Point blade composition

[Deleted]

Are point blades made of the same type of alloys as normal running rails, or are they designed to be a bit more flexible?

[cdr113]

theonekea said:

Are point blades made of the same type of alloys as normal running rails, or are they designed to be a bit more flexible?

Probably the same, i remember a guy i worked with on National Rail said the 60 foot sections were just like rubber when not attached to sleepers, really really bendy.

Perhaps point blades are more likely to need extra hardening due to the additional wear on the gauge corner (correct term?) of the outer most blade?

All random thinkings, any experts feel free to correct me! ;D

[Colin]

Having watched point blades move, particularly at Edgware Road, it's surprising how much 'flex' they have in them ;D

[Deleted]

as far as i know they are exactly the same they are just machined down then matched to a stock rail so they both are installed as a pair

[stanmorek]

It was usual practice to replace a pair of switch rails at the same time so that both would be worn evenly to avoid a rough ride.

Hardening of steel would make it more brittle and increase the chances of it cracking. Also adding certain alloys during the steel making process would make it incompatible with welding.

I was told that if you were to pick up a 60 foot length of rail in the middle and lift it 1 metre above the ground the ends would sag and touch the ground!

Not sure if that's quite true (i suppose i could work out the likely deflection) but a single trackman could lift up the end of a 60 ft rail by some distance using only an iron bar and some leverage. Also when rails were brought up on a battery loco, guys would bar a rail off the edge the flatbed wagon and when the rail hit the ground its ends could whip up.

[Deleted]

The derailment at Archway shows that the toe end of the right hand switch rail fractured, and the top end sprung against the running rail; the train hit the stub end of the rail, rode over it and more or less, dragged the track towards the right!. With the rail springing back against the running rail, it shows how much tension is on the stay bar at the toe ends...

Page 13, www.raib.gov.uk/cms_resources/061211_R242006_Archway.pdf, shows the broken rail...

[stanmorek]

Stock and switch rails are manufactured as matching pairs to form 'half sets'. The stock and switch profiles come as bullhead or flat bottom rails each with two types of matching profile for each rail type.



Undercut and straightcut (for facing moves only) on BH and chamfered to shallow or full depth on FB. The planing length is the length of the planed section of the switch rail.



The switch toe may be straight planed (which gives a very thin section of rail) so the stock rail may be slightly kinked at the mating surface, called a joggle, to protect the toe.



The stock and switch pair are fixed or bolted together with a switch anchor which provides a fixed pivot for the movement of the switch rail. The toes sit on cast iron slide chairs to reduce friction and allow smooth lateral movement of the switch rail. The slide chairs may be lubricated or have a teflon coating.

Each of the stock & switch profiles have subsets with different lengths of switch planing dependent on line speed. The higher the speed the longer the planing length and the overall length of stock and switch rails.

Prior to the BTRs most P&Cs were bullhead type even when the plain line was FB. There was a forged transition rail to connect BH to FB. The minimum flangeway gap required (the gap between the switch toe and stock rail) is 50mm to allow a wheel flange to pass through.

[stanmorek]

Note - The previous post has been updated with some explanatory diagrams (apologies for the scribblings). At some point I hope to move the post to a new thread on P&Cs with more info on crossing rails. If that's ok with the mods.