Chapter 7 - Alternative Developments in Hydroblasting

Abstract

This chapter focuses on pulsed liquid jets, hydro-abrasive jets, high-speed ice jets, and water jet/ultrasonic devices used for surface preparation. Pulsed water jets can be classified into low-frequency water jets, and high-frequency water jets. Both techniques involve the modulation of continuous high-speed water jets. Pulsed jets can be produced in several ways using different driving energy sources. The two most important parameters of pulsed liquid jets are loading intensity and loading frequency. For some pulsed liquid jet concepts water jet velocity and pulse frequency cannot be varied independently from each other.. A hydro-abrasive injection jet is formed by accelerating small solid particles through contact with one or more high-speed water jets. From the point of view of jet generation, the hydro-abrasive jets can be classified into injection jets and suspension jets. The hybrid technique removing lead-based coatings includes three subsequently performed steps of application, which include application of a caustic stripper (NaOH) to the coating; removal of the reacted coating by mechanical means (scraping); and removal of paint and residual caustic by ice jetting. Caustic stripping is, however, possible only if the coating contains drying oil. The process does not work on polyurethane or epoxy coatings. The mechanisms acting during the cleaning include mechanical displacement through ice particle impact, scrubbing as a result of frictional forces, and flushing due to flowing water after the ice is molten.