Sand Casting Aluminum ashtray / bowl

This is a casting I made of a glass ashtray (pattern). In this post I refer to it as a bowl because I am not a smoker. The only small problem was that the inside part of the glass bowl was curved in, so if I would sand mould the glass bowl the way it is the sand mould would break while lifting the cope part, so my solution was to use filler inside the ashtray and smooth the curve the other direction. After the filler was dry I used fine grade sand paper and two coats of clear varnish over it to prevent the sand from sticking. Using glass as a pattern is great because it is very easy to remove it from the sand and the finishing is superb quality. The only thing is while ramming it have to be careful not to break the glass with the rammer.

Here is another small tip: As I've mentioned before always preheat your ingot tray and foundry tools that come into contact with the molten aluminum. Another thing that won't do any harm is to preheat the aluminum scarp or ingots before adding them into the crucible. Molten aluminum is 660C° and higher. Two things can happen if parts are not preheated , one is the safety aspect regarding molten metal splashing out of the crucible and the other is thermal shock or "aluminum freeze". The aluminum in the crucible just turns rock hard and back into a molten state after a few minutes.

The aluminum bowl turned out very well now I just have to think of where to put it : -)

Flamingfurnace.com, Aluminum Plaque

This is a special aluminum casting to celebrate my new flamingfurnace.com Domain.
At this stage I'm building my first CNC router machine and it will probably take me sometime to finish it. I found a cheap and easy solution to make my plaque pattern. I used 8mm MDF routing it all around. As for the letters, I got childrens sticky foam letters in a local supermarket (very cheap). After marking the pencil lines for the letters all that was needed was to stick them into place. As past experience tought me MDF is not the best material for a pattern so this time I gave it a few coats of clear varnish and that did the trick.
After the pattern was ready I constructed a new flask from some scrap timber. Flasks dimentions: W.600mm H.170mm and the depth is only 80mm (40mm cope 40mm drag) because the pattern is only 12mm in thickness.
I started making the sand mould and I was hoping that the gaps I left between the letters and the overall thickness of the letters would be sufficient enough to prevent the sand from sticking between the gaps when lifting the pattern out of the sand.
I don't know if I mentioned this before, but if the sand is being rammed too hard it will stick to the pattern when lifting the cope part.
If the sand is rammed to lightly the mould might break and the casting appearance will be damaged.
The trick is to find the right ramming strength balance.
Sometimes a bit of trial and error is needed ;-) .

In this casting I didn't use a gating system for the sprue and riser. I only used the sprue and riser feeder extension (pressure head) to prevent aluminum shrinkage. The aluminum feeders really work, I made two identical test castings of aluminum eagles. For the first one I used a sprue riser extension and the other without. The eagle casting without the feeder had shrinkage in a few spots. The eagle casting with the sprue and riser feeder was perfect.
In the images you can see three aluminum spikes on the back of the plaque, those are the locations of the venting holes to allow gases out preventing casting defects.

The plaque turned out very well without any shrinkage or major defects. Plaque size: 495x75x12mm. All the extra aluminum was casted back into ingots. I used again my new buffing wheel with the brown buffing compound. In the image of the cut sprue and riser you can see they did their job by "feeding" the aluminum casting.
It's a bit hard to see in the images the shiny finish of the letters but I can see my reflection in them.

I took this image after painting the aluminum plaque with copper paint.

Small Aluminum Skull Sand Casting

In this post I will explain how I sand casted an aluminum skull. This is one of my favourite aluminum objects that I've I casted, it turned out very well. I had this small cast skull on the shelf for the last 30 years I don't even know its origin. I decided to make an aluminum duplicate using it as a pattern. It took me three time to make the cope part but again it was worth it in the end. I also got myself a new buffing wheel and a brown polishing buffing compound (500g soap wax bar) for this project.
I also experimented by using only one sprue without a riser and it turned out very well.
After cutting the sprue I started with the polish proccess. First I used some sand paper and metal wool coarse and fine grades and after that I used my new buffing wheel with the brown polish compound. It didn't take long until I saw a nice shine glowing from the skull. After more polishing I could see my reflection on the skull and I am happy with that at the moment. Here are a few more images of the aluminum skull nice and shiny. I use it now as my paper weight and pen holder.

Aluminum lizard sand casting

In this sand casting project I used one sprue and two risers making sure the mould cavity would be full with molten aluminum and enough aluminum to "feed"the casting without having any shrinkage.

Making a mould with a pattern that is flat on one side is very easy and it didn't take too long to prepare.

In the image you can see that the risers did their part by feeding the mould and preventing casting defects.
The finished Aluminum lizard------>
This is my II aluminum lizard casting I made on July 2011: