Surface modification processing of Co-elinvar for hair spring using Na₂SO₄ electrolyzed oxidizing water

Abstract

This paper discusses the surface modification processing of Co-elinvar alloy (Fe-26.50mass%Co-9.50mass%Cr-15.50mass% Ni-0.50mass%Mn-0.30mass%Si) using Na₂SO₄ electrolyzed oxidizing water (hereinafter to as EO water). Co-elinvar alloy is widely used as the material of watch main hair spring. To improve the disentangled characteristics of hair spring after shape processing, it is necessary to roughen the surface. First, the roughening effect of Na₂SO₄ EO water on the surface of Co-elinvar alloy was elucidated by immersion test. The result of immersion test showed that when using supersonic together, compared with the case of only immersion, the scar of etching in test pieces surface becomes more homogeneous, but the section size and the Young's modulus of sample pieces decrease. Also, if processing time with supersonic use is optimization, the surface roughness becomes smooth and stronger. Next, the relation between roughening effect of Na₂SO₄ EO water and when it was produced was clarified. The results showed that if it was produced within 180 minutes, etching rate of Na₂SO₄ EO water was not influenced by elapsed time and becomes constant approximately, and the micro- shape of the surface isn't influenced by the elapsed time, it was smooth. By this study, we received the suggestion that Na₂SO₄ EO water could be applied to surface processing such as the roughening process of Co-elinvar alloy.