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topic 59034

Filter Pump Cause Pitting

November 7, 2012

Q. I have a 5000 litre bright Nickel watts solution.
NiSO4 150g/l
NiCl4 60 g/l
Boric 60g/l (it's higher but trying to lower it)

Whenever I use high speed filter pump, which turns solution in 1 hour, there is pitting on the items (rims, silencers).
Our tanks have this brown sludge at bottom and on basket covers which develops with time so I am using filter pumps to decrease this issue.

Why is this so? Is this due to high sodium saccharin or throwing brighteners? Where does this brown stuff come from? Is this iron?
I filtered the solution 2 times before running continuous filtration.
Also if I am using continuous filtration when a pump is turned off with power failure, if I turn it on again the sludge collected in the pump gets sucked and thrown in the tank. even sometimes the carbon bed is disturbed by the pump turning on suddenly and carbon thrown in the tank due to sudden jerk.
How can I use the filter pump to take its benefits without creating new problems

ALI Imran
- Lahore, Pakistan

November 10, 2012

A. Hi Ali,

The pitting could be due to micro bubbles generate by filter pump which in turns stick onto plating parts during nickel plating. You may turn on side valve of filter pump regularly (esp. during switch on filter pump after bath idling) to get rid of air trapped inside filter column.


David Shiu
David Shiu
- Singapore

November 13, 2012

A. There are many people here in this forum that have a lot of experience (for example, more experience than me), but I had in the past this problem of brown sludge and also the baskets/bags were colored brown too. The reason was a severe iron contamination; in my case due to bad quality anodes. This does not mean that is the same as your case, but is a possibility.

Too high boric acid mixed with a cold bath leads to insoluble particles that cause roughness.

Pitting is mostly due to hydrogen bubbles formed during cathodic reaction so check for the wetter, we use to do a 4" ring and check is there is a bubble formed on it when you submerge it on the bath, we wait for the bubble to last 30 seconds or more. If it blows before this time, more wetter is needed.

Other reasons for pitting: very low metal content, organic contamination.

Daniel Hernandez Guerra
- Bucaramanga, Santander, Colombia

November 13, 2012

A. Continuous filtration means that the solution gets filtered as it pass in to the filter.

So it does not look good if you see the sludge passing again in to the tank.

a humble suggestion would be that if the sludge is due to iron contamination,do high pH treatment, filter and then dummy plate at pH of 3 until dummy cathodes come out shiny and clean.

Daniel Hernandez Guerra
- Bucaramanga, Santander, Colombia

First of two simultaneous letters -- November 16, 2012

A. Hi,

Check your filter for leaking; that looks like dispersion air (very small air bubbles).
And I also recommend you should do an iron pretreatment to the nickel bath.


Anders Sundman


Anders Sundman
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika, Sweden

Second of two simultaneous letters -- November 17, 2012

Thank you for responses.
I will follow your suggestions.

Q. Can anyone please with experience with filter pumps answer my few questions about the problems I am facing.

I added 0.5 kg carbon in a 200 kg water drum and recirculated in the drum to make a bed of carbon on catridges. In Fifteen minutes pump throws out clean water.
I observed if I move the pump slightly, the outlet nozzle will throw carbon out for a few seconds (I switched pump off and moved it).
Question 1: If pump is running in nickel solution, will collected sludge, carbon in filter pump body be thrown in the nickel solution and cause pitting? How can I avoid this risk?
Question 2: My pump is above the tank level. When I stop the pump, will the filter liquid drain into the tank due to syphon and dirty the nickel solution? How can I avoid this risk.
I do not want to put pump below tank level as I fear risk of leakage due to any failure in piping and full drain of nickel solution.

Any insight and standard practices about this will help me a lot.

Ali Imran
- Lahore, Pakistan

November 20, 2012

A. Good day Ali.
The situation you are experiencing is inherent with "packing" carbon on filter cartridges. The moment you turn off the pump to go from your "slurry tank" (200 L drum)to your nickel solution, you have lost pressure on the cartridges and lost your pack. You need to devise a system where you pack the carbon in your slurry tank and with a series of valves and piping/hosing re-valve your hosing to your nickel tank WITHOUT turning off the pump. The pump must remain running.
A simple solution is to immerse a 20 L bucket in your slurry, draw solution from it (you can valve down the flow/ decrease pressure) and bring the bucket to your nickel tank and immerse the bucket into your solution, this is done while the pump remains running.
If you go to MEFIAG PUMPS website, you will better understand this idea. Their system requires the pump to remain running, and this is done as repiping/valving from your slurry to your tank.
I would suggest that you pump out the solution to a treatment tank, add 0.2% peroxide with air / mechanical agitation, heat to 160 °F/ 70 °C to drive off the H2O2 increase pH to 5.0-5.0 with nickel carbonate, add 10 g/l carbon, agitate 6-8 hours, and allow to settle overnight. Meanwhile, clean the tank AND change the anode bags; try using R rounds nickel anode as they do not generate sulfur/sludge. You will probably lose: 100% carrier, 10% primary brightener, 40% secondary brightener, 100% wetter. Filter solution back with low pressure and change filter media as required. Adjust pH and you will be good to go.
Hope this helps.

Eric Bogner
- Toronto, Ontario, Canada

November 28, 2012

A. Hi Ali
All soluble anodes dissolve more or less incompletely leaving a residue (anode sludge)which is your brown deposit. To control this it is good practice to enclose your anodes in bags.
The purpose of filtration is to remove any deposit which escapes from the bags and any other dust etc that falls into the tank.
Carbon is used to remove organic contamination. If you are running a bright nickel, it will remove the brighteners.
If you stop carbon filtration you will greatly reduce the consumption of brighteners - and the cost.
Continuous carbon filtration is only used on unbrightened baths where it is used to control stress caused by organic contamination.
If you must use carbon, used granular. It is less effective but much easier to keep out of the tank. Never add powdered carbon to the main tank to treat it - it can take weeks to filter it all out - use a spare tank.
You don't need a "high speed" pump unless you are using it for tank agitation - in which case you should consider eductors and avoid pointing the outlet directly at the work.
Boric acid is a pH buffer. There is rarely need to control the maximum concentration. It is common practice to fill an anode bag with boric acid and hang it in the tank; effectively fixing the concentration at saturated (one less thing to control)

geoff smith
Geoff Smith
Hampshire, England

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