P2 Locomotive Company and related matters

not any old George . that is Coronation , by then carrying the number 2663. if any engine deserved preservation , that was it

 

Indeed , I'm no welder but I know things move when you weld even when tacking.

 

Yes, I know it's the former 5000, but if I'd referred to it by name you wouldn't know which Coronation I meant . I think it was LMS No 25348 by this time.
I'd have loved to see a George preserved, but given the magnificent range of names employed, I think I might have chosen Ptarmigan or Otterhound. It's great that a new build George is underway (even if I think a Prince might have been more useful).
And here's my 3mm scale version of LNWR No 5000/1800 Coronation, just to show my bona fides.

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Taken From FB.

Good to hear the whole shebang's going in the oven for a bake at gas mark 600/650C for a few hours. That is the only way you'll stand a chance of such a complex steel fabrication meeting the tolerance requirements for the valves and pistons.

Without this every time you shave a few thou here or there the residual stresses from welding will pull the structure back and forth and you'll be chasing your tail. Leave it alone for a few days and it changes shape again.

The only hope of getting them out is baking them out. Bring the whole structure up to the transition temp of the steel and filler and allow the covalent bonding process to "flow" residual stresses back out of the structure.

The post heat treat proof (pressure) test further washes what residuals are left.

Credit where it's due, this is probably the best way of making a new cylinder in the 21st century as outlined in the posts above, but it aint easy. Kudos to the P2 team.

To be a pedant, CAD Design is like Saying ATM Machine. Computer Aided Design Design.

 

Many thanks for that. As an engineer much appreciated.....where to start on the weld...

 

Edited with some commentary.

mmm tough one. That in itself is a puzzle.

 

As I say I'm not a welder, but I would have thought it will have to done in stages to prevent heat build up....come on welders...give us a clue!

 

I remember seeing the bed for a 25 ton Press being welded up and the welder went to various areas around the fabrication in turn. Then it was put in a large "oven" over the weekend and kept at about 500 deg C for two days to stress relieve. Then it was machined. Castings were left outside for several months/years before machining, where possible. Certainly that was when "Stock" was kept, rather than the current "Just in Time" practise.

 

I designed a pair of transport stands for a 90 ton turbine rotor. When it was being welded some of the welds cracked. We had to cut holes in the plates to allow flexibility and prevent heat build up. The way the weld metal is laid down will also have an effect. If the weld is laid down by weaving the electrode you have a larger localised heat input an greater thermal stress. By laying down a series of "strings" of weld the later passes partly relieve the stress in the earlier ones and reduce the thermal stress.

I am not an expert in this field but have had the good fortune to work with very experienced welding engineers and metallurgists.


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Tender tank now on site following grit blasting.

 

Ah, I'll have a look. I don't like facebook, but admit to having been on it a bit more these last few days. It's not too bad if you can separate the wheat from the (mountains) of chaff!
Thank You!

Richard.

 

In the case of such a complex welded structure, I wonder if stress relieving will need to be carried out at intermediate stages during the construction process, in addition to after completion, with checking and machining to shape at each stage.

 

I'm sure it is safe to assume that the P2 engineering folk know exactly what they are doing and it will be in accordance with all the relevant standards and requirements. They certainly have done a very good job so far!

 

Doubt it. The sequence for these structures is usually fabrication - Post Weld Heat Treat - machine to size.

Components may be warmed with oxy or butane (200 degrees or so) before passes of weld and during tacking but it’s not the same as a PWHT which is a a defined duration and temperature (650 degrees is not uncommon) that is specific to the materials and method of welding. I’d assume MiG in this case.

It’s clear that the Engineering team are well on top of this. It’s hardly the first time such a thing has ever been done either. This is pretty common practice in industry and the processes are well understood.

Looking at the whole block thinking about the assembly sequence my best guess is that you tack as much as possible together and get all the bits in the right position, then selectively start to lay down the full depth welds on bits least likely to move.

I don’t know really, but thats my inclination. Maybe just get the cylinders and frame plates nailed down first and then add the chambers and passages later.
Maybe someone on the Facebook page should ask what the sequence is. They have been pretty forthcoming with answering questions to other folk?

It’s almost a certainty that the welders will use stretchers and support beams tacked in to strategic positions to minimise distortion as much as possible. Once you start putting down the full penetration welds, the heat and subsequent distortion is a guarantee.

It will be an incredibly strong structure at the end easily tougher than a casting as mentioned by the P2 team.

Does anyone have an idea of what the LNER casting weighted? This is 5750 kg, but is that lighter or heavier than the original? Surely it’s lighter just curious by how much....

 

I asked this question in relation to the short boiler: Struck me that with a lighter cylinder block and the boiler centre of gravity a foot further back there was a danger of unweighting the front end. The reply was that the fabricated cylinder block, together with the valve gear was more likely to be heavier than the original and the shorter boiler allowed this to be so...

 

That reminds me of my early days...castings outside...until you got a "green one", one that had chilled quickly making it very difficult to machine or scrape even with a carbide tip as it was so hard.

 

A further cylinder update here:

https://www.p2steam.com/2020/04/02/cylinder-design-and-fabrication-progress/

Foxy.

 

Here's some footage of the tender tank being delivered to DLW and placed on accommodation bogies:



Foxy

 

Nice! Some good manoeuvring from the HGV Driver too (although we didn't see how many goes it took!)

Richard.

 

Fabulous....