Cup #

[jttheclockman]

I use to know this but recently I ran out of plastic cups I use for casting. I use Silmar alot and like to heat the resin before I add catalyst to help with bubbles. I forgot the number on the cup that will withstand the heat when placed in toaster oven on low heat for a few minutes. I am thinking 5 or 6. Any help??

 

[monophoto]

John

#5 - Polypropylene (PP)
#6 - Polystyrene (PS)

PP can withstand higher temperatures than PS. PP is fairly flexible and durable, and food items such as catsup are often packaged in PP containers. But is it also used for disposable beverage containers, eg, by airlines.

But PS is less expensive, and therefore more commonly used for single-use disposable items. But PS can handle only moderately high temperatures (below 100 deg C).

So it sounds like either could be used, depending on how hot you intend to make the casting compound.

 

[Kenny Durrant]

I don't have the details Louie has. I use #5 because that's what was suggested by some of those leading the casters when I first started. I use P.R, Epoxy and Alumilite and I've never had any issues. For the most part I use a candle warmer to heat the resin but when I use my oven I have to watch I don't warp the cup. Needless to say I could turn my oven temp down and avoid that but the main purpose for the oven is drying pieces and warming molds. So rather mess with the setting and have to get the thermometer and reset it I mainly use the candle warmer.

 

[Curly]

PETE (polyethylene terephthalate) recycle code #1 works for PR but we use a water bath (Harbor Freight ultrasonic cleaner) to warm it. Purchased mixing cups from a resin supplier actually. Same plastic as pop bottles I believe. The decanted resin from 5 gallon pails go into milk jugs for more convenient pouring. They don't get heated.

 

[jttheclockman]

Thanks everyone. I remember this from way back when I started casting too, but used my last cup and never did pay attention to the code # and the memory bank is low on battery life. I tried using #1 cups and boy did that fail badly. 10 ounces of resin in bottom of the oven. I even lowered the heat as low as I could. Probably different plastics as mentioned and I have no real knowledge on which ones are which. So till I get some good cups I will use a glass jar to get these blocks poured. Need to get back doing some shop work. Back has been feeling somewhat better.