Casting method vs diameter

[semtav]

I finally got my 410 Snover mold to drop bullets the diameter I wanted.
then I switched from using a bottom pour to a ladle pour and gained about .001.
Using WW + 2% tin @ about 750*

Anybody else experience this or have I done something else to cause this?

[Edubya]

Not exactly! I have noticed that a lower temp does increase the size. Maybe in transferring ithe molten alloy you're giving it a little cooling time and it results in a larger diam.
EW

[243winxb]

The bullet diameters and weights presented in this list
are based on the use of Taracorp’s Lawrence Magnum
bullet alloy (2% tin, 6% antimony, 1/4% arsenic,
91.75% lead).
Bullet diameters and weights will vary considerably
depending on the lead casting alloy used. This variation
can be as much as 1/2% on the diameter, and 8% on
the weight among the most commonly used casting
alloys. For example, a .358-158 grain bullet might
show a diameter variation of .002", and a 13 grain difference
in weight.
Of the most commonly used alloys, wheel weights (.5%
tin, 4% antimony, 95% lead) will produce bullets having
the smallest diameter and heaviest weight, with
such bullets running approximately .3% smaller in
diameter and 3% heavier than bullets cast with
Taracorp's metal. Linotype will produce bullets with the
largest diameter and lightest weights. This alloy will
produce bullets approximately 1/10% larger and 3%
lighter than Taracorp. Other alloys of tin and antimony,
with antimony content above 5%, will produce bullets
with diameters and weights falling between those cast
from wheel weights and linotype.
Alloys containing little or no antimony will cast considerably
smaller than wheel weights and in some cases
will produce bullets too small for adequate sizing.
Within the limitations given above, the weight and
diameter of a cast bullet can be adjusted by varying the
alloy’s antimony content.
The size and weight of bullets of a given alloy will also
vary according to casting temperature. Higher temperatures
will result in greater shrinkage as the bullet
cools, thereby producing a slightly smaller and lighter
bullet than one cast of the same alloy at a lower temperature

[lwknight]

+1 243winxb.
I have not been able to vary cast size by changing temperatures within workable limits.
Only when molds are entirely too cold I get small boolits or when everything is just too hot will the frosting be so bad that they cast significantly smaller.

Alloy is a major player. with a .429 mold I get 0.0015 larger casts with the 92-2-6 than with 20:1. Antimony actually expands as it solidifies. The higher the percentage, the more discernible it is. Tin content does not appear to matter other than the total lack of can cause poor fill out.

[303Guy]

I can think of one pretty good reason for hotter alloy casting smaller. it's quite simple really. Hot alloy will freeze on the mold surface almost as readily as a cooler alloy. Once the 'shell' has formed, the hotter and still molten interior will freeze and shrink the 'shell'. The cooler the interior is when the shell forms, the larger will be the casting. Make sense? :roll:

[NHlever]

I can think of one pretty good reason for hotter alloy casting smaller. it's quite simple really. Hot alloy will freeze on the mold surface almost as readily as a cooler alloy. Once the 'shell' has formed, the hotter and still molten interior will freeze and shrink the 'shell'. The cooler the interior is when the shell forms, the larger will be the casting. Make sense? :roll:

Though I have had some folks in the commercial steel casting business tell me that, I'm not sure I agree with it. My only thought about the lead alloys we use is that they expand as they get hotter to some point anyway. So, you are filling a cavity with a molten alloy that is taking up more space than it would be if it were cooler. In a solid state an alloy has a given size, and grain structure. I don't think there is any way a molten material can cool within a "shell" that would not cause voids of some sort. I think that any given alloy has a given shrink rate, and the temperature it was before cooling would not make a difference if the material wasn't confined in a mold. The mold will only hold a certain volume, and the hotter material just requires less weight to fill it. My thoughts only, and not meaning to call anyone wrong....

[semtav]

First thing I'm going to have to try is going back to the bottom pour and see if I can get back to my original Dia.

[303Guy]

I don't think there is any way a molten material can cool within a "shell" that would not cause voids of some sort.Ah! A very valid point and I was thinking just that as I was 'speaking'. True, but, the shell is still very soft while the core is molten at high temperature - meaning somewhat above freezing point - so as the core freezes from the outside in, it will contract the shell. As for voids forming? Yes, exactly but not always. I have had it when a pencil point thin 'tube' like void develops down the centre of the casting! I still have a sample - I should take a pic and post it.

P.S. Accurate info and observations can only be made when we know we will get challenged on what we say! So I welcome your post. After all, I could be wrong!:confused: Heck, I've been wrong often enough![smilie=1: But I like to think I learned from it after having been 'proved' wrong!:mrgreen:

[243winxb]

Scroll down to Shrinkage & Solidification shrinkage @ this link. http://en.wikipedia.org/wiki/Casting_%28metalworking%29

[NHlever]

303guy, I have seen those tube type voids in boolits, and didn't associate the type of shrinkage you talked about in creating them, but I sure guess it can happen that way!

"For the materials that have narrow solidification ranges pipes can be overcome by designing the casting to promote directional solidification, which means the casting freezes first at the point farthest from the gate, then progressively solidifies towards the gate. This allows a continuous feed of liquid material to be present at the point of solidification to compensate for the shrinkage. Note that there is still a shrinkage void where the final material solidifies, but if designed properly this will be in the gating system or riser.[13]"

This, of course is why we have vent lines in our molds, or other ways for the air to escape, and why some molds require us to keep the pouring spout conneted a bit longer than others. It certainly does appear that 303guy has a valid point. Sometimes there is more happening than we consider! :D


"

[45 2.1]

Something for you to look at:

Pour pressure and volume per unit time....................

See what the difference is between a ladle and a bottom pour.

You will find the bottom pour puts out less volume and pressure into the mold than a ladle does. Magma, RCBS, Lyman and Lee bottom pour pots were tested this way along with Lyman and RCBS ladles. Rowell bottom pour ladles don't count here as they can outdo any of the others.

[303Guy]

Thanks for the link 243winxb.

... narrow solidification ranges pipes can be overcome by designing the casting to promote directional solidification, which means the casting freezes first at the point farthest from the gate, then progressively solidifies towards the gate.That's interesting! My home made molds have a large funnel/sprew cutter that I keep very hot for that very reason. The molds also have more mass toward the casting gate so as to slow the cooling toward the gate. I have sort of perfected the mold set-up and casting technique but I haven't yet built the mold into a 'unit'. Once complete, I'll do a thread under Mould's. I only get those tube voids when the casting funnel is too cold.

[semtav]

cast some with rowell ladle @ 675* this morning, then dumped the alloy into my bottom pour. Came back this afternoon and cast some more with bottom pour @ 675. then cast some at 850.

I lost almost .001 dia when I went to the bottom pour and almost another .0005 when I went up to 850.

[lwknight]

Semtav, Is the bottom pour faster or slower than your ladle?
A bottom pour pot can be entirely to fast to control with a full pot or very slow with a low alloy level.
I have not compared pouring speeds before.

[semtav]

When I used it today, it was fairly full, so it poured fairly fast.
Really couldn't tell you if it was faster or slower than the ladle tho.

[stubshaft]

Thanks for the link 243winxb.
That's interesting! My home made molds have a large funnel/sprew cutter that I keep very hot for that very reason. The molds also have more mass toward the casting gate so as to slow the cooling toward the gate. I have sort of perfected the mold set-up and casting technique but I haven't yet built the mold into a 'unit'. Once complete, I'll do a thread under Mould's. I only get those tube voids when the casting funnel is too cold.


That's why Veral at LBT designed his sprue plates thinner and had a "reservior" to keep a large amount of alloy in the sprue. His theory was that the thinner sprue maintained heat better and the large pool of ally insured that as it cooled it would draw alloy into the mould eliminating voids.

[303Guy]

Here's my mold arrangement. My casting funnel/sprue cutter actually gets plucked off, leaving a hollow nose. Air escapes between the nose gate and the funnel which protrudes into the gate. As long as the sprue puddle remains liquid long enough, there are no voids formed.

http://i388.photobucket.com/albums/oo327/303Guy/ChamferBaseHollowNoseNosepour303.jpg

It takes two pairs of pliers to operate this thing and the alloy needs to be real hot to keep the funnel gadget hot enough.:roll: But the sprue and the boolit just drop out once plucked off.

[prickett]

So is it desirable, with a bottom pour, to pour as fast as possible?

Also, which is preferable for pouring height (distance from nozzle to mould)? Larger or smaller distance?

It seems a fast, high pour would result in greater pressure, resulting in more fillout?