Micro Balls of the air

[mimoletti]

Although I have followed the instructions of this video : [ame]http://www.youtube.com/user/myfordboy#g/u[/ame]
I have noticed in my metal castings in alloy aluminium of the micro balls of air, I would like to know your opinion around this problem.

Thanks Massimo Imoletti.

 

[lazylathe]

There could be many problems to the answer you are looking for.

If you could post some pictures that would help.

1- your sprues may be the wrong size
2- they may be in the wrong place
3- your vents may be the wrong size or in the wrong place
4- your metal may be overheated causing porosity
5- mixing different kinds of metals may cause this.

Pictures of your process would help!

Andrew

 

[mimoletti]

Here are:

 

[lazylathe]

Are you talking about the surface finish?
If that is the case you need to use a finer investment/sand for casting.
The finer the material the better it packs together and will give you a smoother casting.

Also if the alloy is too hot when you pour it degrades the investment/ casting sand surface.
This also results in a rougher finish.

Hope some of this helps!

Andrew

 

[chucketn]

I am just getting into casting Aluminum. What is the proper pouring temp of the metal, considering sand is properly mixed and moisture is correct? That is if I had a way to measure...

Chuck

 

[lazylathe]

660 Degrees C or 1220 F

We have a special laser temperature gun that measures the surface temp of the metal.

Andrew

 

[johnthefish]

When I started years ago before You Tube or even the internet,my castings were riddled with air bubbles when I machined them. I later realised my greensand was far too damp. With a bit more Bentonite and less water it fixed the problem immediately. You can also degas with washing soda .. See Myfordboy. Best of luck.Don't give up.

 

[ShedBoy]

You are doing better than me, mine are rough as guts compared to them. The moist sand seems to be my problems, as for temp I got a thermocouple of fleabay for $34 from china and it goes to 1500°c.

Brock

 

[Orrin]

Are you degassing the molten aluminum before you pour? If you are not, you are likely to get the bubbles that are plauging you. Molten aluminum loves to absorb hydrogen which comes from the breakdown of water. When the aluminum solidifies it can no longer hold on to the hydrogen so it forms the bubbles. In other words, hydrogen dissolves in molten aluminum; but, it cannot stay dissolved in solidified aluminum.

Do a "Google" search for degassing aluminum. You'll find out all you need to know, that way.

Orrin

 

[bezalel2000]

I am just getting into casting Aluminum. What is the proper pouring temp of the metal, considering sand is properly mixed and moisture is correct? That is if I had a way to measure...

Chuck

A cheap galvanometer garden moisture indicator is a good start for the novice to check sand moisture content
Readily available on ePay the one below is overpriced IMHO

when it indicates "Good" in lightly compressed moulding sand it is good for molding
It also tells you "Too Wet" & "Too Dry"

http://item.mobileweb.ebay.com/viewitem?itemId=270763074589&index=19&nav=SEARCH&nid=81326454438
Bez