I bought a propane weed burner to heat parts for soldering/brazing a couple
years back. It provides the base heat load and I use the same handheld to
provide more local heat as needed. It made a huge difference when brazing
aluminum parts and made copper/brass joining a breeze.
Edward
On Thu, Aug 8, 2019 at 10:09 AM Evan Daniel <evanbd@xxxxxxxxx> wrote:
Thanks, this is very helpful!
I switched to MAPP from propane because the propane torch wasn't
working well, and the MAPP torch worked better. It sounds like you're
saying I should instead get a higher-volume propane torch. I'm using a
small handheld Bernzomatic torch with piezo ignition and disposable
cylinders. Do you have a suggested larger torch? I assume I can keep
using the disposable 14oz cylinders, I don't think I need that much
more heat. I don't have a source for MAPP, but I do have a couple
ancient cylinders around still. And I can buy MAP-Pro, which I assume
is hotter than propane but not as hot as old fashioned MAPP.
For context, the braze joints I'm trying to make range in size from
fairly small (1/16" OD stainless tube into printed fitting) to
somewhat larger (5/8" OD copper or stainless tube to printed mating
part). Some of the mating parts for the larger joints have significant
metal nearby that may act as a heat sink.
Pictures:
https://imgur.com/a/EK7vntk
First is the old version of the full injector assembly during test
fitting, with 3/8" copper propellant lines not yet brazed. Second and
third are the most recent designs for the spark igniter, using 5/8" OD
copper or stainless tube for the chamber. The current plan is to go
back to printing the igniter chamber as an integral part of the
injector print, and not have those larger solder joints in the final
version.
Evan Daniel
On Thu, Aug 8, 2019 at 7:18 AM Peter Fairbrother <peter@xxxxxxxxxx> wrote:
guidelines?
On 07/08/2019 18:06, Evan Daniel wrote:
Does anyone have good resources to suggest for braze joint design
joint"
I've been kinda winging it, and had a spark igniter come apart when a
braze joint failed. On inspection after, the joint was much more of a
butt joint than a lap / slip joint (no braze material flowed into the
slip joint area). The joint in question was copper pipe to printed
Shapeways bronze / stainless hybrid material, using a 56% silver
solder wire, torch brazed with a MAPP/air torch. My plan for the next
version is to machine the braze joint surface rather than attempt to
join to the as-printed surface, but I'd also like to learn more about
the topic in general.
Advice on the specifics would be nice, but so would a suggested
document(s) of design guidelines.
Questions I'd like to answer:
- How do I select a proper filler material?
56% eutectic is fine. It should give at least 60 ksi yield 120 ksi shear
strength, considerably stronger than the copper pipe.
- How much overlap do I need for the slip joint to work well?
About 1 diameter is generally a good rule of thumb. 0.5 diameters is
acceptable in this case.
- How much clearance should I have before brazing?
0.1mm
- How much does surface finish on the surfaces to be joined matter?
Clean matters, finish generally less so. However the finish on a printed
part could be problematic, so maybe flux it and cover it in a very thin
layer of solder before assembly?
What's suitable?
- I had applied flux inside the joint, and applied braze wire from the
outside (MAPP torch brazing). When is it appropriate to use braze
ribbon or similar to get filler material into the joint in advance?
Not at this stage :)
(Does this change things like clearances?)
- Any recommended videos or guides on torch brazing technique?
https://www.cupalloys.co.uk/best-practice/ is a starting point, though
we often disagree on details ...!! but the bit on Heating Technique is
(mostly) ok
"the alloy will be encouraged to flow towards the hottest part of a
BTW, propane is better than MAPP here. As long as the torch is big
enough it will give enough total heat without getting too hot locally,
which a smaller but hotter MAPP torch can do.
An aside, where are you getting MAPP? Since the Petromont plant stopped
making it real MAPP has been hard to come by.
Peter Fairbrother
