Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Solitary Sailor]

Given Greg's encouragement, and after some initial trepidation, I have finally come around to the idea of constructing my own boiler ... a horizontal marine boiler of approximately 5"diameter, and 12" length (with a water vessel length of about 8 to 8.5" of that 12" length). Given that I have many years experience in brazing/sweating  techniques, I am inclined to use this method rather than soft soldering. Brazed/sweated joints on central air conditioning systems are often subjected to high pressure operating conditions of 240 - 260 psi normal load, with restriction conditions causing an increase to as much as 500 psi or more, without any adverse affect to the solder joints. Also, I have my own oxy/act set, so no extra cost involved in set up. Given that brazing/sweating with oxy/act torches and 15% silver solder brazing rods, require the joint to be heated to much higher temperatures than used with soft solder (in order to get the solder to flow, due to much higher melting point of solder rods); does anyone know of any possible adverse effects which might be created in the copper being heated to such high temperatures to be soldered, as relates to later heating and cooling of the boiler in action.

The only difficult part I see is in the forming of the end plates; which I would assume can be done by turning a plug form, slightly undersized, then cutting a round flat section of copper plate and by means of hammering and annealing over the plug , form the correct shaped end caps, to be sweated into the boiler drum.

Hate to go to all that trouble, only to end up with a lemon. 

[bogstandard]

For me personally, oxy acet is a little too hot and localised for silver soldering such a large area as a boiler. Normally propane torches are used to bring large areas up to the melting point of the solder so that it flows more evenly and gets a good penetrated joint. Overheating a joint is just as bad, if not worse than not enough heat, as you will be altering the molecular structure of the parent metal.
 
Using the correct flux is a definite yes-yes, I have just gone from Tenacity 4A to the newish Tenacity 5 for all my silver soldering, even though its primary use is for silver soldering stainless. I find it can withstand overheating much better than the easyflo flux, and it cleans off much easier.

I don't know what effect an oxy acet carburising or oxygenating flame would have on the copper either, I wouldn't think it would do it any favours.

Normal soft soldering is a definite no-no for a boiler, but I do know that some of the loco lads use a product called Comsol solder, which I think is a higher melting point soft solder, with more tin in it, but I don't know when and why it is used, or anything about the properties of it.

Just my own views


Bogs

[gondolier88]

Hi Solitary, Bogs,

Good to hear you came to your senses- i've got every faith in you- it's surprising what skills we use in ouir day to day jobs that can be carried over into boilermaking.

Just for the record this is how I silver solder- this is not to say that this is any better than how anyone else does it but this is the way I find works best for me-

first materials-

solder- easyflo no.2
flux- johnnson matthy to suit solder
heat source- rothenberger proffesional soldering/brazing torch using MAPP gas.

I mix the flux to a double cream consistency (don't put it on a scone though!!! ), first though I add a single drop of washing up liquid to the dry powder- this acts as a degreaser for any residual oil on the surface so the flux can properly attack the oxidation- I then add single drops of water at a time bringing it upto the right consistency.

I clean the ciopper thoroughly using a scourer the wash under water- i then spread a thin layer of flux onto each of the surfaces to be sweated, if it's the right consistency it should just stick to the copper- too runny and it dries off before it runs and too thick it tends to bunch up when tthe surfaces mate leading to unpenetrated joints.

At this point i'm probably telling you how to suck eggs but I hope it might be of some help to someone else.

After the two fluxed surfaces are mated I 'cook' the joint - ie. I heat it allover to get the flux to adhere to the surface, once the peice is upto temperature (same as sweating temp. for aircon. pipework 850-870deg.c) and cherry red feed the solder into the joint- if you can do this uprigh greavity and capillary action will do all the work all thats required of you is to keep it hot enough and to put enough solder in- both of which you should be profficient at.

Next let the joint cool of it's own volition- not in cold water!!!!!!!

Use a wire brush once it's cooled down to remove any flux residue then pickle in citric acid (from chemists) overnight to get rid of any flux you may have missed and to clean off any oxidation.

Soft solder and comsol are as Bogs said a complete no no- they eill not stand the combined heat and pressure of a model boiler- however on proper rivetted model boilers- pre silver solder (i've got one at my parents that i'll have to show you) soft solder, then later comsol, was used to plug the rivetted joints- if well done this joint is just as strong as silver solder.

Looking forward to seeing progress- have you made a design yet? Fully recommend 'model boilers and boilermaking' by K N Harris- Tee Publishing- everything you need to know about sheer strengths, inherent design flaws, efficiency, heating surface etc.

Greg

[derekwarner]

Many years ago....Sandy Campbell from ACS Engineering put me onto Comsol high temperature soft solder as being suitable for small tube joints requiring only 280>300 degrees C ...

Bogstandard later referred me to a British product by CuP Alloys [01246 566814] & their 1.6 mm diameter silver solder wire to BS 219 5S which only requires 296>301 degrees C for usage & so the little propane refillable torches are OK

However it was stressed that both of these soldering/welding fusion products were recommended for small components only

I understand the construction of my ACSVB2 boiler included differing silver solder product with the required melting temperatures of 610 degrees C range for shell & drum components & 710 degrees C range for the internal fire tube joints   .......... Derek

[Proteus]

this is worth a read maxitrack are Tig welding boilers for models

http://www.maxitrak.co.uk/grabarticle.asp?article=welded%20boilers.pdf&title=Welded%20boilers

Proteus

[derekwarner]

Sorry all.....stuffed up there no end  

The following  .jpgs confirm......

1.6 diameter Comsol = 296>301 degrees C = high temperature soft solder
0.5 diameter silver solder = 610>620 degrees C  

[Solitary Sailor]

Thanks all for the input. Yes Bogs, my concern is indeed about the changes to the molecular structure of the parent metal, as I am quite positive that the normal sweated joint method I propose would be impervious to any expansion and contraction variations in a boiler under steam conditions, but would the parent metal become brittle or fragile after being heated to such high temperatures. My experience in my own trade would say no, but my lack of knowledge in the field of boiler making says ... be careful ... be sure first.

Thanks Proteus, but Tig welding is an art beyond my means .... my eyesight leaves much to be desired at the best of times ... but behind a welders helmet .... forget it  A shame, because Tig welding is a great way to go, and in the hands of a professional is an extremely clean and effective method. What's more, somewhere in my stack of tools, buried deep no doubt, I even have a miniature Tig welder, and even an argon tank, (if only I could remember where I put all the important bits ... hasn't been used in 10 years though)(See Greg, I told you I was a pack rat for tools    )

I shall dig around some more and may change my plan of action, so keep the comments coming as they are much appreciated. Then again, it would not be too difficult to develop the correct technique to silver solder it, after all, if brazing is something I do without any  second thoughts, a couple of practice runs with silver solder on scrap pipe should see me through to a easy facility with this medium... it just means I will have to get another welders set-up 

As to the preferred design Greg, I shall keep it simple, probably with two flues /twin burner configuration, with a number of longitudinal stays. With all the necessary fittings supplied  by proprietary sources. Probably fit a superheater as that's an easy addition.

 

[Proteus]

My post was just to show that people are still trying to find a better mouse trap,, i


nfo only

Proteus,