bolts rusted in to cast iron bench

[Burlington Bertie]

I've got two park benches which I bought from Sheffield Council 20 years ago. These consist of cast iron ends coach bolted to wooden planks. I had to replace the wood and the bolts and now it needs doing again. This time most of the bolts wont budge and are rusted in solid.

Applying a heavy hammer has resulted in me breaking a section off one of the castings.

I have managed to drill one of the bolts out at the back, but this was where I could get a straight run at it. Most of the bolts go through the seat and the frame work means there's only 20 cm to play with to get a drill in. I think even an angle drill would have trouble getting into that space unless they also make very short drill bits.

The bolts are 10 mm and project about 6 cm through the metal.

Any ideas how to get them out?

[Dave Plowman (News)]

If the wood is scrap drill or cut through it round the bolts and remove so you can get a grip on the shank with Mole grips etc. Apply lots of heat from a blowlamp. The nuts should then undo.

[sm_jamieson]

Heating up with a blowtorch will often free rusted parts - they do it at the garage all the time. Presumably not when freeing rusted-in petrol tanks. Simon.

[Mike Halmarack]

Get it good and hot, then douse with oil.

[TheScullster]

"Burlington Bertie" wrote

Is there room to grind the heads or nuts off?

Phil

[Andy Dingley]

The usual suspects:

Angle-grinder the nuts / heads off. If these are coach bolts, then destroying the nut should allow them to punch out quite easily. Maybe you need to grinder/gorillate the heads off too out of the wood, then worry about tidying up the stumps in the CI later, when you're got access.

Nut splitter. If you can't take a gruinder to the head, use a much smaller screw-in wedge (Halfords etc) to split the nut.

Heat. A dull-red heat on the bolts will shift a lot of rust. Let them cool before trying to undo them though. Often you use a grinder for phase #1 (heads and wood) then heat for phase #2 (bolt stubs out of the iron).

Electrolysis. Electrolytic de-rusting takes a few days but it de-rusts CI beautifully and it can also often free up rusted bolts. It's certainly the best way to prepare for re-painting - much better than abrasives.

I doubt if any sort of Plus-gas / old brake fluid will work too well on cast iron. WD-40 certainly won't.

Destroy something with extreme prejudice. Concentrate on what you nedd (the iron) and what you don't (bolts / wood). Then be extremely brutal to what you can afford to lose (plasma cutter) so long as it doesn't hurt the piece you need to save. Lump hammers aren't picky enough for this.

Don't use a lump hammer around cast iron. If you do, make sure that the iron is well-supported. It needs to be supported directly beneath, so that tehre's no bending. A block of soft timber with a hole in it is helpful, but even then it's risky.

[Peter Parry]

Cast iron is very strong but brittle - whacking it is never a good idea.

If you haven't already done so cut the wood off close to the ends so you can get at things a bit more easily.

Soak the nuts regularly in WD40 for several days. Contrary to popular prejudice WD40 is one of the best penetrating fluids around. If that doesn't allow you to remove the bolts then apply heat from a blowlamp to the end in the wood. Either you will be able to remove the nut when the metal gets hot or the wood will burn off allowing you to cut the bolt with a hacksaw.

[Burlington Bertie]

Thanks folks. I've already chopped all the wood off and I started off angle grinding the stumps of the bolts off, though decided no to do them all given the problems I was having. The nuts haven't been a problem as they either undo or snap off. It's the shaft which has welded itself into the cast iron.

I think the long term approach is to leave them a few weeks immersed in oil, then some heat and gentle hammering. Who knows some of them may then turn with mole grips.

It's the ones that I cut off flush intending to hammer out with a drift that are likely to be the toughest I guess.

I just looked up electrolytic derusting. That could ultimately be the answer though may take a while.

[The Medway Handyman]

At last! Someone else who thinks so!!!!!

[The Natural Philosopher]

if you use an oxy torch on low oxy you get a reducing flame, which tends to turn the iron rust back into iron.

Blacksmiths often have such, also many car repair places..its often worth a cry for help at these places.