How to get aluminum blocks evenly heated?

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  • Last Post 21 September 2023
jtcarm posted this 18 September 2023

Seems like no matter how I heat the blocks, once I start getting good fill out, the edges of the lube grooves look too hot. They’re so heavily frosted, the edges are indistinct and look rounded, like they didn’t fill out completely, while the nose & base may not be frosted at all.

I pre-heat the blocks on a hot plate for roughly 45 minutes (or as long as a pot full of alloy takes to melt.)

I’m guessing that’s because the shoulders that form the grooves are where metal is thinnest, so that’s where the blocks get hottest.

I cast with either COWW + 2 or 50/50 Pb/COWW+2 with the PID on my Pro Melt 2 set at 730.

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delmarskid posted this 18 September 2023

I lower the lead temps and/or cast slower when this happens. I don’t preheat aluminum molds too often beyond dipping a corner in the pot.

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RicinYakima posted this 19 September 2023

 IMHO, the mould is too hot. 

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Aaron posted this 19 September 2023

Looks like you have zinc in your alloy. COWW are now made of zinc, not lead. I suggest purchasing some alloy from ROTO Metals, purging, and cleaning your pot and dipper, then try again with known alloy.

Some of my aluminum molds cast beautiful bullets after a single warm-up cast. Others after 6 casts. No preheating. I just start casting to heat the mold.

 

With rifle in hand, I confidently go forth into the darkness.

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  • Bud Hyett
Shuz posted this 19 September 2023

For handgun bullets, I  see no reason why they wouldn't shoot very well!

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muley posted this 18 September 2023

I just start casting and throw the bad ones back into the pot, happens quickly

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OU812 posted this 19 September 2023

You can try adjusting flow rate and distance of flow. Maybe pressure cast using your new pot or ladle. Some moulds can be difficult. How well do your other moulds cast? BTW my most difficult mould is a 30 caliber LBT mould...why I do not know. My 22 cal LBT mould cast bullets very easy without fuss.

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jtcarm posted this 19 September 2023

Here’s what I’m getting:

https://imgur.com/a/T4p8v34

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Rich/WIS posted this 19 September 2023

IMHO the bullets don't look frosted to me, mold may be too cold.  At the pot temp the alloy is certainly hot enough.  Have that happen if I try to fill too fast moving between mold cavities and don't let it fill with a good puddle on top of the sprue plate.  One thing that helps is, while the sprue is still molten, to lightly drop the mold onto a wood block, seems to settle the lead in the mold.

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jtcarm posted this 19 September 2023

I doubt it’s zinc. The COWWS were meticulously sorted and any floaters (only a couple) removed at smelt time. The Pb is from Rotometals. Plus I’ve cast plenty of good bullets from the straight COWW alloy.

Here’s what the look like after being wiped with a cloth:

https://i.imgur.com/oCsLzT4.jpg

I cooled the sprue plate a few times (with cavities full) a few times on a wet rag.

I suspect what might be happening is the steam produced by my hard-as-a-brick tap water is leaving mineral deposits in the cavities, causing the frosted appearance.

I’ll give the mold a good cleaning and start over sans water.

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TRKakaCatWhisperer posted this 19 September 2023

something to try.  two tests/experiments.

1. keeping alloy at the same temperature, lengthen the time between filling/emptying the mold by 5 seconds at a time.  Watch how the bullets turn out as the mold gets colder.

2. keeping the cycle time constant, turn off the heat in the lead pot.  Watch how the bullets turn out as the alloy temperature decreases.

 

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Glenn R. Latham posted this 19 September 2023

RicinYakima, is right, the mould is too hot, OR not hot enough!  Casting with WWs you will start getting these frosted/incomplete bands as the mould gets above its "proper" temperature.  If you keep casting real fast the bullets will become frosty looking all over, but be perfectly filled out as well.  You have to touch the sprue on a wet sponge too keep going in this condition and not smear the sprue cuts.  It's kind of hectic, but for quenching from the mould you'll get your hardest bullets.  But if you leave the mould open when inspecting the bullets you just knocked out, that will help keep the mould at its "proper" temperature.

Glenn

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OU812 posted this 19 September 2023

What brand mould is it ? I have an older Accurate brand mould that is very difficult. I believe the vent grooves were not adequate. He has since changed the vent groove design.

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OU812 posted this 21 September 2023

Thanks for the trough plate tip...I never tried it. Two minds are better than one.

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Duane Mellenbruch posted this 21 September 2023

 It might be helpful to see the base of a bullet as well.  Inspection of the base and the driving bands is pretty basic and can help indicate hot or cold alloy or mold.  Perhaps these bullets are as large as 45 cal, so could add heat to the mold rather rapidly and over heat the mold.  That would be reason to cool the sprue plate.  BUT, since the base is not shown, unsure if that conclusion is correct.  The steam produced from contacting the closed mold containing the cast bullets would be most like distilled water, leaving the chemicals behind on the sprue plate.  There is nothing to torce the steam into the cavities.  Remember the old method of leaving the last cast bullet in the cavitiy to prevent rust in the cavity?  Sort of the same principal. 

Do I see a damaged area on the nose of one of the bullets in the second photo?  As if it landed on a hard surface on the ogive?  Do I see a crack between the driving bands on one of those bullets?  That might be from the bullet sticking in the mold before dropping free.  This was not mentioned, but if you are dropping mushy bullets, it can happen. 

Can you clarify whether you think you have overheated the mold or the sprue plate?  I would not expect the sprue plate to be a problem and more likely the mold would be over heated, and at 730 F just slow the tempo and let the mold cool a bit between casting cycles.  The cooling between casting cycles will have a quicker response than changing the temp on the casting furnace.  Might be time to watch the clock and let it tell you what you need to do.

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