Fire Bars

I can verify that small engines can be as hot as big ones , I had a scorch mark on my leg for 15 years from one particular day on a 45 tank.

 

This has been a most interesting and potentially useful thread, newly discovered by me 18 months on!

BS 4844 grade 3E cast iron has a 22-28% chromium content, so must be the one that Andy was trying to recall.

 

Well, my informant tells me that his experience is that after a year of use in a pannier tank flogging up gradients with a very hot fire the chrome cast iron bars are as good as new whereas the paid workshop staff have spent hours repairing, making and fitting steel bars to the other locos. However...the cost of the chrome firebars is eye watering and apparently has just doubled.

 

Yes I recommend chrome bars they might be a higher outlay, but the return on investment is higher, i.e. replacing a cast iron grate annually versus a chrome gate at 5-10 years. depending on use.

 

Is it practicable to cut and drill chromium-iron bars? This would enable corner sets to be made from standard bars for the loco I'm working on, saving on pattern equipment.

Or would it be better to have bars for the corner sets cast from the same pattern as the standard bars but in grade 250 (old grade 17) grey iron for easier machining?

Thanks for any advice.

 

Not quite sure on that I haven't experienced a restored locomotive with new bearers, they seam to be able reuse the original BR ones, probably new patterns would be required for new chromium bearers.

 

Thanks, but that's not what I was after.

I'm looking into new chromium-iron bars for a Danish loco, and BR bars/patterns are out of the question.

Ideally, three different patterns would be commissioned, one for the majority of the bars and the other two for shorter and slightly narrower bars that form the corner sets (which, with spacers, were riveted together originally but could be bolted).

The idea is to make the corner sets by machining and drilling full-size bars, which would mean only one pattern being needed.

I'm looking for confirmation that chromium-iron castings can be machined with a conventional milling cutter, or angle-grinder disc at a push, and can be drilled with a conventional HSS twist drill without problem.

 

I've found the answer to my question. Not good but not unexpected.

A technical paper published on the internet states that "the inclusion of large chromium carbides in the microstructure" makes high-chromium cast iron very difficult to machine. Even PCBN (polycrystalline cubic boron nitride!) tools wear out rapidly as a result of "edge chipping and flank wear".

I think that translates as "don't waste your time".

 

David,

Generally experience has shown that ordinary grey iron is quite satisfactory for side and corner bars, even where high chrome iron is needed for the remainder of the grate. Why this is so I cannot say but I assume that it is because the fire is cooler close to the plate work.

You are correct that high chrome iron is nearly impossible to machine, small holes need to be cast in if required. It can be cut with specialist grinding disks but even that is slow.

Hope this helps.

Andy.

 

That's very helpful indeed, Andy! Thanks very much.

Though I'm very familiar with 'ordinary' cast irons, I'm a newcomer to firebars and chromium-iron. Now finding my way, thanks to the help from yourself and elsewhere.