copper pipe brazing to boiler drum

[Backyarder]

When brazing copper tubing into a boiler drum, how is the brazing overlap achieved?

Steve

 

[tel]

Dunno what you application is Steve, but the usual proceedure id to braze (silver solder) in a bronze bush and screw a union or similar into that.

 

[GWRdriver]

how is the brazing overlap achieved?
Steve

Steve,
I'm a bit fuzzy on the term "overlap", it's not one that's common in boiler building usage. I can probably help if you explain what you have and what you are trying to do.

 

[Backyarder]

Hi Guys,

What I mean is, in a vertical water tube boiler, where there is a water drum underneath and a steam drum at the top, if I drill a hole in the drums to take the vertical water tubes, there isn't a lot of contact area where the tubes are brazed into the drums.

Also in a fire tube boiler, the copper fire tubes are brazed at the ends, and the contact area between the tubing and the end plates are also small.

What methods are used to increase this contact area to get a mechanically solid and reliable fit before brazing it? Already, brazing in a bush has been mentioned.

thanks,
Steve

 

[Artie]

Ive been dwelling on this same issue for the same reason.

Ive decided to drill the holes smaller than the tubing and make up a small conical die to press into the hole with a correspondingly profiled base under it to shape the hole into a rounded dimple.

Providing more surface area and a well for the filler to give a more secure mechaincal bond.

I hope Ive explained that well enough.

Cheers

Rob

 

[Backyarder]

Ive decided to drill the holes smaller than the tubing and make up a small conical die to press into the hole with a correspondingly profiled base under it to shape the hole into a rounded dimple.

Hi Rob,

I was thinking of the same thing. Kind of flaring the hole inwards with a little mandrel or similar. I read somewhere the contact area rule of thumb is three times the wall thickness of the tubing.

Pipes have been brazed and welded into boiler drums for many years, so there must be a few tips around I'm sure.

Steve

 

[tel]

OK, now I'm with it. The same as doing tubes in the tube plates of an ordinary boiler. The short answer is 'Don't worry about it' - the tubes are fitted into reamed holes with a couple of tiny nicks filed in the sides to allow penetration - done properly you will have a fillet of silver solder either side of the plate - mucho strongo.

 

[GWRdriver]

TEL is, as usual, exactly right. A well made silver solder joint, even with a relatively small area of contact, is stronger than the parent copper.

 

[joe d]

- the tubes are fitted into reamed holes with a couple of tiny nicks filed in the sides to allow penetration -

That's why I like this place so much.... none of the things I've read so far mentioned that little detail about the little nicks... which will no doubt prove it's worth when I finally get to making a boiler.

Backyarder: Good luck with your project, and remember the HMEM RULE: Photos are NOT optional :big: :big:

Cheers, joe

 

[Backyarder]

Cool, thanks fellas. Sounds like the little nicks are made in the reamed part? Or does it not matter which?

cheers,
Steve

 

[mjp]

You might want to check out Alec Farmer's "Model Locomotive Boiler Making" or Kozo Hiraoka's "Building the New Shay". Alec uses the notches, but in a drilled hole for reasons he explains and does his brazing (silver soldering) with a small oxy-acet torch and a Sievert LP for heating. Kozo steers away from the oxy-acet and brazes with an LP (Sievert) torch only. The trick is in having the right size with lots of heat at the right time and place. Neither flair their tube sheets.

Kozo's book also has a Chapter on Copper Boiler design and safety and one specfically on silver soldering.

As an added bonus, any of Kozo's books are a virtual maodel making course and whether you ever build a small loco or not, his techniques and illustrations are applicable to most any home maching project.

A five inch, 35 tube copper boiler is on the horizon as I progress with building a 2" scale Clayton Undertype Steam Wagon (truck). I plan to do a few smaller boilers this winter along with the chassis build so that I am ready to tackle the real one next winter.

I found both of these books very useful as I planned the project.

Good luck with your project!

Millard (mjp)

 

[Backyarder]

Thanks fellas. Much appreciated.

Steve