Q. Do the black strings stretch on Max Train?
A. Springs are made out of special steel that is very, very strong. Steel is mostly made of iron, but they add tiny amounts of other things to make it stronger or make it so it won't rust. Spring steel has more than the usual amount of carbon added to it, which makes it super hard to bend. Carbon is an element that many things contain, all plants and animals. Your pencil lead isn't really lead at all, it is carbon. Diamonds are crystals of carbon.
Carbon is common and not rare or expensive. The reason they don't add it to all steel is that it makes the steel very hard to work with. It's difficult to drill holes in, and you can't weld it (join it to another piece of steel by melting it). So mostly just springs are made of this material. The other thing they do to make springs very strong is heat treatment. If you heat and cool steel in the right ways, you can change it's properties, for example make it harder or stronger.
Originally uploaded by Big-E-Mr-G.
To see how this works, you can heat treat a coin. Have your Mom help you with this. Get a very shiny nickel, dime, and quarter. Set them on the oven burner on "high". When the burner turns red hot, you will see the coins gradually turn different colors. Probably browns and blues. Use tongs to take them off the burner when you like the color.
Drop them in a glass of ice water. You now have colored coins. Heat treatment works just like this but at higher temperatures. Tell your Mom you have to keep them as part of your scientific research.
So springs are made of very strong steel. If they are designed properly, they will not break, even over long periods of time. But they do tend to, "break down". This means if they are pushed on for many years over and over, they tend to get a little shorter over a long period of time. So now they aren't quite as springy as they used to be. Sometimes they have to be replaced because of this.
— The World’s Best Mechanical Engineer
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