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Thread: Sanity Check

  1. #1
    Join Date
    Jul 2012
    Location
    Belle Vernon, PA
    Posts
    140

    Sanity Check

    Hi all,

    Over the last few days we got in a PBT job that we’re having issues with (first time running this material). To bring the parts close to tolerance (one dimension is in, the rest are under some a small amount, others a large), we’re having to pack the part out big time. Currently injecting around 16k psi with a 60% holding, temps from 440-460 F, mold at 140 F, also a somewhat slow injection to keep the injection profile under control (set at 10-15%). Any suggestions on things to try to get this part to shrink less? We’re cooling around 20 seconds but the parts are barely touchable after they come out.

    Side note, customer provided their set-up sheets which their numbers are less than ours (1100 psi?, 440-450F, cooling for 15 seconds) and we get really bad results when we do this. Any suggestions would be appreciated.

    Thanks

  2. #2
    Join Date
    Dec 2012
    Location
    Serbia
    Posts
    102

    Re: Sanity Check

    Hi,

    If you made price by customers parameters ofcourse they will put smaller cycle time.
    Dont know how big part is but i have somwhere 40-60s cooling.
    One of idea is to try longer holding instead of higher.
    Maybie to try to play, faster injection and longer holding, especialy in first step. Sometimes happens that material "returns" to tool and as resault is bigger shrinkage.
    Also what is worht to check is gate size.
    Regards,

  3. #3
    Join Date
    Aug 2011
    Posts
    623

    Re: Sanity Check

    Hi,
    Those pressures provided are hydraulic pressures. What does that translate to in plastic pressure?
    For PBT, mainly work with pack and hold pressures. Are you sue the gate is sealed? Do a gate seal study to make sure.
    You will need to do a quick DOE. (I can help you at no cost, let me know)
    -Suhas

  4. #4
    Join Date
    Jul 2012
    Location
    Belle Vernon, PA
    Posts
    140

    Re: Sanity Check

    Following up to this;

    I got a last-shot sample from my customer. Their sample measures to the same as what we're getting, so I know it's not an actual process issue.

    They ended up OK'ing our parts. Thanks for the help anyway.

  5. #5
    Join Date
    Sep 2018
    Location
    Portland, OR
    Posts
    46

    Re: Sanity Check

    I hate how often that happens. Glad you got it resolved and thanks for the follow-up.

  6. #6

    Re: Sanity Check

    All too common occurrence. Have a print, make a model, shot parts, approve but don't update drawings.

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