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Tag: steam explosion

Lost PLA Casting – 3rd pour

Today I attempted another aluminium casting session with trees that I had made 2 days ago.  More wheel forks, and barrel trolley brackets.  16 parts altogether.

And this time I installed air release vents, following my previous poor results, and at the suggestion of reader Rob R.

I also made some 50mm extensions of the pouring funnel, to increase the head of melt pressure.  The extensions were “add ons” rather than designed into the system, and the molten aluminium leaked between the extension and the main flask with the tree, so I doubt that they were very effective.

BUT!  Of the 16 parts on the trees, 14 were good to excellent, and only 2 showed any voids, and I assess one of those as repairable.  So, 15/16 is very pleasing.  I feel that I am closer to getting good results every time, if I can make an effective system of increasing the delivery pressure of the molten aluminium.

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These are the extension pieces to the funnels on the investment flasks.  The shape was made with the plastic funnel.  If I had positioned them before the investment plaster had set hard they might have worked better, but as they just sat on top of the already hardened plaster, the join leaked molten aluminium rather badly.  I have a different system in mind for my next pour.

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Previous failures were cut up and thrown into the melt.

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See the tiny silver dots surrounding the central funnel.  That proves that the air vents functioned as intended.

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The aluminium trees.  Not very pretty, but delightful to see.  10 parts on the top one, 6 on the other.  It is odd to see the wax spaghetti turn into aluminium spaghetti.   I will separate the parts tomorrow.

And while the investment burnout and baking was proceeding, I worked on previously cast parts.

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The centre columns have beep painted with etch primer.  A little more filling required, then I will use the best 2 on the models.   The 2 bracket and column assemblies on the right were initially considered unusable due to large voids, but I used some aluminium solder to fill the defects, and they might possibly be OK.  The 2 on the left just need some tidying, machining removal of  melt tubes, and minimal filling.

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I will probably remake this one, but will continue to salvage it and see how well it comes up.  Note the solder fill on the RHS.   That will not be seen on the model.

One more melt and pour, and that should be the last of the castings made for the model Armstrong cannons.  It has been a challenge, and lots to learn, but very interesting and very satisfying.

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Finally for today’s post…  I noticed some black marks on the normally pristine white wall above the casting bench.  They extend about 4 meters above the floor.  Do you know what they are?  The paint has been melted off the wall by bits of flying molten brass, resulting from the steam explosion 2 days ago!

Many thanks to Rob R for his spot on suggestion about the air vents.

Brass Melt. Dangerous!

Today I received by mail 2 new crucibles for my furnace, so I tried a melt of brass.

The source of the brass was machining offcuts, machining failures (quite a few of them), and machining swarf.   The swarf was not very clean, probably containing some aluminium, cutting oil,  dirt and grunge.

It was an interesting experience.

Firstly, the temperature had to increase to 1000ºc.  Later increased to 1050ºc.  It is very hot.  And the impurities came off as smelly fumes, and dross.

But, I poured some ingots.

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And I made another remelt.  And later remembered something which I had read somewhere…..   molten metal and water is dangerous.

After making a few brass ingots, and quenching the moulds so I could remove the ingots, I proceeded to another brass melt.

When I poured the molten brass  into the mould, IT EXPLODED!

IDIOT!!!!

FU**ING IDIOT!!!

I had caused a steam explosion.  Probably the mould was still damp.  And when the molten brass entered the mould, it EXPLODED.   I kid you not.  It went BANG.  Luckily, none hit me, but some of the molten brass had landed up to 2 meters away.

OK.  Lesson learned.  Molten metal must be treated carefully, with respect.  And NEVER put it in a container which is not thoroughly dry.

And after inspecting those brass ingots, I will never try to melt dirty brass, or any other dirty metals.

Meanwhile, preparing for another aluminium pour.

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Here is the next tree.  You might note that there is a spaghetti appearance of wax tubes added to the tree, to allow efflux of air from the cavities, as the melt enter them.

Next aluminium pour on Thursday.  Fingers crossed.  Stay tuned.

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