Yet another anode casting fail - with photos this time :(

[PaulRainbow]

Firstly, thanks to everyone who has offered advice.

I'm starting to think that I would have difficulties in casting this anode in sand. I've never used sand and I know that this is special sand, but I suspect that whilst pouring the zinc I would catch the vertical central edge so that even if it could stand up on it's own, I would probably collapse it!

Does that matter Richard ? You just make it again, re-using the same sand. Unless you're going into production, i can't see where that matters.

 

[RichardS]

Don't imagine that the sand made using the link I posted is something like the stuff you or your children make sandcastles with! It is considerably stronger and holds up well. This is the stuff commercial foundries use for far more difficult casting metals than zinc and considerably greater complexity.

I don't know of any rubber that will take the melting temperature of zinc for any length of time. You might get away with silicone but I suspect it will remain at very close to its degradation temperature for some time unless quenched.

I was thinking of making a rubber version of the anode .... and then using this rubber anode to make the plaster mold as I will hopefully be able to squeeze it out and leave a perfect plaster mold to cast the zinc into. However .......

if you are going down the lost wax method then....
Make a mould using silicone rubber (you can make cake and jelly mould with this stuff too) http://www.makeyourownmolds.com/
Use the wax anode in lost wax casting.

..... Dougal seems to have made the missing logical leap from my somewhat random thoughts. If that silicone stuff can be bought in the UK for a reasonable price (it looks rather expensive at first sight ) I can make a perfect mold from that and cast candle wax anodes from the silicone mold. Once I have the ability to make wax anode replicas I think I'm home and dry and I can churn out perfect zinc versions using the cheapest plaster I can find.

I've been paying £45 per anode online for the last few years and as I have to replace 2 each time, it's not peanuts. Having said that, I just found a supplier who Google has never found on previous occasions, who is currently selling them at £25 each so I've ordered two as, if I do go ahead with sand or silicone/wax molding, at least I'll have a smooth new original to work with rather than that pitted one in the photos.

Richard

EDIT: This looks like the stuff I need http://www.easycomposites.co.uk/#!/...on-cure-mould-making-silicone-rubber-rtv.html

 

[prof pat pending]

Try http://www.benam.co.uk for the casting silicones, we use them quite a bit, they carry a good range

casting a wax, adding a runner and riser afterwards, then coating the whole thing in POP would be my route. You need to add the POP in layers, mix in some sharp sand after you have a few layers on.
TBH it's tricky, hence I didn't suggest it the first time around. You need quite a thick shell or it will probably crack.