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Post by orienteer on Mar 23, 2014 14:33:06 GMT
Can anyone explain how the steel surface and aluminium rail are bonded together? The two metals have very different expansion coefficients, and can also create electrolytic corrosion between them.
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Post by phillw48 on Mar 23, 2014 19:16:19 GMT
I should imagine that there is a thin layer of another metal between the two to act as a barrier or one or both materials are alloys that prevent a reaction (think stainless steel). To cause electrolytic corrosion you need a catalyst, in thermite for example it is the oxygen in the iron oxide that provides the catalyst.
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Post by andypurk on Mar 23, 2014 22:32:28 GMT
I should imagine that there is a thin layer of another metal between the two to act as a barrier or one or both materials are alloys that prevent a reaction (think stainless steel). To cause electrolytic corrosion you need a catalyst, in thermite for example it is the oxygen in the iron oxide that provides the catalyst. No catalyst is needed for electrolytic corrosion. In thermite, the iron oxide is an oxidiser and is needed in equal measure (in molar terms, not weight) to the aluminium metal 'fuel'. The heat comes from oxidation of the aluminium and corresponding reduction of the Iron Oxide (Fe 2O 3 + 2 Al ? 2 Fe + Al 2O 3). Catalysts come out of a chemical reaction unchanged. Note that Stainless steel is not immune to electrolytic corrosion as the process is an electrochemical reaction directly between the two metals. However, stainless steel is more resistant than iron, for example. |
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Post by Deleted on Mar 25, 2014 13:19:28 GMT
It's simply a tight fit over a layer of conductive grease which eliminates moisture and it is manufactured by positioning two J shaped strips side by side and seam welding them together along the length of the rail. I say "simply" as it's clearly a state of the art process and they quote an incredible lifetime. Apparently the early low loss conductor rails were originally tried on the main line but abandoned after the Al layer separated so they must have major confidence in the latest design. These LU conductor rails are made by Brecknell Willis, for more general info check the link brecknell-willis.co.uk/faq_rail.htm. If you want more than superficial data check the company literature on the same site where you will find several fascinating technical papers - if you like that sort of thing! |
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