Cobalt Blue surface dross?...

[Tom83706]

Hi Folks!

I melted my first batch of wheel weights in a new SS pan (6 qt?) with pour spouts. Great learning experience and good results weight wise of lead recovered. However, there was a very persistence cobalt blue surface film that no matter how many times I skimmed, it remained, persistently. I allowed the temp to jump up to 1000 at one point. I'm wondering, have I somehow contaminated the batch? What might have caused this? Please see attached pix. It is a really cool color, but I'm thinking I messed it up.

Another thread suggested using sulfur to floss, might this remove the cobalt color impurity? The standard flossing procedures (candle wax, paper towel, flossing agent) did not work. Is this even something to be concerned about?

Will I need to remelt/re-skim at a lower temp? Have any of you experienced this? How to avoid in the future? Please advise, as I have more weights to smelt.

Thanks in advance for your input. Keep 'em smiling... Tom

[Rickf1985]

The color is simply because you got it so hot. I never, ever smelt wheel weights above 700 degrees. That way if there are any zinc weights I missed they will just float to the surface and can be removed and they will not melt into the alloy. The mess you have stuck to the side of the pan and that separate lump in the second pic appear to possibly be zinc. are you sure you got all the zinc weights out before you did this smelt? At 1,000 degrees the zinc would definitely alloy into the mix. But the color is just the temp. What you are skimming off with the color is the tin that has separated out from the excess heat. You needed to add wax to reduce it back into the melt. I would not throw out the dross you have there. It is probably mostly good lead if you were skimming nothing but the color off. Add it all back in and flux it with sawdust and then with beeswax and you will be surprised at hoe little you have left over. As far as any zinc, let it cool slowly and watch it very closely. As soon as the zinc starts to harden on top of the lead skim it out. The zinc will harden at around 740 degrees and the lead will not harden until around 650. This is not the absolute perfect way to get rid of zinc but it is surely the easiest.

[kevin c]

This explained it for me:

https://castboolits.gunloads.com/sho...e+interference

[ulav8r]

Flux your lead and floss your teeth. You will get better results.

[6622729]

Just to help with some words, you will clean some impurities from the melt with sawdust and beeswax as flux. The junk you skim off is dross. It’s easy to slam the worlds together to get floss. Not picking on you in any way. As other said, I agree the pot was way too hot. Also agree with trying to skim out potential zinc contamination as the pot cools. Try fluxing the melt real well first down around 690-700 degrees to make sure the antimony and tin didn’t separate. You can be surprised sometimes how much goes into solution when you were thinking it was junk in the melt.

[Tom83706]

The color is simply because you got it so hot. I never, ever smelt wheel weights above 700 degrees. That way if there are any zinc weights I missed they will just float to the surface and can be removed and they will not melt into the alloy. The mess you have stuck to the side of the pan and that separate lump in the second pic appear to possibly be zinc. are you sure you got all the zinc weights out before you did this smelt? At 1,000 degrees the zinc would definitely alloy into the mix. But the color is just the temp. What you are skimming off with the color is the tin that has separated out from the excess heat. You needed to add wax to reduce it back into the melt. I would not throw out the dross you have there. It is probably mostly good lead if you were skimming nothing but the color off. Add it all back in and flux it with sawdust and then with beeswax and you will be surprised at hoe little you have left over. As far as any zinc, let it cool slowly and watch it very closely. As soon as the zinc starts to harden on top of the lead skim it out. The zinc will harden at around 740 degrees and the lead will not harden until around 650. This is not the absolute perfect way to get rid of zinc but it is surely the easiest.

Thank you Rick, great info and explanation. A couple more questions: Since I mistakenly heated the initial batch to approx. 1000, can I remelt the ingots to 700, floss, skim and repour them with good results? Will that initial high temp adversely affect the lead's physical properties upon remelt/repour? How do I remove the blue lead from the cooking pot and utensils? And, If I do not remove the blue lead from pot/etc., will it taint the next batch?

I will need to keep a much closer eye on the temp and reduce the gas flow into burner - learning curve strikes again....

Thanks to all for your replies. I sense this will be a great forum moving forward, the response time was quite impressive, thanks for that!!

Keep 'em smiling.... Tom

[Tom83706]

Thanks 6622729, good info, and good assistance with woids - juxtaposing one with another and jumbling 'em up is my forte...T

[Tom83706]

Very good stuff!! Thanks Kevin C!! And thaks to all who entered info into the that initial stream. T

[Tom83706]

Got it, thanks ulav8r! My teeth didn't respond well to the fluxing....

[Rickf1985]

Tom, No harm has been done to the lead. Be careful with fumes at those high temps. It has been said for a long time that lead will fume at 1,000 degrees. Of coarse there is a ton of argument against that but I prefer to go with it and stay safe since there is no need to go that hot anyway. That all said, yes, by all means toss it all back in the pot and remelt it but keep it at 700 degrees. Dump some sawdust in there once it is up to temp and stable and mix it in with a stick. I use old furniture legs since I know they are dry. Do NOT use a branch right off a tree! you will have a fast introduction to the tinsel fairy as the moisture laden branch goes under the lead!!! Let the sawdust burn down to ash and stir that ash into the lead quite well and then gently skim off just the dirt, no metal. Then drop some beeswax in if you have it. If not, candle wax will do. Beeswax will usually not flare up but candle wax or paraffin will so be ready for it to flash into flame. Stir it in very well. This is where welding gloves come in handy because you want to get the wax mixed in good before it burns off. What you will be left with after all of that should be light gray dry ash as the only dross. Skim that off and maybe hit it again with the wax and then you are done. You will be amazed at how much of that stuff you pulled off before is now back in the alloy.

[JonB_in_Glencoe]

a good start, hope you had fun.

The blue is just oxidation, nothing to worry about removing, next time you render some scrap, it'll flux right in.