Bifilm Pouring Basin

These experiments are most interesting! Gonna need some time on the shitter to think how this effects my bronze shell work and how it can be utilized there.
Lots of variables, but somewhat controllable in my world. Preheated shell I'm sure covers my ass every time I pour. Keeps me looking like I know wtf I'm doing!

 

I think the bifilm thing is an excellent discussion, especially if one also considers John Campbell's 10 rules of good castings.

The bifilm theory combined with John's 10 rules has profoundly changed my understanding of the metal casting process, and very much for the better.
Even if I never see any improvement at all from using these ideas (I do think I will see a lot of improvement though), I feel like at least I will have an understanding of the pouring and solidification process.
The only way to even begin to get things under control is to first understand what is happening, and thus be able to rationally analyze what one sees in the final casting.

John Campbell points out in his book that the pouring basin and sprue is a terrible thing, and should be eliminated if at all possible.
That being said, Bob uses a pouring basin and sprue to make his excellent castings, and I think that reflects the reality that if you have to make a lot of castings every day, you may have to use a pouring basin and sprue, and thus you need to make the best of that situation, ie: don't let the sprue aspirate air, don't let the sprue/runner cause turbulence, control your metal velocity, and eliminate any air bubbles before they get into the mold cavity.

The alternative is to use pouring techniques that use direct contact with the lip of the crucible to prevent the metal from falling through the air to reach the mold, and often a tilt mechanism is used for the mold and/or the mold-crucible so that the mold fill rate can be accurately controlled. There are other techniques too, but the tilt mechanism is one of them.

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As I'm stumbling around in the dark, I decided to make a few single changes so I can try to get a feel for how each variable affects the outcome. I think I poured the open top pattern about 1,700F, maybe 1,650F. The frozen one was around 1250F to 1,300F. I don't know the temperature because of the lag from last measurement to metal hitting the sprue. I was expecting a freeze failure of some sort, I was surprised it was so deep.

I am using basically the same stock each time, but it is remelt and it is of extruded origin. I have melted very little 356 or other originally cast material.

I'll repeat I'm not trying to cast this pattern, it's just a convenient pattern which I have cast successfully before with much larger feed system. I am trying to see how applying the bifilm theories will affect the level of defects I've had in the past. These typically include voids and shrink defects.

I like objectivity. I found it interesting that the single open riser still had shrink defects back down into the part. I attributed that to filling slower than I have in the past because of the smaller feed system with the coldest material going into the riser. With the feed system being small it is also cooling rapidly. Reviewing the Olfoundryman video posted here the important thing I see is his riser is on the feed end of his pattern. Perfect sense, provide a riser to feed from the hottest part of the pattern and let the cooler sections cool down. Using the gvcf concept to slow the flow (larger area to enter the pattern) it really seems logical to enter a large riser with a small runner system then use a large gate from the riser to the pattern.

We don't differ there. But I am committed to getting the best results I can with extruded scrap material. I can't explain that, other than the material seems to be free. It is not free with all the processing but that is my basis.

I am most concerned about gross defects, those easily seen with the naked eye. I do not believe remelted stock that has not been degassed will produce porosity free castings. But I do know it will produce leak free pressure parts without gross defects.

I file because sanding and grinding smears the metal and covers defects. In doing weld analysis in steel, smearing by grinding can seal a crack that liquid penetrant will not find. I am approximating liquid penetrant by inking the surface then giving it a very light sanding. When I etch a surface i still ink it and wipe it to see the level of defects I am looking for.

Do you feel all the bifilm defects are microscopic and will never bee seen as gross defects?

I take those claims with a grain of salt. Of course nobody breaks "all" the rules, but there are some rules which are more important than others.

That is quite interesting. How do you polish? And do you etch? Do you have liquid penetrant? It's great stuff.

My manifolds are thick, about 1/4" and I only test them to around 100 psi but I've not had a leaker in the ten or so I've finished. small sampling.

What appeals to me is a pouring basin which lets the air out. I've not tried a cush cup but it seems they would be hard to establish a level in. Then if it keeps floaters out that's another bonus. When I see crap from the crucible go down the drain rather than staying on top I know it's not good. You just can't skim all the oxides.

Thanks for your time to comment. We obviously have a bit different approach to problems. Maximum progress is gained by having people of differing approaches around.

 

Made one more pour of my manifold today. Put an open riser on the end of the runner and a large gate from the riser to the pattern. Unfortunately my green sand basin is almost too large to use with the flask I'm using. I was able to keep the sprue flooded until I saw metal in the riser, stopped pouring and the basin drained out the riser.



Nice results



The only shrinkage was in the top of the riser. I need to make a blind riser pattern and a measured gate pattern. The pouring basin in green sand is working well.

 

https://www.ebay.com/itm/Vintage-Wo...638941?hash=item36478cb9dd:g:4HcAAOSwDcJcYFhH

There you go, Owner does not even know what they got LoL!!!

 

Less than $5 for a 3D print and much more than $60 to have a competent pattern maker make one.

 

the 1957 Foundry Manual shows a picture of a pouring Basin, the 1987 References greatly expound on the pouring basin being preferred, it's unmentioned in the 77 editions (shrug)

V/r HT1

 

I'll sell you Mine $59.99 I never use it

V/r HT1

 

Thought I'd try putting a pouring basin into the cope, since I don't need the extra height and my basin was a little big for the flasks I'm using. So I made a smaller basin.



Rammed the sprue into the cope, removed it, scooped out some sand where the basin would fit and drove it down into the sand.



Then pushed out the sand plugging the sprue. I still used the curved runner buried in the drag and added a fat blind riser (my old settling basin) in the cope and scooped out a curved runner and a large gate so the parting line makes a weir under the blind riser.



Casting came out nice. Side view of weir under blind riser.



Almost all the shrinkage came out of the riser. Less than 0.010" dish on the top boss.



Using an open sprue with a settling basin, runner, and gate, I would occasionally get defects like this in the gate and obviously in the casting too.



This is much better, especially for remelted sprues and runners.

 

The part is looking pretty good.

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That looks encouraging. I ran a test yesterday and video'd it. The aluminum foil appears to be unnecessary in the offset basin. I like ramming the basin in place, that saves having to make a run of them to have available.
Even in the different metal our risers are look a likes.

 

Thanks, Pat.

Actually this pouring basin is a little small. I don't have enough reaction time to try to keep a level in the basin. I'm also going to try smaller runners, a two second pour is hard to control. I should be casting more than one part, I guess.

By old arrangement, I assume you mean the immediate previous with the open riser. Olfoundryman was using a riser right at his part, I'm assuming to trap floaters as much as feed shrinkage.

Now I'm eager to try a centrifugal separator. I'm thinking a bottom exit.

My goal is to get some premade feed system parts so it's easy to incorporate them into each pour.

 

I really like using a green sand basin. I need more practice getting a smooth sprue but the very first one came out ok. And I need more practice pouring, maybe a little larger basin.

 

It is a tapered sprue, about 0.4" square at the base, and 0.4" by 0.6" at the top.