Lead shrinkage and/or zinc contamination

[Pbaker]

Hi there,

New to castboolits, great group of people for sure!

I recently melted down some WW, Being careful not to melt down the zinc. I'm filling some lyman 4lb molds and have some quesins.

Is it normal when filling the entire mold (not just the cavities) to have some shrinkage? I'm also getting rough almost lumpy texture as well. All of the poured ingots are BHN 11-12 (pencil method) so I do not suspect zinc contamination. Any thoughts? I do not preheat my ingot mold, could this be causing the shrinking and rough texture?

[Walks]

Yes it is. The rough texture could be caused by oil in the mold or heavy rust on the mold.

You don't need to preheat an ingot mold. As long as the mold isn't cold as in below 50degrees.
But you're saying the mold itself shrinks ?

[Pbaker]

No the mold does not shrink. The lead will develop a depression or cavity in the middle of the ingot. This is with ladling the smelt. I changed over to pouring direct from the pot, and it seems to be better. I was just worried from the "lumpy texture" on the surface that it might be from zinc. But with my BHN being 11-12, I think it's ok.

[TaylorS]

Mine all shrink in the middle even with my stick on ww lead outside cools first and the molten middle fills any voids. Least that’s what I think happens.


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[JimB..]

I think the outside of the cast cools first and shrinks which sucks down the center as it cools more slowly. Nothing to worry about.

If you just barely melted the lead, to avoid melting the zinc, and then ladled it to the mold maybe it cooled enough in the process to get a little strange. Once you have the zinc out maybe run the temp up a little more and see what happens.

[jsizemore]

A drop or 2 of muriatic/hcl acid will bubble if zinc is there. Even with linotype pigs there will be some shrinkage in the surface. If the mold is cold and has oil or some preservative or sealant on the surface of the mold cavity, it will outgas and cause a rough surface.

[kevin c]

If you could post an image, it'd help to clarify exactly what you're describing as rough or lumpy.

My ingots will have a striated appearance on the sides, like layers of stone, that don't go away until the mold gets hot.

[Rcmaveric]

Lumpy texture is fine if it had antimony in it. Sometimes the melt gets to cool when its cooling or heating. It looks like a slushy when you mix it. Just turn up the heat a little. Fluxing it will help also. Nothing to worry about.

I also get s divot sometimes in my ingots.

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[cwlongshot]

As mentioned the divot is normal For softer lead and yea it shrinks some (heat expands Cold Contracts) harder allows will do this less and less to lino where ya barely see any divot.

[Pbaker]

I've been trying to upload a photo but I keep getting a error/failed message. I will keep trying.

[Bookworm]

There are a few tutorials in the stickies about posting pics. Sort of hard to follow on the first reading, at least for me, but after several readings and tries it became more clear.

[cwlongshot]

Your fine. Its normal. As stated probably something IN the mold leaving the texture. ALSO could be a “cold” melt.. tin makes lead flow could be lacking tin too. In any event none matters. Its normal and your good!

CW

[Sig556r]

A mild divot on the sprues should be ok.
Try pre-heating your mold to avoid to much temp diff.
Slushiness may mean a lot of things but fluxing may eliminate a lot of issues.
Good luck.

[Pbaker]

Thanks everyone for their input. It's my first time casting boolits, and while I am aware of the associated issues, I wanted to make sure I wasn't screwing up my lead.

[JonB_in_Glencoe]

Welcome to the forum.

That looks normal for COWW alloy, when pouring into a cold mold. If the lumps were larger, like cooked oatmeal, that is what zinc contamination looks like.

The small lumps are due to the alloy dancing close to the liquidus temperature as you finish pouring.
If your ingot mold was hot enough for the ingots to freeze many seconds after pouring is complete, then the ingots will look smooth and shiney.

[Pbaker]

Thanks again for all of the input. I still need to get a furnace and some molds. I've made about 300 pounds of ingots, so i have some serious casting to do this fall/winter.

Question, if I have lead that is 11-12 BHN now, and I add 1lb of linotype for every 5 lbs of lead, how much would that increase my hardness? I've read a lot of thread that haven't really said definitively. A lot of people say you can't cast antimony because of the melting temp, but I have found that to be untrue. Is it easier (or better) to add antimony vs adding linotype?

[JonB_in_Glencoe]

You can plug your alloy info into the alloy calculator to find your hardness answer.
http://castboolits.gunloads.com/show...oy-calculators

I'm not understanding your Antimony casting question.

[Burnt Fingers]

It's not easy to dissolve antimony in lead.

[Rcmaveric]

You can cast antimony. But it has a higher melting temp than you can acheive with normal leading melting equipment. Its also very toxic. I have heard of success stories but it wasnt easy from what i read.

Lead with antimony in it is a different story. It melts just fine and is now more toxic than usual.

For mixing. You can use the spread sheat but I like using a mixing cross. It looks like a pound sign. Google "alloy mixing cross". there are videos on you tube on how to use the mixing cross.

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[CLAYPOOL]

In "Jonb in Glencoe",s post there is a nice looking ingot. Where would i obtain such a mold..?