Releasing a clog with a thread

One of the challenges in providing a steady mass-flux of granular material to any industrial process is the intermittent formation of arches that clog an outlet. Typically these clogs are released by an external intervention such as large-scale mechanical vibration or a high-pressure gas jet across the outlet. Motivated by our previous experiments on using slender rods inserted into a flow to suppress the formation of clogs, we have developed a new, low-energy method of releasing clogs once they do form. We have performed experiments on the discharge of spherical glass grains from a cylindrical hopper terminating in a conical outlet. We now introduce a filament down the axis of the hopper and investigate the effect of reciprocating axial motion of the filament as a method of releasing the clogs when they form. We report on the efficacy of breaking arches as a function of the tension on the filament and amplitude of motion along the axis. This is a very efficient method of arch-breaking, first, because unlike existing methods the intervention is very local (the filament diameter is smaller than the grain size), and second, because the axial motion can release frictional bonds without doing work against the granular pressure as would any method based on lateral motion. Arches are delicate structures that support a huge vertical load: our experiments give insight into their weakest failure mode.