Cold rolling steel is one of engineering’s more interesting accomplishments - a way to literally change the very properties of metal so as to better accommodate the types of structures we can build. This applies to buildings, to bridges, to air and marine infrastructure and other metal-based structures.

Cold rolling changes the properties of metal in three ways:

- It reduces the size and thickness of a metal.
- It increases the strength of the metal, for better weight-bearing capability.
- It makes the metal harder.
- It makes the metal less flexible and more prone to cracking

The process begins with a simple piece of metal, perhaps steel or copper or even aluminum or tin. This might typically be a steel bar, a steel plate or just sheet metal. Note that the sheet or bar is typically at room temperature (”cold” rolling does not imply any manoeuvre involving penguins or walruses).

The metal piece is passed through at least two rollers (why it is called “rolling”) that are calibrated for a controlled weight. The rollers’ job is to decrease the thickness of the metal sheet or bar, simultaneously increasing both its hardness and its strength. The trade -off - and there are almost always trade-offs in life - is that the cold-rolled steel or copper has less ductility than the original metal. This means the engineers have to be more careful how they use the piece, as it will be more less flexible and prone to cracking and fractures.

Interestingly, there are more than one cold rolling process. Here are four different cold rolling processes, each one serving a unique purpose:

>> Quarter Hard Cold Rolling

This is the process to use if you will want to bend or curve the metal later on. A sheet using the quarter hard process can be bent or rolled on to itself without a risk of fracturing.

>> Half Hard Cold Rolling

Metal cold rolled with the Half Hard process can be bent only to 90 degrees, which is still a faire amount.

>> Full Hard Cold Rolling

Cold rolled metal with the Full Hard process can only be bent to 45 degrees. This is the least flexible process, but is perfectly fine for most purposes.

The three cold rolling process we have just seen, Quarter Hard, Half Hard and Full Hard, can reduce the size of a piece of metal by up to 50 percent, increasing both the strength and hardness of the metal, but also reducing its ductility.

>> Skin-rolling Cold Rolling

Skin-rolling is used to reduce the thickness of a metal by just 0.5 to 1 percent. This process creates a smooth metal sheet that is significantly ductile than the other three procedures, and is preferable in a situation where there might be a fear of cracking or fracturing.

Cold rolled metal is normally made into sheet metal, foil metal, and plate metal. These pieces are typically smaller than the same (all other things being equal) metal created through hot rolling. Metal produced through cold rolling will be used in varying different types of applications, from industrial products such as steel ducts, tubes and pipes work to consumer products such as aluminum cans.

Cold rolling and hot rolling (otherwise known as induction bending) are very different creatures. In cold rolling the metal remains at room temperature; in hot rolling the metal is - you guessed it - heated to a very high temperature.

This information was provided by Paramount Roll and Forming, a leading metal rolling company in southern California. They have been rolling steel pipe, tubes, beams, sheets, angles, plates and more since 1963, and obviously have done a lot of both hot and cold rolling.