# Resins and silicone and casting, oh my...

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#### Rocket Al

##### Well-Known Member
Let's see if old Al can make an actual useful contribution to the Forum, instead of causing discord and havoc.

Alot of folks are trying to do repro parts out of casting resin, in particular Alumilite, as I guess it's easy to get in small quantities from hobby shops and places like MicroMark. It is, however, probably not the best choice to use. The "Alumi" part of Alumilite refers to the fact that it uses powdered aluminum as a filler. Although one of the lighter metals, it is a metal nonetheless, and therefore will weigh more than a resin that uses other fillers. It's just a matter of what to use, where to get it, and how to use it.

For the real do-it-yourselfers who want to research and find it themselves, any sufficiently industrial city will have a listing in the business-to-business directory for "Mold and pattern makers supply", which is what tis stuff is primarily used for. Making patterns and prototypes. Places where molten metal and plastics may impinge against the material at some point (hence the need for metal fillers...) Specifically, you are going to want to ask about "liquid tooling materials", something with a Shore D hardness of at least 70 or so. Any softer, and while not "spongy", it may not want to hold paint that well.

You are going to need something to pour your resin in, so we'll need to get some silicone. You could also use a flexible elastomer urethane (cheaper) but they are a little harder to work with. The release process is a little more difficult and exacting. Their primary use, before someone said "hey, this sh!t would make great molds!", was as an adhesive. If you've used "Gorilla Glue", you've used urethane elastomer. Sticks like and SOB, doesn't it? That would be your carefully modeled master pattern, if you don't release it properly. Silicone, on the other hard, is easier to release. You will want to ask about "Condensation Cure" silicone, which means it uses a tin catalyst, rather than an additive cure silicone, which uses a platinum catalyst. It's also the less expensive of the two, and tends to be softer i.e. more flex makes it easier to remove parts.

Now if you don't want to do that homework, here are some specific places to go to buy some of this stuff...

Burman Industries www.burmanfoam.com

Supplies special effects needs, here are links to specific pages of good products:

BJB TC-808 quart kit: http://www.burmanfoam.com/estore/ProductDetail.asp?Recordset1_Action=Find('PID','186')&Recordset1_Position=FIL%3ACategory+%3D+%27RIGID+CASTING+URETHANES%27ORD%3AABS%3A20KEY%3A186PAR%3A

Walco VSI 1065 silicone quart kit:
http://www.burmanfoam.com/estore/ProductDetail.asp?Recordset1_Action=Find('PID','4')&Recordset1_Position=FIL%3ACategory+%3D+%27SILICONES%27ORD%3AABS%3A1KEY%3A4PAR%3A

Burman's has a lot of interesting stuff, including larger quantities of these materials. Go to the main page and enter the store to find more information. You can get more in depth product info on the BJB products by going to their page at www.bjbenterprises.com

A really good place to cut the middleman out would be Freeman Supply, at http://www.freemansupply.com/ Their main page has links to a number of free on-line video resources showing you how to use their products to make molds and cast up parts. Some highly recommended products there are Repro One, which is available in quart kits http://www.freemansupply.com/ReproOne.htm
also Repro Fast, also in quarts http://www.freemansupply.com/ReproFast.htm

Another handy thing these folks carry are sample kits of their materials at http://www.freemansupply.com/SampleKits.htm you can get a small kit of some of their silicone, complete with brushes, cups, paddles, etc. to try out, or even do that entire nose cone project. The thing I like about this company is that it's about 10 minutes from my house, so I can pick up whenever i need it. In L.A., I had an hour and a half drive to Burman's or Cinema FX when I needed anything

Al

#### Stymye

##### Well-Known Member
would love to see a picture tutoral on this

#### mike_bar

##### Well-Known Member
Originally posted by Rocket Al
(Snip.) Any questions about this topic, email or PM me, and I'll tell you what I can.
Al,
Wow, that is one detailed overview on mold-making and resin casting. Thanks for the tip on silicone. You do this professionally, correct?

I thought I would bring this thread back to life after searching the TRF history for info on casting nose cones. I like the suggestion's in Scott's message thread as well.

#### mike_bar

##### Well-Known Member
Regarding Scott's message. Maybe we should post all casting tips here (and maybe "re-post" some old messages here too). I am sorry to get Scott's message off-track.

In the meantime, some useful comments on resin casting of small nose cones can be found here:

"Some Cheap BT-5 Cones..." by rokitflite

#### rokitflite

##### Well-Known Member
OK,
I am jumping over here now for resin chat Mike, your cones went out yesterday so you will hopefully have em today or tomorrow. I threw in quite a few extras to keep you busy. As I said these are "seconds" that may require a little sanding to be perfect, but nothing a couple coats of a good primer won't be able to handle. Let me know what you think.

#### mike_bar

##### Well-Known Member
Thank you Scott. I will give you a "review" here on TRF...

#### cls

##### Well-Known Member
Al, thanks for posting the overview. good stuff!

Californians can find silicone & other casting supplies at TAP Plastics. (a couple stores are in Washington.) http://tapplastics.com/

TAP has a bunch of other great rocketry supplies, such as thin mylar in various colors, carbon fiber rods, epoxy & other resins, glass & carbon & kevlar fabric, etc.

#### sandman

##### Well-Known Member
Well, I poured my mold tonight...we will see how this turns out.

I looked at the material data sheet on the RTV silicone I just got. It's Dow Corning HS III with a cured elasticity of 575%!

WOW! I talked to Mike at Alumilite and he told me that means it can stretch 575% before it breaks!

Now that should work but I won't know until tomorrow!.

#### rokitflite

##### Well-Known Member
Originally posted by sandman
Well, I poured my mold tonight...we will see how this turns out.

I looked at the material data sheet on the RTV silicone I just got. It's Dow Corning HS III with a cured elasticity of 575%!

WOW! I talked to Mike at Alumilite and he told me that means it can stretch 575% before it breaks!

Now that should work but I won't know until tomorrow!.
Whatcha moldin' Sandman?

#### sandman

##### Well-Known Member
Whatcha moldin' Sandman?
Parts for the Soyuz kits!

The mold is setting up nicely too!

Makes a big difference when you use GOOD silicone!

I made one heck of a mess of my workbench silicone everywhere!But as it sets up...it just peals off! COOL!

#### rokitflite

I stated earlier that the "good" RTV I got was about $25 per pound. I was thinking that I paid$125 for a 5 pound bucket. In actuality it turns out I pay $125 for a 10 pound bucket... Much more reasonable! Sandman, did you let it set up in a pressure tank? Or was it a slush mold where this is not as critical? #### sandman ##### Well-Known Member My mold is fairly thin at less than 3/4" thick so I don't think I needed any pressure. I was also careful on my mold pour to make sure I didn't get many bubbles in it but we'll see in a few hours. These a tiny parts so my mold wasn't very big. #### shockwaveriderz ##### Well-Known Member sandman: you are of course doing a pictorial how to ,right? #### sandman ##### Well-Known Member Well, no...any pictures are going into the plans sets. Besides I tried to take pictures of it and the mold is just too whitish...kinda washes out. I just opened up my mold and so far it looks really good. The mold is fairly pliable so I can't move it around much while I'm casting but it should make the parts come out easy. This one looks good! #### rokitflite ##### Well-Known Member Originally posted by shockwaveriderz sandman: you are of course doing a pictorial how to ,right? Shock, Just spend the 30 or so dollars on an Alumilite mini casting set and you will get the feel for it fast. #### sandman ##### Well-Known Member The mold looks great! But pouring the casting is a long and tedious process simply because the parts are so tiny that even with relief holes to let the air out I'm still getting bubbles. Unfortunately, the bubbles are the size of the parts! (0.20" in diameter) It's working but the resin sets up so darn fast! I'm working on it. Here is a pic of one set. The good parts are on the left...not so good on the right. I have to just work on the technique. #### sandman ##### Well-Known Member BTW, to give you an idea of the size of the parts. That IS a round toothpick in the middle of the picture! I told you they were tiny! #### rokitflite ##### Well-Known Member Sandman, Try putting the resin in the refigerator. This will cool it down and slow the curing process a bit. #### sandman ##### Well-Known Member Rocketflight, the refrigerator thing worked it gave me like another 3 minutes to play with it and get all the bubbles out. So far I am having about a 90% success rate with every casting pour. Still missing some bubbles but that accounts for the one or two parts per casting batch that I lose. I just make extras! The tiny Escape rocket motors are still a problem 'cause they are like 0.040" and about 0.060" long but I think good old round toothpicks would make a pretty accurate substitute. #### rokitflite ##### Well-Known Member Hmmm, now for the bubbles... I have wanted to try something to get the bubbles out but I have not had a chance. I was thinking of making a small vibrating platform. Perhaps using the vibrator motor from an old pager or cell phone. I am thinking that if as soon as you pour the resin vibrating the mold slightly might help to jar the bubbles to the top. #### 11bravo ##### Well-Known Member I saw something on TV not too long ago, they were mixing silicone for a mold, but they mixed the two parts together and to get the bubbles out they put it under a vacuum jar. They pulled a bit of a vacuum and it looked like 2 part foam! It swelled way up and bubbles came to the top. Let the vac off and let it shrink back down and did it again. Didn't take very long. Just use a much larger mixing container so as it blows up it won't go all over. Greg #### sandman ##### Well-Known Member I saw something on TV not too long ago, they were mixing silicone for a mold, Oh, the mold came out bubble free. The mold takes 24 hrs to cure so there was plenty of time for the bubbles to come to the surface...they're fun to pop! My bubble problem was in the castings. Look at my picture again and judge the size of the part compared to a standard round toothpick in the picture. The parts are just so darn tiny and the resin is so thick that the bubbles won't come out. What I wound up doing was pouring the part with a toothpick in the mold coming out the bottom and immediatly pulling the toothpicks out. This effectivly "sucked" the resin into the hole and pulled the bubbles out the bottom...well...most of 'em anyway. Notice the "toothpick" shapes on the top of the parts...these get cut off. Another alternative to pulling the toothpicks out is to use air pressure on the whole mold. This would compress the bubbles while the resin cures and make them too small to be harmfull. My way is just messier. #### BrnAgainRoc ##### Well-Known Member hey sandman have you looked into the Tinters tube yet? theres quite a few of us looking for nosecones to fit this stuff and maybe you can help create something thatll work perfect for it. To get a sampe a local tint shop should have some or i can look into shipping you a sample of it. Its a 3" inch QT but we have tried multiple cones and they all wont fit. Your input will be appreciated bro. #### 11bravo ##### Well-Known Member Hold up. I think I was thinking something different. Yes, what I mentioned was for the mold, but I intended to mean that you could use it for the casting resin as well. Now I get what you mean though; you are not refering to bubbles mixed into the resin, rather air trapped in the mold as the resin gets poured in. I was still stuck on bubbles in the mix. As for ideas how to beat the trapped air, can we see a pic or a couple of your molds? Greg #### Saks_Russel ##### Well-Known Member A friend of mine turned me on to an excellent book on molding and casting. The Title is "The Prop Builder's Molding and Casting Handbook" by Thurston James. Published by Better Way Books. IIRC, the book was about$20 from Amazon. The book is geared to making props for theatre and movie production, but it really doesn't matter. It covers all sorts of methods and materials. The copyright date is 1989 for the copy I have. There may be a later edition availible that will cover more modern materials. I haven't had any problems finding the materials in the book. The techniques are timeless.

I just flipped throught the book really quick and it looks like I will be up re-reading it again tonight.

A small shop vac should help pull bubbles out of the resin. Just leave clearance or you will suck the goo back into the vaccuum.... voice of expirience. Cooling down the resins before mixing does give more time. Freezing the mold might help too. Some resins aren't not super fussy about getting the ratios of the 2 parts spot on and using a little less of one component can slow down the reaction. You have to expiriment to see unless there are good instructions with the material.

The URLs in the first listing are good places to shop. Lots of the mold making supply web pages have great tips and method pages. Try a search for "Spin Casting" suppliers. Spin casting works good on resins and plastics. It's not to hard to "Rube" up a simple spin casting set up.

Here's another URL for molding supplies: http://www.shopmaninc.com/moldmaking.html

#### shockwaveriderz

##### Well-Known Member
I wonder if the following would work:

lets say you have a nose cone you wish to "clone"....and it balsa..

1st you would fill ther nose cone with epoxy
2nd you would wax it or pva and wax it....
3rd..pour a rtv mold around it
4th remove the nose cone mold
5th mix some 2 part foam up
6th wax the inside of the rtv mold
7th pour foam into mold
8th after foam hardens, remove from mold.

you end up with a very lightweight solid foam nose cone...you could now hollow it out and apply a finsih....

I am going to try this with the aluminite 2 part foam...it starts at a 6lb density and if you compress it can goto 20lb plus you can add dyes to color the foam without finsihing...

#### rokitflite

##### Well-Known Member
Just remember, the foam expands with some force, the RTV mold is FLEXIBLE... Do you follow me here?

#### sandman

##### Well-Known Member
OK that would work except you can eliminate a few steps.

1.) just seal and paint the cone, epoxy really isn't needed.
2.) don't put anything on it! RTV silicone will only adhere to silicone. no release agent needed.
3.) yea, ya gotta pour the mold. Make a box out of Legos for the mold at least 3/8" bigger than the cone.
4.) The silicone should cure to demold in 24 hrs depending on the silicone.
5.) Mix up your foam or resin...whatever...
6.) No wax or release agent needed for RTV silicone...silicone oil is OK but only if you are going to make a whole bunch of parts. Alumilite reccomends just a dusting of baby powder!
7.) pour your mold...get all the bubbles out!
8.) After the foam hardes pop the part out. Alumilite reccomends some rubbing alcahol to make the mold slicker and makes the part pop out easier.

#### shockwaveriderz

##### Well-Known Member
scott: ok, perhpas I need a rtv mold that sets up more rigid?

Im like the idea of foam as it self-skinning....

#### rokitflite

##### Well-Known Member
Originally posted by shockwaveriderz
scott: ok, perhpas I need a rtv mold that sets up more rigid?

Im like the idea of foam as it self-skinning....
Yes, and for a harder skin that wont dent from a fingernail you can put a little bit of regular Alumilite in first and swish it around.

I am going to try a new cone mold today so I will post the results later!