Soldering a mitred tube?

[Bo’sunParticipant @bosun58570]

Good morning All,

I'm about to silver solder a 90deg. mitred joint, between two pieces of 3/4" dia x 20g copper tube. The guidelines simply say "silver solder the joint". I've made a strap clamp to hold the two pieces together, but getting a good, what is effectively a butt joint, doesn't look that straightforward.

Any thoughts or suggestions appreciated, before it goes "pear shaped".

Do I lay it flat, and solder from both sides, or maybe prop it up and solder from the internal corner, hoping the solder will run around under gravity?

Flux before, or add it with the silver solder, or both?

[Bo’sunParticipant @bosun58570]

Best technique.

[Michael GilliganParticipant @michaelgilligan61133]

The solder should ‘run around’ within the joint by capillary force … which, at a local level is much stronger than gravity.

Set it up [fluxed] however is most convenient, get everything hot … then apply more heat at a point opposite where you are feeding the solder, and it should ‘wick’ round.

MichaelG.

.

Keith Hale will probably explain that better

Edited By Michael Gilligan on 30/04/2021 10:29:12

[Martin KyteParticipant @martinkyte99762]

You do need a gap to allow the solder to wick into the joint so beware of butting the tubes up too tight.

regards Martin

[Bob StevensonParticipant @bobstevenson13909]

….Here we go again with the 'joints for silver solder thing'!…….you will get the best results with a very close fitting joint as the molten solder flows like Micheal said, by capillary action……When molten the silver solder is VERY fluid and does NOT readily fill joints…….

Edited By Bob Stevenson on 30/04/2021 12:43:49

[Martin KyteParticipant @martinkyte99762]

Posted by Bob Stevenson on 30/04/2021 12:42:25:

….Here we go again with the 'joints for silver solder thing'!…….you will get the best results with a very close fitting joint as the molten solder flows like Micheal said, by capillary action……When molten the silver solder is VERY fluid and does NOT readily fill joints…….

Edited By Bob Stevenson on 30/04/2021 12:43:49

Totally agree Bob. I didn't mean a wide gap just a fag paper worth.

regards Martin

[Bill PhinnParticipant @billphinn90025]

 

Bit of a rush job preceding a hospital visit, but this is how I held the work:

Edited By Bill Phinn on 30/04/2021 13:19:39

[Martin KyteParticipant @martinkyte99762]

Looks fine from what I can see.

Well done.

regards Martin

[Bo’sunParticipant @bosun58570]

Posted by Bill Phinn on 30/04/2021 13:18:26:

Bit of a rush job preceding a hospital visit, but this is how I held the work:

Edited By Bill Phinn on 30/04/2021 13:19:39

Thanks Bill,

Just what I need to do. Did you do it in one heating, or turn it over and complete the other side?

Bo'sun

[Bill PhinnParticipant @billphinn90025]

Yes, I turned it over, after pausing for 30 seconds, to run more solder down the other side.

The setting up was rather fiddly; making sure the two parts were sitting where they needed to be in relation to one another and not under any tension that might work to drive them apart once heat had been put into them took a lot longer than the actual soldering.

[Bo’sunParticipant @bosun58570]

Thanks Bill,

Just off to do the job. Fingers crossed.

[Keith HaleParticipant @keithhale68713]

Thanks to Michael and Martin for their support in promoting good brazing practice.

 

 

If the filler metal is not retained in the joint or falls through it, the gap is too large. In this case you are not brazing – you are simply trying to block a hole with a very expensive material! Find yourself a cheaper option

 

 

If you cannot achieve a joint gap of 0.05 – 0.20mm, use an alloy with a wide melting range that will bridge wider gaps. Another option is to avoid using an alloy containg tin or silicon that has been added to improve fluidity.

 

 

To obtain sound strong joints the joint gap has to be filled. If this is not achieved, you are in effect, building a crack (stress raiser) into the back of the joint.

 

 

Regards

 

 

Keith

 

Edited By Keith Hale on 03/05/2021 11:20:11

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