Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
10~30~2
This invention relates to electroplating apparatus
Known electrolytic processes have many technical and
environmental disadvantages. The technical disadvantages in-
clude for example, variations in the thickness of the coating,
810w growth, poor density and poor adherence of the coating.
These are, however, only a few of the most obvious difficulties.
The biggest problem probably is the irregular growth of the
coating, appearing mainly as a so called outgrowth, i.e. the
coating grows in certain sections much too quickly.
As far as environment protection and work protection
are concerned, the biggest problem in the known processes is the
abundant formation of gas and mist fumes. The developed;gases
and fumes are toxic and cause occupational diseases.
It is an object of the invention to provide a process
by means of which most of the disadvantages connected with the
known processes can be eliminated. t
According to the invention, electroplating apparatus
for applying a protective metallic coating on the surface of an
object comprises chamber means and liquid electrolyte solution
in the chamber means, said chamber means including a process
chamber which contains at least a part of said liquid electrolyte
solution and in which said object may be submerged in the liquid
electrolyte solution, and the apparatus further comprising means
for leading an electric current to said object and to said solu-
tion, said process chamber being provided with means for effec- ~
tively preventing atmospheric air from flowing through said pro- -
cess chamber, and a pneumatic pressure-reducing pump connected
to the chamber means to maintain a reduced pressure, which is
substantially below atmospheric, above the electrolyte solution
within at least a part of the chamber means.
-- 1
~r
~0930~2
Thorough tests have proved that the apparatus accord-
ing to the invention which effects electrolytic coating at
sub-atmospheric pressure provides a number of unexpected advan-
tages. The quality of the coating is considerably improved and
the mist fumes which normally develop during the process are
bound already at a lowered pressure, for example, 0,85 atm, to
the circulating electrolyte. Since the quantity of mist fumes
also depends on the electrolyte used and the current density, it
is advisable, for additional security, to use a lower pressure,
i.e, a pressure which is smaller than 0.8 atm.
- The most advantageous way is to have the process space
proper only under underpressure and to let the electrolytic
solution circulate through this space. It will then be possible
to utilize the circulation system to provide a proper cooling
and heating. It is alco possible to use an apparatus where there
is no circulation of liquid and where the electrolyte storage
space thus also serves as process space.
10930~Z
It is further possible and in some instance especially
advantageous to simplify the process and the apparatus used for
the application of the process by forming the process space so
that a container which is open at its other end is arràhged in
upsidedown position with the opening below the liquid level in an
electrolyte container and is coupled to a source of underpressure
so that the upsidedown container, due to the underpressure develop-
ed therein, is filled with electrolytic liquid to the desired
level. Through this method, a conventional apparatus can quite
easily be changed for use in the process according to the inven-
tion. The electrolyte container can simultaneously serve as
storage space for the electrolytic liquid of the system, whereby
only one container is required~
As has appeared, it is not necessary for the biggest un-
derpressure to prevail in the process space proper, The main thing
is that the electrolyte circulates through a space where the pres-
sure is low enough. This prevents the formation of mist fumes
and harmful gases which as such is a big advantage. The effect of
the underpressure on the electrochemical process itself will,
of course, be smaller the smaller the underpressure is, but since
conventional quality in many cases is quite sufficient in coating
operations, the process according to the invention can also be
applied as described above. The environmental advantages of the
process can then be utilized in full with extremely simple addi-
tional equipment and at a low cost.
- Good results can be obtained when the difference between
the fr~e liquid level of the electrolyte container and the highest
point in the underpressure system is approx. 1.5 m. The highest
point of the underpressure system can be located outside the
process space itself. When the electrolytic liquid circulates
through the process space and the underpressure system connected
-- 3 --
10~30~Z
thereto, it is advantageous to arrange an air cushion at the
upper end of the process space in order to be able to pull
necessary power supply cables through the process space casing
at a point where there is no contact with the electrolytic
liquid. This makes handling of packing problems easier when the
cables are lead in.
An apparatus for the application of the process according
to the invention comprises an electrolyte container, an under-
pressure chamber and a sluice device, through which the liquid
which has flown from the electrolyte container to the process
chamber can be lead back to the electrolyte container. The
sluice device can be of a type known per se, for example, in
principle of the same kind as the so called releasers used in
milking machines. From the electrolyte container, the electroly-
tic liquid can be sucked directly to the underpressure chamber
by means of the underpressure in the chamber, but it can also be
pumped.
Because the electrolytic liquid is heated in an elec-
trolytic process, cooling is generally required. In an apparatus
according to the invention, cooling can be provided, for example,
by arranging a heat exchanger between the process chamber and
the sluice device, said heat exchanger being connected to the
electrolyte circulation system and to a cooling system. Even-
tually, cooling may also be required in the electrolyte container,
or in some instances heating. In order to ob~ain the required
temperature, the electrolyte container can be provided with
suitable temperature regulators. These regulators are advan-
tageously connected to the same cooling liquid system as the
heat exchanger of the electrolyte circulation system.
1~930~2
An apparatus according to the invention can be advanta-
geously provided with a plurality of underpressure chambers of
different sizes for coating of objects of different sizes.
The system can be so constructed that the various underpressure
chambers can be used simultaneously or alternatively.
The invention will now be described with reference to
the accompanying drawings where
Figure 1 is a schematic view of a first embodiment of
an apparatus according to the invention,
Figure 2 is a schematic view of a second embodiment of
an apparatus according to the invention, and
Figure 3 is a schematic view of a third embodiment of
an apparatus according to the invention.
In Figure 1, 1 denotes an electrolyte container, 2 a
smaller procéss chamber and 3 a bigger process chamber. From
the electrolyte container 1, a connecting pipe 4 leads to the
smaller process chamber 2. Through this pipe, the electrolyte
is sucked from the container 1 to the process chamber 2, and
. .
from there continues to circulate through a pipe 5 and a three
way valve 6 to a heat exchanger 7 where the circulating liquid
is cooled, when necessary. From the heat exchanger 7, the
liquid continues to circulate to the upper chamber 9 of a
sluice device 8. ~he circalating liquid is maintained under
under-pressure because a vacuum pump 10 is coupled to the upper
chamber 9 of the sluice device. From the upper chamber 9, the
circulating liquid flows through a non-return valve 11 and a
pipe 12 to the lower chamber 13 of the sluice device 8 when
1093012
this chamber is under underpressure. After the lower chamber 13
has been filled to a certain level, the control of the sluice
device cuts off the connection 14 between the lower chamber 13
. and t.he vacuum pump 10 and connects the lower chamber to the
atmosphere. The electrolyte then flows by its own weight
through a pipe 15 to the electrolyte container 1.
The electrolyte can also be sucked through a connecting
pipe 16 to the biggér process chamber 3 and from there through
a pipe 17 and the three way valve 6 further to the heat exchan-
ger 7 and sluice device 8. The desired circulation is selected
by adjusting the three way valve 6. The valve can also be
.constructed so that the electrolyte simultaneously circulates
both through the smaller and the bigger process chamber.
The apparatus shown in Figure 1 also comprises a closed
cooling liquid circuit 18 comprising an expansion vessel 19, a
cooler 21 activated by a fan 20, a circulation pump 22 as well
as necessary auxiliary equipment, such as, e.g. closing valves
23 and back stroke valves 24. The cooling liquid circulates
through the heat exchanger.7 and, when necessary, also around
or through the elec.trolyte container 1. Sometimes, for instance
in the initial stage of the process, the temperature of theelectrolyte-may be too cold.and heating is thus required. For
heating the electrolyte, the electrolyte container is provided
with an electric heating apparatus 25.
The actual coating process takes place in the process
chamber 2 or 3, usually activated by an outer supply of
: electric power. The power is supplied through cables 26 and
27. In principle, the process is a conventional electrolytic
coating process.
-- 6 --
.
~09301Z
In Figure 2, the process chamber 2 is immersed in the
electrolyte container 1 and is open in the lower end. Because
the process chamber 2 is connected to a vacuum pump 10, the
electrolytic liquid 34 in the electrolyte container 1 will rise
to a desired level in the process chamber 1. From the process
chamber 2, the electrolyte flows further through the pipe 5
to the sluice device 8 and from there back through the return
pipe 15 to the electrolyte container 1. The figure also shows
quite schematically power supply cables 26 and 27, their lead-
ins 40, electrodes 41 and a workpiece 42. An air cushion 43 is
formed at the lead-ins 40 in the process chamber ~ preventing the
cable lead-ins from getting into direct contact with the electro-
lyte,
The apparatus according to Figure 3 essentially corres-
ponds to the apparatus according to Figure 1, It is, however,
completed with a rinsing fluid container 45 which, by means of
three way valves 46 and 47 can be connected to the circulation
system of the e~ectroly liquid instead of the electrolyte con-
tainer 1. When the electrolyte container 1 is disconnected from
the circulations system and the rinsing fluid container 45 is
connected to the circulation system, the rinsing fluid circulates
from the rinsing fluid container 45 through the pipe 48 and the
three way valve 46 to the process chamber 2 where the workpiece
is rinsed. The rinsing fluid flows further in the usual way
through the pipe 5, sluice device 8 and return pipe 15 as well
as through the three way valve 47 and pipe 49 back to the rin-
sing fluid container 45. This embodiment of the invention has the
~09:~01Z
advantage that the workpiece need not be moved for rinsing,
but can be rinsed in the process chamber itself by using the
same low pressure circulation system as during the actual
process. In this way, rinsing can take place quickly and with
a minimum of waste time.
The following hard chromium plating process can be
mentioned as an example of a successful coating by means of the
process according to the invention. The electrolyte was a so
called self-regulating electrolyte (SRHS), and the temperature
was adjusted in accordance with the recommendations of the
electrolyte manufacturer. With a pressure of 0,85 atm in the
process space, the density of current could be raised up to a
value of 100 A/dm2. Despite this, an extremely tight and even
coating was obtained.
Process conditions:
Electrolyte SRHS 110
Temperature 60C
Current density 80 A/dm2
Object Cylindrical cast iron tube
The invention is not limited to the embodiments des-
cribed, but a number of variations and modifications are feasible
within the frames of the following claims.
., .
