Finish-Grinding of Cement Clinker

Finish-Grinding of Cement Clinker Typically the hot clinker is first cooled and then ground in a compartment mill in closed circuit with an air classifier. To crush the clinkers, balls as large as 5 in may be needed in the first compartment. A roll press added before the ball mill can reduce clinkers to a fine size, and thus reduce the load on the ball mills. The main reasons for adding a roll press has been to increase capacity of the plant, and lower cost. 

Calcined clinker is ground in ball mills, mixed with gypsum, and shipped in bags or bulk. Figure 4-7 depicts finish mill grinding and cement shipping. The type of fuel used to make clinker does not affect these operations. 

A quantity of sulphate (in the form of gypsum or a mixture of gypsum and anhydrite-II) is always added to the Portland cement clinker in the finish grinding... 

Both these reactions would cause excessively rapid setting of the cement paste. Sulphate, in the form of gypsum or anhydrite-ll, is therefore added as a retarder, interground with the clinker in the finish grinding mill. The hydration reaction in the presence of sulphate proceeds as follows ... 

About twenty years ago the specific rate of grinding media wear in finishing mills (clinker grinding) was in the range of 800 to 1000 g per t of cement, whereas the corresponding figure is now only about 50 to 120g/t. 

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