How to unscrew the bottom cover of thermos bottle?

After the shell of iron thermos is rusted, the bottom cover is difficult to unscrew, which makes it difficult to replace the bottle liner. Take a piece of wood with a length of 50 cm, a width of 3 cm and a thickness of 2 cm, put the thermos bottle horizontally on the workbench, put the wood near the thread of the bottle shell, gently press it, roll it back and forth for more than 65,438+00 times to loosen the corroded thread, and then drop a little lubricating oil into the thread to unscrew the bottom cover easily.