BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

As a matter of curiosity where castings have been substituted by fabrications, are the fabrications stress relieved?

 

On that point I will not opine for a number of reasons. If not already done so, I recommend SSLCo's engineers discuss this with their insurer and the VAB to decide these options.

 

Thanks Brian, i dont doubt for a moment that should these components be produced as combined castings, as currently intended, that there would be any problems with certification. I do doubt that short of a major incident that replacements would be needed for 71000, or that the frames of 70000 or 70013 would ever be taken apart to accomodate them so the common user incentive is only a small one here. The other factor is of course that the frames have already been cut and drilled no doubt to the later scheme incorporating these components and perhaps the Patterns have already been commissioned.
Some corners should never be cut but 'over engineering' doesnt come for free either.

 

Thanks folk for those interesting opinions/discussion about the frame stretchers.
All the fabricated ones are made and in storage.
The only outstanding patterns are for the three big stretchers, as fitted to 71000.
The object of the exercise is to build 72010 as it would have left BR Crewe.
Duke has proved the acceptance of the stretchers so I don't really see why a VAB/insurer should have a problem with them, if that was your thought Sean.
Yes, it would be my intention that all these aspects will be discussed with the necessary bodies before we commit any more finance, but that is all part of our current review procedure, to ensure all 't's are crossed etc.
As for cast stretchers being needed for 70000 or 70013, you never know about frames cracking until it happens really do you, and if it did it would be handy to be able to cure it. I seem to remember a certain A4 having cracked frames until fairly recently.

 

My point was that 71000 and 70000/70013 have slightly different methods of construction in this area.
Both should be acceptible to VAB.
The change was to be introduced to the Standard Pacifics following the discovery of cracks at the lower edges of frames in Britannias. A combination of factors arising from the use of two powerful cylinders, the minimal 'play' in roller bearings and lack of reinforcement in a critical area were considered to be contributory.
Ironically with its Three cylinder drive 71000 would actually be less susceptible to these factors so unless 70000/70013 we're thus modified the 'improved' method is actually unproven on the locomotives which exhibited the problem
With Smaller pistons and lower working Pressure 72010 would also be less susceptible.
To my mind there is a choice . Maybe that choice was considered many years ago, or maybe it wasnt and thats my point.
I expect that there are a lot of issues of this nature when building a locomotive.
With 72010 in particular where the overall 'plan' is being revisited the present opportunity to contribute knowledge and ideas that may be useful is now..
Hopefully there are people involved in the overhauls of 70000, 70013, 71000 looking at this forum and this project...

 

Bill Harvey was an expert on Britannia Pacifics. In his book "60 Years of Steam" he does not make any reference to frame cracking problems until they occured from 1957 onwards. To my way of thinking, the cast cross stays on the Duke, the 9Fs and the projected Clans were simply a design development and nothing to do with frame cracking problems.

 

Mr Tank, V. Interesting - I need to check my chronology
Thanks for the book tip, not come across that one, more homework required...
As a casting It is a wondrous thing, but we are still left with a choice.

 

Although the Clans had cylinders half an inch smaller, did they use the same castings as the Brits? In that case did they share drivers with the web behind the wheel and the narrower frame spacing?

Foxy

 

The cylinder castings for both were the same and made out of steel. Cast iron liners were fitted.
They both had the same narrow frame spacing. Also the wheel castings were the same, but what do you mean about the web?

 

In traditional loco wheels the web of the spokes fans out and inwards from the outer face of the wheel boss. On the Britannias Riddles was faced with fitting the largest cylinders within the British loading gauge he could manage - to do this the frame spacing was narrowed to bring the cylinder centre line inwards but this, of course, brought the connecting and coupling rods in too. Riddles therefore fitted the Brits with flush-faced wheels that had the web on the back face (where there was now room because of the narrower frames) - at least I think that is how they were designed!

Foxy

 

Fascinating, the short answer is yes the class 8, 7, and 6 all share the same wheel pattern and 7 and 6 the same cylinder block
Interesting if this factor affected the 9f's which have the same size cylinders as brits but the mounting part of the casting is different - the centres are pushed out by (i think) another 1/2 inch to clear the motion and then the whole pushed up to the running plate and mounted at an angle (to give clearance at platform height)...

 

The 9Fs certainly had the same cylinders as the Brits but I've not seen any front end gauging diagrams to illustrate how they compared. Were the 9F cylinders mounted in a way that avoided the "web reversal" on the Brit wheels? The DoG has much smaller cylinders (illustrating one of the advantages of multi-cylinder configuration) but you say it shared Britannia wheelsets, so presumably it also has the reversed web - I'll have to have a closer look at that! Riddles got into a lot of design tweaks just to get those great big cylinders in place.....

Foxy

 

Interesting comment about the narrow frame spacing. I always thought that the frames were spaced as they were to get them on the centrelines of the axleboxes and minimise the bending stresses in that area as the foremost concern.

 

Correct Steve, It was a Bulleid design adopted by Riddles.

 

Yes steve, idea came from the Bulleid pacifics, which didnt have spoked wheels/webs and as three cylinder machines had a more even cylinder 'moment' and rigid front end. This in combination with the manganese liners resulted in very good stability in this area
(result = reduced axle box wear). This being the case the flexing of the frame would occurr, and thus 'stress', somewhere else.
My homework threw up a couple of things. Frame cracking on standards between the first coupled wheels and the cylinders became evident after several years of service and i think these are the instances detailed by Bill Harvey mentioned earlier in this thread by Std Tank .
ES Cox Mentions frame cracking on the lower edges if the frames as occurring 'soon after entering service' these were initialy patched up. Arevised spring hanger bracket was fitted to the Britts and Clans from 1955 onwards. This is i believe a different item to the integral spring hanger bracket/stretcher type castings used on 71000 and the similar items used on the 9f. form 1954.
Will see if the drawings catalogue throws any light on this.

 

I have had a look at all the relevant drawings and I am able to shed some light on this.
Originally the Britannias and Clans were built with a combined hornblock/hornkeep fixing fabrication which was welded to the frames. The spring bracket casting was seperate and riveted to the frames. It would appear that the hornkeep fixing fabrication was causing stress cracks at the bottom of the frames. The job was modified, with the hornblock only welded to the frames and a combined spring bracket and hornkeep fixing casting riveted to the frames. Also, in both cases, pinned cross stays were placed between the hornkeep fixings.
I struck lucky on this because the frame arrangement drawing for the Britannias was redrawn with a new drawing number (I have both drawings), but the similar drawing for the Clans was only altered and a note added in the top RH corner

 

That ties up with the photo ive seen, thanks for that std tank, been a pleasure learning from you. (Do you have any other recomendations for BR Standard reading materials. I have the Cox stuff, the RCTS Volumes, the Locos in 'detail' and one the HCB Rogers. Am after the RC Bond book and (now)the Harvey one)
This is clearly different (not necessarily better or worse) fron the springhanger/stretcher castings. What inspired the 'development' to this component, be it early instances of cracking, or a neater assembly process one can only speculate.
Add it to my list of ponderables for the AGM...

 

The spring hanger/stretcher castings were originally designed for the Duke (a 1 off) and added to the later Clan frame arrangement drawing. Why design and make new items for a one off? The same question applies to the rear dragbox casting. Far simpler and cost effective to construct a fabricated dragbox.

 

Might have had something to do with having more foundry and rivetting capacity than welding capacity...?
Next on the watchlist is the cylinders... watching with interests one or two attempts out there to fabricate them...
Danger is that you cant fabricate everything and the skills to make castings ? use them or loose them.
Slightly off beat/ thread question to anyone out there - Crank - to - shaft gear boxes as used on Caprotti... whats the Malaysian connection ?

 

I'm happy to be corrected but, I'm guessing this is a broadly similar arrangement to that used by Ivatt on his Cl4 2-6-0s that found its way through to the Std 3 chassis.