OVERVIEW

Though this book has many possible uses, it was designed primarily for those seeking to understand blast cleaning and its applications in industry. The discussion brings together fundamental and empirical research findings to explain practical applications where costs and performance are important. For example, a study of the way abrasives fracture provides important knowledge for selecting which abrasive is best for a particular application. The book is also a valuable resource for information on surface preparation and integrity, organic coatings removal and applications,as well as preparation of surfaces for new technologies such as powder metal coating by plasma spray. The practical-minded manager or engineer will find this book to be a useful resource in the overviews of blast cleaning equipment which discusses air compressors, hose dimensions, nozzles, metering methods and requirements for various types of abrasives media. Tables and graphics throughout provide good comparisons of different methods and coating techniques. The objective discussion without reference to tradename or commerical products offers an unbiased presentation that fosters better understanding and makes troubleshooting easier.

Chapter 1 is an introduction with comments of why this book is necessary. The need is to update information found in older publications, most of which were published 25 or more years ago. The book concentrates on blast cleaning using compressed air use for removing mill scales, slags and coatings and substrate preparation for future protective coatings.



Chapter 2 introduces classification schemes for abrasive minerals and includes characteristics of familiar brand name products. The chapter discusses the various ways abrasives are characterized such as roundness, hardness, friability (fracturing properties), and the composition and impurities that impact practical uses. The chapter shows the international and truly scientific effort to provide standards to evaluate abrasives for blast cleaning applications.



Chapter 3 provides details on the dynamics of air used to propel abrasives with discussions of compressibility, density and noise generation. Nozzle designs (diameter, length wall shape, etc), particle distribution, dispersion patterns are among the topics explored. A section on nozzles describes the science behind airflow including the effect of nozzle characteristics of abrasive flow and recommended values suggested by traditional equipment manufacturers. One section covers the convergent-divergent geometry of Laval Nozzles. Coverage of jet structure includes flow rates and design pressures of nozzles.



Chapter 4 begins with an overview of key system components and explores each in depth including compressors, blast machines (abrasive delivery system), abrasive hose lines, and nozzles. The discussion includes Froude number for airflow, types of valves used in abrasive hoses, types of nozzles and their wear patterns. Included are discussions of metering systems with a table of typical flow rates for the range of conventional abrasives drawn from technical literature.



Chapter 5 is a look at oxide and organic coating and the way that abrasive blasting affects them in one of the two mechanisms of erosion and debonding. Details include characteristics of coating such as hardness, Young's Modulus, and fracture mechanisms. A discussion of impact processes includes the energy absorption, damage number, and friction effects. A discussion on material deformation and removal include mathematical models derived from research. The discussion of mill scale on steel, the brittle outer layer of metals, uses a table on chemical compositions of scales formed on various steels. The removal of flexible materials such as rubber and bulk polymers illustrates the wide range of materials subjected to blast cleaning.



Chapter 6 examines the role of blast cleaning in surface preparation covering variables such as stand off distance and type of abrasive. The chapters include sections for weld seam cleaning and underwater methods.



Chapter 7 addresses non-process concerns such as safety, health and environmental impact. Dust and air-borne emissions, noise, vibration, and the use of protective equipment are among the topics included. Environmental issues such as disposal and hazardous contaminates are summarized in tables drawn from published research. According to some studies, 50% of total costs are spent on disposal. One table provides an estimate of abrasive consumption for various types of abrasives showing consumption rates that vary from 12 kg/m² for coal slag to 130 kg/m² for dolomite. Tables and discussions on recycling illustrate how total consumption can be greatly reduced by the proper choice of type of abrasive.



Chapter 8 addresses surface quality issues covering the many different primary and secondary features that could define surface quality. Beginning with ISO standards for visual cleanliness, Momber discusses the conditions of metal before cleaning begins and the range of cleaning techniques ranging from light cleaning to thorough cleaning and bright metallic coloring showing how the meaning of surface quality depends upon the purpose for cleaning the metal. Methods to quantify measurement of cleanliness range from reflectivity to electrical resistance. One section discusses chemicals that remain on the surface, chlorides and salts that affect the durability of future coatings. Subsequent tables show how different methods leave differing levels of salt residues on the surface. Other surface characteristics affected by blast cleaning include dust and embedded materials, surface roughness and profiles, and surface hardness, residual stress, and fatigue strength. The chapter closes with sections on surface energy, adhesion, and wettablity, all factors affecting future coatings applied to the surface.



Chapter 9 focuses on coating substrates with organic and inorganic materials. The opening topic of corrosion includes tables from standards on degrees of blistering as well as various testing methods. Tables compare different blasting methods and their effect upon delamination, rusting, and blistering of coatings. Graphics help explain the bonding forces for various ways coatings adhere to substrates and other topics related to adhesion. The differing effects of various methods upon adhesion explain the considerable variation in bond strengths of coatings. The concluding section illustrates nontraditional blast cleaning applications such as the surface preparation for plasma spraying on metal substrates.



The extensive list of references in the appendix document the vast library of literature used in preparation of this book. Dates on the nearly 800 citations range from the 1950s to 2007 showing an extensive research effort underway. The 385 figures and 169 tables provide condensed summaries of information drawn from many of those references.