The new Nasrec slipway

[Jerome West]

I am not sure that this is the right place for this question. Yesterday I went on the TBE to the launch of the revamped Nasrec Station. While taking the new Nasric slipway on the bend there was tremendous scrapping noise and the train slowed down to a crawl while negotiating the bend. I am assuming the bogies on 10M5 are fixed which to me would mean that the curve is too sharp for the train. Am I wrong? If so what are the fixes or is it just a mess?

IMG_4318.jpg (93.74 KiB) Viewed 1917 times

This is the TBE on the curve in question

IMG_4253.jpg (84.83 KiB) Viewed 1917 times

Another thing I noticed at the new station is the shoddy workmanship. Some of the steel roof beams were skew and looked like they were hammered and force to fit. I also nearly fell coming down these yellow steps from the concourse to the platform due to the steps been different heights. Other than that is a good looking station.

IMG_4238.jpg (85.89 KiB) Viewed 1917 times

The yellow steps

IMG_4268.jpg (50.98 KiB) Viewed 1917 times

[Steve Appleton]

Hi Jerome, interesting pics, thanks.

I presume the curve you are talking about is the northern leg of the "triangle" just north of New Canada station where that leg also crosses the M10, Canada Rd. In addition, there are also sharp curves at the "triangle" where the Nasrec line branches off the Crown southern bypass line in the vicinity of Riverlea just west of Crown station. Measured on Google Earth, all these curves are about 180 metre radius which although sharp is OK for 1065 mm track. Such a curve would likely have a speed limit of not more than 30km/h, probably less if the track is new and being bedded-in.

The noise you heard was most likely "flange squeal", which happens when the wheel flanges rub up against one of the rails (usually the outer one) on a tight curve. Certainly the bogie is not "fixed" although the axles within the bogie are (exception: the Scheffel bogie). Each entire bogie is free to rotate on its central pivot until the four wheels are roughly tangential (never exactly) to the track at that point.

The running surfaces (tread) of railway wheels are machined "conical" with the inside of the tread nearest to the flange being larger in diameter than the outside. This causes the wheels to run roughly centrally between the rails on straight track and also on larger radius curves, the latter aided by "cant" where the track is tilted down towards the centre of the curve (like a highway). The flanges normally only touch the rails where there are irregularities in the track.

On sharp curves, the "cant" and the "wheel coning" are not large enough to keep the wheel flanges from touching the rails. The conical wheel treads cannot compensate sufficiently for the difference in running length between the inner and outer rail and the wheels are not quite perpendicular to the track. All of this adds up to flange contact and some wheel slip (because the wheels are fixed onto the axle) - hence the noise.

Such curves are a source of consderable wear on the wheels and rails. To reduce this, in most such instances flange greasers (these look like pots that are depressed by the wheel flanges to pump out some grease) are placed at the entrance ot the curve to lubricate the wheel flanges and the inside of the rail head.

The rails themselves might also have been recently ground, leaving a slightly rough surface that may have contributed to the sensation.

See the Railway Technical Webpages at http://www.railway-technical.com/whlbog.shtml for some very good diagrams and a technical explanation.