1. Field of the Invention
The present invention relates to an electroplating device useful for electroplating a work having a hole communicating with the outside, particularly, a ring-shaped work such as a ring-shaped bonded magnet, and a process for electroplating such a work using the device.
2. Description of the Related Art
A rare earth metal-based permanent magnet such as an Rxe2x80x94Fexe2x80x94B based permanent magnet, of which an Ndxe2x80x94Fexe2x80x94B based permanent magnet is representative, is used at present in a variety of fields, because it is produced from an inexpensive material rich in natural resources and has a high magnetic characteristic.
In recent years, in electronic and appliance industries where a rare earth metal-based permanent magnet is used, a reduction in size of each of parts has been advanced, and in correspondence to this, it is necessary to reduce the size of the magnet itself and to form the magnet into a complicated shape.
From this viewpoint, public attention is paid to a bonded magnet which is easy to form into a certain shape from a material containing a magnetic powder and a resin binder as main components. Among others, a ring-shaped bonded magnet is utilized, particularly, in various small-sized motors such as a spindle motor, or in a servomotor used in an actuator.
The rare earth metal-based permanent magnet contains a rare earth metal (R) which is liable to be corroded by oxidation in the atmosphere. Therefore, when the magnet is used without being subjected to any surface treatment, the corrosion of the magnet is advanced from the surface due to the presence of a small amount of an acid, an alkali or moisture to produce a rust, and as a result, the deterioration and variability of the magnetic characteristic of the magnet occur. Therefore, a plated film has been conventionally formed as a corrosion-resistant film on a surface of a magnet by subjecting the magnet to an electroplating, but a higher accuracy is required in the formation of the plated film, attendant on the recent demands for the reduction in size of the magnet and for the complication of the shape.
In the case of the ring-shaped bonded magnet, the high dimensional accuracy is required for both of the outer and inner surfaces of the magnet and hence, a uniform plated film must be formed on the outer surface, but also a uniform plated film must be formed particularly on the inner surface. In the case of a ring-shaped bonded magnet having a large L/D value (wherein L represents a length of the magnet in a direction of a center axis, and D represents an inside diameter of the magnet), the following problem is encountered: An area near a central portion of the inner portion of the magnet is lower in current density, resulting in a plated film formed at a smaller thickness. In addition, if air bubbles produced upon the immersion of the ring-shaped bonded magnet into a plating bath and hydrogen gas produced during the electroplating are resident on an inner upper portion of the magnet, they exert a deleterious influence to the formation of a plated film on such portion.
To subject a recessed portion provided in a work to an electroplating, it is a conventional practice that an anode is inserted into and disposed in such portion (for example, see Japanese Patent Application Laid-open No. 3-6399). However, when the anode is merely inserted and disposed, the distance between the inner surface of the magnet and the anode cannot be averagely regularized. Therefore, an obtained effect is only that a plated film can be formed efficiently on the inner surface, and the variability of formation of the plated film from portion to portion of the inner surface cannot be overcome.
In addition, if the distance between the outer surface of the magnet and a positive electrode plate is averagely not regularized, the variability of formation of a plated film from portion to portion of the outer surface cannot be overcome.
Further, in electroplating processes proposed hitherto, traces of contact with a plating electric current supplying member and a work fixing member are left on a work and for this reason, a post-treatment is required, which impedes the formation of a uniform plated film.
Accordingly, it is an object of the present invention to provide an electroplating device and a process for electroplating a work using the device, in which a uniform plated film can be formed not only on the outer surface but also on the inner surface of a work having a hole communicating with the outside, such as a ring-shaped bonded magnet, and the thickness of the plated film can be controlled to any level.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an electroplating device comprising an anode which is inserted through and disposed in a hole provided in a work and communicating with the outside, and a member for rotating the work about its center axis and supplying a plating electric current to the work.
According to a second aspect and feature of the present invention, there is provided an electroplating device comprising an anode which is inserted through and disposed in a hole provided in a work and communicating with the outside, a member for rotating the work about its center axis, and a member for supplying a plating electric current to the work.
According to a third aspect and feature of the present invention, there is provided an electroplating device comprising an anode which is inserted through and disposed in a hole provided in a work and communicating with the outside, a driving roller made of a metal and adapted to abut against the outer surface of the work to support the work for rotating the work about its center axis and supplying a plating electric current to the work, and a follower roller adapted to abut against the outer surface of the work to support the work.
According to a fourth aspect and feature of the present invention, there is provided an electroplating device comprising an anode which is inserted through and disposed in a hole provided in a work and communicating with the outside, a driving roller adapted to abut against the outer surface of the work to support the work for rotating the work about its center axis, and a follower roller made of a metal and adapted to abut against the outer surface of the work to support the work for supplying a plating electric current to the work.
According to a fifth aspect and feature of the present invention, there is provided an electroplating device comprising an anode which is inserted through and disposed in a hole provided in a work and communicating with the outside, and a means for allowing a plating solution within the hole in the work to flow.
According to a sixth aspect and feature of the present invention, in addition to the first or second feature, the device further includes a means for allowing a plating solution within the hole in the work to flow.
According to a seventh aspect and feature of the present invention, there is provided a process for electroplating a work having a hole communicating with the outside, using an electroplating device according to the first or second feature.
According to an eighth aspect and feature of the present invention, in addition to the seventh feature, the work having the hole communicating with the outside is a ring-shaped work.
According to a ninth aspect and feature of the present invention, in addition to the eighth feature, the ring-shaped work is a ring-shaped bonded magnet.
According to a tenth aspect and feature of the present invention, there is provided a ring-shaped bonded magnet having a plated film on the entire surface thereof, wherein the thickness of the plated film formed on the outer surface is equal to or smaller than that of the plated film formed on the inner surface, and the variability of thickness of the plated film from portion to portion of the outer and inner surfaces is equal to or smaller than 25%.
With the electroplating device according to the present invention, a uniform plated film can be formed on both of the outer and inner surfaces of a work having a hole communicating with the outside, such as a ring-shaped work, of which a ring-shaped bonded magnet is representative.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.