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  • 1.  Extrusion Blow Molding Best Practice.

    Posted 05-17-2019 09:00 AM
    I am trying to understand extrusion blow molding tolerances for bottle neck detail. Bottles are made for HDPE.

    The tolerances I have are:
    • 41.400mm ±0.15mm for the Thread Major diameter tolerance
    • 39.200mm ±0.15mm for the Thread Minor diameter tolerance
    • 37.000mm ±0.10mm for the Bore diameter tolerance
    Are the above acceptable tolerances for this type of extrusion blow molded bottle in HDPE?

    Thank you in advance for your feedback.


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    Peter Turcich
    Packaging Manager
    Eco-tech Solutions Ltd (ecostore)
    Auckland
    NEW ZEALAND
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  • 2.  RE: Extrusion Blow Molding Best Practice.

    Posted 06-27-2019 08:34 AM
    Edited by Lonnie Jaycox 06-27-2019 12:21 PM
    This will be affected by the type of closure applied.
    In looking at this issue, I see that the SPI specifications are no longer supported or published as they used to be.
    There are standard tolerances available, but their use is closure dependent.
    There will be a recommended neck finish drawing, with tolerances, available from the closure manufacturer.  It may likely be the SPI standard tolerances, but that should be checked. 
    I thought GPI still had plastic finishes listed, but they may no longer do this.  There have been changes in the industry in the last few years that have made plastic neck finishes harder to spec from a public source.

    From a general view; those T and E tolerances look tight for an extruded neck.  Those look like tolerances for injected finishes.
    If the closure was designed for an injection neck, you may have trouble holding acceptable performance tolerances on extruded finishes.  


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    Lonnie Jaycox CPP, CDGP
    Saint Louis, MO
    lonnie@jaycoxconsulting.com
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  • 3.  RE: Extrusion Blow Molding Best Practice.

    Posted 06-28-2019 03:00 PM
    Looking back on my old 1-gallon HDPE bottle thread specs, your +/- .15mm thread tolerances look good.  The 1-gallon tolerances specified were +/- .005in. which calculates out to +/-.127mm.  That thread profile was for a 38mm finish.  A +/- .150mm spec should be within molding capabilities.
    Good luck

    ------------------------------
    John Chomistek
    Packaging Lecturer/Program Director
    Transforming tomorrow's Packaging Engineers today
    Phone: 715-232-5399
    Email: chomistekj@uwstout.edu
    ------------------------------



  • 4.  RE: Extrusion Blow Molding Best Practice.

    Posted 07-01-2019 08:26 AM
    Edited by Lonnie Jaycox 07-01-2019 12:59 PM
    SPI tolerances on T and E for standard CT neck finishes were/are +/-.012".  Most blow molders can work within that (+/-.010" or so) but not usually within +/-.005" unless it is a special type of product and the mold/resin/process systems are specifically designed to produce it.  It can be done, at a cost.
    That can be done under certain conditions, and is achievable by molders that have advantageous conditions, but it is not usually how these necks would be specified.  I would not recommend it unless the closure/neck insert required the tight tolerance.  Some closure/neck systems do.  But, you will be paying for that level of tolerance either through slower cycle times, limited resin choices, or limited supplier choices.  Why pay the price if it is not needed?
    I am also curious about the "I" dimension having a 33% lower tolerance than the E.  Controlled I's are common for in-the-neck fitments.  The target for that is set with the blow pin diameter; but it will move sympathetically with E due to neck shrinkage. What mechanism would allow for I to have a lower tolerance range than E, particularly a 33% lower tolerance?
    While those tolerances are achievable under certain conditions, I would want to justify the need for each considering what the closure and neck insert actually require.  Then I would look and see if I could find another system to solve those problems that would allow more standard manufacturing blow tolerances.  
    We saw these types of problems with tamper bands designed for injected PET bottles being adopted onto extruded HDPE bottles.  That is why closure manufacturers at the time designed closures with tamper bands that would work with the larger variances in A that were experienced with extruded HDPE necks.
    I suspect if a salesperson shows up with that spec for a quote; it would be charged accordingly.

    ------------------------------
    Lonnie Jaycox CPP, CDGP
    Saint Louis, MO
    lonnie@jaycoxconsulting.com
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    Original Message


  • 5.  RE: Extrusion Blow Molding Best Practice.

    Posted 07-03-2019 05:09 PM

    Placon is doing a lot with recycled content for PET and PP.  https://www.placon.com/

     

    John Blake

    Gartner
    Senior Director Analyst

    Packaging, Label Artwork Management, Product Lifecycle Management
    Mobile: +1 914-396-7736

    john.blake@gartner.com
    www.gartner.com  l     www.linkedin.com/in/john-blake-pkg-engineering

     

     

     



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    ------Original Message------

    Looking back on my old 1-gallon HDPE bottle thread specs, your +/- .15mm thread tolerances look good.  The 1-gallon tolerances specified were +/- .005in. which calculates out to +/-.127mm.  That thread profile was for a 38mm finish.  A +/- .150mm spec should be within molding capabilities.
    Good luck

    ------------------------------
    John Chomistek
    Packaging Lecturer/Program Director
    Transforming tomorrow's Packaging Engineers today
    Phone: 715-232-5399
    Email: chomistekj@uwstout.edu
    ------------------------------


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