Processing Improve your Size Reduction Expect More from your Horizontal Shaft Impactor Horizontal Shaft lmpactors (HSl) were first implemented in the midst of the last century. Since then they have taken over the size reduction process in many industries. Here's why and how. ERIC MARCOTTE he mineral processing industry usu ally evolves rather than revolution- izes, but the Horizontal Shaft Im pactor (HSI) has revolutionized the crush b ing process in numerous industries. There are HSI, larities are more numerous than their dif. ferences. All varieties feature externally fed horizontal rotors with breaker bars,