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Патент USA US2279580

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-Àprìl 14,-1942.
R . v. MiNER
2y,2 79,580
Filed Dec. 9, 1939
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¿from? I
Patented Àpr. 14, 1942
Robert V. Miner, Chicago, Ill., assigner to
Western Electric Company, Incorporated, New
York, N. Y., a corporation of New York
Application Decemberß, 1939, Serial No. 368,398
l Claim. (Cl. 26S-4Z)
for electrodepositing a coatingfoi gold on an
This invention relates to electroplating, and
article with a minimum loss of gold. The ap
more particularly to the electroplating of articles
paratus comprises a plating tank and two tanks
with precious metals such as gold.
containing wash water adjacent thereto in which
An object of this invention is the provision of
improved methods and apparatus for produc Cil the plated parts are immersed successively.
Wash water is withdrawn continuously from the
ing plated coatings of gold and other precious
iirst tank, circulated through a series of cyl
metals on articles with a minimum loss of pre
inders containing zinc turnings which precipi
cious metal.
tate and extract the gold, and then discharged
it is customary to electroplate articles in an
into the second wash tank. An overflow is pro
electrolytic solution of the desired coating metal
vided between the first and second tanks so that
and then wash the articles in water to remove
the ñrst tank is constantly supplied with water
the plating solution therefrom. This practice
results in the steady withdrawal or drag-out of
solution, with the contained metal, from the
plating bath on the surfaces of the articles.
This prospective loss of metal is not serious in
the usual plating process where relatively inex
pensive metal solutions are employed, but when
from the second tank.
In this manner the wash
water is constantly recirculated and the gold
content in the second wash tank, which deter
mine the drag-out loss, is> maintained at a very
low value.
Following is a more detailed description of the
invention, taken in conjunction with the append
-gold or other precious metals are used in the
- ed drawing, in which the single figure is a sche-y
plating bath, the value of the withdrawn solu- »
tion mounts rapidly. Consequently, means have
been employed to partially recover metal from
the drag-out solution in precious metal plating
matic drawing of an apparatus incorporating
certain features of the invention.
In this apparatus and method a conventional
plating tank lll provided with the usual elec
Under one former practice the plated articles 25 trodes and power supply (not shown) is em
were Washed successively in a series of still water
tanks and the metal Was extracted from the
wash water at intervals. The metal content of
the wash tanks was built up progressively, with
the smallest metal content in the last tank, which
determined the minimum metal loss. The >rate
of metal loss was progressive, as the metal con
tent of the last wash tank increased steadily with
ployed. The tank contains plating solution, such
as a sodium gold cyanide solution and the arti
cles are plated while suspended in the solution
in accordance with the usual practice.
Immediately adjacent to the plating tank are
two open top wash tanks Il and I2 in which they
articles are washed successively after they are
removed from the plating solution. The Wash
changed constantly and also because of practical
tanks can be made of various easily formed ma
terials, such as wood, concrete or metal and are
conveniently made in one body with an inter
limitations in the number of tanks that could be
used in the series and the necessity for inter
rupting the entire process for any changes in
first or initial wash tank H and the second or
iinal wash tank I2.
It was diiîcult to hold this value to desir
ably low levels because the metal content
the tank arrangements. Due to the handling
and processing involved, it was considered nec
essary to have a fairly high gold content in the
mediate partition l3 between them to form the
At the beginning of the process both wash
tanks are ñlled with distilled water.
As more
and more articles are removed from the plating
tank and immersed in the wash tanks the total
preliminary wash tanks, with a relatively high
quantity of gold cyanide flushed from the sur
metal content in the iinal tanks, to justify the
metal recovery operations. Another objection 45 faces of the articles into the Wash water in the
initial wash tank tends to build up rapidly. At
to the former practice was the necessity for a
the Sametime the gold cyanide content of the
final cleaning operation on some parts. For ex
ñnal or second wash tank also tends to increase,
ample, on certain parts plated in gold cyanide
but in smaller unit quantities, due to drag-out
it is necessary to remove all traces of the plating
from the ñrst wash tank. Ordinarily, any- drag
solution, Because the final wash tank in the
out from the second wash tank would be lost
series contained some, and an unknown quan
and in order to minimize this loss, means vare
tity of plating solution, these parts received a
provided for removing the gold from the wash
final washing in running water.
water as rapidly as it is deposited therein. '
In accordance with one embodiment of this
Wash water is withdrawn continuously from
invention, a process and apparatus are provided 55
the ñrst Wash tank I I through a pipe I4 having a.
manual control valve I5 therein and connected
to an opening near the bottom of the tank. 'I‘he
wash water is withdrawn by means of a suit
ably driven pump I6 connected to the pipe.
the oldest zinc, successively with zinc of lesser
service age, finally with the freshest zinc just
before the water is discharged into the iinal wash
With the above described apparatus the loss of
gold is very low. When plating with a sodium
gold cyanide solution of the usual concentration
The pump forces the Wash water through a
pipe I1 into a lower header I8. Extending from
the lower header are ñve spaced branch pipes
the gold content of the ñrst wash tank may run
I9, 20, ZI, 22 and 23, each having a manual con
around .013 ounce per gallon of water. By cir
trol valve 24, 25, 26, 21 and 28 therein. The 10 culating
this wash water through the extraction
upper end of each branch pipe is connected into
cylinders continuously the gold content
the bottom end of a hollow cylinder 29, 30, 3|,
of the second or final wash tank, which deter
32 and 33. Each of the ñVe cylinders contains
mines the drag-out loss, can be maintained con
a quantity or batch of zinc turnings 34.
Connected into the top of each of the four 15 sistently at a value as low as .O03 ounce per
gallon of water. The resultant gold loss is in
cylinders on the left in the drawing (cylinders
significant compared with the rate of loss under
29, 3U, 3I and 32) is a branched pipe with one
former methods.
branch thereof 35, 36, 31 and 38, under control
The above described apparatus and methods
of a manual valve 39, 40, 4l and 42, joined to
the pipe running into the next adjacent cylinder 20 can be adapted for plating articles with other
solutions and metals by merely using a suitable
to the right. The other branch 43, 44, 45 and
extracting agent for the selected metal or solu
46 of each of these branched pipes contains a
tion in the tubes or cylinders. It will be apparent
manual valve 41, 48, 49 and 50 and is connected
that other modifications and adaptations of the
into a common upper header 5I. The right
methods and apparatus are feasible and it is to
hand cylinder 33 is also connected into the
header through a pipe 52 with a Valve 53 there 25 be understood that the invention is limited only
by the scc-pe of the appended claim,
in, and with the left hand cylinder 29 through
What is claimed is:
another pipe 54 with a manual valve 55 therein.
for treating articles coated with a
A pipe 56 connects the upper header with an
inlet into the second or final wash tank I2. In 30 concentrated aqueous solution of gold cyanide
such as is employed in a gold plating bath to
the top portion of the partition I3 between the
remove said solution from the article surfaces
two wash tanks is an opening 51 through which
and recover the gold from said solution, an initial
wash water flows from the second Wash tank I2
wash tank containing a dilute4 aqueous solution
to the first wash tank Il.
of gold cyanide for receiving the articles coated
With the above described system of piping,
with the concentrated solution and ñushing the
valves and pumps, it is possible to withdraw the
concentrated solution from the articles, said di
wash -water from the ñrst tank, circulate it
solution having a maximum gold content of
through the complete series of cylinders begin
.013 ounce per gallon, a second wash tank con
ning with any one of the cylinders, and then
taining ñnal wash water for flushing from the
discharge the water into the second or final wash
articles the dilute solution withdrawn on the
articles from the initial wash tank, said final
As the wash water is brought into contact with
wash water having a maximum gold content of
the zinc turnings in the cylinders, the gold is
.003 ounce per gallon, means for withdrawing
precipitated from the cyanide solution and de
posited in the cylinders, from which it is re 45 dilute solution from the initial wash tank at a
uniform rate, means for supplying final wash
moved periodically. The cylinders or tubes are
water from the second tank to the initial tank
easily dismantled for removal of the accumulated
at the ysame rate at which dilute solution is
gold by removing a threaded cap on the tube
from the initial tank to maintain a
into which the connecting pipes are joined.
constant quantity of solution in the initial tank,
For maximum gold extraction it is desirable
a series of containers each having zinc therein,
to contact the solution with fresher zinc as the
containers being connected in series and the
solution is weakened by partial gold extraction.
in said containers being of successively grad
To accomplish this, the Zinc is replaced in one
uated age, a system of pipes interconnecting the
cylinder at a time, in sequence and at uniform
time intervals. For example, one cylinder is re 55 two wash tanks and the series of containers, and
a pump for circulating. all of the dilute solution
plenished one week, the next cylinder to the
right, or the next in the series, is replenished one
week later, and so on. Under this practice, the
zinc in successive cylinders in the series is of
graduated service age; The circulation of wash
withdrawn from the initial wash tank through
the series of containers beginning with any se
lected container and ñnally delivering all of the
treated solution to the second wash tank to main
tain a uniform supply of ñnal wash water in the
Water through the cylinders is controlled, by 60 second tank.
means of the valves in the interconnecting pipes,
to bring the wash water in contact lirst with
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