Casting Over Flow

Discussion in 'Castings, finishing/ repair/ and patina's' started by John Homer, Jun 8, 2021.

  1. John Homer

    John Homer Copper Banner Member

    I just poured some bronze parts for the first time and had an issue with over flow from my parting lines. Any recommendations on how to fix this? I had my flask clamped together with spring clamps.
     

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  2. Imagine a hydraulic master - slave piston connected where the master is the cross sectional area of your pouring hole and the slave piston is the area of all that bronze flashing in the parting line. Say a 200 to 1 piston area difference and had maybe 150 grams of bronze in the pouring hole, that would give you 30 kilograms of up force over a stroke length of a few millimetres. So you'd need some immovable G clamps able to resist that force and some metal bars over the top of the cope and drag to keep it together. Failing that some heavy lead or iron ingots to stack on top would also work.
     
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  3. Petee716

    Petee716 Gold Banner Member

    What your experiencing is called flash. From the pictures it looks like what Mark is describing above, ie cope and drag are being forced apart. For a small casting the spring clamps would be ok, but what you show above is too big. Even with your flask clamped on the periphery, depending on your cope thickness and/or mass of the casting, your sand can heave as well. I try to prevent both issues by putting a 6” piece of plywood across the width of the flask and clamp the whole thing together on both sides with bar clamps. Not tight. Just enough to keep the clamps from falling off and prevent any movement. With a lower temp metal like aluminum I’ll often just put a piece of plywood on top leaving the sprue exposed and place a couple of brake rotors on top.

    “Doctoring” your molds after they’re rammed can also cause problems with flash, or even runouts.

    Any moldboards or matchplates used while ramming should be in good condition and unwarped. That’s just asking for trouble!

    Pete
     
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  4. HT1

    HT1 Silver Banner Member

    everything Mark and Pete said is true, but given the location of the flash, looks like you pouring temperature was on the high side consider taking it down 50 degrees Fahrenheit .

    if you want to check for sand heave measure the height of the cast parts compared to the pattern, minus shrinkage your part should definitely be smaller then the pattern 3/16 per foot if your parts are bigger you definitely have a problem with the cope lifting or the center of the mold bowing up.

    V/r HT1
    BTW petrobonds green strength is only good to about 18X 18 without supports in the sand, and it looks like you are over it in at least one direction
     
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  5. John Homer

    John Homer Copper Banner Member

    Thanks for the input. I will adjust and see what happens
     

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