3D printing a smokebox

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Mamod sterling
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3D printing a smokebox

Post by Mamod sterling » Sat Sep 24, 2022 6:59 pm

I've been into 3D printing for years. It started as part of my job, but once hobby resin printers became reasonably priced, I set up at home.

During Covid, I print a lot of loco shells for OO, the printers paid for themselves in that respect, and it gave me a decent depth of knowledge with the printers and resin.

One thing I did avoid though, we steam parts. I've done them in the past in polycarbonate on an FDM printer, which are used on my Fred Dibnah KND engine. But I've recently found that my preferred Brand, Siraya Tech, do a high temperature resin that is good to 160degC, making it a potential candidate for smokeboxes and suchlike.

So I lashed up a prototype design, based off the IP Engineering Jane riveted smokebox. Printed in Siraya Tech Fast as a trial before buying the sculpt HT.

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Its designed to fit the Mamod/IP boiler, but at a slightly higher pitch. Its also a bigger outside diameter to give an appearance like Dolgoch has with its large dia smokebox.

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Plenty of space for pipework and a chuffer pipe, with the base left open to avoid gathering up pools of watery oil.

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Other than curing, I've made no attempt to tidy this print up, I just wanted to rough it out to trial it.

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Pictured with my Jane. THe smokebox won't be going on this, its own is lovely as it is. The new design is planned for a mamod bash.

Paul.
Mamod SL1 - ripe for modification
Mamod Brunel - ongoing modification
IPE Jane - rebuilt from 45mm to 32mm gauge, 'globetrotter'

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Re: 3D printing a smokebox

Post by SimonWood » Fri Sep 30, 2022 11:31 am

(a) Your smokebox looks stunning as it is, remarkable quality given you've done no tidying up!
(b) Following with interest how 3D parts cope with heat on a live steamer; I am following in Trevor's footprints building his Kerr Stuart 4420 design which mixes 3D chassis and body with brass and copper motor and boiler (but so far I have only got as far as the chassis!)

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Re: 3D printing a smokebox

Post by Trevor Thompson » Sat Oct 01, 2022 9:51 am

It's good to see someone else stretching what 3d printers can achieve. I look forward to hearing how this smokebox copes with the heat. However I fear that the smokebox might get hotter than 160 degrees. Just have to try it to find out!

I will get back to working on 4420 shortly. The latest prospect is flash steam boilers which might help with keeping heat away from the plastic components.

Trevor

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Re: 3D printing a smokebox

Post by Mamod sterling » Fri Oct 07, 2022 11:43 am

SimonWood wrote: Fri Sep 30, 2022 11:31 am (a) Your smokebox looks stunning as it is, remarkable quality given you've done no tidying up!
(b) Following with interest how 3D parts cope with heat on a live steamer; I am following in Trevor's footprints building his Kerr Stuart 4420 design which mixes 3D chassis and body with brass and copper motor and boiler (but so far I have only got as far as the chassis!)
Thanks Simon,

To be honest, this one was heavily compromised by me printing it straight onto the platen! the very bottom of the flare is oversize as such, but the rest has come out okay.

I've done quite a lot over the years with 3D printed parts at temperature, as I used to design oil separators for car engines, prototyping them, and testing on heated rigs and dynamometers. I used to predominantly work with polycarbonate, and used it for my first on-mamod parts. Materials that were once considered 'exotic' for printing are much more readily available now.

Thanks
Paul.
Mamod SL1 - ripe for modification
Mamod Brunel - ongoing modification
IPE Jane - rebuilt from 45mm to 32mm gauge, 'globetrotter'

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Re: 3D printing a smokebox

Post by Mamod sterling » Fri Oct 07, 2022 11:50 am

Trevor Thompson wrote: Sat Oct 01, 2022 9:51 am It's good to see someone else stretching what 3d printers can achieve. I look forward to hearing how this smokebox copes with the heat. However I fear that the smokebox might get hotter than 160 degrees. Just have to try it to find out!

I will get back to working on 4420 shortly. The latest prospect is flash steam boilers which might help with keeping heat away from the plastic components.

Trevor
Thanks Trevor.

The steam temperature at modest pressures is only in the region of 120-140, so temperature in the boiler due this is going to be of a similar range. Conduction of combustion heat might be a potential issue, but should largely be governed by the presence of water in the boiler. I intend to do some research and verify the surface temperatures as part of this work.

Nevertheless, there is still an element of 'suck it and see' with this project.

Thanks
Paul.
Mamod SL1 - ripe for modification
Mamod Brunel - ongoing modification
IPE Jane - rebuilt from 45mm to 32mm gauge, 'globetrotter'

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Re: 3D printing a smokebox

Post by GTB » Fri Oct 07, 2022 2:21 pm

Mamod sterling wrote: Fri Oct 07, 2022 11:50 am The steam temperature at modest pressures is only in the region of 120-140, so temperature in the boiler due this is going to be of a similar range. Conduction of combustion heat might be a potential issue, but should largely be governed by the presence of water in the boiler. I intend to do some research and verify the surface temperatures as part of this work.
Out of curiosity I looked up what little tech data the supplier has online for that polyurethane-acrylic. Not the most comprehensive I've ever seen..... Don't think I've ever seen a tech data sheet written using a spreadsheet before, either.......

It would appear the quoted temperature of 160C is the HDT (Heat Deflection Temperature), but they don't bother saying what test parameters they used. My understanding is that HDT doesn't predict service life at elevated temperatures, it just indicates when the polymer starts to soften enough to distort under load.

I usually build and use internally fired boilers with gas fuel. Combustion gas temperatures at the smokebox end of the flue are well over 200C in those and I've measured external surface temperatures up to 180C on smokeboxes, depending on firing rate. I've also had an unpainted steel smokebox turn straw when I was testing the boiler output, so the outside of the smokebox got up over 200C at full firing rate.

I've recently been playing around with a spirit fired pot boiler, which is closer to Mamod territory. I haven't pointed the IR thermometer at that yet, or dug out the thermocouple to check gas temperatures, but the firebox shield has turned purple in places, so surface temperatures have been up around 280C.

The only high temp polymer I had much experience of in lab instruments was Polyimide. That will survive working temperatures over 350C for reasonable periods, but after enough hours it will degrade and start to crack, as aerospace companies have found out the hard way. I use Kapton tape for holding down parts to stop them moving while being soft soldered, but the adhesive usually stops working before the tape deteriorates....

Graeme

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Re: 3D printing a smokebox

Post by Mamod sterling » Fri Oct 07, 2022 2:59 pm

GTB wrote: Fri Oct 07, 2022 2:21 pm
Mamod sterling wrote: Fri Oct 07, 2022 11:50 am The steam temperature at modest pressures is only in the region of 120-140, so temperature in the boiler due this is going to be of a similar range. Conduction of combustion heat might be a potential issue, but should largely be governed by the presence of water in the boiler. I intend to do some research and verify the surface temperatures as part of this work.
Out of curiosity I looked up what little tech data the supplier has online for that polyurethane-acrylic. Not the most comprehensive I've ever seen..... Don't think I've ever seen a tech data sheet written using a spreadsheet before, either.......

It would appear the quoted temperature of 160C is the HDT (Heat Deflection Temperature), but they don't bother saying what test parameters they used. My understanding is that HDT doesn't predict service life at elevated temperatures, it just indicates when the polymer starts to soften enough to distort under load.

I usually build and use internally fired boilers with gas fuel. Combustion gas temperatures at the smokebox end of the flue are well over 200C in those and I've measured external surface temperatures up to 180C on smokeboxes, depending on firing rate. I've also had an unpainted steel smokebox turn straw when I was testing the boiler output, so the outside of the smokebox got up over 200C at full firing rate.

I've recently been playing around with a spirit fired pot boiler, which is closer to Mamod territory. I haven't pointed the IR thermometer at that yet, or dug out the thermocouple to check gas temperatures, but the firebox shield has turned purple in places, so surface temperatures have been up around 280C.

The only high temp polymer I had much experience of in lab instruments was Polyimide. That will survive working temperatures over 350C for reasonable periods, but after enough hours it will degrade and start to crack, as aerospace companies have found out the hard way. I use Kapton tape for holding down parts to stop them moving while being soft soldered, but the adhesive usually stops working before the tape deteriorates....

Graeme
Thanks Graeme,

Make no mistake, I would not entertain a printed smokebox for a gas fired flue type boiler, the gas going through it is far too high alone (though with a suitable non-contact flue going through the box, it may well be feasible). I would however use the casting type to produce a metal one with the investment type casting process......

I'm looking purely at pot boilers, and those have sufficient distance from the 'flue' heatshield to keep the bulk of the flame heat onto the boiler and straight up. I'm considering shortening the metal flue/shield on my Mamod project to keep the heat slightly further back on the boiler.

Thanks
Paul.
Mamod SL1 - ripe for modification
Mamod Brunel - ongoing modification
IPE Jane - rebuilt from 45mm to 32mm gauge, 'globetrotter'

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Re: 3D printing a smokebox

Post by GTB » Sun Oct 09, 2022 11:24 am

Mamod sterling wrote: Fri Oct 07, 2022 2:59 pm I'm looking purely at pot boilers, and those have sufficient distance from the 'flue' heatshield to keep the bulk of the flame heat onto the boiler and straight up. I'm considering shortening the metal flue/shield on my Mamod project to keep the heat slightly further back on the boiler.
I figured you knew what you were doing, but others reading the forum in the future may not have that background. Anyway......

I've never pulled a Mamod apart, so what follows is speculation.

Rather than shorten the heatshield, which would reduce the heating area and could limit steaming, using some sort of barrier of ceramic fibre sheet might be a better option at limiting heat radiation and conduction. Putting a suitable size piece of K&S brass tube down the chimney for the cylinder exhaust and packing insulation into the smokebox might also limit heat transfer into the polymer.

I've used wool felt for gas fired boiler lagging without issue and it would be an alternative to ceramic fibre, as it would withstand the temperatures likely to be reached in a Mamod anywhere there was no direct flame impingement.

Graeme

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Re: 3D printing a smokebox

Post by Mamod sterling » Mon Oct 10, 2022 5:11 pm

GTB wrote: Sun Oct 09, 2022 11:24 am
Mamod sterling wrote: Fri Oct 07, 2022 2:59 pm I'm looking purely at pot boilers, and those have sufficient distance from the 'flue' heatshield to keep the bulk of the flame heat onto the boiler and straight up. I'm considering shortening the metal flue/shield on my Mamod project to keep the heat slightly further back on the boiler.
I figured you knew what you were doing, but others reading the forum in the future may not have that background. Anyway......

I've never pulled a Mamod apart, so what follows is speculation.

Rather than shorten the heatshield, which would reduce the heating area and could limit steaming, using some sort of barrier of ceramic fibre sheet might be a better option at limiting heat radiation and conduction. Putting a suitable size piece of K&S brass tube down the chimney for the cylinder exhaust and packing insulation into the smokebox might also limit heat transfer into the polymer.

I've used wool felt for gas fired boiler lagging without issue and it would be an alternative to ceramic fibre, as it would withstand the temperatures likely to be reached in a Mamod anywhere there was no direct flame impingement.

Graeme
Thanks Graeme,

Some very useful ideas. We were thinking on similar lines with the chimney, I was fitting a summerlands chuff pipe, 1 for sound, and 2 to channel the heat.

Thanks.
Paul.
Mamod SL1 - ripe for modification
Mamod Brunel - ongoing modification
IPE Jane - rebuilt from 45mm to 32mm gauge, 'globetrotter'

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