Help with 'Speedy' valve gear and other issues...

[Roger]

Nov 14, 2018 16:39:16 GMT @greenglade said:

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

Hi Pete,
That's fair comment, but the temperatures reached by an exhaust probably don't reach the bright orange where stainless steel starts to really suffer. As long as we don't stray into that sort of temperature, stainless ought to be good enough.

[pault]

Looking back to my Dynocar results I found that the highest gas temperature I measured was 992 °C This was measured in the centre of the firebox tube plate by a long thermocouple poking out of one of the top row fire tubes by about 6mm.

[steamer5]

Hi Rodger,
Very interesting discussion going on here! To throw another 2 cents worth in...... I worked at a petrochemical plant producing methanol. To brake down natural gas it’s passed thru spun cast inconel tubes, skin temperatures of approx 950 C, they ran bright orange. The longest run we had without shutting down when I was there was 3 1/2 years! The other plant close by doing the same thing had a lot of tube failures one night as they let the temperature run away with a low gas flow thru them, never heard what the temp was, but comments like you could see thru them indicate that it must of been a lot more!
Maybe not that relavent to our size but the chance of burning inconel out would be very small.

Cheers Kerrin

[andyhigham]

Just to throw in another thought
Is it just temperature that burns stainless in the firebox? Or a combination of temperature, free oxygen and other gasses?

[Roger]

Good points chaps. That comment on the Inconel datasheet that Pault linked did say about the oxide layer being preserved at high temperatures, so free Oxygen probably doesn't affect it. Whether that's the same with Stainless is the question. Maybe not, and that might explain the difference.

If there's an Oxide layer, one imagines that it doesn't matter what other gasses are present, they can't reach the base metal. If the layer is compromised, then maybe that's where it all goes wrong? If the Oxide layer breaks down, that presumably gets oxidised again, losing some of the base metal. I'm no metallurgist, that's just me trying to think it through logically.

[Deleted]

Well, all I can add is that under full throttle my manifold is a very bright cherry red...something I have witnessed on a number of dyno sessions...

[Oily Rag]

Titanium, I would be interested in seeing how it holds up as fire bars and as an a arch. (I think it would out last stainless by a factor of 10)
It is not as difficult a material or as expensive as one may think.
I am not sure of supply of thin plate these days as it has been 18 years since I purchased some.

[chris vine]

Hi All,

I have to say that I am not sure what the stainless arch is made from in Bongo, but it is around 3 mm thick and doesn't seem to have deteriorated much. I am sure something made out of a bit of old jet engine jet pipe would be ideal for this job!!

Pete, you ask for my thoughts as to why Don suggested more air flow would be needed with an arch in place. I think perhaps what he means is that you would have to have less resistance somewhere else because the switching of direction round the arch will create a small pressure drop. So maybe bigger holes in the grate would compensate. Only a thought.

here is, on ebay, an afterburner nozzle segment. Now that really will resist heat if you can fashion it into your arch. Only a few quid too!!
www.ebay.co.uk/itm/Aircraft-Jet-Engine-Afterburner-Nozzle-Segment-Assembly-1R4C/142578054038?epid=3011241595&hash=item2132507396:g:8KQAAOSwR6RaLpE3


Have fun experimenting!
Chris.

[Deleted]

Nov 14, 2018 19:58:47 GMT chris vine said:

Hi All,

I have to say that I am not sure what the stainless arch is made from in Bongo, but it is around 3 mm thick and doesn't seem to have deteriorated much. I am sure something made out of a bit of old jet engine jet pipe would be ideal for this job!!

Pete, you ask for my thoughts as to why Don suggested more air flow would be needed with an arch in place. I think perhaps what he means is that you would have to have less resistance somewhere else because the switching of direction round the arch will create a small pressure drop. So maybe bigger holes in the grate would compensate. Only a thought.

here is, on ebay, an afterburner nozzle segment. Now that really will resist heat if you can fashion it into your arch. Only a few quid too!!
www.ebay.co.uk/itm/Aircraft-Jet-Engine-Afterburner-Nozzle-Segment-Assembly-1R4C/142578054038?epid=3011241595&hash=item2132507396:g:8KQAAOSwR6RaLpE3


Have fun experimenting!
Chris.

Thanks for your answer Chris...

Seeing you mention jet aircraft nozzles Chris, I did a little reading on both jet and rocket engines. I found one site with a diagram and details of the materials used for the various components within a rocket engine. I wasn't surprised to see for the nozzle that Inconel is used, of course, Inconel comes in various grades (not shown which in the diagram) but I'm convinced that Inconel 625 should last many years if not forever as an arch in our models.

Pete

[Deleted]

Just noticed this too from one of the largest Jet engines out there...

Exhaust


Exhaust from Boeing 787 engine (GEnx, one of the world's largest jet engine - Source)

From FAA Aviation Maintenance Technician Handbook - FAA-8083-30:

Inconel and stainless steel alloys. The Inconel [nickel-chromium-iron] alloys are frequently used in turbine engines because of their ability to maintain their strength and corrosion resistance under extremely high temperature conditions.

[JonL]

Thats who pays my wages! I work on the dark green ones with two big egg whisks on top though...

[jma1009]

I think we are getting into serious thread drift here!

Despite some comments here that stainless deteriorates in a firebox, this cannot be so, otherwise radiant stainless super heaters extending into the firebox would not last long - and we all know they last a long time.

I made a stainless grate for one of my locos and to the best of my knowledge has not been replaced by it's subsequent owner and is now over 20 years old.

Chris's description of the brick arch directing the path of the firebed gases into an extended path is simply so that in a fullsize loco the hydro carbons get burnt off by radiant heat refracted back downwards from the brick arch.

Lots of narrow gauge and large miniature locos have no brick arch fitted. Some of these locos have been running quite happily for over 150 years with no brick arch.

Cheers,

Julian

[pault]

Dont forget that superheaters are cooled by the steam or air going through them.

[Jock McFarlane]

Nov 14, 2018 21:41:58 GMT jma1009 said:

I think we are getting into serious thread drift here!

Despite some comments here that stainless deteriorates in a firebox, this cannot be so, otherwise radiant stainless super heaters extending into the firebox would not last long - and we all know they last a long time.

I made a stainless grate for one of my locos and to the best of my knowledge has not been replaced by it's subsequent owner and is now over 20 years old.

Chris's description of the brick arch directing the path of the firebed gases into an extended path is simply so that in a fullsize loco the hydro carbons get burnt off by radiant heat refracted back downwards from the brick arch.

Lots of narrow gauge and large miniature locos have no brick arch fitted. Some of these locos have been running quite happily for over 150 years with no brick arch.

Cheers,

Julian

I spent a week  in Nov 72 riding on the footplates of standard gauge engines at a coalfield in Ayrshire. None of the 3 engines there were fitted with brick arches and there were no steaming problems.  However the the cost of coal did not have to be considered and maintenance of the arch was also a saving in time and money.

[Roger]

To summarise my thoughts on this having read and absorbed all of the comments....

I get the impression that some boilers will significantly benefit from arches, but some will not. The effects will surely depend on parameters such as how big the firebox is front to back compared to how wide it is? Directing gasses toward the back of a very long firebox would seem to be a logical thing to do, not only to capitalise on the internal area of the firebox itself, but to direct gasses over Radiant Superheaters and also ensure that the top tubes have their fair share of gasses flowing through them.

In a boiler that has a wide firebox that isn't very long front to back, you could argue that gasses rising up the firebox will prefer to exit lower down rather than rise to the top. Either way, it's unlikely that all tubes will receive their fair share without some kind of intervention.

It would be interesting to figure out a way to measure the relative flow through the lower and upper tubes. If the boiler happens to provide pretty even flow without an arch, then I think it would benefit less from having one compared to a boiler with uneven flow.

From the point of view of materials, if the arch only gets to a fairly bright red heat, I can't see any issues with Stainless Steel. If however, it's getting into the Orange heat zone, then that's likely to be an issue. My guess is that's what's happening with those Sweet Pea arches that disintegrate so quickly. If the fire is up close to the arch, I can see how this may well be what's happening. It would be interesting to repeat that video that someone did for a Rosebud grate, looking into the firebox through a transparent (Quartz?) window.

It seems likely that combustion would be improved by giving a longer path for the process to complete in, but whether we'd notice that seems unlikely.

It's certainly interesting and I'm going to fit a Stainless Steel one initially to see how it lasts. I haven't decided on the final shape yet, it's pure guesswork really. You could argue that too large an arch would force too much flow through the top flues which seems to just reverse one of the problems it was there to resolve.

[Deleted]

I'm also going to fit an Arch Roger, I am happy with this decision which IMHO will help with combustion, better efficiency, protect the lower tubes and keep them cleaner. I'm undecided as to whether I fit a small baffle plate too and if so whether it's fixed or adjustable, I have some ideas of how to mount a baffle but won't know for sure until I look into it deeper...we shall see. Thanks to the 'Locomotiveman's pocketbook' that I recently bought I understand the fire, it's arch and damper settings a lot more. I have another couple of LNER crew pocketbooks on their way which may give yet more insight into the operation of a steam locomotive. I do like reading these mini tomes, lots of very helpful info in all aspects with great diagrams.

[Oily Rag]

A well thought out approach by Roger.
A reminder, in regards to arches in full size locos, there is good reason why they were installed and continued to be installed to this day. (the functions of the arch have been mentioned and are well understood in the full size world)
In the smaller choo choos their value has been debated for years and still continues to be debated. I add that the plural of anecdote does not equal fact.
Perhaps a correctly proportioned arch may have a benefit in 5 and 7 1/4" locos. Give it a go and I and others will enjoy seeing the test results.

Nov 15, 2018 8:59:05 GMT Roger said:

To summarise my thoughts on this having read and absorbed all of the comments....

I get the impression that some boilers will significantly benefit from arches, but some will not. The effects will surely depend on parameters such as how big the firebox is front to back compared to how wide it is? Directing gasses toward the back of a very long firebox would seem to be a logical thing to do, not only to capitalise on the internal area of the firebox itself, but to direct gasses over Radiant Superheaters and also ensure that the top tubes have their fair share of gasses flowing through them.

In a boiler that has a wide firebox that isn't very long front to back, you could argue that gasses rising up the firebox will prefer to exit lower down rather than rise to the top. Either way, it's unlikely that all tubes will receive their fair share without some kind of intervention.

It would be interesting to figure out a way to measure the relative flow through the lower and upper tubes. If the boiler happens to provide pretty even flow without an arch, then I think it would benefit less from having one compared to a boiler with uneven flow.

From the point of view of materials, if the arch only gets to a fairly bright red heat, I can't see any issues with Stainless Steel. If however, it's getting into the Orange heat zone, then that's likely to be an issue. My guess is that's what's happening with those Sweet Pea arches that disintegrate so quickly. If the fire is up close to the arch, I can see how this may well be what's happening. It would be interesting to repeat that video that someone did for a Rosebud grate, looking into the firebox through a transparent (Quartz?) window.

It seems likely that combustion would be improved by giving a longer path for the process to complete in, but whether we'd notice that seems unlikely.

It's certainly interesting and I'm going to fit a Stainless Steel one initially to see how it lasts. I haven't decided on the final shape yet, it's pure guesswork really. You could argue that too large an arch would force too much flow through the top flues which seems to just reverse one of the problems it was there to resolve.

[Roger]

Time to add the finishing details on the backhead cladding.


These are the dummy split lines to represent the separate plates this is supposed to be made up from. The engraving is 0.6mm deep and 0.5mm wide, machined 0.1mm deep per cut and 3000RPM and 5mm/min


20181115_151238 by Roger Froud, on Flickr

These are the 1mm holes that are supposed to be for dome headed slotted screws that join the plates together.




20181115_171035 by Roger Froud, on Flickr

The screws would be too small to be real screws with slots, but I found some 1mm Rivets with suitable heads.



20181115_200753 by Roger Froud, on Flickr

This is how it looks with the rivets cropped to length and crimped lightly on the back using the riveting press
.

20181115_200803 by Roger Froud, on Flickr

The back looks like this.

20181115_200820 by Roger Froud, on Flickr

I've had to buy another 100 rivets, I've used all the ones I originally bought.

[Deleted]

nice one Roger...a true work of art...

Pete

[simplyloco]

I thought my Brit backhead was nice, but yours... 
John