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23rd Oct 2012, 04:44 AM #1Senior Member
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Vacuum assisted casting in core-sand moulds.
G'day mates!
Ray has seen the model engine I'm working at.
I think he has also seen my vacuum chamber, but at that moment, I didn't have the time to try it. On a different thread, I promised you that I will report. And to report I have! What a success!
I'll show you some castings first to make you drool.
f8.jpgf1.jpgf12.jpg
Lid for a bearing. At 1, thickness is 2 mm, at 2 it is 1 * 1 mm. Quite good, but doable in oil bound sand (with 95% reject).
g5.jpgg4.jpgg3.jpg
Not necessarily to be done this way, but more convenient (small parts are much less effort this way).
j1.jpgj2.jpg
And the mind-blowing part. Wall thickness is 1.4 mm.
Nick
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23rd Oct 2012, 04:56 AM #2Senior Member
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And how did I do this?
The moulds are made out of cold box core sand. I glue both parts together and add a standardized (my standard) sprue.
Something like this:
g1.jpg
Assembled with sprue
g2.jpg
Core box and cores.
These moulds go into this contraption:
f4.jpg
The box ...
f5.jpg
The lid of the box (of course cast). The screws are M6 and are bleeders to adjust the vacuum.
f7.jpg
The moulds are clamped from the rear with this spring loaded quick release crap.
On the box, there is a tube near the bottom. I connect a vane pump from a milking apparatus (no clue how you call that). This sucks 0.5 bar at 700 l/minute.
I switch on the pump, pour molten aluminium into the lids center hole. The vacuum sucks the metal into the mould, wait a few seconds and I have a new casting.
Nick
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23rd Oct 2012, 04:59 AM #3Senior Member
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and I forgot that I made a video:
Vacuum assisted casting
Nick
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24th Oct 2012, 01:12 PM #4Most Valued Member
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Hi Nick,
Thanks for the video, amazing work.
Pretty sure thats a lot more pump than I have. Though at my current rate its not going to matter for a while.
Is the rest of the box wood?
Did you give any thought to preheating the mould?
Stuart
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24th Oct 2012, 03:00 PM #5
Hi Nick,
Many thanks for the video and excellent description, very clever. and quite simple when you see it all finished and working. I bet there was a lot of experimenting to get to that stage.
I'm very impressed by the finish quality that you are getting on those parts..
On a different thread, I promised you that I will report. And to report I have! What a success! I'll show you some castings first to make you drool.
Can't wait to see the finished engine, it's shaping up to be a real gem.
Regards
Ray
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24th Oct 2012, 06:37 PM #6Senior Member
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Yes, the box is just made of MDF, that's what I had at hand.
I have cut a slot along the top of the box and put a silicone tube inside as sealant.
I'm not preheating the mould, and until now I see no need to do so. The part in the first post, last picture is almost more than I expected.
I got a few more ideas (plan B, C, ...) that I could try if that one failed. But it didn't.
The ideas are around directing the flow of air inside the cavity and thus to direct the suction.
If you look close to the mind-blowing-casting, you see a small nibble (diam. 1 mm, length 1 mm). Plan B was to drill a 1 mm hole all the way through the mould. The molten metal would have been quickly sucked into that part, flown into the tiny hole and solidified there and reduced the vacuum from that moment on. Then, air flow would be more around the separation plane of the two halves. That was Plan B.
Plan C would have looked like this:
Cut small slots from the outside that follow the cavity, leaving maybe 1 ... 2 mm of sand. Would have looked like cooling fins. Again, that would have allowed me to direct the vacuum. As soon as the melt reaches that region, it would have sealed the mould at that place and suction increased somewhere else.
Plan D would be like this:
At the separation plane, cut channels into the core sand. They would stop a bit before the cavity. I could file them into the core sand, or integrate them into the core box. I could glue strips of paper into the core box's bottom (that makes the separation plane). This would make a shallow channel for the air.
If you didn't understand my bad English, ask and I'll try to explain harder.
I bet there was a lot of experimenting to get to that stage.
The only problem with the vacuum chamber was, that I had too much vacuum. The melt was sucked into the core sand, and the part looked like it was sintered out of aluminium and sand. And got a different shape than intended.
After the bleeding holes, all went smooth.
Nick
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24th Oct 2012, 08:21 PM #7Most Valued Member
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Hi Nick,
Didnt mean to imply that your castings needed improvement, as you say they are mind blowing. I was just wondering if heating the moulds was something you had tried along the way and disguarded.
Stuart
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24th Oct 2012, 10:31 PM #8Senior Member
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Didnt mean to imply that your castings needed improvement, ...
I'm not politically correct, and I don't want to be treated that way.
if heating the moulds was something you had tried along the way and disguarded.
Nick
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24th Oct 2012, 11:20 PM #9Senior Member
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And in case someone wants to know where all this crap belongs to and what is the progress of that eternal project ...
I have a thread here. That forum is a bit better suited to my project. So I think you pardon me.
Nick
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25th Oct 2012, 02:26 PM #10
Hi Nick,
Thanks for that link, I've not seen that forum before, but I see a few names that I know and I noticed a link to another forum I'd not seen before either ( I must lead a sheltered life ) http://www.alloyavenue.com looks interesting.
When Josh and I visited you for that memorable day's casting and barbeque I came away thoroughly impressed and blown away by the work you were doing, now, I see that I was only seeing a little bit on the surface..
I now know you are completely insane ( in a good way )
Simply stunning... what a great project..
Regards
Ray
PS... I'm going to try your vacuum casting technique, I've got a part to make that I think it will work nicely for.
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25th Oct 2012, 06:04 PM #11Senior Member
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Just for clarification:
I do not think nor claim that I have invented something new. In foundry work, all has already been invented.
I just combined what I had or got easily.
Nick
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26th Oct 2012, 01:37 PM #12
Hi Nick,
Yes, but it has to be re-discovered by patience and careful experimentation to re-discover what works. You are much too modest.
The books I've read on pattern making have done nothing to make me think it is easy to design a pattern that will cast well.
I suspect that in big foundries producing thousands of consumer goods they have computer modelling software to predict how the metal will flow.
One thing I have learned from watching your work is that I need to do a lot more with cores.
Have you ever thought about die casting?
Regards
Ray
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26th Oct 2012, 06:49 PM #13Senior Member
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I suspect that in big foundries producing thousands of consumer goods they have computer modelling software to predict how the metal will flow.
A friend working in a foundry (QC) will tell different stories. The engineers come up with a new part, and the old foundry man says that this will never work. And then, they discover that they have wasted hundred thousands in something that does not work.
I think a lot can be solved by observing and correcting and following known and working patterns (patterns in both meanings). The old-timers had no other chance. They had no simulation software. But still, they made complicated castings.
Have you ever thought about die casting?
In production, they do it the same way. Heat up the mould, place a burner here and there (by experiment), cast a few parts and throw them away (mould gets the right temperature) and then it works. They run it 7/24, so the temperature stays stable.
It is fun to see what works and push the envelope further with new castings.
You have been talking with Jürgen (from my village, with the BMW spares). I try to make him want a model of the BWM side-car engine. And I'll make an experiment how small I could cast the cooling fins of a cylinder/cylinder head.
Edit:
I learned (I guess), that these moulds are called "shell cores". Is that right?
Nick
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27th Oct 2012, 04:03 AM #14Senior Member
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Have cast a few more parts with vacuum.
But this one is the smallest one. Won't need smaller ones.
k7.jpg
A look at the split separation plane.
k6.jpg
Two on a tree. Parts will be sawn off at the red line. Those two "antennas" are artifacts of the split plane. They are 1.5 * 1.2 mm. Now I know I could cast these too.
The oval feature (seen on the left part) is 1.5 mm wide.
k5.jpg
Core box and shell core.
Nick
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27th Oct 2012, 05:59 AM #15New Member
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Hi Nick,
these are looking goooooood. Congratulations!
Best regards from Sindelfingen
Stefan
Just two remarks
AFAIK / remember "Shell Cores / Sheel Moulds" are made also out of sand in the croning or hot box process. A resin bondend sand is used, this sand is poured on a hot pattern out of metal or into a hot core box. Then the resin bonds the sand because of the heat (melting?) . After a short time the pattern is turned around or the core box is turned over so that the not bonded sand, where the resin did not "melt" falls of /out. This now forms a "shell mould or a shell core" with a relative thin wall. In youtube a video showing shell core making can be find.
Are these parts for a secret bavarian time machine?
The post date is already saturday and here in the office it's still friday.
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