Thermit Welding

[jlancasterd]

M8 Nokton 50/1.5 ISO 160

Thermit-Welding-1.jpg

Thermit-Welding-6.jpg

[imported_peter_m]

Couple interesting shots John.

How dose the process work? First I heard of it and seen a contraption like that.

Peter

[MPerson]

Nice images and shows the process well.

I was watching this being done by a contractor for Network Rail last weekend and forgot to ask: How do you allow for the expansion/contraction of the rail if it welded. Is it the weld material that absorbs the movement?

[jlancasterd]

Originally Posted by imported_peter_m

Couple interesting shots John.

How dose the process work? First I heard of it and seen a contraption like that.

Peter

The process works by producing molten steel. The rusty iron 'contraption' is a crucible, with an aperture at the bottom, which is filled with a mixture of powdered iron oxide and aluminium powder (there may be other additives to produce the right grade of steel, but I don't know) and the reaction is started by a fuse of magnesium ribbon (Picture 1).

The temperature of the reaction produces molten metal that flows out of the bottom of the crucible and into a mould around the ends of the rails, slag also runs off into the collecting pans at the side of the moulds (Picture 2). The weld is created as the molten metal is hot enough to melt the ends of the rails to join them together. After everything has cooled, or at least solidified, the mould is broken off and the excess metal ground off.

Its a process typically used on railway tracks laid in streets (as here) where you want to avoid having conventional fishplated joints where they are difficult to service.

Normal expansion stresses in long-welded rail are taken up internally in the rail and there are very explicit rules about the temperature at which it can be laid - at certain times of year it has to be put under tension as it is laid.

The pictures were taken on the Cross Town Rail Link in Porthmadog - the line being built to connect the Ffestiniog Railway with Phase 4 of the Welsh Highland Railway reconstruction, which is currently being built south from Rhyd Ddu via Beddgelert. Both lines are two-foot gauge.

[stumac]

Impressive pictures John,

the last time I saw this process being used was 50 years ago when the Melbourne tramways were relaying track in the eastern suburbs where I lived at the time, they used a slightly different method where the rail ends were enclosed in a refractory lined cast iron box and then fired. The rails were tied with rods and cast in concrete.

Regards, Stuart

[imported_peter_m]

Thank you John for the explanation.

Peter