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IndustryArena Forum > Material Technology > Plastic injection > Surface finish is "cloudy" injecting TPE
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  1. #1
    Junior Member
    Join Date
    Oct 2013
    Posts
    185

    Surface finish is "cloudy" injecting TPE

    I'm getting a "cloudy" surface when injection TPE. I used 4 or 5 different types/brands of TPE in 3 different molds and the surface is always cloudy. I just can't figure out what the problem might be.

    Here are the parameters:

    I use a Dr. Boy 50 T2
    PCS Hot Sprue Bushing - direct gate (pin point gate with 1mm diameter)
    Used the TPE straight out of the bag and suspected that the cloudiness might be caused by moisture. Started pre-drying the TPE, but didn't fix the problem.
    Played pretty much with every single parameter available but couldn't fix the problem.
    Also tested a polished mold vs a sand blasted mold... same cloudiness is visible.


    BTW: The round black spot in the middle is not what I'm talking about... this is caused by the air poppet valve (it has a polished surface unlike the rest of the mold which is sandblasted)


    Click image for larger version. 

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  2. #2

    Join Date
    Jan 2005
    Posts
    10419

    Re: Surface finish is "cloudy" injecting TPE

    cordvision

    As you know there are lots of things that can cause problems like this, Venting around the parting line is very important, more so in the sprue area venting depth .0008

    Sprue placement

    Mold Temperature thin parts 105 to 140

    Back Pressure up to 710 psi

    Screw Speed up to 75 rpm

    Material Temperature (Barrel Temperature ) 355 to 425

    Dryness of Material
    Mactec54

  3. #3
    Junior Member
    Join Date
    Oct 2013
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    185

    Re: Surface finish is "cloudy" injecting TPE

    Thank you very much for the info. I added more vents but still got the same problem. I noticed that if I raise the temperature of the hot sprue bushing and nozzle up to 530 degrees (which is technically way too high), I can reduce the cloudiness a little bit but it doesn't disappear. I then decided to injection mold the part with PP because it is less heat sensitive. However, the parts are still cloudy. I also cleaned out the hopper, just in case there was some contamination.

    I also took a flawed part to a local injection molding place and talked to a few people. They didn't have a good explanation for what the cause might be.


    I currently have a nozzle with a needle nose valve installed. I'm going to switch if for a regular nozzle, just in case that has something to do with it. Not sure what else I could try.

  4. #4
    Junior Member
    Join Date
    Oct 2013
    Posts
    185

    Re: Surface finish is "cloudy" injecting TPE

    Question: I tried removing my needle valve nozzle today and replace it with an conventional nozzle. I suspect the needle valve nozzle might actually be responsible for the cloudy parts.
    I heated everything up to temperature and then tried to unscrew it (should be regular threads). I used a large hex wrench and a 3-4 foot extension to get more leverage. It just won't unscrew and I'm worried that if I apply even more force, I will break something. Any suggestions what to do in this case? Any tricks?
    (see pic for what the nozzle looks like that I'm trying to unscrew)

    Attachment 291546

  5. #5

    Join Date
    Jan 2005
    Posts
    10419

    Re: Surface finish is "cloudy" injecting TPE

    cordvision

    Try just the heater band on the Barrel & don't heat the nozzle, if that does not work, try it when it is cold, they can be a beast to remove, make sure when you do get it removed, your replacement nozzle put lots of anti seize compound on & in the threads, this will help the next time you have to change it
    Mactec54

  6. #6
    Junior Member
    Join Date
    Oct 2013
    Posts
    185

    Re: Surface finish is "cloudy" injecting TPE

    Thank you very much for all your help. I finally was able to remove the nozzle and it fixed the problem

    I removed the whole base that holds the nozzle, then milled a soft jaw fixture for it, and used a 5 foot lever in combination with a striking wrench get it out of the base. I was seriously worried that I would mess up the threads, but everything is well. The manufacturer of the nozzle told me that it is 19 years old, and I suspect I was the first one to remove it in all those years.

    I switched it with a standard nozzle, and the cloudiness is gone. Making nice parts now

    Click image for larger version. 

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