426 



CEMENTS, LIMES, AND PLASTERS. 



The omission of separators in cement-plants. Practically every 

 writer who has discussed the crushing practice at American Portland- 

 cement plants has noted and deplored the absence of separators. In 

 spite of this general unity of opinion in the subject, only a few plants, 

 to the writer's knowledge, are now equipped with any separators, and 

 none have as many as might be used. In view of the fact that Ameri- 

 can Portland-cement practice, so far as crushing methods are concerned, 

 is to-day far ahead of crushing practice in ore-treatment works, this 

 apparent disregard of one great principle of general crushing practice 

 seems to require some explanation. It will not do merely to assume 

 that separators are omitted because the advantages to be gained from 

 their use are not understood by designers and managers of cement- 

 plants, for that amounts to charging a peculiarly expert clan of mechan- 

 ical experts with gross ignorance. In the opinion of the writer, the gen- 

 eral omission of separators is entirely justified by certain conditions 

 peculiar to the process of Portland-cement manufacture, and the general 

 use of separators would be a serious error in this business. As this 

 opinion may not be generally accepted, and as the grounds on which 

 it is based have never been discussed in print, the advantages and dis- 

 advantages of separators may be worth discussing in some detail. This 

 is particularly necessary because the writer realizes, and freely admits, 

 that the views which he holds may be proven to be based on incorrect 

 premises. In that case a relatively brief series of experiments, which 

 could be carried on in any cement-mill, would be of great service to all 

 interested in the technology of the cement industry. 



Advantages of separators. In crushing any material, if the only 

 things to be arrived at are low cost of crushing per ton of product and 

 high tonnage of product per hour, one fact may be regarded as firmly 

 established; that is, that it is an error to feed to any machine (of the 

 series of reducers employed) material fine enough to go to some machine 

 further along in the reduction process. Beginning with the first or 

 coarsest crusher of the series, while most of its product will only be 

 fine, a certain part of its product will be sufficiently fine to be passed 

 on to the third or even fourth reducer. If this be done the product 

 per hour of the series will be greatly increased, each machine will be 

 working on material of fairly uniform size, and the cost of crushing 

 per ton will be greatly reduced. 



Applying this to the Portland-cement industry it is probably safe 

 to say that in a series of reducers (consisting for example of a coarse 

 crusher, a fine crusher, a Williams or ball mills and tube mills) the 

 product per houi of the series could be increased at least 50 per cent 



