I’m getting started on making a wheelchair frame[link is to another forum where i’ve been logging this adventure], obviously not the kind of frame that is made here, but I’m using 4130 chromoly and brazing it, and the advice and information here and from other frame building forums is fantastic.
I only have OxyPropane available to me, but i cannot find anywhere details on how i should set up the flame, I’ve had some success brazing, but i understand with acetylene a neutral flame is necessary and i don’t know what the equivalent flame in oxypropane looks like.
It appears on your other post that youre not using proper flux, you need type b flux for cromoly , and proper sanding down to shiny metal on your weld prep, this is mostly why you’re not getting proper wetting i think. Also your tubes seem to wrinkle a lot and they have a weld seam so i’m actually not sure they’re cromoly? Lastly the color of your filler indicates a nickel/silver alloy, if you could find low fuming bronze filler instead it would be easier to learn with.
When testing your tubes should break far sooner than your joint, it peeling of like it did indicates poor surface prep and no alloying between base and filler. As such as long as you have a hot enough neutral flame your torch probably isnt the problem
As for the stainless joints, even if it looks shiny stainless is actually even more sensitive to contamination, you still need proper sanding, degreasing and a clean jar of black flux (harris stay silv is my fav). It oxidises faster so you can use a slightly carburising flame in this case. And if you cant get your joints hot enough (as propane burns colder than acetylene) either use a bigger tip/drill out the existing one or more silver in your alloy.
you’re absolutely right about contamination, I worked this out, cleaned up my act and in later posts in the thread you can see how the joint was stronger than the material
the tubes are 7/8 0.035 chromoly, I’m not sure where you’re seeing a weld seam but there are some longitudinal machine marks. I think I may need to increase wall thickness to prevent the slight buckling
unfortunately all the advice on materials isn’t very useful to me, I’m in the UK and I am rather limited in what I can source, I’m using sifbronze no.2, which is cu48ni10znbal originally chosen because I thought I would build out of stainless steel before switching to chromoly. I’m using sifbronze flux because it’s intended for brazing and what my company has available.
could you describe for me what a carburizing flame looks like in propane?
Sure, its a bit harder to see because the colors of the cone and envelope are more similar and it flutters more, but you’re trying to get some wispy tails of of the cone without having a full feather between the two. Also with the different combustion and settings the hottest spot tends to be a bit further than the cone, not right at the tip like with acetylene. Honestly as long as your torch isnt screaming (too much volume for the tip size) or fully oxidising (very pale and sharp cone, almost transparent envelope) the stainless should stick
I found this link with more info if you wanna read