Live steam cylinders, what metal to use?

[syrtismajor]

Hi all!
Here is another question from me regarding my potential design for a 3.5" gauge locomotive...

One of the main components I'll need are cylinders, and unfortunately there are no available castings on the market that'll fulfil my needs (trust me I've checked). I've considered getting some cast but to be honest I am not a fan of them as I have had a bad few in the past, and all from different suppliers.

Now, I know that all cylinder castings available are either Cast Iron or LG2 bronze. I also know that it is possible to 'fabricate' the cylinder blocks (I have seen this done before and read stories of it being easily achieved on club locos) often using brass as the main frame and bronze for the liners.

I have planned out that the cylinder itself will be composed of two brass 'frames' and a bronze cylinder, while the valve block will be of four parts (the liner being bronze again). Together these parts will form a piston valve cylinder closely resembling a standard cast part with similar thickness of materials etc...

Now (finally) to the question!
Is LG2 bronze the best material to use for the cylinder?
I know of a website that offers LG2 round bar (but it also confusingly refers to it as SAE.660 which is a different form of bronze )
There is also a supplier that can provide PB.1 bronze round bar and SAE.660 bronze hollow round bar

So, I know ideally I should follow the casting convention and use LG2 gunmetal bronze, but is there a better material to use?

LG2 Gunmetal? - solid bar only, lots of boring!
PB.1 Phosphor Bronze? - as above and is more expensive
PB.102 Phosphor Bronze? - as above again, and most expensive
SAE.660 Leaded Bronze? - can be bought hollow... cheapest option!
None of these?

Many thanks in advance!

 

[kvom]

What about fabricating from a single piece of CI?

 

[Jasonb]

M-Machine sell hollow LG2 so less waste.

J

 

[rkepler]

I'd carve it out of some Durabar cast iron, myself. Much lower cost and better lubricity.

 

[syrtismajor]

I have considered CI but my mind always starts whispering 'rust' in the event I leave it too long. It's because of this I want to go with bronze.
My research in the past has also failed me. I have searched quite a bit on the internet and come to the conclusion that you could not buy hollow LG2 unless you were an industrial customer. How wrong I was! Even though it will be a long while off before any chips appear for this loco, I may buy a few inches of it now before the prices inevitably rocket again...
Thanks you lot, your help is invaluable!

 

[Philjoe5]

I had the same concerns about using cast iron in a live steam engine. But now after some years volunteering in our club's model building and boiler room I haven't seen any signs of rust in crosshead guides, or cylinder walls or external unpainted surfaces in any of the club engines both large and small.

All have steam oil lubricators attached and they all have acquired a fair coating of steam oil on the outside unpainted surfaces as well. Good steam oil is sticky at room temperature and seems to act like a protective waxy coating.

All my live steam models have cast iron (durabar) cylinders and I haven't seen any sign of corrosion when I pull the heads off.

Phil

 

[lensman57]

Hi all!
Here is another question from me regarding my potential design for a 3.5" gauge locomotive...

One of the main components I'll need are cylinders, and unfortunately there are no available castings on the market that'll fulfil my needs (trust me I've checked). I've considered getting some cast but to be honest I am not a fan of them as I have had a bad few in the past, and all from different suppliers.

Now, I know that all cylinder castings available are either Cast Iron or LG2 bronze. I also know that it is possible to 'fabricate' the cylinder blocks (I have seen this done before and read stories of it being easily achieved on club locos) often using brass as the main frame and bronze for the liners.

I have planned out that the cylinder itself will be composed of two brass 'frames' and a bronze cylinder, while the valve block will be of four parts (the liner being bronze again). Together these parts will form a piston valve cylinder closely resembling a standard cast part with similar thickness of materials etc...

Now (finally) to the question!
Is LG2 bronze the best material to use for the cylinder?
I know of a website that offers LG2 round bar (but it also confusingly refers to it as SAE.660 which is a different form of bronze )
There is also a supplier that can provide PB.1 bronze round bar and SAE.660 bronze hollow round bar

So, I know ideally I should follow the casting convention and use LG2 gunmetal bronze, but is there a better material to use?

LG2 Gunmetal? - solid bar only, lots of boring!
PB.1 Phosphor Bronze? - as above and is more expensive
PB.102 Phosphor Bronze? - as above again, and most expensive
SAE.660 Leaded Bronze? - can be bought hollow... cheapest option!
None of these?

Many thanks in advance!

Hi,

Could you possibly tell us what pressure and temp you are going to use the steam at please? this makes a difference to what material you are going to use for the cylinders and pistons.

Regards,

A.G

 

[syrtismajor]

Hi,

Could you possibly tell us what pressure and temp you are going to use the steam at please? this makes a difference to what material you are going to use for the cylinders and pistons.

Regards,

A.G

I plan to run the boiler at 90psi max where the saturated steam temperature is about 160C. This is based on the existing published designs for locos of this size. These models are also superheated (mine will use stainless steel tubes) and I have heard no problems of this set up.
The pistons will be of the same material as the cylinder liner. The piston rings however I am undecided on, I'll have to see how the PTFE ones behave in my Virginia first

 

[lensman57]

I plan to run the boiler at 90psi max where the saturated steam temperature is about 160C. This is based on the existing published designs for locos of this size. These models are also superheated (mine will use stainless steel tubes) and I have heard no problems of this set up.
The pistons will be of the same material as the cylinder liner. The piston rings however I am undecided on, I'll have to see how the PTFE ones behave in my Virginia first

Hi,

That is exactly what I trying to find out. At that temp and pressure the steam is fairly dry, I think that you'd be safe with CI for cylinder.

Regards,

A.G

 

[Runner]

Hi syrtismajor,

I am building a 3.5" locomotive of my own design, but borrowing heavily from LBSC's Doris (Black 5) locomotive. The castings for the cylinders are available in the UK but unfortunately living in Australia postage costs prohibit purchasing from the UK. This locomotive uses a piston valve configuration and I am attempting to fabricate my own cylinders using LG2 gun metal and have come up with tentative design, but unsure if it is going to work. Because LG2 gun metal is only available in round bar in Australia (as far as I know) I have to use brass to construct the bolting faces etc. Your requirements appear similar to mine therefore I would be grateful if you could let me have your basic design and construction details, which I could utilise.

Thanks in advance.

Brian

 

[syrtismajor]

Hi syrtismajor,

I am building a 3.5" locomotive of my own design, but borrowing heavily from LBSC's Doris (Black 5) locomotive. The castings for the cylinders are available in the UK but unfortunately living in Australia postage costs prohibit purchasing from the UK. This locomotive uses a piston valve configuration and I am attempting to fabricate my own cylinders using LG2 gun metal and have come up with tentative design, but unsure if it is going to work. Because LG2 gun metal is only available in round bar in Australia (as far as I know) I have to use brass to construct the bolting faces etc. Your requirements appear similar to mine therefore I would be grateful if you could let me have your basic design and construction details, which I could utilise.

Thanks in advance.

Brian

No problem Brian!
I am still working on the design but here is a quick sketch I just put together on my computer:

The lighter coloured parts are LG2 while the darker parts are brass. You may also notice that the valve chamber 'chunk' is separate from the cylinder 'chunk'. These will be fixed together with four 5BA bolts (or larger depending on space permitted). This is so they can be manufactured easily and the valve channels can be cut cleanly and accurately (even for an amatuer like me!)
Please also be aware that this sketch is far from 'to scale'

I'm not sure of the exact dimensions of the 'Doris' cylinder castings but I think that the valve chamber does not protrude from the raw casting but is acatually an extension of the separatedly manufactured chamber? (If this makes sense?)
Mine does not follow this layout to make it more prototypical and easier to hone in the timing. This is also why there is a block of brass running along the chamber in my sketch above, this is actually a steam port running the whole length of the chamber thus ensuring a port at the extreme of each end (well, about 1/8" from each end)

I'm hoping this all makes some kind of sense, if not let me know and I'll try to lay it all out step by step.

 

[Runner]

Thanks syrtismajor,

your design is better than mine, but I am limited to the size of LG2 gunmetal round that I am able to get and also the thickness of brass sheet that I am able to obtain. So my design is predicated on two LG2 cylinders with flats cut and silver soldered together to form a figure 8. At this point the two cylinders connect is where the steam passage between the cylinder and piston valve is established. Brass sheet (max 5mm thickness) is used to box in the two cylinders. I have included a rough sketch but not used to technical drawing used confusing dotted lines to show hidden features and afterwards thought of using different colours to separate different parts. I hope you can understand it. Please give me your views on the viability of it.

Thanks again

Brian

 

[syrtismajor]

Brian,
Your drawing makes perfect sense! It looks very similar to a method used on a three cylinder 'Helen Long' named Helen Longish by its builder. He used fabricated cylinders of brass and LG2 rather than castings.

The link to the build log is: http://www.modeng.johnbaguley.info/locos/25inch/Helen%20Longish/helen.htm

The construction of the centre cylinder starts on page 5 while the outer cylinders starts on page 9. He went for a replication of a casting rather than my idea of building the valve chamber and cylinder separately. I'm hoping that my idea helps in that there won't be so much heat required to 'cook' the job. It will also mean that if a mistake is made then the whole piece won't be ruined! He was also working in 2.5" gauge which is a lot smaller than 3.5"

Incidentally, I have also read of two other builds including one where a chap replicated castings by fabricating his own cylinders for a 5" gauge Merchant Navy locomotive, that was one of the largest and most powerful passenger locos in the UK. That means the cylinders would have had a bore of over 1.5"!

 

[Runner]

Thanks syrtismajor,

that URL you provided me is a great insight to what I need to do. It re-inforces the fact that in general if you have a problem, somebody's also had it and provided a solution. It has answered many of the queries I already had and also answered the queries I hadn't even thought of. My residual concern is finishing the bores off after silver soldering.

The URL is added to my favourites list.

Good luck with your 3.5" gauge locomotive.

Brian