Inner-surface polishing of capillary tube with magnetic compound fluid slurry

Capillary tubes used in various medical equipment must be manufactured with ultra-precision roughness to ensure high performance. To this end, this study aims to develop an innovative polishing technology for the inner walls of stainless-steel capillary tubes, utilizing a magnetic compound fluid (MCF) slurry within a rotating magnetic field. The research seeks to clarify the principles and processes of polishing by analyzing and validating the magnetic force conditions of carbonyl iron particles (CIPs) and the behaviors of both the CIPs and abrasive particles (APs) in a capillary tube under a rotating magnetic field. Additionally, the study predicts the material removal profile. It is shown that the CIPs exhibit periodic accumulation toward the magnet's middle and ends under the rotational magnetic field. Magnetic clusters, composed of CIPs, swing, tumble, and stir within the cross-section of a capillary tube, which leads to the continuous renewal of APs in the polishing area, enhancing the polishing efficiency. The experimental results show that the specially configured MCF slurry can achieve an extended and uniform mirror-polished zone on the inner surface of a capillary tube under a rotational magnetic field, significantly reducing the surface roughness to Ra 6.4 nm without leaving any scratches. This demonstrates a substantial improvement of the proposed method over traditional polishing methods in terms of surface roughness and indicates potential success in polishing the inner surfaces of capillary tubes for medical applications.