Printable View
Hi all
I've made some moulds suitable for casting a low temperature tin/copper alloy. The problem is that the casting has a raised section at the top due to the surface tension of the alloy (similar in appearance to the old mercury thermometer). I want the alloy to be flat at the top of the casting. Any suggestions apart from filing the surface?
Cheers
Foccacia
Meniscus is the word you were after, and I'd like to know too.
I think you would need a fully enclosed (or two piece) mold to avoid the surface tension issue.Quote:
Originally Posted by burraboy
I get this same problem when I cast gear blanks, but as I have to machine them to size it's no big deal.
I can't see how you can avoid this with an open mold. Maybe after you pour it you could place a metal blank on the poured surface to level it off before it cools
Cheers
Rob
G'day.
You will need a sprue plate to get a level top.
Bullet casters have done it this way for zonks for the same reason.
Pewter is great stuff. I do the garage sales and buy all I can to alloy into lead for bullet alloy.
Beats paying top price for 50/50 solder just to get the tin.
If you used RTV rubber for the molds, just put the master back in place, cut a few locating dimples in the existing rubber mold, coat the exposed surfaces with a release agent (Vaseline works as well or better than most), build up a mold box around it & cast a back plate. Separate the two parts then cut a casting chanel in an inconspicuous place.
A purpose made RTV drop casting mold with have more space at the top so you can have extra metal in the casting sprue, which will help to make the metal fill the mold properly each time. You may also have to cut some hair thin gas bleeder chanels in the mold too - just run them back up to the top edge until you get the hang of cutting them.
It can also be handy to get a few aluminium plates (1>1.5mm) just a bit bigger than the mold, plus a few spring clamps to hold everything in place without squashing the mold in and keeping you hands away from the hot metal at the same time.
As you will find, the first few castings in an RTV closed mold will be rubbish, until the curing byproducts have fully outgassed, which is accellerated by the heat from the metal. If you are doing a lot of casting it is also a good idea to run several different molds as they can over heat, shortening the life of the rubber. It is amusing to release a casting, then have it collapse like a spoonful of wet sugar because the mold was too hot and only the surface set, the center still remaining semi-liquid - also time to have break & leave the molds to cool down.
Quote:
Originally Posted by glock40sw
Hi, I use to use wheel weights, to cast 357 Magnum bullets, read it in a shooting mag once about 35 years ago.
Kryn
i have had this same issue just yesterday. fortunately the mold i was pouring has a flat surface and excess can be pared off with a plane blade... maybe try a different approach to your pour.. if you want a flat surface at the top, secure the mold onto mdf and find another point to pour in. a countersunk 8mm drill hole should be easy to pare off .
show us your mold, might make it easier to give advise.
i have a jarrah sideboard top that is needing 9 large holes filled, and a dining room table that has 15 holes to be filled... first try at this and I am more than happy with the result..
Attachment 236805 test piece with pewter fillings and finished with Feast and Watson's Fine Buffing Oil