EP2823890A1 - Method and installation for the wet chemical deposition of nickel layers - Google Patents

Abstract

The invention relates to a wet-chemical nickel bath with a magnet (1) for fixing nickel particles.

Description

The wet-chemical deposition of nickel layers has been a well-known and extensively used process for a long time. The layers are also referred to as so-called chemical nickel layers, which distinguishes them from galvanic nickel layers.

Products to be coated are suspended in a suitable manner, for example on a standard electroplating rack, and placed in a special nickel bath, e.g. nickel sulphate-based with a nickel content of e.g. 4g to 8g nickel per liter can be constructed. Hypophosphite can be used as the reducing agent; In general, complexing agents are additionally provided.

Such methods have been used, inter alia, for products which are to be given improved wear resistance or improved corrosion protection by the coating. A well-known example are housing of fuel pumps for internal combustion engines, for example in cars.

The prior art is additionally referred to the EP 02 102 609 , which deals with a container for the chemical metallization, in particular the nickel deposition, and also deals with the filtering of particles from the nickel bath.

The invention has for its object to provide an improved method for wet-chemical deposition of nickel layers.

This object is achieved by providing a magnet for fixing nickel particles in the nickel bath in or on the nickel bath during the deposition.

The inventor has found that the nickel particles are not only in terms of the mentioned in the EP 02 102 609 Thematic wall deposits can be problematic. They can also adhere to the coated products or even grow by further deposition and thus at least affect the surface quality. This may affect the frictional properties, but it can also emanate from separating or separated during operation of the product further problems.

Further, the inventor has found that the recirculation and filtration of the nickel bath already mentioned in the cited application offers considerable improvements in this regard, but leaves room for further improvement. These further improvements relate to the relief of the filter and / or the additional improvement of the particle freedom of the products, depending on the individual application. The improvement of the invention consists of magnetically collecting nickel particles from the nickel bath by using a magnet in or on the nickel bath at least during the deposition.

By the way, the term "nickel particles" also means particles which are originally based on materials or impurities other than those of nickel, but which have been or have been coated in the bath with nickel. They also have the property of being attracted to a magnet by the nickel coating and can thus be directed in the nickel bath to the magnet and fixed in its surroundings or on it. In any case, they are in fact deprived or immobilized in the part to which they migrate to the magnet and remain there. If necessary, they can be removed (with or without the magnet) from the nickel bath.

By reducing the particle concentration in the nickel bath and / or reducing the concentration of at least the larger of the particles (which experience has shown to be more strongly attracted), the adverse effects of the particles are reduced, in particular, depending on the application, the load on the filter in the recirculation system , the growth on the tub walls and / or the adhesion and growth of particles on the coated products.

In particular, the magnet can also be used to collect particles in size ranges which are not detected or poorly detected by the customary filters, in particular particles in a range between 0.1 μm and 3 μm (based on the smallest particle size; other dimensions can be larger ). Particles below the lower limit will not interfere significantly in many cases, and particles above the upper limit may also be detected by the filter. While such small particles disturb less than larger ones, they can grow within a short time, e.g. grow to 30 μm within one hour.

Preferably, the magnet is a permanent magnet, although an electromagnet is also conceivable. The permanent magnet is associated with less effort and experience is basically sufficient. However, relatively strong permanent magnets are to be preferred, in particular those made of alloys of rare earths such as neodymium or samarium. Good examples are NdFeB or SmCo.

The magnet according to the invention can attract nickel particles in the nickel bath in various ways. For example, it may be externally supported on a wall of a tub containing the nickel bath. The magnetic field then passes through the wall into the nickel bath and produces the desired attractive effect. Further, the magnet could also be mounted outside, for example, a recirculation line that carries the nickel bath in a recirculation process. For example, in the case of a magnet arranged outside a circulation line, a line part could be exchangeable, it being possible to switch over between two lines in the sense of a mutual bypass ratio.

In particular, however, it is preferred that the magnet is immersed in the nickel bath during deposition. This means, because of the possibility of separating layers between the magnet and the nickel bath which will be explained below, that the superficial liquid level in the nickel bath is at least higher than the underside of the magnet and preferably as its top side and the magnet at least one larger part of its environment (the full solid angle around it) surrounded by the nickel bath. For example, when the magnet is immersed in a pocket, there may still be a free space without nickel bath above the magnet.

Since the magnetic material, in particular of a permanent magnet, can react with or be damaged by the nickel bath, the magnet is preferably coated, for example painted.

Alternatively or additionally, the magnet can be clad with an interchangeable (including removable and cleanable) Abscheidefläche for example from a film. In principle, this separation surface can also replace the coating just mentioned, but preferably both a coating (including a tight foil covering) of the magnet and an exchangeable separation surface are provided for safety. The latter then has, besides the separation of the magnetic material from the nickel bath, in particular the task of absorbing adhering and growing material on the surface facing the nickel bath and of making it easily removable by removing the separation surface. For this purpose, the Abscheidefläche can in principle be exchanged for a new or cleaned or even easily separated from the adhering material, the latter can be much easier after removing.

A special case of the exchangeable separation surface is a separation surface which is movable during the coating process by a movement device, in particular a film web moved during the process. For example, this can be moved between two windings (an unwinding and a winding winding), wherein the windings are preferably arranged above the bath and above the magnet. The film web therebetween may then travel in an approximate U-shape (not necessarily with parallel legs) from the windings downwardly, around the magnet and back up, preventing the film from adhering or growing too thickly be removed.

In this case, the magnet can be arranged, for example, in a rod-shaped shape in the curvature of the U-shape. The remaining end openings (between the expiring and the auflaufenden film web part) are either tolerable, especially with additional coating of the magnet, or can be at least largely closed by fixed trim parts.

The above explanations also apply to the case of a magnet arranged outside the nickel bath (the tub and the circulation pipe). For example, a sheet material within a wall of a nickel bath tub may be exchanged between and / or moved during deposition processes. Basically, the term "replacement" in the present context is not limited to replacing the corresponding separation surface with another, but may also mean cleaning it and reusing it. It is ultimately about removing the deposited nickel particles from the bath.

Favorable web speeds for the moving separation surface, in particular in the concrete embodiment just described, are approximately in the range of tenths to tens of cm / h, that is approximately between 0.1 and 50 cm / h, where 0.5 cm / h and 1 cm / h. h as the lower limit and, on the other hand, 10 cm / h, 5 cm / h and 3 cm / h as the upper limit, respectively, are increasingly preferred.

As already explained, the invention is preferably used in combination with a pump and a filter for circulating the nickel bath. In this context, the magnet is preferably arranged in the vicinity of the suction port, that is to say it is intended, above all, to serve to reduce the particle concentration in this environment before it enters the filter. This relieves the filter on the one hand; On the other hand, the particles after their residence time in the bath are larger than before upon re-entry into the bath, so that the magnet is particularly effective there. He can supplement himself with the filter insofar as the filter typically only filters out particles of a certain minimum size and the magnet also collects particles below this minimum size in particular. In many cases, very small particles are tolerable and have negligible harmful effects.

As already mentioned in the beginning EP 02 102 609 1, a trough shape with rounded corners is advantageous for the effectiveness of the pump-supported circulation of the nickel bath, wherein a minimum radius of curvature of approximately 5 cm, preferably 10 cm, is preferred.

Further, the adhering to the magnet or its coating or Abscheidefläche material is preferably supplied for reuse.

Finally, it has been found that the invention works particularly well in conjunction with relatively low-phosphorus nickel baths. As already stated, hypophosphite can be used as a reducing agent in the nickel bath (in particular based on nickel sulphate). The phosphorus content is then in percent by weight and, based on the nickel content, preferably at most 6%. On the other hand, it should preferably be at least 3%.

Finally, the invention is also directed to a product accordingly provided with a so-called chemical nickel layer, which, however, can be further processed beyond the nickel coating, in particular may have additional coatings. It is further directed to a suitable system for carrying out the method described, including the implicit disclosure of device details in the above, to the following embodiment and also to the content of the above-cited EP 02 102 609 can be referenced. Finally, the invention is also directed to a corresponding use of a magnet, in particular permanent magnet.

Fig. 1

zeigt eine schematische Ansicht eines erfindungsgemäßen Magneten für ein nasschemisches Nickelbad und

Fig. 2

zeigt ebenfalls eine schematische Ansicht eines solchen Bades mit eingehängtem Magneten gemäß Figur 1.

In the following the invention will be explained with reference to an embodiment. The features described here can also contribute individually and in other combinations to the solution of the problem and should not be disclosed only in the following combination. Incidentally, they apply to all categories of claim. In addition, for better understanding on the EP 02 102 609 directed.

Fig. 1

shows a schematic view of a magnet according to the invention for a wet-chemical nickel bath and

Fig. 2

also shows a schematic view of such a bath with hinged magnet according to FIG. 1 ,

In FIG. 1 1 denotes a permanent magnet according to the invention, specifically a NdFeB magnet with a rod shape, the rod longitudinal axis being perpendicular to the plane of the drawing. In fact, it is a certain number of individual magnets, which, as a result of their mutual attraction, can be easily strung together and thus, as it were, connected in series and, as a result, hold each other together and form a rod. These magnets have a cylindrical shape in the present example. They are protected with a varnish 2, which could also be a tight-fitting, perhaps glued, foil. The magnetic rod 1 is held by a mechanical support 3 from above (the vertical in FIG. 1 corresponds to the gravitational direction), where, for example, the in FIG. 1 below indicated circular plates could be adhered to the end of the holder 3. At the upper end of the holder 3 is a suspension device, which can be brought in a suitable manner via a corresponding bath, but not shown here.

The chemical nickel bath is merely indicated, by the horizontal line 4, which is to symbolize the liquid surface level; the magnetic rod 1 is so immersed. Above the liquid level 4 there are two windings 5a and b, the plastic film web wound thereon being rolled downward in a U-shape from the winding 5a as indicated by the arrows, passed under the magnetic bar 1 and rolled onto the winding 5b on the other side becomes. A typical speed is 2 cm / h, depending on the amount of nickel deposited.

Nickel particles from the bath below the mirror 4 are attracted by the bar magnet 4 and thereby divide substantially outside of the film web 6, especially in the lower semicircular segment of the circular periphery of the bar magnet. The there precipitating material of nickel particles is thus drawn with the film web 6 upwards and on the winding 5b rolled up. It can be removed, for example, after a simple passage of the entire film web 6 with the winding 5b and, for example, by peeling off the films (at high bending of the same) or be replaced in another form and reused.

The bath is a typical nickel-sulfate-based wet-chemical nickel plating bath having e.g. 6 g / l nickel. In this case, 4.5 percent by weight of phosphorus in the form of hypophosphite and also a conventional complexing agent are typically present with respect to nickel.

FIG. 2 additionally shows the bath container, according to the EP 02 102 609 11 shows an outer container with a perforated plate intermediate container 12 and therein a silicone film 13. In it is already based FIG. 1 mentioned liquid 14, which is circulated by a pump 15 with not separately drawn particulate filter. In the vicinity there is, as indicated, surrounded by a circumferential film web 6 magnetic bar 1. The windings 5a, b are only indicated and the mechanical support 3 for the magnetic rod 1 for simplicity omitted.

The nickel bath solution largely freed of particles adhering to the film web 6 is fed through the suction opening 16 of the pump 15 and downstream of it two pumping tubes 17 and 18. These also extend perpendicular to the plane and provide, as indicated in the drawing and in the cited EP 02 102 609 shown for an effective circulation within the inner container 12 and the film 13. Decisive are the rounded corners bottom left and right.

The combination of the effective circulation, the particle filtration and the particle collection by the magnet 1 according to the invention ensures an extraordinarily low particle load. This wall deposits are low and are mainly the coated products of high quality. This may be important, for example, in fuel pumps for e.g. Motor vehicles in which adhering nickel particles can lead to malfunctions in the engine.

Claims (15)

Process for the wet-chemical deposition of nickel layers from a nickel bath (14),
characterized in that in or on the nickel bath (14) during the deposition of a magnet (1) for fixing of Nickelpartikein in the nickel bath (14) is provided. A method according to claim 1, wherein the magnet (1) is a permanent magnet, in particular a rare earth magnet. A method according to claim 1 or 2, wherein the magnet is immersed in the nickel bath during deposition. A method according to claim 3, wherein the permanent magnet (1) is separated from the nickel bath (14) by a protective layer (2,6), preferably coated. Method according to one of the preceding claims, in which the permanent magnet is separated from the nickel bath (14) by an exchangeable separation surface (6), preferably by a film web (6), wherein deposited nickel particles can be removed by exchanging the deposition surface (6). The method of claim 5, wherein the separation surface (6) is moved in exchange through the nickel bath (14) during deposition. A method according to claim 6, wherein during the deposition between two windings (5a, b) arranged above the nickel bath (14), the separation surface (6) is moved as web material through the nickel bath (14) and the magnet (1) in a U -Kehre of the web material between an expiring and an accumulating track part is arranged. Process according to claim 7, with a web speed during the deposition between 0.1 and 50 cm / h. Method according to one of the preceding claims, wherein the nickel bath (14) is circulated during the deposition with a pump (15) and filtered with a filter on particles, wherein the magnet (1) closer to a suction port (16) of the pump (15 ) is arranged on the nickel bath (14) as at a discharge port (17,18) of the pump (15). The method of claim 9, wherein a container (12) of the nickel bath (14) has rounded corners with a radius of curvature greater than 5 cm. A method according to claim 5, also in conjunction with another of the preceding claims, in which nickel material deposited on the deposition surface (6) is reused after replacement of the deposition surface (6). A process according to any one of the preceding claims, having a phosphorus content in the nickel bath (14) of less than 6 percent by weight based on the nickel content. Product, in particular fuel pump housing, produced by a method according to one of the preceding claims. A plant for wet-chemically depositing nickel layers from a nickel bath (14) with a container (12) for the nickel bath (14) and with a magnet (1) for fixing nickel particles in the nickel bath (14) during the deposition, designed for a process according to one of claims 1 to 12. Use of a magnet (1), in particular permanent magnet, for a method according to one of claims 1 to 12 or a system according to claim 14.

Images