A real dumb question

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  • Last Post 29 July 2017
the_buckshot_kid posted this 28 July 2017

Ok just started casting for .44 mag. What I'm getting in the pot is an excessive amount of "powder" on the top of the mix. I'm assuming this is not dross so I'm continually mixing it in. Is this tin coming out and why would it keep doing so?

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TRKakaCatWhisperer posted this 28 July 2017

Not tin.  (Tin will NOT separate.)

Likely an oxide - of whatever is in the alloy.

If it is light weight, I spoon it off and keep a sprinkle of borax on top.  Some folks use sawdust or kitty-litter to keep the alloy from oxidizing.

 

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Larry Gibson posted this 28 July 2017

It is simply an oxide of the alloy.  It will flux back in.  You will get that whether using a dipper or a bottom pour.  The higher the alloy temp the quicker it forms.  If you're using a ternary or binary alloy and the alloy temp is above 725 it is too hot.  I cast with the alloy at 710 - 715.  The oxide really doesn't hurt anything and I don't worry about it as I'm casting.  It gets fluxed back in when I add more alloy to the pot.

 

Some think it is the tin separating out but it is not.

 

LMG

Concealment is not cover.........

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the_buckshot_kid posted this 28 July 2017

I had no clue what was going on but I kept mixing it in. I noticed it forming rather quickly so I guess temp is too hot.

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RicinYakima posted this 29 July 2017

Especially if you are trying to rely on the thermostat! They vary up to 150 degrees between on and off. Plus the scale is just a WAG to begin with, they are not accurate enough to use. Get a thermometer or a PID unit. 

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onondaga posted this 29 July 2017

the_buckshot_kid, you said,
"Ok just started casting for .44 mag. What I'm getting in the pot is an excessive amount of "powder" on the top of the mix. I'm assuming this is not dross so I'm continually mixing it in. Is this tin coming out and why would it keep doing so?"
Either droz or Tin oxide can be a powder of varying colors. There is a good way to tell if the powder is Tin Oxide: A high heat reduction fluxing will return the Tin Oxide back into Tin and alloy it with your potful.
Droz is Lead Oxide and does not as readily return to the pot as Lead..
Reduction fluxing requires enough petroleum or carbon based flux and enough heat for the flux to flame. To reduce Tin Oxide back to Tin in your pot, work under the flame only and add more flux if your flame stops. Use a long spoon with a curve close to the curve of your pot and preferably a wood handle to protect you from heat.. Spoon the dust to the edge of the pot under the fire and rub and push it below the surface while rubbing aggressively against the pot side to break down the particles and the Tin will separate and go into alloy. A  1/4" pile of dust should take 5-10 such separate brisk rubbings under flame to reduce as much as you can back to alloy.. Reduction fluxing with bullet alloys takes at least 750 degrees F or hotter to flame flux and reduce.
When you have gotten as much of the Tin as you can back into alloy, immediately reduce pot to casting temperature, skim and cast.
Gary

 

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onondaga posted this 29 July 2017

the_buckshot_kid, The Tin will keep coming out if your temperature is too high. That is why you should reduce temp to the lowest temp you can cast well at after fluxing. Lead and tin alloys, even with antimony begin oxidizing the Tin at about 725 degrees F. When you run hotter the rate of oxidation increases. An example: cast at 800 degrees and oxidation is so rapid you can't keep up with it and that may be the problem you are addressing.

It is helpful to determine the ideal casting temperature for your alloy, use a thermometer and have a very fluid clean melt in your pot. disconnect power and monitor melt for the very first sign of solidification on the surface of your metal. Record that temperature. The ideal casting temperature for that specific alloy is 100 degrees hotter than first solidification. If you cast well with a nice rhythm of 3-4 drops a minute your bullets will also improve.

Don't put sprue and runoff back into pot until starting a new potful as that dramatically effects alloy temp in the pot and effects casting quality. I cast with my Lee 4-20 until it is down to about 1.5 pounds. Then I start a new pot with sprues and new ingots and a reduction fluxing. The Lee is a bottom pour and I don't flux at all after initial fluxing of the full pot. I run it down and start again. That is a bonus with bottom pour casting, the crap on the top doesn't matter after a clean start, just cast. Actually that is why I don't ladle cast anymore also. Fluxing can be a labor ladle casting and subtracts fun.

Gary

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