Date of Award

Spring 1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical Engineering

First Advisor

E. S. Geskin

Second Advisor

M. C. Leu

Third Advisor

Rong-Yaw Chen

Fourth Advisor

Methi Wecharatana

Fifth Advisor

Zhiming Ji

Abstract

This doctoral dissertation is concerned with the development of water based cleaning technology required by industry which may substitute the traditional approach based upon the use of various chemical cleansers.

The experimental study involves the waterjet removal of various coatings (rust, oil and epoxy based paints, etc.). Cleaning was carried out under a wide range of operational and geometrical conditions (standoff distance, travel speed, water pressure, diameters of sapphire nozzle and focusing tube, nozzle body type). A new designed spiral nozzle body was tested in this work. The use of surfactant was also investigated. Microscope and SEM surface were used to evaluate the degree of coating removal. The effect of various operation conditions on water consumption and cleaning rate are determined. Two new process characteristics, critical cleaning and damage standoff distances, which determine the admissible range of process variables, are first introduced in this study.

The theoretical study pioneers an analytical description of waterjet cleaning. Simple equations relating the cleaning width of stationary and moving jets, which can be used to determine the optimal cleaning standoff distance, were constructed. These relations show that the maximal cleaning rate and consequently minimal water consumption can be attained at a position of 0.55-0.7 of the critical cleaning standoff distance. Experimental data substantiate the results of the theoretical study.

The acquired results of the theoretical and experimental studies identify the practical range of process variables which assure complete paint removal from glass or metal surface without inducing any damage to the substrate. The spiral nozzle body was shown to provide the optimal cleaning performance. The principal result of this study, however, is a demonstration of the feasibility and effectiveness of using a high-velocity and low-volume waterjet as the single cleaning agent, and a "cleanser-free" technology. Also methods of development are outlined. Another major finding is the demonstration of the feasibility of using a conventional analytical description of turbulent liquid jets for the simulation of the behavior of a high speed stream of water droplets, which constitute the jets used in this study.

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