The effects of dilute polymer solution elasticity and viscosity on abrasive slurry jet micro-machining of glass

Abstract

The present study investigated the effect of dilute polymer solutions on the width, shape, and centerline roughness of micro-channels machined using a specially-designed abrasive slurry-jet micro-machining (ASJM) apparatus. A positive displacement slurry pump and a pulsation damper were connected to an open reservoir mixing tank to generate a turbulent jet containing 1wt% 10μm Al2O3 particles flowing through a 180μm sapphire orifice at 4MPa.The behavior of non-Newtonian fluids containing long-chain polymers is affected by both their viscosity and their resistance to extensional deformation (i.e. their “elasticity”). The effects of viscosity and elasticity on erosion were separated by conducting experiments using aqueous solutions of equal viscosity, but differing elasticity. It was observed that jets began to oscillate laterally if the polymer concentration became too high.The width of the machined channels decreased 21% with the addition of 50wppm of 8M PEO, the highest concentration possible with a stable jet. This change was accompanied by a decrease in the channel depth of 46% and an increase in the centerline roughness of 29%. These changes were due to normal stresses generated in the PEO solutions (an elasticity effect), and were not attributable to viscosity. It was also seen with this and other polymer solutions, that the channel cross-sections were more V-shaped compared with the U-shape of the reference channel machined using the glycerin solution. The same changes in shape, channel width, and centerline roughness were observed at a lower concentration of the same PEO (i.e. 25wppm), but to a lesser degree. Similar changes were also evident with more concentrated 1-M PEO solutions (i.e. 25–400wppm), but again to a lesser extent. However, even a very concentrated 2.5×104wppm solution containing 0.1M PEO had no effect, indicating the predominant role of polymer molecular weight in determining the magnitude of fluid elasticity and its influence on particle motion in the erosive slurry. The present results demonstrate that even a small amount of a high-molecular-weight polymer can significantly decrease the width of machined micro-channels for a given jet diameter.