Tuesday, August 25, 2015

Ring the Bronze Bell: Why Using Bronze Will Provide Longer Product Lifetimes


While visiting Philadelphia the other week, I was walking along Independence Mall, where the Liberty Bell is located. I was astonished by the long, winding line of pedestrians eagerly awaiting their chance to view the historic monument with its famous cracked structure.

For centuries, bell makers relied on two main ingredients to ensure longevity and reliability: tin and copper. Both are relatively soft metals that will deform on striking. By alloying the two elements a harder and more rigid metal is created but also one with more elasticity than the use of one of the metals alone.  This allows for a better bell resonance and causes the bell to "vibrate like a spring when struck," (a necessary quality as the clapper may strike the bell at speeds of up to 600 miles per hour). The forces holding the tin and copper together cause vibrations rather than cracks when the bell is struck which creates a resonant tone. This metal combination also results in a tough, longwearing material that is resistant to oxidation and subject only to an initial surface weathering. Verdigris forms a protective patina on the surface of the bell, which coats it against further oxidation

The Liberty Bell weighed 2,080 lbs. at order. Over 200 years since its first ring from the tower of Independence Hall, the Liberty Bell not only symbolizes our country’s freedom, but it also shows how strong of a casting alloy that bronze is and how other products can have a similar lifespan. Now, I know you’re thinking, “Well what about the crack?” 

For me, if it had been made with a better combination of copper and tin, it would have remained in tact. You see even the hardest and strongest bronze contains large amounts of tin and little lead though an alloy with more than 25 per cent tin you will have a low melting point and the material will become brittle and susceptible to cracking. 

To put things in perspective, bronze highlighted much of the Ancient Egyptian lifestyle, from which artifacts still exist today. The Egyptians used it for weapons, armor, tools and, most famously, sculptures – all of which can be found in museums today, still in impeccable condition. So it truly boils down to how it’s cast and the chemistry and cooling!

Bronze can provide products a longer lifetime because it is harder than pure iron and copper. As well, it is also more resistant to corrosion and more malleable than other alloys.

Cast and sintered bronzes perform an important anti-friction function as bearings in millions of home products, automobiles and trucks, and in virtually all heavy industrial equipment, allowing for protection and thus, longer lifespans.

This topic trails back to a previous blog post I wrote, titled “A Sacrificial Metal: Why Bronze is So Selfless.” Although it discusses how bronze can be used to protect other metals, it also detail how strong and durable it is as an alloy.



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