Tyre Flange Profiles

I'm preparing drawings of new brake blocks for the NVR's Danish 0-6-0T loco. These each have an extension that wraps over the tyre flange and follows it closely so as to locate the block laterally.

I'm looking for a dimensioned drawing or sketch of P1 and P9 tyre profiles so as to specify the blocks correctly and would be grateful if someone could point me in the right direction.

 

You could have a look at https://www.rssb.co.uk/rgs/standards/GMRT2466 Iss 4.pdf although it doesn't give a dimensioned detail drawing.
I wouldn't be bothered in closely following the profile, though. As you say, the important thing is that the wrap round the flange back is to prevent the blocks from 'flanging' and being forced outwards. I always leave a generous clearance round the flange profile if I have to make a pattern for a new block. I certainly can't see the logic of having different blocks for P1 & P9 tyres.

 

Many thanks for coming to my rescue again, Steve! The document and your comments together should be all I need, fingers crossed.

I wasn't intending to have different blocks for P1 and P9; I used the plural as the blocks for the leading wheelset are different from those for the driving and trailing wheelsets. Unfortunately the difference is so great that we can't have the pattern for one adapted to make the other so will have to commission two separate patterns.

 

Well, the next question I'll ask is why are the blocks different? The second question is do they need to be? Just curious.

 

Good questions!

The blocks on the driving and trailing wheelsets are mounted partway down hangers in an area with ample space. Those on the leading wheelsets are mounted low down directly on the cross-shaft ends, pivoting from a short hanger, as space is very limited, and they are much heavier. The reason for them being heavier isn't apparent to me but may be related to reduced application leverage (less liable to bounce?).

We couldn't use the same blocks all round as a significant redesign would be needed and this would have safety implications. That level of change would also deviate too far from 'preservation'.

The brake block difference may have originated in Britain, since the engine genealogy goes back to four engines supplied to Denmark by R & W Hawthorn in 1873. In 1887 Otto Busse used the Hawthorns as the basis for his own design, 105 engines being built to this between 1889 and 1923 (one of the differences was the use of Allan rather than Stephenson's valve gear). A further 15 were built in 1949 to essentially the 1887 design as an expedient way of recovering from war devastation, the NVR's No. 656 being one of that batch.

 

Having now looked at a photo of F No.654 I can see what you mean about the position of the front blocks. However, the photo that I'm looking at seems to show all the blocks being the same and not that massive, probably on a par with those fitted to Hs No. 385.
I haven't been able to find a sufficiently good photo of 656 to compare.

 

I know that this is no GA drawing but it looks as though the brake blocks are the same on all wheels.

 

Though the 'wearing' part of each block is similar, you may be able to see that the leading block has a bigger hole and more meat around it. It is also chunkier in (unshown) end profile.

Below is a DSB chart showing the weight and hole diameter differences between type 1671 (driving and trailing) and 1672 (leading), those on 656 'as received' being Mark I. The loco is shown as FII to distinguish from the Hawthorns which were the original class F. I also have copies of the original detail drawings which have legibility problems but confirm the size and weight differences.

You can see from the chart that class Hs used type 1671, fitted to all wheels as you intimated.

 

Very interesting. You've obviously got a lot more fundamental information than me.

 

I've been collecting information, drawings and documents on the class for 16 years, including a research visit to Denmark in 2005.

However I'm still learning when it comes to practical application, so thanks again for the help you've given via the Forum and in Conversation.

 

I'm faced with another problem with the brake blocks. This isn't connected with the flange profiles but I'll post it here as an extension of the subject.

The diameter of the tyres at the centre of the tread prior to turning is shown on a DSB drawing as 1254 mm (i.e. radius 627). The matching part of the brake blocks is shown on drawings as a compound curve, with a radius of 550 for the central 2/3rds and 860 for the leading and trailing ends.

I can appreciate the ends having a larger radius so as to ensure the blocks don't contact the tyres on the ends first, but I'm struggling with the following:
1. Why is the difference in the two radii so great?
2. Why doesn't the innermost radius on the block match the radius of the tyre?
3. Would it be OK for the new brake blocks to have just a single radius, this being slightly greater than that of the newly-turned tyres so that the blocks start to bed in at the centre but soon wear-in to make full contact?

One of the original drawings is shown below. The block on the right (version 1672) is the one for our loco (it's the heavy one I referred to earlier, the others are on a different drawing). Some of the dimensions are illegible, or nearly so, but the compound radii should be obvious.

 

David,
Being practical, I think that you are worrying/looking for problems where they don't exist. When new, tyres are about 3" thick. As they wear and are machined, the thickness and thus diameter, is reduced. Railways didn't keep different sized brake blocks to cater for every conceivable diameter. The blocks will soon wear to match the wheels. It is preferred that the block first touches in the centre as, if they touched on the extreme ends, the blocks would effectively be in bending, which isn't the best arrangement for cast iron If you are wanting to make the block with a single radius, I'd make that radius slightly larger than the tyre radius, as per your third question. (The 1677 block is like that.)

 

Thanks yet again, Steve.

Yes, I'm looking for problems -- to make sure they don't exist! It's the way I work.

My engineering experience goes back to before this 1949 loco was built - I had a family reputation for taking my toys apart to see how they worked before I reached school age (I'm now 76). However brake blocks (and more) on railway locos is a science that's new to me, and guesswork would be foolish.

Now you've given me a better understanding I'll get on with new drawings to replace the cluttered and fuzzy originals.

David.