EP0335277B1 - Method and apparatus for selective electroplating - Google Patents

Abstract

An electroplating apparatus for rapidly depositing a metal onto a selected surface of a workpiece, which apparatus comprises an anode having an active surface with a selected shape to combine with the selected surface of the workpiece to define an elongated gap of at least about 0.050 inches, means for supporting this anode in a fixed position to define the elongated gap; solution circulating means for forcing an electroplating solution with metal cations through the gap in a generally closed path at a velocity to exchange electroplating solution in the gap at a rate of at least 25 times per minute; and, means for applying current flow between the selected workpiece surface and the active surface of the anode through the gap at a current density in excess of 2.0 amperes/in2. The invention also involves the method of using this apparatus to rapidly deposit metal, such as nickel, onto the inner cylindrical surface of a bore on a complex part such as an aircraft landing gear forging.

Description

The invention relates to a method for electroplating a selected surface of a workpiece, in which an electroplating solution with metal cations or an electrolyte solution is passed at high flow rate through an elongated gap which is delimited by an anode and the surface of the workpiece to be plated and by one electrical current with a current density of more than 0.3 A / cm² is traversed from the anode to the workpiece surface. The invention further relates to a device for electroplating a selected surface of a workpiece by the method according to the invention, with supporting devices which support the workpiece and the anode in such a way that an elongated gap is formed between the anode and the surface of the workpiece to be plated, with a pump, which electroplating solution presses longitudinally through the gap with a high flow velocity and with an electrical plating current source connected to the workpiece and to the anode, which generates an electrical current with a current density of more than 0.3 A / cm 2 across the gap from the anode can flow to the workpiece.

From the "Electroplating Engineering Handbook" (published by LJ Durney, 4th ed., Van Nostrand Reinhold Company, New York, 1984), it is known to plate steel strips or the like at high speed, with high current densities of over 0, 3 A / cm² and large relative speeds of over 1 meter per second between the plating solution and the cathode can be used, for example achieve high deposition rates when dipping or bath plating a workpiece. This citation only describes the quick, complete plating of comparatively simple components such as steel strips, piston rings and the like.

In contrast to tank or bath plating, in which a remotely located, consumable or non-usable anode is placed in a container together with a workpiece to be treated, the invention relates to gap electroplating. In bath plating, the metal is deposited on all surfaces of the workpiece that are in the tank using electrolysis technology. In order to plate only a selected surface in such a tank or container method, the workpiece must be masked, provided with a protective coating or be protected in some other way from the bath solution in the tank. A completely different concept is used for gap electroplating. An anode is given a shape and surface which is largely adapted to the shape and the selected surface of the workpiece to be plated. The current flows between the anode and the cathode through a predetermined gap, which results from the geometry of the anode surface, insofar as it contacts the surface to be plated Workpiece surface is adjusted. This gap electroplating can be carried out in a container and is often carried out in a container for galvanic surface treatment; however, gap electroplating does not necessarily require a tank. Rather, it can also be accomplished by passing a plating solution into the gap between the anode and cathode while allowing a current to flow between these two electrodes as long as a closed or uninterrupted flow of plating agent flows through the gap. This type of gap plating is the subject of the present invention.

Closed loop gap electroplating, as is the subject of the present invention, is more generally described in U.S. Patents 4,111,761 to LaBoda and 4,441,976 to Iemmi, where an anode having a cylindrical outer peripheral surface is concentric in a cylindrical surface to be plated workpiece is arranged with which it forms a gap or a plating cell. The rest of the workpiece, including its entire outer surface, should not be clad. To prevent the rest of the workpiece from being plated, the electroplating solution is not brought into contact with the surface of the workpiece that is not to be plated. A modified container system is used in the process of U.S. Patent 4,345,977 to Blanc. Cladding of the outer part of the workpiece is prevented here by seals. The inner cylinder surface is primarily plated by this device due to the anode arrangement and the solution flow, but other parts of the workpiece are also plated because the tank actually encloses more than the selected inner cylinder surface. This patent does not disclose gap electroplating, but it shows, in general form, an apparatus for Plating a selected area.

The process of gap plating has been known for a few years. However, the jigs for these processes were relatively expensive and the work results were not uniform. especially in the case of elongated, generally inaccessible bores in complex workpieces. For this reason, tank plating or brush plating has often been carried out for the repair and reconstruction of oversized bores in various workpieces. The tank plating is extremely slow and does not deliver uniform results on selected areas without extensive, expensive masking. The success of brush plating depends largely on the experience of the worker and can only be used on very special, exposed surfaces. There is therefore a real need for a plating system that can be used to uniformly apply plating to various thicknesses of more than one workpiece, such as a forged part of an aircraft chassis, to a substantial thickness of over 1.27 mm (0.050 ") it is essential that such a plating process can be carried out quickly and with low set-up costs by persons with average experience.

There was also a need to clad in somewhat inaccessible locations on a large workpiece to create a very wear-resistant lubricant surface of substantial thickness to recover complex workpieces, such as forgings, where only certain surfaces were worn beyond acceptable tolerances. Chromium cannot always be used to meet these requirements because of the microscopic cracks in the thickness required to make an oversized bore within acceptable tolerances occur. Even if chrome is mostly used for the recovery or repair of worn parts of complex workpieces, chrome is not always an optimal material. In addition, the tank plating of such surfaces with chrome is not universally applicable. This is particularly the case when repairing holes that have become too large in steel forgings of the highest strength (240 KSI or larger), as are used in spacecraft and aircraft parts. In view of these limitations and requirements, chromium from container plating is not entirely satisfactory for the repair of workpieces, ie for plating the inner surface of a bore in a high strength steel forging. Furthermore, chrome plating for repairing worn surfaces, even if possible and / or desirable, requires extremely long plating times. Higher current densities to reduce this plating time do not significantly increase the rate at which chromium is deposited because the efficiency decreases rapidly as the current density increases.

Even if the tank plating of chrome on surfaces of a complex workpiece has been used to repair, recover or measure surfaces, this method is not completely satisfactory. In fact, in some cases it cannot be carried out effectively. Tank plating with nickel is also difficult and expensive as a repair, recovery or calibration process.

In view of the many experienced difficulties when trying to repair worn or oversized bores in complex workpieces, such as high-strength steel forgings for chassis, a plating process was developed that does not require chromium and that does not require a lot of capital and long Coating times and can be carried out without specially trained personnel, as is the case with the commonly known tank plating process.

The plating method and apparatus according to the invention have been created to achieve substantial advantages over special plating for a specific application, which involves plating selective surfaces while the workpiece itself does not require special treatment, and in which the long coating time which is required when tank plating is not required. With the method and apparatus of the invention, a remarkably thick metal layer is rapidly deposited on a selected surface of a workpiece, even if the workpiece is complex in shape, without masking and other complex, lengthy and time consuming pre-plating processes.

The invention provides an electroplating device for rapidly depositing a metal on a selected surface of the workpiece, which has an anode with an anodically active surface part of a selected shape, which together with the selected surface shape of the workpiece has an elongated gap of at least 1.27 mm (0.050 "). In addition, the electroplating device has a support which fixes this anode in a position to form the elongated gap. Furthermore, a circulating device is provided which in an essentially closed circuit at a speed through the gap, an electroplating solution loaded with metal ions urges that the electroplating solution in the gap be replaced at least 25 times per minute, and a current source is provided to provide a current between the selected workpiece area and the active area of the anode with a current density greater than 0.31 A / cm² (2.0 A / "²) to flow.

This new device according to the invention is primarily suitable for plating a cylindrical inner surface in a substantially complex shaped, high-strength steel forging, in which the gap has an annular cross section and has a first and a second end face. The plating solution is pressed from the first face of the gap to its second face at an ultra high volume exchange rate.

It is particularly expedient if the anode is a non-consumable anode and the plating solution consists of nickel sulfamate. The volume exchange rate through the gap can be referred to as "ultra high speed" or "high speed flow rate" because the volume exchange rate or liquid exchange through the gap is greater than before. The volume exchange rate is preferably on the order of 200 to 1000 times exchange of solution in the gap per minute. The ultra high fluid exchange rate can be up to 2500 times per minute, being limited only by the equipment and available pumps. Using such an ultra high volume exchange rate, current densities in excess of 0.31 A / cm² (2.0 A / "2) can be used between the matched surfaces of the anode and workpiece without overheating or in any way reducing the electroplating solution To influence the uniformity of the plating solution as it flows from one end of the gap to the other, this ultra-high volume flow ensures the separation of gas bubbles, the maintenance of the low temperature and the high contact pressure of the solution on the anode surface and the workpiece surfaces. which forms the plating cell is at least 1.27 mm (0.050 ") and preferably between 12.7 mm and 25.4 mm (0.50 and 1.0"). Gap widths that exceed 63 mm (2.5 ") can be used in the method according to the invention if the flow volume is increased.

According to the invention, a gap is created between the selected surface of a fixed anode and the selected surface to be plated. This gap controls the solution flow along these surfaces. Ultra-high flow rates allow high current densities, which in turn result in rapid metal deposition from the flowing plating solution, which is preferably nickel. In any case, a fresh, unused plating solution with controlled temperature is available in all cross-sectional areas of the gap for a uniform plating, which exerts a high contact pressure on the surfaces delimiting the gap. In practice, the plating solution is pushed vertically upwards, so that all gas that develops in the gap during electrolysis migrates upwards and is expelled in the same direction as the plating solution.

The method according to the invention, which uses the device explained above, serves for gap plating of a selected surface of a workpiece. This selected surface to be plated forms the boundary of the above-mentioned plating gap.

The primary object of the invention is to provide a gap plating method and apparatus which uses ultra high volume exchange rates or flow rates of the plating solution through the gap. The gap is the plating cell between a fixed anode and the special surface of the workpiece that was selected for the plating.

As stated above, the invention has the advantage that current densities exceeding 0.31 A / cm² (2.0 A / "²) can be used, so that the plating speed is increased significantly and the plating time decreases, thereby reducing application previously in a tank over three days lasted, can now go on in less than two to four hours.

With the invention it is possible to deposit a thick metal layer on a selected surface of a workpiece quickly and uniformly over the entire surface in such a way that the process can be repeated from one workpiece to another without the changes caused by the limits of manual work.

Another advantage of the invention is that thick, uniform surfaces can be produced which have so far been difficult, if at all, to achieve without substantial clamping and / or masking by tank plating.

According to a further feature of the invention, a swirling flow of the plating solution through the annular gap is used where the flow is generated by the plating solution itself.

Another advantage of the invention is that the plating solution can be maintained at a uniform, relatively low temperature over the entire length of the gap to ensure uniform plating throughout the gap.

Fig. 1

eine bevorzugte Ausführungsform der erfindungsgemäßen Vorrichtung bei Verwendung an einem speziellen Werkstück in einer seitlichen Ansicht und teilweise im Längsschnitt,

Fig. 2

den Gegenstand der Fig. 1 im Schnitt in einer vergrößerten Darstellung, wobei bestimmte Abmessungen und Parameter einem Ausführungsbeispiel der Erfindung entsprechen,

Fig. 3

den Gegenstand der Fig. 2 in einem Querschnitt nach Linie 3-3,

Fig. 4

den Gegenstand der Fig. 3 in einem Schnitt nach Linie 4-4,

Fig. 5

den Gegenstand der Fig. 2 in einem Querschnitt nach Linie 5-5,

Fig. 6

den Gegenstand der Fig. 2 in einem Querschnitt nach Linie 6-6,

Fig. 7

die bei der bevorzugten Ausführungsform nach der Erfindung verwendete Anode in einer Seitenansicht,

Fig. 8

eine schematische Darstellung, die bestimmte Durchflußcharacteristika der bevorzugten Ausführungsform nach der Erfindung zeigt und

Fig. 9

eine graphische Darstellung, welche einen Betriebsparameter erläutert, der durch Verwendung der vorliegenden Erfindung erhalten wird.

Further features and advantages of the invention will become apparent from the following description and the drawings, in which preferred embodiments of the device according to the invention and the method carried out with it are explained. It shows:

Fig. 1

a preferred embodiment of the device according to the invention when used on a special workpiece in a side view and partly in longitudinal section,

Fig. 2

1 in section on an enlarged scale, certain dimensions and parameters corresponding to an embodiment of the invention,

Fig. 3

2 in a cross section along line 3-3,

Fig. 4

3 in a section along line 4-4,

Fig. 5

2 in a cross section along line 5-5,

Fig. 6

2 in a cross section along line 6-6,

Fig. 7

the anode used in the preferred embodiment according to the invention in a side view,

Fig. 8

is a schematic representation showing certain flow characteristics of the preferred embodiment according to the invention and

Fig. 9

FIG. 4 is a graphical illustration explaining an operating parameter obtained by using the present invention.

In Fig. 1, a device A is shown according to the invention, which is used to apply a uniform layer an electroplatable metal, such as nickel, on a selected surface S in the form of a cylindrical wall 10, which has a lower, conically recessed part 12 and an upper, conically recessed part 14 in a complex workpiece W. For simplification, these three parts of the surface to be selectively plated are referred to below as "surface S". Although the present invention can be used for plating selective surfaces of relatively simple workpiece shapes, one of its remarkable advantages is that it can be used on a complex workpiece as represented by workpiece W, which in the illustrated embodiment is a high strength steel forging for aircraft landing gear, in which the surface 10 is a supporting surface, which may be subject to gnawing corrosion and must be repaired from time to time by metal plating in order to restore the usability of the core forging. In the practice of the invention, the selectively plated surface S is generally cylindrical, as shown on the workpiece W, which has many surface areas that are not to be plated, such as the entire outer surface to which, as examples of unplated shapes, include a gear member 20, an elongated sleeve 22, outwardly projecting areas such as a shoulder 24, a lower flange 26, an outwardly projecting support projection 28, and many other outer and inner surface areas that are not to be plated. It can be seen that if this forging W were plated as a cathode in a plating tank, the entire surface of the forging would normally be plated to a certain extent. In order to plate only the surface S, a considerable amount of fastening and masking would be necessary if a tank plating process is used. In addition, in the Past usually chrome plated on the S surface. However, if chrome is plated on a selective surface, it takes a considerable amount of plating time. An increased current density does not significantly increase the efficiency and the deposition rate of chromium in a tank or even with a modified tank plating system. In addition, chromium cannot be easily plated in a larger thickness, for example 1.27 mm (0.050 "). It is therefore advantageous to apply a nickel coating to the surface S in the application shown.

The present invention now provides a method in which the current density can be increased drastically in a plating process to increase the rate of deposition of a material such as nickel on the surface S. Here, the preferred material deposits at a rate that increases significantly with increasing current density, even if the efficiency may be somewhat lower than that with low current densities, such as less than 0.15 A / cm² (1, 0 A / "²) is reached.

The device A according to the invention can plate a selected surface S with its recessed parts 12 and 14, using a high current density above 0.31 A / cm² (2.0 A / "²) to reduce the plating time is necessary to achieve a predetermined metal thickness up to a size over 1.27 mm (0.050 "). In the invention, a high current density can be maintained so that the deposited layer grows proportionally with the plating time. The invention is particularly applicable to the deposition of nickel on the selected surface S, since the deposit increases with the current density without a significant drop in efficiency, as has been observed with chrome plating in the tank. The workpiece W is one of many complex forgings, in which internal bores often have to be rebuilt after their wear or if they have been worked to excess. In fact, in many cases, internal bores in such forgings are initially oversized so that a metal plating layer can be applied to the surface to provide good corrosion resistance, better wear resistance, and a finer surface. In the past, a tank or a modified tank was commonly used in this recovery or assembly process, with chrome or chrome and nickel layers being applied to the inner surfaces of the holes in the forging. This process was more time-consuming and it often took three days to plate in the tank the particular surface S which is the subject of the embodiment shown in FIG. 1. If the device A is used with the invention, a nickel coating is produced on the surface S to the same depth and with better uniformity in less than six hours and generally between two and six hours. The resulting nickel plating is uniform, forgeable and smooth and can be made thicker than a chrome plating, which can get microfine cracks with increasing thickness. In summary, when using the invention, device A can make errors in a complex workpiece in a relatively short time. Repair, eliminate or correct time so that the expensive forging W can be obtained in an economical manner. This saves many such forgings from the scrap, because in the past, reprocessing often cost more than a new forging, reprocessing was often impossible, or chucks could be severely damaged by immersion in tank plating solutions, especially if the masking was not done properly . With the invention, the same hole in Similar forgings can be plated with the same device without new adjustment.

The device A has components that are made for the surface S. Other holes or surfaces require modified but functionally the same components as those shown in FIG. 2. A lower or first end cap 30 engages and seals gap g , which is the plating cell defined by surface S and anode 40. An upper or second end cap 32 closes the other end of the plating cell on the receding part 14 of the surface S. The end caps are clamped together and sit tightly on the opposite ends of the surface S, the anode 40 being concentrically surrounded by the surface S and itself extends axially through the plating cell parallel to the cylinder surface 10. In order to hold the workpiece W and the two clamped end caps 30 and 32 in an immovable position, a suitable fastening device is provided, which is shown as a support foot 50. This support foot carries an upward, rigid metal tube 52 which connects the support foot 50 to the cap 32, as shown in FIGS. 1 and 2, so that the workpiece W and the end caps 30 and 32 with the surface S in between in layers fixed position are arranged so that the first end cap is under the second end cap. An ultra high throughput liquid pump 60, which has a reservoir for the electroplating solution, which in the preferred embodiment is nickel sulfamate, pumps the solution in a closed circuit P through the plating cell defined by end caps 30 and 32. This liquid flow has an ultra-high volume.

In the illustrated embodiment, the liquid pump 60 pumps 0.315 - 0.74 l / s (600 - 700 gallons / h) of liquid so that the solution flows along the path indicated by the arrows in Figs. 1 and 2 at such a high speed that the solution in the plating cell is exchanged on the order of 200 to 1000 times per minute. According to the invention, the pump has an ultra high volume flow rate to force a liquid flow through the annular gap g at a rate which results in a complete change of the liquid at least 25 times / minute. This extremely large volume flow rate allows nickel to deposit on the surface S from the plating solution if a current density above 0.31 A / cm² (2.0 A / "²) is used. As the flow rate or flow rate increases, so too the current density is increased to at least approximately 1.6 A / cm² (10.0 A / "²) to substantially increase the amount of nickel deposited on the surface S from the plating solution. The anode 40 is a non-consumable anode. For this reason, the gap g remains constant over the plating cycle, which lasts less than six hours in the illustrated embodiment. The same precipitation of nickel has so far required approximately three days, if at all, when plating using the tank plating system.

In order to force the ultra-large volume flow or ultra-high fluid flow through the closed circuit P, the pump 60 conveys the nickel sulfamate or similar plating solution into a high pressure plastic delivery line 62 which extends up the tube 52 into the lower end cap. The liquid stream then moves up through the plating cell defined by surface S and anode 40 and exits through upper end cap 32 into two outflow lines 64 and 66 which open into a larger return line 68. By using two diametrically spaced outflow lines 64 and 66, the outflow through the upper end cap 32 is more evenly distributed by one To prevent cavitation and to achieve a smooth flow of the plating solution through the respective plating cell.

In accordance with the standard design, direct current is passed through the annular gap g from a conventional portable plating power source. Here, an anode terminal 80 is connected to the anode 40 and a cathode terminal 82 to the workpiece or forging W. In the practical embodiment, a cathode is connected next to the end caps 30 and 32 of the device A by placing a clamp around the workpiece W in the vicinity of the surface S. The particular construction for applying a current flowing through the fixed, annular gap g is not part of the invention and can be realized by various electrical connections.

In operation, the electrical current flow between terminals 80 and 82 is adjusted to achieve the desired plating performance, which is extremely high to achieve the greatest benefit of the invention and at least about 0.31 A / cm² (2.0 A / "² The current density can be increased as much as the flow rate provided by the pump 60 can be increased. The currently available pumps deliver approximately 18.9-50.5 l / s (300 to 800 gallons / min.) and as stated above, an ultra-high volume flow in order to achieve an exchange of the electroplating solution in the gap g at least about 200 times / min.

The lower end cap 30 is designed to ensure an even distribution of the plating solution in the gap g at the ultra high flow rate. As a result, all cross-sectional areas of the cylindrical anode surface and surface S are continuously and uniformly coated with a fresh plating solution in intimate, direct, continuous, physical and electrical surface contact. For this purpose, the end cap 30 has a nose 100 which has an outer peripheral surface which is shaped and dimensioned in such a way that it conforms to the contour 102 of the workpiece W. In the drawing, this contour has annular, concentric shoulders 104 and 106 which form part of the overall shape of the workpiece. These shoulders are concentric with the surface S and define the outer peripheral surface of the nose 100 which is shaped for the bore shown. A second part, namely a lower base plate 110, is clamped to parallel end faces 112 and 114 which extend to the side with a plurality of bolts 116 which are arranged at a distance from one another and which pull the nose 100 and the base plate 110 together. An O-ring 118 seals the inner flow openings of the cap 30. These flow openings receive the high-pressure plating solution, which flows through the inflow line 62 with an ultra-high flow rate. The solution moves through the cap 30, as indicated by the arrows in FIG. 2.

The base plate 110 has a central threaded bore 120 which receives the threaded end 122 of the feed line 62, which is used to connect this high-pressure pipe to the base plate 110. A concentric, second threaded bore 130 receives the threaded end 132 of the rigid support tube 52, which carries the device A and the workpiece W in its vertical position.

The nose 100 is provided with the base flow openings of the lower end cap 30 and has an outward shoulder 140 which abuts the concentric shoulder 106 of the workpiece W to align the cap 30. In a recess 144 of the nose 100 an O-ring 142 with a rectangular cross section is arranged such that its outer circular edge 146 with the edge 148 on extreme end of the conical recess part 12 coincides such that the edge 146 delimits the outer edge of the plating area of the plating cell. The edges 146 and 148 can be brought into exact alignment by hand by moving the workpiece W on the nose 100 before the anode 40 clamps the upper end cap 32 in place.

The inner flow openings of the cap 30 include a concentric plenum chamber 150, which has a diameter e and a height of 12.7 mm (½ "). The diameter e is approximately the same size as the diameter a of the cylindrical part 10 of the surface S. , so that a large volume of solution coming from the feed line 62 can collect in the plenum 150 before it is led from the plenum into a distribution space 160 at the upper, exposed end of the nose 100. By the arrangement of a plenum and of a distribution room, a very large volume flow can be distributed from the distribution room after it has been evenly pressurized in the plenum chamber.

According to a further feature of the invention, a novel nozzle arrangement is provided in order to bring the solution from the lower plenum chamber 150 into the upper distribution space. This nozzle arrangement generates a plurality of separate and different, spiral flows of plating solution 170, which are shown schematically in FIG. 2 as spiral arrows 170. The nozzle device for producing this spiral-shaped flow through the annular gap g is produced by a plurality of holes or bores 180 arranged at a distance from one another in the circumferential direction, eight of which are shown at the same circumferential distance from one another. These holes are inclined at an angle of approximately 30 ° (in practice 27 °) against the longitudinal axis in such a way that the liquid flows 170 in the gap g and are not directed against the anode 40 or the surface S. In this way, the jets or streams of the plating solution helically traverse this gap g substantially in the center of the gap to prevent everything else except for the normal, uniform flow of liquid along the anode surface and the surface to be plated. The particular, preferred helical configuration of the flow channels according to the invention increases the surface speed of the solution to a value which is even greater than the exchange speed generated by the pump 60. The actual velocity of the liquid flowing through the plating cell or gap is determined by the distance the solution travels and the time it takes for the solution to flow through the gap. The rate of flow through the cell is even greater than the ultra high speed of the ultra high flow rate in the rest of the range. The holes 180 in the preferred embodiment of the invention have a diameter of approximately 6.35 mm (½ "), which is schematically shown as the dimension f in Figs. 2 and 4.

A central threaded bore 190 is provided for connecting the lower end cap 30 to the anode, which receives the threaded end 192 of the anode 40 and supports the lower end of the anode of device A when the two caps are in the plating position. As indicated in FIG. 2, the nose 100 and the base plate 110 consist of a suitable plastic material which is not conductive and forms an insulation between the positive anode 40 and the negatively polarized workpiece W.

2 and 6 that the upper end cap 32 has a substantially flat plastic body in which there is an annular recess 204 in which a downwardly extending, cross-sectionally rectangular O-ring 202 is located, the lower inner edge 206 of which coincides with the outer edge 208 of the conical, recessed part 14 to be plated. The O-ring 202 has the same function as the O-ring 142 of the lower end cap, so that these two rectangular O-rings limit the extreme extent of the selected surface to be plated during the operation of the device A.

For the assembly of the two end caps, the body 200 has a central central opening 210 which receives the cylindrical shaft 218 of the anode 40. A standard O-ring 212 is arranged in the central opening 210, which seals this opening against the shaft 218 of the anode, which can slide in the opening. An upper collar 214 is fastened to the shaft 218 using a suitable means, for example a clamping screw 216.

The flow openings for the electroplating solution in the top cap 32 are designed to collect any gas that may be formed during the plating process. Due to its buoyancy, this gas can reach cap 32 from cap 30 upwards. In order for the liquid to collect after the plating process and to create a collector for any type of gas generated during the plating process, the body 200 has an outwardly flared conical top plenum 220 with a substantially flat surface that intersects with two spaced-apart bores 222 and 224 which receive threaded nipples 230 and 232 of drain lines 64 and 66, respectively. These lines have relatively large cross sections and must be at a distance from the anode 40. The holes 222 and 224 therefore cut down into the conical surfaces 240 and 242 and form an oblique intersection with the conical surface which forms the cavity 220, as best shown in FIGS. 2 and 6. On in this way the solution flowing through the gap g is collected in the cavity 220, which widens in the transverse direction, ie in a direction perpendicular to the direction of movement on the path P. This reduces the speed of the solution in the cavity 220 for distribution to the two outlet lines 64 and 66. This outward-expanding, speed-reducing portion allows all of the gases that are formed during the plating process to be collected, but increasing the cross-sectional area of the cross-sectional area of surface 10 is not sufficient to significantly reduce the speed.

When assembling device A shown in FIG. 2, end 192 of anode 40 is screwed into bore 190 of lower end cap 30. The workpiece W is then centered on the square O-ring 142 and positioned so that the edges 146 and 148 lie one on top of the other. The body 200 is then slid over the shaft 218 of the anode and guided down into a central position in which the edges 206 and 208 lie one on top of the other. Then the collar 214 is fixed on the shaft 218 with the clamping screw 216. The anode 40 is then rotated on its upper, polygonal part 250 in order to clamp the end caps together by screwing the lower end 192 into the threaded bore 190 of the lower end cap 30. A suitable anode connector 252 is then snapped into the top of the anode and the anode and cathode leads are connected. To start the work process, the pump 60 pushes the plating solution through the plating cell, as indicated by the arrows in FIG. 2, while current flows through the annular gap g . The plating process continues until the desired thickness of the plated metal has been reached.

Turning now to FIG. 7, one sees the anode 40 used in the preferred embodiment of the invention. A standard platinum coated titanium anode bar is machined to have a selected area of section 300 that matches the selected surface S to be plated. According to a feature of the invention, this surface 10 is cylindrical. Therefore, the surface or the selected part 300 is also cylindrical and has a length h which is adapted to the length of the surface S to be plated. When the plating process is initiated, the exposed parts of the anode 40, with the exception of the region 300, are made of titanium, which is anodized and therefore does not generate current flow. The current therefore flows only from the surface 300 which is adapted to the surface S to be coated. Because the anode 40 is not consumable in one embodiment of the invention, the gap g remains constant and enables continuous and uniform flow through the plating cell without causing changes due to depletion or depletion of the anode.

Figure 8 is a schematic illustration of another embodiment of the invention. The solution flow along the path P through the gap from the feed end F to the outlet end D between the end caps 30 and 32 is controlled so that a quick and forced exchange of plating solution in the gap g takes place. In order to accomplish this, the cross-sectional area or the boundary of the outlet lines 64 and 66 is larger than the cross-sectional area or the boundary of the feed line 62; however, the combined area of the outlet pipes is not larger than twice the cross-sectional area of the feed pipe. In this way, the solution flow through the plating cell is controlled so that a rate drop in the cell due to an increase in cross-sectional areas in the flow process is prevented by the cell. Due to the fact that the outlet cross-section is at least as large as the inlet cross-section, there is no back pressure and there is no significant reduction in speed, since the outlet cross-section is not larger than approximately twice the inlet cross-section. This is another feature of the invention which supports a uniform and continuous flow of plating solutions through the annular gap g .

The parameters given in Figure 2 and discussed above represent an example of the present invention. The surface 10 has a diameter of 41.2 mm (1.62 ") and the gap is 15.875 mm (0.625"). In practice, this gap is between 1.27 mm and 51 mm (0.050 and 2.0 "). The length of the area S is 38 mm (1.50") and the current is approximately 30 A. 1135 liters (300 gallons) one Nickel sulfamate plating solution are pumped through the gap g per hour. The cross-sectional area A _{e of} the plenum chamber 150 is approximately equal to the cross-sectional area A _{a of} the bore of the workpiece, which is delimited by the surface 10; however, it is larger than the cross-sectional area of the gap g and considerably larger than the sum of the cross-sectional areas A _{f of} the various holes 180 which represent the nozzles. This example enables nickel deposition to the desired thickness with a plating cycle between 2.0 and 6.0 hours. In contrast, tank plating the same surface using chrome to the same thickness, if possible, would take more than three days.

According to the invention, the exchange rate of the plating solution in the gap g is at least 25 times / min. This is shown in general terms by the graph in Fig. 9, where the highest current density increases with the exchange rate. This ratio defines an operating range that increases to 1.55 or more A / cm² (10 A / "2), while the exchange speed up to 2500 times / min. increases. Of course, the current density used in the process is not necessarily the maximum current density, since other process parameters determine the exact current density that is desired by the operator for a particular workpiece to be machined. The desired current density can be determined by the size of the gap, the temperature in the gap and related parameters that are not part of the present invention.

According to the invention, the ultra-high flow rate is adjusted so that plating can only be achieved using two separate closures or end caps which delimit the plating cell and that the plating solution passes through the gap between the anode and the selected surface to be plated at such a high speed is pushed through, that high current densities are possible. In practice, the plating solution is a nickel solution and preferably nickel sulfamate. The temperature in the gap is maintained between 43 and 55 ° C (110 and 130 ° F).

According to a main feature of the invention, the surface 10 is cylindrical and the peripheral surface 300 of the anode 40 is also cylindrical and defines a non-consumable anode. The plating solution is any of the various plating solutions used in tankless selective plating processes. Chromium is usually not used in this type of process. The solutions normally preferred for selective plating are nickel, lead, copper, iron, tin and zinc. Of course, precious metals could also be used; however, the invention is primarily applicable for industrial purposes which do not intend to use precious metals. Chromium makes use of the present Invention difficulties in that the plating must be carried out very slowly and the advantages achieved by the rapid flow in chrome plating are not fully realized. Chrome deposits are brittle and limited in thickness, which detracts from the utility of the present invention. In all cases, chromium would be difficult to use using the present invention and is therefore not preferred. However, some features of the invention can also provide some advantage for a chrome plating system. Nickel is considered the preferred and best metal to be used in the practice of the present invention.

When using device A, the solution flow is limited to the surface to be plated and the anode surface. There is no need for painting or other insulating coating to prevent unwanted plating. The workpiece W can have different shapes. By providing the high flow volume, there is a constant solution / metal interface at the anode surface 300 and the surface S to be plated. There is no liquid splashing of the solution and no other auxiliary inputs into the gap g , which is due to the uniformity of the rapid axial movement can divert the gap flowing solution. Furthermore, the tendency for gas formation in the solution decreases and there is a high surface pressure between the solution on the one hand and the anode surface and the surface S to be plated on the other hand, so that an extremely intensive liquid / metal interface contact is produced with the flowing solution. The gap g need not be precisely controlled as long as its cross section remains essentially the same so as not to interrupt the high surface pressure contact of the liquid solution flowing axially through the gap. The gap shouldn't be Have areas that collect the solution or reduce the speed of the solution as it moves through the gap. Such a reduction in speed is common in tank plating and leads to stagnation and accumulation of weaker plating solution which is in contact with certain parts of the surface to be plated.

According to the invention, the direction of flow is directed upwards in the vertical direction in order to coincide with the flow of any gas bubbles which arise during the plating process. The term "ultra-high" volume, as far as it relates to the ratio or circulation, means more than 25 solution exchanges in the gap g per minute and preferably more than 200 exchanges per minute. The anode construction according to the invention is geometrically adapted to the surface 10 to be plated, in contrast to the tank plating method, where the anode is located far away from the surface to be plated and has no real geometric relationship with it. The anode surface cooperates with the surface S and forms the gap through which the liquid flows at ultra high speed.

This is an exceptional plating process and very different from any tank or normal gap plating. By using a lower plenum 150 in the cap 30, the inflowing liquid is evenly distributed before flowing through the holes 180 at high speed. This change in speed in the nozzles ensures that the individual nozzle jets, which are generated by the holes arranged at a distance from one another in the circumferential direction, are driven through the gap in a direction between the surface to be plated and the anode surface. As each jet is created as a vortex or spiral, the liquid speed increases in the gap because the solution travels a longer distance on its way from the lower cap 30 to the upper cap 32.

Repeatability from one workpiece to another is achieved by using the cap solution. Of course, each workpiece could have its own specially designed fastening device. This fastening device with the pump for the plating solution and the power supply for it are portable. The solution runs through a closed system and can be refreshed periodically after a predetermined period of use. With the invention, uniform plating is achieved throughout the gap and there are no areas of stagnation, elevated temperature or lower flow rates. This advantage is achieved by the high solution exchange rates, which are primarily limited by the durability and design of the equipment and reach 2500 exchanges per minute, as shown graphically in FIG. 9. The anode is shaped to match the selected shape to be plated; in the one preferred embodiment it is insoluble, i.e. unusable and allows current to flow only from the selected surface, for example from surface 300 shown in FIGS. 2 and 7. In this way, a uniform current also flows through the gap from the surface 300 of the anode to the surface S to be plated.

Claims (20)

1. Process for electroplating a selected surface (S) of a workpiece (W), in which an electroplating solution (170) having metal cations or an electrolyte solution with considerable flow rate is passed through an elongated gap (g), which is limited by an anode (40) and the surface (S) of the workpiece (W) to be plated and through which flows an electric current having a current density of more than 0.3 A/cm² (2 A/in²) transversely from the anode (40) to the workpiece surface (S), characterised in that an anode (40) which is not consumed is used, which has an anodically non-active part (218) and an anodically active surface part (300), which is adapted to the surface (S) of the workpiece (W) to be plated, and in that the electroplating solution (170) or the electrolyte solution is passed through the gap (g) at such a high volume exchange rate that the solution is exchanged in the gap (g) at least 25 times per minute.
2. Process according to claim 1, characterised in that the anodically active surface part (300) of the anode (40) which is not consumed is adapted to the surface (S) of the workpiece (W) to be plated in that an external, anodically active coating is removed from the anode at surface regions which do not correspond to the surface (S) to be plated.
3. Process according to claim 1 or 2, characterised in that titanium is used as base metal for the anode.
4. Process according to claim 1 or 2, characterised in that platinum is used for the anodic surface part (300).
5. Process according to one of claims 1 to 4, characterised in that a nickel-plating solution is used as the solution.
6. Process according to one of claims 1 to 4, characterised in that a nickel sulphamate solution is used as the solution.
7. Process according to one of claims 1 to 6, characterised in that the temperature of the solution in the gap is maintained in the region from 110° - 130°F.
8. Process according to one of claims 1 to 7, characterised in that the current density is in the range from 0.3 to 1.6 A/cm² (2-10 A/inch²).
9. Process according to one of claims 1 to 8, characterised in that solution exchange takes place in the gap 200 to 1,000 times/minute.
10. Process according to one of claims 1 to 8, characterised in that the flow rate of the solution in the gap is so great that it is exchanged 25 to 2,500 times/minute.
11. Device for electroplating a selected surface (S) of a workpiece (W), having support devices (30, 32) which support the workpiece (W) and the anode (40) such that an elongated gap (g) is formed between anode (40) and the surface of the workpiece (W) to be plated, having a pump (60) which forces electroplating solution with considerable flow rate through the gap in the longitudinal direction and having an electric plating current source connected to the workpiece (W) and to the anode (40) which allows an electric current having a current density of more than 0.3 A/cm² (2.0 A/in²) to flow transversely through the gap (g) from the anode (40) to the workpiece (W), characterised in that the anode (40) is a non-consumable anode which has an anodically active surface part (300) which is adapted to the selected surface (S) of the workpiece (W) to be plated, and in that the pump (60) has such a high capacity that the electroplating solution forced through the gap (g) by it is exchanged at least 25 times/minute.
12. Device according to claim 11, characterised in that the anode (40) consists of an anodically non-active base metal and an anodically active coating, the shape and dimensions of which are adapted to the surface (S) of the workpiece (W) to be plated.
13. Device according to claim 11 or 12, characterised in that the coating is platinum.
14. Device according to one of claims 11 to 13, characterised in that the base metal of the anode is titanium.
15. Device according to one of claims 11 to 14, characterised in that the gap (g) is connected at one end (12) by a second end cap (32), and in that the two end caps (30 and 32) support the anode (40) and have flow openings (180 or 64, 66) which form one part of the path for the closed solvent circuit.
16. Device according to one of claims 11 to 15, characterised in that a plenum chamber (150), which is connected to the gap (g) via several flow openings designed as nozzles (180) arranged in the end cap, is arranged in front of the first end cap (30) at the inlet end of the gap (g).
17. Device according to claim 16, characterised in that the nozzles (180) are designed and arranged such that they conduct the individual streams of the plating solution helically through the gap (g).
18. Device according to one of claims 11 to 17, characterised in that the nozzles (180) for producing the individual liquid streams in the peripheral direction of an annular gap (g) are arranged at a distance from one another.
19. Device according to one of claims 11 to 18, characterised in that the second end cap (32) has an inlet opening, a gas collection chamber (220) and a plating solution outlet (D), which are connected to the gap (g), at the outlet end of the gap (g).
20. Device according to claim 19, characterised in that the plating solution outlet (D) of the second end cap (32) has an admission volume which is at least equal to the throughput volume of the solvent inlet (F) of the first end cap (30) and is not greater than double the throughput volume of the solvent inlet (F) of the first end cap (30).

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