SIF bronzing a crack in cast iron.

[Andrew TinsleyParticipant @andrewtinsley63637]

I need to SIF bronze a crack in a cast iron "fire pIt" It is about 6 mm thick. I would normally V out the crack with an angle grinder and use oxy acetylene with appropriate flux and rod, job done.

However I have given up my BOC bottles because of the horrendous rental cost and have yet to source a cheaper supplier. So I am stuck with using propane with either my Bullfinch or Sievert kit (both having a wide range of burner nozzles.

As the SIF bronze process takes place at around 700 centigrade, if I remember correctly, I should be able to use propane kit. But never having done so, I am a touch wary of the type of nozzle to use, a local flame or one that is more diffuse? Any recommendation as to the nozzle to use? I don't want to spend a lot of time experimenting, as it is too cold outside to mess about.

Andrew.

[Andrew TinsleyParticipant @andrewtinsley63637]

[noel shelleyParticipant @noelshelley55608]

I would have thought SIF bronze would be much closer to 900*C To do that job with propane you will need a good hearth and bricks to keep the heat in. If the cast iron is of poor quality and been very hot you may have great difficulty in getting a good joint due to the metal having been burnt. Your right about BOC I have 2 bottles and often ask why ? But then I need to cut, braze or MIG/TIG and then the answer is obvious, I would be lost without them. If you were near I would say use mine. Good luck. Noel.

[Dave HalfordParticipant @davehalford22513]

You may have a problem as Noel says depends on how much you have used it as a firepit

[bernard towersParticipant @bernardtowers37738]

dont forget to use Manganese bronze rods , not silicon bronze.

[Trevor Drabble 1Participant @trevordrabble1]

Andrew , I should have a 2.5mm dia or 3.2mm dia nickle rod you can have for use with a stick welder if you feel it any good for you . Also , for O/A , have you tried Hobbyweld ? Trevor .

[Clive FosterParticipant @clivefoster55965]

Sounds like the sort of job where the field expedient "puddling" technique with an arc welder using ordinary rods can work better than more "proper" methods. It copes well with burnt and poor quality cast iron but its a slow process.

Given a choice choose the most ductile rod you can lay your hands on. In practice the DIY market rods work well as these are generally formulated to be forgiving. Had a white box el-cheapo Far East import that worked amazingly well for this, and all sorts of other jobs. Love to know what it actually was as the number stamped on the box and printed on the rods was for a seriously exotic, and even more costly, blend with very explicit use conditions for special jobs.

Basic idea is to start with a wide Vee and apply several thin layers of weld metal to each side of the Vee using a small rod and lowest practical current. Weld lays should be short and its essential to peen with the chipping hammer during cooling. Lots of waiting around whilst the weld cools properly. Once you have a decent layer of weld metal to "isolate" the cast iron, I usually reckon at least 3 passes but prefer 5, you can move up to a larger rod and higher current. The rod chosen should still be small for the size of the job and several layers used. As before peening while the joint cools is essential to avoid thermal stress. Basic idea is that the peening spreads the weld in opposition to contraction so stresses don't build up.

Inverter welders are much better than old style buzz boxes at this being more controllable at low currents.

If need be you cna stick truely horrible cheap cast iron together with this technique if but are liable to come away looking like a coal miner as all the excess carbon around the joint is burnt out. I claim the iron on one such repair job was over 25% carbon. I had a heck of a job stopping the metal disappearing in clouds of carbon smoke whilst establishing first few layers. A freebee job too. Ornate cast iron gutter brackets for a school.

Clive

[OldironParticipant @oldiron]

Andrew, All Vehicle Parts Oakham are distributors for SGS gases. I use Motor Parts Direct in Corby who are also a distributor. I use the medium sized bottles. You pay a deposit and the cost of the gas then just pay for gas on exchange. I find it much better value than BOC so gave mine up a few years ago.

regards

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks gentlemen,.

My memory is playing false and it looks as though one needs 900 degrees C for SIF bronze. That being so, I shall either have to fork out for new bottles or drag out my trusty Oxford arc !welder! I shall give the Oxford first go, as it is the cheaper of the two options.

Thanks again for everyone's input.

Andrew.

[Dave Smith 14Participant @davesmith14]

Andrew

What about Oxy/Propane. You already have the necessary kit you just need oxygen bottles. I use hobby weld ones. One off charge then I think about £33 for a refill. They are not as big as a portapack bottle (about 500 mm tall) but I use mine about two or three times a week and the oxygen seems to last me about 10 to 12 months. If you were doing a boiler you may need a refill.

Dave

[peak4Participant @peak4]

Posted by Dave Smith 14 on 13/03/2021 23:53:37:

Andrew

What about Oxy/Propane. You already have the necessary kit you just need oxygen bottles. I use hobby weld ones. One off charge then I think about £33 for a refill. They are not as big as a portapack bottle (about 500 mm tall) but I use mine about two or three times a week and the oxygen seems to last me about 10 to 12 months. If you were doing a boiler you may need a refill.

Dave

There is also the possibility of oxy-propane using a medical oxygen concentrator.
I'm certainly no expert, but use one for smaller silver soldering jobs.
It runs up to 5l/min @ about 90% oxygen; much loved by glass bead makers.
My oxy-con came off ebay/gumtree, second hand for <£100, but Tufnell Glass are quite well known, albeit more expensive; they were the original suppliers of my unit.
Not sure of the availability second hand post Covid though.

Bill
https://tuffnellglass.com/contents/en-uk/d2.html

[noel shelleyParticipant @noelshelley55608]

There are plenty of redundant porta pack sets about and you may be able to find some one brave enough to couple up to a full big one and refill it, all be it at a lower pressure than new. You would need 2 x bottle nuts and 2 x bull noses coupled to high pressure hose good for a working pressure of OVER 3000 PSI

YES YES YES !!!! I know it's naughty but it can be done ! Noel

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