Dore beads break up at the time of stripping

[crauther]

Hi, I am from India, works as a assay chemist and new to this field. We are conducting fire assay
to check the purity of gold jewellery and artifacts, and our target is 916.6 purity. While conducting
the fire assay, the dore beads,at the time of stripping, using rolling machine, is breaking up
and getting significant variation in the result. Our inquartation ratio is 1:3 and cupellation
time is 20 minutes. Check gold purity is 999.9 and using 4 gm lead at the time of the
cupellation. It could be a great help if anybody lend me a helping hand from this
blog. Thanks in advance.

 

[fireguy]

Hi, I am from India, works as a assay chemist and new to this field. We are conducting fire assay
to check the purity of gold jewellery and artifacts, and our target is 916.6 purity. While conducting
the fire assay, the dore beads,at the time of stripping, using rolling machine, is breaking up
and getting significant variation in the result. Our inquartation ratio is 1:3 and cupellation
time is 20 minutes. Check gold purity is 999.9 and using 4 gm lead at the time of the
cupellation. It could be a great help if anybody lend me a helping hand from this
blog. Thanks in advance.

Hi Crauther:
The problem you are having is during the rolling of the dore in the roll mill, correct? This would probably be caused by the metal work hardening during the deformation while rolling and could be also caused by reducing the size too fast.

Make sure you are only incrementally moving the rollers closer together. And, you should be annealing the metal after each reduction. This can be done in a furnace at 1000F. This will allow the crystal structure of the metal to "relax" and realign.

You probably should also be doing a preliminary bullion, and using high purity copper in your assay. You can see an excellent procedure for the corrected bullion analysis in Volume 2 of this handbook:
www.lmine.com/product/9051x.html

 

[crauther]

Hi Crauther:
The problem you are having is during the rolling of the dore in the roll mill, correct? This would probably be caused by the metal work hardening during the deformation while rolling and could be also caused by reducing the size too fast.

Make sure you are only incrementally moving the rollers closer together. And, you should be annealing the metal after each reduction. This can be done in a furnace at 1000F. This will allow the crystal structure of the metal to "relax" and realign.

You probably should also be doing a preliminary bullion, and using high purity copper in your assay. You can see an excellent procedure for the corrected bullion analysis in Volume 2 of this handbook:
www.lmine.com/product/9051x.html

Many Many Thanks. I have a doubt about the time that i should need to keep the beads in the annealing furnace. Normally we used to keep the beads, minimum six, in a iron tray for 90 sec, at 750 degree C.

 

[fireguy]

Many Many Thanks. I have a doubt about the time that i should need to keep the beads in the annealing furnace. Normally we used to keep the beads, minimum six, in a iron tray for 90 sec, at 750 degree C.

I'm not sure of the exact time. 90 seconds sounds reasonable. As long as the beads reach temperature- which you may be able to judge by color.