aluminium sand casting porosity

[alucast]

Hi,
we have surface porosity problems with our aluminium castings.We use furane sand forour molds.The pores arise on heavy walls and on areas where cores are cast in.
In my opinion its a metal-sand reaction.
We found that if we modify with strontium the problem is way bigger than with sodium modification.
Is our sulphur level of 0,7% in our reclaimed sand a problem,or maybe our loss of ignition of 6%?
Thanks for any advise.

 

[sbi]

My first thought is , How are you venting the core gas?

also have you contacted the AFS yet, or go to

http://www.afsinc.org

for a start

 

[etch]

Have a look at your weather condition and amout of catalyst you are using.

I have experienced that on very cold days and if using heavy amounts of catalyst you get seurface porosity, is the inside of the sand mould when you break it open covered in small white spots or on the surface of casting?

Try using more reclaimed sand with lower resin content.

 

[alucast]

Hi sbi!
The core venting is not a problem as we get problemswith nad without cores.Strontium makes a big difference.

Hi etch!
U r right about the weather and the catalyst,it makes a difference.But we had the same additions last year and didnt have such problems.We run at 80-90% reclaimed sand and use HA and Eurotek(lately) furane binders.Any comment on the suppliers?

 

[etch]

do you coat your cores? try isomol 460.by the sounds of it you are casting lm6 or lm25?
i would guess your getting the sinks on LM6?
we use Eurotek and have very little problems.

one last thing check your blades on the mixer unit are clean and sharp. We have to do ours daily.

i have found that unsing sodium in some jobs leaves what i would call thumbprint indents in the metal casting, its not shrinkage just a localised depression.