Apparatus and method for abrasive jet finishing of deeply concave surfaces using magnetorheological fluid

Apparatus and method for abrasive jet of a deeply concave surface using magnetorheological fluid. A ferromagnetic nozzle recessed within a solenoid magnetically shields the fluid within the nozzle and serves as a core for the solenoid, thereby increasing the strength of the magnetic field approximately 100-fold, permitting a significant reduction in the size of the solenoid. The exit orifice of the nozzle is recessed within the solenoid, creating a free space within the solenoid having an intense, shaped, axial magnetic field in and near the nozzle. Stiffening of the magnetorheological fluid begins as the fluid enters the magnetic field upon leaving the nozzle; thus, there is no buildup of viscous drag through the nozzle. Stiffening of the jet occurs principally in free space within the solenoid. The nozzle has peripheral longitudinal channels through which compressed air is conveyed to form an air curtain surrounding the jet, preventing spent MR fluid from re-entering and fouling the nozzle.