PDMS clouding

Successful prints based on Model construction, supports, material selection & printer settings.
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Robert Howle
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PDMS clouding

Post#1 » Fri Sep 12, 2014 3:44 pm

These are a few observations on PDMS clouding. I use 1:1 mix (primarily because it shortens build times due to very short exposure times) and on the present vat on my 1.2 HD machine I have 70 hrs of lamp time (started at 35 hrs and is now at 105 hrs). I do leave the resin in the vat between prints unless it needs filtering. I have stoped cleaning the vat with alcohol or water, I only use paper towels. I had noticed that when u put the model in the ultrasonic that the uncured resing came off as a white milky substance, could this be what exasurbates the clouding of the PDMS (reaction of water with the resin that has seeped into the surface of the PDMS). Since I have discontinued water or alcohol in the vat the number of hrs on the PDMS has def increased. I even posted a picture at 50 or 60 hrs and there was no clouding of any kind. I will post it here again. I am just starting to get some clouding and it started at about 65 hrs. The strange thing is that they are not support based clouding (small circles) but a light clouding of the entire print area (30 xy area). Can't really see where prints were done. This is the first time that i have cleaned and strained resin over an extended period and never let alcohol or water touch the PDMS. There must be some correlation here. I wish some others would try cleaning with paper towels only (I do drain the vat well and use a silicone scraper to squeege the surface) and see if they experience the same non clouding PDMS.

I don't know if u can tell from the pic, but there is no clouding at over 50 hrs of printing. I always print at or near the center. I did not move prints around on the PDMS purpously just to see how long it would take to start clouding. All of the 50+ hrs was at 30 xy 30 z and using 1:1 mix. I also think a contributing factor is the short exposure times with this mix. I do 2 attach layers at 6 base and 1 over and subsequent layers at 1.500 and .50 seconds. I always use 1mm subsequent overlift and 4 sec settle time. I am convinced that this extended PDMS life is due to short exposure times (mostly 1.5 seconds and less) and the absence of water and/or alcohol coming into contact with embeded resin in the surface of the PDMS.

The resin u see along the edge of the PDMS (i still cover entire vat, don't use saver method with the dam) is resin that has gotten down between the PDMS and the sufrace (side walls) of the vat. Can't wipe away with paper towels, but it doesn't matter. Resin left in the vat when cleaning is not an issue, particles in the vat are a problem.

Robert
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Metalcaster
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PDMS clouding

Post#2 » Fri Sep 12, 2014 4:55 pm

Hi Robert,
I mentioned many months ago that I was getting long life and lots of prints (about 200) off of a single pdms...I was wiping it with a sqweegy and paper towel. No alcohol. So, yes, it works !

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Robert Howle
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PDMS clouding

Post#3 » Fri Sep 12, 2014 5:25 pm

Thanks, hope others will read this. I remember your posts about the paper towels, but didn't; make the connection to longer lasting PDMS and possible reaction with whatever residue is in the PDMS with water and or alcohol. Have u noticed the light clouding of the entire build area as opposed to just the round support spotting? Curious about this also.

Robert
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mikej
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PDMS clouding

Post#4 » Sat Sep 13, 2014 12:02 am

I've made this post "sticky", hopefully others will try this technique and provide feedback. If you guys have found the "smoking gun" for pdms cloudiness then my hat's off to you! Thanks for sharing!
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PDMS clouding

Post#5 » Sat Sep 13, 2014 1:04 am

I am using pure cherry, mostly 30xy 30z, on the 1.2 machine. No alcohol or water is used for cleaning until the PDMS is ready to be removed. I have done this for several months with the 1.1 machine and 1:1 resin mix. I am now clouding the PDMS as I always have.
I think the short exposure times is the reason.
I have wondered if heat could also have an effect. Do either of you have a extra fan keeping the machine cooler?
How was the PDMS cured?
Is it slygard ?

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mikej
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PDMS clouding

Post#6 » Sat Sep 13, 2014 1:22 am

Could environmental humidity be a factor? Dry climates + no water/alcohol when cleaning = less clouding?
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perpetual_dreamer
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PDMS clouding

Post#7 » Sat Sep 13, 2014 5:20 am

interesting Robert! probably explains why my pdms starts clouding from a single 4 hour print... During calibration of my 1.2 printer, I was washing my vat with water and also wiped the pdms with paper towel soaked with alcohol almost after every print.

Are the exposure times and print settings for the default pure cherry and your 1:1 cherry/red much different? Would you mind sharing your settings for your 1:1 cherry/red mix? I'd love to go back to the 1:1 mix if it has shorter exposure times and lengthens the pdms life.

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Robert Howle
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PDMS clouding

Post#8 » Sat Sep 13, 2014 6:42 am

This is what I use most of the time. 30 xy and 30 z.

I also use 1.500 and .500 for base and over on subsequent layers.

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Metalcaster
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PDMS clouding

Post#9 » Sat Sep 13, 2014 7:22 am

Hi Robert,
Yes, I only got very light clouding on the pdms after an untold number of hours.... probably 10 long prints as I normally load the table
My Method of cleaning:
Use a plastic squeeggy to move all the Liquid to one corner of the Vat. Pour all Grow Juice material through a paint filter / funel .
I don't wipe the PDMS if it does not need it. If there are tiny pieces sticking in the vat, I will use the squeeggy to move it down to a corner and take it out. No Alcohol is used on the tray.

Attached picture of pieces from my 1.2 machine. 50xy x 30 um 14 ringsImageImage
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noahbern
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PDMS clouding

Post#10 » Sat Sep 13, 2014 7:48 am

What were your settings for the 1:1 with the non HD b9? (1.1 b9)
Is it the same deal with cloudiness for your older machine?

Noah


Quote from Robert Howle on September 13, 2014, 12:42
This is what I use most of the time. 30 xy and 30 z.

I also use 1.500 and .500 for base and over on subsequent layers.

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RobertW
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PDMS clouding

Post#11 » Sat Sep 13, 2014 8:53 am

Thanks for posting this topic Robert. I just came here to search for ways to extend PDMS life and boom there's your post!

My PDMS after approx 45 hrs is quite cloudy and pretty much history now. As you can see, I always print at the finest resolution and the projection window area is less than half of the PDMS area. Is there a tried and true method for using the other half of the PDMS? Seems like such a waste (not to mention hassle) to recoat the vat when more than half of the PDMS is still perfectly new.
Rob
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perpetual_dreamer
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PDMS clouding

Post#12 » Sat Sep 13, 2014 9:15 am

200hrs on a pdms? =o that is amazing! i got heavy clouding after 5 hrs.. probably because i cleaned my pdms with alcohol and wash it with water too.

what kind of 'squeegee' are you all using?

I wish someone would offer an add-on to use the other half of the pdms on a 1.2 machine.. I think its cheap to replace PDMS.. its more of a hassle to recoat

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RobertW
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PDMS clouding

Post#13 » Sat Sep 13, 2014 10:46 am

OOPS! Actually I miscalculated big time and multiplied the wrong numbers. I am correcting the post to read 45 hours, based on 13 prints with an average run time of 3.5 hours.
Rob

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perpetual_dreamer
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Post#14 » Sat Sep 13, 2014 12:26 pm

^ lol i should have thought so.. 200 hrs on a pdms is a heck of a long time

Do you all not use any alcohol anywhere at all? I use alcohol to wipe clean the build table before starting a new print also.

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Robert Howle
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PDMS clouding

Post#15 » Sun Sep 14, 2014 1:00 am

I am keeping trak of time on this PDMS and am at 65 hrs. I am sure the short exposuers with the 1:1 mix is helping. Most of the time I'm at 1.5 base and .5 over. I only wipe the build table if i accidentally touch it with my fingers (oils), other wise I just scrape and print again. Will continue to keep all posted. I do "hang" the tabel after each print for about 30 min to allow most all resin to drip off the print before scrape. I squeege off the PDMS with a soft silicone scraper. LIke metalcaster says you don't have to get it all, just no particles left in the vat. Use basically same method he discribes.

Robert
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tim.yoshi
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PDMS clouding

Post#16 » Sun Sep 14, 2014 1:06 am

Well I told this some time ago, maybe half a year, or more. SO +1 here. I do not use water nor iso never to clean vat - only paper towels. Also I'm trying not to overcure and place angled supports. That's basically most important things to increase PDMS life. Can't say for sure how much it lasts, but it is likely a month's.

Regarding how to use second part of PDMS? Firtst of all try to search Kreffel mod here on forum, quite brilliant idea. Second - I uses simler method - unscrewing the projector from it's base, screwing back with 4-50 mm longer screws (with nuts on the inside) and that way you could use second (closer to front) part of PDMS. Just extend the projector :)
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erikgem
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PDMS clouding

Post#17 » Sun Sep 14, 2014 8:04 am

Check my post "Move on over" http://www.b9c.com/support/?mingleforumaction=viewtopic&t=1970 I use both sides of the pdms. It has worked for me.

Dave

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tim.yoshi
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PDMS clouding

Post#18 » Sun Sep 14, 2014 9:11 pm

Yes, kind of :) On old d535 it works just with plain M4 screws - three of them could hold the weight of projector. But for D912HD probably not - too heavy.
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bvwjewelers
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PDMS clouding

Post#19 » Tue Sep 16, 2014 6:54 am

I thought I would pass this along. After talking with someone at Dow Corning for some time, I learned a few things and wanted to pass them along.

1. First off never clean PDMS with Alcohol, even a little amount will degrade it and cause problems due to absorption.
2. PDMS will degrade at a temperature of 200 celsius.
3. PDMS is fully cured at 150 celsius for 10 min for our use.
4.Suggested to only use warm water and mild soap.

The PDMS should last for a very very long time i'm told as light passing through it will not hurt it, only heat will. Case in point she used the example of tall builds using a silicon base to hold glass on the building lasts for a very long time....but exposed to much concentrated heat it will get smoked. She also said problems could be happening due to keeping PDMS in an oven for an hour at 250 celsius like I know I have been doing.
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Robert Howle
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PDMS clouding

Post#20 » Tue Sep 16, 2014 10:54 am

Very good info, thanks.

Robert
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