|Chris Sheward||17/03/2018 11:35:12|
|5 forum posts|
I have been in the process of making coaxial type super heaters x/2 for my 5inch Stirling single. Having 3 times tried to solder (Easyflow 55) the outer stainless steel tube to the copper regulator tubes without success I am now thinking perhaps I`d be better off without super heaters altogether. The tubes are only 10/1/2 inches long are they really going to make that much difference. The steam collector tube high up in the boiler will presumably do an efficient job of producing somewhat dry steam. I would appreciate any members views on this subject. Many thanks
|Speedy Builder5||17/03/2018 11:41:35|
|1776 forum posts|
What flux are you using? You need Tenacity Number 5 in my experience for S/steel.
|Chris Sheward||17/03/2018 14:22:33|
|5 forum posts|
Thanks for that Bob. as far as I am aware the flux we use should be compatible with the grade of silver solder used and not the metals being used, so, one should be able to solder stainless using Silver-flo 55 and using Easy-flo flux. Is it not all to do with the temperature regarding the flux used.
|John Olsen||17/03/2018 15:08:04|
|966 forum posts|
The flux has to be active enough to attack the oxide layer on the material, which in the case of stainless means it has to take off the Chromium dioxide layer that forms. Ordinary flux probably will not do this so as Bob said above you need the Tenacity 5
|Neil Wyatt||17/03/2018 15:13:06|
16098 forum posts
No, you need high-temperature fluxes for good results with stainless steel whatever silver solder you use.
A few here:
|Tim Stevens||17/03/2018 15:39:09|
1043 forum posts
The oxides that form on stainless steel when heated are quite different to those on copper or brass, so you should not expect the same flux to work equally well. And its not just the 'high temperature' nature of the flux, but the exact constituents. It can also matter what grade of stainless you are using as although they all contain Chromium and Nickel, other metals are used in the various alloys.
|Clive Brown 1||17/03/2018 16:12:29|
|234 forum posts|
JM market an Easy-Flo stainless steel flux. It's more aggressive than the normal E-F flux to deal with the stainless steel oxide layer, but works at lowish temperatures.
|duncan webster||17/03/2018 18:10:23|
2111 forum posts
to be real;y effective your superheaters shoul pass well into the firbox, and normal out and return version is better as well
|Martin Johnson 1||17/03/2018 19:52:21|
|116 forum posts|
As noted by others you need a specific flux for stainless, which should make your problems surmountable.
As to whether you need superheaters - yes you do. If you look at Bill Hall's tests at:
Fig. 5 in particular shows that superheat can change the steam demand from the engine over a range of about 2:1. Would you be quite so relaxed about putting in half the grate area, half the tubes and half a firebox? I rather doubt it!
Personally, I would not recommend a concentric superheater, but I see the manufacturing simplicity of such a beast. As Duncan says, a good dose of radiant heat from the firebox will also help matters along.
|Paul Kemp||17/03/2018 21:12:18|
|283 forum posts|
There is no disputing the value of superheating steam. Whether you can actually get any meaningful degree of superheat in a 5" gauge engine is quite another matter. The writer acknowledges his ancient Speedy fails to develop any superheat even when driven hard. I would be surprised if there are many 5" gauge loco's that develop more than a few degrees of superheat let alone the amount required for a noticeable impact on efficiency. Is there any published data for actual superheat achieved for various designs?
|79 forum posts|
It tends to be forgotten that superheaters only work when they are properly hot and this takes some running time to achieve. I have driven 5 inch gauge locos which are not superheated, and they work perfectly well. Possibly they use more coal and water than their superheated counterparts but this is very difficult to quantify, and so what, anyway? In average start-stop running on a club track I am not convinced that superheating makes much difference.
|julian atkins||17/03/2018 22:18:48|
1204 forum posts
I suggest you ditch the coaxial superheaters as they are not very efficient. The LBSC type is far better in copper pipe and spearhead return bends, but the return bends do need to be sifbronzed up to the copper pipe.
The coaxial type originated with Don Young's Mountaineer design in ME early 1970s at the suggestion of Alec Farmer.
A few years ago I became a convert of stainless radiant stainless superheaters extending into the firebox - that have to be TIG welded at the return ends, and is a job far beyond my capabilities. But friends with the requisite skills or contacts have provided the necessary.
I would never build a loco without superheaters in 3.5"g or 5"g. If you are a good attentive driver you notice the difference after the first half lap. The loco is more lively, uses less water and coal, and the valve gear can be notched up further so further using less steam. You also go through a tunnel and spectacle wearers like myself do not get their glasses 'steamed up' preventing seeing signals. The saving of coal and water is quite considerable in my experience.
|David Wasson||19/03/2018 01:57:31|
124 forum posts
I had a professional TIG weld the spear head of my super heater elements. I did the silver soldering of the elements to the headers. This was a copper to stainless steel joint. I used 45% silver solder and high temp black flux.
Do not experiment on your super heater elements to see if you can solder them or not. I made several experiments on test joints to convince myself that I could achieve good penetration between the copper and stainless. The joints were cut to pieces for examination. Only after successful test joints, did I move on to solder my elements to the headers.
Yes, I vote for elements that go all the way into the fire box. I also vote for the spearhead type connected together at the "pointy" end by a TIG weld done by someone that knows what they are doing.
Edited By David Wasson on 19/03/2018 01:58:25
Edited By David Wasson on 19/03/2018 01:59:15
|Simon Collier||19/03/2018 07:16:31|
295 forum posts
I totally agree with Julian and David.
You can talk about all the theory in the world or, you can drive a saturated loco, add superheaters, and drive it again. That will be all the convincing you will need. The smaller the loco, the more important superheating, or steam drying if you like, is. The improvement between saturated, and copper elements withing the flues, is greater than the improvement going from copper to radiant stainless elements, but the latter are the best.
|79 forum posts|
I have in fact driven saturated and superheated locos in broadly similar conditions over many years and I am not convinced either way. As an engineer I think for myself and I take into account all aspects of the problem in hand.
Now the great god julian has spoken and all his sheep bow down to him, instead of having an intelligent discussion. We should be trying to help the OP with his questions. It's all about winning the argument, not solving the problem.
We are only playing with toy trains and anyone who is worried about about fuel and water savings in that situation needs to get a life and get out more. He may enjoy the meetings of the Flat Earth Society, if he isn't already a member.
|David Wasson||19/03/2018 09:46:33|
124 forum posts
Hmmm.....all his sheep? Wow, I wonder how many there are? The must be herds of them!
Yes, we should help the OP with his question. As I mentioned, I silver soldered my stainless superheater elements to the copper headers with 45% silver solder and high temp black flux.
I think you were pretty distracted and you forgot to answer the OP's original question. Since you seemed to have missed it, I'll restate it, if I understand it: What do you use to silver solder copper to stainless steel? As you are a self proclaimed engineer, I'm sure you will have a helpful and insightful answer.
|Andrew Johnston||19/03/2018 11:00:05|
4699 forum posts
That's sheep for you, where there is a small gathering of them more tend to gravitate without asking questions, and before you know it there's a whole herd.
|Neil Wyatt||19/03/2018 11:48:49|
16098 forum posts
As a biologist, I'm familiar with the 'counter current multiplier' principle which the Kidneys use to concentrate salts in the kidneys.
The co-axial superheater is an excellent design for concentrating heat at the hot end of a superheater as the wet steam entering at the firebox end cools the superheated steam coming the other way. This means pretty hot steam is entering the return end at the firebox making the end hotter than it needs to be.
I'm sure such superheaters work, but I bet they give less superheat than one with two separate tubes and wouldn't be surprised if they don't last as long either.
<edit> baaa - I have never made a superheater so what would I know?
Edited By Neil Wyatt on 19/03/2018 11:50:48
|David Wasson||19/03/2018 13:43:24|
124 forum posts
You seem a bit distracted by sheep as well as Redsetter. The question remains: How did you silver solder the stainless steel superheater elements to the copper headers in your locomotive?
|John Alexander Stewart||19/03/2018 14:13:03|
|748 forum posts|
Chris - the only superheater I've made is to LBSC's design, for Tich.
It was not a success - mainly because the flue it's in got plugged the first day out, and I have not been able to clean it out - 20+ years without it has convinced me that the effort is not worth it. I've tried poking a 1/16th steel rod through, but no luck; the front end and superheater are just too cramped, at least in my build.
Now, I'm certain that a radiant superheater makes a big difference to water and coal consumption, as well as condensate on ones' glasses. It does make you worry about lubrication of cylinders, etc. The Raritan build (CI cylinders and rings) does NOT have a lubricator, so one less part to make or purchase. It is saturated, of course.
I think that what we need is for someone to make 3 or 4 locomotives identical locomotives, with the exception of superheaters and, superheater type. Then a valid comparison can be made. Say, a stud of Simplexes, with:
1) Simplex, no superheater;
2) Simplex, in-flue superheater;
3) Simplex, two-tube radiant superheater;
4) Simplex, coaxial superheater.
And, measurement tools for determining efficiency.
Me? Nope! I'm not going to build them! Life's too short; I've got my Shay (no superheater) to get running when the snow melts, my 2-8-2 (superheater removed by previous owner) to fix some leaking pipework, and get my Ivatt 2-6-0 running, which will be made without superheaters, just to get the thing on the rails. Mind you, I'd love to try all 4 Simplexes (Simplii?) one day, so hopefully someone'll get cracking and churn them out.
A fun and challenging hobby, and I enjoy the individualism shown by all - it would be boring if we all made the same thing, right?
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