Automotive Intake Manifold Lid

Discussion in 'Lost foam casting' started by Al2O3, Jun 24, 2018.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    To date, the water necks have been my favorite foam pattern but this one may take over that title…..if I can get it to cast. It’s for a vintage racing induction system. As far as the casting itself goes, it’s going to be the biggest lost foam part I’ve done to date. The part is 22” x 10” x 2” and the typical wall thickness is ¼” so it’s still a relatively thin walled casting with a lot of surface area per pound of metal. I’m estimating the casting to weigh about 12 lbs. With the gating and pouring cup it could be as much as 17 lbs which is more than my A10 crucible can handle so will have to break out the A20 to pour this one and will have some new challenges to address in order to successfully cast the part.

    1 Lid Foam Patterns.JPG

    As before I made a couple simple templates for my over arm router to make the foam patterns. I had already made and used the carburetor flange template from my previous intake plenum project so I just reused it.

    2 Carb Flange.jpg 3 Lid Template.JPG

    The rest of the features didn’t require any tooling, just router bits, a lot of layout, and piece work. It took me the better part of a weekend to do the design work, make the templates, and the first foam pattern. The next two patterns took a couple hours apiece without the wax detailing.

    4 Lid Pattern.JPG 5 Bottom Lid Pattern.JPG

    I got some help from DavidF who printed a logo for me (thanks David). I’ll pull a silicone mold from the pattern, make a wax applique from that mold, and apply it to the pattern.

    6 3D Print.jpg

    With all the fillet work, I have a lot of wax on these patterns which makes me a little nervous. Ideally, I’d have no wax and just polystyrene foam in the pattern but if so, I’d also have no fillets because machining fillets onto the pattern would have complicated things considerably compared to just two simple router templates. It’s a bit of a mystery to me where all this wax goes but as near as I can tell it just vaporizes and escapes through the drywall mud into the sand along with the polystyrene.

    I had to make a new flask for this casting as nothing I had was big enough. I just used medium density fiberboard (MDF). This is one of the beauties of lost foam as any box big and rigid enough to hold sand around the foam pattern is a flask. Ideally it would be metal, and I might be pushing it a bit with only a couple inches of sand between the casting and the wall, but the sand seems insulative enough for the MDF to do the job. The interior dimensions of the flask are 29” x 18” x 6”….and that’s about 170lbs of dry sand. I made some caster/wheel sleds for it. The flask just lifts on and off the sleds and I’ll dump the flask on the concrete driveway to de-mold the part.

    8 Flask.JPG

    I provisioned a plenum and false floor in the flask to enable vacuum assisted casting and also planning to include extra sprue height to produce more head pressure for the first attempt. For the floor I made some table saw lattice cuts with a with a layer of aluminum window screen and fine fiberglass cloth for filter barrier to the plenum.

    9 Flask Floor.jpg

    I decided to position the pattern standing on edge for few reasons. First, there would have been a lot of undercuts and opportunities for poor mold support for the features on the bottom side of the casting if cast in the flat/horizontal position. Those features would probably need to be packed with bound sand. Second, in the horizontal position it would have been a lot of surface area with the potential to float the sand with sprue pressure. This could have been addressed with weights or possible vacuum assist. Third, the selected orientation produces additional hydrostatic sprue pressure at the very bottom of the mold where it is needed as the pour loses heat. Fourth, the pattern is supported on each side by mold medium as the flask is filled with sand so is less likely to deflect under the load of the sand. This orientation does require a slightly longer total distance the molten metal must travel through the foam to fill the mold compared to a horizontal orientation with a central sprue, which is not advantageous, but on balance, I thought it was the best choice. As a side benefit it probably takes the least amount of sand, but still a lot by my standards.

    When I assembled the pieces of the foam pattern the carb flanges were a slight interference fit to openings where they were installed, and this caused the pattern to bow, being about .090” high in the center. I didn’t discover this until I started thinking about the molding and casting process. I think keeping the casting flat may have been a problem anyway and didn’t want to start out contributing .090” to that potential problem. Though a pattern like this is still feather light and holds its form well under its own weight, it easily deflects in handling. I used some more MDF and made what amounts to an external chaplet of sorts to support the pattern by gluing the foam pattern onto it. There are little chunks of foam that space the pattern off the MDF stands. The MDF stands are intended to be sacrificial but I may be able to shave and reuse them a couple times. I think the orientation may be helpful in maintaining flatness as the sand pressure is equal on each side of the pattern as the flask is filled. The whole support board just slides into the flask. The pattern you see mounted on it was a set-up part for proofing the foam machining templates so I figured I’d make a trial run with it to see how things go.



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  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Another process tweak is the introduction of a reusable sheet metal sprue and pouring cup. I just sheared and folded some 22ga mild steel, taped the seams (to keep the sand out), and attached to the in-gate of the foam pattern with foil tape. I decided to give this a try for a couple reasons. One, I wanted some extra head pressure and wasn’t sure if my foil tape sprue method would be up to the task of supporting the sand. I thought about the possibility of introducing iron contamination to my pour but I just don’t think the aluminum is going to be in contact with the steel long enough to matter. When I season the A20 crucible, I'll throw the sheet metal sprue in with to develop a nice oxide layer for a little extra assurance in this regard. I reuse my 2” diameter steel kush cups routinely on other castings and they do fine and have developed a nice dark oxide layer too. I could have made the sprue out of aluminum sheet and let it become expendable but didn’t seem necessary. It may rob a little (more?) heat from the pour than a foam sprue but I think there is much less turbulence in the feed system without the foam and the molten metal seems to settle into a tranquil, laminar, flow more quickly as it proceeds to evaporate the pattern. How much of all of this is necessary? Dunno, but when you’re a lost foam caster and have any significant time invested into making the pattern you want to maximize probability of success.

    11 Sprue.JPG

    With the extended sprue I figure the average head pressure will be about 2 psig for the period until the metal freezes. If the surface area of the part is about 80% of 22” x 10”, that would be ~350lbs force on each of the sides of the flask so I added a couple stiffeners to reinforce the exterior of MDF flask side walls and hopefully prevent them from swelling due to the hydrostatic sprue pressure being applied to all that pattern area. Any applied vacuum assist would tend to counteract this.

    Here is the sprue extender to get some additional head pressure without having to use another 50-100lbs of sand. It’s just some folded sheet metal. I'll fill the flask with sand, vibrate, strike off, screw the top boards in place, then fill the sprue extender and final vibration.

    12 Sprue Extender.JPG

    Nothing but rain and heat forecast for this week. Probably looking at next weekend before I can pour it.

    Last edited: Jun 24, 2018
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  3. oldironfarmer

    oldironfarmer Silver

    Very nice! I was all primed to ask whether it need whalers but you figured that out. :)

    Why the box around the extended sprue? Is the sand intended to be an insulator?
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes! And containment of the sheet metal sprue itself. Three of the sides are folded but one side is just taped in place. The tape will of course perish in the pour but the sand and sprue pressure will carry the day keeping everything in place. When it freezes and I demold, I can disassemble the sprue and reuse it..........that's the plan anyway. I'll post a better picture of the sprue later.

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  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Man, I think we are all looking forward to seeing this pour go well. :)
  6. PatJ

    PatJ Silver Banner Member

    This should be interesting.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Only had a short time after work tonight but was sizing things up a bit. Here’s the sprue. It’s 3”x3” at the top, 2”x1” at the bottom, and 10” tall. The sand in the sprue extender should hold everything in place and when the tape expires during the pour, I should be able to peel the sprue off and reuse it.

    13 Sprue.JPG

    Here’s another shot of the sprue in the extender. The mold is ready to be packed.

    14 Sprue and Extender.JPG

    The A20 is a little cozier of a fit in my furnace than the A10. I have a about 1.25” clearance, a little less at the spout. Plenty for a lift off furnace but will still need to center it on the plinth when returned after the pour.

    15 A20 In Furnace.JPG

    Some time ago I made an open ring shank for the A20 that mounts on the end of my pouring cart. Since the top of the sprue is a fair ways off the ground, Think I’d like to do this pour free hand so I’ll unbolt ring and make a handle and hand actuator for the clamp.

    16 A20 Shank Clamp on Cart.jpg

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  8. joe yard

    joe yard Silver

    Wow! Don’t know what else to say. You are my GOD!
  9. oldironfarmer

    oldironfarmer Silver

    Are you saying you don't have a pouring pit for tall flasks?o_O
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Nope! Nada.

  11. Tobho Mott

    Tobho Mott Silver Banner Member

    Good luck with the pour!

  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Joe. I'll never achieve that status but if the Almighty would like to look in on me during this pour, that would be most welcome. :)

  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Converted the shank from cart to hand guided use, added a slider for the latch, and made a few dry runs snatching and replacing the crucible from the furnace. It'll be a bit of a load but manageable. Not a lot but like to accomplish something every day when possible even if just an hour.


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  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    So for mold prep, I just filled the flask to the bottom of the pattern and then turned the vibe on and fillled the rest a quart at a time. When I got the flask filled to the top of the in-gate, I stopped and added the sprue taping it to the in gate.


    Then I filled the rest of the flask, struck off the sand even with the top, and installed the sprue extender


    I screwed on the flask lids, filled the sprue extender with sand, and vibrated some more. It took 200lbs of sand.


    It was so darned hot today, I didn’t attempt the pour. Will try tomorrow if it doesn’t rain.

  15. DavidF

    DavidF Administrator Staff Member Banner Member

    Did you get the lettering on it??
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    This is just a trial run on a scrap set up foam part and I already had this one coated in mud before I got the 3D prints from you. It's 90% feature complete and will be a good test part. I still have the detailed patterns and will put the lettering on those before they are cast.

  17. Jason

    Jason Gold Banner Member

    POUR POUR POUR POUR!!!!!!! fingers and toes crossed! Live stream it tomorrow. But please wait until 6pm central time. I gotta work tomorrow.
  18. You could probably blow air into the sand via the vacuum port and fluidize the sand to insert a fresh styrofoam piece into the sand ready for the next casting.
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Seems fluidized beds are getting a bit of play on the forum this morning. Very useful for many things including the discussion on shelling. I've built quite a few fluidized beds and also spent a lot of time learning how to pack and prevent granular materials from fluidizing (filtration applications). Depending on the bed size and shape, you need a good distribution header at the bottom of the bed, a means to regulate the air supply, and a lot of compressed air to drive them.

    I have a fluidizing coil on my 5 gal flask. Here's the coil that sits under the filter floor.


    I didn't show it in my build thread because I never use it. You actually need it to both demold and re-mold with the bed fluidized because after vibration and pour the castings are usually locked in so tight, unless they are small, you can't pull them out without either dumping or fluidizing the mold. If you resuse the mold, the sand is too hot and will melt your next foam pattern before you can pack and fill. I coat all patterns in drywall mud which comes off in flakes and chunks in the mold sand after casting. A few pieces doesn't hurt anything but if the sand becomes too fouled it can affect packing under vibe.

    So I just dump the whole mold on my concrete driveway, spread the sand, and it cools very fast. I shovel it into a bucket with a window screen sieve which filters it about as fast as I can shovel it off the driveway and it's ready for reuse.

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  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I got at it early today to try and beat the heat. It was still hotter than blazes. 90F by 9:00 AM and 90% relatively humidity, but it was a good day. I’m not a very good videographer but I try to keep them short and to the point.

    Here’s a video of staging and prep for the pour.

    Here’s a video of the pour.

    Here’s a short video of demolding molding the casting.

    ......And here’s a video of the resulting casting.

    So if you took in the videos, you know it was a successful pour. Here’s a couple pictures of the demolded casting. Any thought I had of being able to reuse the sheet metal sprue is history. It served its purpose well but I had to peel it off with a hammer and chisel. I overestimated the weight of the pour. The total weight of the casting, gate and sprue was 12.7lbs. The casting was 7.9lbs. I had charged the crucible with 17lbs of aluminum and pigged off the rest to ingot molds.

    21 Casting.JPG

    Here’s a couple of close ups of the de-gated casting. As I mentioned earlier in the thread, this foam pattern was a scrap set up part. It cast nearly perfectly. I say nearly because there was just a hint of displaced sand in the two center carb flange openings directly under the gate and sprue, otherwise the pattern seemed to be perfectly reproduced. You might notice the upper porting o the casting is dark stained. That’s decomposition of the polystyrene and burnt mud. I believe the vertical lines between the two banks of carb flanges are knit lines where the metal penetrated the foam pattern at different rates and re-joined. If it was for the witness mark of the decomposed polystyrene and mud, I don’t think I could see them with the naked eye. I won’t know that for sure until I get it cleaned up and cut it apart.


    The board used to hold the pattern flat was a success. I removed the stand-offs that I attached the pattern with and it sits nicely flat. There was very minimal damage to the MDF pedestals and I think I can reuse it as is.


    It was the maiden voyage of my A20 crucible. I was very happy with how my furnace performed. The walls of the A20 are only about 1.25” inches away from the resistive heating coils in the furnace wall so the crucible gets a very good look at the radiant coils. I seasoned the crucible by bringing it to temperature empty. When it reached 1800F I charged it about 6lbs of aluminum at a time. It was 5-10 minutes for each of the 6lbs. With the furnace and crucible at temperature, it was about 25 minutes to melt 17lbs from room temperature (I can’t pre-heat the charge with my electric like you can with a fuel fired furnace). Not sure how long it took to bring the furnace mass to temp because I was busy prepping for the pour but I’d estimate is was about an hour from cold start.


    I’m very pleased with the result; a bit tapped too. Did I mention it was flipping HOT outside! I’ll get busy prepping one of the actual patterns for the next pour.


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