Bob Puhakka on Bifilm theory

I'm going to double check but, I think the units don't matter in the spreadsheet as long as each of the three user inputs are the same units.
Enter inches, you get in/s and in. sq., etc. Enter cm, you get cm/s and cubic cm.

 

It just dawned on me why it's been so hard to find info on sprue taper. The sprue should be rectangular and when you go about making one, you are concerned about area at the top and bottom; the angle is worked out during the cutting.
If you turn a sprue on the lathe, you need the angle.
So, if you are asing for sprue taper, we know you're making a conical sprue. Shame, shame.

 

Good work!

Sorry I didn't look at your included angle equation. Trig is pretty straightforward but I soon figured out I really don't care about the angle. If I know the top and bottom diameters and I'm turning it on a lathe I'm cutting to those diameters then trimming between them (manual wood lathe). And if I'm making a rectangular sprue I'm cutting each end to size. The sprues I'm making now are wedge shaped, tapered only on one side. I don't think the metal can tell and it is a lot easier to cut and fit a taper with three square sides.

I'm guessing for sand casting my friction factor is 0.6, very significant.

Edit: Sorry I missed your post on angles. We were posting about the same time, I'm just slow. By the way, were I to try to use a conical sprue, I would likely cut it by hand since I don't have a taper attachment and then I would make it with a concave curve toward the top to approximate a parabolic curve. That would be easier than perfectly straight.

 

Hmmm, not true. Since the constant g is involved, you need to match those units, and g chosen of 386 is in/sec2. If you chose to work in feet, that should be changed to 32.174 ft/sec2.

 

That's a good benchmark value. I haven't thought through that part yet.

Oh, your right, the equations are for inches.

Just brainstorming here:

 

I have to say with the offset basin you can see whether you are keeping the sprue full. I think your sketch might allow for a lot of churning and mixing with air while filling the sprue. However the idea that the foil is at the bottom is interesting.

 

You fellows are acting like a dog with a big ol ham bone with this...digging right in with gusto! I think that's great btw.

@Al Puddle , with respect to the covered "runner" leading to the sprue, my thought is that you're constraining the flow, then changing direction and accelerating the flow. I'm thinking this gives opportunity to create a low pressure area(s) (primarily the top outside corner of the juncture, then lower inside corner too as flow develops) which will then aspirate air.

Still up in the air regarding the use of foil in the system as a burst disc, effective and may have some benefit for faster priming, but it's also got two oxide layers already on it that get dragged right into the system.

Al

 

Perhaps, but I couldn't find them. Every stopper for this system will have an oxide layer against it. Where does it go when the stopper is pulled?

The radius of the dam is to be the same as the radius of the sprue, and adjacent to the top of the sprue opening in the preferred offset basin.

 

I was thinking the sprue should be covered so, you won't be able to see it. The idea for the cover is to provide a boundary for the oxide film to adhere to. If you can delay the feed until the sprue is full to the cover, there should be no air to be aspirated.

Regarding the initial surge of oxides into the runner system, maybe they get deposited against the wall of the runners and gates. Maybe not. I'll chew on that bone some more.

 

The front of the metal flow is burning up the air creating oxides as it flows. I think it is safe to say there are a lot of oxides at the front, more if you have an uncontrolled dump of a partially filled basin into an empty sprue. Adding the double oxide layer of a foil dam with a full system falling, again uncontrolled, would seem to offset the lack of a dam.

I suspect the volume of oxides in the foil dam are small compared to what is in the fresh aluminum which the basin is trying to settle out.

Have they said the dry oxide layer will stick to the walls of the sprue/runner? I don't know.

 

It may be just as useful to make a mock-up of a typical basin/sprue/runner/gate/mold cavity in plexiglass or some similar material, and just pour water in it, and see what happens to the flow.
And video it when you are trying various things.
I have seen research that did this, and it seems to be very useful in figuring out non-turbulent designs.
The problem with calculations is that they may or may not actually work, and so a mock-up may be an easier way to find a good solution.

Like this video, but manually with water and plexiglass.


.

 

This video is quite interesting, with the understanding that it is only as good as the inputs that someone programs into it.

 

Now you guys have me worried! I admit I haven’t poured any aluminum in up on 20 years now and what I poured then did suffer from varying porosity issues but a lot of that was controllable to a degree.
I have been following this thread very closely and have learned a lot about oxide contamination but I am wondering about the real world verses the math when it comes to viscosity.
Pure aluminum has a viscosity near that of water but with minimal alloys such as zinc everything changes.
My father-in-law when he was alive was a metallurgist at Stellite corporation. He started out in the foundry pouring high tech metals. His advice to me was always fill the cavity from the bottom, pour as slow as possible and above all else keep the sprue full, pour as cold as possible.
They also poured through inert gas. Why not just put an extension box on the cope and give it a once over with a co2 fire extinguisher. Co2 is heavier air by a good bit so it would quickly displace any oxygen. Then just pour with the crucible in the extension box on the cope below the Co2 level.
There is a wealth of new things being discussed in this forum that will surly improve the outcome of our castings. I am just wondering if modeling although good and often an Excellent base line will prove the final word or if following practices laid down by this theory and worked out in the school of hard knocks wont be the last word.
Joe

 

I was reading somewhere (too many links on this thread) that showed a chart of what would react with molten aluminum and CO2 was one of the substances. The chart showed that aluminum would extract oxygen from CO2. Don't know if it's true.

 

Good point Oldirnfarmer. I never thought about that one but it would easily strip a carbon atom off leaving the oxygen to bond to the aluminum. Aluminum is a funny thing. It strongly wants to bond to oxygen especially when heat is introduced. I suppose a person would have to use a noble gas such as argon.
Joe

 

That is Way overkill, just purge the Mold with Argon for a couple of minutes down the sprue, a riser, or a pop-off vent at the highest point, right up til you pour , it's heavier then air so it will fill the Mold and displace the air , you pour and the molten metal should displace the Argon, no chance of picking up O2 or H2 that way, simple and inexpensive , a rig to do it would be as simple as a piece of hose or tubing weighted to keep it in place on top of the Mold

V/r HT1


P.S. same technique pipe welder use to purge pipe

 

I set up some test pours that I videoed and got some amazing shots, but have to get up to speed on posting it.
One is an offset basin with rectangular sprue of no specific size, I just eyeballed the dimensions, a larger gate, and half a split pattern with a vented blind riser.


The other is the same pattern and blind riser with a half tapered sprue and conventional basin with a sprue well. I filled the sprue below the well and gated right off the sprue into the mold.


Both molds were mounted behind a pyrex? glass plate from the toaster oven and poured. Good video as I mentioned, but only part of a casting to show. The older Petrobond was too brittle, so I dug into a fresh bag.



I was awful sloppy with the pour, and as ironfarmer mentions in his thread, a two second pour happens real fast. I overfilled both of them. It was apparent that the foil wasn't needed in the offset basin because the aluminum actually angled up from the back edge to dam before the level rose enough to break over and very quickly fill the sprue, and in fact the entire mold.
Until I post the video, look at the simulation above. I thought that was an exaggeration, but it is not.

 

Popcorn's in the microwave. Where's the video? This going to be interesting.