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Post by Roger on Nov 9, 2018 8:12:36 GMT
Hopefully some others from down under will chip in here. Our fuel situation went south a few years ago and there has been much experimentation with rosebud grates. Unfortunately I am no help as I have a stainless one but still end up with lots of clinker after a few hours of running, but have no clue why. There was an article in a recent issue of the local magazine where someone was playing with steam jets to keep the fire bed just off the grate, so plenty of room for you to experiment Roger! Hi David, That's interesting. I've just googled 'clinker' and it basically says that it's oxidised minerals, Carbonates and possibly Sulphates in low quality coal that fuse together at a low temperature (about 1000C) compared to those in high quality coal. For large industrial boilers, they say not to over fire so that there's less ash and lower temperatures. Deeper fires are more likely to have localised hot spots that allow the ash to fuse. So maybe just running a thin fire is all that's needed to reduce the problem? As you say, there's plenty of room for experimentation. |
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Post by David on Nov 9, 2018 9:36:46 GMT
The coal we get down here now is rubbish. A few years ago we had 'char' that burnt cleanly and well and didn't clinker - so easy in retrospect.
There is much experimentation going on with grates, mixtures of local rubbish with imported Welsh coal, modified firing techniques, etc. There might be something about 'secondary air' too - is that the stuff let in through the firebox door?
There is certainly support for the idea of a thin fire around here. Achieving same is a different matter ;) I find it is all too easy to go from thin fire to not enough fire to recover from in quite a short amount of time! At least if you do go into loco and drop the grate it doesn't take long to get going again with the boiler already up to temperature.
No-one in our club ends the afternoon without some amount of clinker on their grate as far as I can tell. Then add in things like poor front ends requiring over-firing or constant blower to make the loco steam and all the other vagaries of locos built and driven by amateurs and it can be tricky to end the day with as many locos as you started with!
To show I'm not totally inexperienced I used to be a stoker on a steam launch on Sydney harbour with a yarrow boiler, and it had a fairly decent sized grate. Once you learned how to run it pootling around the harbour never put much stress on the boiler so a few shovels here and there and a good feel for the water pump which made it's comforting noise, and mostly controlling the pressure with the damper allowed for a pretty easy 4 hour cruise with not a hint of clinker in sight, and no injector troubles either! The biggest problem was them in the wheelhouse hanging off the whistle cord saying hello to their ferry captain mates wasting my steam! 200lbs from start to finish, no lifting of safeties, managing the smoke around the tourist traps, burning the fire down on the way home to come into the berth with little but some wood burning... I miss that boat, it was WAY easier than these little locos.
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Post by Roger on Nov 9, 2018 9:44:50 GMT
The coal we get down here now is rubbish. A few years ago we had 'char' that burnt cleanly and well and didn't clinker - so easy in retrospect. There is much experimentation going on with grates, mixtures of local rubbish with imported Welsh coal, modified firing techniques, etc. There might be something about 'secondary air' too - is that the stuff let in through the firebox door? There is certainly support for the idea of a thin fire around here. Achieving same is a different matter  I find it is all too easy to go from thin fire to not enough fire to recover from in quite a short amount of time! At least if you do go into loco and drop the grate it doesn't take long to get going again with the boiler already up to temperature. No-one in our club ends the afternoon without some amount of clinker on their grate as far as I can tell. Then add in things like poor front ends requiring over-firing or constant blower to make the loco steam and all the other vagaries of locos built and driven by amateurs and it can be tricky to end the day with as many locos as you started with! To show I'm not totally inexperienced I used to be a stoker on a steam launch on Sydney harbour with a yarrow boiler, and it had a fairly decent sized grate. Once you learned how to run it pootling around the harbour never put much stress on the boiler so a few shovels here and there and a good feel for the water pump which made it's comforting noise, and mostly controlling the pressure with the damper allowed for a pretty easy 4 hour cruise with not a hint of clinker in sight, and no injector troubles either! The biggest problem was them in the wheelhouse hanging off the whistle cord saying hello to their ferry captain mates wasting my steam! 200lbs from start to finish, no lifting of safeties, managing the smoke around the tourist traps, burning the fire down on the way home to come into the berth with little but some wood burning... I miss that boat, it was WAY easier than these little locos. Hi David, What an interesting life you've had with that steam launch, it sounds very pleasant. I'd certainly echo the vagaries of Model Locomotives, it can be challenging to cope with non-stop passengers at our fetes without a moment to get back in shape if it starts to go wrong. I tend to go with a really deep fire so that there's always plenty of mass in there, even if it's not the most efficient way of running things. We can't afford to wait five minutes for a 'blow up' when we're busy. |
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Post by Roger on Nov 9, 2018 23:26:20 GMT
This is one of the pivot brackets being made from Stainless Steel bar.  20181109_201505 by Roger Froud, on Flickr This is the location pocket for the pivot bracket. I've recessed it because the hole for the pivot would have made the bracket very thin.  20181109_224151 by Roger Froud, on Flickr The brackets are a bit thick at the moment, the width can't be wider than the grate.  20181109_231540 by Roger Froud, on Flickr |
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Post by Roger on Nov 10, 2018 22:16:48 GMT
The brackets were held in place using a piece of 4mm Silver Steel and the ends were tacked on...  20181109_234005 by Roger Froud, on Flickr ... then put into a more ergonomic orientation for welding properly  20181109_234729 by Roger Froud, on Flickr The sides were partially welded too, and then machined flush...  20181110_101059 by Roger Froud, on Flickr ... so it looks like this.  20181110_102907 by Roger Froud, on Flickr I wanted to make absolutely sure that the pivot was in the same place on both sides. It's all pretty square, but I thought if I used a mirrored tooling setup for each side, it would be as accurate as I could make it...  20181110_111214 by Roger Froud, on Flickr ... this being the mirrored operation without moving the blocks  20181110_111626 by Roger Froud, on Flickr The end cheek is getting two 4mm location holes here...  20181110_120931 by Roger Froud, on Flickr ... which were spotted through the Copper firebox skirt...  20181110_122018 by Roger Froud, on Flickr ... which looks like this.  20181110_122221 by Roger Froud, on Flickr I made a couple of short shouldered pins which were welded on the outside. The flange on the inside positions the ashpan the correct distance from the end.  20181110_141633 by Roger Froud, on Flickr It drops in the back like this...  20181110_141714 by Roger Froud, on Flickr ... and slides easily into place.  20181110_141725 by Roger Froud, on Flickr The rear of the ashpan is located by two thumb screws. These are the holes for those going in...  20181110_143550 by Roger Froud, on Flickr ... which were spotted through the Copper Firebox skirt again and then a Stainless Steel bush was welded to the back.  20181110_185458 by Roger Froud, on Flickr The idea is that these should only be tightened by hand in case they don't locate properly and damage the Copper firebox skirt. You can feel them enter the holes easily enough though, and they go tight when they bottom out on the threaded bush. The idea is that the ashpan is located with pins and isn't clamped so there's room for expansion. Anyway, it's absolutely rigid when it's on there and I'm very happy with the arrangement. I'm designing this bit as I go along, it's not easy to visualise the consequences of these things even with 3D CAD when you know that there are going to be some small errors due to the nature of Boiler and Sheet Metal work. It's a bit more 'old school' than I'd like, but it's good enough since these are not precision assemblies.  20181110_185643 by Roger Froud, on Flickr |
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,990
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Post by JonL on Nov 11, 2018 14:53:05 GMT
A very elegant solution.
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Post by Roger on Nov 11, 2018 21:37:15 GMT
The pivot for the grate is a piece of 4mm Stainless Steel which has had a centre drill put into the ends and swaged over. Crude but effective  20181110_223142 by Roger Froud, on Flickr I've decided that the area I am going to attach the arch to was too flimsy, so this is a piece of 2mm thick plate to beef it up...  20181111_101142 by Roger Froud, on Flickr ... and this is one weld going in at the end. Note the piece of Copper sheet clamped up behind the joint to stop it overheating on the back...  20181111_111226 by Roger Froud, on Flickr ... the same trick on the other side too...  20181111_112508 by Roger Froud, on Flickr ... then flipped to a position that makes it easier to finish the weld.  20181111_113639 by Roger Froud, on Flickr I already had a 3.3mm drill extended (M4 tapping size) ...  20181111_121050 by Roger Froud, on Flickr ... which looks like this when tapped for the fixing screws. It's a lot stronger now and the threads are long enough not to need bushes.  20181111_123608 by Roger Froud, on Flickr Another change in the design is to make the vertical part of the arch from 2mm Stainless Sheet so it's much stronger and less likely to sag. I can get it to sit up pretty close to the face of the throatplate. It has to come off before the ash pan can be removed. I might make a couple of Phosphor Bronze thumbscrews for this because it would be handy to take it off to clean inside.  20181111_172545 by Roger Froud, on Flickr The grate was deliberately made over size so here it is having the ends trimmed at an angle to suit the front and rear faces of the firebox.  20181111_173201 by Roger Froud, on Flickr This slightly odd arrangement allowed the top face of the ashpan to be set parallel to the table for drilling the hole for the bush.  20181111_193530 by Roger Froud, on Flickr The bush holds a sliding pin which locates with the grate, holding it in position. I've made a thick Copper washer to take the head away from the back of this extensive weld. (It wasn't supposed to be that big really)  20181111_202230 by Roger Froud, on Flickr Fortunately it didn't end in tears because of the washer.  20181111_202444 by Roger Froud, on Flickr |
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Post by Roger on Nov 12, 2018 23:59:31 GMT
I made this adjustable angle plate that's buried in clamps years ago when I made the first batch of quick change toolpost holders for my old Southbend days before I had a mill. Here it's come in handy again to hold the grate at an angle so I can machine the location pocket for the catch.  20181112_214059 by Roger Froud, on Flickr Originally this was welded onto the bottom face of the grate, but I prefer this idea because it locates itself and it's easier to weld on.  20181112_220648 by Roger Froud, on Flickr The bracket was machined from over sized stock because the lathe is tied up with a commercial job that I don't want to disturb, and this piece of Stainless had a flat machined end. It just needs parting off and welding on tomorrow.  20181112_231228 by Roger Froud, on Flickr |
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Post by Roger on Nov 13, 2018 22:41:07 GMT
Just getting ready to weld the lug onto the end of the grate. The lug is at an angle because the grate is sloping but the locking mechanism is horizontal.  20181113_141127 by Roger Froud, on Flickr Picking up on the discussion we've been having elsewhere about the 'brick arch'... I've had one reply offering Inconel alloy 718 whichI'm assured has similar properties to Inconel 625 as follows... 103mm x 227mm x 1.6mm Thick Off-Cut @ £67.50 Lump Sum plus £20 carriage. The size is a bit arbitrary, I asked for 100mm x 200mm just to get some idea of the cost. I guess he has this offcut lying around. It's pretty expensive so I'll wait and see what other offers come back as. We could always get a larger piece than we individually need to try to get the cost down. It's interesting that Julian doesn't have the same experience of rapid degradation of Stainless Steel, albeit in a different application. It might just be worth trying it first before spending out on exotic materials. |
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jma1009
Elder Statesman
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Post by jma1009 on Nov 13, 2018 23:11:46 GMT
Hi Roger,
That stainless strip of quite thin section has been at the back of the refracting bricks in my lounge stove for some 5 years and gets very hot. It was actually cut out of some strips I had made for my Dad (an AA patrol man all his working life) to slide down the rubber seals of front car door windows to latch onto the door locking mechanism for people who had got locked out of their cars.
I can cut you out a section of the industrial ceramic sheet that came out of the old central heating boiler. This would be far more effective than a metal arch, as it will quickly heat up and radiate and burn off hydro carbons - which is the only purpose of a brick arch in fullsize - to reflect back the radiant heat.
My own view is that in miniature our much smaller fireboxes act on their own as a radiant heat refractor, especially if you hone your firing skills and have good coal and a well tuned loco. However, Vince Williams came 3rd in IMLEC with a loco fitted with a stainless arch, and Laurie Joyce came 1st or 2nd in IMLEC in 1970 or 1971 (don't quote me on the dates) with his 3.5"g GWR King.
I would suggest you do have to go back to basics and examine why brick arches were fitted in fullsize!
Cheers,
Julian
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Post by Roger on Nov 13, 2018 23:25:54 GMT
Hi Julian,
That's a very kind offer of the ceramic sheet, I wonder what thickness that is?
I was under the impression that the idea was to prevent the fire taking the shortest route, preferring to go down the lower tubes. The arch not only prevents that but also makes it sweep over a greater area of the firebox. I'm not entirely sure what effect it might have in radiating heat back towards the fire because that doesn't transfer any additional heat into the water. It might make the fire burn more intensely though.
It's all very interesting and worth a few experiments.
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Post by chris vine on Nov 14, 2018 10:27:11 GMT
Hi Julian and Roger,
Personally, I think that an arch (in some material) is worthwhile in our sizes.
As far as I understand it, the arch did several things:
prevent the fire taking a short cut into the lower tubes
make almost all of the fire take a much longer path so that it had longer to burn. Once the flames reach the tubes they are cooled and combustion is extinguished. So more complete combustion results and the locomotive consumes its own smoke. This was a stipulation for locos in the Rainhill Trials, so must have been a problem before arches were introduced.
The radiation will also help combustion, so the refactory material which heats up to white heat will certainly help combustion. However, a stainless arch will still get pretty hot and will still help in the other respects anyway.
If there is a ceramic material which will survive mechanically, that would be perfect of course!! I detect a Roger bit of experimenting coming on...
In fact, maybe you could make the arch out of stainless for strength, then maybe ceramic could be riveted on either side. Best of all worlds...
Now Roger just has to source some inconel/nimonic rivets!!
The stainless arch in Bongo is made from some unspecified stainless and it has lasted for a long time. Once I had got it cut to fit snugly in the firebox, I scribed round it on some more of the material so I could make a replacement in the future. Not needed yet...
Chris.
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Post by Deleted on Nov 14, 2018 10:36:02 GMT
Thanks for that informative reply Chris..could you answer a question for me, please...Don states that more airflow is 'essential' when fitting an Arch, could you possibly explain the reason or your views on Don's reason?
cheers
Pete
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Post by Roger on Nov 14, 2018 10:56:19 GMT
Hi Julian and Roger, Personally, I think that an arch (in some material) is worthwhile in our sizes. As far as I understand it, the arch did several things: prevent the fire taking a short cut into the lower tubes make almost all of the fire take a much longer path so that it had longer to burn. Once the flames reach the tubes they are cooled and combustion is extinguished. So more complete combustion results and the locomotive consumes its own smoke. This was a stipulation for locos in the Rainhill Trials, so must have been a problem before arches were introduced. The radiation will also help combustion, so the refactory material which heats up to white heat will certainly help combustion. However, a stainless arch will still get pretty hot and will still help in the other respects anyway. If there is a ceramic material which will survive mechanically, that would be perfect of course!! I detect a Roger bit of experimenting coming on... In fact, maybe you could make the arch out of stainless for strength, then maybe ceramic could be riveted on either side. Best of all worlds... Now Roger just has to source some inconel/nimonic rivets!! The stainless arch in Bongo is made from some unspecified stainless and it has lasted for a long time. Once I had got it cut to fit snugly in the firebox, I scribed round it on some more of the material so I could make a replacement in the future. Not needed yet... Chris. HI Chris, What you say makes perfect sense to me, and is pretty much how I see things. You can actually buy Machinable Ceramic, just google 'Macor Machinable Glass Ceramic' but it's mighty expensive at £60 for a 100mm square of the 5mm stuff. I have a feeling it would get broken though. I can see the appeal of something that glows and reflects back heat. From that point of view, Inconel might be better than Stainless Steel. This post on a popular welding site says that you only need about 1/3 less heat compared to Stainless which seems to imply that it's thermal conductivity is less. I can't find any definitive figures on that though. I'm rapidly coming to the conclusion that the rate of degradation of Stainless Steel may have been overstated. I might well stick with my original plan and just make one from Stainless to start with. All I need is to weld a piece on top of the vertical plate and that's another job done. With regard to design, that's not so easy on a narrow firebox where you want to be able to remove the arch from the bottom. I might see if it's possible to have one that opens out above the narrow part between the frames. Turning it slightly sideways might still allow it to be withdrawn from the bottom, we'll see. |
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pault
Elder Statesman
Posts: 1,500
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Post by pault on Nov 14, 2018 14:01:22 GMT
My experience of stainless in fireboxes is confined to fire bars, fabricated bars made from 3mm stainless have lasted many years, eventually they seem to oxidize through and fail usually in a small area. They can be seen glowing bright orange after the engine has been working hard so I guess a brick arch will behave in a similar manner.
On the subject of composite arches I think trying to attach ceramic “things/stuff” to stainless sheet could be problematical as ceramics have a coefficient of thermal expansion far lower than that of stainless steel. Given the relatively stiff/brittle nature of ceramics strapping it to stainless would seem to be a bad move.
To me I guess there could be conflicting conditions between a stainless steel arch and a ceramic one. The stainless one would have a relatively small mass so would heat up fairly quickly as the fire heats up when working hard. A ceramic one would have a relatively large mass and so would heat up slower. Until it reaches the same temperature it takes heat from everything.
It would be interesting to see how much it would affect the performance of radiant superheaters, I suspect the negative effect on superheating would outweigh any improvement in combustion. This of course is not a problem on full size locos as they don’t have radiant elements.
I think that our smaller lumps of coal work to our advantage when it comes to burning off hydrocarbons, as the mass of a lump relatively small compared to the surface area. The lack of thick smoke from our locos when running suggests that combustion is fairly good.
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Post by andyhigham on Nov 14, 2018 15:00:57 GMT
This is a subject that the Sweet Pea fraternity have experimented, discussed and argued about from the very first time a Sweet Pea ran under its own steam
My own findings were the 2mm stainless "baffle" would have burnt away after a good afternoon of running, a 3mm baffle would last 2 afternoons. I drilled a few holes in the baffle and applied a layer of ganny (fireclay) to both sides. It certainly lasts longer than stainless and is cheap and easy to re-apply. Looking through the fire door, the baffle is definitely as hot as the fire.
The only difference between the Sweet Pea baffle and a brick arch is the angle it is set at, the Sweet Pea baffle is vertical
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Post by Roger on Nov 14, 2018 15:14:20 GMT
This is a subject that the Sweet Pea fraternity have experimented, discussed and argued about from the very first time a Sweet Pea ran under its own steam My own findings were the 2mm stainless "baffle" would have burnt away after a good afternoon of running, a 3mm baffle would last 2 afternoons. I drilled a few holes in the baffle and applied a layer of ganny (fireclay) to both sides. It certainly lasts longer than stainless and is cheap and easy to re-apply. Looking through the fire door, the baffle is definitely as hot as the fire. The only difference between the Sweet Pea baffle and a brick arch is the angle it is set at, the Sweet Pea baffle is vertical Hi Andy, That's really interesting. So it would appear that it's all about temperature? Am I right in thinking that the grate is not that far from the bottom tubes and that a deep fire could be almost level with the bottom of them? That's definitely not the situation with my firebox which I reckon is about 70mm from the top of the grate to the bottom of the tubes. I can see why this would make a huge difference to the amount of heat the arch receives. It definitely sounds like Sweet Pea could benefit from an Inconel arch which ought to last very much longer than a Stainless one. |
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pault
Elder Statesman
Posts: 1,500
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Post by pault on Nov 14, 2018 15:51:30 GMT
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Post by Roger on Nov 14, 2018 16:19:21 GMT
Hi Paul,
I see the inconel 625 claims to be good up to 980C because it retains a protective Oxide coating up to that. The Stainless Steel data shows that 304 can run into trouble when thermally cycled but the temperature for that is 870C.
Both these figures ought to be lower than we'd see but 890C looks to be Orange on a colour versus temperature chart, and this might be where the problems arise. If the arch looks to be a bright Orange, it's possibly too hot for either metal, but the Inconel ought to fare better.
It seems to me that if the arch only ever glows bright red, you can use Stainless and it ought to last almost indefinitely.
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Post by Deleted on Nov 14, 2018 16:39:16 GMT
I can only give my experience on Inconel 625 when talking about my car..as you can imagine the exhaust manifold on a high-performance IC engine is a very hostile environment...add to this that it's turbo-charged and add again that my particular engine is generating approx twice the power when built with the extra heat that this generates and I think you'll appreciate that this alloy is very good when talking heat. It's also the alloy used in the Nuclear and marine industries to name but a few. Oh, one more thing regarding longevity, my car has now covered more than 220k miles with it's original manifold, that's good enough for me.
Pete
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I find it is all too easy to go from thin fire to not enough fire to recover from in quite a short amount of time! At least if you do go into loco and drop the grate it doesn't take long to get going again with the boiler already up to temperature.
