For easier transportation and storage, a long sheet of steel can be wound or ‘coiled’. White goods manufacturers can ask for their steel to arrive delivered in coils, before cutting it themselves to various lengths at their own facility. Prior to being rolled up, the long sheet is produced to a required thickness in accordance with the waiting client’s particular specifications. But what’s the best type of steel to order: hot rolled or cold rolled?
Heating above re-crystallisation temperature
Hot rolled and cold rolled steel are basically two different types of metal. Many people wrongly assume that steel is only ‘rolled hot’ as that makes coiling the metal easier (being more pliable), before being allowed to cool down and then distributed. But there’s more to it than that. At a metal processing mill steel is handled differently. The ‘rolled’ part of ‘hot rolled’ doesn’t even relate to the coiling or wounding of the sheet before transportation, in fact! It’s to do with the manner in which the metal is processed at a mill.
With hot rolled steel the metal is passed through rollers (possibly several times), but only after it’s been heated to a certain temperature. Working from a spec’ sheet mill workers will set the rolling machine to the necessary temperature level, then continue to control the machine as it shapes the metal into the client’s desired physical dimensions. The suppleness of the metal comes from it being heated above its re-crystallisation temperature until the required form is achieved.
Beware of shrinkage
For hot rolled steel a higher processing temperature is used during rolling. This allows for quicker, smoother rolling, meaning that the metal objects ordered can be delivered to clients faster (than cold rolled steel). Purchasers should beware, however. They need to bear in mind that hot rolled steel may shrink a little in size as it cools. This is definitely something to remember when ordering.
Yes, hot rolled steel usually comes cheaper than cold and can be a fantastic choice where wholly suitable, but if you’re manufacturing goods produced in accordance with exact dimensions and tolerances, cold rolled steel’s what you want. What’s more, it can be used for a wider range of surface finishes, making it a flexible option and worth paying a little more for.