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Thread: Excessive contraction on cores.

  1. #1
    Join Date
    Apr 2019
    Posts
    23

    Excessive contraction on cores.

    Hi, guys.

    Im having some trouble with a new clear cup made of PP random copolymer DATA SHEET

    At the moment of the ejection I feel that the piece contracts too much on the core and fails to eject. In my experience this almost always happens when there is not enough material in the shoot or when packing pressure is too low so I tried those fixes to those problems without success.

    Since this is an IML cup when I run the initial setup I run it without label, and it works almost fine.
    NO LABEL EJECTION (VIDEO)

    But when I add the label the ejection fails almost completly.
    LABEL EJECTION (VIDEO)

    During the setup I use a shoot of 63.5mm and when adding the label to the equation almost everytime I need to compensate by reducing 0.5mm of the shoot.
    Label weight: 2.4gr Thickness: 0.06mm
    WEIGHT
    THICKNESS

    This are my machine parameters:
    INJECTION PARAMETERS
    INTERVAL - SPEED PARAMETERS
    THERMAL PROFILE
    HOT RUNNER PARAMETERS


    I'm having a really hard time and ran out of ideas son thanks in advance form any help.

    Almost forgot: MOLD TEMP is set to 20C, tried with 25C - 15C - 10C

  2. #2
    Join Date
    Apr 2020
    Location
    Traverse City, MI
    Posts
    14

    Re: Excessive contraction on cores.

    Horeki,

    It appears that you have a coefficient of friction issue preventing the product from being ejected. Is the mold coated?
    I would be curious of the water circuitry (how many gpm, pressure, how many MTCU's).

    I would invite you to PM me and we can have further conversations.

    Thanks,

    Cory

  3. #3
    Join Date
    Apr 2019
    Posts
    23

    Re: Excessive contraction on cores.

    I don't think its a friction issue, since the contraction of the piece it's blocking the air ejectors.
    Actually I reached a good result turning off completely the chiller.
    VIDEOS
    CHILLER OFF AND NO WATER FLOW (Works fine)

    WITH CHILLER ON AND WATER FLOW (Check the ending, pieces fail to eject)

    The chiller details are: 5 metric ton chiller, pump pressure it's rated at 60psi.

  4. #4
    Join Date
    Aug 2011
    Location
    Santa Rosa, CA
    Posts
    93

    Re: Excessive contraction on cores.

    I have never run a mold with only air ejection. Stripper would be best. But, without redesigning the complete mold you could try increasing the diameter of the poppet and/or increase the air pressure (possibly add an accumulator to run higher then your shop air). The label will make it harder to eject.

    Running it w/o the chiller may work for a few shots as shown in your video, but that will be a problem when those cores heat up...

  5. #5
    Join Date
    Feb 2020
    Posts
    14

    Re: Excessive contraction on cores.

    it appears that you are running both air poppet in parallel on the same tiny air line, if one release before the other you will lose all pressure to the 2nd and it won't open. I would suggest a larger diameter hose to maybe have more volume of air behind the valve before it release. or maybe run on separate air circuits, but if one part is tighter on the core than the other i would think there is some sort of uneven cooling of the tool.

    based on the DME catalog a standard valve run on 60~90 psi.

  6. #6
    Join Date
    Apr 2019
    Posts
    23

    Re: Excessive contraction on cores.

    Quote Originally Posted by pjhall View Post
    pjhall
    Thanks for the advice.

    I can’t redesign the mold, the thing I did was to alter the ejector solenoid valve activation sequence and got better results.
    Actually I’m not running the process without cooling, I’ve requested a MTC to heat cores and cool cavities, since the problem it’s the ejection from the cores I think the extra heat would help.

  7. #7
    Join Date
    Apr 2019
    Posts
    23

    Re: Excessive contraction on cores.

    Quote Originally Posted by ijchan223 View Post
    ijchan
    Yep, I’ve already installed a new solenoid valve and line for each frontal air ejector and put a little delay of 0.1s on 2 of them and it works better. As you mention I think the issue it’s a over cooling issue, resin it’s contracting really fast and it doesn’t allow for the ejectors to work.

    I’ll be installing a MTC tomorrow to see if a higher temp on cores helps to mitigate the problem.

  8. #8
    Join Date
    Apr 2019
    Posts
    23

    Re: Excessive contraction on cores.

    Mark this one as solved.
    What I did to solve the issue?
    -Installed a new 2 zones MTC set the mold cores at 45C and the cavities at 20C
    -Made a reduction of temp (220C to 215)on the thermal profile to compensate the higher temp on the mold cores.
    -Modified the sequence and solenoid valve configuration of the air rejection system.

  9. #9
    Join Date
    Oct 2018
    Posts
    22

    Re: Excessive contraction on cores.

    Very nice job troubleshooting as a group and thanks for the final feedback on what resolved this issue.

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