Restoring pitted cast iron?

[ian maybury]

Many of the plane threads run into the same issue - pitting in cast iron. I've no requirement, but have been scratching my head and doing a bit of digging out of interest. Even the machine tool refurb guys don't seem to have anything short of the cast iron equivalent of a Dutchman. There doesn't really seem to be a decent solution out there. People like Belzona and Devcon do a range of metal power filled repair compounds (including some quite fancy high abrasion resistance versions), but it's just not going to be the same thing. It'd be interesting to know if they have the adhesion, strength and toughness to function in the repair of e.g. a chip missing in an edge as at a plane mouth.

There's various options for welding and/or brazing. Trouble is most entail heating to red heat (around 1,500 deg F ) and slow cooling in sand or lime, they won't match the colour and will likely require milling, grinding and other machining processes to restore surfaces. (which may not be feasible anyway as a result of localised hardening if it's let cool a bit too fast) Then there's the possibility of distortion and other effects as a result of the heating. There's high nickel welding rods that don't need so much pre-heating, but which won't be a good colour match - and may cause localised hardening/brittleness beside the weld.

There's potentially multiple requirements in a single job. Widespread pitting requires only cosmetic repairs, but would require an enormous amount of reworking if any of the welding or brazing techniques were used. Against that there's only marginal benefit in making cosmetic repairs with a filler the colour of which won't match the cast iron.

Has anybody come across anything that actually works? Maybe some sort of oddball low temperature brazing alloy that looks right afterwards? (thinking of something like a cast iron equivalent of the low melting point welding (more correctly soldering/brazing) rods now available for aluminium...

PS Found two documents just now which may be of interest, especially the second. The first is a discussion of the issues in welding cast iron, the second links a 'low temperature cast iron solder' which if the properties are suitable could be very interesting (but its probably a soft solder):

http://fulltorque.com/pdf/GMRC%20white%20paper.pdf
http://www.esabna.com/euweb/as_handbook/596as2_12.htm

[Dave Anderson NH]

There is a technically feasible answer Ian but it is sort of like killing a fly with a hand grenade. The aircraft industry is able to restore things like eroded turbine blades by vacuum depositing new metal onto the same alloy the blade was originally made with. Since the high temp alloys like Inconel and Hastelloy aren't a problem I would suppose they could do cast iron, mehanite, and steel too. Now price and finding someone to do it is another matter.

[Jim Koepke]

Has anybody come across anything that actually works?

Yes, it is using the tool as is, pits and all.

Those wishing to have a nicer looking example in their workshop can send them to someone like Tablesaw Tom for some machining.

Others will wait and pay for better examples to come along.

For me, if it doesn't present a problem in the performance of a tool, it is okay to wear its patina and scars of old age. I hope to look as good as some of my tools when my age is equal to theirs.

jtk

[ian maybury]

Understand the sentiments guys. Guess i was flying a kite in the general interest in the faint hope that somebody might have found something a little more in the middle than rocket science or not at all.

[Pat Barry]

Yo can get silver solder alloys that will wet to cast iron and which could fill the pits if need be.

[Tom Bussey]

I regrind planes and I have found that the pitting will disapear during the process if it is not to deep. If it is real bad nothing will help because it is not cost effectice. It also depends on if it is a C or if it is an older Bailey. It is hard to do older Baleys , type 10-15, because they lack a lot of material right behind the lower seats on the body.

Only you can decide it it is worth the expence to you. Even body putty has a cost not to mention time.

[ian maybury]

Just to repeat. This is only to get some discussion of repair options off the ground. I don't have any requirement to repair a plane, and have a fair amount of hands on exerience of the stock welding, brazing, grinding etc options out there. Just flying a kite out of interest and in the hope that maybe somebody with specialist knowledge/familiarity with a recently developed technology might have an 'aha' moment and pop in...

None of this is likely to be cost effective, and most of the time not even essential to function - but against that it's nice to get the cosmetics right, and there's times when it's worth putting the time in to rescue something.

Thanks Tom. I hadn't thought of it in that way, but that certainly puts grinding on the list as a possible repair for pitting - but only as you say if the pitting is not too deep, and other critical parts are not badly damaged.

For sure Pat the silver solder option has promise. The ESAB solder linked above targets CI but I couldn't find any hard data on it and think it's a soft/weak/low temperature/not silver solder. I think the ideal silver solder would have a melting temperature below 1,100 deg F to avoid the need for heavy duty pre-heating and slow cooling of the CI to prevent it from hardening/becoming brittle. There's a risk of distortion too. Standard silver solder I think tends to melt a bit higher than that, at very close to brazing temperatures. (around 1,200F) If it managed to combine being hand workable (as in re-shaping with a file or whatever after soldering), a decent colour match and being strong enough to handle structural repairs/chips out of critical areas too it could be very useful….

Brazing (and probably also std silver soldering) is definitely an option, but the trouble is that the temperature is probably high enough to cause problems without heavy pre-heating and slow cooling - and there's no colour match, and it's tough enough to need machining. Done right it's a very good CI repair though.

PS just had a word with Harris. (they do silver solders, braze metals etc) The guy said they didn't have anything that colour matched cast iron that melts below 1,100 deg F. This may or may not be the wider picture...

[john zulu]

TIG welding can repair cast iron. But it is generally use for cracks. In your application you want to fill up pitted cast.....

I am not to sure on the usually need to preheat the cast iron in this case scenario but the general filler for cast iron is silicon bronze.
http://www.weldingtipsandtricks.com/...ng-repair.html

I have the machine to do the repair but I have not used it for such a trivial item.... The cast iron may not be weld friendly.

[ian maybury]

Ta John. I mean silicon bronze when i talk of brazing, but maybe there's some different trans-Atlantic terminologies. Brazing/bronze welding until relatively recently was very common usage in the UK and here - especially on high performance thin wall/stress concentration sensitive high tensile (alloy) steel structures like motorcycle frames because of the concave/minimum stress concentration fillet it traditionally creates, and the reduction in heat damage to the steel compared to welding. Suspect it originated in the aircraft industry. The US in similar applications for some reason has tended to go more for MIG or other forms of welding in similar applications.

The sort of issues that seem to come up with brazing/bronze welding cast iron are that the temperaure at around 1,800 deg F is more than high enough to need slow cooling of cast iron to avoid undesirable hardening and embrittling tendencies, and probably also stress induced warping. (these won't prevent a bond/repair in many cases, but wouldn't be good on a plane body) Plus the choice of flux and correct pre-cleaning seem to be important. (cast iron is quite porous, and can contain a lot of oil etc that messes with wetting by silver solder, bronze welding etc.) The resulting deposit is going to be hard enough to require machining or filing off - much tougher than soft solder.

I'd agree that TIG isn't normally used for the purpose, but suppose that while laborious it could (as could an oxy-acetylene gas torch) be used to fill pits if required. It'd make it a lot more DIY friendly if a suitable (softer, less than 1,100 degF, colour matched and more workable - but still strong enough) filler metal could be found.

TIG (or an adaptation of it using a gaseous flux) works very nicely for brazing/bronze welding on light structures too - it gives very precise control compared to a gas torch. It was the preferred technique for high end competition motorcycle frames in the 60s and 70s, and is still used now at times. Pic here: http://www.customfighters.com/forums...ad.php?t=60099 It presumably could likewise be used with a fancy bronze filler rod on cast iron, but would probably require pre-heating and slow cooling to not mess up the cast iron.

I've been presuming that plane bodies are typically a good quality grey cast iron that will braze or silver solder without problems, but that may or may not be precisely the case….

[Pat Barry]

Here is a link to a silver solder you could try

[ian maybury]

Thanks Pat. It looks to have a melting point of over 1,100deg F which may be a little high - but that seems to be the way it is.

Will take a closer look at the temperatures that matter when cooling the cast iron, maybe there's a bit more room to maonoeuvre than I seem to remember….

[ian maybury]

OK, have done some digging - probably as much as makes sense for the present. Pardon the indulgence and the length - only for those into the topic. All of this is provisional and untested/is not advice - there's no guarantee that it doesn't contain errors - it's just to set a ball rolling on a discussion of the possibilities. It'd be dead interesting to hear from anybody trialling any of the methods.

All of the products mentioned contain compounds that give off vapours that are not good to breathe - and use fluxes that may have similar characteristics. Important to take adequate health and safety precautions as recommended by the manufacturers....

First off there doesn't seem to be much obviously about for soldering (generalised filling of large areas of) CI that melts at lower temperatures than the usual bronze/silver bronze brazing alloys that retains better than moderate physical characteristics - they tend to be soft solders. One that comes up as linked above is a lead free silver containing solder sold as ESAB (DynaGrip 430 kit) or All State (No. 7 solder). It melts around 430 deg F (nice and low) and is recommended for cast iron. Depending on the actual physical properties, colour match, workability, your urge to experiment/acceptance of the risk of disaster etc it may or may not be a candidate for generalised filling of pits. It's used for sealing pinholes in castings and the like among other things though which sounds promising. Can't find a sheet specifying the physical properties of the material, but it seems likely to be quite a bit softer than cast iron.

Arc welding to repair localised cracks etc is possible (typically using nickel containing fillers), but is likely to result in some mix of localised hardening, loss of physical properties, distortion, risk of cracking etc unless very specific pre-heating, post weld heat treatment/controlled rate cooling and other procedures matched to the composition and requirements of the particular cast iron are followed. It's high risk/ a bit of a lottery without a lot of specialised equipment and knowledge including the composition of the material being worked.

Brazing/bronze welding or silver soldering/silver brazing seem to be the most realistic crack/break repair option (but not suitable for large scale filling either - too much heat), but there's potential issues here too. The good news (which contradicts what i surmised above) is that the transition temperature for grey cast iron (the temperature which if exceeded results in changes in the disposition of the carbon and hence potentially disastrous softening or hardening of the iron) varies a bit with composition, but is around 1,300 deg F. Most of the brazing/silver soldering alloys for cast iron/steel melt only a shade above that, and the metal doesn't have to be held at the temperature for long to make a joint. So it's possible it seems (with good technique - it's definitely best not to heat any hotter or for any longer than is absolutely necessary) to braze or silver solder small areas with very little impact on the physical properties of a casting. (large area repairs likely wouldn't be such a good idea) Pre-heating to a moderate/safe 400 - 550 deg F or so is seemingly recommended for larger parts to reduce stresses caused by localised heating, but heavy duty heating and/or control of cooling rates beyond this and the precautionary use of e.g. dry sand to slow cooling seem not to be necessary.

It seems the big difficulty when brazing or silver soldering cast iron using standard filler metals/rods is to get them to wet it properly - to flow out on the surface when melted. The graphite is the main problem, but there's issues with oil, oxidised paint, over heating and oxidising of the iron etc too. It seems that using standard brazing or silver soldering rods/filler metals is as a result likely to be pretty hit and miss - until the 1980s cast iron required pre-treatment in salt baths and the like to get reliable results.

The problem was overcome (with only normal weld prepping) using speciality manganese and nickel containing filler metals. ArgoBraze 49H silver brazing alloy (which might just be a reasonable colour match) by Johnson Matthey in the UK was apparently one of the pioneers, and still holds most of the worldwide market for the brazing of carbide tips on to tooling. (carbide has similar wetting problems - this is the paper from back then: http://www.jm-metaljoining.com/frenc...ast%20Iron.pdf ) There are other speciality brazing/silver soldering alloys about for cast iron - they may use a similar technology, or maybe something else - but the point is that it's likely to be best to use a proven cast iron specific brazing/silver soldering rod.

The above relates to grey cast iron. Ductile iron (which seems to be a spheroidal graphite cast iron of one of the many varieties) seemingly achieves it's properties as a result of sophisticated heat treatment and use of fancy alloying elements is less likely to break, but can seemingly be brazed or silver soldered too. The good news seems to be that it's actually easier to handle because the transition temperature is higher at about 1,600 deg F. The bad news is seemingly that if it is overheated it's likely to suffer a disastrous loss of properties too...

[Tom Stenzel]

Ian,

All of the silver braze materials I used that work well with cast iron and low temps all contained cadmium. Are cadmium containing brazes even available in the EU? Even here in the Wild West USA, they're getting harder to find. Harris discontinued them.

I went to the Allstate site and downloaded the PDF, it listed the flux for Allstate 7 but not the material itself. Could it have been discontinued and you found a dead link?

If you try to skimp on the temperature the metals in the silver braze can separate, but at the same time if cadmium is in the mix it's very easy to make it boil and vaporize. That's when you get yourself into real trouble.

If you're determined to make a user out of a real mess nevermind the looks, how about epoxing a layer of metal on the bottom? That method sounds as haphazard as any other!

-Tom

[Tony Zaffuto]

So much depends upon the size of the pitting and does it harm the performance of the plane. Also, is the plane a collector item? If so, anything done may lower its value.

I'm sure if you were to contact, for example, Lee Richmond, of The Best Things (web tool dealer), he could suggest someone to "restore" the plane. If a user, I would simply have it ground by a knowledgable machinist (knows how to fixture for a surface grinder). I do have to add that I have an A4 (Stanley aluminum plane) with label still on the tote, and virtually no wear on the plane, except for horridly big pits on the sole. Some Liquid Steel epoxy weld virtually matched the color of the sole, so close, that an untrained eye would have to look closely to tell there were pits that had been filled. Bear in mind, the color of aluminum is significantly different that cast iron, so the patches will show.

[Mel Miller]

Seems like you're way overthinking the issue with the pits. I don't think there is a plane out there that is worth the effort to fill pitting with some type of welding. There is also no way you could properly repair a pitted "collectible" plane and make it more valuable.
If the pits bother you, just fill them with something like JB weld (epoxy) and be done with it.