Transactions . a criticism I will state that it was impossible to get a screenedproduct of original unground ore for this purpose. However, the returnand mixed feed tests will indicate that the classified sands did not inter-fere with the good work of the mill, while small tests have proved to usthat the sands were not appreciably harder than the average of the ore. 520 CHILEAN-MILL PRACTICE AT PORTLAND MILL Under the fine-feed conditions, the power upon the mill was held at amaximum, but at that it was found impossible to get more than 80 percent, of that normally used during coarse-feed cond
Transactions . a criticism I will state that it was impossible to get a screenedproduct of original unground ore for this purpose. However, the returnand mixed feed tests will indicate that the classified sands did not inter-fere with the good work of the mill, while small tests have proved to usthat the sands were not appreciably harder than the average of the ore. 520 CHILEAN-MILL PRACTICE AT PORTLAND MILL Under the fine-feed conditions, the power upon the mill was held at amaximum, but at that it was found impossible to get more than 80 percent, of that normally used during coarse-feed conditions. As tonnagewas increased, the mill gradually filled up above the screen; yet the powercould not be raised. But in return for the limited power that may beforced into the miU for conversion into work, by reduction of the ore, thatdegree of reduction, combined with its tonnage, is not sufficient to bringthe mechanical efficiency to within 80 per cent, of that where coarse Chilean Mills with 18 Mesh Screens. Reciprocal Mesh Fig. 4.—Plot sheet No. 3. feed is maintained. See Table 3. The Chilean mill is not a fine grinder,at least in being able to produce efficiently the extreme fines that a ball-mill is callable of giving. Hence, it is natural to expect its efficiency tofall when given a feed such that onl}- extremely fine grinding will allowit to attain a respectable mechanical efficiency. Greater tonnage of thisfine feed is its only hope, and that it cannot handle due to the lack ofquick-enough reduction to pass out through 20- or 30-mesh screens. If the mill is running normally with coarse feed at 110 hp. and issuddenly stopped, the mullers and die will be found to have betweenthem about 2 in. (5 cm.) at the closest point of contact, of combinedoriginal feed of coarse mesh, and from that every size down to the fines LUTHER W. LENNOX 521 wliich have dropped back after having been rejected by the 2 in. at the edge of mullers and die becomes 5 in. of mixed size
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
