A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . by the fanningaction of the upper rowof blades. The finishedproduct is then dis-charged through a spoutwhich may be placed atany one of four quartersof the mill. When themill is in operation, it iscontinually handlingonly a limited amountof material at any onetime. As soon as thematerial is reduced tothe desired fineness, itis lifted out of the pul-verizing zone and dis-charged from the mach-ine. It is customary tostore the cement in bulkand weigh it out intobags or
A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . by the fanningaction of the upper rowof blades. The finishedproduct is then dis-charged through a spoutwhich may be placed atany one of four quartersof the mill. When themill is in operation, it iscontinually handlingonly a limited amountof material at any onetime. As soon as thematerial is reduced tothe desired fineness, itis lifted out of the pul-verizing zone and dis-charged from the mach-ine. It is customary tostore the cement in bulkand weigh it out intobags or barrels as re-quired for automatic weighingmachine similar to thatshown in Fig. 230, page 713 (except that it is single instead ofdouble), is a convenient apparatus for bagging. With this machine aweighing gang consists of three men. The nominal capacity of a singlemachine is 3 000 bags in ten hours, and the authors have known as manyas 3 Qoo bags to be filled in this time. In outlining the cement machinerj^ no reference has been made to themethods for conveying the material from one machine to another. Bucket. Fig. 236.—Lehigh-Fuller Mill. (See p. 717.) CEMENT MANUFACTURE 719 conveyors, belts and spiral conveyors are all more or less used. A. spiralconveyor is a helical blade on a revolving shaft, set in a square 01 circulartrough or tube of larger size than the spiral, so that the material packsaround the circumference, and the blade comes in contact only with thepowdered material. Plaster of Paris (calcium sulphate CaSOJ, or gypsum (CaS04 + 2H2O)the same substance in crystalline form, is an important addition to cementas a regulator of its setting, and from i to 2% is used in nearly all Port-land cement manufactories. The gypsum must be added after the calci-nation and before the final grinding, in order to insure the proper result The laboratory of a cement plant is an important feature. Not onlymust the chemical composition of the raw materials and the finis
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