Rando home made mold questions

[Drew P]

Fun project here been on and off for a while. These are 1lb diving weights. Fit onto rubber belt. I made the mold and have been trying to get the feel of it and it’s been sort of tricky. I’ve found that if I let it cool enough for safe and smooth eject then the mold can be too cold and not fill properly on next one. But if I run it hotter by increasing pace, lead temp, then I find that the large slug (1lb) takes so long to cool anyway and if slightly too warm on exit they can tear and crack. I’m dropping into water bucket.
So I feel like my main tool to implement to help me would be a fast way to check temperature of the mold but my ir laser gun hates any kind of metal. If I paint the mold stove black it might help but that would also reject heat faster and I don’t know if I can trust the reading then either. Would be worth a try I guess. Any other suggestions I can try?
I’m also looking at the sprue location and how it might affect filling.

Any suggestions?

[Winger Ed.]

Get closer to a pure Lead alloy, that should stop the cracking.

[country gent]

Several things might help. It looks like your mold is aluminum so heat retention is low to start. It also appears that there isn't a lot of mass to the mould ( looking at the cross section in the one picture) so that also promotes fast cooling.

You might try a makeshift mould oven and set blocks in it between pours, or if your pot is big enough dip it for a few seconds in the molten lead to pre heat before filling it. This may allow a lower lead temp and still have good fill out. The other thing you might try is adding more mass by welding or bolting some flat material around mould on 3 sides to help hold heat. Gere a less conductive metal like brass or steel might help. Even a coat or layer of clay baked around it might aid holding heat

In big moulds cooling time is longer than a lot think for the cores. I used to cast 10lb counter weights for Freeland scope stands. this was an open topped mould and once filled it took a while to cool the outside would look good but the core was still molten or soft.

[Drew P]

Good ideas. I tried painting the blocks flat black on top and that did help me get reliable readings from the ir gun and I believe with some experiment this will get me in the right pace. Much tighter range than bullet casting I’m finding! The cool time for the weight is long enough that the mold is spending too much time cooling off also, and then isn’t hot enough going into the next pour. So I need to let it cool to right around 440-450 before opening, and then get the blocks back into pour before it goes below 415 or so. So it’s pretty picky I’d say! But got some good pours. I’ll try some almost pure lead.

[rancher1913]

all the diving weights I ever used were poured in an open top mold similar to a ingot mold, they had two slots for the belt to weave through.

[Slugster]

I like your contoured design a lot better than the very uncomfortable square ones I used when I was an active diver. Wetsuit would soften the feeling of the square weights, but wearing a suit in warm water is a no go, at least for me. Never thought to question the design back in the day, just accepted that the weights were uncomfortable and went with it.

Lesson of the day for me: Anything can be improved.

[Dragonheart]

No lead block diggin in for me! I always used a padded weight belt made out of wetsuit material and nylon belt material. It had velcro closure pockets that would hold block weights or in a pinch fill the pockets with rocks or coral sand.

As far as your mold I would spray it with liquid graphite (it's flat black) so as soon as the lead hardens it will release from the mold. I haven't cast weights in a long time, but rancher is right it was just a square block with two vertical pins to allow the belt to weave. I think I still have a weight mold or two.