Sprues for LF

Discussion in 'Lost foam casting' started by Gippeto, Dec 31, 2018.

  1. oldironfarmer

    oldironfarmer Silver Banner Member

    You might look at Kelly's lance. He came up with a great way to make fine holes, and small bubbles is what you want.

    I was melting some dirty scrap making ingots yesterday and I was getting 11 minute cycle time pour to pour. My crucible is small, I was pouring 5 lbs at a time. I'm using a 4-1/2" OD 304 stainless steel pipe for a crucible and have a couple of hundred pours on it. I'll make another when necessary for aluminum.

    In what I do, and your parts so far, all I see with casting alloy is a slight improvement in surface finish.

    What are you burning for fuel?
     
  2. Gippeto

    Gippeto Copper

    Believe I've seen Kellys lance but always worth a second look. My crucible was made from 6" steel pipe, 5.5" id and 5" high inside. The total for the melt yesterday was 9lbs according to the bathroom scale.

    Using propane at the moment, but have a siphon nozzle burner that I run Kerosene in, hoping to eventually get things sorted and run waste oil or waste oil/diesel mix.

    Re-melted the mess and failed part from yesterday to clean out the rocks and tidy things up. Took the opportunity to cast the tops for the air vibrator. The bottom sprued part failed, bits of foam left at the top, top sprued part came out nice...more to play with. :) Pics of the foam pouring cups as well.
     

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    Last edited: Jan 6, 2019
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I took your previous comment as if you were expecting it to help with porosity. My point there; no more or less all other things being equal. I do think the fluidity of casting alloys would increase success rate and there is a surprisingly wide range in solidification temp across aluminum alloys.....so what is adequate in one instance may not be in the next. It's a good idea to video yourself. Whether you post it or not, you can usually pick out areas for improvement, how you stage, pour, etc.

    For instance, how many seconds is it from when you extract the crucible until pouring? Easy to answer by video. Do you skim while it's still in the furnace? I ask because you have enabled yourself to measure pour temp but how about allowing for heat loss? I have a lift off, resistive electric, crucible furnace and snatch and pour with the same open ring shank. I skim and measure temp while still in the furnace. I'm usually around 10-15 seconds from where the furnace starts the lift to when I'm pouring metal. I still figure I lose 50F before the pour and maybe 100F by the end of the pour. The only way I could improve is if I had a tipping furnace and poured directly into the mold.

    Large, full, crucibles will retain heat better than small partially charged ones. It's just surface area to volume. Metallic crucibles probably lose heat faster. If you have tongs and a shank, and you must set the crucible on something relatively conductive, it will sink heat away very quickly. Just things to consider.

    Best,
    Kelly
     
  4. Gippeto

    Gippeto Copper

    Definitely some things to keep in mind there. "Prior planning preventing...." and all. ;)

    Thanks,
    Al
     
  5. oldironfarmer

    oldironfarmer Silver Banner Member

    There is a concern among some that steel (iron) will leach into the melt causing a change of properties. 1,600F for carbon steel is well within the scaling range so you expect loss of material. I lose some SS too but not very much. My original 1/4" wall is down to 3/16" or less however I think most of it is external.

    My drip burner is very simple and works very well on used motor oil and cooking oil. I use propane to prewarm the furnace, about two minutes before I get a good oil burn.
     
  6. oldironfarmer

    oldironfarmer Silver Banner Member

    Last edited: Jan 6, 2019
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Gippeto, I already commented in previous post on this but came across this excerpt from the FOSECO foundry manual regarding Lost Foam top vs bottom spruing and thought of you.

    In aluminium casting, it is mainly the permeability of the coating that controls the filling of the casting and very gentle, turbulence free filling is possible with direct pouring. Iron castings, having higher density and heat content, are usually bottom gated to allow controlled mould filling.

    Best,
    Kelly
     
  8. oldironfarmer

    oldironfarmer Silver Banner Member

    So what about gating for brass and aluminum bronze?
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Dunno OIF. I haven't LF cast anything but aluminum except some lead. Had to super heat the lead and watch the pattern depth because the hydrostatic pressure was so high it would compact the mold media but too shallow and it was easy to produce run-outs because the cup pressure exceeded the sand weight.

    If I had to hazard a guess I'd say copper alloys would behave more like Iron rather than Aluminum because of it's density even though it's a tweener on temp. I've seen video of commercial LF iron & aluminum operations with clusters fed from bottom, top, and side. The commercial lost foam coatings are grouped into ferrous and non-ferrous just like many other foundry products but that is likely more a function of the required refractory of the coating.

    LF can be problematic in some irons because of the propensity to attract carbon from the decomposed foam. Other foams are sometimes used. This makes LF a no go for most all steel casting.

    Best,
    Kelly
     
  10. Gippeto

    Gippeto Copper

    Thanks Kelly, had largely made the decision to stick with top pouring...if it ain't broke right? lol

    Had the day to tinker in the shop, finished the air vibrator but still need to get it attached to try it out. Guess I'll need something else to cast too. ;)

    Cutters for the little cnc (3018) finally showed up in the mail, so had some play time with that as well. Needs some tweaking, but looks promising IMO.

    Regards,
    Al
     

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  11. oldironfarmer

    oldironfarmer Silver Banner Member

    You were sure getting some tearout. How fast does your bit spin? I get really smooth foam cuts with 20,000 rpm but my travel speed is slow too.
     
  12. Gippeto

    Gippeto Copper

    Yes, the cut is "fuzzy", IIRC, the spindle does 10K and I'm running it maxed out...so no where near what a real router turns. May be pushing the feeds considering the spindle rpm, but I honestly don't know...first time playing with cnc. Will be playing around with it a lot more though.

    Edit: Looked it up, 7K is all she'll suffer. No speed demon here lol.

    Hmmm..... http://www.mycncuk.com/threads/3793-Diy-Brushless-Spindle

    Al
     
    Last edited: Jan 8, 2019
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    7krpm on what diameter? Like anything else it's all feed and speed but in soft low melt materials you also need big gullet and cutting edge relief to clear chips. You should be able to make 7krpm work with proper feed but if the cutting edge angle, relief, and gullet aren't right it may not clear chips. I've found that wood working bits are actually well suited for foam whereas a carbide metal burr will just melt foam unless you vastly reduce speed and feed.

    Best,
    Kelly
     
  14. Gippeto

    Gippeto Copper

    A wee little thing....1/8", two flute ball end mill. Did get a 1/4" collet for it so could try a 1/4" router bit and get the sfm up some...if it has enough power to spin the larger bit. Will do some testing tomorrow and see what happens when I slow down the feeds. Looking at some single flute cutters as well.
    Brushless spindle is looking like an option, should be able to bump up the power and rpm quite a bit...what's "another" project on the list eh? :)

    Al
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    What's the spindle wattage? It won't take much for foam. Since you are on the low side of rpm I'd suggest double flute cutters. You can buy double flute carbide cutters for single digit dollars in that size. Don't know what your vertical axis travel is but even if you can cut 1 1/2" depth in one pass you'll still be glad you have that cutting length and more importantly reach. A bottom cutting bit is a plus because you'll inevitably want to plunge and without bottom cutting, foam will melt in the small area in the center of the cutter as you plunge, foul the bit, and/or spin the melted debris out into you cutting path producing tear and unwanted blemishes.

    I have some vary long straight cutting router bits; a 2" cutting length 1/4"D and 3" CL 1/2" ID, both piloted and ad straight cutters. They were inexpensive imports. I'd never use them on anything but foam.....don't think they're safe.

    If at some point you think you may have long run times, and are considering the purchase of another spindle, you may want to leave yourself the option of an enclosed water cool unit. The foam will become ingested over time and can fowl your brush contacts.

    Best,
    Kelly
     
  16. Gippeto

    Gippeto Copper

    Spindle is about 60watt. Depending on where you look, the actual specs are all over the place. The 3018 is sold as a table top engraver...it's tiny, low on power and lower still on rigidity. Z travel will handle 1" foam with a fairly short cutter...otherwise there's not enough travel to get the cutter clear of the work.

    While it IS a machine and it IS a tool...I wouldn't call it a machine tool. I'm sure that if I look hard enough, I'll find "Mattel" or "Hasbro" stamped in it somewhere.;) That said, there are some advantages IMO...for a basically minimum investment, it does add capability to my shop, it is helping me learn 3d modeling, CAM and setting up a CNC. It does not seem to have enough power to hurt itself, so the inevitable crashes aren't hurting the machine.

    Eventually, I hope to get comfortable enough with the whole process to start using with the router dad built without destroy it in the process. It's just sitting there, but it's also 45 minutes away.

    This is what I bought; https://www.aliexpress.com/item/CNC...050.html?spm=a2g0s.9042311.0.0.351f4c4dpUnN8J

    Uploaded a short video of it cutting the part;

    Will add a pic of the one dad built too.

    Al
     

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  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Looks useful to me. Since ~1" XPS foam board is common, I think you'd appreciate the ability to make a 1" cutting depth with a thin waste board under the stock. Can also just free it from the stock with a razor knife.

    I could not get a good look at the cutter but it doesn't look like it's clearing chips very well. Might do better with what you have if it wasn't cutting on both sides for the finish cut. I would think 7krpm on a double flute carbide wood bit would produce a nice cut. At 20krpm with 1/2" double flute cutters, it's of no concern.

    Best,
    Kelly
     
  18. Gippeto

    Gippeto Copper

    I agree that it's useful, just need to learn to use it. :)

    Was doing some tests at different feed rates and with some other cutters, have some router bits for a Dremel and tried those too. Was noticing that with all of the cutters, one side of the cut was smooth and the other furry...that's when the light bulb came on lol.
    I had been setting the CAM program to do climb milling, which is the opposite of what you would do with a router. Adjusted the file and just finished a test part, the file needs some tweaking, but there's improvement, and that's always good.

    Al
     

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  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yah, want to avoid climb cutting where you can. You'd appreciate these. Cuts and plunges nicely.

    https://www.amazon.com/Yonico-31215...547067024&sr=8-10&keywords=yonico+1/4+carbide

    Nice to have for fillets. Comes in your size :). I have its big brothers.

    https://www.amazon.com/Yonico-34221...547067211&sr=8-14&keywords=yonico+1/4+carbide

    The finish is nice and literally a light swipe or two with 220g sanding cloth make for even better.....the details....but with coated foam patterns, improves surface finish and casting quality.

    Best,
    Kelly
     
  20. Gippeto

    Gippeto Copper

    Need a few different cutters for sure, also need to get tool changes worked out...need to be able to set the height but the controller doesn't allow jogging while doing a pause...challenges. ;) Looking at a few options, pre-set stop collars on the bits seems to be the simplest to implement. Have some modified rotozip bits, 1/8" two flute ball nose, 4 flute flat, 2mm 2 flute flat, and 0.8mm "milling cutters". Tooling up...so much fun lol

    Had some shop time today, had glued up a couple of the trigger cutouts and mudded them up. Plan wasn't to make usable parts, only to find out whether the trigger guard would fill. I was pleasantly surprised, it's 1/8" x 1" in cross section, melt temp was 1550F.

    Knowledge of casting thin sections may be important in the near future. File still needs a couple tweaks, will try the emblem with lost foam over the winter, and cut a couple from wood later to make up a pattern board...or patterns on a board if my terminology fails me.;)

    Al
     

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