stainless crucible

[savarin]

A couple of years ago when I first started casting aluminium I used a stainless steel bowl for a crucible and filled it with a mix of unknownium.
dont do this at home kiddies.
This was a bad idea as it developed pin holes and the liquid aluminium started leaking out.
I let it solidify and threw it to the back of the shed.
The outer surface is horrible, pitted, unmelted metal folded over etc etc.

Yesterday I decided to cut it in half so it would fit in a graphite crucible for re melting and was astounded to see the inside, totally homogeneous and solid, no impurities visible by eye.

Maybe I should have turned it into a usable piece.

 

[turnitupper]

Now you have two usable pieces. Or you could weld it back together.
John.

 

[savarin]

Thinking back I think I may have learnt a valuable lesson here.
Most of my castings have tiny black porosity inclusions but this one didnt.
It was cooled as soon as it was all melted, in other words it didnt stay in the furnace until I was sure every bit was molten.
I will experiment with my next cast and pour as soon as possible.

 

[Cadillac]

When casting aluminum you shouldn’t cook it too long. Over heating does induce porosity. I’ve had good luck melting the aluminum into ingots first. Then melt the ingots into your part. I have too had parts with pin holes and parts that look perfect. Wish I could give a exact reason.

 

[savarin]

Hi Cadillac, this rant is not against you or your comment but against ALL use of very high precision instructions such as "Not too long" "Not too fast" Not too much" "Make sure its enough"
I have seen it mentioned before, Dont leave it in the heat too long. How long is too long? Is there a time factor that can be stated such as 1 minute once its all molten or something like that
I see them every where in all forms of warnings and information.
If they actually mean something real why aren't precise amounts given either in times, weights, volumes speeds etc.
It also ties in with the use of volume measurements for what should be weights.
Having said that I have to admit in using them myself in the past. Oops
Sorry mate, rant over (till the next one)

 

[Cadillac]

Ah no worries savarin. I wish I knew what I was doing myself as I am self taught. I've learned acouple things by trial and error and always looking for advice. I too have found pinholes in a crucible during a melt. I still have the slug of aluminum with raw material still unmelted sticking out the top of what was the crucible. To clear up about not cooking the aluminum. I was told you want to have some scrap already in the crucible when you light the forge. When the aluminum starts melting you are at melting temps so the mental clock starts. Get the metal in there no fussing around. I believe the more you cook it the more hydrogen is induced. That's where idk. But you don't want to have it bubbling away while your doing something else. Now there's ways to combat the holes. From using gas argon I believe and shooting it at the bottom of the crucible, to using borax soap. I personally have used "washing soda" which works I think. Ive never kept to a strict recipe to notice a difference. The metals you start with has to do with porosities. Theirs a lot to know about melting and casting metals. I unfortunately got interested in it later in life and just read the cliff notes to try and get by. Good luck