Pre-heating molds - do you?

[paulloseby]

I could have sworn that I saw you should pre-heat silicone molds before casting Aluminite but I can't find it now. Anyway I put my mold in the toaster oven, admittedly set on 200 deg C rather than F as used in the USA and luckily, caught it as the edges started to change shape.

Should I be pre-heating the molds and if so, at what temperature and for how long? I could have sworn that Curtis had said somewhere that for the first use, the molds should be pre-heated for a number of hours - am I right or have I just got confused?

Many thanks for your help

Paul

 

[hornet406]

Yes but I believe it is no more that 200F (not sure of the conversion to C). I do my molds at 175F for about 10 - 15 minutes. they just need to be warm to the touch.

 

[sbell111]

Alumilite recommends that you preheat your molds to 125° F. 200° C is more than three times as hot as you needed.

 

[paulloseby]

I found the details - it was on the Aluminite instructions and they say: Always warm your molds to approximately 125 degrees F before pouring. New addition silicone rubber molds should be baked at 250 degrees for 6 to 8 hours before pouring water clear into the mold.

That does seem a hell of a time and temperature. Does everyone do that?

 

[sbell111]

I have warmed my silicone molds, but I have never 'baked' them prior to initial use.

 

[Marko50]

I would advise against "baking" your molds up to 200 F! However, I do warm all my molds up prior to pouring Alumilite Clear in them. I don't have a toaster oven, so I just use the normal oven and use the "Keep Warm" setting which will only go down to 145 degrees F. They are in there for no more than 15 minutes. It helps to thin up the AL so that your pressure pot has an easier go at squeezing out the air bubbles. Seems to work pretty good for me. …Just my .02¢

 

[paulloseby]

Many thanks for all of your help. It has been invaluable. I can't quite understand why the instructions should say for new molds, bake at 250 deg for 6-8 hours but Aluminite have come back to me and confirm what you have said.

Again many thanks
Paul

 

[Jim Burr]

Silicone, most types anyway are rated to around 400*F. Your 392*C was pushing a bit.

 

[Sylvanite]

FWIW, I don't preheat my molds.

Regards,
Eric

 

[sbell111]

Years ago, I used to cast little geocache containers out of alumilite in the shape of acorns. I found that if I warmed my mold that the alumilite filled the tiny denials of the mold better without bubbles. This is a feature that's not reall needed for pen blanks since I pop those right into the pressure pot.