| 摘要 |
PURPOSE:To reduce an impulse applied to a magnetic powder, especially in case of a collision of each ball, to prevent a needle-like magnetic powder from becoming short, and to obtain an excellent paint by rotating a cylindrical ball together with a paint, when a magnetic paint, etc. are kneaded by means of a ball mill. CONSTITUTION:A material whose specific gravity is >=4, for instance, that of about 4-20mm. of a cylindrical ball 5 of zirconia whose specific gravity is 5.6-6.0, or a ball having a cylidrical curved surface 51 and a flat end face 52, which has covered a mandrel 55 of stainless steel, etc. with a high polymer resin 56 having a good resistance to wear, such as polyamide, etc. is used. In this regard, it is desirable that a chamfered part 53 is provided by a curved surface on the corner part of the ball, or such a diagonal chamfered part as shown by an oblique line 54 is provided. Such a cylindrical ball 5 is used, for instance, for kneading a magnetic paint containing a magnetic powder and a binder resin. A probability of contact of each ball 5 is high, also it becomes a surface contact and an impulse becomes small, an abrasion of the ball 5 is reduced, a foreign matter is scarcely mixed into the paint, and the pait for obtaining a magnetic layer having a high purity and a high performance is obtained in a short time with a high dispersing property of the magnetic powder.
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