Tig welder

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I know you said you weren't sure of alloy composition. Most gold used for jewelry or dental applications is alloyed with copper or silver. It's possible that it may contain additional elements such as nickel, platinum, paladium or even zinc.

Your silver may also be an alloy. It is quite commonly alloyed with copper which has the effect of lowering the melting point of the silver and reducing thermal and electrical conductivity. That would be an asset in this instance as the gold and silver would then be more closely matched in regard to metal properties that directly affect the joining process.

By themselves, that is in their purest state, gold is described as having "good" electrical and thermal conductivity while silver is described as having excellent properties in that regard. Their melting points are fairly close with gold being 1950�F and silver being 1765�F.

Gold has very good resistance to oxidation which is in your favor. That may be compromised slightly by some of the alloying constituents but overall is not of great concern. The shielding gas will easily take care of that. The greatest source of contamination will be your tungsten electrode.

Silver is a different animal all together. If the silver is pure you will find that it will require a great deal more heat input than the gold. This is due to the fact that silver has that high rate of thermal conductivity. It is difficult to control the molten puddle as well because it is so fluid. Molten silver will readily absorb oxygen too. Unless you provide adequate shielding during the solidification process, you will experience a good deal of spatter and porosity as the oxygen that was absorbed in the molten state is being rejected during solidification. You can use either argon or helium as a gas shield. Choose the one which best fits the application. If you have a ag/cu alloy the argon should be good.

Polarity of DCEN is normally used unless the metals you are joining are easily oxidized. With DCEN polarity the weld pool is narrower and the penetration is deeper than when using AC or DCEP. DCEN provides a narrower HAZ and that means less distortion and faster welding speeds. Sorry about the lengthy response. Turned out to be more like a dollar and a half rather than two cents.

Awhile back, gees 30yrs ago and time really flys, I was on a project that I was welding up 1/2", 96% copper brew kettles for Coors that came from Germany. I was using 1100f preheat, Tig at 325amps water cooled torch with a 75% Argon 25% Helium mix with pre/post purge and I was getting porosity intrapment within the weld. The face was spotless most of the time with a small porosity hole showing every now and again. I tore the torch and gas hose apart several times looking for a leak, but there wasn't any to be found. Turned the flow rate up to 25cf/hr without any help. Then naturally I said something to the Welding Engineer that was bird doging the project. We checked and rechecked everything with nothing. He decided to run an x-ray. X-rays at the time were very costly and it had to be a very important project to get x-rayed. X-ray's were developed and the weld was full of extremaly small porosity "pockets". Out came the air v-gouger and we started again. Then it had to be the welder so I got to run the preheat and new meat was brought in and within a short time I was once again back in the saddle. We never did find the cause. I got the prosity down to an acceptable level but never all of it.

Thru the years I kept asking every welding engineer I ran into what he thought and never got an answer that would correct the problem. Then came along my AWS CWI test. While I was studying for that I picked-up one of my old refference books looking for an answer to another hard question and the book fell open to Tig welding. Never guess what was on that page. While welding copper the recomended cover gas is 75%Helium 25% Argon or the weld will have porosity intrapment! I was using 75% Argon 25% Helium. I tried it and the porosity was gone.

Almost no one uses pure Gold or silver for any projects so I was counting on the alloys to have a high precentage of copper, thus the recomendation of 75%Argon 25%Helium. The silver should improve fluidity of the weld.

My brain ain't working today so explain HAZ?

T_Bone

As director of our industrial division I've been involved in numerous projects for salvaging copper/copper alloy castings in foundries. Oxygen bearing Cu contains impurities that combined with residual oxygen can and will cause porosity during welding and brazing.

Oxygen free Cu will absorb Oxygen during extended periods of heating which leads to difficulty during arc welding. I would suspect that this may have been the case in your experience. Brazing or soldering is usually the path of least resistance there.

Precipitation hardening Cu and the free machining Cu have their own individual set of pitfalls to deal with.

Argon shielding is usually sufficient for joining or repairing Cu in thicknesses of less than .13" and the Ar/He mix of 75%He/25%Ar should be used on sections over that. The effect on arc energy goes w/o saying.

In responding to the gentleman who is joining the Ag and Au sheets by GTAW process, I felt that insight regarding the properties of the base materials was pertinent. I would agree that the addition of filler metal, especially in the form of Ag is more of a hindrence than a help. You gave him some good advice by instructing him to fuse the base materials w/o the addition of filler metal.

HAZ is the technical abbreviation for "Heat Affected Zone".

By the way Ken, would you mind dropping a line to the solons at U.S. Alloys and inform them of my less than substantial fair?
Have a good one,
Steve

One thing I would try is 75% argon, 25% Helium gas mix just because of the metals involved you will see a cleaner weld. DCSP would be my only choice with HF start mode and prepurge/post purge. I would perfer welding without a remote foot switch.

There's really nothing special about welding gold and silver. Both will join equally well to one another. Sometimes the mixture of other metals alloyed with gold and silver will give you fits.

Gold and silver are just like any other metal, they oxidize and have to be cleaned with a "new" SS wire brush. They make the SS wire brushes in the non twisted brush design and thats the one I would use. If you use a SS brush thats been used on any other type of metal of carbon alloy, your welds will look terriable and will be weak.

Qxy/acetylene is also a good choice for joining gold and silver. I have a torch thats 6" long with 1/8" cotton covered rubber hose that I use.

T_Bone

Try this method on SS and you'll see what I mean. It'll work for any thinkness upto 3/8" or so. Be sure and tack weld the joint proper or base metal warpage will occur. I also hold the Tig torch with both hands using light leather gloves, draging the weld puddle towards you. The leather lets your hands slide easy on the base metals.

Also use all glass welding lens. Plastic lens will give you a distorted and double weld puddle!!! I use only the glass gold cool-ray lens, shade 11, or 12 if the amps are high, with glass clear lens other either side. If you haven't tried one a Huntsman P-5 welding hood is the finest made and very light weight.

T_Bone

T_Bone