Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-09-03
2001-04-03
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C204S501000, C204S507000, C428S692100, C428S900000, C360S099080
Reexamination Certificate
active
06211584
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a magnet, a stacked core, a motor base or other motor component having excellent in anticorrosion and insulation properties, and particularly to a magnet, a stacked core or a motor base which is covered by an electrocoating, thereby providing superior anticorrosion and insulation.
BACKGROUND OF THE INVENTION
Conventionally, a stepping motor stacked core or other motor component is electrodeposited, thereby assuring good anticorrosion and insulation.
For example, Japanese laid-open patent application No. 58-83559 proposes a method of insulating a stacked core of coil block for use in a stepping motor of a clock. In the method, by immersing the stacked core in aqueous epoxy solution containing amine, a cationic electrocoating of epoxy is formed on the stacked core, which is made a cathode for this purpose. Subsequently, the electrocoating is heat treated at temperatures ranging between 100° C. and 300° C. and is formed into an epoxy coating through condensation.
However, in the prior-art electrodeposited motor component, as shown in
FIG. 7
, when the thickness of the coating on the surface of the component is T, the thickness t of the coating on the edge of the component tends to be smaller than thickness T. The physical quantity defined as t/T is an edge covering ratio. A lowered edge covering ratio causes imperfect insulation. To raise the edge covering ratio, the curing temperature after the electrodeposition needs to be lowered, for example:
Conventionally, to lower the curing temperature, tin compound, for example, the compound of isobutyl tin oxide is generally added by about 0.05% by weight to the aqueous solution of electrodeposition paint, i.e., by about 0.2% by weight to the coating.
It was, however, reported that when the motor assembly of the stacked core, the magnet and the like with the insulation coating formed thereon in the aforementioned conventional manner was used in a hard disc drive unit, the content of memory in the hard disc collapsed. We reviewed this problem and concluded that the problem was caused by the content of the coating.
SUMMARY OF THE INVENTION
Wherefore, the object of the invention is to provide a motor component covered with a novel electrocoating, failing to detrimentally affect a magnetic memory medium, to raise the edge covering ratio and to easily form a coating with improved insulation on the motor component.
Our research has found that by applying an electrocoating to the motor component using an electrodeposition paint containing 12 ppm or less of tin and tin compound in the aqueous solution, the memory content can be protected from collapse.
After consideration, we concluded that the reported memory collapse resulted from the tin and tin compound being released from the insulation coating and sticking to the surface of the magnetic memory medium. We succeeded in solving the problem by eliminating such cause. For this purpose, an electrocoating is formed containing only 50 ppm or less of tin and tin compound. Therefore, in the present invention no further in content is added as in the prior art.
In the electrodeposition paint of the present invention, carbon black is added to the aqueous solution only by 0.5% by weight or less, and, titanium dioxide and/or silicon dioxide is added to the pigment. The pigment thus preferably contains a reduced quantity of carbon black, because the excessive content of carbon black would impair insulation, as further described below.
The aqueous paint solution for use in electrodeposition painting generally contains water and paint in the rate of 3 to 1 or 4 to 1. Upon curing the tin content and the quantity of carbon black in the coating through heat curing, the final tin and tin compound in the electrocoating on the motor component can be 50 ppm or less. The quantity of carbon black in the electrocoating can be 2% by weight or less.
Specifically, the electrodeposition paint for use can include the pigment content of 22% to 40% by weight of total solidified content, i.e., the content of pigment and resin. When using the paint containing the pigment content including titanium dioxide or silicon dioxide in such range, the edge covering ratio as well as the hardness of the insulation coating are enhanced.
The motor component, other than the magnet, the invention relates to is, for example, a stacked core composed of 1% to 3% by weight of silicon and remaining percentage by weight of iron, of low carbon steel, or of pure iron, or a motor base composed of aluminum alloy. For use, such motor component is tightly wound with coil or is exposed to the outside, thereby requiring a thick and hard coating. By using the paint containing the pigment in the aforementioned range, the edge covering ratio and hardness of the insulation coating can be increased.
On the magnet or permanent magnet, the electrocoating is formed preferably using an electrodeposition paint including a pigment content of 16% to 28% by weight of total solidified content. For use, the magnet is wound with no coil and fails to be exposed outside. Therefore, the magnet is different in conditions from the stacked core or the motor base. Recently, motors were made compact, thereby reducing the space inside the motors. The insulation coatings covering the magnet need not to be too thick. The body of the magnet referred to herein can consist of an Nd—Fe—B system plastic magnet, a hot compression molded magnet or a sintered magnet.
When painting the motor component of the invention, first the electrodeposition paint having the tin and tin compound restricted to 12 ppm or less in the aqueous solution is electrodeposited to the motor component. Subsequently, during preliminary heat treating the coating is heated to temperatures ranging between 40° C. and 90° C., and during second-step curing the coating is heated to temperatures ranging between 150° C. and 190° C. The method of painting the motor component is characterized by such two-step curing.
The two-step curing enhances the edge covering ratio. Furthermore, pinholes made in the positions contacted by electrode pins for use in electrodeposition painting can be filled. According to the method of the invention, memory content is prevented from collapsing. Furthermore, the coating is made uniformly thick on the motor component, and good anticorrosion and insulation are assured.
In the painting method, the electrodeposition paint for use contains only 0.5% by weight or less of micro carbon black in relation to the aqueous solution. Instead of carbon black, titanium dioxide and/or silicon dioxide having a relatively large diameter is added to the pigment.
For electrodeposition painting the stacked core composed of 1% to 3% by weight of silicon and the remaining percentage by weight of iron, of low carbon steel, or of pure iron or for electrodeposition painting the motor base composed of aluminum alloy, the electrodeposition paint for use preferably contains 22% to 40% by weight of pigment in the solidified content. For electrodeposition painting the Nd—Fe—B system plastic magnet, the hot compression molded magnet or the sintered magnet, the electrodeposition paint for use preferably contains 16% to 28% by weight of pigment in the solidified content.
The first-step, preliminary heat treating is very important for eliminating pinholes or other made by later-mentioned hold projections in contact with the surface of the motor component or gas discharged from the component being cured. The heat treating time period is selected such that the coating is fluid enough to fill the pinholes or other. The setting of heat treating time period varies with the preliminary heat treating temperature. When the preliminary heat treating temperatures range between 40° C. and 90° C., the time period can be five minutes at minimum, thereby providing considerable heat treating effectiveness. The lower heat treating temperatures especially provide more heat treating effectiveness.
For the second-step curing, the time period is selected to be long enough for the coating to be bu
Anbo Takeshi
Kurosawa Manabu
Yamada Tatsumasa
Daido Tokushuko
Davis and Bujold
Mullins Burton
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