Manufacturing Skyway Cement requires two basic processes, granulation and grinding.
This process transforms molten slag into granules. Skyway Cement receives granulated slag from a US steel manufacturer in Gary, Indiana. In the blast furnace at the steel works, slag is produced when the mineral components of the metal refining process separate from and float on the molten iron. The iron is drawn off to be further refined into steel and the slag is drawn off to be granulated. Granulation occurs when the molten slag (2,650° F to 2,800° F) is quenched with large quantities of water. This results in GBFS, granulated blast furnace slag. The granules are similar in size and appearance to beach sand. GBFS is a non-metallic product, which is similar in composition to Portland cement clinker. After granulation, the material is transported to Skyway Cement Company’s plant to be ground into Skyway Cement.
The first step of the grinding process requires the slag to be dried down to about 2.5% moisture. These dried granules are then pre-ground with two high pressure roll presses. These machines consist of two large rolls, forced together by high pressure hydraulics. The granules are fed between the rolls and crushed. To increase the fineness through this circuit, a portion of the crushed granules is recirculated through the press. The pre-ground material exiting the press is fed to the ball mill, a large tube 15 feet in diameter and 50 feet long partially filled with small steel balls, which further grind the material to ASTM C989 and AASHTO M302 specifications.