Ultem plate out on lens inserts after molding

[Joseph Roberts]

Molding a very small lens using PEI or Ultem for the base polymer. Problem is plate out of the Ultem resin on our diamond turned inserts. I know that there are release coatings that could be used and I am looking for anyone who may have this same issue or someone who already found a cure for this. Tool running around 280'F with a melt temperature of 695'F air shot. Using 35% of shot capacity of press. No issues with residence time in barrel base on .3oz. shot press being used. Any help greatly appreciated.

 

[IRstuff]

Seems to me that this is something that your resin supplier should be very familiar with; have you discussed with them?

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[Joseph Roberts]

Our material supplier has not been that much help. Due to the size of the plate out they can not get enough of a sample to do testing on. The only response that they sent me was that they feel its low level ligamits coming out of the resin. We have tried dedusting resin before molding, tried elevated temperatures on both the resin and even the drying of the polymer but still no success. Longer cycle times no success, nothing I have tried has helped to remove or eliminate the issue at hand.

 

[btrueblood]

Try a lower opening or de-molding temperature?

 

[Joseph Roberts]

I can not run the tool at a cooler temperature. When this is done the clarity of the part is gone and the light transmission going through the array diminishes enough to make the part NG. In order to keep the clarity there I need the 280'F steel temperature. I wish that I had induction heating which would allow me to run the tool at the elevated temperature then cool the tool down to an appropriate temperature for demolding. I appreciate your feed back Thanks

 

[btrueblood]

Yes, I was assuming you had the ability to cool the mold after the shot and prior to opening/demolding. You can't cool the tool with air-blast or even steam?

 

[Joseph Roberts]

Tool running with Electric Heaters, job runs in a clean room so steam or air is not an option. In order to reduce the tool steel temperature down low enough I would need to look at CO2 cooling directed at the insert. I have had someone come in with the unit for a demo but tough to justify for only one job. Thanks keep the ideas coming because I am at a brick wall right now trying to resolve with what we have.

 

[IRstuff]

What kind of clean room? There are those that are already plumbed for LN2 and nitrogen

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[Joseph Roberts]

Ours is a class 7 used strictly for molding. ours only has water and air lines coming into the the room. Air to operate the robotics and water to cool to molding machines. We do not have the LN2 or nitrogen plumbed into it. The unit I demoed in house uses a portable tank for the CO2 cooling device. I just read about another company in Germany that has developed a variotherm process which is similar to what Roc Tool does but it sounds less expensive to purchase. There product wont be available until January of 2018. Have to wait on that one. Thanks

 

[btrueblood]

Is this a compression or injection mold? I'm assuming injection mold. Any chance of running cooling water into one half intermittently (i.e. shut off and drain the tool prior to heating cycle, then open valve and cool after the shot). You'd have to machine cooling passages in the tool, or on a base plate that you attach behind/beneath the tool. CO2 cooling with a hand-directed "wand" or plumbed into the mold with cooling passages? If the first, it wouldn't be too hard to make a hand tool to direct a C02 gas stream.

 

[Joseph Roberts]

It is an Injection mold. I would have to look at the tool drawings and see if there is enough room to adapt cooling line to the inserts themselves. I could rig up a solenoid valve that after injection I trigger the valve to allow the water to enter the tool. I think I would have to be careful since the tool will be running around 280'F do not want to crack the steel from the thermal shock. I have looked at trying to incorporate a line using flex tubing to see if I can get close enough to the insert and try compressed air first and see how it works out. If I see an improvement I could then try CO2 and pipe it in and see the results. The hand held wand would be tough to incorporate. Your mind set makes a lot of sense to me just trying to see which way to incorporate it in the tool. One insert located in a cam which is so small it would be very difficult to put cooling lines in, thats why looking at the tubing as a way to go. You have been extremely helpful here and Thanks again. If something else comes to mind just let me know.

 

[btrueblood]

I get you. I'd also worry about warping the lens due to the thermal distortions...but maybe that is less of a concern than the surface finish?

 

[Joseph Roberts]

I have to keep both of them in mind. Holding center to center on the lens insert to 2 microns so that is critical as well as the surface finish. We are looking into the drawings now to see what is feasible for cooling lines and if that does not work incorporating smaller holes in the tool to allow air or CO2 to be applied. Keep you posted Thanks

 

[btrueblood]

Good luck