The Effect of Immersion Corrosion on the Surface Morphology of a Flank-Locking Precision Locknut

摘要

Precision locknuts are widely used in rotary machinery especially the machine tools operating in high speed with high precision. The flank-locking locknut studied in this paper is mainly employed in spindle and ball screw assemblies of machine tools to secure the preloading in the bearings required for better structural stiffness. In service the locknuts often suffer corrosion from the harsh machining environment. The possible effects of corrosion on the surface morphology of locknut, such as flatness and roughness, and its performance were investigated. The locknut was submerged in a 5% NaCl solution following ASTM B895 standard for different durations- 1, 2, and 4 h to speed up the possible corrosion. The treated locknut was then undergone assembling test following ISO 2320 standard. The flatness and roughness on the end face and threads were measured along with microscopic examination. It was found that with increasing duration of corrosion, the surface flatness and roughness became worse. However, the tightening constant of the locknut showed a positive correlation with the increased surface roughness raised by the corrosion treatment.