Method of torch-cutting steel

#The instantly disclosed invention relates generally to a method of cutting steel; and, more particularly, to a method of torch cutting slab, bloom or billet steel. Slab steel is produced by the continuous casting method. Continuous casting is the process whereby molten steel is solidified into semi-finished billets, blooms or slabs for subsequent rolling in the finishing mills.

#The continuous casting process begins by pouring steel from an electric or oxygen furnace into a ladle. The ladle is raised on to a turret that rotates the ladle into the casting position above a tundish. Liquid steel flows out of the ladle, into the tundish and then into a water-cooled copper mold. Solidification begins in the mold and continues through the forming process. Finally, the billet, bloom or slab is torch or machine-cut, discharged and stored for further processing.

#It is during the torch cutting stage of the casting process that the instantly disclosed method contributes to the efficiency of the process and the quality of the finished product. Near the end of the casting process, the slab, bloom or billet is cooled, straightened and transferred on roller tables to a cut-off machine, which cuts the product into ordered lengths. This cutting is typically effected by torches. And torches, in the slab, bloom or billet casting process, are typically fueled by oxygen and a fuel gas. Fuel gasses are frequently hydrocarbons, such as natural gas (methane). Natural gas is a commonly employed fuel gas because it does an adequate job, it's readily available and it's relatively inexpensive.

#As mentioned supra, the primary objective of this disclosure is to introduce the use of propylene gas to the slab steel industry to improve the speed, efficiency and effectiveness of their slab splitting operations. Propylene is an ideal cutting fuel for the continuous casting process. It is readily available. It's a commodity feed stock for the plastics industry and is currently the tenth most produced chemical in the world. Because of its chemical properties, it has a higher BTU content and flame temperature than methane, and, when used as a cutting fuel, it burns hotter and cuts faster than methane.

#In practice, slab steel is cut into manageable lengths by bringing the surface of the slab to an ignition temperature of about 1500° F. At this temperature, the slab has a bright reddish orange glow. With the slab at this temperature, a cutting torch is positioned about 5″-7″ above the slab. The torch is adjusted to deliver between 5-25 psi of propylene and between 30-50 psi of oxygen to the slab surface. Of course it is desirable if, during the cutting procedure, the cutting proceeds at the speed of the casting, and the increased cutting speeds obtainable by the use of propylene is exactly what has been demonstrated in the mill.

#Test No. 1. A 9″ thick hot slab was cut into slabs at cutting speeds of 12″/min. with the use of natural gas as the cutting fuel. When propylene was substituted for natural gas, the cutting speed was increased to 19″/min, and the kerf was reduced by {fraction (3/16)} ″. (AK Steel)