Patent Application
20140197035
The invention relates to a device suitable for the electrochemical processing of an object, which device is at least provided with a chamber that is to accommodate an electrolyte, means for supporting the object that is to be processed in said chamber, at least one set of electrodes extending parallel to each other, which electrodes are located in said chamber such that during operation at least one electrode is located opposite each portion of a surface of said object that is to be processed, as well as control means for providing an electric current between the object that is to be processed and the electrodes.
The invention also relates to a holder suitable for such a device and a method for the electrochemical processing of an object with such a device.
Such a device and method are suitable for applying a layer on the object or renders remove a layer thereof.
In such a device which is known from WO2006027311A1, the electrodes are located in a raster pattern wherein the distances between the tips of all electrodes are equal, either with respect to each other or with respect to the surface of the object to be processed.
When objects with a relatively complex shape such as for example a turbine blade need to be plated with platinum, it is extremely important that the realized layer thickness of the platinum over the whole surface is as close as possible to the desired layer thickness to prevent excessive plating of the metal, especially because of the high prices of the platinum.
When positioning all electrodes in a rectangular matrix with spacings Δx and Ay that is either equal in each principal direction x and y, or either related (inversely proportional) to the substrate area in front of the tip of the electrode, it is not possible to provide each electrode with a desired current to obtain a desired layer thickness because:
if the current density on the tip of the electrode becomes too high the electrode might passivate (e.g. stainless steel, Ni or Ni alloy based electrodes), which would require cleaning or lead to a fast deterioration of the surface;
near recessed areas, the current density on the surface closest to the electrode would rise much faster than the current density in the recessed area (because further away); hence instead of reaching minimum specifications inside the recessed area, the deposit on the surface closest to the electrode would have a bad quality (rough, powdery, or even burned). In any case the deposit thickness on the surface closest to the electrode would be largely in excess compared to the minimum specifications. Since the prices of precious metals (Pt, Au, Pd, etc) are extremely high, a too thick deposited layer renders the object unnecessary costly.
So with the known device it is not possible to realize the desired layer thickness over the whole object without applying a metal weight, that is far too high and without increasing drastically the process time. The latter also holds true for removing a layer from the object.
It is an object of the invention to provide a device and method for the electrochemical processing of objects with relatively complex shapes, wherein the layer thickness of the applied or removed layer over the whole object is as close as possible to the desired layer thickness.
This object is achieved in the device according to the invention in that the device comprises at least one raster pattern comprising a number of nodes with fixed spacings between the nodes in at least two different directions, wherein a number of electrodes is arranged on the nodes of the raster pattern, whilst at least one electrode is located at a position shifted with respect to the nearest node of the raster pattern.
Due to the shifted electrode, all electrodes are no longer in a complete full raster or matrix. The shifted electrode can be shifted so that it does not coincide with parts of the object which do not need to be processed. The shifted electrode can also be shifted to a position in which it better addresses the surface of the object. The shifted electrode can also be located between the nodes to be able to increase the current density on the surface of the object, without the necessity to increase the current through the electrodes located on the nodes, so that the current per electrode can be limited for practical reasons (avoid fast deterioration or passivation, current range of the steering unit in case of individually steered pens). The shifted electrode can be also be shifted to a position so that another specific part of the object can be treated.
So it is clear that by the device according to the invention additional electrodes are required. It is not a priori possible to define how much electrodes are required for addressing recessed areas and ensuring the minimal thickness specifications, taking into account the fact that the current per electrode is limited for practical reasons. By means of computer simulations each electrode configuration has to be evaluated, and then in an iterative manner electrodes can be reallocated or more electrodes can be defined. Since the electrodes extend parallel to each other, it is relatively easy to manufacture the device after the positions of the electrodes have been determined.
The number of electrodes located at a position shifted with respect to the nearest node of the raster pattern is less than the number of electrodes located on the nodes of the raster pattern, so less than 50% of the total amount of electrodes. Preferably, the number of electrodes located on the nodes of the raster pattern is more than 60% and even more preferably than 70% or 80% of the total amount of electrodes, so that the number of electrodes located at a position shifted with respect to the nearest node of the raster pattern is less than 40% of the total amount of electrodes but more than 0% since at least one electrode is located at a position shifted with respect to the nearest node of the raster pattern.
WO2006127320A2 discloses a device with a number of electrodes which are all located on nodes of a regular patter. In
An embodiment of the device according to the invention is characterised in that the device comprises at least two sets of electrodes, wherein the electrodes within one set extend parallel to each other, whilst the electrodes of the first and second set extend in different directions.
By such an arrangement the object to be treated is located between the two sets. Such sets can easily be moved with respect to each other so that the object can be positioned between the two sets and be removed therefrom.
Another embodiment of the device according to the invention is characterised in that the electrodes of the first and second set extend in opposite directions but parallel to each other.
By moving one set opposite to the direction in which the electrodes of this set extend, the object can easily be removed from the space between the two sets.
Another advantage of defining the electrodes of the first and second set in opposite directions but parallel to each other is that the design of possible embodiments is simplified and subsequent machining efforts will be reduced.
Another embodiment of the device according to the invention is characterised in that the device comprises at least three sets of electrodes, wherein the electrodes within one set extend parallel to each other, whilst the electrodes of the first, second and third set extend in different directions, whereby the electrodes of the first and second set extend in opposite directions but parallel to each other, whilst the electrodes of the third set extend substantially perpendicular to the electrodes of the first and second set.
By means of the electrodes of the third set, recesses in the object which can not be reached by the first and second set can be addressed. Furthermore if two objects are processed at the same time in the device, the first and second set can be used for the surfaces of the first and second object directed away from each other, whilst the third set can be used for the surfaces of the first and second object directed towards each other.
Another embodiment of the device according to the invention is characterised in that at least one of the electrodes of the third set crosses the electrodes of the first or second set.
In this manner areas of complex surfaces can be reached.
Another embodiment of the device according to the invention is characterised in that the distances between the electrodes within a set are in the same range as the diameter of the electrodes.
With such a distances, a relatively high current density near the object can be realized whilst the electrolyte between the electrodes and between the tips of the electrodes and the surface of the object can easily be refreshed.
Another embodiment of the device according to the invention is characterised in that the electrodes have different lengths.
In this manner the tip of each electrode can be positioned at the same distance form the surface of the object or at any other required distance.
Another embodiment of the device according to the invention is characterised in that at least one electrode is curved.
With curved electrodes, areas like recesses which can not be reached with straight electrodes are accessible.
Another embodiment of the device according to the invention is characterised in that at least one electrode is pen-shaped, wherein the pen-shaped electrode is electrically insulated on the outer side except for the end extending towards the object to be processed.
Since only the end or tip of the electrode is exposed to the electrolyte, a controlled electrical current density on the surface of the object opposite to the electrode will be obtained.
Another embodiment of the device according to the invention is characterized in that at least one electrode is pen-shaped, wherein the pen-shaped electrode comprises a pin-shaped inner electrode, a tube-shaped outer electrode and an insulating layer located between the inner electrode and outer electrode.
Such an electrode is especially suitable as electrode of the third set as mentioned above, whereby the electrode is located between two surfaces of the object(s). The inner and outer electrode will be located opposite different parts of these surfaces and can each be optimized for the respective part.
Another embodiment of the device according to the invention is characterized in that the inner electrode extends outside the outer electrode, wherein the inner electrode and outer electrode are each connected to a separate current source.
Due to the separate current sources, the current for the inner and outer electrode can be different and be optimized for the respective part of the surfaces of the object.
Another embodiment of the device according to the invention is characterized in that the device comprises means to force the electrolyte to flow between the electrodes within of one set.
By forcing the electrolyte to flow between the electrodes and along the surface of the object to be plated, a good refreshment of the electrolyte between the electrodes and along the object surface is obtained.
Another embodiment of the device according to the invention is characterized in that the device is provided with a separate current source for each electrode or group of electrodes such that the electric currents originating from the separate current sources can be supplied by the control means to at least a number of electrodes or a number of groups of electrodes separately and in accordance with predetermined current profiles in time during the electrochemical processing of the object so as to realize a predetermined desired current density distribution across the object.
The desired layer thickness can be a precise value or a range from a minimum allowable layer thickness to a maximum allowable layer thickness to obtain an object with desired functionalities.
Due to the separate current sources, the current for each electrode or group of electrodes can be different and be optimized for the respective parts of the surfaces of the object.
For cost reasons the current per electrode is limited in case a steering unit with individual current sources for each electrode of group of electrodes is being used. For cost reasons a realistic value is 100 mA per electrode.
Another embodiment of the device according to the invention is characterized in that the electric potential on each electrode can be measured when a predetermined current is injected through the electrode, wherein the device is further provided with means for checking whether the measured value corresponds to an expected value.
Given a certain electrolyte at a certain operating temperature, the potential of each electrode will be in a certain range, for example 2.5 V when a fixed current of for example 10 mA is imposed. When the measured potential is much lower, it is a strong indication that the electrode makes contact with the object. This might cause burning of the electrode and/or the applied layer on the object. The electrode need to be re-adjusted
On the other hand, when the measured potential is much higher, it is a strong indication that a film (sludge) has been formed on the electrode, or that the electrode is even completely passivated by an oxide film, or that the electrode is poorly contacted at its back end. In this case, the electrode needs to be cleaned or replaced.
The invention also relates to a holder suitable for a device according to one of the preceding claims, which holder comprises at least one set of electrodes extending parallel to each other, characterized in that the holder comprises at least one raster pattern comprising a number of nodes with fixed spacings between the nodes in at least two different directions, wherein a number of electrodes is arranged on the nodes of the raster pattern, whilst at least one electrode is located at a position shifted with respect to the nearest node of the raster pattern.
Such an holder can be used as a replacement element for the device according to the invention.
The invention also relates to a method which is characterized in that the device comprises at least one raster pattern comprising a number of nodes with fixed spacings between the nodes in at least two different directions, wherein a number of electrodes is arranged on the nodes of the raster pattern, whilst at least one electrode is located at a position shifted with respect to the nearest node of the raster pattern, wherein when a calculated expected or a realized layer thickness of the layer deposited on or removed from the object differs from the desired layer thickness, the positions of the electrodes are recalculated and the electrodes are being rearranged.
The desired layer thickness can be a precise value or a range from a minimum allowable layer thickness to a maximum allowable layer thickness to obtain an object with desired functionalities.
The positions will be recalculated and the electrodes will be rearranged until the difference is below the predetermined value. The desired layer thickness can be constant over the whole surface of the object or can vary over the object in a predetermined way to limit the amount of material of the deposited layer.
The invention will now be explained in more detail with reference to the drawing, in which:
FIGS. 6A and 6B-6D are front and rear views of turbine blades processed by means of the arrangement of electrodes as shown in
Like parts are indicated by the same numerals in the various figures.
Each set 6, 7 of electrodes 9, 10 is mounted in a holder 11, 12 by means of which each electrode 9, 10 or a group of electrodes 9, 10 is connected to a separate current source in a manner as disclosed in WO2010032130A2 of applicant.
Each holder 11, 12 is electrically connected by means of a flexible cable 13, 14 via a control unit 15 to a computer 16. By means of the computer 16 and the control unit 15 the desired currents are provided to the electrodes 9, 10.
The device 1 is further provided with a pump 17 and conducts 18, 19 for pumping the electrolyte 3 through the spaces between the individual electrodes 9, 10 and between the electrodes 9, 10 and the turbine blade 5.
As can be best seen in the exploded view of
The turbine blade 5 comprises a blade 31, a foot 32 near one end of the blade 31, a root platform 33 near the other end of the blade 31 and a root part 34 located on an opposite side of the root platform 33 than the blade 31.
To mount a turbine blade 5 between the electrodes 9, 10, the root part 34 is slit into the slot 26 of the first part 25, where after the second part 28 is connected to the first part 25 to enclose the root part 34. When sliding the root part 34 inside the slot 26, the metal spring 27 comes in contact with the root part 34. The metal spring 27 is electrically connected to a metal screw on top of the first part 25 so that the turbine blade 5 can be connected to the negative pole of the control unit 13 if the electrodes 9, 10 receive a positive current or vice versa.
As is clearly visible in the
As for example can be seen in
As can be seen in
As is shown in
It is clear that by the device and method according to the invention, any desired layer thickness and thickness variation over the surface of the object to be processes can be realized due to the re-arrangement of the electrodes to the desired positions preferably combined with providing predetermined different desired currents to each electrode or groups of electrode.
The object to be supported by the device 101 is a double turbine blade 105 comprising two blades 131 which are connected to each other at the foot 132 and at the root platform 133.
The holders 111, 112 are similar to the holders 11, 12 and comprises sets 106, 107 of electrodes 109, 110.
The bottom plate 123 is provided with a recess 170 for receiving the foot 132. The bottom plate 123 and holders 111, 112 are provided with holes to be able to assemble the bottom plate 123 and the holders 111, 112 together by means of threaded rods 171 and nuts 172. The bottom plate 123 is provided with a passage 174 for a third holder 175. When the third holder 175 is located in the passage 174, the third holder 175 is connected to the bottom plate 123 by means of a bold 173 extending through a hole in the third holder 175 and into the bottom plate 123 and into a nut 176.
The top plate 124 is provided with a recess 177 for receiving the root part 134. The recess 177 is closed by means of a removable hook piece 124′ of the top plate 124. A spring 127 is located in the recess 177 for making electrical contact with the root part 134. The top plate 124 is provided with threaded rods 178 which can be inserted in holes in the holders 111, 112 and to fasten the holders 111, 112 with nuts 179. The top plate 124 is provided with a passage 181 for the third holder 175. When the third holder 175 is located in the passage 181, the third holder 175 is connected to the top plate 124 by means of a bold extending through a hole in the third holder 175, a hole 180 in the top plate 124 and into a nut 176.
The most important difference between the device 1 and the device 101 is that the device 101 comprises the third holder 175 with a third set 182 electrodes 183 extending parallel to each other but perpendicular to the electrodes 109, 110. As can clearly be seen in
The electrode 183 is insulted over its length which is not opposite a surface of the turbine blade but will be exposed over a much larger length than the electrodes 109, 110. Furthermore, the pen-shaped electrode 183 may comprise a pin-shaped inner electrode, a tube-shaped outer electrode and an insulating layer located between the inner electrode and outer electrode, whereby different currents can be imposed on the inner and outer electrode. If desired the pen-shaped electrode may comprise a number of tube-shaped electrodes located coaxial wherein the length of the tube-shaped electrode is longer as it is located closer to the central axis of the pen-shaped electrode 183. The pen-shaped electrode 183 might also be bended in order to follow more closely the center line between the two blades for the configuration of
In
The devices according to the invention can also be used for electrochemically removing a layer from an object.
The object can be a turbine blade but also any kind of object with any arbitrary of shape.
If desired more sets of electrodes can be used, wherein for example the electrodes of three different sets extend respectively in x, y and z direction, or by adding a further fourth, fifth or even sixth set with the pen electrodes being parallel to the ones of the first, second, respectively third set of electrodes but opposite in direction.
