Lead sinkhole in cooled lead furnace - uh, what is it?

[ohland]

Uh, Dorothy, are we still in Kansas?

After the cast-a-thon this morning, I reloaded the Lee 4-20 up with 4 muffin ingots of WW, set 'er to 11 (mine goes to 11), and started to sort the last batch of 321297. Sorted, and sordid, and when everything was molten, I skimmed everything off. No matter if it was gold, it came off (no, there was no gold, let me assure you). I left it to cool down while taking off a few hours of quality time with my 7-30 fun gun.

Imagine my suprise to see the sinkhole at the center of the pot. No, it was NOT a result of dripping (it doesn't LEEk...). Notice the little lattice structures?
111761

Just like with baking corn bread, it pulled a little away from the side. If this was (yellow) cornbread, I'd be reaching for the butter and jam (yum!).
111763

111764
A side view of Mt St Helens after she blew....

Am I contaminated?

[Beagle333]

Normal.

[William Yanda]

Since heated lead is expanded, as it cools, it contracts. The center of the mass, loosing heat slower than the exterior, remains liquid after the surface has solidified. As it continues to shrink, it pulls in the weakest part of the surface leaving the little dimple. There, a technical explanation of normal.

[jsizemore]

Very hot before shutdown but normal.

[ohland]

Very hot before shutdown but normal.

Wow, it is such a relief to find out I am normal...

:drinks:

[el34]

(mine goes to 11)



http://www.youtube.com/watch?v=4xgx4k83zzc

[WallyM3]

Wow, it is such a relief to find out I am normal...

:drinks:

Well, that may not be the finding here (chuckle); you cast, don't you! We're all nuts.

[cdngunner]

IIRC the purer the lead the more pronounced.

[John Boy]

Looks like alot of dross in the lead. Did you flux it?

[ohland]

http://www.youtube.com/watch?v=4xgx4k83zzc

Why don't you make 10 a little hotter?

Then it wouldn't go to 11...

[ohland]

Looks like alot of dross in the lead. Did you flux it?

I did earlier. Boy, you put in too much beeswax and it will burn...

111856

After I put in the last ingots, I let it melt and then only skimmed it. I did not flux it since I'll do that when I bring the pot up next time I cast.

[konsole]

Stick-on wheel weight lead ingots will do that. I just sold alot of lead ingots and all the stick-on WW ingots sunk in more then clip-on WW ingots. Partly to do with pure or very close to pure lead is my guess. Try making some ingots out of pure lead, and then some out of 95%+ pure lead and you should see the pure lead ingots sink in alot more. Also I noticed that the larger the ingot the more it will sink in so a 100 pound pure lead ingot, that has a flat top, will cave in alot. If that 100 pound pure lead ingot was a perfect cube it would probably cave in atleast an inch is my guess. Maybe it varies with how hot the lead is or how fast it cools I dont know.

[bmortell]

my 20-1 from rotometals looked like that when it cooled, with the little valleys by the edge and had a cave in the middle

[Outpost75]

A bit of metallugy trivia, but when steel is poured into billets at the mill, you get the same thing. That is why in gun barrel grade steels the buyer will specify "ingot position" and require that the "one top" and "two top" cuts off the billet be discarded and remelted, before sending the cropped ingots to the rolling mill.

The cropped ingots will then be rolled into 30-foot "mill length" bars for shipment to the customer. Good incoming inspection practice requires also that ends be cut off a sample of the bars, as determined by a sampling plan under Mil-Std-414, and those cut-offs would be then sent to the lab to be checked with dye penetrant, mounted and polished for metallography, looking for any nonmetallic inclusions in the center of the bar (caused by elongation of any solidification shrinkage not cut off by the ingot crop), and at the same time having the chemistry and verified structure checked against the material certification provided by the steel mill.

If this is not done, it is possible for a "pit" or other defect to be elongated through the length of the bar along its center axis. In the old days of large-bore, blackpowder guns, it was expected that these elongations would be removed by the gun drill when the barrel blank was bored, and any that were missed would be caught when they failed in proofing.

In the modern era of lawsuits, nobody has faith in that system. I have returned 100-ton railcar loads of steel to the mill when the material didn't agree with the cert provided. I have also seen rifle barrels open up like a banana skin during an endurance test when heated in fully-automatic fire, and a nonmetallic inclusion or lamination happened to let go.

THAT is why the major gunmakers put additional restrictive requirement on gun barrel steel chemistry and structure, and also why after proofing the government requires at minimum magnetic particle inspection using the wet method with continuous circular magnetization, and critical strength parts, such as barrel locking extensions, rifle bolts and revolver cylinders, are both xray and ultrasonically inspected.

The small makers cannot afford to do buy quality steel in 100-ton heat lots and to have their guy at the mill to witness the cropping and follow their material from the rolling mill to the receiving inspection gate at the factory. So what is your gun made of?

[s mac]

Your cave in is like a boolit drawing from the sprue in the mould I would think.