ARTICLE HAVING INSULATION ABRASION COATED LAYER

Abstract: The present invention relates to an article having an in­ sulation abrasion-resistance coated layer composed of glass ceramics containing a given amount or more by weight at least either of oxides of divalent alkaline earth metals of a group composed of BaO, MgO, CaO and ZnO and containing a given amount or less the oxides of univalent alkali metal of a group composed of Na₂O, K₂O and Li₂O on the surface of the metallic base body. As it may be used in bearing, mechanical seal and tape guide post, the abrasion-resistance of the slid­ ing portion may be improved.

Description: The present invention relates to an article having an insulation abrasion-resistance coated layer, such as a glass ceramic layer coated thinly on the surfaces of a bearing of a small-size motor, of a bearing of an ultrasmall-size motor or of the metallic base body of the sliding portion of the mechanical seal. When an insulation abrasion-resistance layer is applied on the sliding portion of the bearing of a small-size motor, the effect of the present invention is considerable. Thus, the bearing of the small-size motor will be described in detail by way of an example as the description of the conventional art. In recent years, small-size motors are promoted not only for household and industrial use, but also for ultrasmall size according to the social demand for lighter, thinner, shorter, smaller motors, thus increasing the ratio of the coreless motor. Fig. 7 shows a cross-sectional view of a coreless DC motor. In Fig. 7, a shaft 5 whose tip end is formed circular is rotatably supported by a sleeve-shaped radial bearing 9 provided on a frame 11. A commutator 7 is mounted, with a plurality of forming windings 6 being integrally formed with the shaft 5 by the plastic forming material 8, to construct a rotor. A magnet 12 is secured to the frame 11 against the forming windings 6. Reference numeral 13 is a yoke. A brush 4 comes into slidable contact against the commutator. A bracket 21 which covers the opening of the end portion of the frame 11 is provided, at the center of the inner bottom portion, with a thrust bearing 20, which is adapted to receive the tip end of the shaft 5. In the above construction, the shaft 5 is adapted to receive the load of the thrust direction by the thrust bearing 20 when the shaft is rotated through the support by the sleeve-shaped radial bearing 9. The load of which the thrust bearing receives at this time becomes 300 through 600 gr in a system where the thrust load is applied by the use of the magnetic force to prevent the vertical motion of the rotor. In the case of the shaft of 1 through 2 mm in diameter, the diameter becomes approximately 0.2 mm in the thrust bearing contact portion of the tip end, the load per unit area becomes 9.5 through 20 Kg f per cm². The thrust bearing 20 which receives the load and rotates at high speeds is likely to extremely wear out. If the bearing is constructed of ceramic material such as partially stabilized zirconia, silicon carbide, alumina or the like, which is superior in abrasion resistance respectively, to counteract wearout, the metallic shaft is inconveniently worn out. Also, the ceramic bearing is difficult to make smaller in size. It is vulnerable to impacts when it is made thinner and smaller. When the impact resistance is improved, the bearing becomes larger, thus making it difficult to design an ultrasmall type motor. However, a bearing which is superior in impact resistance, abrasion resistance, insulation of 20 through 200 µm is desired to be developed as the demand of the present day. Table 1 shows the materials of the bearing using the conventional art, the abrasion amount, the impact resistance, the current change amount thereof. The test conditions of Table 1 are as follows. 1. Test temperature ambient temperature 2. Revolution number 2200 rpm 3. Rated output 0.1 W 4. Voltage 4.2 V 5. Current value 100 mA In Table 1, the o ○ mark shows superior impact resistance, and the X mark shows inferior impact resistance. As shown in the results of Table 1, the bearing materials which were superior in the abrasion resistance, the impact resistance and the insulation resistance are desired. Material Name Abrasion Amount (µm) Impact Resistance Current Value mA 500 H 1000 H 1 66 nylon 20 40 o ○ 105 2 6 nylon 40 70 o ○ 110 3 Polyacetal 40 70 o ○ 110 4 Zirconia 50 100 X 112 5 Alumina 50 100 X 112 6 Silicon carbide 50 100 X 108 A main object of the present invention is to improve the abrasion resistance, the insulation, the impact resistance of an article such as, for example, the bearing of a small-size motor, or a mechanical seal. This object is attained by the features of the independent claim, the subclaims defining advantageous embodiments of the invention. The present invention provides a glass ceramic layer thinly coated on the surface of the bearing of the small-sized motor or of the metallic base body of the sliding portions of the mechanical seal to form a glass ceramic coated layer, which is capable of achieving the various functions such as insulation, abrasion resistance, impact resistance, etc. Thus, is the case of the bearing or the like, the abrasion amount is reduced, the consumption power is reduced, the wows/flutters are reduced and the vibration noises are improved. EP-A-0043639 discloses a forging lubricant for titanium workpieces. The glass lubricant according to this prior art must contain substantial amounts of lead oxide, namely 33 % - 73 % PbO, compare claim 2 and the paragraph linking pages 7 and 8. The properties of this ceramic are largely determined by the major PbO component and the influence of the components this prior art ceramic has in common with that of the invention is negligible by comparison. US-A 3 939 295 discloses a glass ceramic coating for cooking equipment, which contains a catalyst and must be porous. Without the porosity the catalyst would be completely embedded in the glass ceramic material and would be disfunctional. However, an insulation abrasion resistant glass ceramic cannot have any marked porosity. Further, the glass frits described in this art all have very high contents of univalent alkali metal oxides. Both prior art documents provide no limit at very high contents of divalent alkaline earth metals or of ZnO. By the above means, the motor is improved in reliability and in longer service life without being worn out with both the shaft and the bearing being kept insulated with respect to each other. Also, the slidability and size precision of the bearing are improved, thus allowing the motor to be improved in performance and the ultrasmall-sized motor to be designed. These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of a small-sized motor in one preferred embodiment of the present invention; Fig. 2 is a cross-section view, wherein an insulation abrasion-resistance coated layer is formed on the thrust bearing portion of a motor case base material in another embodiment of the present invention; Fig. 3 is a flow chart showing manufacturing processes of the one embodiment of the present invention; Fig. 4 is a graph showing the correlation between the univalent alkali oxide amount in the glass and the insulation break-down voltage; Fig. 5 is a graph showing the correlation between the univalent alkali oxide amount in the glass and the surface roughness (Ra) of the insulation abrasion-resistance layer; Fig. 6 is a cross-sectional view where the present invention is applied to the sleeve type of radial bearing; Fig. 7 is a cross-sectional view of a small-size motor in the conventional example (already referred to); Fig. 8 is a cross-sectional view of the mechanical seal in one application example of the present invention; Fig. 9 is a cross-sectional view of a guide post for video cassette recorder (VTR) use in another application example of the present invention; Figs. 10(A) and 10(B) are a top-face view and a side-face view, respectively, of the tape running system of the VTR in a further application example of the present invention; and Figs. 11(A) and 11(B) are cross-sectional views showing the iron base as the further another one application example of the present invention. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. The embodiments of the present invention are directed to an article having an insulation abrasion-resistance coated layer in such a manner that, for example, the glass ceramics are thinly coated on the single face or both faces of a metal plate as the thrust bearing, and the glass ceramics coated layer is formed only on the functional portion of the thrust bearing on the single face of the steel plate, which is served as the motor case. [Embodiment 1] A concrete embodiment where the insulation abrasion-resistance glass coated layer of the present invention is applied on the bearing wall be described in detail. In order to more effectively employ the present invention, there are various necessary conditions, which will be concretely described hereinafter. (1) Conditions of Metallic Base Material The glass ceramic coated layer of the present invention is provided on the single face or both faces of the metallic base material. As the metallic base material, (a) a low carbon steel plate for porcelain enamel, (b) an aluminized steel plate, (c) a stainless steel plate, or other similar steel plates may be used. However, the thermal expansion coefficient of the metal plate is desired to be within the range of 60 through 140 x 10⁻⁷/°C. (2) Method of Applying Glass Ceramics To effectively apply the glass ceramic coated layer of the present invention on the small-sized motor, the ultrasmall-sized micromotor and the sliding portion of the mechanical seal, a slip composed of glass frit of glass ceramics is required to be correctly coated. As the methods of coating, there are (a) the electrophoresis method, (b) the screen printing method, (c) the spray method and so on. (3) Types of Glass Ceramics A bearing is produced (the composition of the glass is shown in Table 3) by the use of two types of glass (glass A and glass N) representative as glass ceramics. Fig. 1 illustrates the bearing of the present invention, wherein the glass ceramics coated layer is partially applied only on the functional portion 2 of the thrust bearing portion 1 on the signal face of the steel plate 3 which serves as the motor case. It is to be noted that the common numerals are given to the elements common to those in the conventional example shown in Fig. 7. In a function portion 2 of a bearing portion 1 of a metallic motor case 3, a coated layer 15 of the glass ceramics is formed on a base plate 16 with the use of the slip printing ink composed locally of glass ceramics as shown in Fig. 2. Fig. 3 shows in a flow chart a method of forming the insulation abrasion-resistance layer by eleotrophoresis method. The glass material is first dissolved at 1250 through 1350°C so that the cullets of the glass ceramics are provided by a roller quench method. They are powdered to produce the slips with ethyl alcohol or isopropyl alcohol. On the other hand, the metallic base material is cut off into given shapes, is degreased, and the masking is performed to locally perform partial electro-deposition. It is placed in the electrolytic bath. The glass powder particles dispersed in alcohol are electrodeposited by electrophoresis with 2 through 3 cm in interpole interval, 250 through 600 V in cell voltage, and are fired at 760 through 950°C after surface drying to produce the insulation abrasion-resistance coated layer of the glass ceramics. Grease is coated on the sliding face of this coated layer. Returning to Fig. 1 again, the shaft 5, whose tip end is formed circular, is rotatably supported by the sleeve bearing 9 provided on the frame 11. The commutator 7 is disposed with a plurality of forming windings 6 being integrally formed with the shaft 5 by the plastic moldings 8 so as to compose a rotor. The magnet 12 is secured to the frame 11 against the forming windings 6, providing with the yoke 13. The brush 4 is in sliding contact with the commutator 7. A motor case 3 covers the end opening of the frame 11, the glass coated layer 15 having the insulation abrasion-resistance property is provided, at the center of the inner bottom portion, on the function portion 2 of the thrust bearing portion 1 receiving the tip end of the shaft 5. The characteristics provided under these conditions are represented in Table 2. The various motor evaluation test conditions (test temperatures, revolution number, etc.) in Table 2 are the same as those of Table 1. It is found out from the results or Table 2 that in the case of bearings (1) through (3) using glass A, the evaluation results as a motor are different depending upon the forming method of the insulation abrasion-resistance layer even if the material of the glass ceramics is the same. Considering the characteristics, the order of preference is electrophoresis method > screen method > spray method as the forming method of the abrasion-resistance layer. Table 2 indicates that forming the abrasion-resistance layer of the glass ceramics by the electrophoresis method gives highest size accuracy and superior characteristics. It is found out in Table 2 that when the glass N is used, the size accuracy of the thickness is worse, the characteristics of the motor are not so good as we expected even if the electrophoresis method is used. Namely, it is found that the characteristics of the insulation abrasion-resistance property can not be displayed because of some composition of the glass of the glass ceramics even when the electrophoresis method is used. Thus, in the following example, the compositions of the glass ceramics are examined to compare the characteristics. [Embodiment 2] As the insulation abrasion-resistance characteristics are different because of the composition of the glass ceramics even if the electrophoresis method is used in embodiment 1, nineteen types or glass compositions are examined from glass A to glass S in Table 3. Table 3 shows that the electrodeposition property by the characteristics of the glass and the electrophoresis is considerably different because of the addition amount (weight percent) of the oxides (Li₂O, K₂O, Na₂O) of univalent alkali metals in glass composition and the oxides (BaO, MgO, CaO) of divalent alkaline earth metals or of Zi (ZnO). The characteristics of Table 3 and the results of Fig. 4 and Fig. 5 will be summarized. (1) The oxides ((Li₂O, K₂O, Na₂O) of the univalent alkali metals in the composition of the glass should be 0.2 through 2% by weight in range. The 0.2% by weight or lower is a limit for impurity admixture. It is difficult to compose the glass of this percentage or lower. Reversely, when the percentage becomes 2% by weight or more, the insulation break-down voltage quickly deteriorates and the Vickers hardness, the abrasion amount of the glass ceramics becomes also deteriorated correspondingly (E, F, G, A, M, N, O, P). (2) The amount of the oxides (BaO, MgO, CaO) of the divalent alkaline earth metals or of ZnO is to be 55% or more by weight, particularly the total amount of the oxides of the divalent alkaline earth metals is to be 55% or more by weight. The balance between the univalent alkali metal-oxide amount and the divalent alkaline earth metal-oxide amount is required for these relations. (3) When the univalent alkali metal-oxide amount is 2% or lower by weight, the electro-deposition operation is easy to be performed by electrophoresis with 250 through 350 V in cell voltage, the surface roughness, the Vickers hardness, the abrasion amount, etc. are superior in most of the characteristics (A, B, J, K, L, Q). (4) When the univalent alkali metal-oxide amount of the glass ceramic amount increases, a voltage as high as 350 through 650 V in cell voltage is required during the electrophoresis electrodeposition. Corresponding, the insulation withstand voltage becomes 0.5 kV or lower (G, N, O, M), the surface roughness of the glass also becomes inferior as shown in Fig. 5. (5) Generally, the enamel glass (M, N, O) has relatively higher univalent alkali metal-oxide content, less divalent alkali metal-oxide content or has no divalent alkali metal-oxide. A high voltage is required during the electrophoresis electrodeposition. Though it is improved as the insulation abrasion-resistance coated layer for motor use as compared with the conventional method, the characteristics are inferior to those of the other glasses in Table 3. (6) The surface roughness of the abrasion-resistance coated layer of the glass ceramics to be formed on the surface of the metal basic material is desired to be within the range of 0.05 through 0.5 µm, when measured by a Tallysurf surface roughness meter, in terms of the abrasion resistance of the wow flutter. The roughness Ra of 0.05 or lower is not economical, because it cannot be achieved only by the manufacturing process shown in Fig. 3 of the present invention, a lapping process being also required. The roughness Ra of 0.5 or more is not desired in terms of the abrasion-resistance, the wow flutter and the noises of the motor. (7) The thickness of the glass ceramics coated layer of the present invention is desired to be in the range of 20 through 200 µm. Although the roughness of 20 µm or lower may be, also, provided by control of the electrodeposition time, the thickness is desirable to be 20 µm or more in terms of the mechanical strength of the glass layer, the surface roughness of the glass layer, the adherence with respect to the metal base material. Also, the thickness is not required to be increased reversely to 200 µm or more. If the material of the glass ceramics is such a good glass as glass A, the thickness of 200 µm may sufficiently exhibit the functions of insulation abrasion-resistance. (8) In the thermal expansion coefficient of the glass ceramics, it is difficult to compose the glass in the case of 60 x 10⁻⁷/°C or lower as apparent from Table 3. Also, most of the metal base materials are within the range of 60 through 145 x 10⁻⁷/°C. Accordingly, the glasses (A, B, C, D, E, F, H, I, J, K, L, P, Q) are preferable as glasses, which are superior in insulation, abrasion resistance with the eleotrodeposition through the electrophoresis being performed within the range of 145 x 10⁻⁷/°C and 60 x 10⁻⁷/°C in the thermal expansion coefficient of glass. The combination may be decided by the matching of the thermal expansion coefficients through the choice of the metal base material and the choice of the glass. As shown in Table 3, the insulation abrasion-resistance coated layer of the present invention, though it depends upon the composition of the glass, shows the superior abrasion-resistance characteristics as the bearing of the motor. [Embodiment 3] The glass A in Table 3 is used. The glass powder (400 g) and isopropyl alcohol (1 ℓ) are put into the ball mill. They are milled for twenty hours. The glass powder in the suspension at this time is 2.0 µm in average particle diameter. The glass powder is electrodeposited onto the metal base body with the use of the suspension and is fired at 850°C to form the motor of Fig. 1. [Embodiment 4] The same glass as that in embodiment 3 is used and is milled in the same thrown amount for ten hours. The average particle diameter at this time is 7.0 µm. The motor is formed by the same method as that in embodiment 3. [Comparison Embodiment 1] The same material as in embodiments 3 and 4 was used and milled by the same method for thirty hours. A suspension of 1.0 µm average particle diameter was produced. The electrodeposition through the use of electrophoresis was performed. However, when the metal base body was picked up from the suspension, the electrodeposition layer was suddenly dried, thus causing cracks on the surface. Thereafter, peeling off was caused. Accordingly, the insulation abrasion coated layer could not be formed. [Comparison Embodiment 2] The material was milled for eight hours by the same method as in comparison embodiment 1. A suspension of 8.0 µm average particle diameter was produced to form the motor. The evaluation shown in Table 4 is carried out with four motors of the above-described embodiments. The evaluation test conditions (test temperature, rotation number and so on) of the various types of motors in Table 4 are the same as those in Table 1. Sample No. Average Particle Diameter Thickness (µm) Average Roughness Ra (µm) Abrasion Amount (µm) Remarks 500 hours 1000 hours Embodiment 3 2.0 100 0.1 0 10 Embodiment 4 7.0 100 0.3 10 20 Comparison Embodiment 1 1.0 - - - - Impossible to form Comparison Embodiment 2 8.0 100 0.5 12 40 The motor or Fig. 1 is used in a compact disc or the like. As the insulation abrasion coated layer is worn out by 30 µm or more, errors are caused in the reading of the disc, thus making it impossible to be used as the compact disc. Thus, the motor which is worn out by 30 µm in amount cannot be used as a product. Thus, comparison embodiment 2 is impossible to be used. Accordingly, the surface average roughness (Ra) is required to be 0.3 µm or lower to reduce the abrasion amount of the insulation abrasion coated layer, while the average particle diameter of the glass ceramics in the suspension is required to be 7.0 µm or lower to make the surface average roughness (Ra) 0.3 µm or lower. However, as the electrodeposition layer is likely to be peeled off when the average particle diameter becomes 2.0 µm or lower, the proper range of the particle diameter is found out to be 2.0 µm through 7.0 µm. [Embodiment 5] In embodiment 1 and embodiment 2, the application example wherein the insulation abrasion-resistance coated layer of the present invention applied upon the thrust bearing of the motor is described in detail. The coated layer of the present invention may be developed in application similarly even upon the radial bearing of the small-size motor. Fig. 6 is a cross-sectional view of the radial bearing. As the glass ceramics of the present invention is coated on the inner surface 17 of the metallic base material 19 of the radial bearing, the sectional portion of the glass ceramics abrasion-resistance layer 18 is provided. The radial bearing may be also manufactured in accordance with the manufacturing process of Fig. 3. [Embodiment 6] The present invention is also applicable even in the use of the mechanical seal. Namely, it may be used as a complete sealing apparatus for liquid or gas in the rotation portions of each type of machine. Fig. 8 shows the representative construction. The glass ceramics of about 100 µm in thickness in the same method as in the embodiment 3 on the inner face of the seat ring 31 is provided on the mechanical seat. Reference numeral 32 is a rotary shaft, reference numeral 33 is a stuffing box, reference numeral 34 is a shaft packing, reference numeral 35 is a followed ring, reference numeral 36 is a stopper, reference numeral 37 is a gasket, reference numeral 38 is a bushing hole, reference numeral 39 is fluid on the high-pressure side. A corrosion resistance metal such as stainless steel, Hastelloy or the like is used as the conventional seat ring. For comparison between the present invention and the conventional product, the mechanical seal of Fig. 8 is assembled to measure time taken before leakage for the evaluation. It is to be noted that the fluid used for the experiment is 5 % H₂SO₄ at 80°C temperature. Also, the revolution speed of the rotation shaft 32 is 200 rpm in the continuous rotation. The experiment results at this time are shown below. Continuous Operation Test Conventional Embodiment Leakage starts after about one year Present Invention Good operation, three years or more (still in operation) Thus, the present invention shows considerable effect as compared with the conventional embodiment. [Embodiment 7] The glass ceramic layer of about 100 µm in thickness is formed on the outer peripheral face of a spool-shaped guide post 41 for video cassette recorder use shown in Fig. 9 in the same method as in embodiment 3. It is incorporated into the video cassette recorder as shown in Figs. 10(A) and 10(B) to perform the tape running test for the evaluation. In the drawings, reference numeral 42 is a conical guide, reference numeral 43 is tape, reference numeral 44 is a cylinder provided with a head, reference numeral 45 is a supply reel and reference numeral 46 is a winding reel. Also, the conventional guide post made of stainless steel is employed as a comparison embodiment. As a test method, 10,000 hours running test of the metal tape is performed to measure the abrasion amount. Tape Running Test Conventional Embodiment Abrasion of about 5 µm Present Invention 0.1 µm or less Thus, the present invention is considerably superior in abrasion resistance as compared with the conventional example. [Embodiment 8] An iron is manufactured for trial with the use of the iron base of the construction (Fig. 11(A)) where a glass ceramic coated layer 15 of about 100 µm in thickness is formed on the steel-plate base material 51 for iron use, and further of the construction (Fig. 11(B)) where a Poly-Tetra-fluoroethylene (=PTFE) resin coated layer 52 is formed thereon in the same method as that of embodiment 3. As the glass ceramics coated layer of the present invention is superior in the abrasion resistance and simultaneously has little surface roughness, it is superior in sliding, thus allowing the application as the iron base. Furthermore, when the PTFE resin coated layer is formed thereon, the effect is further improved. [Embodiment 9] The application may be performed to the cooking plate use by the constructions same as those of Figs. 11(A) and 11(B). A cooking plate which is superior in abrasion resistance, corrosion resistance and non-tackiness may be manufactured. As described hereinabove, the insulation abrasion-resistance coated layer is effective in the sliding portion of the bearing, mechanical seal, etc. and may be applied as various types of posts for the tape use of the video cassette recorder. As is clear from the foregoing description, according to the arrangement of the present invention, the insulation abrasion-resistance layer of 20 through 200 µm is formed on the surface of the metallic base plate by the electrodeposition, through electrophoresis, of the glass ceramics containing 55 % or more by weight of the divalent alkaline earth metals or of ZnO with 0.2 through 2.0 percent by weight content of oxides of univalent alkali metals. The article thus provided is considerably improved in the abrasion resistance, wow flutter, nose, current value and so on when it is used as the bearing in the sliding portion of the motor. Also, as the insulation abrasion-resistance layer may be correctly formed in thin state on the motor or the function face of the sliding portion of the mechanical seal, the considerable contribution may be made towards the smaller appliance, the improvement in reliability and longer service. Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as included therein.

Claims: An article having an insulation abrasion-resistance coated layer composed of glass ceramics, said glass ceramics being substantially free of lead compounds and containing 55 % or more by weight at least either of oxides of divalent alkaline earth metals chosen from the group composed of BaO, Mgo, CaO, or of ZnO, and containing 2 % or less by weight of oxides of univalent alkali metals chosen from the group composed of Na₂O, K₂O and Li₂O. An article according to claim 1, wherein the termal expansion coefficient of the glass ceramics is within the range of 60 through 145 · 10⁻⁷°C. An article according to claim 1, wherein the coated layer of the glass ceramics is 20 through 200 µm in thickness and the central-line surface roughness Ra of the coated layer as measured with a Tallysurf meter is 0.05 through 0.5 µm. An article according to claim 1, wherein the total amount of the oxides of the univalent alkali metals in the glass ceramics is 0.2 through 2 % by weight. An article according to claim 1, wherein the glass ceramics electrodeposited through electrophoresis on the surface of a metallic base is fired to form an insulation abrasion-resistance layer. An article according to claim 1, wherein the metallic base body is dipped in a suspension with glass ceramic particles being dispersed therein, the glass ceramic particles are electrodeposited through electrophoresis on said metallic base-body surfaces and are fired to form the insulation abrasion-resistance layer, the average particle diameter of the glass ceramics in said suspension being within the range of 2 µm through 7 µm. An article according to any one of claims 1 through 6 in the form of a bearing. An article according to claim 7, the bearing being a thrust bearing. An article according to claim 7, the bearing being a radial bearing. An article according to any one of claims 1 through 6, in the form of a mechanical seal. An article according to any one of claims 1 through 6, in the form of a guide post.

Inventors: HIRAKA, MASAHIRO, IKEDA, MASAKI, NISHINO, ATSUSHI, WATANABE, YOSHIHIRO
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1986
Main classification: C25D13
IPC codes: C03C10, F16C33, C09D5, C25D13, C03C8, F16J15, H02K5, C23D5