SteveR wrote: ↑Sat Aug 14, 2021 11:02 am
Interesting results - thanks for sharing. BTW - in your first post you mentioned that:
This is my second boiler. The first was a 4” pot boiler with a handful of fittings in the shell, and it was challenging, but I got it done.
Were the problems you encountered the first time the same or similar to those on the the second?
And what brand of solder and flux are you using?
No, I made all different mistakes the first time. However, being a pot boiler, it had no internal or tricky joints so there’s not too much difficulty in fixing leaks. Just flux and reheat the metal near the bad joint.
I’m using Harris Safety Silv 56 and their matching flux.
I find the black flux works better. What I'm using comes in a one pound plastic screw top container. It is made by LucasMilhaupt, a Handy and Harmon company and in Toronto I get it from Praxair. A one pound container lasts me for many years (at least 15) and costs somewhere between $20.00 and $30.00. Over time, it may dry out, if it does, just add some water and stir it in. You can also use it dry, it just isn't as convenient.
I started off using the white flux, but I found if I overheated it, which sometimes happens with large pieces, the flux would turn black and once that happened, it didn't work anymore. The black flux doesn't do that, it is much more forgiving.
I hope this may help. This hobby is an example of "What goes around, comes around."
Thanks Richard! I have heard good things about the black flux. Unfortunately I just bought a fresh jar of the white stuff so I guess I’m stuck with it for a while yet. Next time (in 20 years, maybe? ) I’ll try the black.
Since the black flux isn't really that expensive, I would suggest that you should buy a pound and play with it to see what it can do. Really abuse it to test its limits. I haven't really tried to push it, but it has done everything Don and I have tried, especially with the Big Boy boiler and that would have definitely been beyond what is possible with the white flux.
You can continue to use the white stuff for small jobs and use the black for the tougher ones.
Question about the black flux- is it still easy to see when the solder is about to flow? The white stuff takes on that nice clear watery appearance right before the big moment and it's nice to see that coming. Does the black color obscure all the state changes that the flux goes through?
No, you don't get that water clear change in the flux like you do with the white, but you still can see what the solder is doing. Don and I have found that you have to heat the work hotter than the usual recommendation for successful joints. The solder definitely follows the heat and you can "lead" it to where you want it. This effect is in addition to the capiliary action you get as the solder wets the metal surface and is pulled into the joint.
Don't try to "rush" the job. Copper sucks the heat away very fast and you need to allow time for the work to come up to temperature all over at its own rate. If you push too hard, you will get a joint that looks pretty, but the solder won't have penetrated through to the other side and the joint will probably fail. Take advantage of the wash from the torch because it keeps oxygen away from the hot copper. You can see the copper oxidize instantly when the torch is removed, but moving the flame back over the area protects it again and this is quite visible. For our Big Boy boiler, it took at least 10 minutes of steady heating with the large weed eater torch and the oxy-acetylene before the boiler was ready to start working on.
I wold suggest that you play around a lot with the black flux so you know what to expect before you embark on anything serious like a boiler and make sure you plan all the steps fully before you start (like assembling the tubeplates and tubes as a separate operation before putting them into the boiler shell).
You don't want to get in the situation where you can't continue with step 25 because you forgot to do something critical back at step 15. I'm sure that most of us have been in that situation at one time or another. We find that the bit we machined off before, we now need to hold onto the part so we can do what is needed now.
This hobby can be a lot of fun, but it also requires a lot of serious thought and planning if the end result is going to be what you want. Sometimes it also requires "inventions" to make what you build actually work the way it is supposed to.
I am still using a supply of the old cadmium based silver solder which I have. With adequate ventilation, it is OK, especially when I only silver solder now and then. It does make things easier.
Toss the white flux in the dumpster. It cost me a lot of time and money to learn that the black flux is the only way to go. Do it.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
However, being a pot boiler, it had no internal or tricky joints so there’s not too much difficulty in fixing leaks. Just flux and reheat the metal near the bad joint.
) I’ll try the black.
