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All Direct Pressure Blast Machines are filled by "volume", not "pounds" of abrasive.
The weight of each type of abrasive is different per cubic foot of "volume".
The weight is called the "bulk density" of that abrasive.
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It just so happens that the most common of all Blast Cleaning Abrasives, Silica Sand, weighs 100 pounds per Cubic Foot, and a 6.5 Cubic Foot Machine could "Theoretically" hold 650 Pounds of Sand, if it could be totally filled. The Chart below shows the "Bulk Density" (Weight per Cubic Foot) of several common Blast Cleaning Abrasives.
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| ABRASIVE TYPE |
BULK DENSITY |
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ABRASIVE TYPE |
BULK DENSITY |
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| Silica Sand |
100 |
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Nut Shells |
45 |
| Mineral Sands |
127 |
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Corn Cobs |
35 to 42 |
| Flint |
80 |
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Aluminum Oxide |
120 |
| Garnet |
147 |
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Silicon Carbide |
106 |
| Coal Slag |
85 |
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Steel Shot/Grit |
250 |
| Copper Slag |
112 |
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Glass Shot |
100 |
| Nickel Slag |
85 |
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Plastic Grit |
45 to 48 |
| Sodium Bicarbonate |
61 |
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Ferric Oxide |
172 |
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As a general rule, it can safely be figured that a typical Blast Machine can only hold Abrasive in about 75% of its inside space. So, a typical 650 Pound (6 Cubic Foot) Machine will only freely hold 488 Pounds of Silica Sand which happens to weigh 100 Pounds per Cubic Foot (Bulk Density). But, that same Machine can hold 1219 Pounds of Steel Grit, but only 219 Pounds of Nut Shells. But it is still as full as it possibly can be due to its filling angle of repose.
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