Plastic Sleepers

Background


Photo 1. Ground level track
Sleepers are an integral part of track. They support the track, and more importantly, the load (trains) on that track, and also set and maintain the gauge of the tracks. Sleepers (ties) Historically, suitable hardwood has been used, or for models, softwood treated in some way. ALL will rot sooner or later. Another material being used in full size practice, and also for models, is concrete, but that another topic all by itself. Click here for an article on concrete sleepers.


Photo 2. Elevated track
Building track is hard work! And once is has been done you do not want to spend all your time doing track maitenance and the expense of operating trains. And there are ways to minmimise maintenance. Some of the more important ways have to be taken into account when first building the track.

Drainage: It is critical that any track has good drainage. Poor drainage = more maintenance. The road bed accumulates silt/mud and ceases to be a load bearing substance. Accumulated water accellerates rot (in wooden sleepers) and promotes rust on steel rail. The rail also goes out of alignment much faster.

Materials: Untreated wood usually has a poor life span. Suitable hardwoods, woods soaked in oil or creosote (now banned), and pressure treated woods will all eventually rot, and softwoods rot very quickly. Plastic and concrete go a long way to extending life span (and reducung the amount of maintenance). Wood has less than about 7-10 years expected life, with some hardwoods reaching 15 years. Note in Photo 2 the first (wooden) sleeper is starting to decay and its neighbours have been replaced long ago with plastic.

Why Plastic?

There are a number of reasons to use plastic for sleepers:

  1. This material is a solid plastic made from recycled plastics
  2. Using recycled materials reduces the burden on landfills and is environmentally friendly
  3. Expansion and contraction with temperature changes is minimal to enhance gauge stability and minimise ballast movement.
  4. Expansion and contraction with moisture is virtually zero
  5. Plastic sleepers are not affected by insect and termite attack
  6. Plastic is very durable and lasts forever (well almost) even when moist, and do not rot
  7. Plastic is UV stabilised and is unaffected by the sun
  8. Recycled plastic sleepers will not split, warp, crack, expand, or shrink when driving screws in place
  9. Plastic has no grain or knots like wood, both of which reduce screw holding power, and produce localised weak spots.
  10. Screws hold well plastic
  11. Plastic does not split during tamping operations as wood can sometimes do
  12. Recycled plastic is very easy to work with
  13. Recycled plastic will not sustain a flame and self extinguish in a few seconds (once the source of the heat is removed)
  14. Plastic is very rugged and stands up well to rough treatment such as a nick from a derailed wheel flange
  15. No health concerns about absorbing arsenic or other poisonous wood presevatives through the skin, or problems from breathing harmful sawdust
  16. Plastic sleepers have a very long life. Once they are used, future maintenance is reduced to very low levels, and probably won't have to be replaced within the lifetime of a railway. This equals more time running trains and less on mainenance.

Securing the rail

It is all very well deciding to use wood, but how do you use them? and how do you secure the rail to them? One thing that is very clear from experience is that it is essential to pre-drill a pilot hole before trying to drive screws in. Hot dipped galvaised self-drilling roof screws are recommended as they are cheap, readily available and have a very long life before corrosion sets in. DO NOT use zinc plated steel screws - they last only a few months before corroding! Make sure screws are hot dip galvanised. Screws such as 12 gauge x 30mm, hex with shouldered head are quite suitable.

A pilot hole of approx 3mm (1/8") is enough. Some people use two battery powered drills. One with a drill for the pilot hole, and a second with a hex nut driver to drive in the screws - saves a lot of time. Make sure the drill has a clutch type overload, otherwise it is too easy to strip the thread in the hole with the screw spinning uselessly in the hole resulting in little or no 'bite' or strength.

Setting the gauge: - There are various methods for gauge setting and positioning the rail on plastic sleepers. Look at the photographs below.


Photo 3. Using chairs

Photo 4. Using machined recesses

Photo 5. Using steel spreaders (sleepers)

Photo 6. Detail for rail chair

Photo 7. Rail secured into position with a chair

Referring to the Photo 3 above, using rail chairs allows attaching the rail directly to the sleeper, but only when using flat-bottomed rail. The chairs are placed on the sleeper, then the rail onto the chairs, then the screws are inseretd and screwed down. See the 2 photos to the right. Note that the hold down screws do NOT hold the rail tight, they are driven in until they are just tight, then backed off about 1 turn. This enables the rail to slide freely back and forth with temperature and prevents buckling of the track on extremely hot days.

It is usual to lay the rail on one side only, correctly curved or correctly straight, then using a movable track gauge, position and secure the other rail. Try to avoid raile ends at extacly the same point in the track, try to stagger the rail ends a bit if at all possible.

Refer to Photo 4 above. With this method a small recessed slot is machined (to gauge) in the workshop prior to installation at site. Screws (with pre-drilled pilot hole) and then used to hold the rail base in position. Not again that slots are just slighly deeper that the flat bottom on the rail, and the screws themselves are not tight onto the rail, and the rails are free to slide freely back and forth with temperature just like above to prevent buckling. Even with the screw fully tightened, the rail foot will slide under the head of the screw instead of cutting into it. The slotting of the sleepers to correct gauge beforehand eliminates the need for track gauges.

Refer now to Photo 5 above. The rail used in this example is rectangular steel section, welded on edge to steel sleepers. These set the track gauge and hold the rails in position, and a screw, or sometimes 2 screws, then secure the track to the plastic sleeper.

Cost

Cost is always an important factor. Sleepers made from recycled plastic are bit more expensive than timber - but this has to be traded against much longer life and reduced maintenance.

The cost [as at Apr 2013] of (charcoal coloured) plastic sleepers 50mm x 50mm x 350mm long is approx $2.60 each, or $3.25 each for 50mm  x 75mm x 350mm long. The supplier will often cut to size and supply finished sleepers, cut-to-size, for approx $0.20 per sleeper.

By comparison, sleepers made from new CCA treated pine are approx $0.90 for 50x50, and $0.95 for 50x75 (both in bulk lengths, not cut to size). Hardwood is a bit more expensive.

Fire Resistance

Plastic, whilst flammable, has better fire resistance than timber. On a number of tracks there have been no reports of any sleepers catch fire, even with a very high proportion of steam locomotives. An occasional cinder may fall on the track and local charring may occur, exactly the same or less that with wooden sleepers, but none reported as catching fire.

The only report of heat damage has been through arc welding of joints adjacent to the sleepers or our locals lighting camp fires (!) on the track to cook the fish from the local river. In the case of the welding, a quick spray of water (carry knapsack sprayers on the welding car) or a handful of sand thrown over it, and it's rapidly extinguished.

Where to buy recycled plastic?

Below is a list of known suppliers of recycled plastic (as at Feb 2013)

Advanced Plastic Recycling (APR)
Kilburn (Adelaide), South Australia
web: www.advancedplasticrecycling.com.au

Replas
Carrum Downs (Melbourne), Victoria
web: www.replas.com.au

Integrated Recycling
Mildura, Victoria
web: www.integratedrecycling.com.au

Plastic Recyclers
Cavan, South Australia
web: www.plasticrecyclers.com.au

Adroit
Glen Waverly, Victoria
web: www.adroit.com.au

Cosset
Woodside, South Australia
web: www.cosset.com.au