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Thread: dimensional increase after molding - PPO

  1. #1
    Join Date
    May 2018

    dimensional increase after molding - PPO

    Dear Friends

    I am molding a component , material is PPO 30% glass filled. component is like washer but big in size. thickness is 7 mm, outer Dia is 770 mm , inner Dia is 440 mm . shot weight is 2.4 kgs. direct sprue & spoke gates are given in the center processing temperature of around 290 to 300 degree is maintained as specified by material manufacturer . cooling is 45 seconds. circular cooling channels are given in at bottom of core & cavity insert. 800 ton machine is used. a fixture has been used to clamp on both sides of the component to avoid warpage after the component is taken out from the mold.

    the problem is component thickness is increasing by 0.5 mm after taking out from the mold ( 7.5 mm ) & also warpage of around 1.8 mm in thickness & twisting is occurring. it iwll be helpfull if somebody can suggest a suitable remedy
    Attached Thumbnails Attached Thumbnails IMG-20180420-WA0009.jpg   IMG-20180420-WA0014.jpg  

  2. #2
    Join Date
    Aug 2014
    Saint Paul, MN

    Re: dimensional increase after molding - PPO

    Is the part thickness consistent at 7.5 mm, or is it thicker in the middle & thinner at the edges? If it’s uniform, you may be blowing the mold open (plastic pressure overcoming the clamp). I estimate your clamp force at right around 5 tons per square inch, which should be adequate – but that assumes you are getting the full 800 tons from the machine. If the thickness is not uniform try increasing the cooling time. You might be seeing effects of stresses in a hard skin over a soft interior.

  3. #3
    Join Date
    Feb 2016
    San Francisco Bay Area, CA

    Re: dimensional increase after molding - PPO

    Cooling is 45 seconds, have you tried cooling for 90 seconds, 120 seconds or 180 seconds for kicks?

    How long is your pack time?
    Do fill-only parts (no pack time used) exhibit the same, better, or worse warpage as your nominal process?

  4. #4
    Join Date
    Aug 2011
    Upstate of South Carolina

    Re: dimensional increase after molding - PPO

    What is your pack/hold pressures and times? Have you performed a gate freeze study? Is the thickness change in the same areas or say just between the gates? Are you sure the cavity plates are properly supported or have enough Pre-load to resist deflection?

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