Need urgent help with lost foam casting

Discussion in 'Lost foam casting' started by Tika, Dec 29, 2022.

  1. Tika

    Tika Lead

    Hi Kelly, thanks so much for your help, your advice is spot on. The results are getting better fast.

    Some more updates.

    Here is a video showing the air pockets that were not able to escape from the pour through the drywall compound.

    I think I will add some extra pieces of foam as sacrificial bulbs for the air bubbles to collect in and then cut them off later. Thoughts?

     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There are a number of factors affecting your results; melt management, mold packing, and the feed system,

    Melt Management: Argon degassing is the industry standard of sorts, but it isn't as simple as just bubbling gas through the melt. Fine dispersion of gas and minimal agitation are key. Besides creating a lot of dross at the surface, if the melt is strongly agitated it can actually reintroduce H2 at the surface.

    Degassing Lance | The Home Foundry

    I watched the video of your furnace. It blows air (and fuel?) from the top? You mention adding to the floor and using a ladle. Are you using a crucible to melt the aluminum charge or is this a reverb furnace and the furnace itself contains the melt which is then ladled out? Seems that it would be very difficult to observe and control the tune of the burner flame in this arrangement and having it impinge directly on the melt is very undesirable, especially in poor/rich burner tune. You need to measure your metal temp. There are threads with build/buy info here. Superheated aluminum will always have greater capacity to hold H2 gas.

    Mold Packing: We already covered this but bare in mind, compromises were made in the positioning of the pattern in the mold to allow better packing with lower vibratory energy.

    My New Lost Foam Casting Rig | The Home Foundry

    Feed System: In a top fed system, ideally you would like the metal front to progress evenly from top to bottom. In practice this is more difficult to achieve. However if you distribute (as opposed to just attaching the sprue in one corner) the metal across the top of the pattern/casting it will encourage and more closely aproximate this flow. This in part is why I use low density EPS in the feed system, because it evaporates more rapidly than the XPS and starts the fill with the metal front better positioned above the part.

    Tarek - 2.jpg

    You should consider making yourself an offset pouring cup with wier. You can read here:

    http://forums.thehomefoundry.org/in...le-offset-pouring-basin.688/page-3#post-38781

    It would not have to be reusable. It could be made from bonded sand or green sand surrounded/packed in unbound lost foam sand. Or maybe just a square sheet metal cup instead of round.

    Round/cylindrical cups, cones, and round untapered sprues tend to aspirate air into the melt (coriolis affect) as it enters the mold. This is why I mentioned a square sprue is prefferred. I had already made several of my cups before I concluded this so they use round sprues, otherwise they would use square sprues like my larger more recent pouring cups. The offset pouring cup made surprising improvements for me in reducing casting defects, much more so than I expected.

    Other: You should apply the refractory coating thin, just enough to turn the colored XPS foam white. Many misunderstand the purpose of the coating. It is not structure for the mold. It is only there to control the rate at which gas escapes. Materials not formulated for such will be less permeable so applying the coating thicker slows/traps gases beyond wat is optimal. You get the added benefit of improved surface finish thinner coating will dry much faster.

    Your part is very massive. Can the wall thickness be reduced? I design most of my parts with .25 inch wall and consequently, they have very high surface area/volume ratios which makes it easier to expell gas. Your wall thickness looks to be 3x to 4x that, and since part volume goes up as a function of the cube ^3, you must expel much, much more gas through the coating and mold.

    In part, the reason I suggested a longer sprue is it generates more pressure. This higher mold pressure increases the ability to drive and expell gas through the coating and the moldmedia. It also makes the portion of the mold where the pattern resides more stable because it is burried deeper in the sand.

    Long discussion. All of it is very technical and nuansced, but if you want to make engineered parts instead of ornaments, everything matters.

    Best,
    Kelly
     
  3. Tika

    Tika Lead

    Thanks Kelly for the long explanation. Love the discussion. Thanks.

    I think I have to prioritize solving the most obvious defects first that I am getting. I attached pictures below.

    Yes, of course, I learned that nothing is simple when it comes to metal casting. I watched your video and your degassing setup looks great. I will put that aside for now because it is more of an optimization issue.

    Yes, The furnace is a reverb type furnace and the melt is ladled out, and it is kinda hard to tune the burner.

    I do measure the metal temperature with a thermocouple, I think it is a J or K type, It goes upto 1372C. I am pouring at around 750C. I will post a picture of the thermocouple in a couple of days.

    Yes, we did cover this. I was thinking about vibration a lot and I am thinking of building a vibrating platform type machine that rocks the barrels from side to side (pivotal oscillation) as explained in this article https://www.vibrationtherapeutic.com/vibration-plate-buying-guide.html. And turn it on as I am filling it up with sand. I will work on that but it is a bit lower on the priority list.

    The feed system is a high priority for me now

    I will. I saw your video with the square offset pouring cup. Ceramic fiber board is expensive here, so as an alternative, I tried grinding up loose ceramic fiber and mixing it in with refractory clay and forming it on a foam plug but it shrank too much and cracked.

    Bonded sand with sodium silicate is a very simple idea that will not introduce any moisture or ceramic fiber bonded with sodium silicate will also work. Both housed in a metal box. Great idea!

    I will make square sprues.

    I see that now and I will reduce the thickness of the coating. I was also thinking of adding a vacuum to assist in gas evacuation as I saw in one of your videos.

    The finished part should have a wall thickness of 12mm after machining so I am casting 15mm or so to allow for shrinkage and surface defects and all that. Very good point about the amount of gas being generated, it is alot. Maybe that is why LFC production lines all have vacuum assist because they are casting water pumps and large items.

    And again I think that is why all the LFC production castings seem to have very long sprues.

    These are my last castings, I did not make the offset pouring cup or distribute the sprue across the top yet. I will. It seems like I am getting oxides and turbulence coming all the way down the pattern.

    The plan for the next casting is.
    1. Distribute the sprue across the top
    2. Make square sprues
    3. Make and offset pouring cup with weir
    4. I will also add vacuum for good measure.
    5. Make a thinner coat on the pattern

    Thanks a million,
    Tarek
     

    Attached Files:

  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    1-5 should prove helpful. I would caution you on adding (4) vacuum though, because it can cause any many problems as it solves, especially if you have inadequate vibration. I almost never use vacuum, but you can give it tryto suit yourself. If you do so, measure the vacuum level you are able to achieve. It is needed in iron lost foam casting because the production of gas is so much more rapid from the heat of iron. It might be helpful since you have a lower surface area/volume ratios than I typically pour, but you'd probably be better off with just a little more sprue length.

    When you make your offset cup, shoot for it to contain >25% of part volume. When you pour, fill the cup immediately to the top and then then wait in ready position for it to start taking metal, because when it does, it will do so rapidly. Keep adding metal trying to keep the cup mostly full. It does not have to be full at the end of the pour. This is tremendously helpful in reducing cup turbulence because the only exposed foam is the top of the sprue which gets covered immediately with molten metal and even the 3-4 inches of metal pressure helps displace the gas through the sprue surface instead of buoyantly back through the cup. The molten metal then starts consuming the sprue in a tranquil and more orderly fashion, and when it reaches your pattern, the rate at which it takes metal will increase.

    When you don't use a cup and have a large amount of foam protruding, it burns in contact with air creating flame, black smoke, and metal turbulence in the cup from rapidy vaporizing/combusting foam, oxidzing the melt surface as this occurs. In an offset cup with weir, most of this will float and not join the stream entering the sprue. In the mold, mostly deprived of oxygen, the decomposed foam is white instead of black from combustion. If you look at the last video where I cast the intake manifold, I pour 30+lbs through a 1.25"x1.25" sprue, and had just a small flash and puff at the instant the metal initially hit the sprue, which burned briefly on the surface of the cup, followed by a pour of 20-25 seconds in duration with absolutely no flame or smoke. When I demold, there is only white vapor contained in the sand. -This is good!

    I think you'd be better served focusing on your furnace tune and melt quality than vacuum. Blowing combusted fuel on an aluminum melt is just unhelpful to melt quality.

    Best,
    Kelly
     
  5. Tika

    Tika Lead

    I am going to trying to organize the tasks with the help I have on hand.

    I am will start working on making a vibrating platform, right now we shake the barrels as we are filling them. I think the platform will help. What kinds of problems might happen from vacuum? I will add a gauge to measure the vacuum level.

    I do have bigger castings down the pipeline that I am stressing about, a 1.2m long mold. I am not sure how to do that part. Maybe I will start another thread for that.

    I saw your video, it is great casting, amazing! I watch many of your videos multiple times.

    For the pouring cup. I also took a look at vacuum-forming ceramic fiber blanket, and maybe try mixing in some binder like Kaolin or something. This looks promising, like in this post.

    http://forums.thehomefoundry.org/index.php?threads/molded-ceramic-fiber.2028/

    Any suggestions on how to tune the furnace and melt quality? I have basic information about that and haven't started researching that yet. I know that it is best not to disturb the oxide layer on the surface of the melt to reduce the flame contact with the metal below. The oxide layer is insulating though.

    Here is the task list,

    1. Distribute the sprue across the top (easy)
    2. Make square sprues (easy)
    3. Make an offset pouring cup with weir (easy, but needs a plug and some experimenting, with sodium silicate bonded sand, bonded ceramic fiber and vacuum formed ceramic fiber)
    4. I will also add vacuum for good measure. (easy, I already have a vacuum contraption, need to add the gauge to it and quick connect coupler, needs construction)
    5. Make a thinner coat on the pattern. (easy)
    6. Make a vibrating platform (medium, needs experimenting with different designs and construction)
    7. Make a vibrating screen (easy, needs construction)
    8. Research tuning flame and melt quality (not sure how long that will take.)

    Cheers,
    Tarek
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    A vibrating platform is good because you can mold multiple flasks. I use that method on my small flasks. On my large flask, since it's impractial for me to handle 500lb molds, I built the vibe into the tipping mechanism for demolding.


    If you have a well packed mold, vaccum can actually make the mold more stable. If you dont have good packing, the vacuum can destabilize localized areas of the mold and the metal will pentrate the sand creating a sand and metal composite that's impossible to machine. Vacuum can also accelerate the propogation of the metal front which allows cooler pouring temp and greater travel distances within the mold. I can pull 1/2 atm of vacuum. That's quite high and takes a high volume device. I used two 3-stage vacuum motors.

    Vacuum/Forced Air Cart | The Home Foundry

    Here's an extreme case where I used it but there are few others.

    Saucer Cup & Spoon – The Lost Foam Edition | The Home Foundry

    You just need to decide if it's worth the ffort for you to make it reusable versus expendable.

    For lean tune, start your furnace and reduce fuel flow until it will no longer support flame, then run fuel flow just slightly above that for stable operation. I'm not sure you answered if you are using a crucible for the melt. If so, a crucible hat may help avoid fuel air impingment on the melt.

    http://forums.thehomefoundry.org/index.php?threads/degassing-lance.204/page-2#post-3884

    I adapted many of my processes from commerical practice: Here are a couple of my favorites.




    Best,
    Kelly
     
  7. Tika

    Tika Lead

    Of course I saw your video about the saucer cup and spoon. That was incredible, unbelievable!

    So, I didn't finish the vibrating platform yet, I should have a prototype tomorrow, hopefully. I'm not sure how to move it from one barrel to another? Or move the barrels over it. I know in commercial they move the boxes on rails and keep the vibration stationary.

    I tried casting with vacuum today. I don't think I had enough suction and I think the sand that I am using is too fine. I will find out tomorrow the result after machining.

    I will sift the sand by size to remove dust and that will hopefully increase vacuum. I will try to look for 40 and 60 mesh. I will also buy another vacuum motor and connect it in series to the one I have.

    Here is a video of my thermocouple for temperature measurement.

    https://youtube.com/shorts/JmGsMEw91B8?feature=share

    Here is a couple of failed experiments in making offset pouring cups. I didn't have CO2 gas to cure the Sodium silicate, I assumed it would cure in the air. I will just make one out of sheet metal.



    No, I'm not using a crucible.

    Cheers,
    Tarek
     
  8. Tika

    Tika Lead

    So I improved the vacuum in the barrel and made it like yours Kelly and added a screen on the bottom of the barrel to create a space for the vacuum and attached a vacuum inlet on the side, like the picture below.

    I also sifted the sand between about 0.25mm and about 1mm and both those things made a huge difference in the vacuum level as you will see in the video.



    Still working on the pouring cup and the vibration platform

    Best,
    Tarek
     

    Attached Files:

  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not sure how you sifted the sand, but getting more uniform grain size and eliminating the fines will help. There's a member here (FishBonzWVa) that introduce me to the winnowing method of seperating sand. Basically layout a tarp, and sift sand in front of a fan. The breeze carries the fines farther and you can seperate grain size by distance from the fan.

    I mentioned that I adapted many things from commercial practice. I also made many practical compromises for a home/hobbyst. One is the use of silica sand. commercial outfits would use a more rounded media, and if iron casting, higher refractory like mullite or Al2O3. But they have fluidizing furnaces to burn off and seperate contaminates and reclaim their media. Sand is cheaper than the energy to do that for me. The grain shape is not ideal for packing, but if you get them well packed they stay so. Round(ed) media will flow easier. I just cant pay >$1lb, when $20/ton works fine. That sand I buy for covenience is actually fairly consistent size, with >80% being between 40-55 mesh......and it's 10c/lb. I reuse it a lot with just coarse sifting before I replensih it.

    Best,
    Kelly
     
  10. Tika

    Tika Lead

    Thanks Kelly, I have some updates and some additional problems that I would love your help in addressing.

    I tried adding vacuum to the pour and got the aluminum sand composite that you mentioned. It wasn't that difficult to remove, I used an angle grinder and it came right off.

    I added a vacuum gauge and bypass to control the amount of vacuum and I will reduce it so that I don't get these defects in the next pour.

    In the video my worker shut off the vacuum midway through the pour for some reason.

    https://youtube.com/shorts/ub3qHlxcYyo?feature=share

    The problem that I am facing now karma is I am still getting air bubbles inside the Casting. I'm suspecting that they come from the wet drywall compound between the layers of foam. I saw this by coincidence when separating 2 layers of foam that were already coated. I will pay much more attention when gluing the layers and seal them with super glue.



    Thanks,
    Tarek
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Use low melt point wax. Toilet ring gaskets are very low melting temp wax. Still suspect more an issue of furnace and melt managment but those gross defects in the sprue area look like entrained air/gas. Are you using an offset pouring cup with some added sprue length?

    Best,
    Kelly
     
  12. rocco

    rocco Silver

    Before you do that, check your glue on a scrap piece of foam, most super glues are NOT foam safe and will melt foam.
     
  13. Tika

    Tika Lead

    No, I had not made it yet. The soothe length is 8". Here are the videos of those pours. The pouring height was too high, I think that might have contributed, not sure how much.

    https://youtube.com/shorts/AwV_PBEDyx0?feature=share

    https://youtube.com/shorts/5IKrL5IyAus?feature=share

    And here is that casting after machining. I suspect a couple of things.

    #1 the drywall compound was still wet between the layers of foam.
    #2 pouring was too high.



    Here is the offset pouring cup I made it out of 3mm steel plate. The pour was not successful, the temperature was about 680C. It did not run.



    I increased it to 730C and it was still not enough. Here is the result.




    I know, but it is the only glue that could glue sheets of foam and dry completely.
    White glue will not dry. Hot glue hardens too quickly and gums up the endmill. I'm trying to find quick setting epoxy here. Any other suggestions, please let me know.

    Thanks,
    Tarek
     
    Last edited: Jan 11, 2023
  14. Tika

    Tika Lead

    Hi Kelly, need your help please. I'm having trouble with this.



    Thanks,
    Tarek
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Oh boy. Those do look really bad. We seem to have gone backwards. Lot's of things are changing.

    You'll recall I cautioned on the use of vacuum. I really think you should abandon using vacuum for the time. The molds are not adequately packed and I could see the sand move when vacuum was applied. This is probably not the source of the internal casting defects but as you have already experienced, can create other modes of failure.

    I did notice some new things in the videos. Let's try to isolate the problems.

    Ha! This is a rather important detail we have not discussed and likely a major contributor to the problems! Laminating foam sheet is very difficult when it comes to lost foam casting. I'm really surprised the wet glue joint didn't load up your cutters when machining the pattern. The best solution is to use foam of a thickness that does not require it, but I also cannot practically get thick XPS. EPS yes, and at the correct density (1.3-1.5lb/ft3), it can be machined satisfactorily.

    Do not use epoxy it will be a waste of time. It will certainly stick the foam together but it is far too dense and will not melt or vaporize similar to foam at all, will float in the melt, and cause casting defects. The wet glue joint no doubt is a major contributor to some of the gross defects you are seeing. Water turns into steam which occupies about 500x-1000x the volume of liquid water. The problem with laminating foam is anything that will vaporize satisfactorly will gum up cutters and everything else is too dense and too high of a melt point. Believe me, I've tried about everything imaginable.

    When I have a pattern thicker than 2" (which is thickest stock commonly availabe to me), I machine it in two pieces and assemble it afterward. This allows better control of the glue joint and a much short path. I use heat 100F which greatly helps drying. Alcohol based glues are better because the alcohol has high vapor pressure and alcohol will not attack polystryrene foam. Most other solvents will. Keep in mind, most all of my patterns have thin walls ~.25". Yours are thicker which makes curing/drying the joint more difficult.

    But, I have a suggestion for you: Machine the part in layers and glue them together after they are machined with thin two-sided tape. I've used this product.

    Amazon.com: ATack Extra Sticky Clear Double-Sided Tape, Removable, 2-Inch x 20-Yards - Wall Safe Heavy-Duty Double Sides Self Sticky Wall Fabric Tape for Wood Templates, Furniture, Leather, Curtains and Craft : Arts, Crafts & Sewing

    There is nothing special about the brand but it is high tach and very thin, <.003 inches and it's typically a vynil or acetate material, which chemically similar to dried white glue but very thin. Cut strips the width of your wall thickness. Position the pattern pieces carefully because it will bond instantly (I'm sure you will like that). If you are tempted to laminate with the tape and machine the patterns in one piece; don't! The adhesive will instantly gum up your cutters.

    You don't want thick two side tape like used for wall hanging pictures and some carpet tape. You want the clear thin film with two sided adhesive. You may be able to buy something similar at an office products store in the width of your wall thickness. You only get one chance to position it because once you seperate it, the foam transfers to the adhesive and it will no longer stick, so aim well!

    This is because there is a gap in your glue joint and capillary action pulls the slurry into the joint. Best is to smeer a very low melt point wax over the joint. Candle wax wont do. I mentioned toilet gasket if wax rings are used in your part of the world. If you have no other options you can try one sided clear thin film tape. Again, very thin film tape, like the common "Scotch" brand. Apply <.5" wide strip around the joint perimeter outside and inside. I say this is if you have no other option because you really dont want anything in the mold accept foam pattern because anything else is just a defect looking for a place to happen.

    In one of your short videos, the drywall coating looked very thick. This will make it less permeable and take much longer to dry. How are you applying and how long are you drying the coating? When I was brush coating, I'd thin the coating to where it would just run off the brush in a steady thin stream. Apply just enough to change the color of the foam to white. Dry thorughly. If you use a heated room, <40C. I'f you are in a warm climate outdoors in the sun and gentle breeze is also very effective.

    Yes, and I noticed a lot of flame and smoke which is indicative of cup turbulence which can cause defects from entrained air. Your offset pouring cup was much better in this regard, BUT (see comments below).

    For better pouring, you don't have to have the pattern and cup in the center of the flask. If you position it closer to the edge and with the cup opening at the very top of the flask, it is much easier to pour a more steady tranquil stream from the ladle.

    I liked the shape of the cup and the much improved affect it had during th epour (little smoke/flame, and tranquil metal flow]. But, 3mm of steel will rob a lot of heat of the melt. I think you'd be far better off with bonded sand. If you cant get CO2 to activate the sodium silicate, You can use a small amount of epoxy (usualy <5% by weight). Many people make cores this way.

    You really need to directly measure your metal temperature or your just guessing, and it's too important of a parameter not to control. I heard the "oven temperature" referenced in one of the videos. In most cases, furnace temp is very unreliable indicator of metal temperature. Also, I noticed you are using a metal pouring ladle. Is it preheated before adding the aluminum? The combination o fthis and steel cup can significantly reduce your effective pouring temp.

    Besides creating cold shut fails, being too cold will exacerbate problems with higher (than foam) melt point materials used on the pattern. Too hot and you increase H2 porosity.

    A couple other minor things, is the sprue ~30mm x 3omm in cross section? Where it attaches to the pattern, use this to better distribute the metal:

    Tarek - 3.jpg

    All of the above discussion will hopefully get rid of the gross defects and the rest is furnace and melt management. -Hang in there.

    Best,
    Kelly
     
  16. mytwhyt

    mytwhyt Silver

    Just a thought, maybe you could use shellac as a glue.
    Fredo
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I have used it in the past. It can be applied thin and dries fast which are pluses, but it does not burn out cleanly. Polyvinyl Alcohol burns out better.

    Best,
    Kelly
     
  18. Tika

    Tika Lead

    Hi Kelly,

    Thanks so much for the long explanation. I'm really trying to hang in there.

    Experiments and Tests

    These experiments were made on Thursday before I read your post.

    So I am going thru a process of elimination. I suspected the glue and the moisture in the drywall compound in between the layers, so I made a series of tests. I also suspected the watering down drywall compound because it created cracks in the coating

    Process: I machined a number of foam pieces, single layers, so no layers therefore no glue. The only thing that was glued was the sprue and I used super glue. (I know super glue is quite dense). I think I need to try eliminating super glue and using just hot glue gun. All parts were placed in a heated cabinet at a temperature of 60C until the drywall compound dried completely. All parts were vacuum cast at about 5"Hg. Steel offset pouring cup was always used. The temperature was inconsistent ranging from 750C to 840C in the furnace

    First test, One coat of watered down drywall compound.

    Second test, One coat of just drywall compound.

    Third test, 2 coats of drywall compound.



    Vacuum


    Absolutely, I will make some casting without using vacuum. Like you said, The possible defects from vacuum are,

    - Shifting sand due to not adequate packing
    - Getting the aluminum sand composite

    I also suspect that the vacuum enlarges any of the entrapped air pockets in the casting or even maybe pulls out the hydrogen in the aluminum as it cools. I don't know this, I am just guessing. I saw this video on TKOR in which he put molten aluminum inside a vacuum chamber at was bubbling, here is the link. I have come to the conclusion that melting aluminum is such a fussy material that any new process I add to it will create problems.




    Glue

    I am trying to find foam in thicker sections but it is difficult. Laminating sheets of foam is very very difficult. I think it is easier to machine foam and glue together at the end, like you said.

    Ok I will not use epoxy.

    I will machine single layers and glue everything at the end with double-sided tape. I think I found the same tape you suggested.



    Coating

    Good idea, scotch tape is easy to come by. I also look for toilet gasket, if I need it.

    In the experiments below, I did notice that putting 2 layers of drywall compound I did notice that the pour was a lot slower, similar to your videos Kelly. So I thought maybe that is good. Before when it was just one coat, I was rushing to keep up with the pour when it started to run. What are your thoughts on this?

    Also, I noticed that when I don't water down the drywall compound and don't dip it, only brush it on. I don't get the capillary action that pulls the drywall into the gaps between the layers of foam.

    Offset pouring cup

    Thanks Kelly for your help. I did notice that the turbulence was on one side of the cup and it settled alot before reaching sprue. Sand with resin is a good idea, I have never tried it. I am also going to try the sand that they use in shell casting. Maybe aslo making the pouring cup a bit long to for the turbulence to settle completely before reaching the sprue.

    I will position the cup much closer to the edge in my next pours.


    Why does the aluminum bubble when I pour it into the offset pouring cup like in this video? It has been doing that consistently.


    Melt Temperature Consistency

    I do have a problem with metal temperature consistency. I have not been using the lid on the furnace which I discovered was making a huge difference. I was heating up the whole world except the melt!! It was taking a really long time to heat up and consuming a lot of gas cylinders. I will install a hinge on the furnace lid similar to the devil forge to make it easier to operate and fix all these problems. Hopefully!

    Then I am hoping, things could be calm enough for me to temperature the from the laddle, because as you can see in the videos, things are a bit hectic.

    H2 Porosity

    I think the easiest way to reduce H2 porosity is by reducing the melt temperature and then think about degassing. I read about degassing a bit, the degassing gas or salt needs to be dried well before adding it to the melt otherwise it will make things much worse. I saw a person wrap some salt in aluminum foil and plunge it to the bottom of the melt. My experiments with the Argon gas and lance earlier might have made things worst because I am not sure how dry the gas was. Are there any readily available compounds to use as degassing tablets?

    A bit of a distraction here (or new degassing technology), using Ultrasonic Vibration to Degas Aluminum. I attached the pdf below.

    Sprue Design

    Ok thanks, I will do that modification. Yes 30mm 30mm is the cross section.

    Thanks a million, Kelly you are the best.
    Cheers,
    Tarek
     

    Attached Files:

  19. Tika

    Tika Lead

    Hi All,

    Here is a video of us machining through the part to see where the airpockets are. I am suspecting this is the super glue floating around and getting stuck in places.



    Best,
    Tarek
     
  20. FishbonzWV

    FishbonzWV Silver Banner Member

    Tarek,
    I've been following this thread and Kelly is feeding you good information.
    In that last video, what I see is terrible porosity.
    I think you need to concentrate on producing clean ingots before proceeding with the foam.
    Lean out your burner, turn off the burner as soon as the metal reaches pouring temp. If you continue to blast the molten metal with a rich flame it becomes laden with H2.
    With gas fired burners, there is a fine line between lean and rich.
    There is an old saying, An ounce of prevention is worth a pound of cure. Degassing is the pound of cure. A lean burner is the ounce of prevention.
    Good luck!
     

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