Bob Puhakka on Bifilm theory

OK, the answer to easy bottom gating

Switch over to vertically parted molding

Similar to this test bar perm mold



This system is not optimal, but shows the idea, the entire system is molded on the pattern, no sprue cutting, digging out gates, easy to make a tapered sprue, etc.

Try it you'll like it

Also Campbell is dead set against horn gates, his entire design idea is to always keep metal flow below a critical velocity where it gets turbulent and folds back on itself causing the dread oxide film

So a long drop down a tall sprue creates velocity which is shed into a large expansion chamber to slow flow rate

The key is slow flat filling

Bob had a video (since taken down) looking down the risers into a casting, the metal rose as a flat smooth mirror surface - no oxides created since there is no folding

I can't share my videos because of a non disclosure agreement but the same thing - slow, smooth, slow, slow, non turbulent, slow

My molds pour so slow the guys have to take a coffee break halfway through

I will try to dig up some pictures

Again, if these are not structural castings, any old way of pouring will work, have fun and have at it

 

Once again, makes sense. No higher speed explanation needed. ;-)

Denis

 

So, let's say you were casting as I-beam 5" by 19 pounds and 36" in length. The flange thickness is on the order of .270 an the web is .400 more or less. Now drill some 3.5 inch holes in the web every 5 inches. https://www.engineeringtoolbox.com/american-wide-flange-steel-beams-d_1319.html

I would think it would freeze up with very slow pouring. I ask because I pour iron (for sale) for a more or less similar casting repeatedly. But maybe it would not freeze. What do you think? I have felt the need to pour that casting hot and fast. I did have early turbulence problems that I have eliminated with fairing gates and added risers. As soon as we get ten inches of snow off the ground I am anxious to try a few variations based on some of the above discussion. Not likely to try the vertical casting though...

Denis

 

I have a real interest in the pouring basin. The OP video shows a second man pulling the plug which would be a neat trick for a one man show, but I wonder if a foil plug in the top of the sprue or maybe even foam would provide enough of a delay for the pourer to get ahead of the flow. Lost foam casters are quite familiar with that brief delay. It seems like it could be used to good advantage.

Pete

 

A person could use a chip of light fire brick that would float as soot as the metal hit a level high enough to displace it.
Joe

 

Just use a little foot operated lever mechanism.
Step on the pedal, the plug rises.
Very similar to a foot operated lid lifter.
It would be easy to do.

.

 

Agree. Floating plug would float and allow metal to flow and then plug, float, plug etc.

Besides a foot operated lever, a spring or counterbalance and thermal fuse (e.g. soft solder pin) could be used for the plug. Pin would be down close to pouring basin and soon after metal contacted the plug heat would melt the pin and it would release a spring or balance to raise the plug.

Denis

 

I swear you Guys would Complicate eating Pudding. I had to Make a video to explain the simplest way to put a guard on a sand Muller... "DONT PUT YOUR HANDS IN THE MULLER (duh!)

I pour 9 Plaques at a time, 9 Molds, the Last thing I wanna do is be looking for the Foot petal, or Making 9 "mechanisms ". just Pour

As to the Float idea: you are adding variables,
1) what if the float only partially dislodges and acts as a strainer letting extra drossy metal slowly fill your Mold,
2) or it doesn't float at all so you have a perfectly cast pouring basin,
3) as it pops loose it breaks loose some sand that goes directly into your casting


V/r HT1

P.S. I'm beginning to feel Like Glumpy... "just Burn Oil"

 

I like your frankness.
Its very refreshing in this PC world.

.

 

That's a pretty thin casting - we used to call it "rangy" > long and thin

Do you need to improve in any way over what you are doing now?

Can you send a few pics of current gating?

If you want to try vertical pour (and I'm not saying you need to) look at how the test bar mold has a riser with a web connection to the test bar, you may be able to do the same connecting into the bottom (side?) flange

Thin Iron flows better with high Phos and Sulfur.

Stoveplate was made from cupolas with poor quality metallurgical coke (high in you guessed it) and was cast really thin

It will be brittle of course, but if not subject to impact loads may be OK

You can even get Ferroalloys to add Phos and Sulphur, heresy to add to an engineering casting

This gating system is the last 10% improvement and isn't needed for everything...

I agree with HT! don't add complexity unless there is a benefit to be had

I was taught hot and fast like everyone else

It has taken me decades to unlearn and move a little bit towards slow and cold

Probably close to 20 years ago I was doing a designed experiment and one of the combinations was cold metal, cold die

We "knew" that the thin wall casting would misrun because of course it would

Turns out they filled out fine

The very senior foundryman that was pouring looked at it and said "we have learned something very interesting here"

And of course we ignored it and went off on another false lead

 

My question was aimed at exploring your experience pouring “rangey ” molds. Have you found (other than the experiment years ago) that slow filling works well?

My limited experience with thinning castings is that I have had to open up the gating to prevent cold shuts and pouring short. Still, some aspects of gating and pouring by hat I have done I know have not been ideal. So, I’d be willing to take another look if there is good reason to believe that slow filling, done properly, should work.

It would seem that large bulky castings would be easily suited to cooler and slow. But what about long and thin ones?

I am presently getting pretty consistent good results after a fair bit of trial s good bit of error, so I’d be reluctant to change much (certainly plan to ditch the funnel pouring basin) on current castings. But future work is a whole different matter.

Here is an example of a 36” casting I do.

 

Might be one heck of an opportunity here. Thoughts?



Al

 

As with most things in life, experience, skill, and technique trump automatic machinery which has to have very consistent input.

 

+1

 

And here’s an attempt at an improved (for me) sprue and pouring basin. The glue is still curing.

 

Cool.

Edit:
From the videos, it appears that the plug and at least the top of the sprue (perhaps the entire sprue) are square in section.

.

 

I attempted to make a reusable one out of refractory that could be just set in position on top of the mold after normal ram-up and sprue forming but the basin was entirely too shallow and it failed.


That was before any of this discussion and of course I was flying blind. I think it's worth another try though. One of my concerns was not making the basin unnessisarily large so as to not eat up crucible capacity. After use I'd rather peel out foil than an ingot.

Pete

 

Yes, Pruhakka has obviously modeled all the options and with the curvilinear sprue form he calculated a square (just how sharply square we don’t know) cross section may be best. At the same time square corners in an ordinary tube with liquid flowing in it is known to generally significantly increase turbulence. At the same time maybe the square would actually be better as it would inhibit swirling. So many unknowns ...
The other factors I considered were convenience of fabrication and my ability to make a smoothly tapered sprue that actually has a little lengthwise elliptical shape. So, my best compromise, not knowing what his modeling software might show for my mold, was to just make the tapered (the perspective angle of the photo makes it look straight!) sprue on the lathe and hope.

I may get to try it out in a couple days when the snow has melted, but there may be more snowfall. Uggh! We rarely get snow that lasts even a day or two.

Denis