Heat soak

Bliksem

Active Member
Been pondering something I have noticed with molten casting alloy that if I let it soak at the casting temperature for 15~20 minutes before starting to cast that I get good mold fill-out from the get go.

My casting setup is a 50# bottom pour which is PID controlled along with a hot plate to pre-heat the mold. Alloy is Lyman #2.

I’m sure I’m not the only one to notice this and there is probably a scientific reason for this behavior of the alloy.

Thoughts and comments?
 

Rick

Moderator
Staff member
Only thing that comes to mind right off is if your also "heat soaking" the mold on the hot plate for the same 15-20 minutes.

One thing you could try as a test is segregate those very first pours at the get go and weigh them later comparing with the weights of bullets after 10-12 pours and later. If the mold is up to temp for decent fill-out but not quite to proper casting temp the early pours should be a tad lighter.
 

Walks

Well-Known Member
I agree.
I turn on my pot and hotplate at the same time. Molds must sit there for 20-30min. I get good fill out from the start.
Just never thought about it.
 

Ian

Notorious member
I like to stir the heck out of the alloy after it all melts, scrape the bottom and sides of the furnace liner, and give it another real good stir to make a vortex in the middle, then let it sit for 10-25 minutes before casting. Fines take a long time to migrate to the top and I probably don't let my rendering furnace settle long enough before pouring ingots, so they get in my casting furnace and do seem to affect the alloy flow and casting quality.

Bullets that I've cast from my own scrap always cast a lot better the second time.
 

Walks

Well-Known Member
Anyone ever try stiring/fluxing with a paint stirrer?

Wondering how that would work. Is there a finish on a paint stirrer or plain bare wood ?

Wood Flux to light off or burn the heck out of your hand/glove. Maybe good for scraping the sides & bottom of the pot, if you're fast enough.

Just occurred to me.
 

Ian

Notorious member
I recommend against scraping the bottom of a bottom-pour furnace with a wood stick. Stirring about halfway down and scraping the edges works well, but keep the sticks very dry or they'll sputter and pop lead. If you scrape the bottom you plant ash down there below the surface tension of the melt and it migrates to the spout causing inclusions in your bullets that aill drive you crazy until you drain the pot and clean it. Dumping sprues or ingots in does the same thing, the cooler, denser solid metal falls to the bottom and donates its oxide skin to the pour spout. The oxides can't re-enter the molten metal and float up because they were held at the bottom under the weight of the molten alloy before the sprue/cull/ingot melted in. I float a steel plate on top of the melt and put the sprues etc on that so they melt back in without carrying their oxide skins to the bottom.
 

Rick

Moderator
Staff member
I recommend for what it's worth to not stir with a wood stick. I know, a lot of people do it but . . . The stick will char while in the melt, it can't burn because there is no air but as you scrape the sides the charred wood flakes off. While the charred wood is far lighter than lead some of it will be held in suspension in the melt because of the density of lead. No wood sticks under the melt for me thanks.
 

Mitty38

Well-Known Member
Just wondering how a toaster oven would work to pre heat an Iron mould. :headscratch:
Turn on upper and lower burner, set to 400 degrees, stick the mold in with handle sticking out. set for 20 min. and ding, you are ready. Just a thought, figured since my casting and Powdering will be done right next to each other. Might just double purpose the toaster oven. As I have not bought a hot plate yet. Only cast from Iron twice and know not to dip them, so last time just heated over the pot then used a rose bud attachment and some map gas, real quick.(carefully)
 
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Brad

Benevolent Overlord and site owner
Staff member
I have a feeling that would give you some warm handles.
I have a hot plate but rarely use it. I just place the mould on the edge of the pot while it heats. If it takes me a few few pours to get it right I don’t mind.
 

Winelover

North Central Arkansas
I casted for many years, before hot plates became the norm. Judicious use of a propane torch, gets the mold up to temp.
 

RBHarter

West Central AR
Pot resting during warm up works to some point . I haven't pin pointed it and gave up on it . I know it doesn't work in the brass HB/PB 462-420 MP or the sub 26 cal NOE AL 4-5 cavity moulds . Once up to temperature cooling on top of the pot and pouring helps keep them warm . 25s I've had good luck keeping running 22s not so much . The little 37 gr I had would go 5-6 pours an had to go back in the hot box the 62 gr is hit and miss but if it's atmospherically warm and I can really rush it with 750-775° alloy cool on the pot and shoot for 10-12 pours/min sometimes I can keep it running . NOE 5 Cavs AL .
I have a 4 cav Lyman 25 cal that I tried to get up to temp on the pot no luck there or with the 8 cav H&G .

I use an electric hot plate , #10 can with a doghouse door just big enough for the MP mould to slip into , over a cast iron kettle plate . If I plan on a long run in the 20# pot I'll put a pre load of ingots on top of can to take the chill off and reduce the tinsel fairy visit probability . It's not perfect but it mostly serves my needs .
 

Mitty38

Well-Known Member
So basically just keep on doing as I do until , or if I decide to get a hot plate. Still, I might give it a try next time I cast just to see. If I burn the handles, I will order some more wood,and we just won't mention the results.;)
 

Walks

Well-Known Member
Mitty38,
NOPE, if you screw up you HAVE to share.

Hotplate is a great way to preheat lead ingots. I like them to hang over about an inch. That way they can be grabbed with a pair of channel locks and dropped into the pot.
 
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Bliksem

Active Member
Only thing that comes to mind right off is if your also "heat soaking" the mold on the hot plate for the same 15-20 minutes.

One thing you could try as a test is segregate those very first pours at the get go and weigh them later comparing with the weights of bullets after 10-12 pours and later. If the mold is up to temp for decent fill-out but not quite to proper casting temp the early pours should be a tad lighter.

Rick,

I always heat soak my molds on a hot plate and the only thing different is that I wait 15~20 minutes after the temperature of the alloy has stabilized before starting to pour. I have weighed the first pours and done some weight-sorting but the variations are well within standard deviation.

I have observed that in cooling ternary alloy there are what appears to be dendrites forming within the still molten alloy. From what I have read the bonds formed in dendrites are quite energetic so my best guess is that the alloy needs to be at a high enough temperature for long enough before the alloy is truly evenly molten. This could explain what I am experiencing when I wait a while before starting to cast.

I'm an engineer but no chemistry boffin but what I do know is that waiting for a few minutes before starting to cast improves the outcome of my casting sessions.
 

Bliksem

Active Member
I recommend against scraping the bottom of a bottom-pour furnace with a wood stick. Stirring about halfway down and scraping the edges works well, but keep the sticks very dry or they'll sputter and pop lead. If you scrape the bottom you plant ash down there below the surface tension of the melt and it migrates to the spout causing inclusions in your bullets that aill drive you crazy until you drain the pot and clean it. Dumping sprues or ingots in does the same thing, the cooler, denser solid metal falls to the bottom and donates its oxide skin to the pour spout. The oxides can't re-enter the molten metal and float up because they were held at the bottom under the weight of the molten alloy before the sprue/cull/ingot melted in. I float a steel plate on top of the melt and put the sprues etc on that so they melt back in without carrying their oxide skins to the bottom.

Ian,

I used to use a piece of wood to scrape the inside of my pots but got bit once because of the moisture. Also, as you pointed out the ash will migrate and get to where it is not wanted or needed.

I now use only a stainless steel spoon to stir or scrape the pot. My flux of choice is pieces from beeswax-based lube, stinky and lots of smoke but works like a charm.

I had not thought of oxides on the sprues causing trouble but it makes sense. I like your solution to the problem.