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trialuser
06-09-2012, 10:57 AM
Hi, newbie here.
I am now having trouble casting scrap sterling silver in a small reversible ingot mold (rectangular ingot one side, cylindrical rods the other.
When I first tried it - it worked very easily, now it solidifies before getting to the base.
My technique is the same as far as I can tell.
I have tried, cleaning the mold, with and without fluxing the mold, with and without oiling the mold, with and without pre heating the mold, adding charcoal to the molten pool.
I ply the flame onto the pool and the lip of the mold as I pour.
The scrap I am now trying to cast has been melted perhaps 10 - 20 times (by me) - does this change the properties, perhaps burning off either silver or copper?
Anyone shed any light why I'm struggling please?

Kwant
06-09-2012, 11:55 AM
I have been using one of those for a couple of months now and have not encountered a problem (previously all my casting was in cuttle bone). The mould has to be heated that is a cert, I do not add charcoal (never heard of doing that) I do add a little borax, once molten play the flame over the pool and watch the scum slide off to the sides and when you pour it is the lip you need to concentrate your flame on, as it is here that the metal has a chance to cool and pour quickly and smoothly in one motion, any hesitation will result in the metal bunging up.

If you have any fine silver you can add to your melt this will help "refresh" the metal, I do this regularly as I too melt and remelt and want to make sure it is always up to assay quality.

The oil on the mould is to prevent it rusting and there should not be an excess of it, I don't think it has anything to do with the casting process. I do not flux the mould either and to date have had no problems.

trialuser
06-09-2012, 07:07 PM
Thanks for the reply. I think you are right in that I am probably being a bit feeble with my pouring, I need to go for it.
The charcoal bit comes from the Jinks Mcgrath book - The new encyclopedia of jewellery making techniques, page 17, recovering and reusing metal. I've not seen reference to it anywhere else though, I assumed it was to try and scavenge any free oxygen from the melt? The oil bit came from a youtube video somewhere - albeit on a more industrial scale, interestingly I did get it to cast sometimes with the (olive) oil! smells nice.
I'll give it another go tomorrow
Cheers
Martyn.

Didi
09-10-2012, 11:30 PM
Trialuser. I am so with you on this one. I CANNOT get the silver to pour into the mould. It jams at the top and spills all over the sides. I've heated the mould, sprinkled borax and nothing is working. In the end I dug a rectangle out of a charcoal block, piled all the scrap in, melted it and .... Hey presto - one ingot. Destroyed the charcoal block but reduced the bad language. There must be trick to doing it that I have completely missed.
Didi

Wallace
09-10-2012, 11:44 PM
Trialuser. I am so with you on this one. I CANNOT get the silver to pour into the mould. It jams at the top and spills all over the sides. I've heated the mould, sprinkled borax and nothing is working. In the end I dug a rectangle out of a charcoal block, piled all the scrap in, melted it and .... Hey presto - one ingot. Destroyed the charcoal block but reduced the bad language. There must be trick to doing it that I have completely missed.
Didi


before using a charcoal block, did you condition it? Best way is to put some binding wire all around it and tighten it a little by twisting the wire on each straight edge so allowing for expansion. Heat and quench in water a couple of times. The block may still fracture, but the binding wire will keep it together for longer.

regarding heating of the silver, I always put some fresh stock in and never use any part that has been soldered. These get snipped off and saved for the big pot that goes off for the big boys and girls to recycle.

Keeping the silver 'fluid' is really important. If it touches something cold, it will solidify really quickly. The bigger the amount of metal, the more heat and longer you will need. A nice little boxed area to keep your heat concentrated may help... you may already do that, so apologies if that is the case. You don't need to do much to the mold other than keep it clean and then hot for pouring.

again apologies if this is too much like repetition.

vernon
26-02-2013, 08:57 AM
I use carbon blocks and machine out the ingot shape and sprue, fill with scrap and then use my homemade furnace or kiln to heat the carbon blocks, You can machine out rectangles and rods etc. To make a usable coffee can furnace I put a thread on the forum last year on how to make and use the furnace, search coffee can furnace.

trialuser
26-02-2013, 09:34 AM
Thank you - sounds sensible.
I've got it sussed now - bought a large multi jet nozzle for the little torch and it's all good.
Previously I had been doing it with a rothenberger plumbers torch.
Could you just clarify what you mean by carbon block, is it a charcoal block or are there other types of carbon block?

vernon
27-02-2013, 01:02 PM
i use carbon block similar to that used in carbon brushes used in electric motors. I use a piller drill with a wood router to machine the blocks or for rod drill with the size I want and then counterbore for the sprue to hold the scrap.
For example a 4mm rod by 25 mm. radius squared x 3.142 x 25 =314.2 (Volume)
divide by 1000 to give Cubic Centimetres=0.3142 then multiply by density of silver approx 10.4 =3.27 gives you grams needed to fill mould, but you need to add a little more to help wiegh the molten silver and flow into the mould. I currently use a kiln and set it to 1000c I put the mould into the cold kiln allow it to come up to temperature and switch off when it has reached 1000c, leave the kiln to cool and remove the mould with casting.
I also will clamp two block together and drill down the join so it is easy to remove the cast rod, holding them together with binding wire.
the furnace which I built takes about 15 minutes to melt a castin like the one above.

trialuser
27-02-2013, 05:10 PM
That's all ingenious, thank you for sharing that.