What should I do if the lock is rusty and cannot be opened?

　　When there is a lot of rust in the lock, adding pencil powder may not necessarily solve the problem. You can pour gasoline into the lock core, insert the key and turn it repeatedly until it turns freely. Then place the lock on the stove (a similar method will work) with the keyhole facing up to allow the gasoline to slowly evaporate.

　　It should be noted that only gasoline can be used, because gasoline is volatile and will not remain in the lock core. If kerosene or engine oil is used instead of gasoline, it will not volatilize completely. The remaining oil will absorb dust and make the lock more difficult to use.