Single/Double Blockjoints

[stanmorek]

Hi, thought I'd venture into the Signalling section!

After speaking to another forum member, I thought I'd pose the question to the rest of you.

A short length of rail known by track guys as the "ten-ten" rail (nominally 10'-10" in length) with insulated blockjoints at both ends is sometimes used between track circuits. AFAIK the ten-ten is electrically dead and is some sort of redundacy against track circuit failure as opposed to the usual single blockjoint.

The question is why is it necessary in some locations whereas single blockjoints are the norm? First I thought it may be related to a trainstop but 3.3m is way too short for an overlap.

I took a photo of one between Northwood Hills and North Harrow but can't recall any signal nearby (memory failing). The other place I remember seeing one was between Baker Street and Finchley Road Met line.

lu-engineering.fpic.co.uk/p22820293.html

[Deleted]

stanmorek said:

A short length of rail known by track guys as the "ten-ten" rail (nominally 10'-10" in length) with insulated blockjoints at both ends is sometimes used between track circuits. AFAIK the ten-ten is electrically dead and is some sort of redundacy against track circuit failure as opposed to the usual single blockjoint.

I would be interested to hear about what this is / does, as I have never heard of the term ten-ten before....

[Deleted]

In the original thread on the signalling at Turnham Green, BAET said that a ten-ten is used in both the w/b platform road and the w/b road beyond the points to isolate part of the berth track circuit and the points track circuit from the rest of the track circuits on the w/b line. IIRC he said that it was installed to protect the LU track circuits from the NR track circuits used by signal GB1.

[Deleted]

there could be a few reasons why these ten ten sections have been installed :

1 going from different sub station gaps (33 1/3hz - 125hz)
2 going from one signalling system to another (olympia line uses JTC signalling rest of district uses conventianol signalling)
3 where you have anti - opposition tracks
4 on some tight curves incase one blockjoint fails (barking - east ham springs to mind)
5 whitechapel uses them instead of delta track circuits so you have a small track circuit inside the normal track circuits
6 going from NR to LUL (gunnersbury - turnham green)

there maybe more reasons why but they are the ones off the top of my head but all they do is isolate 2 track circuits side by side with a dead section

[q8]

Erm............now where was I?? oh yes before I so rudely flounced off I was contibuting to this 'ere forum wazzent I?

Now I once asked about these double block joints [ten tens]many years ago and the explanation I got was that they were primarily put in to prevent 'bleed' This it seems, occurs where tracks circuits adjacent to one another have different cycle rates. Some being 50cps and other 33/3cps and in rare cases some DC and some AC.

Under the right conditions I was told there could be bleeding over a single blockjoint and therefore cause both tracks to drop.

Another factor for the installation of ten ten's was that a lot of the older stocks had cast iron brake blocks and the residues from them used to build up on the inside of the rails and being magnetic was attracted to the nearest blockjoint and cause a signal failure. Anyway that was told me in the 70's

[Deleted]

q8 said:

Erm............now where was I?? oh yes before I so rudely flounced off I was contibuting to this 'ere forum wazzent I?

Rude? Nope. Unexpected? Yes.

q8 said:

Now I once asked about these double block joints [ten tens]many years ago and the explanation I got was that they were primarily put in to prevent 'bleed' This it seems, occurs where tracks circuits adjacent to one another have different cycle rates. Some being 50cps and other 33/3cps and in rare cases some DC and some AC.

aetearlscourt said something similar. In the case of Turnham Green w/b it seems rather obvious that the NR track circuits would have a different operating frequency than the LU ones.

q8 said:

Under the right conditions I was told there could be bleeding over a single blockjoint and therefore cause both tracks to drop.

Another factor for the installation of ten ten's was that a lot of the older stocks had cast iron brake blocks and the residues from them used to build up on the inside of the rails and being magnetic was attracted to the nearest blockjoint and cause a signal failure. Anyway that was told me in the 70's

Cast iron brake blocks?

w3rd.

[Dmitri]

theonekea said:

Cast iron brake blocks?

Moscow Metro used to use cast iron brake blocks during its first year of operation (1935). However, they wore out very quickly, and the metal dust that was generated tried to short-circuit everything within its reach. So, since 1936, we use composite brake blocks that generally behave better but literally stink when heated.

[q8]

Oh yes. My beloved old 'Q's had cast iron blocks as did the standard tube stock but only on the motored wheels. They did, as Dmitri says, wear out rather quick and were changed weekly. [They were also bloody heavy] A 6 inch thick block wore to tissue paper thinness in that time and you got an indication that the blocks needed changing by squealing during application. The nice thing about cast iron block was that you had a lovely hot metal smell waft up from down below on release. Another thing with CI block was that you got a 'ring of fire' in the dark! This was only observed if you were on a train standing in a platform or tunnel and a train coming the opposite way was braking for a signal or something. All the motored wheels of that train had a red ring of fire around them due to the heat being caused by the friction. You could not touch those wheels for at least ten mniutes after being stationary as you would get a serious burn.

[stanmorek]

Thanks guys.

I didn't get much of an explanantion from the track people but they only know as much as they need to know. The location of the photo was nice straight track on Met line north, no junctionwork nearby, no NR but happened to have an out of gauge rail close by.

Common block joint failures are caused by defects to the insulating T-piece inbetween the rail joint. A step between the rail ends can cause one rail end to burr over and make electrical contact. Or the T-piece itself can deform due to thermal expansion of the rails or movement from excessive train accelerating and braking forces.

Q8, on the subject of brake blocks, how common was cast iron and for how long was it in use? I also keep hearing that abestos was also commonly used in brake blocks and . I ask because I'd like to know what I've been breathing in as this stuff would've found itself into tunnel track ballast over time.

I think back to my time with P-Way renewing sections of sleepers and peering through the thick dust haze digging out beds that have been undisturbed for years. No one bothered with dust masks as the ones supplied were not much use anyway.

[q8]

Well SK cast iron blocks were used right up to the demise of the Q stock ala 1972. Only on the motored wheels though. As for asbestos that was indeed used for all other wheels and if you were driving towards the sun and saw another train braking in the open sections you could SEE the dust coming off the wheels.

As a guard you could smell the stuff in the tunnels. Damn funny smell hard to describe. It's what gave me my cancer. [That and smoking] These blocks used to be made by Ferodo and were rather soft. After the asbo blocks were abolished I dunno what they used but it was nowhere near as good for braking with.

[stanmorek]

q8 said:

As a guard you could smell the stuff in the tunnels. Damn funny smell hard to describe. It's what gave me my cancer. [That and smoking] These blocks used to be made by Ferodo and were rather soft. After the asbo blocks were abolished I dunno what they used but it was nowhere near as good for braking with.

q8 I'm sorry to hear that and hope that all is well.

[Tom]

Ten-tens are generally used in one extra place (and this is the most common of all): approaches to platforms or other places where heavy braking is likely to occur. The idea is to prevent scaling on the first joint causing a track failure, as there are two blockjoints which must become contaminated first. To separate differing frequencies, while a reason, are not the main purpose for them

The phrase 10-10 is a slight misnomer anyway - the nominal distance should be 10' 6" and 10' 10" is the maximum permitted. It is however the dimension used on the Coded track circuits alongside the widened lines, where the 10-10 section is tied electrically to the other running rail which acts as the traction fault conductor, as opposed to the Victoria line where opposite rails on adjacent track circuits are tied to the Traction Fault Conductor.

50Hz Track Circuits were only ever used on the BR signalled areas and the Eastern part of the Picc Line - the other frequency would be 125Hz.

[russe]

What are "anti-opposition tracks" (ref aetearlscourt's posting) and what is "scaling" (ref Tom's posting)?

Russ
(who owns up to being the instigator of SK's original question)

[q8]

What are "anti-opposition tracks" (ref aetearlscourt's posting) and what is "scaling" (ref Tom's posting)?

Russ
(who owns up to being the instigator of SK's original question)
------------------------------------------------------------------------
'Scaling' is a deposit from cast iron brake blocks that builds up on the inner [4ft] side of the running rails and is prevalent mostly at points where trains brake frequently. To look and touch it is exactly like the flaky rust you get on a car body. Being metal it get's magnetised by the track circuit current and if not removed gets worked along the rails by wheel motion. When it gets to a blockjoint it bridges it and causes a signal failure

[Deleted]

russe said:

What are "anti-opposition tracks" (ref aetearlscourt's posting) and what is "scaling" (ref Tom's posting)?

Scaling is a condition where the repeated hammerblows of a train wheel across the blockjoint cause the metal of the rails to deform downwards (i.e. towards the sleepers). With sufficient blows at the right speed, the metal of both rails will spread across the blockjoint and eventually make contact, dropping the track circuits on both sides of the blockjoint (I think).

A ten-ten forces both blockjoints to become scaly before the track circuits are dropped.

EDIT: beaten by Q8.

[c5]

Scaling happens when the soft metal part of the train's wheel known as the tyre is scraped off by the sharp edge of the end of a rail where a blockjoint is positioned. Over time this softer metal can build up and connect the two track circuits