Industrial sand and gravel generally are mined from open pits of naturally occurring quartz-rich sand and sandstone. Artificial sand making is a complex process involving different stages. The materials will be primarily crushed at the mine site before being transported to the processing plant.
Depending on the degree of cementation, several stages of crushing may be required to achieve the desired size reduction. Gyratory crushers, jaw crushers, impact crushers, and cone crusher are used for primary and secondary crushing.
After crushing, the size of the material is further reduced to 50 micrometers ( m) or smaller by grinding, using smooth ball mill, high pressure mills, autogenous mills, hammer mills, ultrafine mill or jet mills. The ground material then is classified by wet screening, dry screening, or air classification. At some plants, after initial crushing and screening, a portion of the sand may be delivered for final construction applications.
Sand Crushing Process Design
To ensure high quality sand is produced, all feed material must pass the crusher at least once. The preferred circuit selection is post-screen closed-circuit, with oversized material recirculated back to the crusher for further reduction. Manufactured sand typically contains an excess of fine material between 0-0.25mm, compared with the concrete grading specification envelope widely used in the industry.
This is outside the practical operation range for most conventional vibrating screens, so traditionally these fines were removed using wet process equipment, such as sand wheels or hydrocyclones. Crusher selection is based on the abrasiveness of the source rock, the feed fraction to the circuit and the nature of the sand required. In an application where there is a long feed curve (ie X-0mm) VSI crushing is the preferred method.