Draken Castable

GaryGary Member, Backers
I have been trying to generate a dependable workflow for the new castable resin. So far my results are mixed. The castings have a good deal of texture - but not horrific.<img src="http://www.garysnyderjewelry.com/data/uploads/DrakenCastable1.jpg"/><br><img src="http://www.garysnyderjewelry.com/data/uploads/DrakenCastabe2.jpg"/>  <p>
My kiln has no venting (table top furnace), so I burn out with the door cracked open.
schedule is (note my controller doesn't understand ramp rates, it ramps over a period of time)  
room to 300F over 15 minutes
300F for 45 minues
300F to 700F over 15 minutes
700F for 1 hour 45 minutes
700F to 900F over 15 minutes
900F for 45 minutes
900F to 1650 over 15 minutes
1650 for 4 hours
1650 to 975F over 15 minutes
Hold at 975 till cast.

Using plasticast w/bandust in a 3.5" flask, cured for4-6 hours and soaked for one minute before loading into the kiln at 300F,

 I have been having a lot of trouble getting reliable prints. Lots of failures. In Ron's posting on mj castable he pictured an array of rings with all cracked in the same spot - I've experienced exactly this with the draken resin.

All 4 rings cracked in exactly the same spot.  <img src="http://www.garysnyderjewelry.com/data/uploads/DrakenCastabe3.jpg/>;
I don't see how it could be a peel issue, due to the way the rings are supported, but I here to learn. 

Exposure times are about twice what I need for MJ SR Yellow - my times don't compare to ron's because I'm using a stock viewsonic projector in slot 3, and my times are generally about twice what ron uses with his rig. 

I've also experienced a lot of separating from supports, print throughs and fill ins. , etc. it's tough to hone in on optimal exposure. 

I'm using one of the clear sided vats - which has served me so well I'm afraid to put the new yellow sided vat into use. No problems with sticking to the build plate, but frequent problems with model separating from the supports. 

I cure under a uv led array, and have had no issues with crazing or cracking during/post cure. Only during printing.

I'm not sure if the texture in the castings is due to burnout, or if the texture is in the models to begin with. I will start experimenting with pre-finishing the print before spruing and see how that works out.



Comments

  • GaryGary Member, Backers
    edited March 14
    Sorry - screwed up an img tag ---image;
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Some of the texture you see (and it isn't nearly as bad as I've seen others) can be attributed to either uncured resin interaction with the investment or ash/residue from the burnout. I don't see what appears to be damage due to expansion during the cure phase.

    Q1: Your prints are not tacky and do not smell of resin after you clean and cure them, right?

    You can try to use a barrier like I mentioned in previous posts. That creates a layer between the resin and the investment as it cures to help prevent the acids in the resin from weakening the investment, creating the orange peel surface.

    Q2: How accurate is your pyrometer in your kiln? 

    Running at 1650°F is 300°F above the recommended maximum temperature for these gypsum bonded investments since it will cause a reaction that releases sulfur into the metal which causes problems. 

    I use 2-1/2" flasks for my casting and run 1350°F for 3 hours. With a 3-1/2" flask, you may need more than 4 hours at the burnout temp to ensure complete combustion.

    For the printing, you do need to be careful of surface area during peel. Tilting objects that present a lot of surface area to the build plate will help minimize the stress incurred during the peel process using the castable resin. If you are not using my slow peel gcode or modified firmware, it might be worth trying to help change the stress profile.

    I do find I need to use thicker supports with more contact to prevent against separation during the peel. The splitting of bands may also be attributed to shrinkage during the print process, so the thicker supports help better stabilize the print to prevent them from breaking apart.

    Another casual observation is that I wouldn't recommend using resin to make gate sprues, just because it chokes down the point where the resin can try to burn away and might make it more difficult to get a clean cast because of excess residue.

    Looks like you are almost there Gary! Just a little more tweaking of the process and you will be set.

    -Ron

    Ron
  • GaryGary Member, Backers
    Sorry -- 1650 was a typo. It is 1350.  Not tacky and well cured. I am using your slow peel. 
    Re resin sprues and gates - I haven't had a problem with them. image
    I have issues with erosion 
    These castings were wax sprued

    First an MJ SR Y model (before I received my draken castable) image

    Same model cast in the green resin
    image
    image

    I pre-finished the back if this piece. It was smooth and dry. Weird to see the holes and erosion areas. However, there is significantly less texture than on the ring below - so I'll be looking closer for texture on the prints.

    I'm wondering if I'm casting too hot a flask? Spruing the wrong spots? I'm casting at a flask temp of 975.

    I have not used a surface coat yet, After visiting 4 different ace stores none had Clean-x, so waiting for my amazon delivery.

    I did get a decent cast on the one print out of 15 that didn't crack - 

    image


    Another day - another burnout :>)

  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    What ratio of Plasticast? I usually ran 36:100 to make the investment as hard as possible. You might be able to get away with 38:100 but that would have to be a trial-and-error run.

    Are you casting silver? You probably want the flask temperature at like 750-800°F for such a heavy piece. I think 975°F is way too hot.

    For the rectangular print, there is serious erosion at the one sprue point in the corner closest to the main sprue. The farther one was better, maybe due to the extra length it had to run into the space? Centrifugal caster or vacuum?

    I'd sprue that rectangular one on the outer edges using at least four feeder sprues to distribute the metal and slow it down so it doesn't tear up the investment. It also looks like you have ash residue along the outer walls (the holes in the metal), so you may need to up that burnout high-end period by another hour. If you still get too much ash, airflow would need to be addressed.
    Ron
  • GaryGary Member, Backers
    38:100 4-6 hour cure, 15-20 minute water soak prior to burn - which is what has been recommended and sets up almost too fast. Vacuum cast. Yes casting silver - deox 50/50 from Rio. I will add a Stuller deox 935 in the future. I will try a cooler flask temp next time - will be easier on the silicone gaskets anyway. . Next cast I'm going to put a failed print on top of the flask and watch it at different temps. When I burned one with a torch I noted that it spent a long time in a liquid state before it flamed and finally went to ash. I'm wondering if a sprue down burn prior to the 1350 phase might not be more effective.

    Many more print failures today - supports too thick  - surface bruises are too hard to finish and supports are difficult to remove without cracking the work, supports too short, too hard to clip. Supports too long,separate and  fail. The resin definitely has a shrinkage issue. Seems like it will only work for a sweet spot of model geometry and thickness.  For  air flow - there isn't a whole lot more I can do. I'm burning with the kiln door cracked open. There are no vents, and electronics below the floor.  

    This is the fun part - wouldn't it be boring if things just worked?   
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Haha that is true.

    As you saw with the burning, that is what happens inside the flask, but in a less oxygenated environment so the risk of incomplete combustion is greater. I have an aquarium air pump hooked up to a piece of steel brake line tubing that I work into my kiln under the front door to provide at least some forced airflow. I also have a duct attached to a blower fan at the vent up top to send the fumes to the outdoors. I think that creates enough of a draft, but some day if I feel like taking my Paragon SC3 apart, I can drill through the muffle bottom and allow it to suck in air through the bottom and get rid of the brake line.

    Depending on the supports, I've found that there are times where you can cut them pre-UV and times afterwards. They are still soft enough pre-UV that you can get close and not have it snap off at the model. You need to be careful when handling the print because it might not be stiff enough. I use the cutters that came with the printer, as well as a jewelers saw or an x-acto knife depending on the situation. If you do get a divot, you can always fill the dimple with some melted wax and then deal with the finishing after it is cast.

    I traditionally try to leave no more than 3-4 mm of support or I have separation issues as well when it gets to something solid. I change my supports to extend further into my model to have a better attachment point, but like you said, it gets to be a little challenging repairing the print after support removal.

    Keep us informed of your progress!
    Ron
  • GaryGary Member, Backers
    Well - I got the Clean-x and the results are somewhat better, but not significantly so. I've cast two trees with the kiln door open, so I don't see a lot of opportunity to improve oxygen with my current kiln. Here's the good, bad and ugly:


    image
    image

    image


    image
    image


    For reference, the triangular piece with the female symbols was printed in wax by shapeways. It's surface was true.

    The remainder of both trees was draken green (or blue?) whatever.  I was able to finish the ring on the first tree.

    image

    image

    I tried to make lemonade out the the pendant in the second tree, but the back is so rough I doubt it's salable.image


     Not sure where to go from here. The burnout is already very long, and I don't see much improvement in lengthening it.  The printing aspects are also a challenge and I've identified that it's due to shrinkage, during, and after printing - without taking curing into account. The green prints shrink to the point of fracture, or severe warping  of flat surfaces.

  • GaryGary Member, Backers
    Forgot to mention - dropped the flask temp on these trees from 975 to 875F. The first tree was cast with metal too hot (concave button), the second tree was cast near optimal (flat button). Other variables?

  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Hmm....

    First photo, beside the air bubbles on the disks, I do see some erosion of the investment from what is likely resin residue.

    The pendant - do you have any photos after you print it? Is that the one that warps/cracks? Based on the design, you print that flat on the build plate, right? If you can, send me the STL and I will give it a try on both of my printers (the Vivitek and the Acer) to see what I get out of it.

    For casting the pendant, this looks better, but not anywhere near what you want. I'd try to put the feeders on the short edge away from the three line bar detail to see if you can get that to print right. I think all that metal rushing in right into that cavity causes it to be worn away. It might be hard to make though because it requires a longer flask.

    While not ideal, maybe try casting a single copy of something in the resin using a small flask just to see if a single resin part can be run through the process properly. I use 2-1/2" x 2-1/2" flasks 95% of the time for my work. It isn't efficient for a larger scale operation unfortunately, but we need to try to narrow things down to get you a successful cast.

    Now, I do want to check into your curing process again. What are you doing specifically in your clean/cure process and how long do you let a print sit in between during the clean/cure and investing? Also, with the Clean-X, how long do you wait between dips, and before investment?
    Ron
  • GaryGary Member, Backers
    I have been unable to locate a perforated flask smaller than 3 1/2. Any smaller flask would be solid and only be able to have vacuum drawn from a small spot on the open bottom. Cant' see how that would make things better. Can you? I don't think there is room in a 2 1/2 inch flask to hold this piece and have clearance for the mold walls. 
    Process: print, IPA rinse. Soap and running water rinse. Ipa rinse. Cure under uv until color change (note thickest parts do not change). Dip in clean-x allow to dry (not timed, I usually go off to do things), sprue, tree, dip, air dry - untimed, compressed air just for good measure. mount in flask, invest - 4 - 8 hour cure - 1-2 minute water soak - burn out.

    Here is the 
    stl

    The kiln is a tabletop furnace - PID controlled and calibrated. Burnout sprue up (I have tried both up and down, and flipping from down to up after the 700F phase. Orientation doesn't seem to matter.

    I will try spruing at the bottom short end, and an 8 hour 1350 phase. 
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Gary,

    Yeah, since I don't do vacuum casting, I am not as familiar with the methods, so it makes doing a small batch difficult. I would suggest the ring with the three stones first, since that one is not super complicated and it allows you to get the feel for the rings.

    I was able to download your STL and pull it up in Meshmixer. I will pull it into Rhino and put some supports on it to see how it works.

    For cleaning, I avoided the use of water and soap. My cleaning process is as follows:

    1) Put part in glass beaker and add used IPA to cover the part. Put into ultrasonic for 3 minutes
    2) Pour out used IPA, clean beaker and then put part back in and add slightly used or fresh IPA to cover part. Put in ultrasonic for 3 minutes.
    3) Pour out slightly used IPA and use compressor to blow dry the part
    4) Put under 3Dfacture curing lamp on a rotating turntable for 5 minutes.
    5) After 5 minutes check to make sure nothing is going wrong, then put in for up to 20 additional minutes.
    6) Verify color change on thin parts and improved stiffness of print.
    7) Usually leave it out on the bench for about 6-12 hours before I would invest it. If I will not get to it in a while, I put it in an airtight container (I have noticed cured models that have sat out turning back to a darker green from what I assume is due to moisture absorption.

    Too much alcohol, too much water, too much UV (especially in water), caused my prints to start to crack or split at the surface.
    Ron
  • GaryGary Member, Backers
    Eeesh - such a complicated dance! I've had to switch back to MJ SR Y for some case furniture builds. I'll go back to this after I hear about your results. Meanwhile I'm seeing how well SR Y doesn't get along with platinum cure silicone :) How many layers of paint will I need :).  Meanwhile - thanks for your interest and help!

  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    I got hung up with my primary job, so I haven't set up the print job yet. I did get your STL into Rhino and worked some supports in to see how it works. It is all fixed with netfabb so I will set it up tonight and see how it turns out!


    Ron
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Hey Gary, I finally got the time to print your model.

    Added supports (auto) via RhinoGold 6:

    image

    Printed on the flex vat using 5000/10000 (normal/base) exposure settings:

    image

    image

    image



    Unfortunately it broke in the upper corner. The print took about 4 hours using the Vivitek.

    I threw it under the UV light but haven't checked on it to make sure it didn't warp.
    Ron
  • GaryGary Member, Backers
    What a bummer! I didn't have any problems printing it flat on the build plate. It was after it had been sitting on my bench that I noticed the warp - and also in the casting. Shrinkage also explains why the rings split, but only when supported in a certain way. I had no problem printing them using only the prongs as support - it was after I added the center spruing that the models split. 

    I have some small designs to try for the next cast cycle, probably tues. It bugs me to use up $3 worth of investment and another $3 worth of power to cast a single pair of earrings that will sell for $15 or $20- though - I'm not sure I can bring myself to do it. But I will try to force myself!. 

    Thanks for trying Ron. Make no sense to try to cast a broken model though. I'm sure you have plenty else to do.
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Yeah, I wouldn't bother casting it, but I did want to see if altering the placement would help with the overall print quality.

    Getting the process in tune with your config does take a little time. I wish it was "Plug and Play" but we aren't quite there yet. I wonder if cure is still an issue. We'd have to get some input from the chemist at 3Dfacture that put the green resin together to get some more technical insight.
    Ron
  • GaryGary Member, Backers
    shrinkage, warping, and breakage during the build continue to be the biggest problems. image


    Clean-x did not resolve any surface issues, and in fact, made the surface quality of casts poorer.  However, a dip in polycrylic  image image   does provide a significant improvement in surface quality (clean-x left, polycrylic right). 

    Due to the print quality/breakage issues I'm going to switch over to Castsolid for a while to see if it prints any better. I'm also going to change investments to MAXX and raise the max burnout temperature, once this box of plasticast runs out.  This flask burned at 1450F for 4 hours. I also place the flask on the vacuum table button down while melting the metal. There should be no loose ash remaining, The surface artifacts on the ploycrylic dipped sample are mostly crazing from the cure. 
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Gary,

    It is too bad you are running into these issues with the printing. I wonder if this round of resin is a little too sticky for the FEP film on the vat. My last print ran into issues too, so I will to change my FEP film in the flex vat. I tried to use some of the Clean-X on the FEP film to see if it helped with the release, but whatever benefit probably wore off quickly.

    You should let Andrew know about this and see if they have any ideas of whether or not they can modify the resin in any way to deal with the breakage.

    Interesting find on the polycrylic. I will have to look that up. There is definitely an improvement in the surface finish from your photos.
    Ron
  • GaryGary Member, Backers
    Minwax Polycrylic is a high gloss protective surface designed for wood. Almost like spar varnish. It was mentioned elsewhere in the forums here as a way to get extreme optical properties with clear resins. It's on the thick side, so very fine details could get filled in or over - but then again, it did a great job of showing the curing craze  Did fill in the drill hole at the top, but that's and easy fix. 

    As to the resin distortions - maybe the new batch is flawed. The earrings in the tree should be flat bottomed and rounded tops. In addition to the print breaking apart 7 hours into a 9 hour print, the shapes are distorted - looking more like mushrooms. It's like the gates sucked resin from the edges, but the edges print after the gates.  I would hope that @andrew_3dfacture has been following along - there's not been much else happening here in the support area. If we don't see him comment soon I'll send him an email.

    I happened upon an interesting paper on burning out RP materials. Supposedly by diddling with the chemistry  of the investment (adding a bit of boric acid and calcium nitrate to the mix) oxygen can be produced within the flask facilitating carbon elimination. http://www.mjsa.org/publicationsmedia/tech_sheets/resin_models_part_2
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    edited April 2
    I tried the calcium nitrate and it was hard to tell if there was any significant effect except I noticed a discoloration on the metal castings that came off in the pickle. The one side effect I did worry about was the release of nitrogen dioxide, which isn't exactly a friendly gas to breathe. The reaction also liberates 4x more NO2 than O and may recombine the O with the NO2 during decomposition, reducing the amount of oxygen available.

    I thought about using potassium nitrate instead because its decomp. temperature is lower than calcium nitrate, but I am a little skittish about that due to KNO3's use in gun powder. ;-)

    I wonder if some other oxidizer could be used, like a carbonate instead of a nitrate? Nope - it is insoluble in water and decomposes into carbon dioxide, not oxygen. :-(
    Ron
  • GaryGary Member, Backers
    I just had another build plate full of earrings shatter and deform, all in different ways. Printing the same layout now with castsolid. Will be interesting to see if the results are similar. Just from exposure tests, one thing about the cast solid is that it seems much less brittle than the draken resin. It will still break when stressed, but has a lot more bend to it. Right now I'm just trying to get past the first step to a successful casting - a successful print. To be remotely economical  I need to be able to print and cast a full plate per run.  One ring or 40, it's still hours to build.  Currently the cycle of print/invest/cast is well more than a day. Casting in silver  a ring or two a day just isn't going to justify the effort. 

    What's the definition of insanity? I'm hoping the addition of boric acid and calcium nitrate and a different resin yields a predictable process - time will tell.  The calcium doesn't arrive till wed. Boric acid will be added to the next cast, probably tomorrow eve at the earliest. meanwhile I'll continue to explore mold making for waxes.What would life be without a challenge, no?
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