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Thread: vacuum assisted venting

  1. #1

    Talking vacuum assisted venting

    Hello to all,

    We have an issue, and would appreciate some help/feedback.....

    We have a few tools that are front panels for dishwashers made out of abs.... All these tools with this material has the same issue.....at the end of fill, at the parting line, you can see a row of tiny "oil droplets". They easily wipes off, but come back in as little as 30 minutes with the tool running, and if you don't clean the mold every 30 minutes you will get intermittent "gas trap blobs" on the part at the end of fill, ...not very big, but big enough to cause a defect in the customer's eyes.

    I believe the tool is properly vented,(and taped too) and the issue lies with the material, but we are stuck with the material...... so I was wondering what would happen if we retrofit the tools with vacuum at the parting line to give a constant vacuum (at least when mold is closed) to the vents/ vent dumps. This would hopefully pull out those "oil droplets" and leave the parting line vents clean(er).

    Has anyone done this before? Is there an aftermarket kit for such?

    Thanks! Joel

  2. #2
    Join Date
    Aug 2011
    Posts
    496

    Re: vacuum assisted venting

    Done it with an "O" ring on PL and also used porcerax inserts. It worked. Inserts were cleaned ultrasonically during PM


    KOM

    brent

  3. #3
    Join Date
    Aug 2011
    Location
    Upstate of South Carolina
    Posts
    552

    Re: vacuum assisted venting

    I think if you could reduce your barrel temperatures you may not drive this additive out of the resin. BTW- Is this pre-colored or colored at the press? It may be from the carrier resin or UV package in the color. We have a mold that has cavity vacuum on it. Word is they had air trap and poor knitline strength at end of fill. You have to O-ring seal the ejection plate and return pins to make it work.
    Rick.

  4. #4

    Re: vacuum assisted venting

    Thx Brent!

  5. #5

    Re: vacuum assisted venting

    Quote Originally Posted by rickbatey View Post
    I think if you could reduce your barrel temperatures you may not drive this additive out of the resin. BTW- Is this pre-colored or colored at the press? It may be from the carrier resin or UV package in the color. We have a mold that has cavity vacuum on it. Word is they had air trap and poor knitline strength at end of fill. You have to O-ring seal the ejection plate and return pins to make it work.
    Rick.
    Rick, If I tell you this is pre-colored ABS..... what would that imply? ........we might be able to reduce our barrel temps... although we are in the middle of the recommended range currently.

    Thx! Joel

  6. #6
    Join Date
    Aug 2011
    Posts
    496

    Re: vacuum assisted venting

    We used a standard vacuum pump (small) from McMaster-Carr and were happy with the results.

    KOM
    brent

  7. #7
    Join Date
    Aug 2011
    Location
    Upstate of South Carolina
    Posts
    552

    Re: vacuum assisted venting

    Joel,
    Well it means to me that you might still be too hot, residence time or color or additive degrading in melt, melt induced shear degradation, or maybe you’re even too cold causing the issue? I’m not a fan of special screws, barrels, NRV’s, or nozzles due to loss of flexibility in production requirements.
    BTW can you read the actual screw pressure while charging the barrel for another shot? I’m curious to know what is the pressure required. That is what I use to truly determine residence time.
    Rick.

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