Stainless Steel Silver Fillets

[rusbycycles]

Hi there,

I know this has been discussed a bit here already but I am having some trouble with fillet brazing some Reynolds 953 tubing. I'm finding that the tubing starts to turn dark blue/gray just before the metal and flux get up to temperature- the colour that surrounds the silver in my photo. This seems to be stopping the silver from flowing properly and adhering to the metal. I have been trying this out on some practice bits and the join doesn't seem strong enough (when I take a hammer to it).

silver joint.jpg

I am using an oxy-actylene setup with a number 2 tip. I'm using a small neutral flame about 7cm long and heating from about 3cm away. I'm using Cycledesign stainless light flux paste and some 60% silver BrazeTec rod. The metal was prepared by degreasing, sanding with 120 emery cloth, cleaning with acetone and a fair bit of flux.

Any help would be much appreciated!

JAKE RUSBY

[dbohemian]

rusby cycles. I am glad you are practicing before just building away. It actually looks quite fine as far as the flux is concerned but you have not done an adequate pre-heat. You cannot just drive on in there like you are used too with bronze filler. Take you time to pre-heat the area and then build you fillet. The fillet needs to be larger BTW. You cannot break the normal rules of fillet depth to tube wall ratio. Also the melting temperature of most 60% silvers are higher than those that are of lesser silver content. You may be pushing the boundaries of stainless light flux (it is light you know) If you wish to stick with this rod you may consider testing with a nickel silver flux . Stainless light was designed to work with fillet pro filler which has a substantially lower melting temp. Best of luck

[rusbycycles]

Thanks a lot David. I've been doing some more tests and I feel much more confident with it now- pre-heating helped a lot. I think I was not getting it hot enough quickly and the darkening metal was freaking me out. I have used Xcr before with success and this didn't happen with so I think I needed to get used to 953. I'll be using bigger fillets on the frame- the tests were just getting a bit expensive. Thanks for the tip on the flux also- I have switched back to fillet pro as the flux I have for the BrazeTec rods looks like melted chocolate so you can't see what's going on at all! Thanks again!

JAKE RUSBY

[Will Neide]

.....the flux I have for the BrazeTec rods looks like melted chocolate so you can't see what's going on at all! Thanks again!

"Melted chocolate" sounds like the nickel silver flux that Dave mentioned.

[EricKeller]

it could also be something like Harris Stay Silv. Hard to see through, but it lasts a while at heat

[rusbycycles]

The brown flux is BrazeTec brand as well, specifically for that type of silver. It works but you just have to be confident that you're getting a good fillet underneath it (which I wasn't). It didn't have good sticking power either so wanted to run off as soon as you put the heat on it. Fillet pro and Stainless Light for me for the time being I think.

JAKE RUSBY

[steve garro]

IMG_4803.JPGTry 10 parts type "U" with one part type "H" - works really good on SS.
- Garro.

[arregui]

I'm finding that the tubing starts to turn dark blue/gray

the darkening metal was freaking me out.

Hi all,

So, whats the black/grey coat of the tube?. As David said the flux it´s ok. How came the tube change color under the cover of the flux?

I have also found that i need longer pre heat with 953/LFP than with brass and that the effect disappear, but don't know why.

Any idea?

Thanks!

[Mark Kelly]

Probably chromium oxide (CrO3).

Flux works by creating reducing conditions to overpower the formation of oxides by reaction with air. If conditions are less than ideal, it may not be able to keep up with the formation rate.

[rusbycycles]

How came the tube change color under the cover of the flux?

I have also found that i need longer pre heat with 953/LFP than with brass and that the effect disappear, but don't know why.

Well, I'm still not sure but I have only seen this dark grey coating with 953. It doesn't seem to happen with Xcr or 17/4 stainless. I think it is being caused by the outer cone of the flame (rather than the hot part) when this spills onto the parts of the tube you're not brazing. I have been using a slightly hotter flame recently and once I have an area preheated, I try and work quite quickly. This has caused less oxidisation and I've been getting some very good fillets like this.