GB425048A - Improvements in the manufacture of portland cement - Google Patents

Abstract

In the manufacture of Portland cement, the calcareous material is less finely ground than is usual for normal Portland cement, the clay is either coarsely or finely ground, and the materials are burned in the kiln in such a manner that some of the lime remains uncombined, this free lime in the clinker being then changed to calcium hydrate without substantially hydrating the cement, e.g. by treatment with steam at 170-400 DEG F., during or after the grinding. The coarsely crushed and pulverized calcareous material can be mixed with the clay before it enters the kiln, and the mixture may be dry, semi-dry or in a slurry state. The mixture is not finely ground together, but if desired the calcareous material may be coarsely pulverized together with the clay. In no case will the residue of raw mix on a No. 170 sieve by less than 20 per cent, and in general it will be between 20 and 45 per cent. Instead of mixing the materials before entering the kiln, the clay may be fed in separately, e.g. by being blown into the kiln by preheated air. The resulting cement may be divided by passing it through a suitable separator into two parts, one part containing a larger share of the calcium hydrate than the original product, and the other part containing a smaller share. Specification 389,872 is referred to.