Ductile Iron and Franklin Submersible Turbines… not just jargon

Advertising and product literature are full of jargon and buzz words. They are thrown at us with such authority, with such confidence, that we are made to think something must be better because it sounds better. My cell phone has an “advanced Lithium Ion battery”. Must be better… I guess… not sure why.

I thought of this recently while reviewing a literature piece for Franklin Electric’s ST Series of turbine pumps. The discharge brackets, suction brackets, and the bowls are all made from ductile iron. I like the way that sounds, but my bet is that most people in our industry can’t tell you what ductile iron is, or why it’s better. Here’s why it actually is…

As it turns out, ductility refers to the ability of a material to flex without breaking under tensile stress. That is, from stretching, pulling or bending. Ductile is the opposite of malleable, which is a material’s ability to bend and deform without breaking under compressive stress, such as being beat with a hammer.

Ductile iron isn’t just iron, but an alloy. Alloys really took off a few thousand years ago when someone discovered that mixing melted tin with melted copper created a new metal that became known as bronze. This metal had completely different properties than either copper or tin. In this case, it was greater hardness and a superior ability to hold an edge. This turned out to be especially handy in the manufacture of the weaponry of the time.

In the case of the alloy ductile iron, it’s a melted combination of iron, carbon (in the form of graphite), and silicon. What’s remarkable is that the graphite and silicon only make up about 6% of the total material. But, what really gives ductile iron its ductility is that at the microscopic level, the graphite is in the form of spherical nodules. This is what inhibits the creation of cracks and gives ductile iron its superior “ductility” over other materials such as grey iron, where the graphite is in the form of flakes.

So, as it turns out, ductile iron is perfect for those parts of a submersible turbine that get the most bending and pulling stresses during installation and throughout the pump’s lifetime. It really is better and not just jargon.

One thought on “Ductile Iron and Franklin Submersible Turbines… not just jargon

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