Heat is, still, my friend...

[prs]

Over the winter lull months, I read on this forum some very good reasons NOT to cast too hot; chiefly depleation of tin through oxidation and oxidation of lead. Although I have been a fast and hot-frosty caster for years now and have not been overtly aware of tin loss or lead oxidation problems; I decided to heed such advice on next opportunity.

Last week a new mould arrived on the brown truck, the Lee 6 cavity 401tl-175-SW (if I recall the descriptor correctly). Very nice mold that needed very little correction proir to use (relieved the edge of the spru cutter slightly). Casting with lead plus 2% tin and 4% atimony and probably a scant trace of arsinic I got the 20# Lee pot up to its, full temperature, then backed it off to setting #6 and went for cup of Joe before casting. Returned and took a temp reading of 620F and mold was too hot at 750F, but air cooled quickly as I lubed the pins and final fluxed and added my kitty litter to the top.

The mold cast really well, but I was getting some faint wrinkles on the preliminary drops on a few boolits, but not specific to any given cavity. I started keeping boolits after about 6 fills and had to pick-out a cull or two on many drops. I experimented with bottom pour rate and angle and spru volume, no real improvement. I jacked the heat up to 700F (almost wide open) and got perfect boolits every time. They are frosty again, but I kinda like frosty. So, I am a bad boy. I tried to do right, but my old ways got the best of me. I may be losing tin though; what do ya think?

My casting time to depleat the 20# pot is not very long with even just one 6 cavity mold, so is there really enough time to lose much tin? My clay based oil dry or kitty litter covering the top might isolate the hot alloy from the air anyway; NO, YES?

I may try to be good again someday, honest I may.

prs

[rbertalotto]

Good questions.......I'd also like to hear the answers.

[geargnasher]

The answer is very simple. THE MOULD WAS TOO COLD BECAUSE YOU WERE CASTING TOO SLOW.

Mould temperature is what controls boolit fillout and quality, NOT alloy temperature. Pouring overheated alloy into a mould that's too cold works sometimes, but is a band-aid at best.

Frosty boolits can be made from a 600 degree alloy if the mould is hot enough. Wrinkled, shiny boolits can come from a 900 degree alloy if the mould is too cool. Try it, you'll see what I mean. 96/4/2 is a perfect alloy to exemplify this.

That being said, and it is meant in a general way, in the particular scenario with a six-banger draining the pot fast, and using a barrier layer, I see nothing wrong as long as it made good boolits. 700 degrees isn't hot enough to make a tremendous amount of dross, especially with a barrier layer of kitty litter on top, so no big deal really, but you might find that if you were using a two-cavity iron mould that overheats easily, you would benefit from turning the pot down to 650 or so so you don't have to wait as long for the sprue and boolit to cool, and not get over-frosted, pitted, sandblasted-looking boolits.

Gear

[Calamity Jake]

Take your alloy to its boiling point and you MIGHT boil off the tin but I don't think so.
Unprotected, tin will oxidize on the surface, if left undisturbed it can not oxidize further
as the oxygen can't get to it. The kitty litter on top makes a good insulator/barrier and
stops oxidation along with anything else laid on top that won't burn away

I never cast under 700° as I to like forsty. Seems that all my 6cav alum. molds Lee or otherwise needs 750-775° to produce good boolits and there are allways culls in the batch.

I started using kitty litter after hearing about it on the old ammio board many years ago and
have never looked back. I add the sprus/defective boolits thru the litter, when it is time to add alloy I put it in the pot thru the littler let it come to temp stur with a stick(flux) and go back to casting.

[prs]

The answer is very simple. THE MOULD WAS TOO COLD BECAUSE YOU WERE CASTING TOO SLOW. Gear

LOL Well, I get the best harmony if I wait at least long enough for the spru to freeze. If you could see me cast, I doubt you would think slow. I typically blast through 60# of alloy by half time of a football game using two 6 cavity 250gr moulds. This session was with just the one mould and I was pushing it in regard to letting the spru freeze. Even at that, it seemed to me I was piddeling around looking at boolits for flaws and such because the alloy was not freezing quickly.

Actually, I wait just long enough to notice a tiny little resistance to the spru cutter plate upon opening, probably about 15 seconds after the last cavity is poured on this occasion. But, when it takes over about 15 seconds I do place the mold blocks down on a heat sink instead of upon plywood; so maybe I am letting it get too cool. Now, when I came back from my coffee break before starding to drop boolits, my mould was way too hot, I filled it and the lead remained molten for a very long time and still smeared the top when I opened it after for what seemed to be a very long time. I can measure the mould temp, should it be (a.) the same temp as the alloy, (b.) X degrees lower than the alloy, or (c.) just experiment until you find the sweet spot. Most of Life's experiences seem to follow foil (c.).

Gear, I appreciate your input and now I think it was your previous posts that inspired me to cool the alloy temp a bit. I will try again next time, gonna need some PRS 454-250-RFs before too long. Instead of pre-heating on top of lead pot, I may try a hot plate so I can get mould hotter than alloy, at least to begin with.

prs

[geargnasher]

CJ, why do you STILL think that pot temperature controls the "frost"? Mould temperature controls whether the boolits are shiny or frosty. Period.

Please read this, you might find it helpful: The fact that the rate of tin oxidation increases as a function of temperature has nothing to do with your belief, it has everything to do with the laws of physics and chemistry. The oxygen barrier will tend to eliminate the drossing, but it will NOT eliminate the fact that any tin in the alloy will be rendered ineffective as a surface oxidation barrier to the liquid stream as it fills the mould. THIS is why we add tin in the first place, and at temps above about 750 degrees the tin loses it's ability to control the instantaneous surface oxidation of the stream, and this makes boolits even harder to get to fill out properly.

I've analyzed dross skimmed repeatedly from an intentionally overheated pot of WW alloy with 2% tin added, and reduced the resulting dross back to elemental metal, it contained over 80% tin. It took about half an hour to reduce the tin percentage of the alloy to 1% plus what little was in the WW to begin with, the pot temp was maintained at 850 degrees. That might not sound like much, but if it can sure make a difference in boolit hardess, ductility, and the way it shoots from the beginning of a session to the end.

Gear

[geargnasher]

LOL Well, I get the best harmony if I wait at least long enough for the spru to freeze. If you could see me cast, I doubt you would think slow. I typically blast through 60# of alloy by half time of a football game using two 6 cavity 250gr moulds. This session was with just the one mould and I was pushing it in regard to letting the spru freeze. Even at that, it seemed to me I was piddeling around looking at boolits for flaws and such because the alloy was not freezing quickly.

Actually, I wait just long enough to notice a tiny little resistance to the spru cutter plate upon opening, probably about 15 seconds after the last cavity is poured on this occasion. But, when it takes over about 15 seconds I do place the mold blocks down on a heat sink instead of upon plywood; so maybe I am letting it get too cool. Now, when I came back from my coffee break before starding to drop boolits, my mould was way too hot, I filled it and the lead remained molten for a very long time and still smeared the top when I opened it after for what seemed to be a very long time. I can measure the mould temp, should it be (a.) the same temp as the alloy, (b.) X degrees lower than the alloy, or (c.) just experiment until you find the sweet spot. Most of Life's experiences seem to follow foil (c.).

Gear, I appreciate your input and now I think it was your previous posts that inspired me to cool the alloy temp a bit. I will try again next time, gonna need some PRS 454-250-RFs before too long. Instead of pre-heating on top of lead pot, I may try a hot plate so I can get mould hotter than alloy, at least to begin with.

prs


Like I said, I don't think that in your particular instance here you were necesarily overheating the alloy. I do maintain, however that if you were waiting 15 seconds for the sprue to freeze, you were waiting too long. I cut my sprues, especially with a six-banger with the weak sprue cam handles, just as they get firm enough to not smear molten lead no the blocks, that means ONE second before they solidify.

If you were waiting fifteen seconds just for the sprue to freeze, your mould is cooling off the whole time. Now, if you are putting alloy that's way too hot in that mould, and cast like a demon (four pours a minute for 5 minutes!!!!) you will overheat the mould. You should be able to make at least three pours a minute with 650 degree metal until the pot is dry and never have to quench the plate, and get nice, satin, fully-filled out boolits the whole time.


Most aluminum moulds take about three to four pours a minute from 650-700 degree ww alloy to maintain a good MOULD casting temperature. The brand, style, configuration, and boolit type of the mould all change the ideal mould temperature, but the alloy temperature should be figured on about 100 over full liquidus for the most casting productivity, and least amount of drossing if casting in open air, LIKE LADLE CASTERS DO. If you ladle, you want the alloy as cool as you can get it to still work, and keep the mould hot by casting fast, since this reduces the dross formation in the pot and reduces the fluxing/oxide-reduction intervals greatly as compared to running a hot alloy.

Gear

[prs]

Gee, I've only been using the clay based oil dry granules for about 10 years or so.


Gear, I will try again one of these days and report back. I will record the alloy and mould temps.

One thing that might have helped significantly reduce the culls has to do with this pot having a slight case of Lee-arrhea. The spout tends to have a little bead of alloy hanging off of it at the beginning of each pour. That droplette has to be cooler than what is in the pot. I started opening the spout and letting the alloy hit upon the heel of the mold before guiding it into the first cavity, keeping the pour going as I moved to other cavities and letting spru waste "grow". Now, if this really did help (I believe it did); it could support Gear's methodology as that bit of extra alloy would have added to mould heat. On the other hand, it could support Jake's theory as the cooler alloy drip may have been the source of the slight wrinkle tatoo I was seeing.

prs