Problem with alloy mix

[Bird]

Here is a strange one...........
I was casting with coww with no problems. Pot level was getting low, and down to about 4 pounds of lead remaining. I added 1 pound of lino and 3 pounds of coww, a mix I have used often, and never any problems with.
Pot temp at 720 deg. I had trouble with getting the lead to flow through the spout. Increased temp to 730,740 and 750, and the results were no better. I was casting outside, and the air temp had fallen to 50 deg. The spout started to clog, and on top of that the retaining bolt on the edge of the pot that keeps the lifting rod in place came out. I managed to drain the pot, and figured after 200lbs of lead through it, it was about time for a clean.
The cast bullets looked normal, and to my usual standards. Cast size and finish were the same as any other bullets I have got from this mold. I sized the bullets down from 0.311 to 0.310. These are the hardest bullets I have ever sized. I could feel every lube groove as it passed through the sizer.
Next day, back to the pot. It was as clean as a whistle. bolted it back together and fired it up with a couple of pounds of coww to start. Everything normal. Added some of the previous days mix, which melted at 523 deg, and looking normal. At 620 deg started to see lumpy dross on top of melt. Fluxed with beeswax, and it didn't really go away.
At 720 deg and a little flux, all looked normal, but did not cast well, and similar problems to previous session.
I dropped the pot temp back to 620, and took off about 3 teaspoons full of the dross off the top, until the surface looked clean and normal.
Got the pot back up to 720 and was once again casting perfect.
I never drain the pot completely even when finished casting. It seems I may have too much antimony in the mix???? I get all of my alloys in their raw state and smelt them myself, so the possibility of zinc contamination is very minimal.
what do you think my problem was?
Is there a saturation point for antimony in the mix?

[kmrra]

I cant help you , but I do have a stupid question , what is COWW mean , I see it refered to that here a lot

[Bird]

Clip on wheel weights

[MaryB]

Sounds like some zinc snuck in...

[Bzcraig]

Did your boolits weigh the same? Are you using a Lee bottom pour? Did you clean the spout? If you suspect zinc drip some muriatic acid and check for fizzing. Sorry can't help with the antimony question.

[Bird]

I will weigh the bullets in a little while. Yes, it's a lee 20 lb bottom pour. The pot did not need any cleaning at all. I saved the dross I removed, and somewhere here I have muriatic acid.
I suppose a zinc wheelwright could have got onto the mix. I smelt 20 lb at a time, and if a couple of zincs did get past me it would put 1% zinc into the mix, plus it may show up in other ingots somewhere in the future.
It seems strange that there is dross at 620' but not at the higher or lower temp.

[runfiverun]

grey and foamy/bubbly like?

[Bird]

Bullet weights are the same 157.2 to 157.4. Rcbs 30-150 go mold.

[Bird]

r5r,
no. Pouring at the nozzle started to get a bit thick and syrup like. Then ceased to flow. Cleaned nozzle with wire, and was good for a couple of pours. Lead wisps were setting up from below the spout.

[Bird]

One other thing I forgot to mention. While fluxing with beeswax, it was difficult to keep the lead from sticking to the teaspoon I use for stirring the mix. Also, the mix would not let go from the sprue plate on the mold, Had to pry it off the plate with the spoon. It is still doing that to a lesser degree with the most recent casting session.

[Nick Quick]

The temperatures you're talking about were taken with a thermometer or what the thermostat knob was reading. I ask as I used to have weird issues when trusting the pot thermostat without reading the temp with a thermometer. Found out that the thermostat was ill.

[Bird]

I use a thermocouple and pid controller, but pot temp is controlled by lee dial, and I just use the pid to read temp.

[Bzcraig]

The acid test will determine if it's zinc or not but I found one of my Lee bottom pours started acting like yours (slow pouring and I too use a PID) that was making me crazy, I had to keep hitting the spout with my little butane torch to get it flowing but if I stopped for more than maybe 10 seconds it would freeze up again. So I emptied the pot, removed the needle valve and looked closely down the spout and found there was gunk caked in there acting as an insulator. Once I got that completely cleaned out and it took some doing (previously I just used a small drill bit with pliers), lapped the needle valve all those problems went away.

[Bird]

I found my acid. Dross samples fizzed heavily after a couple of minutes. I guess it must be zinc.

[runfiverun]

try turning up the temperature some more.
it doesn't really sound like zinc more like copper or nickel.

[Bird]

R5R,
I tried higher temp, and it did not help. I had 4 dross samples from the past 6 months, and they all fizzed with the acid test. The oldest samples barely fizzed, and each sample got progressively worse. I think I had a small amount of zinc in a batch of lead, and because I never drain the pot, the zinc level may have stacked up over time.
I scraped off 3 teaspoons of dross/zinc, and added more ingots to the pot, and all is well again.
That bad batch was sticking to the sprue plate, and I had to cut the sprue really quick after pouring to prevent it from sticking to the sprue plate, to the point that it was starting to smear on the top of the mold blocks.
I think a little bit of zinc in a mix does no harm. The bullets fill out just as good as ever. I took a sample of my other ingots, and tested with acid. No signs of zinc, so I should be ok. I will test ingots from now on before I put them in the pot.
Thank you for your advice, I appreciate it.

[Oklahoma Rebel]

very interesting thread, this was the first time I have heard an example of the acid test being used in a real world situation. and now I know what to look for with zinc contamination, just in case

[runfiverun]

muratic acid will show zinc.

usually it doesn't muck up your alloy until it gets close to 2%.
the extra hardness is usually a clue. [and is why some use it in their alloy]
about the time the oatmeal shows up on the top of the pot your troubles really start.
getting the oatmeal off and a good fluxing with some sulpher will generally clean/strip the alloy of enough zinc to make it quite useful.
to get a bunch of it out, you turn the temp down, as the alloy cools the zinc will start to separate out and lump up on top.
you'll pull a bunch of the tin out of the alloy along with the zinc.

[gpidaho]

I'm thinking like RFR I've had a melt act like that when alloying with copper hard babbit. Any chance of copper in your mix? Gp

[Bird]

No, there was no chance of copper in the mix. The bad alloy was sticking to the sprue plate, which I am sure was a result of zinc and was effectively trying to hot zinc galvanize the sprue plate, and any steel or iron it came into contact with.
r5r, yes I agree. The zinc rose to the top of the pot at 600 to 620 deg f. If I did remove tin with the zinc, it made no difference to mold fill out. The bullets were well filled out and sharply defined. I may actually start adding a small amount of zinc to the mix, if and when i require harder bullets.
Okie Rebel. If zinc is present, submerge the sample in the acid and within a minute it will start to slowly fizz. After a couple of mins, it will fizz violently, and heat up the acid. The heat output is amazing.
I just cast a few hundred bullets and went through 12 pounds of lead with no more contamination issues.