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Hard spots


#1

Dear Sir,

Warm Wishes to you

I Introduce myself as Prakash V Pai, working as a Senior Manager at
M/s Jewelex India Pvt. Ltd. Mumbai, Maharashtra, India. We use gold
alloys from 9k to 18k, (both yellow & white)& Silver, Palladium &
Platinum alloys for our production purposes. The cast results are
stunning in all alloys, But I have been facing a nagging problem in
14kwg alloy containing (46% Silver, 18%Copper & 18% Zinc).

The casting for 14kwg is done at a temperature of 980 -1020 degrees
& the oven being at temperature of 600 degrees. Most of the trees are
of Stone in Cast type & we use a Boric Powder based investment
powder for casting. We also add to this powder, 8% Boric acid water
solution to further prevent Diamonds from burning or surface damage.

The skin of the cast pieces is very white & clear. But when its
Filed & Polished, It shows HARD SPOTS or PIN like structure on the
surface of the ring. It appears to be some sort of CONTAMINATION.

There are two types one when processed is removed totally & the
other it re appears again & looks like metallic (white spots). It
also appears in YG sometimes. Although the intensity is very low, it
is there. We even clean the oven, Casting chamber of the machine,
Have kept separate crucibles & rods for casting separate alloys YG &
WG. Make shots of the used gold before casting, Do not use sprues
again, so much so that 14 KWG is used once for casting &then it is
sent for Refining??.. we observe all the healthy parameters to
achieve a clean surface in castings??. But it goes in vain. Even
after repeated repairing of the same it remains on the surface.

What could be the reason for these spots & how should get rid of this
problem? This is the only nagging problem which is existing on
14kwhite gold?? it is not there in any other alloys, cast in & at the
different temperature?? why it is so e?

Please do help us out in sorting this issue & you can revert back to
me on this mail id given below for the same. Is Refining the causee?
We use Ferrous Sulphate in Precipitation of Gold. Is Open graining
healthy e? Or Closed chamber inert atmosphere healthye? What could be
the root cause for these Hard spotse

Can the above problem be because of Refining??. As we are using
different alloys of Zinc, Nickel, Copper, Palladium, Platinum,
Silver etc.

Are some of the metals getting released in precipitation of golde?
Specially Nickel. as the three alloys we are using for 14WG contains
high percentage of Nickel. 17.5%,23% & 17%…e We are also using
TALCUM POWDER while injecting wax pieces in wax department. Can this
be a reasone? Please help?? Awaiting for your reply,

Best Regards,
Warm Regards
Prakash V Pai


#2
14kwg alloy containing (46% Silver, 18%Copper & 18% Zinc). 

How do your alloy percentages make 14k?


#3

Can you post a picture ?


#4

Dear Prakash,

Which brand of alloys are you all using?

What is the type of casting machine?

What is the alloy number?

What is the thickness of the pieces?

What are the sprueing systems?

How is the embedding being done?

If they are hard spots of grain refiners normally appearing black
under the microscope & have to be leached out. Please go up on
temperature.

If they are patchy white then it is investment powder.

In this case you need to send your scrap metal to professional
refiner? I am visiting SEEPZ on Monday.

Warm Regards
Umesh


#5

14k is 58.3333% (58.5) gold, the rest is alloy.

Adding up 46, 18 and 18, yields 82%.

Perhaps you miswrote or I misunderstood?

In any case, silver usually yields a greenish alloy…


#6
 How do your alloy percentages make 14k? 

I think the OP mean that the 14K gold was prepared by using 58.33 %
gold and the rest is the alloy metal that contains 46% Silver, 18%
Copper & 18% Zinc).


#7
I think the OP mean that the 14K gold was prepared by using 58.33
% gold and the rest is the alloy metal that contains 46% Silver,
18% Copper & 18% Zinc). 

That still doesn’t add up. 46+18+18=82% o if it is the master alloy
there is still 18% undefined.

James Binnion


#8

An interesting mix for white gold…


#9

Perhaps you are getting hard spots from metal crystallization. try
annealing one of your castings to see if this gets rid of the
problem. Possibly look for chlorine contamination in water used for
investment, bleach used in cleaning, even bleach on the glass cleaner
in your display case.

Mark Zirinsky


#10

Sounds like the alloy is right