Cleaning Rust Off Cast Iron

Needle guns are very inexpensive to buy from the likes of clarkes machine mart etc ( although I haven't actually used one of theirs) but I think quite a large capacity compressor is required.

Reply to
ChrisR
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70-odd quid, which is quite expensive for an air tool.

I guess you're posting from a sailing group 8-)

Reply to
Andy Dingley

£35.19, uses 4cfm, Machine Mart.
Reply to
Graham Frankland

Ah the sounds of many a cruise ship refit, wandering back from the nearest bar to the melodic song of the night shift needle guns shooting th S**T out of the upperworks !

Oh the joys just dont think about trying to make a phone call afterwards Doug

Reply to
Doug Noble

Yip, phone your local undertaker

Reply to
Davie

Whatever method you use if you end up with bright metal it is important to prime it VERY quickly before the salt air gets to it.

I was chatting once to a surveyor who had supervised the antifouling of a large ship. He noticed that a layer of ferrous chloride was forming less than 2 hours of shotblasting.

Reply to
Tony of Judicious

Just a word of caution and something to be checked if using rotary brushes.

Blakes state that such brushes polish the metal and can cause adhesion problems for blacking. I know we are probably talking antifouling here but to be sure I think I would follow the brush up with a grinding disk to give the keel surface a key. This should be fairly fast and remove the worst of any surface corrosion that took place after rotary brushing.

Reply to
Tony Brooks

a grinding disk will do exactly the same thing!

its the raw speed at which the disk/brush passes over the metal that causes the polishing. A grinding disk may leave a scored surface, but inside the grooves the metal will still be polished (even more so)

You really need to use an etch primer to get a good bond after attacking metal with a grinder, this eats into the metal a little bit and anchors itself to any voids.

regards,

Reply to
Iain Hibbert

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Cutting tools do not polish unless they are dull and rub. Wire brushes can be kept sharp

Reply to
ChrisR

How do you sharpen/keep sharp a wire brush. I have a both cup and dish? type wire brushes for my angle grinder, it has never ocurred to me their sharpness was under my control. Is the same true of grinding discs.

Reply to
Nigel

who said anything about cutting tools?

a grinder with a grinding disc is not a cutting tool

a grinder with a cup wire brush is not a cutting tool

a grinder with a sanding disc is not a cutting tool

For cutting, you would probably want some kind of saw. Please try to keep up.

Reply to
Iain Hibbert

Without getting too involved with technical explanations both are cutting tools.

A proper hardened wire cup brush on an angle grinder can be sharpened and fettled on a grindstone by an experienced tradesman if it has been allowed to dull by rubbing. If you examine the end of an individual wire on an effective brush there will be a sharp corner at the end of each wire on an ineffective brush the end will be rounded and or bent over so there is no sharp edge. One problem with "as cast" finishes, cast iron keels for example, is that there will be a chilled (iron carbide) skin that is very hard and will dull a hardened brush very quickly reulting in rubbing. The brush is only really effective at removing material on the cast iron skin in this case. Rubbing the iron skin itself will not be terribly effective as it will merely glaze and polish. Depending on the grade of iron below the skin a soft grey iron is relative soft and machjineable, quite a different of course.

A grindstone or grinding disk consists of hard grit embadded in a softer usually polymeric matrix. The grit will be hard with randomly disposed sharp cutting edges. As the exposed sharp edges of the individual pieces of grit dull they are shed exposing new grits with sharp cuting edges. The composition of the wheel or disk must be matched to the material being ground if the wheel is not to glaze or clog. Lubricants canbe very effective to aid cutting and cooling some materials. A blunt brush or grinder is just as useless as a blunt knife.

Reply to
ChrisR

And after all the responses, and with the keel now laying very heavily next to my boat at the sailing club, I think a shotblasting and epoxy coating is the way to go - many thanks to all who responded!

Artie

Reply to
Arturo Ui

I'd use rust converter. You can never be sure that you've removed all the old rust otherwise.

Reply to
glenn P

And you reckon that will penetrate right through to sound metal?

Reply to
Rob Morley

No, it will not penetrate to bare metal, but the coating it provides will protect the remaining steel from rusting.

Reply to
glenn P

Whatever are you talking about, glenn?

Reply to
Chris Bacon

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