metal bel-lows mechanical seal

例句：

1. 1. The car is made of steel.
   这辆车是用钢做的。
2. 2. He found a piece of gold in the mine.
   他在矿井里发现了一块金。
3. 3. Copper is often used in electrical wiring.
   铜经常用于电线的制造。