Thursday, 5 July 2018

Melting Aluminium..near disaster

I've been following The King of Random and noted he had some success melting aluminium. This seemed attractive to me as a 3D print could be used to make a mould, and pouring in liquid aluminium resulting in a casted part.

I watched his video exploits here:

Starting off with a metal bucket and a smaller plastic bucket inside, I poured plaster of Paris into the gap in between the buckets until the plaster reached to about an inch below the rim of the outer bucket. I then used pliers to remove the plastic bucket, leaving a void.

Using a holesaw, I drilled through the bottom of the bucket to allow me to insert a steel pipe for the air inlet. I 3D printed an adaptor to allow me to connect my DeWalt vacuum which has an air outlet to the pipe.

The kiln needs a lid and this had to be made from scratch. This was to be made from plaster of Paris too. I cut a piece of cardboard so that it formed a circle that was the outer diameter of the lid. Then I covered it in packing tape to prevent water ingress.

This was hot melt glued to a sheet of cardboard to for the outer circumference of the lid.

A small cardboard cup was placed in the centre and hot melt glued to the cardboard base. This would form the hole in the kiln lid.

After spraying the exposed cardboard with varnish to seal it, I then poured the plaster of Paris, inserting two B&Q 8mm threaded rods that I had bent into a 'U' shape as handles.

I trial fired the system using barbecue charcoal with a crucible made from a Berzomatic tank with the top hack sawed off. With the blower on this took about half an hour to melt the aluminium, but the overall temperature was too low. And when I attempted to pour the aluminium started to set before it reached the end of the crucible.

"Ah ha!" says I. "There is insufficient energy going into the system". "How can I get more energy in?". This is when I decide to vist my local coal merchant who sells me some Welsh anthracite.

With this burning I get a fair flame going.

This looks really promising as the aluminium is much hotter...

However....the thermal energy of the coal was much greater than I expected, and 'The Incident' occurred.

The melting point of aluminium is around 660C. I clearly needed more than this to get where I wanted to be. The crucible I was using was made of steel, which has a melting point of 1500C. The bottom of the crucible melted, dropping the molten steel and aluminium onto the burning coal. The aluminium then burnt in the presence of so much oxygen from the air feed. I had the good sense to pull the air line from the kiln to minimise the damage.

Needless to say I almost shit my pants. The immediate aftermath was a pool of molten steel on the concrete patio.

The Bernzomatic tank was destroyed, as this pic taken a few days later shows.

And the missus was most unimpressed with the hole it blew in the concrete slabs...

The lesson learned here is it is OK to increase the energy capacity of the fuel, but there needs to be a corresponding reduction in the amount of air available. Next time I will:
1) Have a variable air flow feed.
2) Do it on a slab that is not part of the garden.
3) Wear more protection (this is the important bit. I cowered in the garage after pulling the air feed and thought "Oh shit! What do I do now!"

The main lesson I learned was: Blindly following potentially dangerous youtube videos without research is a recipe for disaster.

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