In 1990, a research project was undertaken to study a number of abrasive grits used for sandblasting to find a viable alternative to silica sand. Recent years have seen an increased concern over the associated health hazards resulting from silica sand use. When silica sand impacts a surface at high velocities, the sand particles break up releasing free silica into the air. This free silica, suspended in the air, can be carried downwind where it may be ingested into the lungs. The result of long-term exposure to free silica in the lungs – silicosis – has a similar health impact as does asbestosis. In 1993, silica sand use in sandblasting was banned at KSC.
This abrasive grit study analyzed silica sand and 27 grits using a number of tests and measurements. The grits were categorized into the three types of grit: steel, mineral, and slag. Four steel, seven mineral, and seventeen slag grits were selected for testing. A complete list of the grits, types, and manufacturers is shown in the table. Seven 4- by 6-inch carbon steel panels were blasted to a white metal condition for each candidate grit. Three of these panels were then coated with Cathacoat 302 for salt fog and beach exposure tests. Testing also included two high-humidity tests on bare panels, surface profile measurement, soluble contaminants, grit composition, geometry profile, and Toxicity Characteristic Leaching Procedures (TCLP's) for heavy metals.
Results yielded that overall the grits performed well in the coated panel exposure testing, and no relationship between grit type and coating performance could be determined. However, the most critical aspect of selecting a grit appears to be chemical analysis in the form of TCLP and soluble contaminants. Several of the grits had high readings of lead or other heavy metals, making them poor selections for use. Using a grit with readings close to the allowable limits for heavy metal content would most likely make the postblasting cleanup a hazardous waste problem. In addition, a few of the grits had high levels of chloride or sulfate, increasing the chances to accelerate corrosion of the base steel. There is a correlation between the grit particle size and the surface profile for the grits. Surface profile can also be controlled by adjusting the pres-sure of the air/grit passing through the nozzle.
| Grit Name | Type | Manufacturer |
|---|---|---|
| Amasteel 40 | Steel | Ervin Industries, Inc. |
| Amasteel 50 | Steel | Ervin Industries, Inc. |
| Black Beauty 20/40 | Slag (coal) | Reed Minerals Division |
| Blastite 46 | Slag (aluminum oxide) | Washington Mills Electro Minerals Corp. |
| Blastite 54 | Slag (aluminum oxide) | Washington Mills Electro Minerals Corp. |
| Copper Blast All-Purpose | Slag (copper) | Union Pacific Resources |
| Copper Blast Medium | Slag (copper) | Union Pacific Resources |
| Exolon ESK 16/30 | Slag (silicon carbide) | Exolon ESK Company |
| Exoblast 24/48 | Slag (aluminum oxide) | Exolon ESK Company |
| Fairmount Coal Slag | Slag (coal) | Fairmount Abrasive Systems |
| Fairmount Silica Sand | Mineral | Fairmount Abrasive Systems |
| FastBlast 20/40 | Slag (aluminum oxide) | Exolon ESK Company |
| FastGlass 20/40 | Slag (glass) | 3R Mineral and Manufacturing Co. |
| Flintabrasive | Mineral | MDC Industries |
| Garnet (GMA) | Mineral | Barton Mines Corp. |
| Green Lightning 40 | Mineral | Applied Industrial Materials Corp. |
| Met Grain 40 | Steel | Chesapeake Specialty Products |
| Niagara Blast 40 | Slag (aluminum oxide) | Washington Mills Electro Minerals Corp. |
| Niagara Blast 50 | Slag (aluminum oxide) | Washington Mills Electro Minerals Corp. |
| Poly-Grit 40 | Slag (copper) | MDC Industries |
| Stan-Blast Fine | Slag (coal) | Stan Blast Industries |
| Stan-Blast Medium | Slag (coal) | Stan Blast Industries |
| StarBlast | Mineral | DuPont Company |
| Staurolite, Coarse 15/54 | Mineral | DuPont Company |
| Steel Grit RG 50 | Steel | 3R Mineral & Manufacturing Co. |
| Tri-Mix 20/40 | Slag (glass) | 3R Mineral & Manufacturing Co. |
| Tufblast 24/36 | Slag (aluminum oxide) | Abrasive Materials Inc. |
Key accomplishments:
Contact: C.A. Finchum, LO-MSD-2T, (321) 867-4619