[AR] Re: Braze joint design guidelines?
- From: Peter Fairbrother <peter@xxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 8 Aug 2019 22:26:34 +0100
On 08/08/2019 20:59, Evan Daniel wrote:
I don't have the package in front of me, but I believe it's a
potassium fluoroborate flux. Do you have a recommendation?
Ordinary flux isn't very good at removing oxides from stainless,
generally you use a flux specially formulated for the purpose. Some
"black fluxes" contain elemental boron, there are others. The one I use
is called HT5, but I doubt you can get it in the US - nor would I
recommend it particularly, I just have a very big tub of it.
Your supplier will sell a flux for stainless. Fluoborate-based flux
isn't bad, but there may be better, and precise properties depend on the
precise composition.
Flux being cheap-ish, and properties like active range and time being
important, get a local recommendation for use on stainless with the
solder being used.
This joint was copper tube to the Shapeways bronze/stainless hybrid
printed material. Info and datasheet, if you haven't seen it before:
https://www.shapeways.com/materials/steel
https://static1.sw-cdn.net/files/cms/materials/data-sheets/Steel%20data%20sheet.pdf
It's 60% 420SS sintered powder, infused with 40% bronze (90% Cu / 10% Sn).
There's another joint that's 304SS tubing to the same printed
material. Ideally, I'd like to do all the braze joints at the same
time using the same flux and the same solder wire, so I can keep the
working time short and the brazing operation simple. But if I have to
use different fluxes or whatever I can. For welding, the data sheet
recommends TIG with a silicon bronze rod.
Quick'n'dirty fix, pre-tin the nozzle :)
You might consider using a (phosphorus-free) brass rod and flux, it
fills gaps better than 56% and is likely stronger at high temperature.
(40% or 50% silver with 2% or 3% nickel) is good on stainless and gaps too.
Peter Fairbrother
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