Note: Descriptions are shown in the official language in which they were submitted.
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79.023/BT
Method and ~pparatus ~or the Elec'cro--Deposition
of Lead Alloys
This invention relates to a method and apparatus for the
electro-deposition of an alloy coating on to a backing
member, such a process being of particular intcrest to the
coating of a load carrying bearing surface on to the backing
member of a plain bearing.
Such a bearing may comprise for example a half shell
backing member of steel with a bronze substrate bonded there--
to and on to which is electro-deposited a bearing surface
coating of lead~indium or lead-antimony-tin. ~inary and
ternary alloys can be co-deposited electrolytically as is
described for example in British Patents 577335 and 628L~59
and in U.S.A Patent 2605149. In British Patent 577335 it is
stated, and has been verified in tests, that coatings of
ternary alloys such as lead-antimony-tin or lead-tin-copper
can replace the more usual lead-tin or lead indium binary
alloy coatings as bearing surfaces.
However in the electro-deposition of ternary alloys
containing antimony or copper, there is a displacement
reaction when a soluble metal anode is used. For example in
British Patent 628459 it is stated that antimony will immer
sion plate on to a lead, lead-tin or lead-tin~antimony anode.
In Patent 628459 it is stated that this immersion plating is
adherent eno~gh so that the anode may be used two or three
times and then the antimony may be scrubbed off and reclaimed
and~ whereas such a procedure may be acceptable for small
scale operation, it would not be feasible tG operate a
continuous production plating process wherein anodes were
required to be removed many times durlng the working opera
tion for scrubbing.
$~
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Simi.larly if a lead-tin--copper electrolyte is utilised,
the copper .in the plating solution immersion p].ates out on to
metal anodes such as lead or lead-tin and, although such an
electrolyte has been in prodv.ction use f'or many years, the
removal of~ al] the anodes frorn the bath during idle periods
is required, and frequent additions of copper fluorobvrate
are necessary to replace losses from the electrolyte.
It is the object of the present invention to provide an
improved method and apparatus which will prevent the undesir-
able immersion plating of a soluble metal anode containi.nglead by metals from the plating solution which are more noble
than lead.
In accordance with one aspect of the invention there is
provided apparatus for the electro~deposition of an alloy on
to a cathode comprising a first cham'oer within which the
cat.hode is located and which contains a catholyte solution; a
second charr.ber w.ithin which the anode is located and wh.ich
contains an anolyte solution, and said fir~t and second
chambers communicating with one another only through the
medium of a cation exchange membrane~
In accordance with a further aspect of the invention
there is provided a method of electro-depositing an alloy on
to a metal cathode comprising the steps of immersing the
cathode in a first chamber containing a catholyte solution,
immersing a metal anode in a second chamber contai.r,ing an
anolyte solution communicating with said catholyte solution
only through the medium of a cation exchange membrane and
applying a direct current between the anode and cathode.
ln use of the apparatus and method according to the
invention the anolyte will not contain elements capable of
immersion plating on 'o the anode. Thus if the catholyte
comprises a lead-antimony tin plating soluti.on then the
anolyte ~ili not contair. any antimony. Sirni.larly i.f the
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catholyte comprises a lead--tin--copper plating solution then
the anolyte will not contain copper.
When the apparatus is in use, metal ions arising from
the anode pass through the cation exchange membrane towards
the cathode under the influence of the plating potential.
Since the anolyte contains ro metal capable of immersion
plating on to the anode the anode will remain clean. A~ the
end of a plating operation, when the plating potential is
disconnected, the antimony or copper or arssnic in the
catholyte (depending on what alloy is being co-deposited) is
prevented f`rom entering the anolyte by the physical barrier
of the cation exchange membrane. That is to say, metal ion~
can pass in one direction only, i.e towards the cathode, and
then only under the influence of the plating potential
applied between the anode and cathode. Thus the anolyte
solution in the second chamber remains free of ions capable
of immersion plating on to the anode.
A further advantage of the use of a cation exchange
membrane tc physically separate the catholyte and anolyte
solutions is that the composition of the catholyte may be
controlled more readily since metal is not lost therefrom by
immersion plating which in turn means that the electro-
deposited alloys have more consistent compositions.
Other features of the in~Jention will become apparent
from the following description given herein solely by way of
exampla and with reference to the accompanying drawing which
shows, in diagrammatic form, a plan view of a plating bath in
accordance wlth the invention.
Referring to the drawings there is shown a first chan.ber
10 within which is locatable a member 12 to be p]ated and
which comprises the cathode; such member may comprise a
steel bac!cing member with a bronze substrate bonded thereto
and on to which is to b- co-~-po~ited a ternary ~lloy as a
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bearing surfacc. This first chamber 10 is capable of being
filled with the catholyte solution.
At the end of the first charnber lO remote f`ro~, the
cathode 12 there is provided a second chamber 14 wholely
contained within the ~irst chamber and communicating 'chere-
with only through the medium of a cation exchange membrane
16. This second chamber 1L~ is conveniently of box like
rectangular configuration having an open top and an open
front across which is secured the exchange membrane 16 by
means of detachable clamping plates and gaskets. To provide
support and protection for the exchange membrane 16 a sheet
18 of porous polyethylene may be sealingly located by the
gaskets on one or both sides of the membrane 16 the polye~
thylene sheeting 18 being provided to prevent physical damage
to the exchange membrane 16 and also providing support
against sag or swelling of the exchange membrane whieh may
occur in use.
The cation exchange membrane is a proprietary item and
may be of the type available from Permutit-Boby of Brentford,
1 ~0 Middlesex, England.
The anode 20 is locatable within the second chamber 14
¦ and the chamber 14 is capable of being filled with an anolyte
solution to at least the same level as that of the catholyte
solution in the first chamber 10. It may be preferable for
the level of the anolyte solution to be above that of the
catholyte solution to provide a slight hydrostatic pressure
I in favour of the anolyte.
The following examples of use of the apparatus will
serve to illustrate the inventi~n:-
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_x~le 1
The apparatus was used for the electro deposition of aternary alloy of lead-antimony-tin to give a coating having a
basis of lead and containing between 9.5~ and 10.5% by wei.ght
of antimony and between 5.5% and 6.5~ by weight of tin in the
deposited alloy. The anode was a lead-tin anode containing
5% to 25% by weight of tin
The cathode comprised a steel backing member on to which
was bonded a bronze substra'ce. It is preferab].e to electro-
plate a base coating of cobalt or nickel on to the bronzesubstrate thereby to give a better surface for the deposition
of the required ternary alloy particularly for the preventior
of dispersal of tin into the bronze.
The catholyte solution in the first chamber was as
follows:-
Lead 150 grammes/litre added as lead
fluoroborate
Antimony 6 grammes/litre added as anti-
mony trifluoride
Tin (stannous) 22 grammes/litre added as tin
f1uoroborate
Resorcinol 7.5 grammes/litre
Gelatin 0.75 grammes/litre
Free fluoroboric acid 20 grammes/litre
The tcmperatl1re of the catholyte was maintained at l'QC
and a cathode current density of 30 amperes per square
-. foot ~as utilised for approximately 20 minutes to gi.~te a deposited alloy thickness of 25 um.
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The second chamber was fi.lled with an anolyte solution
of the following composition
Lead 150 gramMes/litre added as lead
fluoroborate
Tin 22 grammes/litre added as tin
fluoroborate
Resorcinol 7.5 grammes/litre
Gelatin 0.75 grammes/litre
~ ree fluoroboric acid 20 grammes/litre
The temperature of the anolyte solution was maintained
at 40C
Example 2
In this example identical constructions of anode and
cathode were utilised as in the preceding example but the
electrolyte solutions were chosen to give a ternary alloy
deposit on the cathode of iead tin-copper having a basis of
lead and containing between 8% and 12% by weight of tin and
between 2% and 3% by weight of copper in the deposited alloy.
A catholyte solution of the following composition was
used:-
Lead 100 grammes/litre added as lead
fluoroborate
Tin (Stannous) 10 grammes/lltre added as tin
fluoroborate
~' 25 Copper 3 grammes/litre added as copper
fluoroborate
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Resorcinol 5 grammes/]itre
Gelatin 0.5 grammes~litre
Free fluoroboric acid 40 grammes/litre
The temperature of the catholyte solution was maintained
at 25C and cathode current density of 20 amperes per squarefoot was utilised for approximately 20 minutes to give a
deposited ternary alloy of 25 um thickness.
The anolyte solution was identical in all respects with
the catholyte solution with the exception that no copper
fluoroborate was present in the anolyte.
In both examples it was found that the anode remained
clean and that the platillg elemellts had been lost from the
catholyte to the cathode at a controlled rate.
