What causes this casting flaw?

[old_haidouk]

Casting with my Master caster and Magma molds today and I had this happen a lot. The only thing I changed from what I normally do was the alloy, trying a new harder mix of two parts isotope and one part lyno, all nice clean lead. This problem has probably been raised before but it's my first time dealing with it.

Deep holes right at the edge of the sprue plate ring:

[stubshaft]

Sprue puddle not large enough allowing voids to form when cooling.

[old_haidouk]

I tried a longer pour with a bigger puddle and it didn't help.

[mpbarry1]

Hotter Alloy? maybe it needs to be warmer with the additional Antimony?

[Echo]

My guess is that your alloy isn't hot enough to get/keep the sprue plate hot enough. This would let the sprue puddle harden before the boolit interior, causing the void when the alloy cools & contracts. Or maybe you are not casting fast enough to get/keep the sprue plate hot enough.
Pure rationalization on my part...

[leftiye]

Maybe hotter mold to prolong liquid state. Maybe larger sprue hole so passage stays liquid while boolit draws from sprue puddle. Bigger sprue puddle as was said. Maybe different alloy with lower melting point. Got any tin in your alloy? Hotter melt maybe (as was said). Hotter melt usually means hotter mold, but with a mold heater mold can be hotter while melt isn't.

[fredj338]

I get an occasional hole in the base, just chalk it up to an air bubble. I run pretty much straight ww in my Magma molds, try fluxing the alloy more.

[geargnasher]

Trapped, super-heated air bubble from filling the cavity too fast, not swirl-pouring, sprue plate too cold, and poor venting from sprue plate possibly too tight or top vent lines in the mould plugged.

Try tilting the mould slightly handles-down and dropping the stream into the left or right edge of the sprue hole to set up a "vortex" within the mould like water does when flushing a toilet, this will help purge the air out the sprue hole rather than trapping it Also cast faster and make a larger sprue puddle to keep that sprue plate plenty hot. Adjust your stream size so the lead can settle as you fill, but not so slow you get rounded bases and poor fillout.

Gear

[Lloyd Smale]

my guess would be not enough heat. It looks like the base of that bullet has rounded edges too and the bullet looks to be shinny like it was casted a bit cold.

[HangFireW8]

Trapped, super-heated air bubble from filling the cavity too fast, not swirl-pouring, sprue plate too cold, and poor venting from sprue plate possibly too tight or top vent lines in the mould plugged.

Try tilting the mould slightly handles-down and dropping the stream into the left or right edge of the sprue hole to set up a "vortex" within the mould like water does when flushing a toilet, this will help purge the air out the sprue hole rather than trapping it Also cast faster and make a larger sprue puddle to keep that sprue plate plenty hot. Adjust your stream size so the lead can settle as you fill, but not so slow you get rounded bases and poor fillout.

Gear

Bingo. I put my money on not swirl-pouring. I get the same cavities on some molds when I drop straight in and the sprue plate overflows before I'm done counting the pour time.

HF

[captaint]

Just a guess, but you might try loosening up that sprue plate too. Gotta have good venting up there. enjoy Mike

[cbrick]

Alloy temp is probably fine, sprue plate temp isn't. A too cool sprue plate will do that right along with your rounded bases.

I pour a huge sprue puddle simply to add the heat to the sprue plate. The plate doesn't have the mass to hold heat that the mold does plus at least part of the time it's sticking out in the air and it will cool far more rapidly than the mold. Get and keep the sprue plate hot.

Rick

[old_haidouk]

I will try with a hotter sprue plate. The thing is that with the old alloy there were no problems. I kept things the same including temp. I have a laser thermometer that I use. I keep it at the same angle and always measure the same spots to get consistent readings.
Maybe this alloy needs a hotter mold and sprue plate. I upped the lead temp by 25 degrees and it didn't seem to help but this time I'll let the mold get hotter too.

[Walter Laich]

I get them sometimes when the flow is too fast. Adjust the flow down and they go away

[fredj338]

Bingo. I put my money on not swirl-pouring. I get the same cavities on some molds when I drop straight in and the sprue plate overflows before I'm done counting the pour time.

HF

The problem is on a Magma machine, tough to do anythbing but straight into the mold. I used to cast straight lino in mine, most of the time bullets are perfect, but th occasional hole in the base happens.

[HangFireW8]

The problem is on a Magma machine, tough to do anythbing but straight into the mold. I used to cast straight lino in mine, most of the time bullets are perfect, but th occasional hole in the base happens.

Hmm. You could make the hole oval, so it bounces off of one side and breathes through the other.

I've noticed that some of my molds tolerate straight-in fill while others don't. I suspect the difference is venting, but if a mold is otherwise working fine, I won't mess with it, it is easier to adapt my technique (and keep notes!).

Since the Magna defines the technique, improving the venting or enlarging the sprue hole might be in order.

HF

[geargnasher]

.....or filing vent lines in the top of the blocks at right angles to the handles across the center of each cavity, and "breaking" the edge of both mould halves where they meet on top to make a small "vee". Key word is "SMALL".

Gear

[btroj]

I have made that small "V" vent by breaking edges of the blocks. Works quite well.
Go ssssssssllllllllllllooooooooowwwwwww! It is darn hard to put that metal back!

[geargnasher]

Go even slower if you cut a vee across the blocks! One slip with the file and it's permanently ugly at best. I use the "draw" method and a padded vise for better control. Sitting down helps too.

Gear

[old_haidouk]

I called Magma today. They said to try lowering the alloy temperature(set at 690 right now). So I'll try that first, then I'll try getting the mold hotter.