SLAG CEMENT: LIME, MIXING AND GRINDING. 661 



this prepared lime are then mixed, and the mixture receives its final 

 reduction in Davidsen tube mills. 



At the plant of the Birmingham Cement Company,* at Ensley, Ala., 

 slag is obtained from the furnaces of the Tennessee Coal and Iron Com- 

 pany, located in near-by towns. The slag is granulated at the fur- 

 naces. On arrival at the mills, carrying about 40 per cent of water, 

 it is dried in Ruggles-Coles driers. Two of these, of the A2 style, 

 are in operation. After drying, the slag and slaked lime are fed together 

 to West ball mills, four of which are in use, and the mixture is finally 

 reduced in West tube mills. 



The Southern Cement Company, at North Birmingham, Ala., dries 

 its slag in a style A2 Ruggles-Coles drier. The dried slag is crushed 

 in a Kent mill. After mixing with the slaked lime, the final reduction 

 takes place in West tube mills. Two brands of slag cement are mar- 

 keted. One, a normal slag cement, is said to average about CaO 55 per 

 cent, Fe 2 3 , A1 2 3 , 12 per cent, Si0 2 , 27 per cent. The other brand 

 is quicker setting and is said to carry about 10 per cent less CaO and 

 about 10 per cent more Si0 2 . 



At Skinningrove, England, slags were used of a composition varying 

 between the following limits: Si0 2 , 30 to 32 per cent; CaO, 30 to 33 per 

 cent; A1 2 O 3 , Fe 2 3 , 25 to 28 per cent. The slag on issuing from the 

 furnace was run into w ter; ground, before drying, under edge runners, 

 and dried on iron plates in a drying chamber. The dried material was 

 ground under millstones; sieved, and mixed with lime (which had 

 been slaked and screened) in the proportions usually of lime 33 Ibs., slag 

 100 Ibs. The resulting cement varied in composition between the follow- 

 ing limits: Si0 2 , 24 to 26 per cent; CaO, 45 to 47 per cent; A1 2 3 , 

 Fe 2 3 , 20 to 22 per cent. 



At Vitry, France, the slag is struck by a jet. of water immediately 

 upon issuing from the furnace and carried by it into a masonry storage 

 tank. From this tank the granulated slag is elevated and carried to 

 the mill. Five driers of the style shown in Fig. 162 are employed, the 

 dimensions being slightly different from those used at Choindez. After 

 drying the slag is sieved, to remove the coarser particles, passed through 

 six mills of different types, and again sieved. After having been thus 

 reduced to the proper fineness, it is mixed with the slaked lime in ball 

 mills operated discontinuously ; the proportions being about 40 Ibs. 

 of lime to 100 Ibs. of slag. 



* Eckel, E. C. Engineering News, Jan. 23, 1902. 



