Securing smokebox number plate

[Derek DroverParticipant @derekdrover32802]

I have obtained a brass numberplate for my 5″ L1, to go onto the smokebox door, but I’m worried about how to secure it. I have a hole already in the door to take a 5Ba screw, so I’m considering soldering a brass countersunk screw to the back of the brass plate using Comsol.

My worry is the temperature the smokebox could get to when running.. will the Comsol hold ??

How have others secured theirs?

[parovozParticipant @parovoz]

My £0.02

Assuming the number plate is not painted, just use silver solder. Then guaranteed secure at all smoke box temps. I once saw a comsol soldered chimney band ping off due to melting. Engine was working pretty hard though….. I have also riveted this kind of stuff in place with fine 3/64″ brass rivets then carefully countersunk and dressed off a the front. Then paint it and nothing shows.

 

[Speedy Builder5Participant @speedybuilder5]

Question is – how were they originally attached, I doubt cosmsol or silver solder.

Bob

[bernard towersParticipant @bernardtowers37738]

As Paravoz  use rivets fit and forget.

[duncan webster 1Participant @duncanwebster1]

On narrow gauge locos I’ve worked on they are held on with brass screws. Possibly the only time I’d contemplate using a 12ba screw. 14 ba would be even better, but there are limits. A friend of mine who worked on full size locos reckoned 12ba was a surface finish, not a thread

[Derek DroverParticipant @derekdrover32802]

Thanks for your replies guys.

I was concerned about silver soldering due to the level of heat required and the possibility of creating distortion to the plate.. so I’ll cut a scrap piece and give it a try first.

As it’s a flat plate going onto a radiused door I don’t like the idea of riveting it on.

[SillyOldDufferModerator @sillyoldduffer]

This depends on how hard the engine is worked.   One of my books mentions the smokebox of a full-sized freight engine glowing dull red in twilight whilst hauling a heavy coal train up one of Britain’s steeper incline.  (Must have been a wonderful sight!)

But are model loco’s ever driven that furiously?   And if they are, does the steam blast heat the firebox faster than the heat is lost?  My guess is not, so Comsol should hold in a model, though not in full-size.  As for narrow gauge, I don’t know.  My guess is the Ffestiniog engines aren’t flogged today as they might have been when hauling slate.

Anyone measured engine temperatures at their club?  Not difficult to do now IR pistol style thermometers are so cheap.

Distorting the plate I don’t know, but could be a problem, which is why the experts above suggest rivets and screws. I’d heed their wise words!  Why risk otherwise?

Dave

[JasonBModerator @jasonb]

My fowler ones are screwed on with brass roundheads as per original. I spent some time bending the photo etch plates to follow the curve of the door so the screws are not under any real load. The full size were cast with a suitable compound curve to the back.

Dave it is not the blast of steam from the blast nozzle that heats the Smokebox (not firebox that is the other end of the engine) as that is aimed straight up the chimney but the flue gasses coming out the boiler tubes though there is usually a baffle plate inside the door to help keep the heat away.

[Charles LamontParticipant @charleslamont71117]

In full size there are brackets so that the plate sits flat and vertical slightly in front of the door. A quick surf suggests there was no smokebox number until they were painted BR black.

 

[duncan webster 1Participant @duncanwebster1]

Loaded slate trains on Ffestiniog rly were helped by gravity, the locos hauled empties back. I reckon they work harder now as they have to pull heavy passenger trains uphill.

Steam in the smoke box will be at relatively low temperature as it has expanded in the cylinders. Even before expansion it isn’t hot enough to get a smoke box visibly red hot.

[Brian Baker 2Participant @brianbaker2]

The red hot firebox doors on full size locos were due to a leak on the door allowing air to enter and burn unburnt coal in the smokebox thus further distorting the door so more leaks etc.  Not likely with our high standards of machining.

To fix my plates I make two small spacers, thick enough to allow for the curve of the door and through bolt, with small size bolts, thus they are rigidly attached and able to stand vigorous cleaning that “helpers” always employ.

Brian B

[duncan webster 1]

On duncan webster 1 Said:

Loaded slate trains on Ffestiniog rly were helped by gravity, the locos hauled empties back. I reckon they work harder now as they have to pull heavy passenger trains uphill.

True!!!

Steam in the smoke box will be at relatively low temperature as it has expanded in the cylinders. Even before expansion it isn’t hot enough to get a smoke box visibly red hot.

It’s exhaust gas from the tubes that’s the source of heat, not steam.  Locomotive tube boilers are very inefficient in that most of the heat generated by the fire escapes up the chimney.   The boiler, tubes and firebox are all kept at boiling water temperature, so no danger of them reaching red-heat unless the water leaks!   Not so the gases coming out of the tubes; they are at much higher temperature, and, particularly when forced, contain fragments of burning coal that blast into the smokebox.  The amount of heat and temperature increases when exhaust steam is used to force the draught, burning coal in the firebox faster & hotter by pulling more air through the grate.

I’m sure Brian is right that a loose smoke-box cover greatly worsens the problem in full size by providing the air needed for unburned coal to burn completely inside the smoke-box.  That really would get things hot!

None of my engineering books gives the exhaust temperature at tube output end for reciprocating steam locos.   A Marine engineering book quotes 400-500°F at battleship funnel-tops, bad for lookouts on a nearby mast!  Doesn’t say what the gas temperature is as it leaves the boilers a 100′ below, I guess double or more.

That said, I suggest red-hot smoke-boxes are much more likely in hard-driven full-size locos than in models. Be surprised if Comsol could get too hot because small boilers lose heat faster than big ones, and there’s not much space or time for coal to burn inside model smoke-boxes, plus, as Brian says, models are unlikely to let air in due to poor fitting doors.

Does anyone know how hot model smoke-boxes get?  Could be easily be measured.  Hard driving a heavily loaded model loco up an incline whilst pointing an IR thermometer at the smoke-box would soon reveal if Comsol is in danger of softening.   Or, in the absence of temperature facts, note that screwing and riveting entirely avoids the risk of a Comsol failure.

Dave

 

 

[Brian Baker 2Participant @brianbaker2]

Interesting question, Dave, I once, a long time ago measured a hard working Simplex by simply sticking a high temperature thermometer into the smokebox when it was standing and got 230 degrees centigrade, perhaps the blower was on as well.

I expect we will have thermometers sticking out of every loco chimney now!

Regards

Brian B

[duncan webster 1Participant @duncanwebster1]

Loco boilers, both model and full size, tend to have efficiency around 70% unless they are overloaded. Jim Ewins did lots of tests on boilers. The results need to be taken with care as its difficult to measure gas temperature close to a source of radiant heat. You need a suction pyrometer, which is a bit of overkill

There is also the results of tests carried out at a South African University in ME somewhere.

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