Help please ! Problems with resin and rotocasting !

[Madrid Boba]

Hello all,

I need some urgent help ! :wacko

I am having some problems with the rotocasting process because of the resin. I use poliurethane resin (two components) at a 50% ratio.

If i make a normal piece (solid) without rotocasting, the resin result is perfect. The part that i am showing is small (like 2 inches by two inches)

The problem occurs when i rotocast. Then i get some spots, like sun burning. At the beggining i did not know that they were huge bubbles until i scratch them with a knife...

Here you can see that it is hollow. The spots/bubbles are everywhere !!

I have tried changing the mixture ratio, with less hardener... but nothing happens... :unsure


I have read in some forums about heating the silicone molds before using them... which i will try in a few minutes...


Has anybody had the same problem?


How did you solved it? :confused


Thanks guys!! :thumbsup


Alfredo

 

[trooper]

you must seek the all mighty oricle...aka iedbountyhunter

IEDBOUNTYHUNTER | the RPF

ive never seen anything like that before so i cant help you there, but im pos. AL can

 

[mslz22]

That looks like a lamination issue to me. Meaning that as the rotocaster is spinning the liquid is gelling but not sticking to itself as it builds the layers.

What is the pot life of the resin you are using?
mike

 

[Madrid Boba]

That looks like a lamination issue to me. Meaning that as the rotocaster is spinning the liquid is gelling but not sticking to itself as it builds the layers.

What is the pot life of the resin you are using?
mike

Hello and thanks for your fast answer

here is the tech spec , sorry it is in spanish !! :wacko

Temperatura de trabajo....................................18 - 25 ºC
Tiempo de trabajo.............................................80 seg. aprox a 20ºC (200gr. masa)
Tiempo de desmoldeo......................................110 seg.aprox. a 20ºC (200gr. masa)
Densidad DIN 53420 gr./l.............................1.25
Dureza DIN 53504 SHORE D...................75
R.Tracción DIN 53504 Kg/cm2......................350
Elongación DIN 53504 %................................9
R.Flexión DIN 53423 Kg/cm2......................500
Flexión mm........................................................13
Contracción %..................................................<3











The time is around 80 secs

Thanks

Alfredo

 

[mslz22]

From what it looks like the resin is setting up too fast, 80 seconds is not a lot of time to pour the resin and get it spinning. What i think is happening is that the liquid resin is setting up in semi cured layers instead of gelling at a much more even pace. I would use a 3 minute gel time/pot life resin. Depending on the mass you should not have too much of an issue with the lamination thing. Of course there is other factors depending on the resin. If available i would use smooth on smooth cast 300 or smooth on 65D for rotocasting, I have had good luck with both rotocasting.

Also keep in mind the rate of rotation on a rotocaster, not sure if you are using a motorized machine or hand cranked but faster is not better, it tends to sling the resin, resulting in the mass being greater in one area of the mold, instead of a nice even coat. The nice even coat should distribute the mass more evenly and slow the "kick"
mike

 

[Madrid Boba]

Thanks Mike !!

I was thinking something like that, and that is why i changed the mix ratio. Maybe i should try with an even lower ratio, like 30 to 70 or 25 -to 75%


I will try

Thanks all

Alfredo

 

[mslz22]

i don't think you can change the ratio with polyurethane resin all that much. If you change the ratio too much to favor the urethane part (usually part b in the USA) you will wind up with too much of it and the resin will leech oil. I am not sure how that works with polyester based stuff but it usually does not work well with PU. I would really just see if you can get a slower setting resin and stick to correct ratio.

mike

 

[Madrid Boba]

Thanks Mike again !!

 

[Madrid Boba]

Hello again...the nightmare continues


I have changed resin (for Axson F16) and i am getting air trapped in between two layers (the bubbles move...) and once i brake the bubble i have a nice and clear resin piece under it. It is like if you get burn by the sun, and your skin peels off...

I have tried everything.... adding baby powder, cleaning the molds, heating the molds, putting some mold releaser.... slowing or increasing the rotocasting machine speed, ...


I am going to get nuts !!!


H E L P !!!

Thanks

Alfredo

 

[Madrid Boba]

Any ideas?

 

[Ray22]

Maybe it's the type of resin your using not all are configured for rotocasting you may need a resin that sets up slower and is made for roto casting. Like Mike said try the Smooth On 65-D which I have used I also have gotten good results with Specialty Resin Model Pro black for roto casting.

 

[Madrid Boba]

Hello guys !!!

Problem solved !!!

I did solve it by adding around 25% of baby powder to the mix....

Now the cast is perfect !!! I will post pics tomorrow.


Thanks all for youl help....


Alfredo