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Soldering copper onto copper


#1

I’m learning to solder copper sections overlaid onto a copper cuff
bracelet and finding it quite difficult. I suspect that I may not
have enough heat and may be using the wrong flux. I’m using Batterns
liquid flux, hard silver solder, and a simple propane torch that you
buy in the hardware store. The torch has difficulty bringing the
copper up to that cherry red color required for soldering, the
solder either balls slightly or does nothing, and the flux is
overwhelmed by the oxidation.

George
Vancouver Island


#2

You need a good paste flux, Batterns is ok for gold but for copper,
no way just not enough fluxing ability for such an oxide friendly
material.

James Binnion
James Binnion Metal Arts


#3

I would try buying a syringe of copper solder paste containing the
flux and metal;I get a good quality paste solder from auto parts
stores, or home /hardware centers. Another thing to consider is a
butane torch. Bernzomatic makes a really good one with a base for
under 30 dollars at the same home stores.they are great for quick
soldering jobs getting to 2400 degrees F fast without O2 assistance
and the flame can be adjusted or concentrated with the attachments
that are included in the better torch set- Do not buy the butane
torches without a base ( blue or black and pen like in shape- they
are wrought with problems.I had 2 of the 10-14 dollar blue" tube"
type torches: both did not work out of the box from two different
states 1200 miles apart!.Their black hand held torch is a different
story entirely- it has preformed well for years of use with the same
model and is transportable for work out of the studio, and will even
do small melting jobs of a few grams silver or gold ( will not work
for Pt melting,soldering, etc.) for direct casting or scrap
reclamation.The paste solder is the key- slump a pool of it under
your sections and heat the body of the bracelet on a tripod or other
set up to circulate the heat evenly, then apply some pressure to
position the sections where you want them- a titanium wire works well
for moving parts on a piece as long as you keep it clean and free of
hardened solder, etc.

If your solder is balling up your work or the join is not clean or
you are moving your heat away too fast- easy to do with a standard
plumbers torch ( a fuel cylinder with a burner screwed on) because
one fears melting the work.work with some scrap pieces until you get
the learning curve down- slump some sections onto a larger piece.You
don’t need silver solder with copper unless you want the colour as an
accent or inlay ( carve a groove or design with gravers, burs, bits,
etc. to your design specs and flood the depression with a contrasting
colour of solder, then clean up any stray solder with sanding drum
bits, burs, or a bench knife then successive finishing papers or
films to a 6 micron finish or whatever your desired finish may
be…hope this helps…rer


#4

The problem may be just not enough heat. A large mass of copper such
as in a cuff bracelet needs a lot of heat to get up to soldering
temperature

Jenny


#5
I'm learning to solder copper sections overlaid onto a copper cuff
bracelet and finding it quite difficult. I suspect that I may not
have enough heat.... 

Insufficient heat is definitely part of your problem. Copper
radiates heat like crazy. Try “burying” your copper cuff in a
heat-resistant material (like in your annealing pan), and just work
on the visible part. Or, set up a little “furnace” (with one open
side) of firebricks around your cuff. Anything to keep heat in. Do
you have access to an acetylene torch? HTH.

Judy Bjorkman


#6
The problem may be just not enough heat. A large mass of copper
such as in a cuff bracelet needs a lot of heat to get up to
soldering temperature 

I’ve got to get that copper up to cherry red quick before the
oxidation overwhelms the flux. I think I need an acetylene/air torch
like the Smith “Silversmith” with a #2 or #3 tip.

George
Vancouver Island


#7
Insufficient heat is definitely part of your problem. Copper
radiates heat like crazy. 

Your absolutely right, you need high heat to solder copper on copper
and I don’t have it. It seems to me that copper must be heated high,
but very quickly as well. The oxidation of copper seems to overcome
the flux if the heating process is too long. The flux I’m using is
also not standing up to the heat and oxidation; I’ve read that 75 %
Borax and 25% Boric acid in a paste may be a better flux for high
heat soldering.

George
Vancouver Island


#8

Hi George,

I've read that 75 % Borax and 25% Boric acid in a paste may be a
better flux for high heat soldering. 

I have a friend that uses that, but I’m finding it difficult to find
Boric acid in Australia (well I can’t find it outside of a
scientific chemical supply company). Apparently ant poison in the
States has a large percentage of Boric acid.

I’ve just been using borax, but I’ve got a pot line smelting flux
that I haven’t tried for jewellery just yet.

Regards Charles A.


#9
I've got to get that copper up to cherry red quick before the
oxidation overwhelms the flux. I think I need an acetylene/air
torch like the Smith "Silversmith" with a #2 or #3 tip. 

For heavy jobs I fit a rosebud tip to my Smith’s little torch on
oxy-propane. I originally bought this tip for melting but don’t use
it for that purpose now that I have a crucible furnace. I have even
used this setup to solder copper plumbing pipe at times so it puts
out plenty of heat. Oxidation is a problem especially with copper. It
does help to ensure the flame s slightly reducing (i.e., fuel rich).
It’s a sort of soft and bushy flame rather than bright and hard
edged. When the flame is right you will notice that the oxide coating
is reduced back to metal as the flame plays over it.

All the best
Jenny


#10

The borax/boric acid mixture was/is used by traditional coppersmiths
to flux their work. There’s a really good book on coppersmithing from
Lindsay, a reprint from a turn of the century work that’s got a lot
of good stuff in it, including a bunch on vessel raising, and of
course soldering.


#11
I've just been using borax, but I've got a pot line smelting flux
that I haven't tried for jewellery just yet. 

I think you will find a great improvement in your flux if you get
some boric acid into it. Borax doesn’t melt till 743C (1369 F) so you
get no fluxing action below that temperature. Boric acid will begin
to melt at 170 C (340F) so it protects at a much lower temperature.

James Binnion
James Binnion Metal Arts


#12

Hi Charles,

I have a friend that uses that, but I'm finding it difficult to
find Boric acid in Australia (well I can't find it outside of a
scientific chemical supply company). Apparently ant poison in the
States has a large percentage of Boric acid. 

Australian Jewellery Supplies sells boric acid, but it is priced
much higher than ant poison!

Anna Williams


#13
The borax/boric acid mixture was/is used by traditional
coppersmiths to flux their work. There's a really good book on
coppersmithing from Lindsay, a reprint from a turn of the century
work that's got a lot of good stuff in it, including a bunch on
vessel raising, and of course soldering. 

Good tip, I’ll track that book down. I read an article by Brain who
suggested that Welding supply shops sell white brazing flux; that
sounds like a good idea for brazing copper on copper as well.

George
Vancouver Island


#14
The oxidation of copper seems to overcome the flux if the heating
process is too long. The flux I'm using is also not standing up to
the heat and oxidation 

George, you could try the black flux that is meant for higher
temperatures (e.g., Harris’ Stay-Silv Black Hi-Temp Brazing Flux,
probably available at your local welding shop – it contains
fluorides, unfortunately).

Judy Bjorkman


#15
George, you could try the black flux that is meant for higher
temperatures (e.g., Harris' Stay-Silv Black Hi-Temp Brazing Flux,
probably available at your local welding shop -- it contains
fluorides, unfortunately). 

Excellent suggestion Judy, and great minds do think alike, as I
picked up a small can of white Stay-Silv from a welding supply this
morning. Yes, it does contain fluorides and the warnings on the
instruction sheet paint a scary picture. Obviously hard soldering is
not something to be taken lightly without proper ventilation.

George
Vancouver Island


#16

Hi George. I use 2 torches at once, my oxy/propane Meco Midget in one
hand, and in the other an EZ Torch or a Bernzomatic run on bottled
propane. You have to really pay attention, but it heats stuff up
pretty quick.

Allan


#17

Allan,

Two torches at once, now that takes dexterity. But it does
illustrate the point of getting the copper up to temperature quickly.
Soft soldering on copper is so easy because the solder’s melt temp is
reached in a flash. The trick I believe is to get the copper up to
the hard solder melt temp before the oxidation catches up. It’s a
little more difficult that working with sterling.

George


#18

Hi James,

I think you will find a great improvement in your flux if you get
some boric acid into it. Borax doesn't melt till 743C (1369 F) so
you get no fluxing action below that temperature. Boric acid will
begin to melt at 170 C (340F) so it protects at a much lower
temperature. 

Not for want of trying to find Boric acid. I can get it if I do one
of three things. Pay a lot of money, get a permit (which is really
difficult to get), or find it in a common house hold product (ant
poison in the States, but I haven’t found anything here yet).

Got my calcium carbonate (ground up my wife’s Caltrate calcium
pills), got my Sodium Hydroxide (caustic soda), couldn’t get copper
acetate (fortunately TAFE has this on hand, as well as copper
sulphate). Even crushed kitty litter is useful.

The pot line flux is a bit dry, but it works nicely for smelting and
alloying, so it’s worth a shot.

Of course if anyone knows a product in Australia that has a large
percentage of boric acid in it’s make up, please let me know.

Regards Charles A.


#19
Australian Jewellery Supplies sells boric acid, but it is priced
much higher than ant poison! 

Thank you Anna,

This is just what I needed to know.

Buying from them will be cheaper than buying from the scientific
chemical supply company… they also wanted a goverment permit
before they would allow me to part with any money.

Thank you again :slight_smile:
Regards Charles A.


#20
The trick I believe is to get the copper up to the hard solder melt
temp before the oxidation catches up. It's a little more difficult
that working with sterling. 

It is not more difficult to work with copper than with silver. Copper
simply is a different metal and requires different technique.

The solder for copper must in rod form of the same gage as metal been
soldered. 10% silver, 5 to 10% zinc, and the rest copper, makes
decent solder. If commercial flux is not available, regular borax
will do. Fancy additives are there to compensate for errors in
technique.

Borax should be in powered form, no liquids, no paste. Warm up solder
rod and dip it into borax. Solder must be hot enough to melt borax
and have it adhere to it.

Bring joint to red heat using reducing flame. Flame must be such that
held at certain distance metal must appear clean and shiny. If torch
moved further the area would blacken, moving it closer again would
restore the shine. Copper must be heated in that zone. Observe the
metal while heating. First it will oxide, but than oxidation will be
gone and metal appear clean. Solder must be applied at this moment
simply by touching the area with point of solder rod covered in
borax. It should flow nice and easy and leave bright joint behind.

Leonid Surpin
www.studioarete.com