Need Advice From Resin Casters Here

[raildogg]

O.K. I got me an Alumilite Molding Silicone Rubber Kit and made a mold. It failed, again.

I made a box sprayed it with a release agent and poured the first half. It cured as expected.

After De-molding I again, sprayed the mold, and poured the second half.

The result, after the instructed curing interval was, it stuck to itself. I had to tear it apart and, of course, lose the whole thing.

The part was a model tire.

What the hell did I do wrong. I followed all the instructions, all the normal steps.

This is not my first time around the dance floor. I used to make two part urethane molds for sand cast foundries, very successfully I might add, so I'm familiar with molding. Any ideas as to what went wrong,

I just wasted a weekends work and $50.00 on junk, HELP

[Greg Wann]

http://smcbofphx.proboards.com/index.cgi?

Hi Richard,

Here is a forum where I post some of my casting work. This forum moves at a much slower pace. If you are familiar with Pa Kettle, it's like that. Scroll to the bottom of this forum to the resin casting subject. I started posting in 2007 while I was learning. Ok, I'm still learning. There are a lot of winner projects and loser projects posted here. I know how you feel. I have wasted lots of time and money too. If you were here in the Phoenix area you could just come to my home and I would show you what I do. I have no idea what you might be doing wrong. I might be concerned that the silicone is past it's date. I can tell you that when science decides on an expiration date for these materials they are on the money.

[Chief Joseph]

What did you spray onto the first half of the mold to seal it off from the second half? One of the best and most inexpensive barrier coatings is plain old vaseline. You can (optionally) thin it with mineral spirits or naphtha, brush a light coating over the rubber, and you won't have any trouble separating the two halves.

(edited for spelling)

Edited September 22, 2013 by Chief Joseph

[Danno]

I agree with the chief . . . sounds like you didn't apply a mold release to the 1st half before you poured the 2nd half. Thus, the new silicone bonds with the old and you have a 1 piece mold with a master trapped inside.

I also agree with The Master Caster. Check out all his post threads on the Phoenix Model Car Builders Forum . . . he shares his learning curve, his triumphs, and his false starts alike. He's very humble but VERY talented and his products are exemplary!!

[Greg Wann]

You will need to be careful of using something that is thick like vaseline. If you happen to get a tiny goober on your master it could mess up the fine detail of your part. I would stick with a good spray that is meant to be used as a mold release. I use Price Driscoll paintable mold release Ultra 4 urethane parfilm. Spray it on and allow it to set for twenty minutes or so to allow it to gas out. The instructions say you can pour in resin or silicone right away but do not do it. Resin parts will come out rubbery and silicone on it will still be difficult to separate. If you call Price Driscoll they might still send you a can for free. They used to do that.

http://www.price-driscoll.com/index.html

This is the mold release that Jeff, the Time Machine Resin guy told me to use.

Thank you, Danno

Edited September 22, 2013 by Greg Wann

[raildogg]

Oh yes I did use the release agent before I poured the silicone onto the first half. The product I used is Huron Technologies Inc. High Performance Silicone Mold Release. The can also says in contains no chlorinated solvents. I just ordered the rubber from Alimilite this week so it should be good. I sent them an email citing my issues. O.K. I emailed those guys and requested a sample of the stuff Greg uses. Now lets see if they send it. I did most of the stuff you did Greg to get good results and still left something out. I';ll try again if I get the release, if not I'll use what I always used for industrial two part urethane, good old bowling alley wax.

Edited September 22, 2013 by raildogg

[Greg Wann]

Richard, I sure hope your project turns around and becomes a success. I can tell you that when something goes wrong it can sure take the wind out of my sail. I have to regroup and get all psyched up again.

[raildogg]

Yep it just about ruined my week. But I'll keep on trying because I've got a lot of ideas I want to put into reality. Thanks for your comments and support.

[chris02719]

So after you poured the first half and it cured, you put the mold release on the the contact surface between the first pour and the second? It sounds from your post that you used the mold release before the first pour but not between the first and the 2nd.

[TSHobbies]

I use Smooth Ons silicone, and seal the first half using Krylons cleat gloss..never had any issues getting them apart.

[shucky]

I've used the same mold release mentioned by Greg for 3 years without ever an issue. I also do not wait more than a couple minutes after spraying the mold release. I have NEVER had an issue with sticky parts, un-cured rubber, etc. Do not use Vaseline unless you'd like a mess on your hands and parts. If you use the proper materials you'll have far less issues.

[raildogg]

Guys I used the mold release between pours. The time interval between applying the release and pouring the second half was the time it took to mix 4 tbs. of silicone rubber and complete the pour, approx. 90 sec. The one thing I was sure to do was apply release.

[pharoah]

I get my casting supplies from Miro M**k ,and they have a rubber to rubber mold release.

It's as thin as water,but smells like carbontetrachloride. Works great.

[Art Anderson]

What did you spray onto the first half of the mold to seal it off from the second half? One of the best and most inexpensive barrier coatings is plain old vaseline. You can (optionally) thin it with mineral spirits or naphtha, brush a light coating over the rubber, and you won't have any trouble separating the two halves.

(edited for spelling)

Over 12 years, several thousand RTV rubber molds, all I used for a mold release (to prevent a second pour of RTV onto previously cured rubber) was ordinary Vaseline heavily diluted with ordinary Testors enamel thinner. In all that time, with all those molds, I NEVER, EVER had two halves of a mold, with that release agent on the mating surface, stick together.

Art

[raildogg]

I have sent emails to smppth-on but they can't get past the fraud detection on my system. I know it has to do with the release so I am going to go back my tried and true Minwax Brown Polishing Wax. I used it for years in the pattern shops I've worked in and, it never failed me. I use it straight from the can, either brushed on or applied with a cotton rag, then polished to a sheen. It's always worked before so it should work now.

[shucky]

Richard, you said in your original post that you used Alumilite so why contact Smooth On? Regardless, I'm sure it has to do with your choice of mold release. Sure ... other release agents and concoctions may work, but why bother with the mess and clean up? Call Price Driscoll and order Ultra 4 paintable polyester parfilm. IMO its the Cadillac of mold release. You may still be able to get a free 12 oz can if you request it, just call and ask. Never ever have had an issue with it. Zero clean up, zero mess, and its paintable straight away (no soaking or washing). Its a dry film and a little spray goes a long way. Your wasting your time and energy using methods from 30 years ago. Quick spray ... and done.

[raildogg]

Shucky, that's exactly what I did, I hope to get some action from Price Driscoll soon as I requested a sample. If I don't hear from them I'll just order a can and be done with it. Thank you

Edited September 26, 2013 by raildogg

[raildogg]

Still no reply from price driscoll, guess that's a dead end along with the other two mfg.'s. I quit and give in. I used up the last of my just purchased silicone, waxed the parting line and it still stuck together, this is insanity!!! O.K. I call uncle and surrender, I'm through trying. This has major impact on my scratch building plans, as most of the models I want to build have specialized tire, wheel combinations not commercially available, or perpetually out of stock, IE Sauerkraut's Shop. I guess I'll have to stick to kits and O.O.B. models. BUMMER!!!!!!!!

[Art Anderson]

Still no reply from price driscoll, guess that's a dead end along with the other two mfg.'s. I quit and give in. I used up the last of my just purchased silicone, waxed the parting line and it still stuck together, this is insanity!!! O.K. I call uncle and surrender, I'm through trying. This has major impact on my scratch building plans, as most of the models I want to build have specialized tire, wheel combinations not commercially available, or perpetually out of stock, IE Sauerkraut's Shop. I guess I'll have to stick to kits and O.O.B. models. BUMMER!!!!!!!!

Richard,

I posted this above, on September 24 (did you read it?):

<<Over 12 years, several thousand RTV rubber molds, all I used for a mold release (to prevent a second pour of RTV onto previously cured rubber) was ordinary Vaseline heavily diluted with ordinary Testors enamel thinner. In all that time, with all those molds, I NEVER, EVER had two halves of a mold, with that release agent on the mating surface, stick together.>>

To elaborate on this, I cast in polyurethane resin, using silicone RTV (same type of rubber sold by Alumilite, although a different brand) and used the mold release agent I described that day for ALL two-piece rubber molds. To repeat: I settled, very quickly on vaseline petroleum jelly (brand doesn't matter, any drugstore generic brand of petroleum jelly will work, trust me on that one!). This I thinned by adding about half a teaspoon of the vaseline to 4 ounces of Testors Modelmaster Enamel Thinner (chosen because it will not attack styrene--but Naptha--an enamel thinner sold in paint stores everywhere works just as well and is less expensive). I had to stir and shake this mixture up quite a bit, but vaseline will dissolve in this solvent readily.

I then brushed that on the "mating surfaces" (where freshly poured rubber will come in direct contact with the previously poured, and cured RTV) and allowed that to dry for a few minutes. Even after the solvent evaporates, there will be a thin coating of vaseline on the cured rubber part of a 2-piece mold, and vaseline ABSOLUTELY will prevent the fresh, still liquid, rubber from adhering to the previously poured and cured RTV--literally thousands of molds over 11-years of casting proved that to me--and being as I was in the business of resin-casting, I could ill afford to lose a master, or waste rubber.

This material, and the method, will work to prevent fresh RTV from ever sticking to cured RTV--and it's less expensive, AND more reliable than any commercially produced "mold releases" in my experience. I used a lot of Price-Driscoll Ultra-Parfilm as a mold "barrier coating" on cured molds to delay the "leaching" of solvents and other components of liquid polyurethane resin into the cured rubber--that is all I ever used the stuff for--in production, that made my molds last a lot longer, and gave a much more consistent, smooth surface to the castings.

Art

[raildogg]

So Just because I'm a little confused here, although I don't think I should be, let me get this straight. Because I'm stubborn and want to do this for myself. I should mix , one teaspoon Vaseline, with four ounces naphtha, for my release agent and brush it on the parting line. I will get 99% success rate with part off using this mixture. I will try that later this week, because buying the wheels wnd tires I need will cost too much for this or any other project I have in mind. I will try this. Thank you for the formula Art.

[shucky]

So you gave up because you couldn't get a free can of mold release? Last time I ordered they were $7.30 per can I believe and 1 can lasts a looooong time. You can either slop that mixture on your master and rubber and anticipate the clean up after or order a quality mold release spray. Up to you, good luck.

[raildogg]

Heck no shucky, I got sick of failures. In my time I've made several thousand industrial two part urethane, multiple parting molds for items from machine gun triggers, to jet engine compressor vanes, and everything in between. It's failures I can't stand!. If I didn't need the flexibility of the mold, for the tread and spoke patterns, I'd make hard mold. It's what I know, I do, best!!!

[Deano]

In the words of Homer Simpson advising Bart: "If it's hard, it's not worth doing."

[raildogg]

Not so! Nah Ahh , If I continue on the same course and get the same results, physics says , I am the definition of INSANE, ha ha ha ha ha ha as I go screaming into the night. L.O.L.

[Joeys Models]

I have to agree with Art. I myself was into commercial casting. Doing prototype products for the design industry. I used Vaseline exclusively on all two part molds. Never ever had RTV stick together. And It didn’t matter how long I wanted to pour my RTV. The only time I would thin the Vaseline is when I used it close to the part. Otherwise I used it just as it came out of the container. Used a good brush to brush on. Don’t worry if it has brush marks. It will not matter to the mold. Plus like Art said. Its cheep and easy to get! If you get some on the master, don't worry either. You can take a Q-tip and whip it off. Then when you’re ready to pour your second half. Use spray mold release on the master. Then pour. And Richard, all is not lost on your first mold. You can salvage that mold and part. If you have cut it out and did a careful job. What you have created is a book mold. One shop I used to work at. Did these for all their molds. But we used a translucent RTV. We could see into the mold somewhat and cut the mold open. And as far as rubber and urethane. I use Smooth-on. I am just getting back into model making and I am fortunate to live in the Denver area. I can place my order and pick it up locally with out shipping charges. I have found them very helpful. I can call them anytime and get answers. You may have to call the closes dealer to you. Mine is Reynolds Advanced Materials in Denver Colorado. Smooth-on is much cheaper that Aluminite! I went to my local hobby shop and Aluminite kit cost $35. for the RTV. And its only a pound and half. Smooth-on is only $25. Since its is on my way home from work. I just pick it up. Look on Smooth-on web site for a dealer close to you. You can save shipping cost.

Joe

Edited January 11, 2014 by Joeys Models