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Fire Bars

Discussion in 'Steam Traction' started by brennan, Mar 7, 2017.

  1. brennan

    brennan New Member

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    Any thoughts as to how long a set of fire bars should last on the average heritage line? e.g. seven miles long with five or six coach trains with about four trips a day. Which is the better material for overall cost, cast iron or steel? Who are the favourite suppliers for cast bars?
     
  2. andalfi1

    andalfi1 Active Member

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    Chilled Cast Iron (Grey Iron) Gave the best results for us, in my previous life on the Worth valley.
    Andy
     
  3. Aberdare

    Aberdare New Member

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    Brennan,

    Much will depend upon the coal supply in use and any gradients encountered on the journal. Some railways can be operated by locomotives with a quite cold fire and others will require a white incandescent fire. From your question we can assume that fire bar life is a problem which requires some rectification.

    Fire bars are not cheap items and so a life of years rather than days is a prime requirement for any operator.

    The WSR has for many years used welsh coal up reasonable gradients with locomotives loaded to their limit, because of this we have explored options to prolong fire bar life. Some will recommend mild steel, others cast iron etc. About 15 years ago we carried out an experiment on the BR rocking grate of 80136 by fitting finger bars of various materials into the grate to see which lasted the best in actual service when all subjected to the same conditions. From memory the materials were:-
    • Ordinary grey cast iron, one of the traditional choices.
    • Flame cut mild steel with welded on spacer lugs, another choice which is popular on several railways.
    • SG cast iron.
    • Stainless steel, can't remember which grade but expect that it would be an 18/8.
    • Grey cast iron with added chrome.
    There were about a dozen of each material fitted, they were all mixed together but in a set pattern so that we could later identify the materials. After a short period of time in service the results quickly became apparent.

    • Grey cast iron gradually deteriorated as expected, clinker stuck to it, it burnt away and distorted.
    • Mild steel was fine until the temperature of the fire reached a level at which the steel melted away, quite dramatically, and the bar became a like an overheated chocolate bar.
    • SG cast iron was the same as the grey cast iron.
    • Stainless steel was better but had cost issues.
    • The grey cast iron with added chrome came out looking exactly the same as when it was fitted. In addition clinker did not adhere to the bars lifting off easily.
    Since then the WSR has changed over to high chrome cast iron for nearly all fire bars with excellent results. 9351 ran for 9 years with the same grate fitted (apart from a few broken bars) 97,000 miles. Previously ordinary grey iron bars on similar duties lasted max 2 years and mild steel bars 2 months.

    The only down side of the high chrome iron is the cost, about 50% more than ordinary grey cast iron, and the high chrome iron is more brittle but this is not a problem provided the bars are not thrown about.

    I can't off hand remember the BS number but the grade is 3E and the chrome content is 28%. Not many foundries will cast this material.

    Hope this has helped.

    Andy.
     
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  4. sleepermonster

    sleepermonster Member

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    Locomotive Maintenance Services at Loughborough now specialise in the supply of chrome iron firebars.
     
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  5. D1039

    D1039 Well-Known Member

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  6. meeee

    meeee Member

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    The F&WHR have experimented with chrome iron fire bars as well on both the Double engines and the NGG16. Engines on both railways typically run with white hot fires however a switch to Welsh coal had caused a few problems with grates due to the increased heat in the fire bed. Despite the cost they are incredibly long lasting and clinker not sticking to them is an added bonus. I would say that the cost effectiveness of the chrome iron fire bars depends on the work your loco is doing, especially given the 50% or more cost increase. On the F&WHR you're talking about engines that work every single day from March to November so as you can imagine fire bars can become a major expense.

    Finding a foundry that will cast in this material isn't easy though. I believe they have to clean everything it comes into contact with before casting anything else which is why foundries don't like it.

    Mild steel firebars with lugs welded on have also been used, particularity when the foundry lost the pattern :p They didn't work out any cheaper, and they do work for a bit but as mentioned above deteriorate quite rapidly.

    Tim
     
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  7. bob.meanley

    bob.meanley Member

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    This has been a frequent debate for far too many years now. I truly believe that the life of firebars is far more influenced by choice of coal and crew competance, their material is almost irrelevant. In the first instance it has been my experience over nearly 50 years that the sort of "Welsh" coal which has been available have almost exclusively not been the types of bituminous Welsh used by the GWR (in particular), tending towards the dry Welsh favoured by the marine industry where level, relatively thin firing techniques were used in conjunction with constant steady controlled draughts. All Welsh coal can have a tendency to cake (not clinkering!) restricting or blocking the air flow through the firebed and hence the grate, leading in many case to overheating, or even melting the firebars. This requires sometimes frequent lifting of the fire with a slice or chisel bar in order to aerate the firebed, and that is why the GWR provided very substantial chisel bars rather than prickers, and also why it also provided fireiron racks at the side of the firebox to house them in the larger loco's. I clearly recall a chap called Eric who I worked with as an apprentice who gave some very interesting tales of working with Welsh coal when he was firing Dreadnought battleships at the end of the first war, in particular how they frequently had to use the slice bars to break up the firebed, and the draconian measures if you were careless enough to dislodge a firebar; "it was a King's capital ship and they were not going to slack way just because you had dropped a bar in the sluice..."

    It is perhaps worth recalling that wrought iron was quite extensively used at one time for firebars which were of rolled section and supported in racks or "combs" as they were sometimes called. This tended to diminish in the 1920's with the downturn in wrought iron manufacture due to greater availibility of mild steel which had somewhat better properties and was cheaper. However mild steel was used from time to time, and I was told years ago by a BR boiler inspector, that towards the end of steam on the LMR there were shortages of bars coming from the mechanised foundry at Horwich, and that an impromptu facility was set up at Crewe to fabricate steel bars to suit. There was an additional comment that they were far superior, and that comment led me to use steel bars over the last 40 years. It is also worth noting that bars were chill cast on their top faces mainly to harden them in order to resist the abrasion from fireirons and fuel. Chilling does little to change the melting point of the material.

    There have been comments that mild steel will melt much as cast iron does and that is true to an extent. What does however have to be pointed out is that cast iron melts at around 1127 to 1200 deg C, steel at around 1400 to 1540 deg C, and wrought iron at an even higher 1482 to 1593 deg C (all dependent on composition); perhaps the Victorians knew something about firebars after all. It should therefore be clearly obvious that whatever the material, if the crew allows the firebed to become caked or clinkered thus blocking airflow through the grate, the firebed will generate the sort of temperatures above 1500C which will melt anything, even inconel. That includes high chrome iron which is really intended for somewhat different purposes than the aggresive conditions of a firegrate, particularly where increased elevated temperature properties and corrosion resistance are required. Improved corrosion resistance is hardly required in a firegrate and ordinary cast iron is perfectly strong enough, so why waste your money on high chrome iron, it will melt just the same. I can say that all of our loco's at Tyseley have mild steel firebars, 4965 has most of the bars which were in it when it returned to the main line in 1998, and 5043 has bars which have been there throughout its current 25,000 miles or so on the main line, and some even did service in 7029 before that. It is also worth recalling that in my time with 6201 we were given a substantial quantity of fabricated steel firebars whilst at Shildon in 1975, and quite a few of those bars were still in it in 2010. The engineer at that time fell for the high chrome cast iron sales pitch and replaced the last of the 1975 steel ones with them; sadly many of their new high chrome replacements were judged unfit for further service within a very short time.

    In conclusion what I can say is that steel firebars are the cheapest, particularly if you are equipped to weld on the spacers in house rather than contracting a supplier. The outputs are that if you are unable to educate your crews in the ways of avoiding blocking airflows through the grate, and particularly so if you opt to use the currently available fuels from the principality of Wales, it is likely that you will be burning bars whatever they are made of. Certainly we have never given the idea of using more expensive high chrome bars a moment's thought, why would you, when you can get far cheaper mild steel bars to do 35,000 miles of quite heavy main line service in a Hall?

    Best Regards
    Bob
     
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  8. Aberdare

    Aberdare New Member

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    Bob,

    Only 35,000 miles with steel bars? High Chrome Iron ones in 9351 lasted for 97,000 miles and are still fit for being returned to use again.

    I can only reiterate that when we experimented with using a selection of bar materials in the same grate subjected to the same conditions the High Chrome Iron bars won hands down.

    But I do fully accept that differing circumstances may suit differing materials.

    Andy.
     
  9. Steve

    Steve Resident of Nat Pres Friend

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    All very interesting from both both Andy & Bob. I can't really add to the discussion in terms of material but I'd be interested to hear about modes of failure. Are bars being changed because they have melted, burned away, fused, warped or simply broken? As regards the arrangement with combs supporting bars, as mentioned by Bob, I am associated with a couple of industrial locos that have this arrangement and I one has wrought bars and the other cast. Neither seem to perform well due to warping of them and this can be in either the vertical or horizontal plane. In my experience, bars that are a loose fit tend to warp fairly easily and this is also true if they don't have a central spacer.
    I do have a comment on the use of dampers in relation to firebars in that I believe that closing the dampers on a white hot fire is a recipe for damaging firebars. A fireman that does this is not going to do the bars any good, especially if you have an otherwise air -tight ashpan.
     
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  10. Aberdare

    Aberdare New Member

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    Steve,

    Modes of failure.

    Most materials distort, burn away and will be subjected to clinker mixing with the parent metal and forming some sort of misshapen encrustation on the top/sides.

    The high chrome iron almost stays as cast apart from occasional burning of the extreme top edges in places. The mode of failure is invariably caused by expansion cracking which starts in the bottom of the web which is the "cold side" of the bar. Eventually this cracking will result in failing of the bar but only when the crack has progressed to at least half way through the section. A change of design to reduce the section depth would probably resolve this issue.

    With a hot fire a degree of primary cooling air needs to be maintained up through the ash pan to avoid damaging any fire grate, shutting dampers on a hot fire is something that all firemen learn not to do at an early stage of their training.

    Andy.
     
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  11. Scrat

    Scrat New Member

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    Without wishing to shatter any illusions, but working a mogul flat out at slow speed for 5 or 10 minutes in between station stops doesnt come close to working a Stanier pacific or even a castle flat out with 12 or 13 coaches on routes such as the west coast mainline at express speeds for 70 plus miles before a stop!!
    The grate on say 6201 would have to stand far higher consistant temperatures for far longer periods, particulary on routes such as Shap and the S&C.....
    All in all not really a comparable example....
     
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  12. Aberdare

    Aberdare New Member

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    Scrat,

    Not at all similar since the variables involved will affect the fire bar temperature in different ways.

    All I can say is that when we subjected fire bars of different materials to the same service conditions the Chrome Iron won hands down, steel was absolutely useless and melted/distorted within a few days of use, ordinary grey cast iron showed signs of deterioration at the next washout. The Chrome Iron remained unaffected and that has been our experience since.

    Brennan originally asked for advice on fire bars since they were evidently having problems, I was passing on my experience which has saved the WSR many 10's of thousands of pounds over the years, this experience has been with a variety of coals and locomotives for over a million miles in service.

    It is a shame that we never had the opportunity to trial Chrome Iron bars with deep mined "Lady Windsor" coal, that was truly a coal that burned with an intense high temperature heat in the firebox when working an engine hard. Just because a firebox is smaller it does not mean that the grate temperature is lower. Large wide firebox locomotive boilers are generally designed as such so that they are able to produce the same heat output at the lower fire temperatures created by lower quality coals. I suspect that footplate staff on the Ffestiniog and Welsh Highland would agree that a small firebox can reach the same temperature as a large one.

    Andy.
     
  13. Jamessquared

    Jamessquared Resident of Nat Pres

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    I don't think that is quite true.

    Firstly, the absolute peak temperature that can be attained in the fire (the limiting case for considering the properties of the metal fire bars) is limited by the specifics of the chemical reaction between coal and oxygen. That will vary a small amount given that different types of coal have slightly different compositions, but to a good approximation, for a given type of coal, the absolute peak temperature that the fire can attain will be the same regardless of the loco or its duty. A big mainline loco on a big load may develop more power than a smaller loco on a smaller load, but that is a function of the grate area and therefore the rate at which coal can be burnt. It isn't dependent on the absolute temperature of the fire.

    The second point to bear in mind is that when the fire is really hot, it is probably beyond the melting point of the bars. What saves them is the cold airflow coming in from underneath, which draws heat out of the firebars. Essentially the firebars are exposed to a fierce draft of cold air (cold when considered against the 1200C or more temperature of the fire) which protects them. Hence the strictures about suddenly shutting off the air supply on a very hot fire; hence also why clinkering causes firebars to burn away (because it prevents an airflow locally round the bars which are still exposed to the full heat of the fire). A loco working very hard will also be drawing a proportionately large volume of air through the firebars keeping them cool. The rate at which heat can be removed from the firebars per unit area of grate is dependent on the mass-flow rate of that cold air, which also happens to be the limiting factor on how fast coal can be burnt.

    What is potentially true on the mainline is that high temperatures may be sustained for longer periods. But the peak temperature of the fire will not inherently be higher than a smaller locomotive working very hard on a heritage line; and assuming an adequate airflow is maintained (which is essential for sustained steaming anyway), the firebars should reach an equilibrium temperature beyond which they don't continue to heat up just because the peak power output is sustained for longer.

    Tom
     
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  14. Steve

    Steve Resident of Nat Pres Friend

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    There's nothing really to add to this.
     
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  15. Scrat

    Scrat New Member

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    I would agree with this, but for the last paragraph.
    Are you suggesting that a loco running at 25mph in say 25% cut off and full regulator would have the same firebox temperature as it would running in the same cut off and regulator setting at 75 mph?
    With the massive increase in steam flow, just wondering how the extra steam is made with no increase in heating temperature.....?
     
  16. Steve

    Steve Resident of Nat Pres Friend

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    Tom is quite correct. There would be an increase in heat produced but not temperature. The two are fundamentally different. In simplistic terms, it is akin to volts and amps. the voltage stays constant but the current goes up as the demand for power increases. In your example, again being simplistic, the loco at 75 mph would be using three times the amount of steam and thus three times the amount of coal reacting with three times the amount of air but the temperature would be the same. You will reach the maximum temperature when you have stoichiometric combustion, which is the ideal ratio between fuel and air. It is not related to the amount of fuel burned.
     
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  17. sleepermonster

    sleepermonster Member

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    Talking of firebox temperature, boiler size and the ffestiniog, I read many years ago that cast concrete firebrick arches were developed for 9F locos on the Consett iron ore trains. Later on the FR decided to try the same idea and the manufacturers sent them the Consett mix. It melted.
     
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  18. Jamessquared

    Jamessquared Resident of Nat Pres

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    The fire generates hot gas which transfers its heat to the water via the heating surface. So hypothetically, if you need to double the rate of steam production, you do it by doubling the rate at which you produce hot gas, not by increasing the temperature of that gas. That in turn means doubling the rate at which you burn coal and the airflow needed to burn that coal, but the burning takes place at the same temperature. Somewhat akin to taking an internal combustion engine and then increasing the revs: you will get an increase in power because you are burning more fuel per unit time, but fundamentally the temperature generated by the burning fuel in each piston stroke does not change; you just have more such strokes per unit time.

    As an aside, at the weekend I was firing a class 1P tank engine with a load of 144 tons on a line with sustained gradients between 1 in 55 and 1 in 75, and I can assure you the fire got blinking hot at times! The difference between that and a large mainline engine is that I had 17sq ft of incandescent coal, rather than say 40 or 50sq ft. So the sustained power output was less than a large mainline engine on a big load, but the temperature of the fire was very much as hot - just less of it.

    Tom
     
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  19. Big Al

    Big Al Resident of Nat Pres Staff Member Moderator Friend

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    So having read the expert comments above it seems that there are two influencing factors:
    1. The extent to which firemen really understand their job and what they do to maintain optimum conditions in the firebox.
    2. The 'wild card' of the coal that is provided and what I gather is its variable quality nowadays, even from the same source.

    Obviously, the first is in the hands of those with that responsibility and the training that goes with the role. However the second is more random. I am told that if one pays 'top dollar' for coal that is probably the best 'spend to save' policy but I also gather that nothing is guaranteed in that respect.

    Do those with the knowledge agree?
     
  20. Steve

    Steve Resident of Nat Pres Friend

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    What the fireman does can certainly have an effect. Dampers, condition of the fire and use of fire irons are all contributors under the control of the fireman. As you say, coal is a bit of an indeterminate. I don't think 'top dollar' is necessarily the criteria to apply. Your coal factor will give you an analysis on request but, unless you perform your own on each load, you are taking pot luck on what you actually get. Most people can't tell good from bad simply by looking at it; I certainly can't. Back in the days of steam, coal was largely got by hand filling and transported out of the mine in pit tubs. It was fairly easy to segregate the different seams and even segregate coal in part of the seam, if it was like the Barnsley Bed, which had good and bad coal in the same seam. (I forget whether it was the top or bottom coal that was good.) With mechanised mining and opencast methods, it all tends to get mixed together, whether it is good or bad. This was very much the case when the main supply was to power stations and lump coal was a by-product. Coal, like wine, is a once use product and you can never exactly repeat what you have had.
     
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