Frosty.......

Gnoahhh

New Member
I like frosty well filled out bullets too. What I don't like is the smearing that occurs on top of the mould and underside of the sprue plate when casting high antimony alloys at obscene heat with iron moulds. The alloys and heat aren't open to change, but is there something I can do to alleviate said smearing? I wait a full ten-count after the sprue frosts over before opening the mold. I've put up with it for many years, and have grown adept with a single edge razor blade for removing it but I know there has to be a better answer.
 

Rick

Moderator
Staff member
What temp is your alloy while casting, the pot temp? An iron mold holds heat pretty well and once it's up to a good casting temp it's simply a matter of a casting rhythm to keep it at that temp and not over heat the mold. Finding and maintaining the sweet spot with mold temp and casting rate should cure the problem.
 

Rick

Moderator
Staff member
I do believe we have found the problem. A good casting temp for your mold will be around 400 degrees give or take a little. An alloy temp of 700 degrees is 300 degrees hotter than the mold needs to be and will easily keep the mold up to a good casting temp. 850 to 900 degrees will cook the Sn out of the alloy and it will radically slow down the casting as you wait between pours for the mold to cool and the alloy to freeze. Thus your smears at the sprue cut-off.

A typical WW alloy will be at full liquidus around 550 degrees and flow well filling out the mold. Casting at 700 degrees is 150 degrees over full liquidus, 300 degrees over mold temp. I suggest dropping your pot temp down to 680-700 degrees and see if Gnoahhh isn't a much happier camper and a faster caster without all that waiting. Depending on ambient air temp using 700 degree alloy will still at times require a fan blowing on the mold to keep from over heating it.
 

KeithB

Resident Half Fast Machinist
Pretty much agree w/everything Rick said. I use 700-725 for most of my 6 cavity Lees, a little cooler for iron 1-2-4 cavity molds.
 

fiver

Well-Known Member
i do too.
I generally start out at 725 but will find myself turning down the pot closer to 700 before too long.


one way to avoid the razor blade is to put a barrier on top of the mold.
I use a little nickel anti-sieze [for sure on aluminum] or a little oil that burns off leaving a bit of carbon behind.
I know others skip that and just go straight to using a pencil to put a carbon layer down.
this allows you to just wipe off the smear of lead and keep going without cooling the mold down.
 

Winelover

North Central Arkansas
At the start of my ancient casting career, I always used iron moulds. Never a problem with sticking lead on mould surfaces, that a handy piece of 0000 steel wool wouldn't take care of, if a canvas gloved hand wouldn't. Bamboo skewer on cavity edges. Never heard of sprue plate lube before the casting forums appeared. Only place I used anti seize for is on the handle screws.
 

RBHarter

West Central AR
I read somewhere that Teflon heat breakdown is very bad for people to breathe . Ceramic works in aircraft cylinders on the barrel walls and nothing on rings and pistons except lots of heavy oil . 2 faces might work well . See Cermachrome for aviation use .
 

Ian

Notorious member
Teflon breaks down and off-gasses stuff tha will kill you real fast in small quantities once it reaches its melting point which happens to be the same as pure lead. It reacts with aliminum at high temperature, too. Bad idea all around says me.

Cerakote...now that might be brilliant. Keep it off the block faces if you don't want elliptical bullets.
 

Pistolero

Well-Known Member
A trace of Bullplate lube has always eliminated any problems with mold/sprue plate galling for
me.
Teflon does not sound good. In cooking applications, max is 500 F, far below casting temps.
 
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358156 hp

At large, whereabouts unknown.
I've heard the same thing about teflon. My thinking on Cerakote is to coat the sprueplate on both sides and cure normally. I would mask the blocks off and coat the tops individually after masking, but I would only partially (tack) cure then, then clean off any overspray with acetone on the parting faces and the cavities before doing a full cure on them. I think I can get my hands on a small quantity of high-temp air cure Cerakote to try this out, the 800* stuff will be far more than plenty for this project.