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Plaster-of-Paris Properties?
Steve Hignett - 20/2/11 at 06:02 AM

Does anyone have a clue what temperature Plaster-of-Paris will take?

Cheers in advance!
Steve

Ivan - 20/2/11 at 08:05 AM

High enough to cast molten bronze in - see here:

http://www.ehow.com/way_6463143_homemade-investment-compound-casting-bronze.html

And commonly used for heat resistant coatings

http://www.basearticles.com/Art/42203/275/Heat-resistant-plaster-the-facts.html

Richard Quinn - 20/2/11 at 08:12 AM

quote:
Originally posted by Steve Hignett
Does anyone have a clue what temperature Plaster-of-Paris will take?

Cheers in advance!
Steve

Disclaimer - This is a semi-educated guess!
I think that as long as the part has been cured properly (controlling the heat of the reaction) and subsequently baked at more than 120 deg C for a while to get rid of excess moisture it should be good up to around 600 deg C.

mookaloid - 20/2/11 at 10:29 AM

One property of Plaster of Paris is that it can get very hot and cause severe burns if in contact with the person whilst setting

BenB - 20/2/11 at 10:50 AM

quote:
Originally posted by mookaloid
One property of Plaster of Paris is that it can get very hot and cause severe burns if in contact with the person whilst setting


It certainly does get hot. When I was doing paediatric orthopaedics I was on the ward when the teachers came round to teach the long term patients (those on traction etc). They were making viking helmets by putting paper machet onto blown up balloons, then once it had dried chopping off the bottom. I'd done all my work so decided I'd join in and help (okay, i just wanted to make a viking helmet too, okay?) but decided to make it out of plaster of paris impregnanted bandage. You can probably guess what happened. The heat from the PoP heated up the air in the balloon which of course then burst, flinging plaster of paris over me, the kids, the teachers and the ward in general. The kids thought it was hilarious. The nurses were less than pleased. To be fair though I did single handidly clean the ward until it was spotless (okay, the ceiling is still a little textured ).

liam.mccaffrey - 20/2/11 at 11:51 AM

check out on backyardmetalcasting.com I'm sure there are people using it as an investment base for lost wax casting bronze!

Its a very interesting forum actually.

norm007 - 20/2/11 at 12:34 PM

quote:
Originally posted by mookaloid
One property of Plaster of Paris is that it can get very hot and cause severe burns if in contact with the person whilst setting
=======================================================================================================================



Saw program on telly about bizarre injuries. (think it was called bizzare E.R).

Anyway, there was a woman on who tried to take a plaster cast of her hands.
She ended up losing most of her fingers due to the heat build up during the curing process!!!!!!!!

Rod Ends - 20/2/11 at 03:36 PM


Schoolgirl loses eight fingers after plunging hands into burning plaster during art lesson

plentywahalla - 20/2/11 at 03:36 PM

We used to use a dental plaster called 'Kaffir D' IIRC.

It was much more stable during casting than PofP and I don't remember any of the problems quoted above and we used to mix up bucket fulls, and bought 25kilos sacks of the stuff.

We were casting moulds from wood or wax patterns and then casting vacuum forming tools in iron filled epoxy. The main reason that we used Kaffir D was that on curing it expanded at 6 thou per inch which was exactly the same rate of shrinkage as ABS so the final product came out exactly the same size as the pattern.

Don't know if it still available ... ask your dentist!

Ivan - 20/2/11 at 04:34 PM

quote:
Originally posted by plentywahalla
We used to use a dental plaster called 'Kaffir D' IIRC.

It was much more stable during casting than PofP and I don't remember any of the problems quoted above and we used to mix up bucket fulls, and bought 25kilos sacks of the stuff.

We were casting moulds from wood or wax patterns and then casting vacuum forming tools in iron filled epoxy. The main reason that we used Kaffir D was that on curing it expanded at 6 thou per inch which was exactly the same rate of shrinkage as ABS so the final product came out exactly the same size as the pattern.

Don't know if it still available ... ask your dentist!


Definitely not available by that name anymore

JeffHs - 20/2/11 at 04:43 PM

Wasn't there an artist who took casts of famous people's erect members - Jimi Hendrix was certainly one of them. I guess she wasn't using PofP