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Posted 01 July 2011 - 09:09 AM
I am working on a model and want to pour something in an aluminum mold (not lead) like Plaster of Paris, Bondo, Water Putty but I don't want it to stick to the mold. The shape is a 1/2 a cylinder so removable should be easy if it doesn't stick to the aluminum. Has anyone had any good success with one of these materials?
Posted 01 July 2011 - 09:31 AM
I have done this copy method, only in an RTV mold. I cannot see Plaster of Paris sticking to the aluminium, but for the kind of bait you are probably working on (thin sections etc), it will be too delicate.
My choice would be polyester resin with a release agent of floor wax or something similar. Do a test pour of the resin on a flat surface (back) of the aluminium, to test the release. I am not sure whether resin would stick to the aluminium, but you do not want to take a chance with a valued mold.
The wax will leave an uneaven surface, but if you flash over it with a torch flame, it will level out. I usually melt a knob of wax and brush it on with a dedicated brush for the job, but an old piece of towelling material will do the job.
There will be shrinkage with resin. If this is a problem, you can add microballoons (if you have any) to reduce this or mix resin with polyester filler, to keep it pourable.
Posted 01 July 2011 - 10:19 AM
Thanks Dave. One other thing I failed to mention was this model will be used in a vulcanized mold. the temp will be 320 F and polyurethane resin won't take the heat I have used this with different vulcanized silicone (which I am not using for this project) that vulcanizes at 160 F and works good for this. This resin will start to soften at 200 F.
I have used this in aluminum molds and it doesn't stick to the aluminum.
Is polyester resin different than polyurethane?
the piece I need to make is .200" (5mm ATG (according to google)) cylinder by 1/4" long.
I can only pour 1/2 of the cylinder at a time. I only need to make 80 of these models.
I am looking at some brass tubing that I may end of using.
I am trying to make a slot for a screw lock attached to a jig.
Posted 01 July 2011 - 10:28 AM
Polyester is more heat resistant, If I remember correctly, somewhere above 400f.
I don't remember what temp you use to vulcanize your molds so not sure if it would work.
Posted 01 July 2011 - 10:41 AM
polyurethane is different to polyester resin, but I don't know about the properties. I think the shrinkage is less, but as for temperature resistance, I do not know.
Even if the resin softened under the vulcanizing heat process, it would probably still hold its shape, but we are now outside my level of experience.
I am not picturing what you are trying to do, due to my lack of knowledge with wire and plastic baits. Sorry I could not help more.
Posted 01 July 2011 - 11:18 AM
Oops sorry Aery, just saw you posted your needed temp, but yeah, polyester should take that heat.
Like Dave said though, shrinkage is more of a factor with polyester resin. maybe undercatalyzing slightly will negate shrinkage as much as possible.
If you can work the brass rod or tube, it seems the easiest route, yeah?
Posted 01 July 2011 - 11:40 AM
thanks guys, I'm off to town to see if I can find some tubing.