Anyone Use MicroBalloons in Casting?

[pnolan48]

Just wondering if anyone here has any advice on using microballoons (or microspheres, or other fillers) while casting resin parts? The 3M-derived suggestions are pretty clear, although I doubt I'll ever reach a 50:50 volume. While they might save weight and volume (hence dollars) in the casting, I'm more interested in how they might affect the working time, or pot life. I hope they might increase it. I will find out next week, when I try them for the first time.

[DKS]

I have some, and I've not done any extensive testing; however, my feeling is that they don't affect pot life--that is determined by chemical reaction, and I don't think changing the density of the materials has much impact on that.

[pnolan48]

David,

I think you know I've always appreciated your analytical approach and experience. Let me explain why I am asking this question in a little more detail.

My first pour for the Aggressive-class minesweeper was a total of 420 cc (14 oz) or 210 cc (7 oz) of each part of the casting materials. Let's just use metric measures from here on in! I could barely mix and pour this amount before it started setting. And it got hot while setting.

Then I built a plug to hollow out the hull casting. This reduced the pour to 300 cc or 150 cc of each part. It seemed I had much more time to mix and pour the materials, and place the plug. Then it seemed that the mix didn't set nearly as quickly, nor with as much heat (although the plug might have absorbed some of the heat).

I think a common idea is that the more casting materials, the quicker the set, and the hotter the set. So, I'm wondering if microballoons, by further reducing the amount of reactive materials (i.e., Part A and Part B, by perhaps 25% to start) might further extend the set time and lower the temperature.

I also seem to know that, when casting small parts, I have much more time between mixing and setting, a not much heat.

BTW, I think that 420 cc is about my limit for the setting time and heat produced. I'm mixing and pouring about as fast as I can.

[pnolan48]

OK, the expert at D&S (Arty) confirmed that the addition of microballoons, because it reduced the amount of reactive agents, would extend pot life a little. I'm not really looking to push this to the fullest, as 30 seconds extension will be fine. Pushing it to the fullest means mixing the microballoons with each separate component to the max, max defined as "just able to pour." I don't want to get to that stage.

This is important as I build larger and larger hulls. I'm learning to make the walls thinner--or the plugs bigger. I'm at 6 mm thick walls now for large castings. For small boat castings, I'm down to 0.5 mm, with some failures. I think I've learned that I can carve out a master with hull walls so thin I can't cast them.

[DKS]

Why don't you simply use slower-setting resins? I have some that have a pot life of over a half-hour. Cure time is of course extended as well, but I use that to my advantage--I can pour more molds, and the mold detail will be more reliably filled, whereas resin that kicks fast doesn't get a chance to completely fill all of the detail.

[pnolan48]

Why don't you simply use slower-setting resins? I have some that have a pot life of over a half-hour. Cure time is of course extended as well, but I use that to my advantage--I can pour more molds, and the mold detail will be more reliably filled, whereas resin that kicks fast doesn't get a chance to completely fill all of the detail.

I'm still learning, David. The suppliers seem to assume a level of knowledge that I haven't achieved. I haven't found a good forum or knowledge base for resin casting, or a trusted source for what I should be buying for both molding and casting. I'm really a beginner in this aspect of production, so I'm asking all the dumb questions. I'm out on the Web searching, but sometimes you have to know what to search for in order to search for it. I wasn't even thinking of resin a year ago, and have had some disasters (relative), so I'm going with what has worked, and just looking for what might work better.

My problems with setting time have occurred while pouring a large volume that requires the insertion of a plug (i.e., a ship hull), or when trying to fill a ten-replica mold that is a two-part mold requiring only 60 ml of material that is injected via syringe in ten separate holes (i.e., lifeboat shells). I've had problems with moisture because, while I'm going through a lot of material very quickly, I never knew of nitrogen. And, at times, I use a lot of mold materials and, at others, a lot of casting materials, or vice versa.

I hope I'm not annoying folks here with my questions. I think I have a history of pretty good modeling; I'm asking questions because I'm trying to manufacture some of my models, and haven't found the textbook that would help me understand all the problems. If this is not the place, I'll stop, and look elsewhere.

[DKS]

While I agree the Smooth-On website is not the most user-friendly, it does have all of the information you need; it's just not all in one place. Here are some recommendations...

I use their Smooth-Cast line of resins, which are all mixed 1:1 by volume. http://www.smooth-on.com/index.php?cPath=5_1120

80% of the time I use Smooth-Cast 305. The stated pot life is 7 minutes, so it's best for one-part molds that you can fill quickly. Demold time is 30 minutes, but I usually give it a minimum of one hour.

When I need more time to pour, or I have a complex mold with a lot of fine, deep detail, I'll use Smooth-Cast 310. Pot life is ~20 minutes, and demold time is ~4 hours, although I give it 8.

Here is their technical bulletin on these resins: http://www.smooth-on.com/tb/files/Smooth-Cast_300q,_300,_305___310.pdf

I've used almost all of their products at one point or another (as well as many from other companies), and I haven't found anything I like better.

Incidentally, if you don't go through supplies quickly, give each container a shot of this (it's not nitrogen; it's tetrafluoroethane): http://www.smooth-on.com/index.php?cPath=1203

[pnolan48]

Thanks, David!

I truly appreciate your advice. I'm just plain dumb stupid sometimes, and even dumber and stupider the rest of the time.

But at least I'm trying.

[DKS]

No problem. NZT has sold approximately 5,000 cast resin items so far, and had no complaints, so I must be doing something right.

[pnolan48]

Just a quick summary of my molding and casting experiences, for those who might be following this thread.

I'm having very few problems molding and casting small items such as outboard motors, and rescue boats, up to 125' USCG cutter hulls. I am using vacuum for the mold materials as the difference is very visible. Foaming under vacuum has not been a problem, as I am using big containers (at least 3x the amount of material.) I've had no problem with air bubbles in the castings, except the occasional big trapped bubble in some complex molds. Just for comparison, I'm using about 10 ml (about 1/3 oz) for 20 outboard motors at the smallest end, and about 230 ml (roughly 8 oz) for the cutter hull.

So the whole variety of parts, from outboard motors, to capstans and booby hatches, to rescue boats from 19' to small patrol craft up to 30', to superstructures and smaller ship hulls, have been uneventful to mold and cast. There have been few problems with soft molds, air bubbles, or casts setting too fast.

The bigger stuff has presented some problems in casting, but not in molding. My biggest mold has required 1.3 liters of material (650 ml of each). I can't fault the mold material, only my oversight in not sealing absolutely every absolutely every joint, seam and pinhole. No, the materials didn't leak out, but instead caused very thin layers of mold material leaking into layered parts, which later caused the castings to stick, and pull out the mold in small pieces. This is just an annoyance, requiring a little more finishing of the casting than I would like.

Casting the bigger stuff was interesting. The biggest hull took about 420 ml (14 oz) of material, and that will set up very quickly indeed, with a lot of heat. But, by putting a 120 ml (4 oz) plug into the mold, making part of the hull hollow, I reduced the materials to 300 ml (10 oz) and that increased the pot life (setting time) by quite a bit, so that I wasn't racing to fill the mold before everything started to set, or putting my house in danger of burning down. As David has recommended, I think I'll try slower setting casting materials once I finished the 4 gal I just bought.

I am going through materials quite quickly--although the molding materials, which are nastier than the casting materials, have been opened probably 100 times. In all these efforts, I've used about 5 gal of mold materials, and perhaps 7 gal of casting materials (each hull does take a lot.)

The next ship--the Reliance-class USCG cutter--will take an enormous amount of molding material, and even more casting material. I tried to build this as a built-up styrene hull, but it was just too difficult. I did waste three months trying to make this ship work, so I'm hoping a cast hull, with a different method of building the superstructure, will work better.

[DKS]

Pete, there are some 1:1 resins that are even slower than the slowest Smooth-Cast I normally use. Micro-Mark's CR-900 has a pot life of almost a half-hour, and takes 12-16 hours to set. I understand that Smooth-On makes the casting supplies for Micro-Mark, and I have found the equivalent products from Smooth-On for everything Micro-Mark sells except the CR-900. The Smooth-On casting products with these characteristics are not 1:1 by volume, so I'm scratching my head on that one, so I keep some CR-900 around for particularly challenging castings.

I will say that the only mold-making materials I use now for production are the 10:1 Mold Max flavors; the 1:1 volume, 4-hour stuff makes pretty poor-quality molds. I will use it on occasion when I need to make quick test castings to "proof" complex masters before committing the 12 hours required for good molds. This way I can save time as well as good mold material to fix mistakes.

[Zox]

Pete,

Might some of your larger hulls be big enough that fiberglass would be a viable option? That would probably be stronger, lighter, and less expensive than a huge resin casting.

(It's not something I've ever tried myself, but I watch a lot of car shows on TV.)

[pnolan48]

Pete,

Might some of your larger hulls be big enough that fiberglass would be a viable option? That would probably be stronger, lighter, and less expensive than a huge resin casting.

(It's not something I've ever tried myself, but I watch a lot of car shows on TV.)

I think I am right on the borderline between casting and fiberglass. I'm obviously going to have to do larger freighters in three parts, bow, center, stern, with the center section basically a lightweight box. If I were doing an aircraft carrier, large container ship or tanker, then I would lay up some fiberglass, although I haven't touched the stuff for 40 years.

On Monday, I'm going to try the 210' cutter, which is about 30% bigger than the 173' minesweeper. There's not anything I can do about reducing the volume of the mold, but that's not really a worry as long as the mold box is strong. The minesweeper has turned out to be very manageable, once I got the casting volume down to 10 oz. The cutter won't be so easy to fabricate a plug to reduce the volume, so we'll see.

In the future, I'll just have to get resin that sets in a longer time period. I just couldn't find a 1:1 formula readily, and wasn't prepared to do the 10:1 formulae.

[DKS]

This is the stuff I have not found an equivalent for in the Smooth-On line (although I'm still looking--it must be one of Smooth-On's many flavors of Task products): http://www.micromark.com/cr-900-high-strength-casting-resin-26-fl-oz,8154.html

It's 1:1, 20-minute pot life, 12-16 hours before demolding. Probably the biggest drawback is that it doesn't come in gallon containers.

[pnolan48]

Thanks, David.

But that would make about 2.7 hulls. and I think the 0.7 hull might be a reject, and cleaning out a partially filled mold is a real PITA.

I think I am "miscommunicating" about the volumes I'm using. I just poured a 60 oz mold or the big cutter hull. It could have been smaller, but the resin part of the mix was getting old, thick and lumpy, so I did a unit box rather than a stepped box. I wasted a lot of material, but the resin part was going bad by the hour, just getting thicker and thicker, and I didn't have nitrogen or CF3, which is next on my buy list.

If there is a degree beyond stupid, stupider, and stupidest, I think I'm there. The fourth degree of stupid is . . . expecting a 60 oz. pour to turn out right.