Gripping and frictional-conveying characteristics of fine protrusions formed by sputter-etching of stainless steels

Abstract

Argon ion sputter-etching of SUS420J2 and SUS316 stainless steels was carried out at a power of 250W for 10.8ks to form cone-shaped sharp protrusions with bottom diameter of 10-30 μm and fine quasi-column-shaped protrusions with diameter smaller than 500 nm respectively by using a radio-frequency magnetron sputter-apparatus. Effects of two types of plasma-nitriding on gripping ability were examined; one is the nitriding of both steel specimens using nitrogen gas of 0.53 Pa mixed with argon gas of 0.67 Pa at a power of 50W for 1.8 ks to maintain the original sharpness of protrusions, and another is the nitriding of SUS420J2 steel specimen using only nitrogen gas of 1.2 Pa at a power of 200 W for 7.2 ks to obtain the cone-shaped protrusions with round top. The coefficient of static friction, or gripping ability, of the plasma nitrided sharp protrusions of SUS420J2 steel specimen to polyethylene, polyvinyl-chloride, polyethylene-naphthalate sheets and a copy paper was about 1.8, 2.4, 1.1 and 1.5, respectively, at a large nominal compressive stress of 18 kPa. The reason for such large frictional coefficients is due to localized deformation of sheet under the sharp protrusions or piercing of the protrusions into the sheet. Although the sharp protrusions were partly broken, the frictional coefficients of these sheets were still about 1.6, 1.8, 1.1 and 1.4 after the second series of tests, which are more than twice as large as that of the specimen ground with #100 emery paper. The plasma-nitrided round protrusions of SUS420J2 steel and the fine protrusions of SUS316 steel were not broken during the friction tests of the polyethylene sheet and the copy paper but the frictional coefficients are smaller than those of the sharp protrusions. The protrusions with large frictional coefficients can be applied to the surface of a frictional conveying roll.