Water cooled side blast repair

[Joel OF]

Hi folks, I'm curious for people's opinons on this ramble...

I'm tempted to buy a water cooled side blast forge from a local farrier, approx dimensions 80cm x 80cm, it needs a lot of repair work and he doesn't know how much he wants for it so told me to make him an offer.

Parts that need repair = some of the hearth sheet, the hood, a little bit of lightweight angle iron in the hearth, nuts and bolts, but for me most concerning is the water cooled tue which has a small crack and is leaking.

Parts that are ok = galv back bosh, cast brackets that support the bosh, legs and main angle iron framework made from approx 50 x 6mm, cast back plate.

I've suggested that I take away the cast tue so that me and the fabricator I work next to can have a go at welding it, if that works I'll give him £200 for the rest. If the cast repair weld doesn't work then it's not for me as new tues are expensive and the rest of the repair work is generally a big repair job that I expect will take 2 days + £200 for materials.

I see used water cooled side blast forge on eBay / BABA now and then for approx £500 ...but they're a long drive away and will need collecting. New water cooled side blast forges made from mild steel to similar dimensions are £1,100 delivered.

What do people think about cast welding the tue? The tue is the thing that makes me most unsure about the situation because I don't know how well the weld will stand up over time.

It's a tricky one because he's a lovely guy and very very generous - he's already sold me a decent twin burner gas forge for £200, given me about 30 decent rasps and an old rounding hammer (small chip on the flat face) so I really don't want to offend him with a silly offer or come across as really harsh for something that he's still got a bit of sentimental attachment to.,,on the other hand I'm not made of money, far from it.

Penny for your thoughts...

[David Einhorn]

Pictures would help.  Unless the forge is something special, it sounds to me (sight unseen) that it would be less work and less expensive to just build one myself.

[Joel OF]

Pictures would help.

​Yeah I don't know why I didn't take any, maybe because it was tucked into a slightly awkward corner of a shed. I'm sure I'll go see it again soon to discuss and I'll take some pics then.

[arftist]

A lot depends upon why the crack occurred. If it was from freezing you can probably fix it. If it is burnt out from overuse then probably not. 

I don't think there is anything offensive about your plan to try to repair it first. You are still risking at least the funds to pay for the repair after all. 

[Joel OF]

A lot depends upon why the crack occurred.

​Sorry, my OP was rubbish for detail! The shed he's been storing it in had a leaking roof which he didn't realise until recently so that's caused the hood/sheet to rust, and as far as I know that's also the cause of the rusted/cracked tue.

[HWooldridge]

There are some really good cast welding rods on the market but it's always problematic that the repair holds without cracking later.

Brazing might hold, depending on the location.  I realize the nose gets pretty hot in the fire but the water inside should be enough to keep it from getting so hot that the braze melts while you're working.  I brazed up a bottom blast (with no water cooling) and it has held for several years.  Just a thought.

[yahoo2]

Hi Joel,

The most practical solution, if you are going to use the forge, would be to fabricate a replacement out of steel pipe. It doesn't need to be an exact copy it just needs to function the same way. Find a length of pipe with roughly 5mm wall thickness that matches the inside diameter, your fabricator should have some 12mm plate to cap the end that is in the fire then sleeve it with some 3mm wall thickness pipe. Should be good for minimum of 10 years provided that you plumb it so it can thermosyphon correctly.

Put the cast tuyere on the shelf and find someone to tackle the job later.

[Joel OF]

Thanks for the replies folks. After no having heard back from the farrier for a few days he rang earlier to say he didn't want as much as £200 for it & I can have it for £75. I told you he was a good guy.

To be honest £200 was more than I felt comfortable with but as he's been so good to me already I thought I should repay him. Needless to say I don't feel so nervous about the project now & having a bit on an experiment. I found a good size hood for £60 at a salvage yard too so if that works out that'll save me some material & hours too!

[LastRonin]

Pictures! Please?

oh yeah, and congrats

 

[Everything Mac]

Well done Joel, glad you got it for cheap. From the sounds of it it definitely wasn't worth £200... 

 

The crack in the tue is a bit worrying, I've seen them fixed in the past but it seems a risky way to go. Sounds like the frame can be saved at least. 

All the best 

Andy

[Alan Evans]

My experience of trying (and failing) to weld cast iron definitely puts me in agreement with the brazing advice from HWooldridge. I have had success brazing cast motor car manifolds, which are likely to get as hot as the water cooled tue.

My first hearth was a second hand Alcosa side/back blast unit frame that I fabricated a mild steel tube tue for. It lasted for five or six years, and was replaced (still working) with a bottom blast system. This was concocted to give a 600mm (24") fire when I needed longer heats to make better use of the newly acquired power hammer.

I did have to replace the 25litre (5 Gallon) oil drum bosh occasionally when it rotted out. The main disadvantage was that the Ø1/2" rubber motor car heater hose I used for the thermo syphon connection would freeze in the winter…anti-freeze would boil away if not constantly refreshed!

In six years, the only damage the heat had done to the steel tue was on the mouth of the inner pipe which projected through the face plate and had a weld fillet around. This put it 20mm (3/4") away from contact with the water so it got hotter than the rest. Vee-ing out the hole in the face plate and keeping the weld within the thickness of the plate would have prevented any over heating problems I think. The brazing should be fine, that will never be too far away from the water.

Alan

[Joel OF]

Well it seems the cast tue has well and truly danced its last tango as the crack runs from the top, over the tip of the cone, and into the inside.

My local small steel yard has huge chunk of 120mm diameter (near enough 5 inches) solid round bar. I asked how much they'd charge for a 400mm length of it (approx 16"), they said £20 which seems pretty cheap to me. For the sake of simplicity I'm thinking I might just buy some of that and make it into a dry tue by putting a 25mm (1 inch) hole length ways through the middle. I can't see that burning up in any great hurry.

[Dan P.]

I'd go with the option of welding up a tue, as per yahoo2's suggestion.

I have a welded tue that has given me 5 or 6 years service, looks set to give 5 or 6 more (except that the back bosh is knackered and the one is welded to the other). About 100mm diameter, maybe 5mm thick wall?

Concerning the dry tue option, I tried exactly what you are proposing, except the stock was smaller, maybe 3 inches. It was burnt to buggery after the first proper forging session. 5" might do better. At £20 it might be worth a punt? I'll be interested to know how it goes, though mightn't 1" hole be a bit big?

The only person I know who uses a "proper" solid tue is Hector Cole. His is an almost hemispherical piece of cast iron maybe 8" across? He also uses coal/charcoal mix, which might be a bit more forgiving than coke. I think the hemispherical shape is probably important as it has no corners to overheat.

[Joel OF]

Concerning the dry tue option, I tried exactly what you are proposing, except the stock was smaller, maybe 3 inches. It was burnt to buggery after the first proper forging session. 5" might do better. At £20 it might be worth a punt? I'll be interested to know how it goes, though mightn't 1" hole be a bit big?

Blimey I didn't expect that. The wet tue hole is 25mm so I guessed the same for a dry tue. I'll go with the wet tue consensus as the fabricator I work next to will have all relevent scrap & it sounds like a tried and tested method. Cheers all.

[HWooldridge]

Slightly OT but I am planning to fab a side blast (water cooled) so this brings up an important point.  Is 25mm too large for the blast opening?  Should it be closer to 19mm (3/4") or does it make much difference if a damper is used to control the air to the fire?

Another idea I had was to take a solid piece of stock (maybe 4") and drill good sized holes into the back that don't go thru (like bubblers in a mold).  This is easier to make if one has access to lathe or mill and saves all of the welding that would occur with pipe and plate.  A half dozen 12mm holes drilled from the water side to within 6mm of the tue end should allow quite a bit of water into the nose for cooling.

[Alan Evans]

Tue bore will depend on size of fire required and air supply mainly I think. If you have high pressure though you will get away with Ø20mm (Ø3/4") and if you have an enormous fan you can always reduce the air flow. The standard cast wet tues ones here are Ø1" I thnk.

I seem to remember seeing a nose dovetailed onto a wet tue somewhere. I think it was cast iron, that would be the best thing to make your nose piece out of perhaps. I don't know if it was solid or hollow. The dovetail would make it replaceable so maybe solid. Re-sealing would be a bit of struggle.

I think you really need to go one way or the other though;  Either a dry tue from heavy solid, preferably cast iron, and just reckon it will clinker up and burn away eventually…Or…Wet tue constructed so that it has no more than 12mm (1/2") away from the water jacket at any point.

A more heavily constructed wet tue is likely to overheat and burn and has the advantages of neither I fear.

I got fed up with the size restrictions of side-blast. The first bottom blast furnace I made was a 12mm (1/2") plate about 500mm (20") by 200mm (8") with a double row of holes down the centre. The holes were burnt in with the gas torch so that they tapered, in order for clag and ash to fall through. I would reduce the length of the fire with a couple of drop on plates. That worked for a few years until I improved it with a heavy fabricated slotted version which gave me a 600mm (2') fire, again sometimes used with reducing plates.

Occasionally I do miss the convenience of precise heat that I used to get from a side blast fire. Oxy acetylene tends to deal with most of those needs. I have been using gas furnaces now for so many years that even the bottom blast fire has only been used once in the last two decades and only then to show a student how to do a fireweld.

Alan

Edited May 17, 2015 by Alan Evans

[HWooldridge]

Alan,

I have a conventional Buffalo bottom blast fire pot with factory blower and rheostat (puts out enough blast for multiple forges).  The pot is about kaput from years of work so it's time to replace - but my coal makes quite the clinker and will clog the fire in a short time.  I have read that side blasts allow the use of of dirty fuel with less cleaning so that was my intent in changing styles.  Like you, I also seldom use coal anymore in favor of propane but the gas forge will not get hot enough to weld.  Perhaps it is easiest to simply replace the existing pot and get on with life...

Thanks,

Hollis

[Dan P.]

A bigger bore means you need a blower with more poke.

My life has been rich in under powered blowers, which is why I'm wary of a bigger bore. I do have one fire with an old cast tue with a big hole, hooked up to an old blower which is "proper psycho" and can blow a piece of coke through a 1" oak board from 20 feet away. Not really. But whatever the case, big or too big holes can be made smaller by plugging them with, literally, a mild steel plug with the bore of your choice. I used a tue with such a plug for many years, held fast with a few tack welds.

Edited May 17, 2015 by Dan P.

[Alan Evans]

Ah... that is interesting. My early days with cylinder blowers and old oil fired central heating blowers makes me inclined to an almost opposite view!

If your fan had the pressure you could use a smaller hole, but if the fan had volume but not pressure you needed a big hole to get sufficient air.

I gave up with other fans in the end and managed to buy a second hand Alcosa hearth fan from a school. It has been used on my coke fire variations and now for the gas furnace…brilliant thing I have replaced the brushes 5 or 6 times and the bearings once in around 35 years.

Alan

[Dan P.]

I am sure that you are quite right and that my understanding of the situation is based on some notion I had years ago but have been to mentally sluggish to ever revise.

[Alan Evans]

The difference is in our descriptions rather than actual performance observation I think. Your under power equates to my low pressure....hope this comes through, I can only see a command line version of the site at the moment! Alan

[yahoo2]

Well it seems the cast tue has well and truly danced its last tango as the crack runs from the top, over the tip of the cone, and into the inside.

​Don't chuck it out Joel, there is no such thing as a small crack in cast, it always looks bad. Cast fusion repair work (not patching/brazing) always looks severe when it is done, it is best it you dont hang around to watch and see how many pieces it ends up in and how much metal is removed to chase the cracks and get back to uncontaminated material. Particularly with items exposed to water and burning, sometimes I have to jig and sculpt complete new sections with the oxy and cast filler rod. You might have a heart attack if you see it at this stage of repair.

Usually takes me 4-6 hours work over 3 days to a week to get something like this prepped, welded and finished, a full time professional with serious skillz and motivation would do it far quicker. To copy and fabricate in steel would take me 20 minutes to find the steel and mark out the job and 40 minutes to cut, forge and weld (including waternecks ) and U can take it with you that afternoon. There is a big price difference between the two options, there is an even bigger price difference if the cast has been previously brazed. Bear in mind a fabricator not used to replicating old gear will take a lot longer to get his/her head around it all.

the fundamental detail you are missing is the science-ey bit of water cooling.

You need to reflect as much heat as you can into the fire to keep its core temperature up, dragging heat away with a bulky tuyere will make the combustion reaction cooler and you will lose some of the best heat producing chemical reactions if you drop below a critical temperature. that means the exposed frontal area should be small and heat reflective if possible. The tuyere walls/front exposed to the highest temperature need to have good thermal conductivity and the correct thickness so that heat that get passed the reflective shield will be drawn into the water jacket rapidly and not stored close to the hottest areas where it can continue to build more heat. Lastly the water, this is the important bit, it takes an extreme amount of energy to convert a liquid into a gas so the temperature of the water will not exceed 100 degrees Celsius while this is happening unless you pressurize the system or all the water is steam. this means the liquid water inside of the water jacket is always at or below 100 no matter how hot the fire on the other side is, this is why it needs to circulate, to dump that absorbed energy and remain (mostly) a cold liquid.

that's more than 2 cents worth i know. But hey, it just rained here for the first time in 10 months and I am in a good mood!

Edited May 19, 2015 by yahoo2
grammatical error

[Joel OF]

Cheers all, great info. I'll go down the route of fabricating a new water cooled system as suggested...when I get the time!

By the by, regarding blowers (as they got mentioned), I currently use a bouncy castle blower with a sliding gate to choke off the hurricane. Anyone know how these compare in electricity usage against "proper" blowers, e.g the new ones they list in the back of BABA magazine? From memory they're about £175 and are advertised as economical to run. (2nd hand eBay bouncy castle blower, £40).

I'm in a shared workshop a.t.m where I don't really get charged for electricity but as I'm hoping to move into a solo space soon I'll quickly become more frugal.

Edited May 22, 2015 by Joel OF

[Alan Evans]

The Alcosa F20M ones are fractional horsepower…only 1/3 I think. +/_ 0.25kva so is probably the least of your power consumption worries, even if running flat out all day. The coke or propane bill will make it pale into insignificance.

Alan