Internal brazing

[Scottowner]

It is necessary for me to braze a thin mild steel divider in a thin mild steel tube. The tube is 4" in diameter. I have cut the divider (disc) to 4.5" diameter. The tube is 9" long and the divider will be situated 3" from one end. The extra .5" will allow me to create a .25" flange around the circumference of the disc.
My question is....as I can only braze the disc from the 3" end,should I have the flange on that side of the disc,or should the flange be internal so I have a smooth face to braze ?

 

[voipio]

The key to good brazing is to keep the gap between the parts to be joined as small as possible, thereby maximising the capillary effect to flow the filler metal, or spelter between the two parts to give a good joint. With well-fitting parts, brazing should be no problem 3" from the end with the flange facing in either direction. Good lighting will help to see the brazing metal flow and help to judge when and where to apply the brazing spelter. Apply the heat as evenly as possible around the outside of the tube. A 1/4" flange seems overkill if it's thin metal being brazed. If the pressure difference between the two sides of the mild steel divider is going to be small, no flange should be necessary, just a good fit and nice clean surfaces to be joined and, of course, brazing flux. The parts will need to be kept in position by some means, since there is a chance the divider will slip as the outer tube expands when heated.

 

[Scottowner]

Thankyou for that information. the metal is 3mm thick. The container I am making is in fact a petrol/oil tank for a vintage motor cycle. I made the decision to flange the disc thinking it would hold it in position more securely when brazing. Again,Thanks very much.

 

[hotrodder]

As said in the other thread http://www.mig-welding.co.uk/forum/threads/forming-a-flange.59011/ if the disc is 3mm thick forming a flange neatly and accuratly ain't gonna be easy

What's the tube wall thickness, 1.5mm is the lightest wall thickness commonly available for 4" ERW tube? personally i'd cut the tube into two, trim the disc down to somewhere between the OD and ID of the tube, stack everything together and weld or braze from the outside. If the tube is heavier wall (say 3.25mm wall) can always bevel it lightly too

 

[Turbo]

It's probably too late now but it probably would be better to make the tank in stainless steel, then you wouldn't get any problems of the tank rusting inside, probably the reason you are making up a new tank!

If you can't source 4" s/s tube you could roll some sheet into a tube and weld the seam. Any decent tig welder should be able to knock something like that up easily, including the baffle. Try asking on the forum in the tig welding section, one of the members might be able to help.

 

[Justme]

How about slotting the tube. Slide a bit of sheet in to the slot, braze it up then trim of the outside back to the round?