Bronze pour time

Discussion in 'Castings, finishing/ repair/ and patina's' started by John Homer, Jul 25, 2021.

  1. John Homer

    John Homer Silver

    Just a general question about melting bronze. I have a number 10 crucible and was wondering what the melt time is to pour. I know I know it will vary for the most part but.... I'm using propane for heat in a small furnace. I don't have a way to check temperature on my melt times. Right now I'm about 30 to 35 minutes on my poor which I'm not sure is going to be hot enough due to the fact that some of my molds are not filling properly. Any help is appreciated.

    Thanks
     

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  2. Petee716

    Petee716 Gold Banner Member

    What kind of bronze are you pouring? I pour everdur (silicon bronze). The top surface when skimmed has an almost mesmerizing swirl and hue to it when it's ready to pour. I'm ready to pour in generally 45 minutes from a cold start in my oil furnace, 15 minutes for a second heat. Once everything is molten I dip a hot steel rod to make sure theres no slush and then start to take periodic measurements with the pyrometer. From liquid to super-heat is about 5 minutes.

    Pete
     
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  3. Zapins

    Zapins Gold

    Make a thermocouple its about $55. We have threads on the forum how to make one. Then you can check and pour exactly at the right temperature.
     
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  4. John Homer

    John Homer Silver

    Pouring the same silicon bronze. What is super heat? I am a rookie at this still. Thanks
     
  5. HT1

    HT1 Gold Banner Member

    you NEED a pyrometer, here is mine, you can cheap out on the probe, otherwise, it doent get simpler then this


    V/r HT1

     
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  6. John Homer

    John Homer Silver

    Ok. Does the probe go into the metal to check temperature?
     
  7. Jason

    Jason Gold

    YUP...
     
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  8. Petee716

    Petee716 Gold Banner Member

    Super heat is (for our purposes) the heat above the metal’s point. If the metals melting point is say 1750F, then you want to heat it past that, perhaps to 2225F so it remains molten and sufficiently fluid long enough to fill the mold. Once the metal is completely molten it’s temperature goes up fast:
    Others can probably explain it better but my understanding is that when the solid metal is at its melting temperature, it take a significant amount of additional heat to make the phase change to liquid. Once it has reached that point, its like pulling out a cork and the liquid’s temp shoots right up. I’ve had aluminum gets ridiculously overheated in minutes.

    Pete
     
    Last edited: Jul 25, 2021
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  9. John Homer

    John Homer Silver

    I have a cheap one and it is junk. Put it in the metal and it read "HI" which made me think it didn't reach the temp I needed even though it said 2200
     
  10. John Homer

    John Homer Silver

    Thanks
     
  11. Jason

    Jason Gold

    John, I built a meter like Henry's... (HT1) The probe is about 60bucks and I stuck it on a 5buck meter from fleabay. It's worth every penny. I've gotten pretty good at eyeballing the temp of my bronze, but with the probe, it gives me confidence that I haven't overheated the hell out of my metal.
     
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  12. John Homer

    John Homer Silver

    Going to get me one
     
  13. John Homer

    John Homer Silver

    So I built a similar thermocouple. It works great. Problem is it's melting the thermocouple. I've used it twice. Should I buy the one from Mifco? I paid about $13.00 for this one. I'm pouring bronze @ around 2200 degrees.
     

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  14. Petee716

    Petee716 Gold Banner Member

    I dont know if the mifco probe requires a sheath or not. I think HT1 uses a mifco. maybe he'll chime in. I have one from Mcmaster Carr bought on Raspers recommendation. I sheath mine with 5/8 diameter "graphite" gouging rods also from mcmaster. I can get part numbers if you like. At any rate I drill the gouging rods out with a 12" long 1/4" drill bit from harbor freight. Couple bucks. I do it on my lathe. I start with a good twist drill to get a good guide hole and then mount the 12" drill and peck it down to depth. The probe is too tight to fit the hole so I put the drill bit in a vise and clamped a pair of vise grips on the chuck end of the bit and gave a little (slipping) twist. Just enough to raise a burr, (You know what that burr looks like. Lol), then run it back into the gouging rod for clearance. The gouging rod has to be replaced every 20 heats or so depending on how long I hold it in the exhaust stream to preheat it. Of course I only dip it in the melt with the furnace turned off. Otherwise I'm sure I'd burn the insulation of the wires.

    Pete
     
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  15. John Homer

    John Homer Silver

    Thanks for the information. I watched HT1s video it looked like he puts it in a tube and the end is just sticking out.


     
  16. Jason

    Jason Gold

    The mifco one is used as is. NO sheath req'd. How come I can never find a thread around here when I want the damn thing?:mad:
     
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  17. Jason

    Jason Gold

  18. HT1

    HT1 Gold Banner Member

    it's pretty obvious how much of the probe is supposed to stick out

    https://mifco.com/shop/thermocouple-for-ht-furnaces/replacement-8-thermocouple-tip-2/

    The 8 inch version is still $53.00


    I place it into a 1/2 inch electrical conduit bent 90 (very gradually) out towards the end, the bitter end is slit with hacksaw about an inch and a hose clamp pinches the end shut holding the thermocouple in place,

    I have used 3 in the 12 years I have been casting mostly Brasss


    V/r HT1
     
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  19. Zapins

    Zapins Gold

    Yeah mifco one is nice. I use it. Get the longer probe. I think its like 12 inches. It doesn't melt. Lasts for years as long as you don't smash it.
     
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  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Just curious Petee, why preheat? I would think that is drastically reducing the life of the carbon sheath and am thinking you should get a lot more than 20 dips. My use is just aluminum but I get at least a hundred dips (maybe several hundred) but I think Rasper reported similar life with his in bronze. I don't preheat and just accept the response time to 95% of temp is going to be 30-60 seconds, but with some experience, you can tell where you're going to land as the temp rise slows down. Then I remove it to minimize exposure time. The portion of the sheath exposed to the furnace atmosphere is often consumed more than the part that is immersed. I hold the sheath in a 3/4" stainless tube. There is a Inconel sheathed k-type wrapped in ceramic fiber inside the tube. I'm still using the same Thermocouple 5 years on. Since I started minimizing the exposure time, I have only worn out one sheath from use but have broken two by inadvertently walking into them :mad: as they are stored on my furnace cart. At a little over $1 a piece it would be worth the worry except the time needed to drill them.

    Best,
    Kelly
     
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