| 摘要 |
PROBLEM TO BE SOLVED: To control the undersize ratio of a specified-opening screen in a specified range and to make a concrete strength higher by grinding crushed-stone sand with the undersize ratio of a specified-opening screen below a specified value to correct the angular grain shape and adjusting the water content and grain size by a screw conveyor and a drier. SOLUTION: Crushed-stone sand with the undersize ratio of a 0.15 mm- opening screen controlled to <=4% and having 6-9% water content is supplied to a VX mill 3 by a first sand conveying mechanism 2 and ground to correct the angular grain shape, and the grain size is decreased. The obtained sand is discharged into a second sand conveying mechanism 4, conveyed to a special screw conveyor 6 and dried by the hot air from a drier 5 to <=5% water content. The dried sand is further finely crushed in the screw conveyor 6 by the rotation of the screw and the grain size is adjusted. The separation of sand grains is improved as the water content decreases, and the sand is finely crushed with ease. As a result, the production of <=0.15 mm undersize is increased to 10-20 wt.%, and the undersize ratio of the screen is controlled to 10-20 wt.%.
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