- Surface finish is "cloudy" injecting TPE
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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)
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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
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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.
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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)
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Member
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
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- Surface finish is "cloudy" injecting TPE
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