For several years around 1960 I worked for a Swiss company, MATISA, (Materielle Industrielle SA) that made and sold rail track maintenance machines around the world. These machines encompassed the very small such as portable saws for cutting rail on site to the huge, such as Ballast Cleaners which weighed in at around 50 tons.
I believe that the first specialist maintenance machines supplied to British Rail were MATISA Standard Tampers and many sidings where working MATISA tampers were stabled were known as " The Matisa siding " and these were quite numerous up and down the country. I don't know whether this is still so.
The two main machines concerned with Railway track maintenance are the Tamper and the Ballast Cleaner. Most of the work can be done with standard versions of these machines but of course there are specialised machines for maintaining non-standard track like points and crossings.
Track
description
Rails are supported
by sleepers (ties) which in turn are supported by around 12inches (300mm)
depth of ballast. Quality of track is dependent upon several factors.
Substratum
I am not a Civil Engineer so know little about preparing the foundation for
a railway track. However, it's obvious that it must be firm and well drained
Ballast
Ballast should be hard, sharp stone. Sharp means that is angular in form.
Over a period of use ballast gets its sharp corners rubbed and chipped off
and then will not form the solid bed for the sleeper that is necessary. Imagine
trying to construct a dry stone wall from rounded stones. At long intervals,
therefore, ballast has to be renewed or cleaned. This is done by huge machines
which excavate the ballast, sieve it to remove the detritus and replace it,
together with a top-up of new ballast under the track.
Sleepers
or Ties
At one time these were exclusively of timber, but reinforced concrete is used
now on all mail lines, although examples of wooden sleepers can still be seen.
Rails
These are made from a manganese steel which is easily weldable, self-hardening
with use but reasonable to drill or saw.
There are two cross-sections of rail used - bullhead or flatbottom. The bullhead rail is supported in a 'chair' and secured by wedges; the flatbottom rail rests directly on the sleeper.
Bullhead rail is seldom seen now and is obsolete.
Rail fixing
Chairs used with bullhead rail are usually secured by coach bolts into wooden
sleepers.
Methods of fixing flatbottom rail to sleeper vary a lot and there are many
patented solutions. Some use screwed fittings, others employ spring clips.
Top of page
Tamping
Over time the constant movement of traffic over
the track causes gaps to form in the ballast structure
known as 'voids'. Often,
from the trackside, sleepers can be clearly see bouncing up and down as the
wheels pass over them. Excessive movement is dangerous, of course, so the
voids need to be filled. This has been done
in the past directly by manual labour but today is done by the tamping machine
The tamping machine works by vibrating the ballast and forcing it under the sleeper. These combined actions cause the ballast to form a close matrix which can support the track effectively.
The original Standard Tamper was totally mechanical with screws providing the in and out movement of the tools and a cam mechanism providing the vibration. Over time these functions were provided by hydraulics.
Later tamping machines combine lifting, levelling and aligning functions to enable track to be set geometrically correct before tamping. Of course it still needs human intelligence to programme the machine.
These machines move and stop at each sleeper to be processed which involves a lot of energy as the machine is first accelerated, then braked. Nevertheless they can tamp sleepers at up to 15 a minute although this slows to 11 sleepers a minute when levelling and less when lining is also employed.
Today some machines carry their tamping heads on a constantly moving carriage which cuts out the acceleration and braking. By using two sets of tamping heads on the carriage two sleepers at a time can be processed.
Speed in tamping is important because it allows more track to be processed between trains.
Stoneblowers
This is a new concept by a USA company, Harsco Corporation. Nozzles are inserted
into the ballast on either side of a sleeper, the sleeper is lifted slightly
and air is blasted horizontally to blow ballast under the sleeper. It's claimed
to be 3 to 5 time more effective than conventional Tamping. A number of these
machines are in service on British railways and so far 6,500 miles of track
have been processed. Learn
more from the Harsco website
. Products and Services > Click on Stoneblower
Click to download video (190 KB; needs Windows Media-player or similar)
I think it's true to say that the jury is still out on the efficiency of Stoneblower but it's an interesting concept capable of development.
Ballast
Cleaners
These machines excavate ballast from under the track with an ingenious chain
mechanism. The chain, comprised of links about 200mm deep with hardened teeth,
is passed under the track, over chainwheels at the side of the track then
up and over a chainwheel at the top of the machine to form a triangular shape
from the front view.
Each link, as it passes under the track, pushes out ballast, then as it passes over the lower wheel to commence its journey to the top of the machine it travels up a trough, taking the ballast with it ie, it becomes an elevator. When the ballast gets towards the top of the machine it is diverted on to vibrating screen which separates the detritus and dust from the good ballast.
The sieved ballast is returned to the track and the rubbish is deposited alongsite the track or into a train of open wagons on an adjacent line. New ballast is added as required to keep the ballast level and the ballast cleaner is followed by a tamping machine.
This work is undertaken at times when the track is closed; at weekends or during the night. Following ballast cleaning a speed restriction is usually applied until the track has settled down and properly processed.
Footnote
Railway track work is hard, unrelenting, and dangerous even with modern machines
and I take my hat off to all who do it regularly. Whilst testing machines
or training personnel in this country and others I have worked in heat, cold
and extremely wet conditions.
Despite the rough and tough
environment track maintenance has to be carried out to a high degree of accuracy
to ensure safe travel and a smooth ride.
Grandad
