Titanium firebox

[the_viffer]

As most of you will know the Sweet Pea design has a marine firebox. The boiler has a cylindrical firebox. The grate is mounted on a front plate which is can be removed and refitted to the boiler at will (and very handy it is too). There is two part baffle at the back. The lower part keeps the fire in place and bolted to it is a further plate which forms a combustion chamber between the front of the grate and the back of the tube plate.

The whole doings takes a real beating as it gets kin hot when the loco is working hard especially near the front of the fire. I’ve burnt out the original grate and replaced it with one of the late Mr Spink’s fine stainless grates which is standing up well to the punishment.

However after running this weekend I noticed that not only had the bolts holding the baffle on to the front of the grate been oxidised away and the angle which holds the thing together is looking distinctly iffy but also the baffle which I think is 1/8th 304 stainless has got very thin where it sticks in the fire. Some refurbishment is necessary. I was going to order in some 316 stainless sheet and bolts for this but in poking around the ‘shop I noticed some titanium (grade 2) in fairly thin sheet: about 1/16th which I can easily cut. I am thinking about using that and titanium fasteners but wondered if anyone had any comments.

I’m aware that titanium has a much lower coefficient of linear expansion than steel or stainless but on a rough calculation there shouldn’t be more than 1mm relative movement which I thought I’d deal with by making the holes oversize and not nipping up the fasteners too tight.

I’m not sure whether the thin titanium will stand up to the conditions or whether I need to use thicker stuff which of course is harder to cut. Thought on that are welcome.

[jackrae]

Perhaps you could sandwich two sheets of the thin material together. The slight gap that will inevitably form between them will act as an insulation layer and then, each time you clean the grate out you could inspect the hot layer for failure and replace as necessary.
Jack

[greasemonkey]

Hello
Not really much help to you but I think I would try and use some furnace grade stainless steel rather than try and machine/ cut titanium! I believe college engineering can supply it. Otherwise use some Nimonic, not easy to get hold of but unlikely to burn away in a hurry, Les Warnet used it for the brick arch in the 9F.

Andy

[SteveW]

Guys,

I can confirm that a stainless steel 'brick arch' in our club sweatpea does take a beating. A while back the integral 'arch' disappleared and I've been nailing secondary 'arches' to what was left.

By nailing I mean I use cut down 4" nails as simple rivets.

Some time ago after burning a big hole in a CI grate I tried one of Mr Spink's finest in there. One busy public afternoon later and that had a big hole in it. I think the coal type has a big impact on how quick anything in the fire hole gets burnt away.

Thinking about it, we were using a batch of coal from a previous bout of grate burning last Sunday. Now I've got some more nailing to do.

[the_viffer]

Thanks to all for the replies.

I'm going to try a single layer of 1/16th Ti. I can cut it with tin snips if I've eaten lots of spinach and it is to hand. Watch this space for news.

I've never managed to do anything to a Spink grate but may be really sulphury coal would attack it.

Talking of Sweet Peas SteveW what coal do you use? I can only get mine to burn steam coal. It does not like anthracite at all.

[ridleyian]

Regrettably Mr Spinks grates were not available for some time before he sadly passed away. Does anyone know where similar material can be obtained. I did hear a rumour once that something called 'riddling grate' was obtainable ex power stations. Can anyone confirm this or otherwise?

[David Thompson]

My (very good) book says Titanium alloys have high temperature properties as good as all but the specialist creep-resiting steels. It can also be a pig to machine - galls on cutting tools. Some can machine similar to 18-8 ss if annealed, but some alloys require age hardeneing so annealing might not be what you want to do.

If you get a titanium fire, don't add water - it will explode. Use sand.

If you are still considering stainless steel, try 310 in place of 316. I believe you can get it from the people who supply model gas turbine materials. I have made a GT rotor with it, but I forget where I bought the sheet.

There are dozens of Titatnium alloys, but I cannot find one called "grade 2". There is Ti 1, Ti 3 , Ti 4 etc etc - everything but 2, and I still say it is a very good book.

[the_viffer]

Grade 2 is probably the most common commercial grade. See for example www.severnmetals.co.uk/notes_tit.htm .

While the reaction of titanium with oxygen should be strongly exothermic (ie giving out heat) I was under the impression that the tightly bound oxide coating slowed down the reaction so much that it is pretty well inert to oxygen even at elevated temperature.

Your book implies that titanium is flammable. Since I'm proposing to stick it in a very hot fire that is rather important information. Can you tell me more? Is it dust fires or can bulk catch fire too? Under what conditions?

You do get rather good white hot sparks when grinding it.

Way back when we used to have a deal of fun with titanium IV chloride ("tickle 4") which is a purple liquid which is not only a very powerful oxidising agent but also could be guaranteed to create huge white clouds of titanium oxide when exposed to the moisture in air. I often thought that it would make a perfect "steam" for electric trains. Apart from the cost, the hazard and the corrosiveness of course!

[SteveW]

the_viffer, all,

Re: Source of coal....

The short answer is out of a tatty old poly bag from the back of the bunker. Previous to that I think it came from a supplier from near Dursley, half way between Gloucester and Bristol off the A38/M5. It was quite hard stuff but crumbled following a big whack with the poker. It also produced a fair bit of coarse ash.

I've seen various type of black stuff in this sweatpea with varing results on the grate and surround.

Using the stuff described above we came close to not being able to boot it up the other day simply because I forgot to bring the charcoal. The problem with the 5" sweatpea grate (I'm told) is that it isn't deep enough to get going on wood alone. Later in the day it nearly when out through lack of attention and blower.

Usually I can get to operating pressure from cold in about twenty minutes using white spirit soaked wood topped with charcoal, I find the shaped cobbles best to use but the tree-wood type works OK. Once the charcoal is going in goes the coal. The draft is maintained using my Electrolux vacuum impeller on the end of an ex-photo-copier shapler unit on 12v (@500ma). Our near disasterous no-light needed 24v (series batteries) to get enough heat to get it all to go.

We were using our portable track at Winchcombe on one of the GWR's Thomas days. I was quite close to the engine all day and got home feeling very strainge and had a very red/flushed face. I have heard that getting too near anthracite can get you a dose to much of CO poisoning. I did feel queer that evening.

[the_viffer]

Thanks for that SteveW. I've been using Signal Fuels steam coal as obtained from Donington. There have been some iffy batches around which clinker badly but I pick some of it out before firing and have to drop the fire after a couple of hours because of the dross. However it steams on it but is very reluctant to burn anthracite.

I've not tried starting on wood alone. Wearing my cowboy hat I have reason to believe that a blowtorch stuffed in the ashpan can help start a Sweet Pea without charcoal. You do need to have the aux blower going to do it.

The symptoms you describe are consistent with CO poisioning. They are also consistent with having just carted a couple of tons of portable track around. Coke fires were the notorious source of CO poisioning and you can read in books like The Autobiography of a Supertramp how men would start to sit close by a coke fire on cold evenings and then over the course of a few months weaken and die.

[SteveW]

the_viffer,

Yes it was a very strange feeling I had and, given the time actually driving the beast and the out door venue, I was quite surprised to feel as I did.

I was wearing my Auz-type cowboy hat (but no corks) without which I would have assumed I'd bagged too much sun, i.e. the red face.

So, another new experience for the logbook and one to watch out for so that I can have a next time.

Using a blow lamp!!! Ain't that cheating?

[the_viffer]

"Using a blow lamp!!! Ain't that cheating?"

If you are not cheating you're not trying hard enough.

[SteveW]

Re: "If you are not cheating you're not trying hard enough".

You'll be fitting an immersion heater next and joining the turn on and go brigade.

[David Thompson]

Sorry to be so slow to come back about the fire risk. It appears to be Titanium grinding dust that can be explosive. The dust from polishing or grinding should not be allowed to accumulate in a closed space. Keeping it wet removes the danger, but water should not be added to a Titanium fire as it will cause an explosion.
The melting point is 1665 degrees Celsius, so I agree the fire risk in normal use should be minimal because as you say, if it does not tend to corrode then it should not tend to burn. Presumably the extra surface area of the dust changes the energy balance. We machined some not long ago and took no special precautions, but I have no experience using it in a firebox.
Why not put a blow torch on a small bit and see what happens, while you have a well planned procedure to extinguish it with dry sand if need be (or run away and leave it burn). If it can survive that, I would think it would be OK as a firebar.
I don't know whether firebox temperatures would be higher than other "high temperature" applications or not. For gas turbines for example, stator metal temperatures never get much over 1100 C (rotors about 1000 C) and these are normally nickel based "Nimonic" alloys rather than Titanium. You don't need exotic metals for firebars, so perhaps they don't get as high as this. On the other hand, firebars are not highly stressed whereas gas turbine bits are.

[the_viffer]

Thanks for that David

I've often played a blowtorch on titanium. I do a fair amount of jewellry making and one of the things I do is titanium jewellry. You can get lovely colo(u)rful oxidation interference patterns on titanium by using electrochemistry. I put my cowboy hat on shout "yeehaah" and play a blowtorch on the stuff for the smae effect quicker and more cheaply.

My uncle used to be in a well known police force. The examination for inspector allegedly contained the question that you saw a train about to come off the viaduct, some terrorists about to blow up the supermarket, an armed gang raiding the bank and a widowed mother of 12 about to step off the pavement into the path of a bus. What do you do? The correct answer is remove your uniform jacket and leave the scene. So your advice has some familiarity.

Iron dust, and steel wool, is very flammable. (As is flour dust and I seemed to spend most of my youth making explosions with it) Bulk iron and steel is not very flammable. I've decided to put some small off cuts of titanium in the fire when I next steam a loco to see what happens. If they survive then I'll go on to try using a piece of plate as I planned. If I live I'll report back.

The oxygen content in and above a fire should be much less than a pile of hot dust just lolling around off a grinder and that too may help.

I think Jim Ewins measured the temperature in a fire. I don't remember the exact figure but it would be quite high I imagine.

Melting is not essential for combustion: I'm fairly confident the flour I used to explode wasn't molten.

I used to work a lot in Aberdeen on titanium for a man called Jimmy Milne. If the name rings a bell leave me a message.

[jackrae]

Would that be the one who started off growing mushrooms, then went into machinery manufacture under the name Aberglen and is now known as Balmoral

When I was in the fish processing business we attended several of his unbelievable social bashes

Jack

[the_viffer]

jackrae said:

Would that be the one who started off growing mushrooms, then went into machinery manufacture under the name Aberglen and is now known as Balmoral

When I was in the fish processing business we attended several of his unbelievable social bashes

Jack

The very same. A fine, fine man. Few people remember his parties. Many remember the following day.

Aberglen went t**s up owing my firm money. When he started up Balmoral he had them send me the money which Aberglen owed me. He had no legal obligation to do that but he wanted to do business with me and felt he ought to square off the debt which impressed very much. I got involved in some very interesting and scary engineering with him.