BLAST CLEANING ABRASIVE PRODUCTS
As a general rule, the blaster should use the finest abrasive necessary to attain the required surface preparation characteristics. A fine abrasive will give you more impacts per volume. The more particles in the stream, the more work is accomplished in the same time. When blasting concrete or wood, you don’t need a hard, expensive abrasive, or a coarse particle: crushed glass makes an excellent, inexpensive choice for work on relatively soft surfaces.
However, when preparing iron and steel for a protective coating system, there are additional considerations. Coatings adhere poorly to hard, flat surfaces, so the blaster is required to develop a pattern of indentations that the coating can anchor to.
The Anchor Pattern
When a sufficiently hard abrasive particle strikes steel, it deforms the surface into a valley and pushes up peaks. The distance between the top of the peak and the bottom of the valley is known as the depth profile.
The shape of the article effects how deeply it cuts into the coating and underlying substrate. Shapes are classified according to angularity.
Angular particles cut through soft coatings and rust, cleaning faster, and producing sharper anchor patterns. Rounded particles produce a more even, peened surface, good for breaking away hard brittle coatings and mill scale.
Sodium Bicarbonate (Soda Blasting)
ALUMINUM OXIDE - Hardness 9; Size range- 16-240 grit; Shape: angular. Aluminum oxide is our most popular cleaning blast media. We only offer virgin quality material which contain none of the many impurities found in reclaimed or reprocessed Alox (also known as Aluminum Oxide.). Aluminum Oxide conforms to all major Industrial and government standards including, MIL A21380B and ANSI B74. 12-1982. White Aluminum Oxide is also available. Specially treated for removal of Iron and is used where surface contamination is unacceptable: cleaning and deburring electrical circuit boards.
GARNET - Hardness: 7.5; Size Range - 5 sizes from 16 to 100 grit; Shape: Blocky particles. This natural mined material is fast cleaning and is an excellent alternative to sand and coal slag (black beauty). It is not as effective as Aluminum Oxide on difficult applications. Garnet is used widely in waterjet cutting and has a higher Iron content than Alox while sizing is on the "loose" side. Sold usually in bulk containers, but bags are available.
GLASS BEADS - Glass beads are formulated from chemically inert soda-lime glass to produce a metallurgically clean surface for parts and equipment. The beads are spheres of uniform size and hardness to impact the surface of the part. Metal Preparations glass beads meet OSHA standards for cleaning operations and release no free silica or toxins that may harm workers or the environment. Breakdown of glass beads is generally caused by fracture and does not contaminate workpieces. Another advantage of using glass beads is the disposability, spent glass is environmentally friendly as compared to chemical cleaning methods. Normally this simplifies the disposal which results in reduced cost and required paperwork. Glass beads are often used for stress relief. Metal Preparations has available mil-spec (MIL-G-9954A) glass beads at absolutely no extra charge.
CRUSHED GLASS - Hardness: 6; Size Range: 8 sizes, from coarse to very fine; Shape: blocky. Crushed glass is an excellent low cost alternative to various reclaimed blast abrasives. Although the breakdown rule is somewhat higher, it has the benefit of being silica free with minimal Iron content (2%) and produces a "light luster-white metal finish." Other applications include: Stainless Steel and non-ferrous metal blasting because of it's no metal content and limited impregnation capabilities. Sold in bulk containers but available in bags.
STEEL GRIT AND SHOT - Hardness: 6 Size Range: various from .007 to .078 (inches) Grit; Shapre: angular shot round. Steel grit and shot have one of the lowest breakdown rates of all blast media. Mostly used in Wheel Blast equipment (steel shot) where steel grit is excellent in large blast room applications. It should not be used on stainless steel where iron impregnation is a concern. Cast stainless steel shot is available for nonferrous castings other items where ferrous contamination is a problem. Reclaimed steel grit is also widely used in blast room applications and steel fabrication blasting and an inexpensive alternative, and is available through Metal Preparations. Grit- comes in various hardness' . Hardness' are usually 40-50Rc; 50-60Rc and 60+Rc. Shot is also used for widely shot peening (see our Job Shop Page ).
CORN COB/WALNUT SHELLS - Hardness: 3-4; Size range: coarse, medium and fine. Most common sizes are 10/14, 14/20, 20/40. Soft friable dried shells or nuts. Called "organic" or agri-shell abrasives. Used for removing contaminants, such as carbon deposits or old paint from delicate parts or soft materials such as aluminum. Also used for plastic deflashing but "dusty". Also good for blast cleaning with portable equipment in factories and buildings to knock off dirt, debris and loose paint prior to repainting. This material is also widely used in vibratory finishing as a drying agent.
PLASTIC GRIT - Hardness: 3-4; Size range-12 to 60 mesh. Plastic blast media covers a wide variety and range of options. "Plastic Grit" is granulated plastics of specific make and hardness' popular in hand blast cabinets for paint or coating removal. There is also specific materials used for deflashing rubber and plastics. These are Poly-Carb. Used in cryogenic equipment. Polystyrene Beads- excellent when deflashing sensitive electronic components. Nylon Pellets- A variety of types are available for the effective flashing of thermoset parts, rubber, electrical small parts among other items.
BAKING SODA - Hardness: 2.5; Shape: Angular, Baking Soda blasting is unique because it's biodegradable characteristics. Clean up after use is easy because it is water soluble, you can literally "wash" it away. Baking Soda is commonly used where one pass coverage with no recovery is acceptable or desirable, and the substrate is delicate or sensitive. Typical applications include: graffiti removal, boat hulls, large printing press rolls, even cleaning interior smoke damage from fire because it de-odorizes also.