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How to prevent oxidization in rose gold alloys? like 9k to 18k


#1

Dear All
This is p

How to prevent OXIDATION in ROSE alloys??? like 9k to 18k… wax set castings…Please help…
Have taken lots of trials but i get oxidation in the cast rings. I am using lots of alloys with silver content & high copper content of various range… but i am stuck with this problem …
Can please somebody shed light on this issue…??
Awaiting for your replies eagerly… & take trials…
Best regards,
Prakash V Pai
INDIA…


#2

are you using a reducing flame to melt your metal?? Start with that. When open pouring and melting alloys if you have to much oxygen in your flame you will get oxides and porosity.

a reducing flame is just a bit gas rich. This is assuming that you are using acetylene when melting and not electricity.

Also don’t skimp on the flux. You need enough borax in your crucible to be able to see it flowing a bit across the molten metal. This is assuming your using a ceramic crucible.

Also try making your alloy before using it in a casting. Alloy the metals and turn them into a round or bar ingot then role it out into thin sheet. This way you are not over heating the metal in the casting crucible while trying to mix it. It will also reduce coring (when metals do not alloy evenly producing an inconsistent malleability over the casting)

when the metal starts to flow you need to cast as quickly as you can, spending to much time waiting for metals to alloy together will cause issues.

Are you using a vacuum assist or centrifuge.

Les


#3

Dear Les… Thanks for replying…
I am using the following alloys which I am sharing with you for your information.

  1. C 185 N1: contains 11% silver 87% copper & the rest Zinc. used for 9K Rose
  2. OR 134 : contains 6% silver 92% Copper & the rest Zinc. used for 10k Rose
  3. 534 united alloy: Contains 4.5% Silver 91.5% Copper & the rest Zinc for 14k Rose. All the above alloys are cast in YASUI Induction based Vaccum machines under Inert atmosphere.
    The melting & pouring is done at 1080 deg Celcius with Flask at 600deg celcius.
    We quench the flask in the following manner; After cast & holding it in inert chamber for few minutes we dip the button in the water for two minutes & later keep it for air cooling for 15 minutes & then quench the flask after 15 minutes to remove the investment powder.
    The problem is after finishing & polishing the oxidation shows up… as DARK spots or cloudy surface on the ring…
    Regards,
    Prakash V Pai
    INDIA.

#4

I am familiar with your casting method but do not have very much experience using it. your dark spots and cloudy surfaces sound like fire scale, it is common with alloys using copper although less common with gold.

this scale is just a little more than on the surface, it will come out with more finishing. I will refer back to one of my previous comments about the alloys not mixing properly. If you are mixing the alloys together at the time of casting it might not be alloying properly so you are getting fire scale. The gold content should make the other metals relatively inert if enough time is taken to ensure they are well mixed. The paradox is if you take to much time you will over heat the metal. It sounds like you are very capable of controlling your heat so allowing a few more seconds before casting tithe help, I do think you are casting with flasks that are a bit hot. what investment are you using? Dose it specify such a high flask temperature when casting? This might be an issue. I usually leave my flasks to settle at 500C for an hour for detailed work and 475C for heavier castings.

Others might have more insight on this if they are using similar equipment.

Les


#5

Thanks Les …
Will do the audit & take trials. Will get back to you on this…
it was great discussing the issue with you…
Regards,
Prakash V Pai
INDIA


#6

Dear Prakash,
The alloys you are mentioning if you are using Yasui KT18 work well. With UPMR Neutec works best. Never faced this problem. Are you using K2 or K3 machine. A detailed step wise scrutiny will help you ascertain the problem.
Is it a patch or just spot you gauge out.
Since it is coming after polish I presume it is not the casting but something else.

Regards,
Umesh


#7

Dear Umeshji,
Extremely happy to hear from you after soooooooo long. Welcome sir.
I have this problem of OXIDATION in rose color alloys. This problem occurs after the pieces are steam cleaned & let to fry … small patches & pin point oxidation spots occur on the surface of the polished article. We are using the best alloy available in the market with silver content & with Anti oxidation contents but still this problem occurs. The alloy contains 87-92% copper with up to 11% silver & up to 6% zinc.So these alloys are very good for closed Type inert atmosphere castings.
I am working on it.

Also secondly why do Platinum ring crack during polishing?

The alloys used are as follows:

95%PT+ 3.50% PD + 1.5% RH &
95%PT+ 4% COPP + 1% COBALT. Temperatures used for casting is 1790 -1820 Deg C with flask temperature at 950 Deg C.

Eagerly Awaiting your reply…Kindly help for this problem.

Regards,
Prakash V Pai
INDIA


#8

Dear Prakash,

The red gold is a different problem.

As far as Pt is concerned it is a issue you have to look at.

What is the alloy manufacturers guidance.

Do you have Standard Operating procedure?

Do send it to me.

Regards,
Umesh


#9

Dear UMESHJI,
we are using

  1. 95% PT + 2.5%COPPER + 2.5% COBALT.
  2. 95% PT + 2.5% RUTHENIUM POWDER + 2.5% PALADIUM for casting.
    We mix the alloy in a ceraic crucible coated with Zirconium Oxide & then under vacuum & inert atmosphere we do the melting & casting …
    We also do the inhouse refining of the platinum in Aqua Regia Acid to recover pure metal from scrap & rejects.
    Regards,
    Prakash V Pai

#10

Dear Prakash,
It is tough to understand from what you are saying what exactly is happening. Somewhere something is wrong must look at things more closely to locate the fault.
Regards,
Umesh