Atomization of silicones to eliminate outgassing?.....

[EddieFr]

...has anybody had experience with conventional/airless spray application of catalized silicones into a mold without prior outgassing first? My thought was that during atomization, a portion of the reaction gasses could be dissapated in the spray mist/vapors. I was toying with this as a possibility to also increase pot life and create a dense, uniformed first coat in the mold....

EdF

[mg4]

I have giving this idea some thought to, seems to me this could work, after the spray is apply, then bring the mold together and pour in the silicone useing the bombs away method. No vacume pot needed. But I dont really know yet, have not try it. And then there is the problum cleaning the airless each time.

[EddieFr]

...a 2 qt. pressure pot or gravity-feed cup gun would probably be the most efficient and easiest to use and/or clean. You might also be tempted to try an HVLP turbine setup, although you would have to modify the silicone's viscosity, in which case you would lose the ability of the thinned silicone to adhere to vertical surfaces. Also, the HVLP's turbine produces warm air which further affects the viscosity. You would want the silicone to be thick enough to cling vertically, but thin enough to spray, and capture detail. One consideration with conventional (or airless), is that you must have very clean hoses, and a super-functional water/oil separator in place, lest the atomized silicone is infused with oily or dirty compressor air, or oil from leaking pump seals. A ruined batch. A short 10' hose on an airless pump would allow for less wasted material in the lines and pump. I have a nice Binks airless I just rebuilt, and I am thinking about ruining it here shortly...will let you know!

EdF

[8balls]

Maybe of interest:

In one preferred embodiment of the invention, metering pumps are used to combine the parts of the silicone elastomer together in a mixing chamber or conduit in the appropriate ratio. The combining of these materials is done is a gas-free environment inside the mixing equipment so that no air entrainment results. The mixing equipment preferably comprises a high-viscosity mix machine. Such a machine is capable of pumping and ratio-metering the silicone components. The part A and part B components of a two-part silicone (for example) pass through a static mix hose wherein they are properly blended and delivered to a hand-held spray gun. One suitable high-viscosity mix machine is sold by Graco, Inc., Minneapolis, Minn., under the trade designation HYDROMATE VARIABLE RATIO PROPORTIONER, SERIES 954-864.

The properly mixed and pumped uncured silicone resin is sprayed through a hand-held high-viscosity spray gun, such as Graco's 200A gun (Graco, Inc., Minneapolis, Minn.) on which is mounted a high-viscosity silicone spray head (available from A.E. Yale Enterprises, Inc., San Diego, Calif.).

Full article here:
http://www.patentstorm.us/patents/53265 ... ption.html

[EddieFr]

...great read! I'm pretty familiar with Graco/Binks/DeVilbiss plural component spray rigs, where you can use the FireBall, Monarch, President, Bulldog, or King pumps, thru dual metering regulators, and plural component gun, but not so much with the static mix hose. Typically, both components would "mix" in the fluid tip/mixing chamber and/or atomized air stream under pressure, as in a polyester/MEKP application. Yale is a big-time supplier and sounds like this might be part of a Mil-spec contract requirement or the like. This type equipment would likely be in service with large production facilities, producing military parts on at least one shift, where materials would remain in the lines for days. Still, I still think there is a way to pull it off on a one-off or low order basis. It's one of those areas which will need to be explored and the failures discussed. The equipment being touted in the article is likely above $10,000...way too rich for my blood. Thanks for the article!!...very nice!!

EdF

[handymk]

Interesting info. The only comparable equipment I have seen is used to apply the two part polyuethane foam insulation (Icenene and others) There the two parts are pumped from barrels under pressure to a meetering/ratio head which then sends both parts to a spray head block.
The polyurethane is mixed at the spray head as it exits. cure time is fast -aproximatly 10 to 15 seconds. That equipment is expencive too. The whole portable spray outfit was in the 25k range. I am not sure the exsisting silacone gel times are fast enough to be mixed just in the spray head.
If the materials mfg can come up with a quick curing silacone that can be sprayed --watch out-- doll moulding in a couple of hours instead of days.

[mytime]

Of coarse it would do the job...,
But isn't it a way too expensive solution?
A two stage vacuumpump that can achieve the needed 27 inch vacuum and a vacuum chamber with a gauge are together something like 500 bucks a lot less than 10 - 25 K.
Its a solution from which we are sure that it works because most dollbuilders use it.

Mytime & Helen & Carmen

[timetraveler1]

yeah theirs nothing worse that i hate than a doll thats outgassing !! ok i'm done !

[femdoll]

Of coarse it would do the job...,
But isn't it a way too expensive solution?
A two stage vacuumpump that can achieve the needed 27 inch vacuum and a vacuum chamber with a gauge are together something like 500 bucks a lot less than 10 - 25 K.
Its a solution from which we are sure that it works because most dollbuilders use it.

Mytime & Helen & Carmen

29 inch even...

nah, for a good vacuum system, you probably go over 500 bucks... most pumps are already 300 bucks. And then you have to find a good vacuum chamber, which aren't easy to find, and most are not cheap either, and making them yourself, can create uge problems (im/explosion when not properly made).

Good on from smooth-on 500 bucks
http://www.smooth-on.com/Tools-Supplies ... catdepth=1

Btw, with that 'airspraying' one, smooth-on just sells such, or do you guys means something else??
costs 800 bucks... so ... almost as expensive as 'vacuum system'... (ok you also need compressor...


Funny, for silicon you need vacuum system, but for liquid plastic and so, you need a pressure system (also to reduce airbubbles). I'm into this stuff now, because I make a waterproof casing for my camera.... It's fun, but it's also clear to me that it's not cheap!! Need a lot of material to start with and knowledge about the stuff.... but it 's good fun!
Bought some dragonskin also, just to see how 'nice' that stuff is....

[Siliconeismylife]

Metering/dispensing equipment for silicones is also available from Fluid Automation, Inc. in Wixom, MI and Michaels Engineering / Rook Metering.
They make systems for both 10:1 and 1:1 silicone systems.
Spraying silicone is currently popular in the fiberglass industry, for boats and windmill blades; they make a "bag" by spraying silicone into a mold with a part in it, creating a semi net-shape "bag", which is then sealed to the mold over a fiberglass preform, so that polyester resin can be infused under the bag. A gun similar to the one pictured in this thread is used.
In the doll industry, several folks will simply brush on a layer of silicone into their molds, prior to pouring the doll. This also creates a "skin" over any trapped air bubbles, making it easier to repair.
Self-leveling silicones are also available, if you're spraying and want a reasonably smooth opposite surface (away from the mold).
Silicone does not outgas very much during the cure process. Most of the trapped air you see is created when hand-mixing, which is another great argument in favor of dispensing equipment.

[EddieFr]

...that would be a perfectly acceptable practice for "production" doll manufacturers, I suppose. Instead of degassing before a pour, just vacuum bag the mold w/silicone already in it. I don't know if that would be more troublesome or not. I guess the bigger reason is that still at this point in time, there are no "production" studios. Everything is still "one off" and done on an as-needed basis. Maybe in a few years, some resin transfer or reaction injection production techniques could be brought into play, but not as of now. That equipment IS expensive. My whole premise is geared toward the small time applicator/user. I will be testing some ideas I have in regards to spray application here shortly...I will post the results.

EdF

[femdoll]

Vacuum bag around whole doll is not a good idea. First you need to go to a negative pressure of 29 inch, which is already difficult to get with 'heavy' equipment. Besides, you're mold must be able then to with stand that vacuum pressure to (will be 'squeezed'), risq of deforming your mold.
Secondly,... silicon will rise when put under vacuum. That's why you need a bucket 3 times the size of the content you're gonna pour. If you put a bag under vacuum, you'll ending up sucking up silicon into the vacuum system I guess...

There are though vacuum bag systems... when laminating boats with epoxy and glassfiber, they use it to remove airbubbles and squeeze the glassfiber as tight to the wood as possible. I'm not sure the go all the way to 29inch pressure though...

[EddieFr]

...all true. One thing I have found, however, is that maufacturers can and usually do find a way to overcome obstacles which can hinder production; whether timelines or quotas. The creation of a silicone doll in a one-off studio setting, falls outside the parameters of industrial production techniques...at least for now.

EdF