What's going on here?

[Peter_T1958]

Today I wanted to arrange some of the resin castings
to check whether the gear wheels would finally fit together properly.
But what's that? The styrene sheet had been softened by the resin parts!



I never had problems with resin parts like this. What went wrong?

Regards, Peter

[Design-HSB]

Hello Peter,

if you 2K adhesives have used the latter may become very hot during setting and deform the polystyrene.

[finescalerr]

Yes, it looks like a problem with the glue. To be sure, put a resin casting (without glue) on a scrap of styrene and leave it for a while. if you find no problem, then Volker is right. -- Russ

[Peter_T1958]

Ok, once again my bad English created confusion - sorry! The resin casting stood more then two weeks on that piece of styrene. So I discovered the deformation only today when I wanted to fit the parts together.

[Ray Dunakin]

I wonder what kind of resin was used for the casting? Polyester resins can give off fumes for a very long time, which might attack styrene. I think that epoxies and urethane resins don't have this problem.

[Malachi Constant]

Hi Peter --

I do not think it's a problem with the glue.  I have made 10's of 1000's of resin parts ... and I think you're looking at a chemical reaction between the resin and plastic parts ... because the resin is either "bad" (aged, incorrectly mixed, etc) or "very bad" (defective batch from manufacturer) ...

If you are casting the parts yourself, try this:

-- There will be two parts in the mix, the resin (often "A" or "1") and the activator (often "B" or "2") ...
-- Try using more of the activator than usual.  So, if it is a 50:50 (or "1:1") mix, try using 45% resin and 55% activator.
-- Make a couple of castings and let those cure for 24 hours after removed from the mold ...
-- Place one on a piece of scrap styrene / plasticard (without glue) and let it sit there for 24-48 hours ... then check it ... if the resin is "very bad" (kaput), then the resin part will stick to the plastic ... (or you will see an oily residue on the plastic when the resin part is removed) ...
-- Paint one casting with some fast-drying, solvent-based primer ... then let that sit for 24-48 hours ... then check it ... I suspect that you will find that the paint is slightly sticky ... that means the resin is definitely bad and will never properly cure ...

If the resin is "slightly" bad, then using the altered mix (45:55) might help ... but it's time to get new resin ...

If the new resin parts stick to the plastic and/or do not accept paint, the resin is kaput ... and it's time to get new resin ...

If you have to get new resin, DISCARD any bottles used to store the material and get NEW HDPE bottles ...

If someone else is making the castings, explain the problem to that person ... and see if he/she can test the material and make some better castings!

Good luck!
Dallas

[marc_reusser]

I agree with Dallas.

Looking at the resin part itself, it looks like there is something wrong with the resin. Looking at the shee on the surface, the part actually appears to be weeping/leaching some form of chemical residue.

I have seen/had this happen with old rein, as well as some of the early model kit rubber tires, that became unstable over the years, and would melt the styrene parts they were laying on/touching.

[Peter_T1958]

Hi Dallas and Marc

I do not think it's a problem with the glue.  I have made 10's of 1000's of resin parts ... and I think you're looking at a chemical reaction between the resin and plastic parts ... because the resin is "bad" (aged, incorrectly mixed, etc).

... if the resin is "very bad" (kaput), then the resin part will stick to the plastic or you will see an oily residue on the plastic when the resin part is removed ...

That's exactly what happened. On one resin part some oily liquid leaked out again and again and the primer became rubber-like.
Tomorrow all resin bottles have been disposed of!

Thank you very much for your help!
Peter

[Malachi Constant]

Tomorrow all resin bottles have been disposed of!

Good idea! 

While waiting for some new resin:  dip a cotton swab in isopropyl alcohol and use that to clean the mold that was used.  Do not "soak" the mold in alcohol, as that will dry out (dessicate) the rubber -- just wipe it with a wet swab and let it dry naturally.

When the new resin arrives:  make several castings in the same mold and discard those -- as long as the new resin is good, the new castings will help "clean" the mold further -- the first one or two may collect any residue left by the defective resin (... and for this reason, you will discard the first two or three castings from the same mold).

After that, everything should work!  Good luck (and your project looks very interesting)!    -- Dallas

[Chuck Doan]

Sorry you had this problem Peter. I had never heard of such a thing being possible.