| Re: bubbles in investment||Hits: 1119|
Bruce Fink [bpfink]
on 09/25/01 08:18pm
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|Too bad... sounds like you meet the salesman from hell. Probably wishes he could have been a lawyer so he was always right and did not have to face reality. Actually US Gypsum does make the plaster retarder and also sells it with the plaster but separately. You may have to order it expressly. May be hard to find because they disguise the name of it as " USG PLASTER RETARDER". (I am reading it off their can just got another shipment in a few months ago).|
It comes in 1.25 lb. plastic cans with 6 to a box for about $24. Each can will do from 500 to 800 lb. plaster and when
mixed with the fillers or sand that means about 1000 to 1600 lb of dry investment mix. You should be able to buy just one can... I get several boxes at a time so it is always on hand. (Smells good too when mixed with water... like Boston baked beans and anchovies).
The detergent you mention can be regular liquid dishwasher type that does not foam or bubble if this is to get the wax to have less resistance to the investment. Stick to the liquid ones though, mix with mostly water and spray a fine coat on the wax before you invest it. Then you may even let it air dry first... it works well for me.
They also make special plasters with detergents already added in but those are the foaming type for a different function and you whip the investment up mechanically so the bubbles are legion, but very small and it expands the mix by filling it with air. Makes it lighter in weight, and able to withstand shock more. I don't normally use these
but it is available. USG has a book on it and they are free, just don't ask that salesman for his copy cause I don't think he knows about it yet.
I have gone over the reasons plaster sets up before here on the artmetal sites... and it can be found via the search engine we have.
Agitation times, water temperatures, proportions of the plaster mix to water, and mixing in buckets used before for the last batch all can accelerate it. Also any minor salt in the water sends it up off the chart. Got to have clean water, consistent water temperature (less important what it is as much as it is the same each time... thus fill a big drum or large bucket with it before you start), use the same proportions each time in relation to the retarder % and listen to soft music to keep your adrenaline down... hey it is only life and then all seems to flow with the go.
As mentioned before, I do big investments since it cuts down assembly and welding and makes the interactive complexities less complex. I use digital photos so I can recall where the parts go again due to my puzzle like interactions (have a great memory at this age, it is just so damn short). Allows me to move slower and smile wider also. My larger investments go to about 7 ft high x 44 inch diameter unless I want to get silly and try another reason to get BIG. (Hey it happens). The 1 inch chicken wire (or poultry netting mesh ) going from 1 1/2 to 2 1/2 turns around the mold makes it so I can handle it alone and turn it over several times without it falling apart. Without it I could not even lift it out of the kiln except from a bottom cast iron plate floor and chains. I will include a shot of the plastic molding flask that is used to cast it in, as well as the mixer which is nothing but a Milwaukee 1/2 inch drill with a barrel plaster mixer attachment. Use other kinds and sizes also but this is enough for nearly anything I attempt. I do it in about 20 gallon batches in a 35 gallon plastic drum and then hand lift and pour the mixes one by one via a 1/2 gallon plastic bucket. (The kind fresh New England oysters come in. But that's another story...) (Not only am I redundant and superfluous, but I also tend to use more words than necessary. Hope you get the point though.)
The chicken wire is inside the plastic so you will not see it in this shot. Also has a floor of it so the hot metal droping down will not blow the bottom out when poured....
All this has been written here before so if in question yet do a little search and then lets get down to new sharing. I got a lot to learn yet myself. bpfink
I will send the jpg along with this now as it shows the mixer I use, the size of the plastic wrap flask and a general look of it in action.