Non-Chemical how to know how much flux to use

[ericrm]

i have tryed to melt with flux computer components and the result was realy not what i expected... how does one calculate the amount of flux to use? is it by the ash weight, the metal weight, the expectedoxide weight? do it only mater? how much fluorspar is realy needed to tin flux normally, i have put 3/4 pounds fluorspar(a big spoon at the time) for about 1/4lbs of borax and it was still honey like and full of beads...
starting material was ~ 1lbs of incinerated chips/mlcc/pins/copper plate, no fiber glass. how do i calculate the amount of borax to use?

 

[cnbarr]

Eric, did you use sodium carbonate in your flux mix? Sodium carbonate will help your flux mix to be less viscous.

 

[butcher]

Way too much fluorspar a tiny bit goes a long way, if it is needed at all.

Looks like your melt was to the point of foaming over, trapping beads in the foam and slag.

You may have to experiment with the flux ( combination and mixture of ingredients and amount of each) in your melts to get the right mix, to get the properties of the melt, and the reaction right.

You also may need a collector metal, in your flux.
The chemistry of the melt can be important, depending on your goal of reducing or oxidizing the metals involved in your melt.

I would start off with a basic flux, like the the one in Hoke's book on page 219, and adjust it as needed, adding other flux ingredients to change its chemical property as needed to get desired results, powdering it and the material together well mixed before the melt, double or even triple the amount of flux compared to the amount of material you plan to melt.

Not only having the melt fluid enough for metals to join or combine with a collector metal (which may need a reducing flux depending on metal used), but also keeping the mix hot enough and long enough for metals to combine into one lump which can sink in the crucible, or when poured off into a warmed cone mold.

 

[ericrm]

Eric, did you use sodium carbonate in your flux mix? Sodium carbonate will help your flux mix to be less viscous.

no i didnt,i was thinking that sodium carbonate act as a reducing agent in the flux and i was trying to get as much oxide as possible in the slag.

Way too much fluorspar a tiny bit goes a long way, if it is needed at all.

Looks like your melt was to the point of foaming over, trapping beads in the foam and slag.

i doubt it because it wasent expending at all in the crucible. might be a stupid question but could it be because i used too much oil in the mold?

could i reuse some of the slag as it contain too much of fluorspar on my other batch , or is fluorspar on time only?

i have been looking around the forum and google but i dont find any number anywere...

 

[Lou]

Too much oil in the mold is dangerous because it can cause spattering. That means loss of values and a re-melt if you're lucky, or a bad burn, particularly if the slag gets on you.

Let me tell you this: molten slag is far more injurious than any molten metal. Metal usually doesn't stick to skin and spalls off, but viscous slags are bad news, especially if they are full of carbonate!


Some advice:

take a small (10 g sample) and mill with your flux mixture, then try out in a muffle furnace with proper ventilation.

Material with a lot of carbon present will always present difficulties in a static melting furnace because the gas evolution suspends values in the slag (hence use of fluorospar/nitre/carbonate to adjust viscosity) and prevents proper fluxing. Conventionally, these are done in big, rotating barrel furnaces to increase the available surface area.

 

[ericrm]

thank you for the advice