Have you ever wondered how different things are created? How a semi-truck is produced or what your water heater is made out of? If you are anything like me, this is a daily occurrence. The likely answer is that it started in a rolling steel mill in the form of a slab of unfinished metal and was worked into a hot rolled coil.
How Hot Rolled Steel is Made
Hot rolled steel is the most basic carbon steel product mills produce. It is used to manufacture products in which the surface finish is not critical, including automotive, truck frames, water heaters, agriculture equipment, compressor shells, guard rails and the list goes on.
The Heating Process
The process in which hot rolled is produced begins with heating slabs of steel to approximately 2,300 degrees Fahrenheit. The amount of heat directly affects the properties of the steel. Meaning, if the temperature is not high enough it can cause defects in the material. This is likely due to carbides (compound of carbon) and nitrates (polyatomic ion-an even more complex term) not fully dissolving.
When the hot material is being transferred from the furnace it reacts with the oxygen in the air. This reaction forms a mill scale or a flaky surface of iron oxides. The mill scale can affect the surface quality of the hot rolled steel if left alone. To remove the iron oxides the material is then sent through a mill scale cleanse. It is sprayed with high pressure water (much higher than your power washer at home).
Rolling Mill and Stands
The cleansed material is then sent through a rolling mill and is rolled from a thickness of roughly nine inches to an inch. The process consists of a series of four to five stands (set of rollers) that decrease the thickness and increase the length by horizontal rolls. The material is also squeezed vertically to control the width.
At this stage the material’s ends are sheared to create a transfer bar. The transfer bar is sent through another series of stands to further reduce the thickness to the desired sheet gauge.
The Cooling Stage
The flat-rolled steel is delivered across a runout table that consists of cooling sprays. The cooling rate may be modified for each strip to create the desired properties of the coiled end product.
After the material is cooled it enters coilers. Once coiled, the product is ready to be delivered to service centers, like OFR Metals, for further processing. It may also be delivered straight to fabricators.
The hot rolled material can also endure additional processes, including pickle and oiling, cold rolling, and other coatings.
The process of creating hot rolled steel sheets is much more interesting with visuals. Check out this great video to learn more about the hot rolling process.