Customs: Resin casting and vacuum chamber question

Discussion in 'Creative General Discussion' started by Insane Galvatron, May 15, 2012.

  1. Insane Galvatron

    Insane Galvatron is not insane. Really!

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    Okay, for those that have done casting, I have a question.

    Years ago, I used Alumilite resin and had no problem getting good casts to come out. Recently, when I was doing the casting for the Cliffjumper gas cap, I had to buy some new resin due to the other I had being so old. I noticed that it had a "New Formula" sticker on the box, so it looks like Alumilite changed the formula. Now when I do the cast, it's a bit thicker and doesn't go into some of the corner areas. Especially the tip of the antenna. I also tried to cast the myclone Arcee head, and it didn't fill the tip of her nose. It's like an air bubble was trapped in the mold. I tried tilting, shaking, and bumping the mold against the table to dislodge the air bubble. Nothing worked. Something else I noticed about this new formula, is that the extra resin ( on top of the mold, or left in the mixing cup ) appears to have bubbles in it. The old formula would be smooth as silk ( and fill in the areas like the tip of the nose ).

    So would a vacuum chamber fix this? I'd heard about people using them to remove bubbles back when I first started casting, but never learned anything about it since I didn't seem to need it. If so, how is the best way to use it? Do I pour the resin into the mold, then stick it in the vacuum chamber before it hardens? Do I need to leave it in until it hardens, or just long enough to draw the bubbles out? If I need to pour the resin in while in the vacuum chamber, how do I manage that since I can't fit in the vacuum chamber with the mold? lol
     
  2. OMEGAPRIME1983

    OMEGAPRIME1983 Well-Known Member

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    I'm sure you've already seen these, so I'm not sure that I'm helping or not, but there's this: http://www.tfw2005.com/boards/tutorials-how-tos/214566-random-molding-casting-tutorial.html, and this: http://www.tfw2005.com/boards/tutorials-how-tos/214541-tips-molding-casting-your-own-parts.html. In the first link, it shows to make small air hole from the tips of the pieces to the top to allow air to escape and not leave those little bubbles in there (I think). I know it doesn't answer our question, but maybe it'll help? Hope it does anyway :) .
     
  3. Insane Galvatron

    Insane Galvatron is not insane. Really!

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    Thanks for the links, but it doesn't help. If I could cut holes in just those spots, then it would mean I'd have to trim the excess resin off that gets into those holes. That would mean a blemish on Arcee's nose. ( plus, the gas cap and antenna for Cliffjumper are just too small to be able to do that. ) I'm really more curious about the vacuum chambers. Supposedly, the vacuum will pull the pocket of air out, thus forcing the resin into those spots. I'm just not sure exactly how to do it. I'd like to get by spending as little money as possible on the air chamber itself, so I need to know exactly what I need it to do so I can get the bare minimum features.
     
  4. project9

    project9 White n' Nerdy

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    Vacuum/Pressure pot molding & casting would solve it. Though, you're talking $100+ for a pressure pot and $50-100 for an air compressor (if you don't already have one). It's also a little dangerous if you don't set it all up correctly. Same with vacuum casting and the vacuum pot and pump. I'm pretty sure the only difference being pressure casting compresses the bubbles into microsized ones that you can't really see, vacuum sucks them all out (degasses).

    How to pressure cast clear resin

    To be honest, I haven't messed with my molds and castings in more than a year due to getting discouraged with all the trapped bubbles. But I'm also not confident enough to try and do the pressure casting and I don't really have a place to set up the whole operation. I've mainly been doing it on my kitchen table. =)

    Just keep in mind you have limited space depending on the size of your pot for the mold and you need to pressure mold the original piece too (which may open another set of issues).
     
  5. Megatron31

    Megatron31 I Belong to Nobody!

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    i use allumilite regularly and it sounds like you have a bad batch of resin (its happend tome before as well).

    i bought new bottles a couple of weeks back, and its actaully thinner than the original. contact allumilte they usually take care of customers in situations like this.

    i will say the resin has a shelf life, and when it reaches that it begins to do exactly what you are describing, gets thicker and will not cure smoothly and as it heats up begins to bubble. making entirely useless parts.

    now that said a vaccum chamber could fix this issue but i would try swapping the resins out before spending the money on a vaccum setup to make sure. unless you just intend on adding that to your usual method of produciton.

    but vaccum chambers can be made on the cheap quite easily (far chepaer than even the allumilte one sold on their site)

    got to lowse get a large sheet of plexi and a either a paint can or a large section of pvc tube, find or make a rubber seal to match and the pump will create enough suction to for a seal. if you have ever gone snorkling or scuba diving its the same premise as putting the mast on and either pushing it to your face or breathing in with your nose it creates a seal.

    the only thing is the expense of a vaccum pump im sure they can be purchased for much cheaper then the ones offered by smooth on or allumilite but i havent found one.

    a final note to consider if you are using the store bought version of allumilte im guessing its the short pot life (90 second)

    this is not long enought for pressure or vaccum to have an effect on the part. it needs to stay in liqued form for atleast 15 minutes for either of those to work as intended.]

    i am about to start pressure casting myself so im gonna test the time limits, but i know 90 seconds wont cut it and the smooth on resin i have has a 3 minute pot life and im afraid even that is too short.

    becasue you have to consider the time it takes to pour, place in the chamber, and add the vaccum or pressure.

    i am by no means an authority on the subject and hopefully Venksta will chime in as he has more experience than I do, but i looked into both options before i got started and pressure was just easier becuase i already owned a small compressor and you can convert a 2.5 gallon paint can from harbor freight into a pressure pot (it was on sale for 79.00)
     
    Last edited: May 16, 2012
  6. project9

    project9 White n' Nerdy

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    HarborFreight has 2.5 & 3 cfm pumps for like $100-150 but the Alumilite one they sell for $350 is 6 cfm. Not sure what effect the more power has.

    Alumilite's HowTo videos are great. How To Mold Rubber & Cast Resin I mainly use Smooth On since their shop is about 30 minutes from my house (saves me some $$ on shipping) but Alumilite's how to videos are awesome. You can watch their Vacuum Pump and Chamber assembly video to see what Megatron31's talking about. There's nothing to it - the pump is the biggest thing.

    I don't know if Venksta or anyone has experience between pressure and vacuum casting. I'd like to know if one is really better/easier than the other. I'd assume pressure casting is easier but technically doesn't degas like vacuum does.
     
  7. Megatron31

    Megatron31 I Belong to Nobody!

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    higher cfm rating would have an effect on how quickly it could reach the desired vaccum (allowing for varied potlife)

    i know with pressure you hit 40psi but not sure how many pounds of vaccum is required and its a lot easier to push the than pull once you reach higher values.

    everything i have read comparing the 2 never delivers a stand out argument for one over the other, just always seem to boil down to a user preference. but i would be curious to hear from someone who has done both referring to the kind of things radicons would cast


    for point of reference though this was one of the more convincing argmuments i found although it doesnt give a lot of detail on vaccum




    Now you went and did it!!!!!! all the Vacuum guys will start in
    about how great it is and all us pressure guys will start in
    about how great pressure is...........................this time
    I be First'

    So before that all gets underway may I suggest that bubbles are
    not really why pressure is better than vacuum.
    The real question is in defining the detail you are after, in
    general using vacuum will remove most intrained air (bubble) and
    of course these bubbles get their by way of stiring and mixing
    two RTV or resin parts. However when the material is poured into
    a mold or over (around) a master and left to setup and cure,
    more air can get into the material and there is no means of
    ensuring that there are no trapped bubbles (voids) around fine
    detail.

    Pressure on the other hand introduces two seporate and important
    forces at the same time. First is forces some of the intrained
    air into solution and compresses reall large bubbles into really
    small ones. More importantly the physics of pressure in a liquid
    against a solid cause what amounts to a dense skin to form
    around the master reduicing the chances of voids remaining
    behind. The second and even more important result of using
    pressure is that the pressure forces the liquid RTV/resin into
    every nook and crany to the point that detail right down to the
    cellular level can be reproduced. We used to use RTV to copy
    very small biological samples, gold plate the mold and scan it
    in an electron-microscope and see the cell fibers in nerve
    cells.

    My preference for a pressure system is it cost less, is less
    messy, less waste and less expensive to get started. Plus there
    is just one step............pour in the material and
    pressurize........finished.

    I would suggest that if you are doing things with large smooth
    surfaces then it's a matter of choice as far as vacuum vs.
    pressure, but if fine detail and void free molds and casting is
    important you should give pressure a lot of consideration, If
    you go to my sight >immerse@...< and look at both areas
    you will see what can be done with just pressur RTV molds and
    pressure cast polyurathane resin casting. I believe there are
    some fossil skeleton photos in the list files showing 40" T-Rex
    skeleton resin casting and possibly some model car bodies may
    still be in the files..

    I hope this was of some help.......................
     
    Last edited: May 16, 2012

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