680 CEMENTS, LIMES, AND PLASTERS. 



Hardening in steam-cylinders. A new method of slag-brick manu- 

 facture has recently been introduced * in Eng and. In this process 

 the use of lime is dispensed with (except when slags carrying less than 

 35 per cent CaO are used), while a hardening cylinder is employed exactly 

 as in the manufacture of lime-sand brick (see pp. 136-140). The slag is 

 allowed to cool normally; it is then broken up and fed to an edge-runner 

 mill, where it is crushed and ground, and falling thence into a deep 

 pit under the mill, it is collected by an elevator and thrown on a 

 10-mesh screen All capable of passing this goes to the mixer, the 

 coarser particles being rejected and returned to the mill for further 

 grinding. "The ground slag is moistened in the mixer with from 5 to 

 10 per cent of water, and is then delivered by the mixer into the brick- 

 making machine, where it is molded into bricks under great pressure, 

 the pressure employed being from 100 to 150 tons on each brick. As 

 the bricks are made they are stacked onto steel platform-wagons made 

 to carry from 700 to 800 bricks. The loaded wagons are allowed to 

 stand for twelve hours, to allow the bricks to take a slight initial set, 

 after which they are run into the steel chamber, and the bricks are here 

 subjected to the action of steam at a pressure of from 105 to 120 Ibs. 

 per square inch. Ten hours under this treatment is sufficient to harden 

 the bricks and render them on withdrawal ready for building purposes. 



" It is necessary that the machinery employed should be of a very 

 strong and durable character. For effecting the grinding an edge-run- 

 ner mill is most suitable, as it is not easily put out of order by the iron 

 which is often found in the slag in large pieces. The roller rims and 

 false bottom should be of steel, preferably manganese steel; and the 

 perforated grate should also be of steel, the rollers should be made 

 of a suitable weight, depending upon the hardness of the slag generally 

 from three to five tons each. Their width should not exceed 12 inches. 



" A specially designed brick-making machine is employed. This con- 

 sists of a rotating table containing the molds, a feeding-pan, and power- 

 ful toggle-press. As the table revolves, the molds pass alternately under 

 the feeding-pan where they are fed with the charge of material, then 

 under the press, and a further rotation brings the mold over the ejecting 

 plunger and the brick is discharged ready for removal. The machine 

 is capable of exerting a pressure on each brick of 150 tons, and is fitted 

 with a simple contrivance to insure the corners of the bricks being well 

 pressed up. Its operation is first to give the material in the mold at 



* Sutcliffe, E. R. Utilization of blast-surface slag. Amer. Mfr. and Iron World, 

 vol. 74, pp. 555-563, May 5, 1904. 



