wow, the firebox is made of copper…
Greg, that’s for good transfer of heat. I am kinda surprised that copper would withstand the heat and pressure in the firebox of a working 1:1 steam locomotive.
yep, actually though, making the firebox itself sounds weird, the transfer of heat is mostly through the tubes I thought?
Gre
Water actually surrounds the whole firebox.
Greg, yes the boiler tubes transfer a lot of the heat. But when locomotive builders started putting water tubes in the firebox side sheets, the locomotives became more efficient. So many later designs have the firebox surrounded by either water tubes, or a whole water jacket. But I am still amazed that copper can withstand the pressures and heat of being used on the firebox. I know, the water keeps the copper cool enough, but its still darn hot.
The first photo is one of my boiler for my 1-1/2" scale Allen ten wheeler. The boiler is 8 inches in diameter. The front flue sheet is at the top and the rear flue sheet is at the bottom of the tube in the front of the firebox. The welds are the stay bolts that keep the boiler together under steam pressure. The rectangular welded area is the bottom of the water jacket around the firebox and is called the mud ring (where the particulates drop from the boiler water. The 1/2" diameter copper flues go all the way from the front flue sheet at that ring in the top down to the wall where the firebox starts.
The second photo is a close up of the firebox showing the firebox door, water jacket, mud ring and stays.
The threaded plugs are for the blowdowns and drain plugs.
Edit: Added photo of the firebox and the rear flue sheet. The firebox IS surrounded by water…the crown sheet (shown at the bottom in the shot) and on all sides of the water jacket. When water is added to the boiler, the water line is usually kept about a 1/2 inch above the topmost set of flues and also covers the crown sheet by that amount. In the cab, the water level would show a “half-glass” in the water level glass gauge. Burning through the crown sheet was the major cause of boiler explosions. The existing water remaining in the boiler would almost immediately turn to steam and therefore the pressure has to be relieved somewhere…explosion. Usually the boiler would rotate off the smoke box in the front lifting the rear of the boiler including firebox area and of course the entire cab including “occupants”…engineer and fireman.
There shouldn’t be any pressure in the firebox (unless there is a leak in the boiler).
Huh? The firebox water jacket is connected to the boiler, or else what is the point of having water in the jacket?
yes, there is pressure on the firebox, from the outside inwards… note the number of copper rivets in the article… lots
Greg
I understand about the fire box being surrounded by the water in the boiler, but there is no pressure IN the fire box only around it.
Joe Zullo said:
I understand about the fire box being surrounded by the water in the boiler, but there is no pressure IN the fire box only around it.
Joe,
You are correct. In your diagram above there is pressure in the blue and yellow in the pressure vessel. None in the firebox interior where the coal burns on the grates.
I think David is the only person that said pressure “in” the firebox, and I believe he meant what the rest posted here pressure “on” the firebox.
The rest of us did say “on”, not “in”.
In any case still seems unusual… are many fireboxes made of copper? I have never seen one of copper in 1:1…
Greg
I mis spoke, I meant that there is pressure inside the water jacket around the firebox.
Actually, I cant see where I mis spoke, so maybe it would be more accurate to say I wasn’t clear in what I was trying to say.
I said that the water jacket was connected to the boiler, and I was wondering how the jacket could withstand the pressure (inside the jacket) and the heat of the firebox. I didn’t say the inside the jacket part in my post, so that’s probably why it was misunderstood that I was referring to pressure inside the firebox.
Actually, if the draft is working properly, there should be a slight negative pressure inside the firebox, to draw fresh air in to sustain combustion.
Greg Elmassian said:
I think David is the only person that said pressure “in” the firebox, and I believe he meant what the rest posted here pressure “on” the firebox.
The rest of us did say “on”, not “in”.
In any case still seems unusual… are many fireboxes made of copper? I have never seen one of copper in 1:1…
Greg
Greg,
When I built my first live steamer starting in 1956 with a Little Engines 0-4-0 tanker, the firebox and the rear flue sheet was a huge one-piece bronze casting with the stays cast right in place. I then bought a 5 inch diameter copper tube about 16-17 inches long, 1/4 inch wall thickness. TheRe was a cast bronze front flue sheet. Everything was riveted together using silicon bronze flat-head rivets. Essentially a copper flue/bronze boiler. State of the art in 1960! Most large scale ride-on boilers are normally steel with copper flues. The really pricey boilers are copper. A steel boiler can be made for about $4500-$5000 today. OTOH, an all copper boiler will be almost double that. I would think that you could have a 1:1 copper boiler. I don’t see a problem with that.
David Maynard said:
I mis spoke, I meant that there is pressure inside the water jacket around the firebox.
Actually, I cant see where I mis spoke, so maybe it would be more accurate to say I wasn’t clear in what I was trying to say.
Actually, if the draft is working properly, there should be a slight negative pressure inside the firebox, to draw fresh air in to sustain combustion.
David,
You are correct about the “venturi” action in the smoke box caused by the draft in the stack. The distance between the top of the exhaust nozzle and the bottom of the petticoat under the stack is very important. that space gives a negative pressure which causes heat to be drawn from the firebox through the flues to heat the water.
Gary, I see how copper or bronze works for our models… I would like to see if there are any other prototype (that’s what I meant by 1:1 (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)) locomotives with an all copper firebox.
Every picture of a loco restoration I have seen they have been steel.
Greg
Greg Elmassian said:
Gary, I see how copper or bronze works for our models… I would like to see if there are any other prototype (that’s what I meant by 1:1 (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)) locomotives with an all copper firebox.
Every picture of a loco restoration I have seen they have been steel.
Greg
Greg,
OK, I think I have an answer…just NOT the only answer. In my reading about boilers for 1:1, copper was used primarily for locomotive boiler fireboxes in the mid to late 1800’s when burning WOOD. When they started firing with coal, they found the coal ash was much more abrasive and they went to steel fireboxes.
Ahh… now that makes sense… and also didn’t coal burn hotter too?
Thanks Gary!
Greg
Gary Armitstead said:
Burning through the crown sheet was the major cause of boiler explosions.
Hence a lot of steam locomotives that worked steep inclines (rack assisted) had boilers angled down in the frames so that the crown sheet didn’t get exposed as the loco tilted up the incline. Check “Snowden Mountain Railway” pictures.
All those stays, what appear as “rivets” on the outside, are there to stop the firebox inside collapsing from the surrounding pressure.
Copper fireboxes, as are the tubes, were pretty much standard practice on British steam locomotives. However new build “Tornado”, a close design relative to “Flying Scotsman”, has an all steel boiler built by the Germans at a former GDR depot. Had a lot of problems initially popping its firebox stays. Max.