Abrasive Blasting Materials-Metallic & Nonmetallic Abrasives
The abrasive blasting materials are important because they determine the surface profile produced. There are two general categories of abrasives: metallic and nonmetallic. Metallic abrasives are used primarily to blast clean steel and forged or cast iron where a surface profile is seldom critical on the finished product. Nonmetallic abrasives, depending on the type used, can produce the desired surface profile and cleanliness on hard, dense ferrous metals or on soft metals (aluminum, brass, bronze, or copper) without damaging or altering the metal surface.
Metallic abrasives include cast iron shot, cast iron grit, and steel shot. Cast iron shot is hard and brittle and is produced by spraying molten cast iron into a water bath. Cast iron grit is produced by crushing oversized and irregular particles formed during the manufacture of cast iron shot. Steel shot is produced by blowing molten steel. Steel shot is not as hard as cast iron shot, but is much more durable. These materials typically are reclaimed and reused. Other products include shot cut from aluminum, copper and zinc wire.
There are three basic types of nonmetallic abrasive blasting materials: naturally occurring, byproducts and manufactured.
Nonsilica or heavy mineral sands (magnetite, olivene rutile, straurolite). These sands are typically tough, dense, round-shaped materials. They are effective for blast cleaning new steel but are not recommended for maintenance coating work. Degree of dusting during blasting operations is medium.
Flint, garnet, novaculite (siliceous rock), and zircon. These are dense, tough, angular or cubic abrasive blasting materials that, because of their high costs, are used primarily in special cleaning applications. The degree of dusting during blasting operations is medium for flint and garnet and low for novaculite and zircon.
Slag (coal, copper, nickel) abrasives are generally a glassy, homogeneous mixture of various oxides that are sharply angular or cubic and are efficient for blast cleaning new, rusted, or painted surfaces. These abrasives are not recycled. The degree of dusting during blasting operations is high for coal and nickel and low for copper.
Agricultural products (corncobs, peach pits, walnut shells) are generally regarded as tough but lightweight abrasives used in special cleaning applications for removing paint, fine scale, and other contaminants without altering the metal substrate or distorting thin metals. The degree of dusting during blasting operations is low.
Synthetic (aluminum oxide, glass beads, silicon carbide) abrasives can be produced with specific properties for varying degrees of hardness and toughness and with specific shapes. High cost restricts the use of these abrasives to special cleaning applications, and they must be recycled to be economical. The main advantages of using synthetic abrasive blasting materials are fast cutting capability and non-rusting of the substrate. The degree of dusting during blasting operations is low.
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