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Resin Masters for Metal spin casting.

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Resin Masters for Metal spin casting.

Postby KoS » Sat Mar 27, 2010 10:31 am

Hi all,

After some information and advice. I have been doing my own resin casting to try and produce high quality resin masters for spin casting to produce metal copies of my sculpts to sell. I think Im almost there on getting it right but I have had a couple of hiccups and want to try and Iron them out. B4 I go in to full production. :)

Because I sculpt in fimo this is the best process to go through. As a resin master is the closest representation of the original sculpt.

Main problem Im having is casting the resin masters. Im doing it under pressure of about 50-60 psi which is giving me reasonable casts. But the main problem Im having is way too much flash to clean up. What can I do to go about getting an almost seem less cast?
The process I go about casting is, I clamp the moulds with rubber bands in between 2 pieces of wood. And I inject the resin through the spout with a syringe then place it in the pot under pressure to cure.
I this caused by a problem when Im making the silicon mould?
Should I be using a tougher silicon?

The other is I need a higher temp resin I have been using 4PU and Easycast from Barnes. These have a HDT of around 75℃. The vulcanisation temp is close to 150℃, the 4PU and Easycast almost go the distance and produced a reasonable metal cast. I have been considering using TC852 which has a head Deflection of around 104℃.

Any help would be awesome.

Or if there is anyone willing to do the silicon moulds and resin casting in Australia for me,as Im really looking at out sourcing this part of the process. Means I have more time to sculpt, :) and run other parts of my business.
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Re: Resin Masters for Metal spin casting.

Postby paulson games » Sat Mar 27, 2010 2:48 pm

I don't have any experience with metal casting, but when I cast with resin the source for flash is usually not having a tight enough seal between the molds. It's generally comes down to two things, either the molds aren't held together tight enough and it's allowing airspace between the halves which the material is leaking into and forming flash. Having a good number of mold keys helps keep the mold in the proper place and keeps it from being offset as easily.

The second cause can also be how the mold is constructed, if you are using clay you have to be very careful to make sure the clay is very tight against the object to form a solid seal and you also need to make sure the bond doesn't break when cleaning the clay off. The smoother the mold line is against the master part the less flash you'll generally get.

I usually spend a lot of time when constructing the master mold the smoother I can get the clay work the better results I typically have with reducing flash. I've started using a pasta rolling machine to make the sheets of clay as flat as possible before inserting the parts and then a flat edged sculpting tool to go all around the edges to seal up even the smallest of gaps.

I place the molds between a pair of boards when casting and hold it with rubber bands, if I see flash forming in an area I try and get another loop in the rubber band or add additional rubber bands so that it holds the mold tighter and that usually works. Depending on the mold size you can also use "C" clamps like what you use for holding wood pieces together for glueing etc, That can help you get a tighter pressure on the mold while keeping it dipersed a bit more evenly with the boards.

Because silicon molds are flexible you need to sandwhich them between something rigid and apply even pressure, uneven pressure from the rubber bands or other bindings will concentrated in a single area and allow air pockets where the silicon bulges out where the pressure isn't being appiled. It's important to have rubber bands to cover the mid sections of the boards as well and keep an even pressure across the mold, if you rubber bands only the top and bottom of the mold it'll allow the middle to open slightly and have gaps.

Normally I run my sets of rubber bands horizontally across the molds but on troublesome molds I somtimes have to add a few vertical ones in the center to help keep it sandwhiched tight in the center as the middle seems to flex out sometimes and allow gaps.

Also you don't need to inject the resin with a syringe, you can get great results from gravity alone as long as you have enough entry ports and exit ports. It could be that squeezing the resin in with the syringe is forcing it between the molds a bit more than usual.

On my good molds I get virtually no flash, the flash that does occur is very thin and is almost transparent and it flakes off very easily. If I have a sloppy or rushed mold it tends to have fairly thick flash and it's almost always due to having rushed the clay part and not getting a good enough seal against the master part. I can also get the occasional odd ball bits of heavy flash if I don't rubber band it evenly, or it the silicon halves aren't seated right as it allows a slight air gaps around the parts which forms flash.

Also as the silicon gets older and starts to wear out from repeated castings you'll slkowly get more and more flash as the silicon dries out and tends to shrink a bit at the edges and loses it's flexiblity, this again allows for gaps resulting in flash.
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Re: Resin Masters for Metal spin casting.

Postby mangozac » Sun Mar 28, 2010 7:57 am

^^ What he said ;)

Seriously though, really strong clamping would seem to be the only solution. I like to use big fat rubber bands and wrap them around a few times.

That said, you have to be careful that the force doesn't warp the moulds. The possibility of warping can be reduced by ensuring that there is plenty of silicone thickness between the model and the edge of the mould. Warping like that may not be such an issue on small figures though, and I expect there will always be decent enough wall thickness.

Try out the c-clamp idea and see how it goes. I only use vertical rubber bands as well on moulds that I know may have leakage problems on the very bottom.

If you can get away with it the tougher silicone may be better. Try some Barnes Maximould - its much stiffer than the ultrasil.

I would email Barnes about the temperature question. They will often take up to a couple of days to respond, but they will get back to you (or ring them if you're in a hurry).
Oh yeah I can make that....
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Re: Resin Masters for Metal spin casting.

Postby KoS » Sun Mar 28, 2010 8:52 pm

Thanks for the advice and replies. Great detailed explanation.

I created a new mould today and have been casting in it with great success. I focused on making sure it is clamped well. I also created in one pour (not sure what the exact method is called) in stead of creating a 2 part mould. I find this is a good method for 1 piece bodies. Provided you have thought it out a little b4 hand and don't get the mini trapped in the mould when you need to cut it open. :o
I clamped the mould in place in 2 lego walls with to massive rubber bands to make sure that it was nice and secure.

The only problem I have is insufficient air release. Out of 6 casts I have 5 that have a massive air bubble in the face. Might have to cut the mould fully in half and create another vent. I only need a hand full off really good casts.

hehehe, I called them up already. But I didn't really get a yes or no answer they don't really have anything that goes to that HDT I also called Dalchem and they said only industrial material goes that high and I don't think I need to go that far. The 4PU and Eastcast goes OK, I just need something that is fractionally more heat resistant.
Based on working with the Ultrasil today. I think it will do the job. Have used tufsil b4 and it was pretty good. But it has been discontinued.
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