Grinding cement

From experiments to grind cement clinker to —80 pm, as compression is increased from 100 to 300 MPa, the required recycle ratio decreases from 4 to 2.8. The energy required per ton of throughput increases from 2.5 to 3.5 kWh/ton. These data are for a 200-mm-diam-eter pilot-roll press. Status of 150 installations in the cement industry is reviewed [Strasser et al., Tiock Products, 92(5), 60-72 (1989)]. In cement clinker milling, wear is usually from 0.1 to 0.8 g/ton, and for cement raw materials it is between 0.2 and 1.2 g/ton, whereas it may be 20- to 40-in ball mills. 

Figure 2.20. The typical mean dimension of Portland cement particles is 10 pm, which is achieved by grinding cement clinkers in tube mills as shown. During the grinding process, part of the mechanical energy added to the clinker charge is consumed by the work connected with the increase of the surface area of the solid clinker minerals.

Concept Chedl 13.3 Explain why it is important to grind cement into a fine powder. [The answer may be found at www.wiley.com/coUege/callister (Student Companion Site). ... 

Plastic cements are hydrauHc cements that have plastici2ing agents added to Pordand cement during the grinding operation to make them dow better. The primary use for plastic cements is in plasters and stucco. 

When calcium aluminate cements are made by the fusion process, the solidified melt must be cmshed and then ground. The material is very hard to grind and power consumption is high. 

In joining reinforced thermosetting pipe it is particularly important that the pipe be cut without chipping or cracking it. It is also important to sand, file, or grind any mold-release agent from the surfaces to be cemented. Joints are built up layer by layer of adhesive-saturated reinforcement by following the manufacturer s recommended procedure. Application of adhesive to the surfaces to be joined and assembly of these surfaces shall produce a continuous bond and provide an adhesive seal to protect the reinforcement from attack by the contents of the pipe. Unfilled or unbonded areas of the joint are considered defects and must be repaired. 

Air separator Vow (N-S) Similar shape to hydrocycloue, hut higher included angle. Internal impeller induces recycle within classifier. 0.5 to 7.5 2 mm to 38 im to 2100 4 to 500 Used where solids must be kept dry, such as cement grinding. Air classifiers may be integrated into grinding mill structure. 

Frequently ball and tube mills are combined into a single machine consisting of two or three compartments, separated by perforated-steel diaphragms and charged with grinding media of different size. Rod mills are hardly ever used in cement plants. The compartments of a tube mill may be combined in various circiiit arrangements with classifiers, as shown in Fig. 20-59. 

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