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machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Tag: aluminium casting

My Daughter Has Caught the MetalCasting Bug

For some reason which I do not really understand, my youngest daughter has become interested in my metal casting activities.

First she watched me do a molten aluminium pour.

Then she rang me a day or two later and asked if she could have a go.  She really wanted to do it in brass or bronze, but as a relative beginner myself, and with only one episode of molten brass, and that one did not go so well, I demurred, and said that her first effort would have to be in aluminium.

So I prepared 3 flasks, printing the plastic parts, and gluing them into a wax tree, then slowly heating the flasks in the potters oven, up to 750ºc over 8 hours.  Then lowered the oven temperature to the pouring temp of 710ºc.  And preparing the aluminium melt at 710ºc.

When Eleanor arrived, we had a couple of practice runs with flasks full of sand, so she could get used to the weights and handling the tongs, and the various movements while wearing the protective gear.

Then the pour.   This is Eleanor’s video of the event.

 

I admit to some substantial reservations about this exercise, but Eleanor listens carefully, asks intelligent penetrating questions, and follows instructions precisely.   Full marks.

And, a very successful pour!

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.

Video of Casting Small Complex Cannon Parts

This video was taken and edited by my daughter Eleanor.  I was doing an aluminium pour of some parts for the Armstrong RML cannon, explaining the process to her.  I was hardly aware that she was videoing, so the interaction is conversational.

Although the pour was not a success because none of the parts were good enough to use, it does show the process as seen by someone who previously knew nothing about it.

 

 

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There is also a 20 minute video of the whole process which I will add to this post when it is available.

Reader Rob has suggested that the positions of the defects suggests that air entrapment is the cause of the voids and that the fix is to position some vents at the positions at risk.  I will try that with my next pour.  Thanks Rob.

Here is the 22 minute video.  Just as recorded.  Not planned or edited.

 

 

 

 

 

 

 

Metal Pour

50% preparation of the PLA originals, 45% preparation of the investment, and 5% management of the pour.   You have seen making the trees with the PLA originals.  Today I melted metal, poured, and held my breath.   First metal pour.   I also made some videos, but the autofocus on the Panasonic LX100-2 is so crap (or maybe it was the operator who was more focussed on the metal pour), that I have scrapped the videos. But some stills are OK, as you will see.

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I purchased an ingot of casting aluminium, and bandsawed some pieces to fit into my melting crucible.  Then I washed and wirebrushed the pieces in hot detergent.  There was minimal dross in the melt, so this step was worthwhile, and the ingots must have been fairly free of contaminants.

Next, was measuring the investment powder and water, using kitchen electronic scales.  After mixing there is a 10 minute window for thorough mixing, removal of air bubbles in the vacuum chamber, and pouring into the investment moulds, which had been prepared beforehand.  (see last post).

10 minutes sounded like lots of time, but this was a real time and motion study, having everything ready, with no delays.   But when I saw the clouds of silica dust I remembered that I should be wearing a mask.  So, quick dash, pull on mask, find hearing aids dislodged by the mask, and back to mixing the investment mixture.

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Then, 1.5 hours for the moulds to set hard, and remove the rubber caps with the pouring funnels built in.   That exposes the bottom of the wax trees.  The hose clamps were to assist security of handling the steel cylinders with flask forceps.  Next time I will position them closer to the funnel end.

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The moulds, after removal of the rubber ends, are placed in the investment oven, for 4 hours at 250ºc, 2 hours at 400c, and 2+hours at 750ºc.  The wax and PLA plastic is burnt out and the investment powder sets really hard.   The steel cylinder is red hot.  The wax and PLA comes out as smoke, with no other remnants seen.

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The aluminium ingots are melted at 710ºC, and any dross is scooped off the surface.

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Meanwhile, I have placed a sheet of cement sheet on the floor, a tray of dry sand, and moulds for any excess aluminium melt.  There is a bucket of cold water ready.

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when the mould has been at 750ºc for at least an hour, and the aluminium has melted at 710ºc, the mloten metal is poured into the moulds, which have been removed from the investment oven.  Made a video, but not showing because very poor quality.  After about 30 minutes, the still very hot mould is plunged into cold water, which blows out much of the investment.

And here is the result……

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These are the rear wheel forks.  I need 4.    2 were unusable, and will be remelted.  4 are good to OK, and after some filling with JB Weld, and painting, will be fine.  The 2 failed forks were those closest to the funnel.  Not sure why.

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These are the centre columns.  I need 2.   All 3 are repairable.  One is very good.   Again, the top one, closest to the funnel, (RHS) will be remelted. I did not vacuum the melt into the moulds, and the weight of melt is lowest at that level.  (maybe the cause for the poor result there?)

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so, when I had a closer look at home, none of the pieces are perfect, but they are not too bad.  For a first run, I am really pleased.

With many thanks to Stuart Tankard for his advice and encouragement.

 

 

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