how to tell if there is zinc in the alloy? verses other forms of contamination?

[kevin]

Hey guys!
I've got some alloy that is really causing problems. Its mostly stick on wheel weights and some range scrap(using for low pressure 38 specials)so not to sure how there could have been much of a chance of contaminating with zinc having sorted all the stick on W/W(anythings possible though). At my typical casting temp for some harder rifle alloys 650-700 it clogs the bottom pour spot in the lee 20lb pot. Also my typical "rifle" casting process is to only flux with new clean paraffin(seems to work well with the harder of the two alloys i have). That doesn't seem to flux the dross that forms on the top of this softer alloy very well, and it gets that look of tin oxidizing on the surface very rapidly(gold)and at these lower temps. The only way i have been able to get this batch of alloy to work is to run ridiculously hot 800-900!(not so good for the soft lee aluminum moulds!) and flux with saw dust and leave the insulating layer on top the whole casting session. The saw dust causes problems when i switch back to casting for rifle, and is out of a home depot chop saw dust vac collector so there likely cutting wood products that contain a lot of adhesives(chip board, MDF ect..). and i have determined the residue it leaves in the pot reeks havoc with my cooler temp casting calibers in the form of odd surface contamination on the finished bullets. so any time i switch its the old drain the pot and scrub out with a wire wheel on a drill and soap and water then let the pot dry for a couple days just to be safe. it a real pain in the ***

This "surface contamination is very odd it is a darker gray and is rite on the very surface of the bullet always near the nose of the bullet or the bottom of the mold(when held sprue plate on top)and it can in some cases be wiped of with a rag. On the other hand it is the reason i have a 50% throw back rate on my rifle bullets.

So a few thing going on there: perhaps could all this be due to zinc contamination? Anybody else fluxed with home depot saw dust and had it leave "residue" in the pot or on the bullets?

Thanks for everybody's say!
what a great forum still blows my mind every time.

Kevin

[Yodogsandman]

Try a search for "zinc acid test" in the white search box, upper part of this page to the right side. There's a few different ways to test for zinc that are described in the results of that search.

[lightman]

Home Depot sawdust is a mix of everything that they sell. It will have glue and resin from plywood and other stuff.

[Dusty Bannister]

Is there a chance that you have too much of a draft across the casting pot? I have issues when trying to cast below 700 degrees with the spout "freezing" to cut off the flow. I cast in an unheated shed, but know the temp due to a PID control. The next question is are you putting clean ingots in the pot? You comment about using a mix of sawdust from many materials. The fumes will not be good for you. Clean sawdust in the cleaning of the alloy to cast into ingots is great, but many prefer to keep things like that away from their casting furnaces. If it is not in the pot, it does not cause problems later.

[runfiverun]

your not getting zinc.
your getting too much crud in your alloy.
the stuff on top is oxides it will get in your alloy and can clog your spout.
the other stuff is carbon and it too can get in your alloy and clog the spout.

Dusty brings up a good point about the breeze.
it can cause more grief than most realize.
if your using a fan turn it around.

[Bent Ramrod]

I agree with RFR. The closer your alloy is to pure lead, the hotter it will melt and the quicker the oxides will form and build up. The yellow, blue and gray colors are the natural progression of the oxidation process. If you cast pure lead ingots for storage and later use, you will see those colors form as the metal cools.

If you had serious zinc contamination, your dross would not be your problem. Your alloy, at whatever temperature you raised it to, would look like silver oatmeal. It would not flow through a spout, plugged or not, or fill out a mould cavity.

[triggerhappy243]

I do all my smelting and melt/cast out of a large dutch oven.(because I am still learning...........). I have noticed that when I smelt and use the sawdust, wax, used oil....BLA-BLA-BLA.... There is a lot of black carbon sticking to the bottom and sides of the pot. If this is occurring in my pot, it is occurring in your pot too. Home depot saw dust is not helping much because of all the other foreign matter that is in it. So some here have stated.... many- many times, smelt in one pot, melt/cast in another. clean ingots is the start of good clean boolits. I will say this, I have a bottom pour lee pot. And because I still deal with this carbon in the pot, I am hesitant to cast with it til I can get the carbon issue under control. I recently cast a bunch of muzzle loader boolits for a fellow member. Boy, they did come out lookin purdy.

[kevin]

hey thanks everybody for the great thoughts. runfiverun i agree its defiantly a crud issue, i wonder about super filthy wheel weights sometimes some of the freebies i get are soaked in motor oil. wonder if that stuff actually gets removed when cleaning.

[runfiverun]

well it kind of does.
carbon is good for your alloy. [it helps everything in there bind together better]
it sucks to get back out though.
it will find the sides and bottom of your pot and stick there you have to pull it up, some will ride to the top on heat thermals but that would take forever to pull it all up.

if you have a bunch of the material I would re-run it in my cast iron pot and just keep working the gunk to the top then hitting it with wax and fire at a higher temperature.

[fredj338]

When I have had zinc in the alloy it gets kind of oatmeal looking & won't flow unless you crank the heat up to 750+. As noted, pure lead will want a higher temp than an alloy. I like clean sawdust for fluxing. Turn the heat up, flux with sawdust & toss the crud off the top, see if that doesn;t get rid of the bad stuff & get you back to casting temps.

[WRideout]

Cedar shavings for pet bedding might be preferable to sawdust from plywood, particle board, etc. After I smelt wheel weights, I can still find a fair amount of entrained crud in the ingots, unless I flux again before casting.

Wayne