Black dust occurrence in injection molding optical lens

[ahmid2003]

Hi, I worked in an injection molding company that produces optical lens. My problem is how to eliminate black dust occurence in the lens?
I badly needed help.

Thank you.

[Suhas]

Hello Ahmid,
Define 'black dust' is this loose on the surface? Or embedded? Also do you still work in the company?
Suhas

[jeffieg]

if it is black specs in the part it is burning the mat. in the compression zone in the barrel so slow the screw down to just get back before mold open.

[ahmid2003]

if it is black specs in the part it is burning the mat. in the compression zone in the barrel so slow the screw down to just get back before mold open.

Black dust occurrence is inside the lense not in surface. zone temp. are 272,275,268,230. back pressure are 30,30,20,0 with a screw rev. of 40 rpm. pull back is 2mm @ 20mm/sec.do I need to lower down zone temp and back pressure/screw rev.?

[rickbatey]

I would cool the first three zones, but how much depends on residence time. Does this press run 24/7 or is shut down? You have to know how to shut PC down or that could be the root cause.
Rick.

[ahmid2003]

machine runs 24/7. we have conducted many trials. still black dust occurs.

[Suhas]

As Rick says, shut down is important with PC. When you say 24-7 you must be shutting it down some time correct? What happens when you start off after pulling the the screw and barrel and giving it a good clean? After how much time do you get the black specs?
Also tell us what is the total shot weight - runners plus parts? and what is the shot size of the machine?
Suhas

[pjhall]

I worked in molded optics for a few years. It is very important to bank the heats when not running the machine. Do not turn the heats off. Once the material cools down it will pull off of the barrel wall. I'm trying to remember what temp we used to bank. I believe it was 300-350 F. I'll go back and looks through my old notes...

Another thing we did (cost big time $$) was have quick change barrels. We could disconnect the entire barrel and install a nice clean one. We would then take the screw / barrel into the Maint. Room where we had a control unit to heat the barel /screw and clean them. Man was that a time saver!!!

[tim12871]

I work with PC myself and have found that shut down is the key.. I would recommend the screw be pulled and cleaned. You also might try some purging compound. Thru DOE I have found ASACLEAN to be the best performer in cleaning the screw.

[arturo aguirre]

Ahmid,

is necessary that you calculate the remanent time of the resin in the barrel if you have a shot size to small the material is this degrading.

regards