melting techniques

Hi,

Melting with an electric furnace just wondering if people would like to share their technique in achieving a homogeneous bar. I've been told different things by different people.
IE Put the metal in after the crucible is red hot VS put the metal in at 600, or stir it well pour straight away vs stir it well let it sit then pour. Anyone like to share there secerts with me would be greatly appreciated

If your not using an induction furnace I would put the metal straight into the crucible and heat to molten, stir well several times add a little borax stir again and pour the metal into a warmed mould allow to set and quench while still hot to remove the flux. If your using an induction furnace you need to load your crucible to start but you don't need to stir as the action of the induction coil will stir the metal for you.

Hi Nick just to clarify...

1: Heat to 1100C
2: Put Metal in
3: Add Borax
4: Wait to Molten
5: Stir well
6: Add little more borax
7: Stir again
8: Pour immediately

Is this correct?

michael1311 said:

Hi,

Melting with an electric furnace just wondering if people would like to share their technique in achieving a homogeneous bar. I've been told different things by different people.
IE Put the metal in after the crucible is red hot VS put the metal in at 600, or stir it well pour straight away vs stir it well let it sit then pour. Anyone like to share there secerts with me would be greatly appreciated

Click to expand...

For clarity (as many people will read this thread), just what is it you are melting?

You state you want "a homogeneous bar", which would indicate you are not refining anything to purity, just melting (what, we don't know, though presuming you mean various gold bearing material...). This is not usually recommended in this forum, so a more clear explanation of what you are doing (or attempting) would be helpful, I think.

I know that when I started out, my first thought was "melt a bunch of gold bearing material and all the different metals will separate because of temperature differences". Well, reading this forum, I found out that is certainly not the case! I had a lot of newbie ideas that have been proven wrong time and again. That may not be your situation, but that's why I think a clarification of what you are planning to achieve would be important to know here.

If you are combining metals (to produce karat bars of known composition, for example), then that would be a different situation.

In any case, a bit of clarification on your final destination would be nice to include for the post, if for no other reason than to help future readers understand this process.

Hi MMFJ,

I am melting mixed carats from 9 - 22k 300 - 700grams in weight. No i am not refining to purity.

Michael personally I'd put the metal into the crucible cold and then start the furnace and don't overdo the borax if the material is clean. When the metal is fully molten you can see it moving stir it then and add a little borax, leave for a minute stir again and pour into a heated and pretreated mould to avoid it sticking, allow the metal to set and then drop into a container of old water, this should fracture the flux off leaving a clean bar.

Hi Nick,

Yes the metal is reasonably clean, maybe a few small stones in a setting you can't remove but 99% of the springs should be removed. (Sometimes a small one sneaks past) So you are saying to only add a little borax at the end once the metal is molten? Stir a second time then pour immediately? or stir let it settle, then pour?

Stir and pour is my way but I'm sure others have their own view.

Il try your way Nick and report back over the next few days.

Michael,

Nick & I are both old jewelry dogs and Nick is very talented while I am just an old dog. Lots depends on what you are trying to achieve. Getting a true homogenous mix can be a challenge do to solidification and straitification. When we melt with a torch and mix, I get up to a 20% difference from one side to another. When I melt in an Induction Melter and pour it immediately, I get about 1 to 11/2% variance. Understand, I have a bigger XRF and I cash out usually twice a week. I usually pour in a tilted ingot mold to get the max difference to calculate my returns. Pouring in a larger thinner ingot can minimize the differences. A Alpha Mirage SG scale, can be very beneficial in determing the purity as it averages everything out as long as it is a solid bar.

A lot depends on what you actually are trying to do. No matter how well the metal is mixed, you are going to get some differences in the ingot in the cooling process or at least that has been my experience.

Dan

Hi Nick,

I found if i pour straight after putting borax in, i get bits of gold stuck in the borax. I tried today waiting about 10 - 15seconds then pour i got 0.2% difference between top and bottom with no gold stuck in the borax. I might try it like this for a while and see how it goes.

Michael my reply to your last query was perhaps too short, I meant get the metal molten, stir well and add your borax, allow it to swirl over the metal for about 1 minute stir again and pour. You are doing nearly the same but I'd allow a little more time for the borax to work. I know what Dan is saying about melting and segregation but I rarely find less gold than my calculations lead me to expect by doing multiple drill samples top and bottom of the bar, perhaps I'm just lucky or I'm losing with there been more gold there than I calculate.

Nick,

Top and bottom drilling should average out but you Brit's have an advantage to us State side with your Assay Office. Usually, we are stuck with one longer XRF read or a pin sample taken from the center of a tilted crucible. After hundreds of cash outs using both SG and XRF, it's at best an educated guess. A good long term relationship with a local refiner is very important component. Too many things can and will go wrong to be right 100% of the time. Using both XRF and SG is a great double check which keeps most cash outs in a acceptable range. To quote Chris, "the refiner is the last liar!"

Peace,

Dan

The only problem i find putting too little borax is after you pour, the borax only settles in the middle of the bar creating a dint which makes it harder to XRF the top accurately. If you pour and the entire bar is covered with borax, its nice and flat at the top, which is what you want for XRF assay. Most bars are around the 45 - 55% range once you average out all the scrap you are buying.

Michael all I can say is melting is as much an art as a science, I'm sure Dan will agree with that statement, the more you do the better you become at knowing what's happening, when to add the borax and or other fluxes, when to pour and when to quench the bar to remove the flux. I don't doubt Dans comment about the assays of the bars throughout their structure so make sure you get multiple samples or readings to try to average it out.