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Thread: Processing Troubleshooting

  1. #1
    Join Date
    Jul 2012
    Location
    Belle Vernon, PA
    Posts
    126

    Processing Troubleshooting

    Good Evening,

    I'm injection molding some parts from homopolymer Polypro. We're getting these white marks on the same spot on every part. I'm trying to troubleshoot what it is and how to fix it. It's a white mark that is causing shortness in that spot. I was thinking it's some type of "pre-burn," as when I bump the injection speed up, it does burn there. I can't seem to get this to go away, even with treating it like a burn (lowering injection speed and pressure, lowering temp, lowering residence time). Any suggestions would be appreciated.


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  2. #2
    Join Date
    Sep 2013
    Posts
    114

    Re: Processing Troubleshooting

    cant see pictures, cant se gate positions, set the full picture including runner,

  3. #3
    Join Date
    Jun 2014
    Location
    EU
    Posts
    85

    Re: Processing Troubleshooting

    Hi,

    its trapped air. It means You have to provide proper airventing, but first start with parameters.
    Check the clamping tonnage first and set it safe low as possible. Than play with temperatures and injection speed. Try to moove it a bit to the corner. Part have probably only one injection point so it will not work at all. Than ask toolmaker to make a proper air venting there.
    First by slightly roughing the split line surface of the tool at the place of white spot only (roughing pater 600-800grain) - DONīT TOUCH THE PARTING LINE NEVER!
    Than by groove the the airventing channel close to the point of burn mark - The skilled tollmaker should know how to do it.

    J

  4. #4
    Join Date
    Jul 2012
    Location
    Belle Vernon, PA
    Posts
    126

    Re: Processing Troubleshooting

    Quote Originally Posted by Josue View Post
    cant see pictures, cant se gate positions, set the full picture including runner,
    I can't post anything more than I already have, sorry.

    Quote Originally Posted by Jendalf View Post
    Hi,

    its trapped air. It means You have to provide proper airventing, but first start with parameters.
    Check the clamping tonnage first and set it safe low as possible. Than play with temperatures and injection speed. Try to moove it a bit to the corner. Part have probably only one injection point so it will not work at all. Than ask toolmaker to make a proper air venting there.
    First by slightly roughing the split line surface of the tool at the place of white spot only (roughing pater 600-800grain) - DONīT TOUCH THE PARTING LINE NEVER!
    Than by groove the the airventing channel close to the point of burn mark - The skilled tollmaker should know how to do it.

    J
    That's what I was thinking too, but we have run this tool over the last year and this has been the first time we've had this issue. This is also the first time we've run this color, maybe that's causing an issue as well. I'm going to play with it this week and see if I can get any differences out of the other colors we run.

  5. #5
    Join Date
    Mar 2017
    Location
    South Africa
    Posts
    10

    Re: Processing Troubleshooting

    Use a small piece of masking tape on the vent is a quick way to check if venting is your issue.

  6. #6
    Join Date
    Jun 2014
    Location
    EU
    Posts
    85

    Re: Processing Troubleshooting

    Quote Originally Posted by Crabstix View Post
    Use a small piece of masking tape on the vent is a quick way to check if venting is your issue.
    Thats good point to check how the contact surfce looks like.

    When You do the soft airventing than after some months this airventing is completly off or different how the tool halves are touching each other.

    Check that with the paper or spotting colour also.

    Share pictures if you can,

    thx
    J

  7. #7
    Join Date
    Jul 2012
    Location
    Belle Vernon, PA
    Posts
    126

    Re: Processing Troubleshooting

    I lowered the tonnage and it seemed to go away. Thanks!

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