Sand Casting Suggestions

Discussion in 'Sand Casting' started by oldironfarmer, Dec 5, 2018.

  1. I'm trying to cast a pattern for somebody else. The pattern is 3D printed and has been finished smoothly with a clear coating. It's about 7" high and 1/4" thick.

    IMG_4685.JPG

    I made the extended depth cope to handle the depth of the pattern and allow the core to stand instead of hang. After a few missteps I'm putting a bolt in the cavity and a large washer in the drag to hold the core together.

    IMG_4690.JPG

    I poured the first mold too cold, second try was hot but still did not fill. I'm trying to pour 9" into a settling basin and feed into the 1/4" flange on the pattern. That's not cutting it. This pour froze before filling so I finished off by pouring into the riser. You can see the cold shut. But the flange did not fill.

    IMG_4696.JPG

    So, what are the options? I assume I need a ring feeder to feed material from several places but not sure it will still fill to the top.

    Thought about pouring through the riser, a little erosion on the inside would not be an issue.

    Also thinking about making a NaSi core and pouring onto it from above.

    I don't really want to increase the pattern wall thickness.

    Any ideas on how to pour this in brass?
     
  2. PatJ

    PatJ Silver

    I have had a lot of trouble getting brass hot enough to fill the mold without burning all the zinc out of the brass.
    AT 1/4" thick, you should be able to get it to fill with some hot brass.

    Maybe use a very generously sized horseshoe runner with large dual gates, and maybe vacuum assist.

    There is really no substitute for having the metal hot enough for good fluidity.

    Edit:
    When I first started casting things in 2012, I toyed with trying to melt iron, but assumed that I would never figure it out, an so I thought I would always have to use aluminum, or perhaps brass/bronze.
    I considered iron as just too HOT to handle and deal with, and was told that by several people, including one who did a lot of brass/bronze work, that I would just spontaneously combust when trying to pour at iron temperatures.

    I was never satisfied with aluminum parts though, since they just do not wear well in engines, and the flywheels lack the necessary mass for some engine types.
    I decided brass/bronze was the metal for me, but after a number of miserable attempts to melt and pour it, I conceded defeat, and decided to either master iron or die trying.

    At this point, I can superheat the heck out of iron, without any zinc boiling off issues, and while iron requires some good refractory and generally an oil burner, it machines and wears like a dream, and has a mass that feels right (if you are into the mass-feely thing).

    I know this does not solve your brass problems, but that is where I went with brass/bronze, ie: straight to cast iron.

    .
     
    Last edited: Dec 5, 2018
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    OIF,

    From the picture, I can't really see the runner/gate on your casting. I'm assuming that everything colored grey on the pattern are casting features. One thing that is fairly surprising is the flange at the base of the mold poured short, yet apparently the casting still filled a fair ways up the mold. To me this suggests cold metal and a maybe a (very?) cold mold. With a sprue that long, there is a lot of opportunity for the feedstock to lose heat on the way to the part. If the contact area at the feeding gate is small compared to the sprue, that would be a compounding problem slowing fill rate. I would think you would want at least 1:2:2 and preferably 1:4:4 sprue/runner/gate. If the entire part is only ~1/4" wall, that is a lot of mold surface area for the relative mass of the casting....but still should easily in the go zone.

    First thing I would do is make a generous ring shaped runner in the drag around the outer perimeter of the flange, then gate in at four locations clocked around the flange and check your pour temp. -I think it will run.

    It looks like it might only have a couple inches of sprue height above the highest point in the mold which means there isn't much head during the last stages of the pour. If enhancements to the gating system don't cut it, adding a little more sprue height with an extender might finish the deed.

    -My 2 cents,
    Kelly
     
  4. Thanks for your responses, PatJ and Kelly. Yes, the gray is the pattern.

    1 The mold was cool, probably 60F.

    2 In my mind a larger diameter sprue would allow more hot metal to get to the pouring basin. So I'm a little confused by the thought process. I use a small sprue with aluminum and wanted a larger one to go this deep. My runners total were probably only equal to the sprue area. 1:4:4 sprue/runner/gate would make a very large runner area, with a 0.44 sq in sprue that would be 0.88 sq in for each runner. I guess 7/8" wide and 1" deep. I can try that, it will mean a new flask as I don't have room in this one. I had considered a ring runner in continuous contact with the pattern from the drag.

    3 Pour temperature - I can't measure anything above k thermocouple range except optically, and I seem to get wildly variable results with an optical pyrometer so I'm judging by color. What are the contact pyrometer options? I know it was hot because I was seeing zinc flash off in the stream going into the sprue. I had added copper phosphorous, and it may have been some of that flashing.

    4 Thanks for the reminder on sprue height. Not sure it would have helped as I didn't pour fast enough to ever get the sprue full until it was setting. Maybe my pouring speed should be increased. I tend to be methodical and not spill anything.
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Sorry OIF I thought we were talking aluminum. I thought the last sentence in your post meant you were considering switching to brass (from aluminum) not using it.

    Whether brass or aluminum, I don't think it changes my comments on the gating. A large sprue won't flow appreciable more than a small sprue if they are both choked elsewhere down stream. If the melt dwells in the sprue, it's just losing heat. For aluminum sand casting I was always taught and used non-pressurized gating systems, choked at the mouth of a tapered (less turbulent) sprue, thus the suggested ratios (lost foam is a completely different ball game). I've observed that most backyard casters use much larger sprues than what the foundry texts would teach.

    As before, I thought we were talking aluminum. What do you consider the limit of a K-type TC? My contact pyro is home made carbon sheathed k-type TCs 1300C/2300F. I know Rasper uses his for bronze.

    http://www.alloyavenue.com/vb/showthread.php?11337-Original-Post-of-How-to-Make-and-Use-a-Pyrometer

    Rasper's post was more or less my song sheet. I just packaged mine a little differently to suit my casting rig. Check this thread out.

    http://forums.thehomefoundry.org/index.php?threads/cheap-pyrometer-parts-list.33/

    Higher temp options discussed here.

    http://forums.thehomefoundry.org/index.php?threads/iron-rated-pyrometers.41/

    To me this still says combination of insufficient gating x-section and pour temp.

    Best,
    Kelly
     
  6. HT1

    HT1 Gold Banner Member

    here; REAL simple, your metal was too cold, your Sprue is WAY too big around and you need a tapered sprue, 3/8 - 1/2 inch at the bottom, yes do the Horseshoe runner, do not let people here freak you out about burning off the Zinc... I pour Yellow Brass almost every weekend probably better then a pour a week average. I plunge about 3% (about 1/2 Lbs for 30 Lbs of brass) makeup zinc to the bottom of the heat anytime after it is all fully molten, bring it to pouring temp 1096 Celcius . pour HARD and fast, big pouring cup so you cant miss... please tell me you preheated or at least surface heated that green sand mold and closed it just before you poured.

    V/r HT1

    P.S. i think it is a terrible practice and try to avoid it myself but you may have to resort to just pouring down the riser straight away. I have to do 10 inch bells that way because I cannot melt enough metal to include a gating system
     
  7. JoeC

    JoeC Copper

    Good advice, a few other thoughts

    Check Omega link for thermocouples, get a long type K one for under $50

    https://www.omega.com/pptst/JQIN.html
    JQIN_l.jpg
    Preheat in the flame till it reads close to melt temp

    Then get in and out of the melt fast, dont go deep, dont stay long - will last quite a few immersions

    Then write it down to build history

    If you have any refractory coating apply it to the tip

    Temp measurement is your best investment, it is vital

    Current gating concepts use unbelieveably small sprues, look at your pinky, no kidding

    It won't frezee, the hottest metal is always going through it

    But this is for slow fill and oxide control for ultimate mechanical properties, overkill here, perhaps half the current diameter

    Also pouring head is your friend, make a pour basin extension to get way up above your mold

    Greater distance gives greater metallostatic pressure - more force to fill thin sections

    Raise the sprue at least half as much again

    Any possibility tthe mold lifted causing that flash/near run out

    Weight/clamp so the pressure isnt lost

    Good luck
     
    Last edited: Dec 6, 2018
  8. Thanks for that caveat.

    Thanks again guys. Great forum here.
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That link JoeC posted to Omega actually has pretty darn good prices from Omega direct. I went to near the bottom and selected a 24" Inconel sheathed K-Type and it was $31. I'd suggest Inconel over 304 because it handles the heat better. Only thing I didn't like was the molded on plastic connector. JoeC may have suggested the long sheath to keep the connector and junction away from the heat.

    I have also seen others suggest a preheat and minimal exposure time to the dip and just using the TC as is and considering it to be expendable. I haven't tried that. I'm too cheap.

    My TCs are 1/8" diameter and I drill 12" by 5/8" D carbon gouging rods for sheaths. I insert them through a hole in my electric furnace lid and that keeps the connection at ambient temp. I'm still on my original TC after hundreds of dips. The carbon sheaths are expendable but they are cheap, like $1.25 each. I've gone through 4 carbon sheaths but only 3 since realizing they should only be used for momentary dips and not protracted exposure to hot air (which rapidly reduces them. I prematurely broke two of the three or I'd probably still be on my second. Granted this is all aluminum service, but as I mentioned, Rasper seems to have good luck in bronze.

    Since you have a gas fired furnace, I think if you built one like mine, with an insulating plug you insert in your furnace vent hole, I think you could keep your melt in the hot furnace, shut the burner down, and pause to take a temp reading with minimal if any heat loss. If your not there just remove it and flame back on until you are there. Takes alittle effort but removes all the guess work and allows repeatable results and good troubleshooting.

    I think MIFCO's metal contact rated K-Type tips are SiC coated. I cant say what life you might get out of sodium silicate. I can tell you I tried a Mullite kiln sheath. It's response time was horrible slow and failed in short order. There are some excellent washes mad for metal tools that might greatly extend life....but again most of those I've research were with an eye to aluminum.

    Best,
    Kelly
     
  10. Thanks, Kelly!

    I've shied away from a carbon sheath for aluminum as I was concerned about response time. As you may have noted earlier on other threads I began just dipping the bare thermocouple into aluminum and got over 100 measurements with it. That was a $1.10 thermocouple. I've only used up two of them. Nobody believes the good service I'm getting out of cheap thermocouples dipping directly in aluminum. After much service I checked the first one in my kiln against a new one (my unit has two ports) and got identical readings even though the insulation was burned off the wires and bare thermocouple wire was wrapped around itself and kinked.

    My 316 SS sheathed ones are $5.25 each and I haven't destroyed the first one. But I was unsure of the temperature capability after unwelding an unsheathed one in bronze (yes, I did learn). Looking back at the sales information they say 1,200C.

    Since I have satanite I thought I'd try coating with it.

    I'm usually firing on oil now, but can switch back to propane for testing. With my drip system I get a lot of smoke if I just shut down so I usually go back to propane for a couple of minutes to let the residual oil burn off cleanly. I have been shutting down mid-melt to add charcoal to the top of the melt as soon as the chunks have leveled off.

    It frustrates me to have the equipment but I seem to still prefer to guess at temperature. Not a good personality trait.
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Never heard of 100 dips with a bare metal sheath TC even in aluminum so you win the prize there. Response time for my carbon sheath TC is about 30seconds, to 95%+ of where it is heading. Stabilizes to with 10F-20F within a minute or so. I rarely need more than a 30sec dip to know where I'm at. The carbon sheathed approach keeps my cost of measurement at ~penny(s)/dip which works for me!

    Bottom line, everyone has there own method and should use what works.......but your brass is being poured too cold :p

    Best,
    Kelly
     
  12. That's a bare thermocouple, not a bare metal sheathed thermocouple.:eek:

    I do get a less than ten second response time.:D
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Do you know the gage of the TC wire?

    K
     
  14. I think it's 29 or 26 gauge, I measured it at 0.011", and at 0.016.

    IMG_4709.JPG
     
    joe yard likes this.
  15. HT1

    HT1 Gold Banner Member

    you are looking to warm the sand enough that the steam has a place to go into the sand, combined with good venting the moisture if it is excessive will go into the sand, and not get trapped in the metal.
    do not F around with mystery thermocouples for your pyrometer Buy the real shit, and yes they respond slowly... what is your rush. cant stand next to your furnace for a minute? get a new hobby whimp!!!!
    http://mifco.com/shop/pyrometers/replacement-12-thermocouple-tip/
    V/r HT1
     
    dennis and joe yard like this.
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    OIF, I honestly don't know how that (continues to) works but if it does all the power to you. I do seem to recall you mentioning it before and speculating it may have become encased in dross that formed a protective layer because I would think it would have been reduced by the molten aluminum by now.

    Best,
    Kelly
     
  17. I don't need any new hobbies, I've got too many as it is.:(

    I'm going to try my cheapy clad thermocouple tomorrow. I think if I keep it under 2,300F it will be OK.

    I can't stand next to my furnace too long, I might sweat. Or get my fingernails dirty.

    Actually my furnace is small and the temperature increases fairly rapidly, so if I'm measuring while it's heating it seems a fast response is good.

    Thanks for your input.

    Thanks for the advice on the sand warming. I'll try
    This one is toast, but it lasted a long time for $1.00. I was surprised too, but wanted to advertise it because you don't really have to have any prep time to measure aluminum economically. It went a long time before getting the layer of aluminum oxide on it. That stuff won't melt off.
     
  18. joe yard

    joe yard Silver

    Old Ironfarmer HT1 is just rattling your burner. I think it is the military along with the foundry sense of humor. I use to like to work in the foundries when doing repairs just because the thick skin of anyone who entered the place. Not only did I get to watch and learn from the smaller 500 Lb inductive furnace up to the 10 tune capacity of the larger foundry but, you could always yuck it up with the guys. Just be prepared to cuss spit and work as hard as the biggest man on the shift or at least never admit you could not. God forbid the guy who left work clean without breaking a sweat "wimp!". Remember this country was built on iron and steel The people who pour or work with it built the U.S. and the world. I even gave HT1 a like just for the memories.
    Joe
     
  19. DavidF

    DavidF Administrator Staff Member Banner Member

    Not a fan of the "burner rattling" :mad:
     
  20. joe yard

    joe yard Silver

    If I offended any one I apologies. I have All the respect in the world for HT1 and Oldironfarmer along with everyone in the hobby. Its just happens after years in the military, 7 in my case and having the opportunity to work with some of the great people in foundries. Where men are men and women are men too. You develop a course sense of humor. I VERY seriously doubt HT1 meant to offend any one in any way. I will give that as my apology for what it is worth. I would not expect HT1 to give an apology for something that was so trivial and not meant to be a swipe. Beside everyone knows us short time army guys are just nicer than those old 20 year navy salts!
    Joe
     

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