P2 Locomotive Company and related matters

Lots of incredible progress!
One question I have, why are the areas in yellow not welded? (Excuse the markup, it was done on the phone!)

 

Brilliant progress, and another very interesting read! Thank You for posting the link.

Richard.

 

The fabricated cylinder block is like a 3-dimensional jigsaw which requires welding bits together in a very precise sequence so that the welder can gain access as required. I'm guessing that the current image of the block only shows the welds for which the sequence has been worked out.

 

Purely out of interest, what is the life expectancy of a fabricated & welded cylinder, as compared with a cast iron one? Obviously the P2 Group have the CAD and assembly / welding drawings to hand if another block is required, but I'd be interested to know - Manufacturing another block wouldn't probably be as difficult as say manufacturing another V2 monobloc, but it certainly wouldn't be a small job either...

Richard.

 

I’d be surprised if it’s not being made as a life of engine component in the same way a cast one would. I presume the fabrication will still have liners in the bores and these are the components (together with valve seals) that see the most wear and are regularly serviced and replaced.

Its getting a full PWHT so to me nothing suggests it’s going to be coming out of the frames any sooner than a cast component.

In the days of yore large castings of this size were entirely the norm. Nowadays fabrication is the norm. It’s a sign of the times more than anything in my book.

Castings aren’t perfect. They often live life with significant residual stresses in them that given enough use and time will initiate cracks as has happened to the V2.

I think the P2 group in using the more standard (nowadays) fabrication method and aiming to get all the residual stresses from welding out in a post weld heat treat are creating a superior cylinder assembly
to a cast one.

All that being said, the method by which that heat treat is conducted is important. An electric oven is the ideal, there must be some big ones in the country somewhere? Sheffield? Port Talbot?

Failing that heat blankets could be used in abundance inside (or outside) a fabricated box, an ISO container could actually be bricked up on the inside in theory if you wanted a makeshift oven.... Did someone say Heath Robinson....?

600/650degrees or so for 6 hours. The precise parameters are set by the welding engineer but that’s roughly what I’d expect to see.

 

Thank You for your input Sir! Very much appreciated... I was wondering if it would be a lifetime assembly, or whether it would require renewal more frequently... I was basing this on my very limited knowledge that cast iron does not rust away as quickly as steel, but I appreciate that we are talking heavy section components, not thin platework.

Richard.

 

I think A1slt did enquire about having a cast cylinder block made but their supplier looked at the complexity of the casting and declined.

 

Think the company that did Tornado's looked at it and laughed, have seen the footage on a roadshow somewhere on YouTube, presented by Mark Allatt.

 

I started to type something similar but then abandoned it. Steel will definitely corrode faster than iron and anyone with an inside cylindered locomotive will know that corrosion of the cylinder block is its achilles heel, even as an iron casting. At least with steel there is more chance of a repair.

 

Thermofax in Dudley will put 10 tonnes of steel over 1000 deg C in a 4x3x2m electric furnace for you, if you want it and can cover the electricity bill, I'm sure there are others. Also a couple of big vacuum and inert gas ovens out there, although I doubt anybody with a nice clean vacuum oven is going to want a nasty carbon steel fabrication in it.

 

I hope the mods don't mind me posting this here as well as the A1 thread but both A1 and P2 are covered in the Trust's first 'virtual' convention but each is likely to generate different replies.

 

I apologise in advance for going off-topic, but I have a question which has arisen from watching the very interesting Annual Convention presentation above....

I am restoring a 71 year-old bus, and have just had a new front scuttle plate made in MS. I was going to screw it to the timber framework and MS support brackets using stainless wood screws and setscrews, replacing the original and much-corroded MS original fasteners... My thinking being that the whole would wear better than it has done so far.

From the presentation, I have learned that electrolytic corrosion takes place between Stainless Steel and MS - I didn't know that. I know all about the electrolytic corrosion of alloy panels mounted over steel flitching brackets, but I was wondering if anyone could give me an idea of what the rate of electrolytic corrosion is between Stainless and MS, as compared with aluminium alloy and MS?
I am now having second thoughts, and will probably revert to MS fasteners.

Richard.

 

Could you use good old brass screws?

 

Unless the components are permanently submerged I suspect that the electrolytic corrosion will be negligible and certainly much less than MS to Al. A bit of mastic between the stainless screw and mild steel sheet might help. Sounds like an interesting project - worth a few pics in 'Everything else heritage'?
Ray.

 

I suspect you'll see (if you live long enough - it's not a rapid process!) far more damage due to oxide jacking from the rusting ms screws than you would galvanic corrosion of ss screws But, as previously suggested, a switch to brass screws would solve the oproblem.

 

Thank You for your replies Gents! Much appreciated.
I appreciate that the operating conditions of the bus are vastly different to those under the cab floor of a steam locomotive - I expect the front of the bus to experience rain, but not the acidic mix of being submerged or covered in coal dust... I may stick with the stainless ones after all. The brass beading screws I've so far removed during the restoration are buggers... They start to turn, but have a propensity to shear part-way down the shank. The easy way round this is to turn the beading strip upside down and start with new holes, otherwise I'll be building a totally new body!
I'll add some photos in the "everything else heritage" section.

Richard.

 

You should be fine with stainless screws in that environment. One of the important factors with electrolytic corrosion is the relative surface areas of the two materials in the galvanic cell; so if you have a large area of the more noble metal with less noble fasteners then the fasteners are going to have a hard time. Since you're proposing the reverse of that situation, with large MS panels and small SS screws, the rate of corrosion of the MS should be much reduced. Or, as also noted above, if you can seal the surface of the mild steel, especially where it's in contact with the stainless fasteners, then no significant issues should ensue.

 

Once again, Thank You! I have a choice of brass or stainless for the wood screws, not sure if I can obtain brass countersunk machine screws though. But if the rate of corrosion isn't significant, I'll probably stick with the Stainless ones. The old plate itself had delaminated to 3 times its original thickness in some places, but oddly enough, around the screw holes it was fine. In other places it had thinned right down to paper thickness. The screws had rotted to a fraction of their original diameter too! I think I can safely say this time around it will outlive me!

Better get back to the P2 now, otherwise I'll be getting shot for waylaying the thread!

Richard.

 

I would have thought that Road Salt and Damp retention would be the main problems for a bus framework.
I know road salt does horrendous damage to Rails through level crossings, often within a few years of installation.

 

You are quite right. Strangely enough, it's the rear and offside framework on my bus which has suffered the most. It's usually the nearside, as it trawls through all the build-up of slush and crud at the kerbside. I'll be treating the wheelarches with a coating of pitch paint or similar, as well as the underside of the rear chassis extensions. London Transport did that and as a result, Routemasters have always been difficult to break up due to their solidity.

Richard.