Using Heat Expansion on Iron Mills No.36 Base Plug?

[peregrinvs]

I need to remove the cast iron base plug from a rusted WWI Mills No.36 drill grenade which has seized into the body. It occured to me I could try rapid heating and cooling with a blow torch to loosen it, but I am worried there is a risk of it cracking as cast iron is relatively brittle.

Has anyone else tried this (or something similar) and did anything nasty happen? How much rapid heating/cooling can the metal handle?

Thanks,
Mark

 

[BMG50]

I assume that this mills bomb is already deactivated and there are no filling detonators or caps in the thing. When trying to expand metal to remove an object you need to heat only one part, usually the outer. Heat both parts, in your case the plug and body you will find that they will expand together. Heat from a hot air gun will be enough to expand the outer body, while it's hot use some penertration oils to soak into the threads.

 

[HAZORD]

In addition to just heating, you can temperature cycle the item. Stick it in the freezer of your refrigerator so it is completely cold, then heat the outside. The outside will expand away from the cold plug. It also helps if you can beat on the item with something that is hard enough to shock it, but not hard enough to mark it. The sharp blows will help break the two items apart from each other. You can use wood blocks, a rubber or leather hammer etc. I usually heat up the outside piece and beat on it when it is still hot and expanded. When the tone of the impact changes, you know the parts are loose.

 

[pointblank0]

I had this problem with a mills where the center tube had been ripped out leaving the thread screw bit still rusted in. I gently broke down the rust within the threads with a drift and careful hammer blows. I then covered the body in cloth and clamped it in a vice between two bits of thick card and heated the uncovered top (at the bottom of the vice) with a propane torch and gently tapped against the thread on the jammed piece with the drift. It didn't take long and it wasn't hard work, but you will need to be careful not to damage the body or threads, so light tapping there. Also a tried and tested technique for removing those filler plugs that previous owners had tried to remove and ruined the slot, but you will need to get a stud extractor or similar in there. Also, if there is any original paint on the body, do not heat that part directly, or you will lose it! Oh and please make sure it is inert before torching it in a vice