INSTITUTE OF MATERIALS FINISHING
The fascinating world of electroplating
John Burgess FIMF
Following on from my
previous article, (IMFormation
Feb 2020) I said that I would
share with you about an
experience I had with
problematic nickel bath.
At the time I was working for M & T
Chemicals (as it was known), and I was sent
to a customer who was experiencing issues
with roughness on settling surfaces.
The customer was nickel/chromium plating
brassware for bathroom fittings and on all
the settling surface there was roughness as
bad as sandpaper.
Now one of the problems with plating brass
sand castings, especially where there were
hollowed sections as in bath and wash basin
taps is that the current density is so low up in
the tubular part of the tap that plating does
not take place but because of the acidity of
the solution there is a chemical attack on the
inner surface of the brass. This attack will
cause the sand from the casting to leach out
into the plating solution and subsequently
contaminate the solution with sand.
As plating continues the sand in the plating
solution will settle upon horizontal surfaces
leading to roughness.
Other factors have to be taken into
consideration when looking at roughness
and that it to ensure that the make up of the
plating solution is correct. Weak solutions can
cause roughness through the fact that there
is insufficient metal content to support the
current density that the solution is running at.
As the company did not have a laboratory as
such and technical representatives were only
equipped with a set of 3 off Twadell
Hydrometers, a set of pH papers and a
thermometer I set about assessing the
concentration of the Watts nickel bath.
Now some of you may not have heard of a
Twadell hydrometer but it was a scale that
1 Two was equivalent to about 1 oz per
gallon therefore a nickel plating solution
should be about 48 ozs/gal (300 g/l) and
require a No. 2 Twadell hydrometer.
The bath volume was around 1000 litres so,
taking the hydrometer and lowering it into
the solution I carefully let it go only to see it
disappear at a vast speed into the bottom
of the tank.
Hmm, I thought, that wasn’t a clever move,
so carefully I lowered the No 1 Twadell
hydrometer in which gave me a result of about
22 Two which was about 22 ozs/gal (140 g/l).
Obviously the bath was weak in fact about
half strength, so chemicals had to be added.
I decided that 3 bags of nickel sulphate, 1
bag nickel chloride and 0.5 bag of boric
acid should be added. At least this would
bring the solution up to somewhere full
strength, enough to get it going and follow
up later with a full analysis.
Now back in the good old days Nickel
Sulphate and Nickel Chloride were supplied
in 50Kg hessian bags which were lined on
the inside with polythene and labelled
“INCO MOND Nickel Sulphate or Chloride
50Kgs. INCO supplied nearly all the
nickel-based products.
Boric acid, like now, was put into paper bags
so the operator at time said to leave it to him
and I could follow it up the following day.
The following day arrived, and I rushed to
the nickel tank in the hope that I might see
my No 2 Twadell bobbing up and down in
the solution but alas it was not to be, so
I ruled that out as a lost cause.
It was decided to put a job round to see if
there was an improvement and after about
2 hours it came off the line in a worse state
than when I arrived the previous day.
The roughness had now developed into
elongated whiskers and completely useless
with a technician that was lost for words.
We decided to drain the tank and see what
might be in the tank. I was guessing that the
original roughness was due to the sand from
the castings which was not being filtered out
but, as the solution slowly emptied out of the
tank the words “INCO MOND Nickel Sulphate
and Nickel Chloride came into view together
with a paper sack with the words Boric acid.
Now I understood where the problem lay.
It is always useful when wanting to increase
the strength of a plating solution to open the
bag and pour the contents in but because
the operation was being carried out close
to going home time (and it was a lovely day)
it was decided to drop the bags in and
hope that somehow the contents would find
their way into the solution. Unfortunately,
the inner polythene lining is not soluble,
but the hessian bag certainly did decide to
break up and cause untold problems.
Obviously this was a one off experience in
my career but it goes to show that when
trouble shooting a problem you do
sometimes have to think outside the box.
The problem got resolved by passing the
solution through very fine filtration and the
Twadell Hydrometer….it was lying behind
one of the anodes still intact considering
the ordeal it had been through.
John Burgess FIMF
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10 JUNE 2020 twitter: @surfaceworldmag