also see something we call "zebra stripes" on the mid current density areas at [Zn}>= about 80 ppm.

I'd probably look elsewhere to solve this one.

Good Luck

A. Sir:

What you are seeing is the start of zinc contamination. It starts out as a white haze in the LCD but goes to black or even zebra stripes with the increased contamination of zinc.

Switch your primary brightener (saccharin) to dibenzene sulfanomide. It will allow you to plate with much greater concentrations of zinc in your nickel bath. Some say up to 100 PPM.

Barrel plating parts burnish against each other creating greater zinc contamination. There are also many LCD areas that are not getting covered well. Perhaps a Low metal copper strike would cover better.

It may be necessary to drag your nickel tank or even pump it out on a regular basis to remove parts that getting out of the barrels. Dummy your bath @ 5 asf with the pH @ 3.5 with steel grate. Ramp rectifier to 40 ASF every hour to seal zinc on dummy. Use as much surface area of grate as possible.

Hope that helps.

A. Sergio. I believe you have iron contamination in your nickel solution. Talk to your supplier to clean your nickel solution by pH cleaning or with a filter with ion exchange cleaning type NP-A supplies by Atotech.

Regard,

A. Sergio,

Copper usually shows up as cloudy gray to black in LCD areas with roughness at higher levels. Anders has a good point about iron contamination. I have used Atotech's NP-A and it did a fine job of keeping the effects of iron contamination away. Iron (as well as silicates, phosphates, ammonia ⇦this on eBay or Amazon [affil links] and very high levels of potassium or sodium) will cause white to gray looking stains. Can't tell you much about your cycle. Sounds OK but don't know amps/ft2. When iron was a problem in my tanks I usually experienced roughness. The point about saccharine brighteners is a very good one. They have practically no zinc tolerance as I learned the hard way.

I think your trace metals analysis will show you the correct solution.

A. MAXIMUM LEVEL OF IMPURITIES IN NICKEL PLATING BATH IN PPM

1. Al 60
2. Cu 40
3. Lead 02
4. Zn 50
5. Iron 150
6. Hexavalent Cr 10

A. The Metal Finishing Guidebook has a chart that agrees with Ajay's posting except for suggesting 50 rather than 150 ppm Iron. Optimum would be zero, Emre. Unfortunately, the chemical world doesn't have go/no-go gauges where 49 ppm is okay and 50 ppm results in failure. The Canning Handbook [on eBay, Amazon, AbeBooks affil links] has more detailed information, but also reveals that the sensitivity to particular contaminants depends to an extent upon the particular brightener systems used. If you use proprietary solutions, the technical data sheet should contain these numbers.

To expand upon your question just a little bit, probably the preferable thing to do, as the Canning Handbook suggests, is to frequently run Hull Cell test panels -- watching for the usual effects of this contamination in the lab before it becomes it becomes an actual problem on production parts; your technical data sheet will then give you hints at what is causing the Hull Cell problems, you will remove the contaminant on a sample per the instructions, and verify what levels of contaminant cause problems at different current densities. Good luck!

A. It depends on your customer. If you are plating 24K gold, it is probable that the contaminant level could be sub part per million. If it'ss a commercial plate job of some metal, the contaminant level could easily be where it affected the cosmetics of the plate. Another limitation is the point where it poisons the bath to the point of slowing down the plate rate too much.

In short, it will be very specific to your plating application and your customer.

A. Mr. Tuna,

Mr. Mooney is (as usual) right. I've had several different brightener systems for my nickel tanks. Some were somewhat tolerant of contamination (zinc is my biggest problem), and some would show the effects at very low concentration (zebra stripes and dark plate in LCD @ [Zn]>5 ppm). My current brightener can plate acceptably at < 80 ppm [Zn}. If you are plating zinc die castings and you anticipate parts falling into your nickel tanks, I would purchase a small electrolytic purification cell for continuous low current dummy loading. It has helped my operation. In any case, contact your vendor. Good Luck.

A. Hello again, Mr. Tuna. Yes, sorry I was away; but I think your question was well answered by Mr. Raina and the other respondents.

⇦[this on eBay, AbeBooks, Amazon affil links] gives generic values for iron contamination of 5 ppm as normal and 50 ppm maximum, and zinc contamination as 1 ppm normal and 10 ppm maximum. The Metal Finishing Guidebook says 50 ppm maximum for each. But as related by Mr. Kaufman, these values really depend on the particular nickel plating solution.

So your contamination values sound quite normal. I don't think metallic contamination is a major cause of pitting anyway. Besides insufficient agitation or wetting agent, other causes are porosity of the substrate, organic contamination, too much acid or too little nickel, particles in solution, or parts not being clean.

Because the Hull Cell panels look good, and you have trouble with both brass and steel parts, I'd suspect part cleanliness. Are you sure you see a waterbreak-free surface on the way into the nickel plating tank?

opinion! Parts should not be allowed to fall off the racks, and should certainly not be allowed to dissolve into the solution. This is a 1960's situation, not acceptable in this new millennium. If you make it a policy to stop the line and "magnet it" immediately every single time a part falls, you are on your way towards corrective action of no more parts falling. If you talk yourself into some particular number of parts being allowed to fall off the racks before it is a problem, you've already lost the QA war :-)

A. Mr. Tuna,

This message is long so grab a snack from the kitchen before you start!

The nickel sulfamate solution I use has the following contaminants:
Calcium <5 mg/L Cobalt <1 mg/L Copper <0.5 mg/L Iron <4 mg/L Lead <1 mg/L Manganese <0.5 mg/L Zinc <2 mg/L ammonia 180 mg/L sulphates 0.1 percent

This is directly from the manufacturer. Once I get the solution I dummy plate onto a corrugated plate at 5 A/sf and 0.5 A/sf to preferentially remove metallics such as copper, iron, etc. I also run continuous carbon filtration to reduce the organic contamination. The only catch is that you have to monitor the surface tension of the bath since wetting agent is removed by the carbon filters. After some time the filters become partially saturated with the wetting agent and consume less but, from experience, are still effective at removing organics.

As for your problem, pitting and hazy products I can offer you my experience. I believe I read another post of yours where you stated you electroform rather than plate. If this is incorrect I apologize.

I electroform optical reflectors for the projection market. For our first generation reflector module I used rotation and masks to achieve uniform reflector thickness. When we were in high production the motors were running nearly continuously. This caused the motors to become warm which caused the grease and lubricant to become less viscous. Over time a small trail of oil made its way down the rotating shaft and into the bath causing an oil slick on the surface. When a mandrel was lowered into the bath the surface received a thin coating of oil/grease. The result was a hazy optical surface. If I remember correctly, pitting was also observed.

My suggestion to you is to dummy plate to remove metallics run carbon filtration while washing the surface of the bath with your wetting agent. The wetting agent will trap the organics so they can be filtered by the carbon. Also check your agitation.

Best regards,

A. Hi Sastry,

Below metallic impurities tolerance for your ref:

1. Iron < 150 ppm - Speckling surface.
2. Aluminium < 60 ppm - Reduce limiting CD and create rough deposit.
3. Zinc < 50 ppm - Whitish or dark deposit at low CD area and shiny black streaks on deposit.
4. Copper < 50 ppm - Dark deposit at low CD area.
5. Hexavalent chromium < 10 ppm - Skip plating at low CD area.
6. Lead < 10 ppm - Dark, brittle and poorly adherent deposit.
7.Stannous tin < 10 ppm - Dark deposit at low CD area.


Regards,
David

A. Good day Hama.

That all depends on the make-up of the pickle solution. What are you pickling, steel? Check for iron. What is the composition of the pickle and is there a wetter involved (organics)? Have you run hull cell panels on your bright nickel and analyzed for chlorides, pH etc.? More info would be helpful. I would try peroxide/permanganate with the carbon. What concentration carbon, temperature etc
Regards,

A. Hi Hama,
Peroxide/permanganate and carbon treatments are for removal of organic contaminants. They will not help with your problem.
If you give us a clue what your pickle bath is and what was treated in it we might be able to help. But the only safe option is to replace the bath.