Metallurgy help (jeweler at a loss for a solution)!

Im am posting here hoping that someone would be able to help me with
an issue that my company is having. If you have any background in
jewelry you will understand the whole issue, if you have any
questions, please feel free to have me elaborate further.
We make wedding and engagement rings. One of the alloys that we use
to make our rings is an 18k Gold alloyed with Palladium, Copper and
Silver (the palladium is to eliminate the nickel to be sold in
Europe). We do not cast our metals/rings. We pour bars into a
thickness of appx 1 inch, roll them down into thinner bars of appx .
135 inch, we blank out discs from them, and then we form tubes through
extrustion, and cut blanks with a cnc machine off of those tubes. We
have sold a significant amount of these rings to blank manufacturers,
etc. However, we have one customer that has had many issues with our
metal.
They are getting it from another supplier, whom they state they have
had no problem with. We got one of their rings, had the alloy tested,
and made an alloy to the EXACT specifications of theirs, so we know
its not the alloy (assuming for the alloy supplier not messing up)
The rings we have made for other people, for polishing, swisscutting,
etc, have had no problem. Even rings that have been bead set, havent
had many issues if any. The rings for this customer with the problems
are prong set diamond rings and earrings. They are stating (and with
photo proof too) that the prongs are simply cracking, or just too
brittle to hold up. We anneal all of the pieces for all of our 18k
palladium customers the same, in the same ovens, using the same
machines, and the same alloy without issue. My customer says they do
nothing different with OUR rings, then they do with their other
supplier, yet they said they have had no issue at all with them
I have stretched our rings from size 3 to a size 14 without cracking
(BIG DIFFERENCE), so I cannot understand what might be happening in
this situation. Any insight that you might have would be GREATLY
appreciated.
Scott
Reply to
Ratedr
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not an expert, but it sounds like they have something else in the other alloy, that you don't, that allows for a tougher final product after anneal.
how sure are you that the "exact specification" doesn't allow for an odd-ball element (say Bi or Pb. could be something else) to be slipped in?
clearly, there's something different between the sources of supply.
Reply to
beav
Compare impurities in your copper with that of the other supplier's. Specifications are given only for a few elements.
That you anneal it does not say very much.
Reply to
not here
Sounds like it's time for a visit. Alloy issues aside, it sounds to me like they ARE doing something different in their processing that they aren't telling you. It might be time and money well spent to find out first hand instead of guessing...while at the same time a customer gets increasingly unhappy.
Reply to
Harry Andreas
Scott:
Something about your material or processing is different. Possibly you are deforming the material more and thus getting higher hardness and less ductility than the competition.
Look at Raw & Corti's March 2003 article on "Cracking up"
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Also look at your composition versus some other White Golds
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at compositions in Table 3
Pittsburgh Pete
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Reply to
metalengr
well this is free advice anyway...
Your procedure indicates you are rolling from 1.000 inch to 0.135 inch thick (assuming I have read the post correctly). Is this done in one pass or several passes? If several passes let us know the intermediate steps, e.g. 1.00 to 0.85, 0.85 to 0.70, 0.70 to 0.65, etc.
If this is done in one pass, then the thickness reduction is 87%. That seems to be a lot of thickness reduction and cold work to the metal if the anneal does not come until the final step. Even if it is done in several passes, 87% cold work seems like a lot. Perhaps you could reduce the amount of cold work to 70% before the anneal. To do this, if you wish to make a sheet that is 0.135" thick then start with a cast bar of 0.500 thickness. When you roll to 0.135 the % reduction in area will be 73% (for example). If you must start with a 1.00 in thick bar, then roll to approximately 0.300" thick, perform an anneal, then roll again to 0.135" (a 55% reduction the 2nd time) and anneal again.
Would you state the temperature of your processing anneal and the sequence? I think 18K gold should be annealed at about 1000-1100 degrees F. Choose the aneal temperature to the low side. The effect of the anneal will be to refine the grain structure considerably. The hardness will lower but the formability of the material will be greater.
When you extrude the blanks you are cold working again. Do you perform another anneal, to maximize elongation.
Your company's process will have to strike a balance between hardness desired and elongation desired. You may find with the intermediate anneal in the rolling step the problem is solved.
See final comment below.
You might try testing the other alloy for hardness. I can't advise on what scale to use because I don't know how big the tst piece is, but you might have to use a microhardness testing scale. A lab could advise you.
I'm not an expert on gold alloys but the above is based on general metallurgical principles.
I'll watch for any postings you might do to let us know how it worked out.
Mark
Reply to
Mark Fields
Scoot,
The type of fracture must be fractographically classified with a SEM scanning electron microscope.
A highly ductile fracture may indicate the metal has too low tensile strength (annealed too much) - i.e. metal deformation (strain) is beyound its tensile strength (diffues and concentrated "necking" ). Brittle cleavage fracture would indicate a low ductlity not enough restoration during annealing. Brittle intergranular fracture could indicate a contamination from rogue element (not specified , knonw or check - as one post recommeded).
Regardless, the fracture and mechanical worked state of the metal (roughly measured by a Vickers hardness test- as another post syuggested) must be known (along with a full chemical analysis) for a proper diagnosis of cause of the fracture. This work will require and expert and a judgement by you in consideration of the "triple constraint" i.e. Is the quality of the answer worth the cost and time?
Ed Vojcak PE
Reply to
Ed
Scott,
Whatever you choose to do would you post a follow up message?
Mark
Reply to
Mark Fields
I don't think this person will bother !
Reply to
Grimly Fiendish
We have been experimenting with making an x-ray spectrometer just for jewelry that will be able to resolve trace elements and peak overlaps that cannot be resolved by other systems. If you can send us a tiny flake of both, we will do analysis for you (free) if we can use this as an application note. We do Wavelength Dispersive Spectroscopy with x-rays. Contact me at:
prlax#mindspring.com (replace the # with @)
Reply to
Frogwatch

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