Title of Invention

NON-ORIENTED ELECTRICAL STEEL SHEET FOR SMALL-SIZED PRECISION MOTOR

Abstract

The present invention provides a non-oriented electrical steel sheet for a small-sized precision motor capable of suppressing the connection incidence between steel sheet and a copper wire to a low level when the electrical steel sheet is punched to prescribed shape, laminated and clamped, and then insulation is secured only by coating the copper wire, omitting the insulation by insulating paper or plastic parts and relates to a non oriented electrical steel sheet for a small-sized precision motor, characterized by having inorganic-organic coating of 1.2 to 3.0 g/m² consisting of organic resin and inorganic components comprising one or two of a phosphoric acid system and a chromic acid system on the surfaces of the steel sheet consisting of, in terms of, in terms of wt%, C: 0.005% or less, Si: 0.05 to 4.0%. Mn: 0.1 to 1.5%, P: 0.15% or less, S: 0.008 to 0.014%, Sol. Al: 0.15% or more, N: 0.01% or less, T. O: 0.02% or less, Sn: 0.01 to 0.3%, and the balance consisting of Fe and unavoidable impurities.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "NON-ORIENTED ELECTRICAL STEEL SHEET FOR SMALL-SIZED PRECISION MOTOR" NIPPON STEEL CORPORATION, a Japanese corporation, of 6-3, Otemachi 2-chome, Chiyoda-ku, Tokyo 100-8071, Japan, The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- Granted 10 JUL 2001 7-4-2005 NON-ORIENTED ELECTRICAL CTEEL SHEET FOR SMALL SIZED PRECISION MOTER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet for a small-sized precision motor. 2. Description of the Related Art Non-oriented electrical steel sheets are used for cores of electrical apparatuses such as motors and the like. A motor is manufactured by punching a non-oriented electrical steel sheet into a prescribed shape, laminating and clamping the punched electrical steel sheets, and subsequently winding a copper wire around portions of the core. In the wire winding process, the electrical steel sheets and the copper wire are usually insulated from each other by applying insulating papers, plastic parts or the like to the portions where the copper wire is wound. Recently, motors have been used in the vibrating units of pocket telephones and the controllers of game machines and the like, and ultra-small-sized motors having a diameter of 10 mm or less are also being used in great numbers. In ultra-small-sized motors, there are many cases where the insulation is secured only by coating a copper wire and the insulation, by insulating papers or plastic parts is omitted. SUMMARY OF THE INVENTION However, since there exist pin holes in the coating of a copper wire and portions where the copper wire is exposed, without a coating, cannot be avoided, there are cases where the electrical steel sheets and the copper wire are electrically connected. The object of the present invention is to provide a non-oriented electrical steel sheet capable of suppressing the incidence of connections between electrical steel sheets and a copper wire to a low level. The gist of the present invention to solve the aforementioned problem is as follows: a non-oriented electrical steel sheet for a small-sized precision motor, characterized by having inorganic-organic coating of 1.2 to 3.0 g/m2, consisting of organic resin and inorganic components comprising one or two of phosphoric acid system and chromic acid system, on the surfaces of a steel sheet consisting of, in terms of wt%, C: 0.005% or less, Si: 0.05 to 4.0%, Mn: 0.1 to 1.5%, P: 0.15% or less, S: 0.008 to 0.014%, Sol. Al: 0.15% or more, N: 0.01% or less, T. 0: 0.02% or less, and Sn: 0.01 to 0.3%, and the balance consisting of Fe and unavoidable impurities. Subject of invention relates to a non-oriented electrical steel sheet for a small-sized precision motor, characterized by having inorganic- organic coating of 1.2 to 3.0 g/m2 consisting of organic resin and inorganic components comprising one or two of a phosphoric acid system and a chromic acid system on the surfaces of the steel sheet consisting of, in terms of wt%, C: 0.005% or less, Si: 0.05 to 4.0%, Mn: 0.1 to 1.5%, P: 0.15% or less, S: 0.008 to 0.014%, Sol. Al: 0.15% or more, N: 0.01% or less, and T. O: 0.02% or less, and Sn: 0.01 to 0.3%, and the balance consisting of Fe and unavoidable impurities. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an illustration showing the cross section of a punched portion of a steel sheet. Fig. 2 is a graph showing the relationship between a sheared face ratio and the incidence of connections. Fig. 3 is a diagram showing the relationship of a sheared face ratio to the contents of S and Sn. Fig. 4 is a diagram showing the relationship of a connection incidence with the contents of S and Sn. Fig. 5 is a diagram showing the relationship of a core loss at W15/50 with the contents of S and Sn. Fig. 6 is a graph showing the relationship between the coating amount of a insulating coating and a connection incidence. DESCRIPTION OF THE PREFERRED EMBODIMENTS. The present invention will hereunder be explained in detail. The present inventors conducted a series of studies to develop a non-oriented electrical steel sheet having a low connection incidence between electrical steel sheets and a copper wire, and as the result thereof, discovered that it is very effective to control the steel composition and the insulating coating on the steel sheet surface very precisely. Here, the "connection incidence" according to the present invention is defined by the proportion of the number of the motor cores wherein connections are generated between electrical steel sheets and copper wires to a certain number, in the order of a thousand to ten thousands, of cores for small-sized precision motors, when the copper wires are wound round the cores immediately after the cores are fabricated and then a voltage of several hundred volts is imposed between the steel sheets and the copper wires. Fig. 1 shows the cross section of a punched portion of a steel sheet. It is known that the cross section of a punched portion consists of a shear droop, a sheared face, a fractured face and a burr. The present inventors investigated at which portion in electrically disconnection between electrical steel sheets and a copper wire occurs, and discovered that the electrically disconnection occurs between the copper wire and the sheared face. Then, the present inventors carried out an experiment as shown below. Prepared as a test material was a non-oriented electrical steel sheet containing 0.002% of C, 0.3% of Si, 0.18% of Mn, 0.07% of P, 0.002% of S, 0.3% of Al, 0.0031% of T. N and 0.001% of Sn, and having inorganic-organic coating of 1 g/m2 consisting of chromic acid and organic resin on its surfaces. Cores were fabricated with the sheared face ratios varied by changing the clearance of punching dies, copper wires were wound immediately thereafter, and then the connection incidences between the electrical steel sheets and the copper wires were investigated. Fig. 2 shows the relationship between a sheared face ratio and a connection incidence. From Fig. 2, it is observed that the lower the sheared face ratio is, the lower the connection incidence is. Although it is understood that connection incidence can be reduced by the adjustment of a die, on the other hand, there also occurs a problem that a burr and a shear droop become larger if a clearance is made excessively large. Further, since the adjustment of a die is a complicated work and a sheared face ratio varies also depending upon the extent of the wear of a die, it has been impossible to keep the sheared face ratio always stably at a low level. Namely, in the aforementioned non-oriented electrical steel sheet used for the experiment, even though the clearance of a die was adjusted so as to have the sheared face ratio of 35% at the beginning, it was difficult to always keep the connection incidence to 0.8%. To cope with the problem, the present inventors tackled the development of a steel sheet that keeps a sheared face ratio always stably at a low level. As the result of a study on the influence of steel composition, it turned out that it was very effective to control S and Sn to narrow ranges. More specifically, products were produced by cold-rolling hot-rolled sheets containing 0.002% of C, 0.3% of Si, 0.18% of Mn, 0.07% of P, 0.002 to 0.03 % of S, 0.3% of Al, 0.0031% of T. N and 0.001 to 0.1% of Sn, continuously annealing the cold-rolled sheets at the temperature of 850°C, and coating inorganic-organic coating of 1.0 g/m2 consisting of chromic acid and organic resin on their surfaces. 1,000 units of iron cores for motors were fabricated for each case by using the steel sheets thus produced as the test materials and setting the clearance of a punching die at 5%, copper wires were wound immediately thereafter, and then the connection incidences between the electrical steel sheets and the copper wires were investigated. Fig. 3 shows the relationship of a shared face ratio after 1,000 units of cores for motors were fabricated in each case with the contents of S and Sn, and Fig. 4 the relationship of connection incidence with the contents of S and Sn. It is observed that the shared face ratio decreases as the content of S increases, but the shared face ratio decreases with the low content of S if Sn is added in combination. Then, the connection incidence decreases as the sheared face ratio decreases. Fig. 5 shows the relationship of a core loss at W15/50 with the contents of S and Sn. It is observed that the core loss deteriorates as the S content increases, but the deterioration of the core loss is suppressed if Sn is contained by 0.01% or more. It is also observed that the core loss values of the test pieces containing Sn in the range of 0.01% or more and S in the range of 0.008 to 0.014% are almost equal to the core loss values of the test pieces containing 0.002% of S and 0.001% of Sn. Next, the influence of an insulating coating on a steel sheet surface was studied. Products were produced by cold-rolling the hot-rolled sheets containing 0.002% of C, 0.3% of Si7.0.18% of Mn, 0.07% of P, 0.011% of S, 0.3% of Al, 0.0031% of T. N and 0.020% of Sn, continuously annealing the cold-rolled sheets at the temperature of 850°C, and coating inorganic-organic coating of 0 to 3 g/m2 consisting of chromic acid and organic resin on their surfaces. 1,000 units of iron cores for motors were fabricated for each case by using the steel sheets thus produced as the test materials and setting the clearance of a punching die at 5%, copper wires were wound immediately thereafter, and then the connection incidences between the electrical steel sheets and the copper wires were investigated. Fig. 6 shows the relationship between the coating amount of an insulating coating and a connection incidence. From Fig. 6, it is observed that the connection incidence decreases remarkably when the coating amount of an insulating coating is 1.2 g/m2 or more. It is considered that, when the coating amount of an insulating coating is 1.2 g/m2 or more, the insulating coating get into the sheared face and serves as an insulating layer and the connection incidence decreases remarkably. Reasons for specifying a non-oriented electrical steel sheet for a small-sized precision motor according to the present invention will be explained hereunder. The components below are expressed by the amounts contained in steels (in mass %). C is controlled to 0.005% or less since the amount of C beyond 0.005% deteriorates the magnetic properties caused by magnetic aging. Si below the lower limit of 0.05% increases the eddy current loss and good core loss can not be obtained, but, if its amount exceeds 4.0%, it deteriorates the workability remarkably. 0.1% or more of Mn is added to increase the hardness of a steel sheet and improve the punching property. Its upper limit of 1.5% is determined based on economical reasons. P is added to increase the hardness of a steel sheet and improve the punching property. The amount of P beyond the upper limit of 0.15% makes a steel sheet brittle remarkably. S is controlled to 0.008 to 0.014% for suppressing the short circuit incidence and obtaining an excellent core loss value (refer to Figs. 3 to 5). 0.15% or more of Sol. Al is added to improve the magnetic properties and reduce oxide type inclusions. N is controlled to 0.01% or less since it becomes nitride such as AlN and deteriorates the core loss. T. 0 (total oxygen) is controlled to 0.02% or less since 0 becomes oxide and deteriorates the core loss. 0.01% or more of Sn is added for suppressing the short circuit incidence and obtaining an excellent core loss value (refer to Figs. 3 to 5). Its upper limit of 0.3% is determined based on economical reasons. Since Sb, Cu, Mo, Ge, B, Te, As, Cr and Bi improve the magnetic properties, 0.003% or more of the each element may be added if desired. Its upper limit is set at 0.3% based on economical reasons. One or more of these elements may be added. An insulating coating is a coating consisting of a mixture of organic resin and one or two of a phosphoric acid system and a chromic acid system. The reason for containing one or two of a phosphoric acid system and a chromic acid system is to reduce the surface tension and improve the wettability, adhesiveness and insulating property, and the reason for containing the organic resin is to improve the punching property. Here, the phosphoric acid system is: any one or a mixture of two or more of, for example; phosphate of calcium, magnesium, aluminum or zinc; and phosphoric acid wherein divalent or trivalent oxide, hydroxide or carbonate of calcium, magnesium, aluminum, zinc or the like is dissolved: or the phosphate and/or the phosphoric acid wherein one or more of titanium oxide, colloidal silica, colloidal alumina, boric acid and the like are further added. Then, the chromic acid system is: any one or a mixture of two or more of, for example; dichromate of calcium, magnesium or zinc; and chromic anhydride wherein divalent oxide, hydroxide or carbonate of calcium, magnesium, zinc or the like is dissolved: or the dichromate and/or the chromic anhydride wherein one or more of titanium oxide, colloidal silica, colloidal alumina, boric acid, an organic reducing agent and the like are further added. The coating amount of an insulating coating is set to 1.2 to 3.0 g/m2 for suppressing the connection incidence (refer to Fig. 6). As described above, the present invention simultaneously attains the stable low sheared face ratio and good core loss of a steel sheet by adding 0.008 to 0.014% of S and 0.01 to 0.3% of Sn in combination, and further suppresses the connection incidence by controlling the coating amount of the insulating coating of a steel sheet to 1.2 to 3.0 g/m2. The method of producing a non-oriented electrical steel sheet according to the present invention is as follows: Molten steel is cast into a slab or directly into a steel strip. In case of casting into a slab, the slab is finished to a coil in a conventional hot-rolling method. Then, the steel strip or the hot-rolled coil is cold-rolled, or cold-rolled after hot band annealing, to a final thickness, then continuously annealed and finally coated to produce a product. Example 1 products were produced by cold-rolling the hot-rolled sheets containing 0.002% of C, 0.5% of Si, 0.19% of Mn, 0.07% of P, 0.0020 to 0.0223% of S, 0.3% of Al, 0.0029% of T. N and 0.001 to 0.020% of Sn, continuously annealing the cold-rolled sheets, and coating inorganic- organic coating of 0 to 3 g/m2 consisting of chromic acid and organic resin on their surfaces. 10,000 units of cores for motors were fabricated for each case by using the steel sheets thus produced as the test materials and setting the clearance of a punching die at 5%, copper wires were wound immediately thereafter, and then the short circuit incidences between the electrical steel sheets and the copper wires were investigated. Table 1 shows the relationship of the connection incidences with the contents of S and Sn and the coating amounts of the insulating films. From Table 1, it can be seen that the connection incidences are remarkably reduced in the range according to the present invention. Table 1 indicates that the data are outside the range specified in the present invention. We Claim: A non-oriented electrical steel sheet for a small-sized precision motor, characterized by having inorganic-organic coating of 1.2 to 3.0 g/m2 consisting of organic resin and inorganic components comprising one or two of a phosphoric acid system and a chromic acid system on the surfaces of the steel sheet consisting of, in terms of wt%, C: 0.005% or less, Si: 0.05 to 4.0%, Mn: 0.1 to 1.5%, P: 0.15% or less, S: 0.008 to 0.014%, Sol. Al: 0.15% or more, N: 0.01% or less, and T. O: 0.02% or less, and Sn: 0.01 to 0.3%, and the balance consisting of Fe and unavoidable impurities. Dated this 10th Day of July, 2001. (RANJNA MEHTA-DUTT) OF REMFRY & SAGAR ATTORNEYS FOR THE APPLICANTS

Documents:

641-mum-2001-cancelled page-(7-4-2005).pdf

641-mum-2001-claims(granted)-(7-4-2005).doc

641-mum-2001-claims(granted)-(7-4-2005).pdf

641-mum-2001-correspondence(27-7-2007).pdf

641-mum-2001-correspondence(ipo)-(30-11-2005).pdf

641-mum-2001-drawing(10-7-2001).pdf

641-mum-2001-form 1(10-7-2001).pdf

641-mum-2001-form 1(27-7-2007).pdf

641-mum-2001-form 13(27-7-2007).pdf

641-mum-2001-form 19(6-10-2004).pdf

641-mum-2001-form 2(granted)-(7-4-2005).doc

641-mum-2001-form 2(granted)-(7-4-2005).pdf

641-mum-2001-form 3(10-7-2001).pdf

641-mum-2001-form 3(11-10-2001).pdf

641-mum-2001-form 3(2-12-2005).pdf

641-mum-2001-form 3(7-4-2005).pdf

641-mum-2001-form 3(8-1-2002).pdf

641-mum-2001-form 5(10-7-2001).pdf

641-mum-2001-power of authority(30-10-2001).pdf

641-mum-2001-power of authority(7-4-2005).pdf

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