SLAG CEMENT. REQUISITES AND TREATMENT OF THE SLAG. 645 



Methods of granulating the slag. The success of the granulation 

 depends on bringing the slag into contact with the water as soon as 

 possible after it has left the furnace. The effects of the process will 

 be found to vary with, (a) the temperature of the slag at the point 

 of contact; (6) the temperature of the water; (c) the amount of water 

 used, and (d) its method of application. 



Taking up the last point first it may be noted that two general 

 methods of application of the water have been used. In the first method 

 the stream of slag, as it issued from the furnaces, was struck by a jet 

 of steam under pressure. This method, which was used at one time 

 in slag-cement plants in the Middlesboro district, England, had the 

 effect of blowing the slag into fine threads with attached globules. It 

 is, in fact, much the same as the process still used in the manufacture 

 of mineral wool. From an economic point of view it had the distinct 

 advantage of putting the slag in a condition in which it was easily pul- 

 verized by the grinding-machinery ; but it had certain inconveniences, 

 and has been almost or entirely superseded by the method now to be 

 mentioned. 



The second way in which the water may be applied is to allow the 

 stream of slag as it issues from the furnace to fall into a trough contain- 

 ing a rapidly flowing stream of cold water. Care must be taken that 

 the fall into the trough is not too great, and that the stream of water 

 is deep enough and fast enough, for otherwise the slag will acquire 

 sufficient momentum in its fall to solidify in a mass on the bottom of 

 the trough . This method is in use at all slag-cement plants of the present 

 day, being occasionally modified by the use (either in addition to or 

 in place of the flowing stream of water in the trough) of a jet of water 

 playing on the slag before it strikes the trough. 



The following two examples, taken from present-day practice at 

 American slag-cement plants, will serve to indicate two methods, dif- 

 fering in minor details only, of slag granulation. 



At the first plant the furnaces are located on an embankment 

 about 8 feet above and 20 feet away from a standard gauge-switch 

 track. A rectangular trench about 1 foot in width is dug from the 

 furnace to near the edge of the embankment. Here a section of semi- 

 circular sheet-iron troughing, 12 to 15 inches in diameter and about 10 

 feet in length, meets the trench. The inner end of the trough is fixed, 

 and is at such a level that the bottom of the trough is about 6 inches 

 below the bottom of the trench. The outer end of the trough is free 

 and supported by wire ropes so that it can be readily swung into 

 position over a box car on the switch track below. 



