Extreme manufacturing danger: the steel mill cobble

  • While a steel mill cobble might be fascinating to watch, akin to a light sabre, they are extremely dangerous and unpredictable.
  • Once a steel mill cobble begins it will only stop when the individual line of steel comes to an end.
  • We are dealing with materials touching temperatures in excess of 1200°C which would cut through human limbs like a knife through butter.

While many of us will be well aware of the dangers of working in a steel mill, the excessive temperatures and molten steel, few people will have heard of the steel mill cobble. Unfortunately for those working in these challenging and dangerous environments the term “steel mill cobble” does not really reflect the dangers associated with it. So, what is a steel mill cobble and how do they occur?

Shaping molten steel

The temperature of molten steel is in excess of 1300°C (2500°F) and it goes without saying that those in the vicinity of strips of molten metal need to be extremely careful. This steel is heated to such temperatures to make it more manageable and allow strips to be gradually reduced in diameter to the required size. This is done using a line of rollers through which the steel is pushed (akin to a conveyor belt) to gradually reduce the diameter of the strip. At the end of the process when the required diameter has been achieved the molten steel is cut by huge chopping blades which are able to operate at extreme temperatures.

The rollers are also designed to accommodate such excessive heat but there are instances when either a roller malfunctions or the end of a line of steel cracks and separates and is unable to pass through a roller. This is where the fun begins!

What is a steel mill cobble?

There are images aplenty of steel cobbles because while they are extremely dangerous they happen on a daily basis in many steel plants. Indeed when producing steel via this process you will regularly hear people quote the cobble rate which is in effect the rate of waste.

A cobble will occur when there is a roller malfunction, the line of steel deviates from the roller path or, as mentioned above, the end of the steel splits. All of a sudden the continuous roll of steel will come to an abrupt halt although the steel behind is still being pushed through the working rollers at speeds which can reach up to 30 mph. The steel at the front of the line has nowhere to go, the pressure builds very quickly, the material begins to coil up and then all of a sudden it will flick into the air creating enormous loops which have been likened to a “light sabre”.

Interesting to watch, dangerous to be near

The size and shape of a steel mill cobble will vary depending upon the diameter of the steel and the speed of the steel line behind it. When you consider these steel cobbles consist of materials heated to well over 1000°C there is really nothing you can do once a cobble has begun – except clear the area!

The cobble will continue to grow until the individual line of steel has run through the system at which point the cleanup process begins. Trying to stop a steel cobble mid-flow could potentially damage the rollers as the material cools and becomes almost unmanageable. Steel cobbles have been known to not only fill floors and run across machinery but also become attached to the roof of a building. You can imagine the potential dangers when literally molten hot material comes into contact with compostable materials.

Over the years there have been numerous accidents and unfortunately a steel cobble will pass through any part of the human body like a knife through butter. Thankfully great strides have been made in the area of safety surrounding steel mills. However, while steel mill cobbles are extremely dangerous and still common place across the industry they can be fascinating to watch.



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