Metal treatment – Stock – Magnetic
Reexamination Certificate
2000-06-14
2002-01-22
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
Reexamination Certificate
active
06340399
ABSTRACT:
This application claims priority under 35 U.S.C. § § 119 and/or 365 to Japan Patent Application No. 11-169759 filed in Japan on Jun. 16, 1999, the entire content of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrical steel sheet used for rotors or stators in motors and a method for producing the same. More particularly, the present invention relates to an electrical steel sheet excellent in punchability and interlocking performance in processing it into a core as well as excellent in magnetic properties, and a production method thereof. The core produced from the electrical steel sheet of the present invention is extremely superior in magnetic properties required for the core. Accordingly, the electrical steel sheet of the present invention is particularly suitable as a material for cores used for inverter-controlled motors, such as compressor motors and electric vehicle motors and the like.
2. Description of the Related Art
In recent years, it is strongly required to reduce energy consumption from the viewpoint of the protection of the global environment. Accordingly, an improvement in the consumption amount of electricity becomes an important task for electric equipment. Therefore, the improvement in the motor efficiency is strongly required for motors which are frequently used and continuously worked such as those of refrigerators and air- conditioners.
A power substitute for a gasoline engine in an automobile has been studied as a countermeasure to solve the problem of global environment. In particular, the power generated from a motor, a combination of a motor and a gasoline engine or a combination of a motor and a diesel engine is under development and attention is being paid to electric vehicles and hybrid vehicles applying such powers. To improve the efficiency of energy of these vehicles, it is essential to improve the motor efficiency.
In order to control the motors for compressors used in electric refrigerators and air-conditioners, an inverter control system where the rotational speed is continuously controlled by frequency is mainly used to improve the motor efficiency. Further, since the rotational speed of motors in automobiles should be controlled to an optimum value between low- to high-speed according to the running speed of automobiles, inverter-controlled motors are mainly used.
In these motors, a non-oriented electrical steel sheet having a sheet thickness of about 0.20 to 0.65 mm and a Si content of 2% or more, where the content of Si and Al in total is about 2.5 to 4.5%, is usually used as a material for a core. However, a workability such as punchability for forming the steel sheet into a core shape and automatic interlocking performance for laminating the punched sheets is not sufficient. Therefore, the productivity of motors is low and in some cases the motor cannot satisfy the performance required in the above-described situations.
For example, in continuous punching processing for forming an electrical steel sheet into a core shape, a die is used. The die is easily abraded, and if the die is abraded, “burr” occurs at the edge of the punched sheet. If abrasion of the die proceeds to cause a large burr of more than 50 &mgr;m, the thickness of a core made of the punched sheets laminated therein tends to be inaccurate. Further, an electrical conduction is generated among the laminated sheets, and the eddy current loss easily increases. Accordingly, the burr should be minimized and accordingly, abrasion of the die should be prevented.
Abrasion of the die is affected by the characteristics of the steel sheet. When punching conventional very hard electrical steel sheets containing a large amount of Si, the die would be easily abraded, thus increasing the frequency of exchanging the die. As a result, since the frequency of suspending the punching operation for exchanging the die is increased, the efficiency of production of the core is lowered while the cost for polishing the die for further use is also increased.
In an automatic interlocking step, the punched steel sheets are laminated and stuck in an indented part formed on the sheet in the punching step. The strength of interlocking and the space factor of the laminated and stuck core after interlocked are affected by the material, surface state and thickness of the electrical steel sheet, and in the case of inferior interlocking performance, motors excellent in efficiency cannot be obtained.
JP-A 8-49044 and JP-A 10-25554 disclose non-oriented electrical steel sheets for motors in electric vehicles and inverter-controlled compressor motors, and these steel sheets are excellent in the motor efficiency. However, it cannot necessarily be said that the workability, such as the punchability and the interlocking performance is enough, and there still remains a room for further improvements in the motor efficiency.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a non-oriented electrical steel sheet which is excellent as a material of a motor core in punchability and interlocking performance for forming it into a core and which is excellent in magnetic property when used as a core, a process for producing the same, and a core produced thereby.
The non-oriented electrical steel sheet of the present invention is 0.1 to 0.4 mm in thickness with the following chemical composition and characteristics.
Chemical composition on a mass-% basis:
C: 0.01% or less,
Si: 2.5% or less,
Mn: 2% or less,
Al: 1 to 5%,
Si+Al+0.5×Mn: 2.5 to 5%,
Sb: 0.3% or less, Sn: 0.3% or less, B: 0.01% or less,
the balance: Fe and impurities.
Characteristics: Average grain diameter: 50 to 180 &mgr;m, and
Vickers hardness: 130 to 210.
If the thickness of the steel sheet is 0.2 to 0.4 mm and the Mn content is 1% or less, the magnetic property is further improved. In the steel sheet, the Al content is preferably 1.5 to 5%. The ratio (Al/Si) of Al to Si is preferably 0.7 to 1.4, more preferably more than 0.8 to 1.3.
If the surface roughness of the steel sheet in terms of arithmetical mean roughness Ra is 0.5 &mgr;m or less, the space factor of the core is high, and thus when used in a motor, the motor efficiency can be improved.
The non-oriented electrical steel sheet of the present invention can be produced in the following steps:
(1) preparing a slab having the above-mentioned chemical composition;
(2) heating the slab at a temperature of 1300° C. or less and hot rolling the slab into a plate;
(3) after the hot rolling, cold rolling the plate into a sheet until the thickness thereof becomes 0.1 to 0.4 mm; and
(4) finish-annealing the sheet at a temperature of 700 to 1150° C.
In production of a steel sheet with a surface roughness of 0.5 &mgr;m or less in terms of arithmetical mean roughness Ra, a roll having a surface roughness of 1.5 &mgr;m or less in terms of arithmetical mean roughness Ra is preferably used in cold rolling. Annealing at 600 to 1000° C. may be conducted before cold rolling, or before cold rolling and between plural times of cold rolling.
The motor core of the present invention can be obtained by a process such that the non-oriented electrical steel sheet of the present invention is punched, and the punched sheets are laminated and interlocked. A motor using this core exhibits good motor characteristics because the core is excellent in magnetic property such as magnetic flux density, iron loss etc. Accordingly, the core of the present invention is very suitable for inverter-controlled motors such as compressor motors, electric vehicle motors etc.
In this invention, the interlocking means a work where the plurality of the punched steel sheets with indented portions formed on the sheet in the punching step are laminated one above the other in a manner that the indented portions of one sheet are inserted into those of another sheet, and then the laminated sheets are pressed so that the sheets are mechanically bonded to each other.
DETAILED DESCRIPTION OF THE INVENTION
To improve the efficiency of i
Honjou Noriyuki
Maeda Mitsuyo
Mita Shinsuke
Nakayama Taisei
Tanaka Ichiro
Burns Doane , Swecker, Mathis LLP
Sheehan John
Sumitomo Metal Industries Ltd.
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