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Thread: Resin change.

  1. #1
    Join Date
    Apr 2019
    Posts
    23

    Resin change.

    Yesterday some corporate fool decided that it was a good idea to change production resins, so this morning I received a few tons of formoleme 2550A (pp coopolymer) and not my usual formoleme 4142T (pp homopolymer).

    So short tale is that I’m unable to reach any results with the new resin (my line is IML cups) one of the pieces keeps stuck on the core (mobile part), air ejector inflates the piece and it breaks and the nozzle in that cavity (No.2) has leakage.

    1.- Tried reducing Back Pressure to avoid over packing and no change.
    2.- Tried augmenting Hold Pressure, injection force and reduced cooling to avoid under packing, no change.
    3.- Reverted Hold P and Cooling, reduced RPM, reduced Back P and Reduced barrel temp, it worked, but... without a label and as son as I start the IML robot and there’s a label in the cavity the problem is there again.

    My job is on the line because of this and I’ve been stuck on this problem for hours.

    Mold Diagram 3 zones hot runner:
    C1
    Z1
    C2 (this is the cavity with the problem)

    Process details:
    Thermal profile - 230, 227, 220, 210, hopper OFF C
    Z1- 230, C1- 230, C2- 230 C
    Back P: 7kgf
    Screw Speed: 150rpm
    Decompression: 3mm
    Injection speed 210mm/s
    Hold P: 550kgf, 0.9s
    Injection Force: 1450kgf
    Cooling: 2s
    Mold temp :15C
    Cycle Time: 9.6s





    Click image for larger version. 

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  2. #2
    Join Date
    Mar 2017
    Location
    South Africa
    Posts
    23

    Re: Resin change.

    At a quick glance - The copolymer is tougher than the homopolymer. Up the cooling a fraction?

  3. #3
    Join Date
    Apr 2019
    Posts
    23

    Re: Resin change.

    I’ve tried already augmenting cooling time alone and the problem persists.
    All guides and the processing guide of the resin maker points that core sticking is caused by overpacking and suggest to reduce packing pressure and time and augment cooling, but... nothing gets better.
    As I mentioned before without label the cycle runs normally but as son as there is a label in the cavity drooling stars to occur and the piece sticks to the core.

  4. #4
    Join Date
    Feb 2016
    Location
    San Francisco Bay Area, CA
    Posts
    199

    Re: Resin change.

    Parts sticking to the core or cavity?

    Verify fill-only parts - The melt flow from your first material is higher then your new material, you may need to adjust shot size or melt temps as a result.
    Plastic shrinks hard to colder steel - try running the cavity slightly colder than your core. Or vice versa
    Use a profiled pack pressure - Pack parts out more at distal end and less at the gate. Or vice versa

    If you (or someone else) had been using tools to remove parts from the steel, it's very possible the steel could have little burrs or scratches preventing ejection of parts

    Does mold release help?
    find out if the mold release helps on the cavity or the core, then you can narrow down where it's sticking

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