Expanding fire tubes

[kelvin2164]

I'm building a Briggs type boiler for a 5" gauge loco in steel with copper fire tubes. I'm new to this and a liitle unsure. The boiler code says the only connection between the the tubes and the end plates is an expanded fit. No soldering. I assume this works, but I'm a bit worried about it. Would it be ok to smear the end of the tube with a bit of gasket goo before expanding, just to be sure of no leaks.

 

[RonGinger]

No, I think the gasket goo would ruin the seal. You want a nice clean, round hole in the tube sheets. A close sliding fit to the tube. Anneal the tube.

In full size boilers I have used a proper tube roller- a rig with some hard steel rollers on a tapered mandrel, but I dont think it would be reasonable to make one small enough for this size. I have read that a rubber cylinder with a threaded rod through it works. You insert the rubber in the tube and tighten the rod to compress and expand the rubber enough to stretch the copper tube.

 

[bazmak]

The rubber expansion is good but i have not tried it.Suitable masonary expansion ftittings can also work,or something similar made up.I also think that the joints should also be silver soldered.I have only partly built 2 locos so i am not an expert,perhaps someone else can chip in.Regards barry

 

[kelvin2164]

I think the reason for no soldering, is the problem with different expansion rates of copper and steel. Maybe the expanded tubes slide a little. Anyway at least with a Briggs boiler they are easy to get at if it doesn't seal.

 

[Steve J]

what size are the tubes? I have a half inch tube roller I would sell. $75 + postage. Hopefully you are in the u.s.

 

[gus]

We used Fuji Tuber Roller Expender to expand 1/2'' tube end into tube sheet.The tube sheet holes are drilled and reamed. An expander plug gage must be used to gage expansion.Over-expansion and under-expansion lead to tube leaks. Do not use power drills to do rolling/expansion. Copious qty of lube oil required to prevent premature wear to expander.Best to buy a new tube expander to avoid buying replacement. Was making shell and tube heat exchangers.