Repairing cracked castings

you can get cast iron welding rods, but they require a degree of prior experience, lots of people seem to be using metal stitching now with good results.

generally speaking I'd class this as one of those jobs that if you don't already know how to do it, you're best paying someone who does and looking over their shoulder...

Cast iron MMA rods are not that good an idea for thin castings, as they impart a lot of heat, and this can cause cracking adjacent to the weld repair.

MMA welding can be very efffective on thicker castings if the weld is peened as it cools to relieve stress, or alternatively the part is pre-heated, and allowed to cool very slowing after repair.

Best method of all for a repair like this would be powder welding, which is a microfusion process, which imparts a lot less heat than MMA.

Bearing in mind the fact that few people are able to carry out powder welding, the best method to repair your part would be to TIG braze it, and failing that to gas braze. It may need pre-heat, but that is dependant on where the crack is and the type of cast iron.

k-

You could ask on the welding NG sci.engr.joining.welding John

If in doubt, don't ?

if it's not required to be mechanically strong, then other methods (epoxy, Oyltite, chewing gum) are far simpler and generally work adequately.

If you really must try welding it, the excellent newsgroups sci.engr.joining.welding will tell you pretty much everything you could want.

I restore woodworking tools, which often involves welding iron castings. I can do it, and after a fair bit of practice I'm not bad at it either. But it's still a damned awkward process that I'd avoid as much as I possibly can.

Are you referring to the hot metal spray process, or the newer high-tech lower heat versions?

I picked up some metal spraying kit a while ago, the type which uses an oxy-acetylene torch with powder feed, it seemed like a potentially useful thing to have. I haven't tried it yet, but it came with a couple of powders for casting repair and I've wondered how effective this might be. I'd be interested to hear from someone with practical experience of this sort of thing.

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

Have you considered brazing it? The lower temperature and better workability make it a much easier repair. No guarantees though.

John

Thanks for all the advice so far, a few more details might help: It supports the read bearing of the alternator via 3 'legs' of which the two thinnest are cracked right through, so no need to stop the crack running with a hole 8-(. What's left isn't strong enough, in my guestimation, to be left as is. I don't have gas welding gear, though I have done it in the past so realise what a specialised job cast iron is, I only have stick and MIG. Even if I did I wouldn't dream of trying it myself. I don't have brazing gear anything like big enough for this, and no oven to pre-heat it. I'm quite prepared to hand it to a specialist, in fact I'm very reluctant to try anything for myself because if this part is lost the only hope of salvaging the set in it's original form is to find someone with a replacement, not easy would be my guess. Unfortunately I'm in a backwater near Filey so specialists are few and far between, I'm really hoping to discover what type of specialist I'm looking for, welding, brazing, powder spraying etc.

Greg

top tip, find the closest "old fashioned" foundry that still has staff that use wooden forms and sand casting, give them the problem.

Beijing ?

Stick is fine, if you have some gas to pre-heat with. Either stick it in the kitchen oven, or buy yourself a 20 quid propane weedburner (baked-bean tin on a stick and a hose with no regulator) from Screwfix or Northern Tools and pick up a half-empty propane tank for a coupel of quid from the local dump.

Hardest problem seems to be buying nickel rods. I used to be able to buy these as handfuls from our local welding shop, but now they're only doing them in full boxes. For nickel, a whole boxful is expensive.

If the casting you are attempting to repair is thin in section.then TIG brazing would be the way I would repair it. Could possibly need pre-heat, but this is no where near as critical as if you were using MMA (stick) welding process, which is better employed on heavier castings.

Anyone thats good with a TIG set should be able to help you with this sort of thing, and you might find a local marine engineering shop who could help with this.

As to having a new part cast, this would be very costly and is really only a senisble option if your original part is beyond repair or missing entirely.

Hot spray is the way to repair a casting, the cold spray process is generally used for building up shafts etc, with the parts to be repaired held and turned in a lathe as they are being sprayed.

Hot spray process is highly effective for casting repair, but you do need to have the correct nozzle sizes to get the casting hot enough, so heavier castings are perhaps easier to do with MMA process, unless you have a good method of applying pre-heat.

The powders you use for this are pretty expensive, and its critical that they are kept dry or they just wont work properly, as damp powders tend to clog the fine passages of the torch, as they are being drawn into the O/A flame.

One major advantage of the H/S process, is that you can build up broken parts extremely precisely, only adding material to area needing to be built up or repaired, and of course the lower levels of heat required for microfusion processes in comparision to other more generally used methods.

I suspect our local foundary, est 1947, would have someone with the required skills they use "Ceramic mould precision castings up to 45kg in carbon, alloy, stainless steels and special alloys. Precision cast pump impellers etc"

Wonder why anyone would want to pay quite a lot of money to have a new part cast, when the existing part can be easily repaired?

I would certainly take lots of dimensions and pictures - just in case. If a new part is cast, it would need machining and that's another problem.

John

jesus.......... logic people..........

it's a CASTING, nobody knows more about castings, whether making them or repairing them, than a foundry

If with your wide knowledge of welding you cant come up with better than that, why not just keep quiet? That nonsense doesnt help the OP in the slightest, and strangely very few foundrys would either be equipped or willing to carry out small casting repairs.

Why? Why should a foundry know anything about repairing them ? They're a foundry - they have the pattern - easier just to knock another one out.

That's also assuming that a foundry knows anything about patternmaking. Now these days (with the relative scarcity of them) it might be true, but it used to be the case that the foundry who did the pouring had no connection with the patternmaker. One of my relatives was a moulder (years ago - foundry long gone) but they didn't even have a pattern shop in the whole company.

Because it's the best and most helpful answer the OP could possibly get.

fact

in your very humble opinion, which has been proven wrong on just about anything you care to name.

strangely the three closest foundries I can think of are all equipped, experienced and willing, but hey, what the f*ck do I know, I've only designed and developed bespoke castings for HMI/SCADA equipment in association with said foundries, you're right, the OP should listen to you, the welder who'd never heard of Stubs rods for cast iron, whereas the advice I gave re see a foundry or specialist rod or metal stitching before we knew exactly what the problem was was spot on....

now we know what the problem is It doesn't make a blind bit of difference, because unless the OP is going to do a bullshit repair on kit that will never see a duty cycle the facts that its a bearing web that's gone means line boring after it is repaired.