Furnace (part V)

(Green-sand casting - finally!!)

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Finally the flask has been constructed, the sand is mixed, and we are ready to send some stinking hot metal into these moulds!

The only thing I had missing were some objects to actually make a casting out of! So I grabbed the first thing I saw - it just so happened to be one of those decorations that are meant to be put on bed posts or something.

Anyway, so be it. Here is the sand all rammed up, cope lifted off the drag, gate cut, and ready to be closed up and to receive some metal.

A completed "bed post decoration" mould

The mould ready to be poured into

Here the cope is lowered back onto the drag, and ready for casting.

The large hole is the sprue hole, and is where aluminium will be poured into. The smaller holes are vent holes, which allow any water vapour to quickly escape before bubbling back into the molten metal. Had these not been constructed, the gas inside would form large voids inside the metal and rendering the casting pretty much useless.

Aha, this time I did bother using the self timer function, and glad I did so, for this shot totally sums up the process of pouring metal. Well not really, but the most interesting bit anyway.

I was suprised at how fast the mould filled up with aluminium, since I was expecting it to hold quite a large amount of metal.

Pouring of the mould

Original vs. casting...

The casting turned out very nicely. In this picture the sprue and gate have already been cut off the finished casting, and a little sanding has been done to brush up the surface a bit.

You might notice that the lower skinniest part of the casting turned out thicker than the original part. The reason for this is that I used glad wrap as the parting compound (used to separate the cope and drag). Evidently the glad wrap was wrapped a bit too tightly, resulting in some "stretchy" bonds.

Well I have to say I was quite happy with that last casting, so just for kicks, I decided to turn an old mobile phone into a solid aluminium one. I mean, why not?

This is a seriously old Motorola phone, but I think it would be more representative of a phone because of the visible antenna and large pop out buttons.

An "old school" mobile phone mould

Freshly opened mould

Tada! Another successful pour yields a beautiful new shining fully functional solid aluminium Motorola mobile phone. Hmm, perhaps skip the "fully functional" bit.

Sand in the immediate area around the casting loses its moisture content and forms a hard brittle composite much like hardened clay. The sand can be reused by thoroughly crushing it up and adding more water to bring the moisture level back up to the workable level.

Heres a comparison between the original and the aluminium clone. The level of detail in the casting is not bad considering I didn't bother to sieve the sand beforehand. All the buttons are very evident, and even the speaker holes turned out quite well.

A faint outline of the screen area can also be seen.

The phone casting weighs in at 284g

The Motorola logo is not visible in the casting

Here are the undersides of both phones. It is here where the lack of minute detail is clearly demonstrated - the engraved Motorola logo does not show up on the casting. Perhaps next time I will attempt this again with some finer sand.

Next, a demonstration of how useful having a backyard foundry can really be. For some while now, the wood plane in the shed has been gathering dust due to this broken piece. Prior to metal casting, I had not ever imagined it be possible to repair this AND stop it from ever snapping again!

A broken segment of a wood plane

The new prototype segment ready for moulding

Here I have cut small foam strips and taped them in place of the missing wood. I have found that foam is sometimes too soft a material to be rammed in sand (it can shrink), but wrapping it in electrical tape increases its strength.

The mould is prepared for the new replacement part and a nice smooth pour results in a beautiful metal version of the wood + foam prototype.

I haven't yet figured out how to remove the casting without disturbing the mould so that a second casting can be poured immediately... perhaps next time I will try pouring the metal only half way up the sprue so that there is no "cone" to disturb the soil as the casting is pulled off the cope.

The freshly repaired and cast segment

Rough edges and flash are visible prior to "cleaning up"

Here is what a casting looks fresh from a mould, with both sprue and gate still attached. Notice the shrinkage on the top of the sprue - this is caused by the metal on the mould shrinking as it cools and thus sucking down more liquid metal from the sprue. Preventing shrinkage is in fact one of the most important functions of the sprue.

There are also jagged edges around the casting where the cope met the drag - this is known as flash and is quite normal in a greensand casting. It is, however, easily removed. A good sanding and a bit of polishing will make this piece look good as new!

I decided to make an aluminium plaque of some sort. After a bit of thought on what text should go on the plaque, it was without doubt that "Penguin's Lab" would be the most appropriate!

I have heard of others getting their patterns laser cut so that the words are nice and flash, but I wasn't too fussed. First, a nice block of pine is cut to size to use as a base and the text pencilled in.

Then 10 gauge enamel coated copper wire is cut and bent into the shape of the letters. For complex letters (pretty much anything other than "U"), I used two or more lengths of copper wire. The copper wire is then super-glued on to the base.

Its a lot of work, but with a bit of practise its not too time consuming. Besides, this is probably the cheapest way!

After the superglue has dried, the gaps in between and around the lengths of copper wire are filled in with PVA wood glue. This is so that there will be no undercutting (wedges where sand will lodge, and thereby destroying that part of the mould when the pattern is removed) underneath the copper wire. Copper wire, being cylindrical, is not the ideal material I suppose.
Once the pattern was dry, a mould was made and the furnace fired up! Due to time constraints, I had to fire up at night. But the amazing photos are definitely worth it. Here the furnace is just being lit, and the flames are the ones coming off the firelighters.

Well, unfortunately the pour didn't go so well. The charcoal underneath the crucible was not lit, and thus the bottom half of the aluminium load was still solid. Ignorant of this fact, I skimmed and started to pour and only then realised there wasn't going to be enough. The good news is, the text still turned out pretty well and the corners are nice and round since the aluminium didn't have enough pressure to ram right in. Perhaps its better this way...

Now onto the more serious furnace that uses alternative, cheaper sources of fuels...



Next - Furnace (part VI)

Previous - Furnace (part IV)


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