There are many studies and proposals on metal fibers including approach on new materials and developments of their use and the applicable fields are becoming wider and wider.
As a process for producing a metal fiber, various processes have been known, for example, as follows:
(1) A process wherein a rod-like metal material is drawn by using a die made of hard metal or diamond.
In this process, a multistage wire drawing treatment is required to obtain a fine fiber. In addition, in order to remove internal strain generated in the wire drawing step, an annealing step is required and, therefore, many steps are required, which makes the process complicated and adversely affects productivity.
(2) A process wherein a solid metal material is cut to obtain a chip-like wire.
In comparison with the above process (1), this process is more convenient and simpler and requires fewer steps. However, in this process, cross sections of the fibers obtained are not uniform and, further, cut defects and the like are liable to be caused on the surface of the fibers. Therefore, there is a problem in homogeneity of fibers
(3) A melt spinning process wherein a molten metal is extruded from a nozzle having a small diameter, a slit or the like, and then solidified by cooling.
This process includes a glass coating-spinning process, spinning in a flowing coolant, spinning in rotating liquid and the like. By using these processes, crystalline or amorphous fibers of various metals or alloys have been produced. Particularly, developments of many new materials have been advanced by utilizing a quenching solidification phenomenon.
Under these circumstances, the present inventors have studied a process for producing a metal fiber using a melt spinning process, particularly, spinning in rotating liquid. As the results, the present inventors have already filed patent applications, i.e, Japanese Patent Kokai Nos. 61-87849, 62-56393 and 63-75118.
These applications are directed to a potential improvement of a melt spinning process of an iron alloy and a process for producing a metal fiber having a specific structure wherein single crystals of various sizes are linked serially in such a way that grain boundaries are present between respective single crystals like "bamboo".
By the way, as the technical revolution progresses, a demand for miniaturizing and weight-saving of electromagnetic apparatuses is increased more and more. In order to satisfy such a demand, for example, molding of a magnetic material into fibers can be considered as one of the methods for miniaturizing an electromagnetic apparatus. In this case, in order to improve magnetic properties of a fiber-like magnetic material, it is of importance to obtain an easily magnetizable structure by minimizing defects such as grain boundary and impurities as well as internal strain. Further, in order to obtain a soft magnetic fiber which is anisotropic toward the fiber axis direction and has a high permeability, a high squareness ratio, a low coercive force and a high saturation magnetic flux density, it is necessary to arrange directions of the easily magnetizable axis of crystals toward that of the fiber axis of the soft magnetic fiber.