Foam Plug in a Pouring Basin

Discussion in 'Foundry tools and flasks' started by oldironfarmer, Mar 16, 2019.

  1. I hope this warrants a separate thread. Lot's of methods to plug the sprue at the pouring basin until it is covered in liquid to minimize surface oxide and air being drawn down the sprue, by a single person (or a married one to, I guess) were discussed on the bifilm thread.

    A foam plug seemed to be the cat's meow to me. Not only does it do the job and then gets out of the way, the products of combustion should be benign to any metal which is used in lost foam casting. That includes aluminum and cast iron. So the foam plug may give the additional advantage of allowing the metal front to push the foam vapors instead of pushing air. Perhaps there would be a bit less oxide generation just by having the foam in the system.

    I cut a piece of foam to match the sprue then squeezed it like an earplug and stuck it in. It recovered enough to make a little seal. I'm still learning to use a spout so please excuse that. This is a little deeper pouring basin.

    Do something, even if it's wrong:

     
  2. OK, for my last trick of the day (I had a busy day) I made a third pour. This time I spent a little more time and squared up the pouring basin and put a more defined weir in it. Also with a foam plug. At this point I see no downside to the spout or foam plug.

    IMG_5316.JPG

    I also made an overflow at the back of the basin. The greater surface area provides a reservoir to slow the rise and fall of the liquid surface down.

    Pour went very smoothly.



    Here's the three castings I made today. Left to right. I was extending the runner length to establish a limit but none so far for the 0.05 sq in runner. Weights are labeled. Long runner is 7-3/4"with three 90* direction changes.

    IMG_5322.JPG

    Pouring times varied from 1.72 ounces per second for the first, 1.41 ounces per second, and 1.13 ounces per second for the last. With increasing basin sizes I would have thought the rates would have been reversed. I think each weir was successively deeper, so apparently the height the metal falls rules the day.

    Weir on the last pour was decent.

    IMG_5324.JPG

    You can see discoloration at the top of the sprue where the foam took it's last stand. The sprue is tapered, but mainly in the other direction. About 2:1 ratio top to bottom. Picture makes it look bigger at the bottom.

    On the last pour I thought to look at the sand in the foam area.

    IMG_5319.JPG

    Looks like lost foam sand. :rolleyes:
     
    Tobho Mott, Jason and joe yard like this.
  3. Jason

    Jason Gold

    Interesting.. So what's the verdict? See any noticeable differences in the castings themselves?
     
  4. No differences in the castings. But I haven't cut them apart. I really want to get set up to polish specimens so I can properly examine them under a microscope. I am remelting scrap so I don't expect to eliminate micro porosity. But with any of the pouring basins I am not sucking air down the sprue. With the weir under the blind riser that may or may not trap major air bubbles.

    However, I've not seen any 0.050" size porosity and larger. With the short pouring distance there are definitely less oxides being generated and I can see those staying on the surface. You can see a solid tube of oxide dross encasing the pouring stream. Also the basins filled with very little if any turbulence. Even without the foam plug the liquid front ran right over the tiny sprue without any visible aspiration.

    The changes have to improve the castings, although the improvement may not be noticeable except in one in ten when a defect would show up. If the changes become routine and do not appreciably add to the time to cast it makes sense to incorporate them. After I spend twenty or thirty minutes ramming up a mold then hurry with a giant open sprue and dump air and fresh dross down the hole, which is going right into the casting, I can spend five more minutes making a proper pouring basin.

    The large basin and big riser use more aluminum but as long as I'm using remelt anyway it is really not an issue.:eek:
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    Interesting idea to use the foam. What does it do with respect to timing the ingress of metal into the sprue? Is there a delay of a millisecond or 300 or what do you think?

    Your pour spout looks like it allows excellent placement of aluminum and has the obvious bottom-tapping advantages. Those pours looked very very nicely controlled. I wish I could use a spout for iron. (I am presently thinking about a basin modification that might improve CI pours. Thinking and doing are two different things)

    It is also interesting to observe (somewhat similar to my recent iron experience) that your runners that look “way too long and skinny” still functioned just fine.

    The increased surface area to reduce meniscus height in the basin is clever.

    Denis
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The pour rate, duration, and transition to the pouring well look greatly improved. What was the purpose of the90 directional changes in the runner? Just packaging?

    Best,
    Kelly
     
  7. Very pleased with the results.

    The 90 degree changes were primarily to fit the longer runner path into the flask. They also increase the flow resistance, effectively making the path longer.

    In evaluating the ounces per second pour, I missed that the longer flow path of the third pour was also a contributing factor.
     
  8. I don't know what delay is afforded by the foam, but it is significant. I really don't need a delay, just want the sprue covered before it starts to flow. But given the delay, maybe as much as 500 milliseconds, the pool of metal has an opportunity to stabilize.

    I'd like to see you try one pour with a foam plug just to see what it does under an iron cover.

    I am trying to go with smaller runners, primarily as a result of watching the metal flow behind glass. The splashing from ESC's test was an eye opener, then the sedate flow from my test was gratifying.

    I don't guess the meniscus height changes with increased area, but how fast the level goes down if you aren't adding metal is slowed and that makes pouring easier. I've seen basins which appear too large and I've used basins which were too small. A middle ground is the goal.
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    Arrrgh, typo alert: I meant to write meniscus height FLUCTUATION.
     
  10. I got the camera closer to the basin to get a better view. I used a larger pattern, a 6" trivet I've cast about 40 times. I've always used a big sprue and it has large runners on a match plate. I'm curious as to how the spout and basin will handle a larger volume. Instead of the smaller sprue (which was too short for the flask) I used a 3/8" copper tube. Of course the straight sprue going into a large basin will flow a lot more metal.

    IMG_5325.JPG

    Here's the pour. I forgot to keep the spout close to the pour. The foam plug took about 0.22 seconds to melt. It melted before I had the basin full and I could not get it full. I saw a little eddy over the sprue a couple of times so it may have sucked some dross down.



    Total time pouring was 14.5 seconds for 36.22 oz of metal, or 2.5 oz/sec. That is about the limit of the 1/4" pipe spout.

    I've been mulling my sand too dry and this mold fell apart but I was ready to cast. I picked it green too, it was hot short and the basin broke in half and off the sprue while I was getting it out of the sand.

    IMG_5327.JPG

    This pattern pours all right, so I don't think I'll revise the match plate. Some of you may remember this.
     

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