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Thread: Cast ally blocks
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15th Feb 2021, 07:44 PM #1Senior Member
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Cast ally blocks
Needed a few lumps of ally about 75x75x50 so scrounged some engine parts from my friendly mechanic and cast some.
The alloy is very nice and machines wonderfully. Was a bit of porosity near the top but by the time the shrinkage is removed there seems to be no porosity remaining. First step in a fun project. Crucible and mould from some heavy wall pipe and the blocks come out quite easy. Metal was from a Kia motor from 2011.
IMG_20210210_131643.jpg IMG_20210212_175126.jpg IMG_20210210_155137.jpg IMG_20210213_144322.jpg IMG_20210215_155548.jpg
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17th Feb 2021, 09:18 PM #2Senior Member
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Major disaster
There is a small bubble of metal right in the center of the shrinkage depression but apart from that there is no visible signs of problems, but i knew there was.
IMG_20210217_180421.jpg
A 10mm slice off the top reveals the hole.
IMG_20210217_180444.jpg
And another slice 30mm thick reveals the total disaster. The hole is about 20mm diameter and about 15mm deep. There is a small channel so I can see all the way through the 30mm to the first cut
IMG_20210217_180457.jpg
Moral of the story don't dribble water on the top to force it to cool faster. Poured more and left to cool slowly and no signs of this. In fact the shrinkage was far shallower than the forced cooling ones.
Back into the pot will cure all
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18th Feb 2021, 12:50 AM #3
Hello Mike,
Way of the world always something to spoil the fun .Best Regards:
Baron J.
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18th Feb 2021, 09:17 PM #4Diamond Member
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Let me inform you Oldbuggermike, that water and molten aluminium is not a good combination, and a bit of porosity could be be the least of your problems. Many years ago I worked for a short time at Comalco, the aluminium smelter here in Tasmania, and as part of the very thorough induction process we were shown photos of one of the furnaces on the potlines with what we told was ten tons of aluminium heaped in front of the furnace. It seems that the unfortunate furnace operator failed to ensure that the sampling ladle was completely dry before driving the bowl through the fluxing crust on top of the molten aluminium to retrieve a sample for quality control. We were told that it was most likely only a couple of tablespoons of water, either from an evening dew or some rainshowers which had collected in the ladle while it had been stored outside the main building, out of the way. From memory the water not only boiled instantly and turned into steam with something like 1600 times the volume of the water, but the steam then reacted chemically with the molten aluminium with somewhat explosive results and just emptied the furnace on top of the operator.
The correct procedure that we were to follow was to turn the bowl of the ladle upside down to empty any moisture and then lift the bowl onto the feed roller at the front of the furnace. we then had to go to the handle end, of the ladle which was about 20 feet away, and push the ladle into the furnace interior, keeping the bowl on top of the floating crust, allowing any moisture to evaporate, before rolling the bowl over and raising the handle end to drive the bowl through the crust to collect the sample. the ladle was withdrawn and the sample emptied into a small mould to solidify for later collection.
Thankfully, I never witnessed any similar events, but the photo remains as a vivid memory in my ageing brain which seems to be slowly turning to porridge some unkind folk keep telling me.
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19th Feb 2021, 12:29 AM #5
Hi Rob, Guys,
Yes the effect can be very nasty !
The water sinks into the molten alloy before it has chance to boil and turn to steam, then you have an explosive condition as the molten metal closes over the steam pocket.
Mike was quite lucky there !Best Regards:
Baron J.
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19th Feb 2021, 11:05 AM #6Senior Member
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I never put it on molten metal, i know i am dumb but certainly not stupid. The surface had skinned over for a time before i sprinkled the water on, i could tap the surface with a metal rod and it was hard all over and not mushy at all. That's why i was so surprised with the cavities. I put it down to the cold made it shrink, locally to the water, and crack so the water could get into the interior.
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19th Feb 2021, 03:11 PM #7Senior Member
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Sorry but never, never and I mean NNNEEEVVVVER put water near a fresh casting even if the top appears to be solid.
Water just might find a way into a cavity and when it turns to steam it will come back out as a high velocity jet stream. If there was still molten metal in the cavity you can end up with steam and molten metal flying at you.
Spent enough time working in foundries to experience a few exciting (or is than poo runner down your legs after you have blown out your undies) times.
Tony
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19th Feb 2021, 06:59 PM #8
I've had the same thing happen a couple of melts ago. No water even touched the metal! I immersed the steel molds full of seemingly solidified aluminium into a dish of water. The aluminium level instantly dropped by about 20mm and on cutting, there were voids all through the ingots! lesson learnt. Seems like you need to wait for all the metal crystals and structures finish occupying whatever space the need....
Cheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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19th Feb 2021, 09:12 PM #9
Mike,
Sorry if my post came across as an insult, it wasn't intended that way !
The cavity you showed in your picture almost certainly was produced by steam. I've several times, seen iron sand casting mould casings, where the sand has had damp in it. The steam produced lifting the case and molten iron being blown out of the gap. That is why foundry men wore thick leather aprons or leggings right down to their boots.
One of my mentors owned the Lightowler Foundry, so I often spent time there !Best Regards:
Baron J.
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19th Feb 2021, 09:26 PM #10Senior Member
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Casting lumps of aluminium can have its problems.
If not degassing before casting, entrapped gases and small foreign material can cause cavity problems.
Entrapped gas will usually show up as cavities with a smooth surface finish to them. They can form any shape not like a bubble you see in water.
Foreign material provides the nuclei for crystal growth. Once this happens especially near the top of an open mould the metal crystallises solidifies and that's it, it has no chance of flowing back into the cavity.
If no feeder system or insulation material is being used the top chills, increasing crystallisation production reducing any chance of metal flowing back into cavities.
Forced cooling (water or not) is not the cause of cavities. If there, they were there in the first minutes after poring the metal.
Pouring temp can have a big effect on end results as well.
Tony
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19th Feb 2021, 09:37 PM #11Senior Member
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21st Feb 2021, 02:08 PM #12
The bloke charging the cupola would swallow salt tablets by the handful.
We always went to the ‘Pot for a few cool drinks after a pour.
Ballina. S G White slipway and foundry 1974.
H.Jimcracks for the rich and/or wealthy. (aka GKB '88)
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