Thursday, 27 February 2020

Not So Grate!

Most of the Sentinel 7109 articles I've written in this 'blog over the last 8 or so years have been fairly upbeat although I did get frustrated with gland packing not so long ago.

However, not all goes as well as I'd like and I've had a new downer to deal with. I've shown the photo below a number of times to illustrate the how the fire-grate began.
The Fire-Grate as new prior to first steaming in 2016
With an eye on environmental issues, at the beginning of 2019, at Midsomer Norton, we began using a cleaner Welsh coal. All seemed fine for some months and I did the usual half-yearly boiler and fire-box washout in August. However, shortly before the start of the four Santa Specials in December, the centre section of the fire-grate decided to disappear spectacularly as shown below.
Fire-Grate after cleaning at the start of December 2019
(After the first of four Santa Specials)
(This was the reason a diesel shunter was used as banker for the Santa Specials).

Obviously this was not great news and the timing was particularly inconvenient.

I've had to dig deep to figure out how this could have been caused to prevent it happening in the future. I think there are basically two causes, both to do with the coal.

The Welsh coal is clean; it produces very few 'volatiles' (the nice-smelling but smoky stuff) and burns hot. It also tends to disintegrate through agitation and during combustion. In either case, it forms a lot of 'dust' which sits around underneath the coal nuggets. Our nuggets were large, some about the size of three fists.

The dust tends to form into clinker and block the grate in places. Air then has to be concentrated through the remaining unblocked areas and causes hot spots which melt the fire-bars, a bit like a blow-torch. As the year progressed, the coal in our storage bunker became more dust than nuggets and so the amount of grate blockage increased as the year went on and finally precipitated the damage.

Anyway, in summary, that is my interpretation of what happened. All we have to do now is to prevent further damage and replace the fire-bars.

Traditionally, fire-bars have been made from grey cast iron. However, I've had advice that a 20-30% alloy of Chromium and iron is much longer-lasting than plain old grey cast iron.

I've taken this advice and, to be ready for the first 2020 steaming on March 22nd, I rapidly placed an order for a pattern to cast the new fire-bars from Chromium Cast Iron (the pattern has to be specific for the material as the metal would not cool to the right size otherwise). I had to purchase a minimum quantity of 30 fire-bars (which should keep us going for a while!).

The bars arrived just ahead of the delivery date and I am grateful to the staff at Cerdic Foundries Ltd for their help in a time of difficulty.
Quite a car load!
I've not tried a funding appeal before but this is one occasion when I think it is the right thing to do.

Including VAT, the pattern will be £2,400 in round figures - I have bought this.

Including VAT, each of the 30 fire-bars is £120 in round figures.

Please consider donating a fire-bar for Joyce. Donations can be made via PayPal or cheque (preferred as PayPal takes a percentage) by clicking here. I would be more than happy to entertain donors with a cab ride on your next visit.

Go on, you can do it! Thank you in anticipation.

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