[metalmansteve]

I'm making some 304 stainless manifolds and we're having problems and need some help. Basic problem is the surface finish on the parts is too nice so the parts wont braze.

How would you roughen up a 3 x 2 x (.036", .093" and .25") without changing dimensions and maintaining flatness? A rough belt sander takes off too much material on the edges. Rubbing on a flat sheet of sand paper with 80 grit paper yields a 26 Ra finish...we need no better then a 32.

Any suggestions?

Thanks!

[mactec54]

metalmansteve

The 304/316 ss does not like to be brazed, you normally tig this material, you can braze it but it will never be very good, no matter what the surface finish is

[metalmansteve]

We can't tig weld it as we're trying to isolate different gas chambers on the inside of the plates. I've attached a drawing.

I get told what to do by my customer (brazing shop) who in turn is getting told what to do by their customer (end user) They're calling out for 304. What material would you recommend?

[mactec54]

metalmansteve

The tubes are not to big, if they bead blast before brazing it will go better, & they should try silver solder, that will work better than normal brazing, if they get it to hot in the weld area, they will have to blast it again, because once they overheat it, the brazing that they are trying to do, won't take, it will just roll around on the surface, so they have to control the heat very well

I don't know the size of what they are doing, but it looks like most could be done by tig

[mikerfbs]

could you bead blast the surfaces you are going to braze?

[mactec54]

mikerfbs

Yes you can, you may have to wash the dust off the surface, before welding, You can do this after welding as well to clean the flux off, If they over heat the weld area they will have to blast it again to get it to weld/braze, The blaster has to have clean media or you will contaminate the surface

[metalmansteve]

Thanks for the input guys, I really appreciate it.

I will try bead blasting and see how that works. My concern would be media embedded into the surface causing a problem, especially in the gas chambers. Doesn't hurt to try but I'll need the blessing of my customer first.

I'm not sure how tig welding would work at all on these parts as there is no way to get in between the plates to isolate the chambers.

These are brazed in a high-end vacuum furnaces and heat can be controlled accurately.

My customer is asking me to roughen up the surfaces so I'm trying to figure out the best way of doing this while maintaining flatness and size....which is my ultimate question.

Thanks again!

[mactec54]

metalmansteve

Just make sure the media is clean, & the surface is washed clean of any media left on the surface,if the tubes go right through the end plates they could be tig welded very easy

[metalmansteve]

tubes? there aren't any tubes

[mactec54]

metalmansteve

I though by the PDF you were puting tubes in it, so all 3 plates are Brazed together

[HuFlungDung]

I wonder if you could emboss the surfaces to make them rougher? I'm imagining something like rolling a (new) fine round file (like a chainsaw file) between each pair of plates. You'd need some way to apply pressure, and at the same time, feed the top plate across the bottom plate, with the file in between. Essentially, flat knurling is what would be happening.

If you had an old horizontal mill kicking around, maybe you could rig up a pressure roller in place of the arbor, and some sort of feed guides to get the whole thing working. I dunno!

Does it really need to be rougher, or does it just need a controlled gap so that there is room for the braze to flow? Don't they use copper to braze this sort of thing?

[mikerfbs]

another thought, you could electro chemical etch the parts. they are small enough. I had one to mark serial numbers on some part a few years back.