OK, so I have a big block to cast from steel (steel waste actually), with a Jersey Barrier-like form (much smaller though, ) see four of them in the mould below).
What I am pondering on is the mold, which I hope do give dimensions so it wouldn’t “melt away” from the steel being poured into it, while still having a form which easily would release the cast when turned upside down.
My question is, if any engineer with experience reading this could give some general advice for my prototype drawing. I’m not after any final design, only indications good enough so that I could send a drawing to a casting facility without ending up being embarrassed.
One constraint: The mould together with the cast steel poured into it must not weigh over 18 metric tons in total.
Desired: Dimensions not critical, but each piece (per slot) ending up being as close to 2 metric tons each it would be very good.
I guess that critical designs is about thickness of walls to be able to cool down the contact surface of the steel fast enough, and radii which doesn’t melt down due to heat, and general form here and there which wouldn’t crack the mould due to the rapid heat change when filling it up.
Fig 1. Mould with “channels” between four slots to allow steel to leak between slots.
Any advice would be very welcome. Thank you in advance. When I get home I can post the mould I had already drawn some years ago (actually in 2010, as can be seen in the picture).
Perhaps it would make a good finite element analysis study. Both weight and heat studies could be done. Alternatively, making or 3D printing a model, and just bending it in your hand could give you an idea as far as strength. If it’s 3D printed (solid), PLA filiment has a relatively low melting point, and perhaps something heated could be carefully poured to see what gives away first.
Just from layperson, I would expect any part of the mould that’s any thinner than any other to have issues. I would expect the center moulds to have a harder time with heat. I would expect the outer corners to have a harder time with stress.
If total weight is an issue, I wonder if the bulkheads guards on the end need to be as thick, and if more material could be used to make the actual mould parts.
Is that enough draft angle for a steel ingot?
If those are forklift slots in the bottom, are they large enough and spaced wide enough for the forks? also if they are for forklifts (then this is a big mould), is there enough clearance for the taper of the forks.
Is there enough strength to keep it form twisting in ice-cube tray fashion?
Do you want the outer sides to be a little higher to contain the melted steel? Or can your foundry pour the steel slow enough to stop between the volume of the gates and before the steel goes over the sides?
It’s an interesting project. Please post pictures in use.
I don’t think “general strength” will be an issue (this is 5+ cm thickness steel all over the mould). Heat dissipation and cracks due to heat shocks perhaps could become a problem though.
Regarding melt-experiments with plastic I suspect that that wouldn’t give very realistic results since the heat dissipation would be very different. The transfer of heat to the mould would cause the molten steel to make a “skin” and from then on the heat dissipation (or, heat transfer over to the mould) wouldn’t be very big.
So the mould would mainly have to absorb that initial heat, and then it would be on the safer side after that. I think (but I could be wrong, but what I do know is that the “skin” will start to insulate the molten steel after being formed, which is why not everything melts down…
True. Question is only how much heat they need to absorb to allow the skinning to happen. After that it should survive.
The most difficult stress to predict would be heat shock (more below on the second significant stress factor). So, complex transitions in the mould shape could cause tensions and that seems to me to be the trickiest to predict.
Well, the important thing is to have sufficient heat absorption, but I don’t know how exactly much material thickness would be needed in the mould for it to be able to absorb that initial heat until the “skinning” occurs on the molten steel.
The reason why the sides are quite massive in the picture (I had a later version with three big holes in the upper sides to allow for more material for the walls between the pockets/slots) is that the mould is meant to be tilted (or “flipped”) after a while so that the set cast steel drops down on the ground.
If you have a number (the angle), please let me know.
Yes. This was only a draft draw. I would check the true dimensions. They perhaps should be bolted on the mould as to not provide for yet another fracture line (term?)
Same could be said about the sides - making a separate mould box (the middle part) and sides, with big square holes to lock the sides to the mould. That would also reduce the stress/fracture lines preventing cracking from heat shock. But splitting it up increases complexity though. The moulds should be cheap to produce.
Huh? What does that mean?
No. They are high only to keep the mould high above ground after flipping it over to empty the mould. Therefore the height is not critical. 10 cm plus would suffice.
I think that I initially made them this high before I realized that if the fork-slots are “closed loop”, they can be used also for lifting a flipped box with the forks (no need to get the forks under the mould-pockets, so to speak).
I think I have all the general ideas covered. My question is more about advice from experience about draft angles and about shape-features that can cause problem, and of course material thicknesses with enough capacity to absorb the initial heat shock.
Good questions.
// Rolf
Edit: Here a picture of a later idea-sketch with the mould being flipped over to empty it (holes allow for more material to be placed between the “pockets” separating the final pieces:
I understand your question. The reason is that there will come more than 10 tons of waste steel at once, and must be put somewhere quickly, so several moulds would be placed near each other.
Too small moulds would be hard to “hit” with a 40+ ton crane which needs to get rid of the steel immediately, meaning… asap, no time wasted. Quickly. At least there’s no time or precision for 1/4 size moulds. Otherwise a split up of the moulds would have been less unpredictable, yes
You are asking “foundry art” questions. I’m not sure you’ll find anyone here with the answers, but I’m sure that the foundry you will be dealing with will have exactly the answers you need, and far from embarrassing you will more than likely be delighted that you are asking beforehand and allowing them to educate you with their “right” answers.
They will also probably be delighted to explain the preferred formats and standards for communicating your desires and intentions to them.
I would think that anyone you would call upon to melt 10 tons of steel would like to talk to you. 10 tons is not a big melt (think one main battle tank turret), but it’s not trivial either.
Hello,
I have no ecperience with casting steel. Just some composites eperience.
Google tells me, that similar to composites steel will shrink a bit while cooling down. Don´´t know how much, but I would expect problems with your geometry, cause shrinkage might lead to a collision in an area that might have - even without that collision- a lot of stress in the part as well as in the mold.26052019-2.pdf (456.0 KB)
OK, that was a good point. That shape can be changed to a more sloping angle, so that the cast “climbs up” instead of stressing the notch right there. No problem.
Still a bit dangerous geometry. I think only the foundry can answer what is possible to produce.
Maybe best to test via first making some simple sand castings, before buiding a rigid mold.
We´ve had some aluminium castings to our design that had to fit into a bigger ( 200 mm ) aluminium extrusion. That´s not easy to get right, if you don´t have high quantaties to be able to pay for several molds and the scraped parts.
