Getting rid of sticky residue on resin castings

Since these posts are no fun without pictures, here are a few things I'm working on casting.  Chrysler Turbine Ghia engine and exhaust manifold and a couple of the casts of the repaired STP Turbine car exhaust pipe.  Dark stuff on the engine is putty to cover missing bits and fill bubbles, which, without a vacuum chamber, are pretty much impossible to get rid of.

Hi!

      Having worked for a mfgr. of plastic and resin related products, "Making the juice" as my boss said.  We also used the products for "How To" books and Instruction Sheets.We sometimes but not always used almost full strength DAWN to get rid of the "Sticky". NO! it didn't always work either.

So far, the MPK silicone has been working fine.  We have an electronic kitchen scale I use to measure the product out to get the right mix.  So far, so good.

The resin version of my fixed and cast STP turbine car exhaust turned out quite nice.  That is a good thing, as I seem to have misplaced the kit original.  The cast parts have a little bubble issue, but I think I've fixed that with some Tamiya putty.  We'll see.  

Now sorting through the best casts of the Chrysler turbine car engine and trans so I can put together a drivetrain for an original Batman batmobile I recently acquired.  It was a turbine-powered car, after all.  

The MPK silicone showed up, and the instructions kind of scared me.  I'll mix up a batch by itself just to 'play' with it and see how it does in application before actually pouring it over any parts I want to mold.  They have many, many, MANY options for silicone, and while I think the stuff I chose is the right stuff, I'm not 100% certain.  Testing will help here, I hope.

So I figured I'd just use up the rest of my Alumalite, but mix it 1 oz of base with one 'scoop' of catylist (instead of the instructions saying to use one scoop to 2 oz of base).  The catylist is a transparent pink color, which really helps with the mixing.  It's water-like, so shaking the bottle won't result in a lot of trapped bubbles, which happens when attempting to agitate the base, which is more viscous.  Even after shaking the catylist, when I was getting to the bottom of the bottle, a blob of almost red catylist came out.  I'm thinking that the stuff has settled significantly, and even after thorough shaking, didn't really mix well.  

We'll see how this second molding comes out.  One is a molding of the Jo-Han turbine car trans, and the other is the exhaust stack for the STP turbine car No. 40 that I fixed due to a short shot of the plastic parts and am now re-molding so I have a good piece to use.  

Been a while, and I've tried some things, so thought I'd follow-up.  Even with a fresh batch of Aluma-Res, I still had sticky spots in my castings that never went away.  On a whim, I searched, and ended up ordering some 2-part resin from MPK Enterprises.  I'm still heating my molds, just to keep all the bases covered, and since they even hint that that can help, but out of about 5 casting sessions using different molds I've had ZERO sticky sections in my parts.  Still fighting bubbles a bit, but that seems to be part of the way the molds are made, so I may try re-molding some of the parts.  

I had a transmission that I had molded, in two pieces, with the transmission pan separate from the body of the transmisson.  After having trouble getting good parts cast, I cemented the pan to the transmission, and am in the process of re-molding it.  

The trouble is, even though I started with a brand new Alumalite silicone rubber kit, which has about a two-hour demolding time, the stuff was still gooey after 8 hours of sitting.  Frustrated, I started pulling the molding walls away from the mold, but kept getting silicone on my fingers and everywhere.  I set things down and walked away trying to figure out how i'd get that transmission back.  After another day of sitting, the silicone seemed firmer.  After waiting about 4 days, it seems to have finally set enough i will continue to try to finish my mold.  Now I KNOW I mixed the silicone and catylist correctly.  I even re-checked the instructions multiple times, so I know it's right.   There's just something with the Alumalite silicone that's not right.  Perhaps the stuff has been sitting on a shelf a long time before coming to me.  I don't know.  

I've paused the molding for now, and am awaiting some 2-part silicone from MPK, since I've had good luck with their resin.  We'll see, and I'll update as I can.  

the Baron

Y'know, the comment about putting them in sunlight makes me wonder whether it's the heat, the visible light, or the invisible light, that helps improve the cure.  I wonder what result you might get using a UV light. There are dental resins that cure with exposure to UV light, for example.

 

Both resins are thermal cure, and do not require UV light.  There are some that are like that, but not the ones I have here at the house.  Heating the molds is also not a 100% cure for the problem.  I may just try another brand of resin.  The last time I used the Alumalite resins, about 5(!) years ago, I had ZERO issues with the stuff using ambient-temp molds.  Something in the chemical recipe Alumalite uses has changed, and not for the better.  

I started cleaning up the last casting, and it appears the mold halves slipped some.  I may shelve this project for a while until I can find a different brand of resin to try.  

Edit to Add:  I just ordered some MPK-70 - 5 Min Polyurethane Casting Resin from MPK Enterprises.  We'll see if a different brand makes any difference.  Updates as they occur.  

Y'know, the comment about putting them in sunlight makes me wonder whether it's the heat, the visible light, or the invisible light, that helps improve the cure.  I wonder what result you might get using a UV light. There are dental resins that cure with exposure to UV light, for example.

Following up on this.  I finally got my order of Aluma-Res in.  It's the beige resin that I'm used to using.  Reading the instructions, they state to heat the molds to 150 deg-F, which I do NOT remember doing with my previous molds, but in order to hopefully get the best possible outcome, I did here.  

First attempt still resulted in some soft spots.  Not too bad, and as noted above, putting them in the sunlight seems to help some, but not 100% cure the issue.  The second attempt worked much better.  I left the molds in the oven for a lot longer, which seems to have helped.  I finally got good castings of my Chrysler Turbine Ghia engine and STP Turbine car exhaust.  

I'll give these a soak in the sun while I mold up some more of the Chrysler engine parts and route out the exhaust deflectors in the STP car exhaust so I can fix the short-shot it has.  

Since the Aluma-Res only sort-of worked after heating the molds, I guess I'll try heating them again and trying the other white resin I have so I may not necessarily have to throw it out.  

Gene Beaird,

Pearland, Texas

missileman2000

Try setting it outside in good sunlight.  If it is insuffient curing, that should help.

 

 

I actually did leave it outside, in direct sunlight, in 100-+-degree F heat for about half a day.  It didn't seem to do much.  The vendor says to heat the mold to 125 before pouring.  I'll try that, but have their 'tan' resin on order, and will wait to get out the mixing equipment until after that new order arrives.  

The primer seemed to have covered nicely, and hasn't reacted to anything yet, but the surface was a bit rough, so I'll make a new casting when the new stuff arrives.  Thank you.

Regards,

Gene Beaird,

Pearland, Texas

Try setting it outside in good sunlight.  If it is insuffient curing, that should help.

Oh My!

      Did you not say Soap and Water? First and foremost, We used to use W.D.40 as a de-gunker on molds for resin besides a good long WARM water Baby Toothbrush bath.At least ten minutes. Our balconies and Victorian Train and Building bits worked out well then. The Soap and water? A mix of stronger than normal DAWN and Medium Hot Water. Work the part submerged, til the water becomes tepid! Oh, and quit trying to look at it every two minutes! Rinse well while brushing with another brush used only for this.The Brush MUST be a BABIE'S toothbrush ONLY!!!

I'm half-tempted to try another resin.  I worked hard to make certain the stuff was thoroughly mixed, so don't understand why it acted like this.  As mentioned above, there's another two-part resin that Alumalite has that I've used and had zero issues with, so may go that route.  

I DID drop a couple of parts into a bowl of Windex and brushed them down with a toothbrush before rinsing them off, and it does seem to have helped some.  Letting the parts completely dry to see how they feel.  If they seem good, I'll shoot them with a coat of paint to see if I have any reactions there.  

I've also read that people will heat their molds some to help with getting the resin to 'light off' and start the curing process, so may try that, although I stirred the mix until I could feel the heat in the mixing cup.  One car modeler used a heat gun on his, but most of his were one-piece or 'envelope' type molds, so getting heat to the object being molded was fairly quick and easy.  

Thank you.

Regards,

Gene Beaird,

Pearland, Texas

You could try a de-greaser, like a dishwashing detergent or SuperClean.  But it sounds less like a surface issue and more like an issue with the resin and curing, as you suggested in your original post. I'm not sure that a surface cleaner will resolve the issue, in that case.  I think you're on a better track to try a different casting material/product.

I have no experience with this casting material at all. The only other thing I can think of that might work is perhaps amonia based cleaners such as windex. 

Rob