A big boiler build

[Bluecat]

Hello!

I'm going to try and build a quite big boiler. If I remember correctly, it's 4x7.8 inches. The measurements are purely theoretical, as the boiler shell is being riveted together from 4 plates. End caps are going to be copper riveted as well.
Anyway, I decided it's going to have 13 0.4 inch flues, and the boiler itself is going to be a stationary, in some way a Scotch boiler being fired from the wrong side. Just because I don't like real Scotch boilers for some odd reason. It'll function as a pot boiler, but some hot gases will pass through the flues eventually. A steam blower will make that happen. Oh, wood or charcoal fired. Or anything else that burns. Wood and charcoal are preferred though.

Now, for the questions. Some time ago I bought some silver solder, an alloy like L-Ag40Cd. What I'm worried about is the cadmium in it - what precautions should I take? I only got six rods of about 20 inches and they cost a bloody arm and a leg. I can return them as well and get a different alloy, e.g with copper added.

Secondly, about boiler codes. I live in Estonia, it's a small country in Europe, right below Finland. Here, I'd be surprised if even full size boilers get tested in any way. And even if there is something like that, then model boilers are something unknown to the law.
So, should I build the boiler how I like it or should I build it to correspond to a another country's boiler code?
And, what's the max safe pressure to use silicone tubing as a sight glass? I'll change it to glass if I come across some suitable glass tubing.


I shall be putting up my progress here as well. But for now, I have a lot of thinking to do.
Good night,
Timo

 

[bentprop]

Hi,Timo.I'm not the best person to inform you about boilers,but a boiler of the size you describe will generate quite some pressure.I would therefore suggest you build it to a standard that's been tested .As for the silicone tubing,this would bulge at any kind of pressure,and eventually burst,so no use for a sight glass.

 

[GWRdriver]

Timo,
The correct material for sight glasses is technically borosilicate glass. Borosilicate glassware and small diameter tubing is heat and pressure resistant (but not heat and pressure proof) and is commonly used in medical and scientific laboratory facilities. There are most certainly mail order suppliers to modelers in France and Germany as well as the UK who will have gauge glass.

 

[Jasonb]

There is no reason to return the solder just because it has cadmium in it. Just use in a well ventilated shop or preferably outside. If outside try to avoid working in strong sunlight as its difficult to see the colour changes of the metal and you don't want to overdo things.

Jason

 

[GWRdriver]

If outside try to avoid working in strong sunlight as its difficult to see the colour changes of the metal and you don't want to overdo things. - Jason

I often do my boiler silver-soldering at night . . . Strewth! . . . for just the reason Jason states.

 

[Bluecat]

Thanks for the response.

What I'm worried about with the cadmium is that the condensate coming from the boiler. Could I just throw the condensate away somewhere like I would do with normal water? This issue might sound stupid, but I need to be sure I'm not poisoning myself or anybody else around me with what I'm doing.

I'll visit the store again someday. I might just change the rods - I've only got 6 of them, and they cost too much. Those other brazing rods were cheaper and there were more of them, the only thing stopping me was the melting temperature. But, it's starting to look like I'm going to need another torch anyway..

 

[steamer]

I believe there will be little to fear of a silver soldered joint once made up ...at least from the cadmium perspective. I would be more worried about the cadmium during the silver soldering process.


Harris makes a line called Saf-t-silv and its good stuff..no cadmium

Check it out

Dave

 

[GWRdriver]

Bluecat,
The cadmium is a fluxing agent and goes away as fumes during the soldering process. The fumes are highly toxic and should be avoided thus the previous (and usual) recommendation to provide adequate ventilation during soldering. Some folks feel that the flow characteristics of cadmium-bearing silver solder are superior to those of non-cadmium bearing solders and I would agree there is some small improvement in flow, but personally, despite working in agressively ventilated areas, cadmium fumes cause me respiratory distress so I avoid using it at all.

 

[Bluecat]

So far I've riveted three plates together, out of four to make the boiler shell. Why am I riveting the shell instead of just using a tube? Simple, probably the closest place to get a pipe of such diameter is nearly 100km away.
Anyway, I've considered a lot of possibilities, so far I've decided I'll build the boiler to a return-tubular design for bigger efficiency.

I have many projects going on at the same time, it's better that way.. One thing I learn doing one project comes in handy when doing a second one... Ah, I just love scratch-building.

Just a little note that the build is still going on.
Cheers, Timo.

Ps: A problem. The end caps are going to be made of a pretty thin copper sheet, so I was wondering this. The flues would act as longitudinal stays anyway, but I thought of riveting angled pieces of copper to the end cap, which would add strength and would stop the end cap from deforming in any way. Will this help?

 

[terrywerm]

The angled brace you are talking about may help, as similar tube sheet stays were used in the steam space of some full size boilers. There is no way for readers to know for certain, since you do not include any actual dimensional data. Additionally, you indicate that the material for the end cap is thinner than the shell, which may make other problems to begin with. Proper boiler design is a very involved process, so you most likely will not find anyone here that would be willing to say "this will work" or "this will not" based only on the vague descriptions you are giving. Due to liability concerns, you may not even find anyone here that would be willing to assist you with your design engineering to any level of detail. Sad, I know, but liability concerns certainly are a sign of the times.

Whatever you do, please make absolutely sure that you perform proper hydrostatic testing on your design before you fire your new boiler. Most of my boiler experience is with full sized stuff, but the principles are still the same.

 

[GWRdriver]

There is no way for readers to know for certain, since you do not include any actual dimensional data. . . . so you most likely will not find anyone here that would be willing to say "this will work" or "this will not" based only on the vague descriptions you are giving.

Yes, at least so far. For instance what is ". . . pretty thin copper sheet."? I wouldn't make a 4" head of less than 11gauge (.094") copper and then only if adequately stayed.

While I can't say the "beam" reinforcement you propose is common, it's certainly used in model boilers from time to time and I've used them myself. It's important that the beam stays be rigid so as to not bend and collapse laterally, and a thin angle won't be rigid enough. For a 4" diameter head the beam material will need to be at least 1/8" sheet and the most effective shape is an elliptical arch, thickest in the middle and tapering off at the ends. There may need to be multiple beams.