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Thread: White streaks or spots

  1. #1
    Join Date
    Oct 2020
    Posts
    12

    Question White streaks or spots

    Hi all,

    New day with a new challenge in injection molding. the problem that I face in the injection is white spots or streaks in the intern of the part, the material I use is Nylon with Glass Fiber 35 %. first I worked on temperature, the maximum is 290 C as mentioned in the material datasheet for the mold the temperature 80 (DS between 60-90). Then I try to work in Injection speed (I lowered them) but the Glass Fiber ASpect was good.

    Additionnal information :
    Backpressure 70 Bar
    injection speed 30/50/60 (mm/s) (the spots appeared between 30/50)
    Pressure 800 Bar
    Mold with 4 cavities (all of them have the same prob.)

    Any suggestions would be appreciated.

    Thanks.
    Attached Thumbnails Attached Thumbnails image.jpg  

  2. #2
    Join Date
    Oct 2020
    Posts
    12

    Re: White streaks or spots

    N.B: I think that is a fiber accumulation.

  3. #3
    Join Date
    Aug 2014
    Location
    Saint Paul, MN
    Posts
    181

    Re: White streaks or spots

    Is the location of the defect always the same, or is it random? Where is it in relation to the gate? Is the problem consistent throughout the run, or is it better/worse at start up? If it is segregated fiber at the surface, you might be able to bury it by raising the mold temp to 90 - 95C.

  4. #4
    Join Date
    Oct 2020
    Posts
    12

    Re: White streaks or spots

    Hi,
    1- yes the location is the same.
    2- the part is like a "cup" and the location of the gate is in the bottom "direct injection", the defect is between 30/50 mm/Sec (between 30/60 mm for injection course).
    3- No, the defect appeared in all parts between 30/60 in the injection course, but sometimes it appeared at the start of the injection.
    4- the defect appeared internally in the parts and externally it appeared a few times.

  5. #5

    Re: White streaks or spots

    Based on your description listed above and the defect shown I would suggest you check your nozzle heater bands and or thermocouple. It appears your injecting a cold slug of material because of the direct gating.There is no other place for the cold slug to go except for the surfaces of the part. All too the nozzle thermocouple is placed directly under a heater band causing the heats to appear to be up to temperature but actually be much lower.

  6. #6
    Join Date
    Oct 2020
    Posts
    12

    Re: White streaks or spots

    thank you I will check them.

  7. #7
    Join Date
    Sep 2014
    Location
    albuquerque
    Posts
    65

    Re: White streaks or spots

    Greetings;

    I would suggest looking at your dryer also. Drying temp? Drying time? Dew point? Does the part run well for a while after it has been down and then start with the streaks? Does the material pop and hiss when purging?

    Just something else to look at

  8. #8
    Join Date
    Oct 2020
    Posts
    12

    Re: White streaks or spots

    thank you for your suggestion, I will check them.

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