Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Reexamination Certificate
2000-01-03
2001-10-09
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
C205S109000, C205S110000, C205S220000, C205S222000
Reexamination Certificate
active
06299750
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a method for coating elongated metal blanks.
In the series of books “Produktionstechnik heute” [Production Engineering Today] (published by Prof. H. J. Warneke), a description of so-called sliding grinding is given in volume 14, Entgraten, Theorie, Verfahren, Anlagen [Deburring, Theory, Methods, Apparatus] by F. Schäfer on pages 93 to 98. A multiplicity of blanks located in a rotationally driven drum slide against one another and against added abrasive media during the rotary movement of the drum. The manner in which they slide against one another is dependent on the speed of rotation. At low speeds, sliding against one another takes place. As from a certain speed, the sliding zone breaks down; workpieces and abrasive media described there strike one another. This and the sliding against one another effects a surface-removing effect.
In the case of the method of the type in question, blanks which have at least two portions of different cross section aligned axially, one after the other, are treated. In a chemical electroplating bath, particles of a hard material are embedded into a metallic delimiting layer on the surface of a first portion which has indentations or the like, the particles projecting from the surface of the layer. The exposed surfaces of a second portion remain to the greatest extent free from hard material particles. The exposed surfaces may be the circumferential surfaces of a cylinder. The base of the cylinder may be a circular surface, an oval surface or a hexagonal surface. The base of the cross section of the portion having the indentations may have a serrated or star-shaped contour. The tooth or star flanks of this portion are to be provided with an embedding of hard material particles. The application of hard material particles to reduce the wearing of workpieces or to increase friction is known in particular in the case of heavy-duty machine parts and also in the case of tools. It is also known, however, to reduce by such measures the susceptibility to wear of portions of other types of metallic objects that are subject to friction or pressure. In the case of known methods, regions of the workpieces that are not to be coated must be covered by means of lacquer or the like. For example, laid-open patent application 29 20 593 shows a method by which particles are introduced into a metal surface by means of locally supplying current. From patent specification 28 55 054, a method is known in which the stator blade of a turbine is coated with a layer of metal with incorporated foreign particles. In this case, only the portions of the blade covered by a clamping device remain uncoated.
SUMMARY OF THE INVENTION
An object of the invention is to find a method of the type in question which, while avoiding covering parts of the workpiece, provides coatings, in particular diamond coatings, which gradually vary in size over the subregions of the workpiece.
This is achieved by a multiplicity of blanks being freely rolled around in a rotating drum in a dispersion of hard material particles kept suspended in the electroplating liquid in such a way that hard material particles adhering to the exposed surfaces can be removed again by the blanks rubbing against one another.
The correspondingly pretreated, degreased, rinsed and pickled blanks are filled in large numbers into the drum, in the walls of which openings are formed. These are smaller than the diameter of the blanks, so that the latter remain as intended in the drum. The filled drum is lowered into the electroplating medium and rotates within the same. Within the electroplating medium, the drum performs rotary movements, taking the pretreated blanks with it. The electroplating medium passes through the openings in the drum into the latter and comes into contact with the surface of the blanks. In regard to the electroplating medium, there is in question a dispersion that is kept in motion of hard material particles and a metallic component. Both the metallic component and the hard material particles are deposited on the surface of the blanks. The motion of the drum has the effect here that the hard material particles adhering to the exposed surfaces of the blanks are removed again by the mutual rubbing of the blanks against one another. On the other hand, the hard material particles remain in the region of the grooves which are flanked by the working surfaces. In other words, no abrasion takes place in this region, so that the desired frictional particle density is achieved there. What is generally regarded as disadvantageous in sliding grinding, namely that unworked pockets are present on the workpieces, is used as an advantage in the method according to the invention. In order that the hard material particles occur in the same density in the electroplating medium and are not deposited, the agitating mechanism is provided. This keeps the hard material particles in suspension in the electroplating medium. Furthermore, the drum is formed to be of cylindrical shape and is driven about its horizontally disposed axis of rotation. For example, the drum may have a cross-sectionally polygonal contour, by which during rotation of the drum, there is established good rolling around of the blanks accommodated in the drum. It is possible in this case for the drum to be filled with blanks approximately up to half-full, so that a large number of blanks can be coated during one coating process. It is of advantage here that the rotating drum is fully submerged in the electroplating medium. The electroplating liquid concerned has a nickel component, which is precipitated in the form of metallic nickel on the surface of the blanks without electrical voltage. The hard metal particles kept in suspension in the electroplating liquid during this process are preferably diamond grains, in particular of an order of magnitude of from 10 to 30 &mgr;m. This means that the diamond grains partially protrude in certain regions out of the layer located on the working surfaces and represent for example a nonslip layer or an abrasion-protected layer. The layer of nickel accordingly represents the delimiting layer for these diamond grains. The larger the particle size of the diamond grains, the more the “cam-out effect” decreases. For optimum coating of the working surfaces, it is of advantage for the movement of the drum to take place with intermittent breaks. After a phase of rotational movement of the drum of an appropriately long duration, there is a suitably matching break, in which the adherence of the hard metal particles within the electroplating medium takes place. Before coating, the blanks fed to the drum are degreased, pickled and treated in a nucleating bath (nickel strike). The apparatus for carrying out the method is distinguished by the fact that the drum has a polygonal cross section with journals extending from the end walls of the drum, one of which journals can be brought into coupling connection with the rotary drive of the drum. For removal of the drum from the electroplating bath, the coupling connection between journal and rotary drive is released, while the coupling connection between these parts is established when the drum is inserted. The openings for the electroplating medium to pass through are provided in the walls of the drum. This electroplating medium is situated in the tank, which is provided with an agitating mechanism in order to keep the hard material particles in suspension in the electroplating medium. The workpieces produced by the method are created such that the exposed surfaces are also coated with hard substance particles with a surface density which is at least ten times less than that in the region lying in the grooves. It is thus ensured that the main hard material particle coating takes place only in the intended region, that is to say on the surfaces flanking the grooves. In a certain respect, the removal of material by sliding grinding also affects a subregion of the grooves, however, in such a way that the surfac
Cavallaro Vincenzo
Pilgenröder Horst
Farber Martin A.
Wong Edna
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