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Discussion in 'Engines From Castings' started by rweber, Mar 6, 2018.
Your right barnbikes !
I cannot fiish the cylinders until some material is delivererd. So I'm moving forward to the cylinder head. This will be an alu casted part again. If it works I started creating a computer model and let it print on the 3d printer.
(Don't blame about the printing quality ;-) My 3D printing guy switched to a new filament vendor and this requires some adjustemt to the printing paramters for proper results. In the meantime now I have about 5 cylinder heads and they are looking better from print to print)
I tried to build the cylinderhead via lost wax technique. Therefore I created a 3D printed model made of Moldlay.
I put it into some leveling compound and lety it dry. Then I put it into the curing oven and sloooooowly increased the temp to 270°C to let the wax melt out. This took about 2 hours, but the wax dropped out completeley. Great, so far.
Highly motivated, I moved on to the casting process.
But the result was very disappointing.
It looks to me that the Alu was not able to push out the ambient air. Perhaps I filled it in to fast. I don't think the Alu cooled to fast, it came out very "liquid" from riser. Alu was at 700°C, the mould was pre-heated to 200°C, I used some salt as flux and wash soda for degasing.
I'm not sure where the problem resides. Maybe there is more than one
Or it is even not possible to make it this way
Any comments and suggestions are welcome!
I have been told that you must use a vacuum under the flask to pull air out of the investment. I was able to spend a few days in a professional investment shop and all their flasks were perforated and placed into vacuum containers before pour.
For small items jewelers use centrifugal spinners to throw the metal into the mold, but I think your part might be to big for that.
I also saw a write up of a n idea to use s team force. A cover is made for the flask and has a big wad of wet newspaper in it. As soon as the metal is poured the cover is placed over the flask and held down so any steam generated forces the metal into the mold.
Bottom line is gravity alone is not enough to get metal flow fully into the mold.
Die casting is the last solution.. There is 2 difference die casting: Low pressure die casting with air pressure or high die casting with piston.
thanks for your thoughts. Especially the steam method looks interesting dangerours. There are some videos around where they press a can filled with moist paper on the mold. This is only for the brave ones.
The centrifugal method you mentioned looks feasible to me. I will have to do some investigation about this. I think I should be able to handle it.
at the upper picture, there are no ejectors where the air can leave. Does this require a porous mould where the air can get through?
It must be ejectors to reduce air pressure inside when the molten meatai is pressed into the mould. Mould an be made of steel or similiar material. The ejectors are smaller than you find in sand casting.
Thanks for all of that casting hints and tips. I will have to think about this in a quiet minute. In the meantime I will proceed with activities that I am familiar with. I started silver soldering the transfer ports and the intake.
Putting them into 65°C sulfuric acid (about 12%) greatly removes the flux.
Silver soldered the water jacket and pipes.
Mounted and centered it on the lathe and used a fresh sharpened HSS turing tool. Unfortunatley I have no internal grinding tool.
Unexpectedly found some time yesterday Time to build the cylinder head for the water cooled version.
Flat countersink and drill the holes on the milling machine and final turning.
Put it all together. Slowly it takes shape.
Now beginning to work on the crankshafts. I will build them of C45 to harden and temper the pin. They will be pre-turned and later grinded.
Facing and centering the back-side.
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