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Thread: Blush or Graying at molded part edges

  1. #1
    Join Date
    Sep 2019
    Posts
    2

    Blush or Graying at molded part edges

    Good day all.

    This is my first post to this forum so I'll try to be as specific and brief as possible.

    I have been working in injection molding in China for 16 years and this is the first time I have experienced this issue.

    We make a variety of part sizes (PC/ABS blend resin) and we are getting what might be called 'blush' on the textured appearance surface (MT-11020) and is quite undesirable.

    The blush appears as a graying of the dark blue color along the sides of the parts adjacent to the terminating walls of the part, being the transition between core and cavity creating wall thickness.

    There is no discoloration on the core half surfaces nor does the graying 'wrap' onto the edge of the part. Safe to say my issue seems to be strictly related to the texture and where the melt may be either cool enough and/or the injection pressure has decreased near the end of the shot.

    Fill looks good and geometry as close to perfect as I need. There is no warp in the part(s).

    Photos attached to save a bit of time.

    Any ideas would be greatly appreciated. I'm thinking possibly the tool needs additional venting and perhaps higher tool temperature.

    Thanks for any and all feedback.
    Attached Thumbnails Attached Thumbnails Blush 1.jpg   Blush 2.jpg  

  2. #2
    Join Date
    Aug 2019
    Posts
    13

    Re: Blush or Graying at molded part edges

    It looks as if it could be sticking to the mold on that line... I'd try heating the mold more....

  3. #3
    Join Date
    Sep 2019
    Posts
    2

    Re: Blush or Graying at molded part edges

    Thanks iamplwirtz.

    The part pulls without issues, not sticking to either core or cavity halves of the tool and no scraping on the texture.

    I appreciate the thought and reply though.

  4. #4
    Join Date
    Aug 2019
    Posts
    13

    Re: Blush or Graying at molded part edges

    Has this always been an issue? Whats your mold temp?

  5. #5

    Re: Blush or Graying at molded part edges

    By my opinion it is a pressure issue. Wall thickness and cooling of the melt in the tool. Please try to check, if it appears also on the part without holding pressure. than you will see, from which stage it comes.

  6. #6
    Join Date
    Aug 2011
    Location
    Upstate of South Carolina
    Posts
    636

    Re: Blush or Graying at molded part edges

    Looks like a wall thickness change reading through. I think you’ll have to adjust wall thickness change on underside to fix the issue.
    BTW how much draft is on the part? Little draft could create a dragging incident with the grain as the tool opens.
    Rick.

  7. #7
    Join Date
    Jun 2017
    Location
    Ningbo zhejiang Province China PR
    Posts
    9

    Re: Blush or Graying at molded part edges

    Yes, I agree, it is probably due to the uneven thickness, in inner side, there is probably some cutout inside.

  8. #8
    Join Date
    Sep 2019
    Posts
    5

    Re: Blush or Graying at molded part edges

    I see this a lot myself being from a wall thickness area, someone has mentioned above about turning your hold psi off to see if it is there or not.
    I've been able to fix these issues by dropping pack and hold time.

  9. #9
    Join Date
    Jun 2014
    Location
    EU
    Posts
    64

    Re: Blush or Graying at molded part edges

    :X Someone!

    So whats the result Steve? With PC/ABS it not so clear, can You also make some additional pictures (detail, B side, where are gates, crosscut of the part)
    J

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