powdering resin??

[Anvils Hammer]

So I did an epic casting run last night and ended up with the usual pile of sprue on the floor..

I did a few quick caculations and its pretty horifying- approx 50-70% of the resin I pour goes into sprues and then in the bin.

So If I buy 10kg of resin, only 3-4kg gets shipped to customers.

I need a way to recycle the sprue.. obviously it cant be put into small parts again, but next year Im planning to release a range of terrain and vehicles, which will be much larger molds.

Im thinking I can get a big food processor/blender, or maby a mechanical meat mincer? and turn all my scrap sprue into a pile of small peices of resin. These could then be dumped into larger molds, taking up at least half the volume or more. The new resin should in theory then flow round all the scrap stuff and when it demolds, be indestinguisable from a "pure" component.

Questions-

has anyone tried anything like this?

Would the larger parts being 60% or more recycled sprue resuly in a loss of strenght? or would the new resin bond strongly to the old stuff?

Ideally Id like to be able to completly recycle all my waste resin, as Anvil Industry grows, the ammount of resin I use, and the cost of it, is going to increase dramatically (fingers crossed) and I need a way to deal with it.

AH

[blind pig]

For my larger moulds, I'll put old/miscast PU resin into them the pour around it. They are pretty much not noticeable, unless yolu use differnt resins and one floats to the surface.

If you turned it into almost powdered consistency, then there would be little differnce between using powdered resin, talc and slate powder as fillers. I regularly use talc powder (bought in 25Kg bags for AUD$25) at 20% by weight to bulk out my PU resins when making large models or for rotation casting.

The finished model is *slightly* softer than 100% PU, and does not flow quite as well (perfect for rotation casting), but is otherwise indistinguishghable from a 100% PU model. Mix the powder into one part (Part A for example) until fully combined, then mix the two resins together and pour as normal. It dosen't affect the curing time or pot life.

[Anvils Hammer]

Thanks,

Ive got a couple of filler powders I could use for bigger models. To be honest so long as it was strong enough, I would use both filler power and reuse resin! Means I can keep the price of say, a tank, down as much as possible.

what equipment do you use for rotation casting? Its somthing im considering for making vehicles- a two peice mold for the entire tank, fill 1/4 with resin, close it up and spin it lots in every direction.

Would centrifugal force ensure no air bubbles if it was spinning fast enough initially?

Would value your input as have no experience of rotational casting.

Cheers,

AH

[Lane]

Rotational casting uses a slow cure resin and low speed rotation.

[Anvils Hammer]

how does it get forced into the details? could I shake the mold back hard for a few seconds to get it into the rivets and so on, and then stick it on a slow rotate?

Im interested in rotation casting for making ultra cheap hollow vehicles..

AH

[mangozac]

Well here's some of my thoughts:

1. Look at the wastage on injection moulded model kits: all of the plastic in the sprue. It can be quite a high percentage of sprue to actual parts. Wastage is just a fact of life with casting and you're simply not going to be able to remove it completely. That said however minimising the wastage is certainly a good goal

2. The rotational casting relies on agitation to get the resin distributed into all of the details (and ensure that no bubbles are left near the model's surface).

3. Centrifugal force (spin casting) is a valid option, however it's relying more of the centrifugal force to push the resin into the details rather than the agitation.

4. I doubt that the rotational casting could be done economically, otherwise the major players like FW would be doing it. Want a hollow vehicle? Make the hull in two parts (upper and lower or whatever) so that when they glue together there is a void left inside.

5. I reckon a large part of your wastage is probably due to the fact that you have a separate pour channel for the gravity feed. Going to vacuum and pressure casting will help with this.

6. I wouldn't bother grinding up the sprue leftovers. If you want a filler just get the talc and use that - it's cheap enough and I wouldn't be comfortable with the dust generated from grinding up polyurethane.

So with all this talk of tanks I'm expecting to see some WIP stuff soon!

[paulson games]

I suspect that as much as 80-90% of my resin ends up as waste at least when I'm making small parts. In order to ensre proper flow the sprue is often considerably larger than the parts and takes up most of the actual material use.

It's one of the reasons I've been looking into metal casting as left over sprue material can be recycled.

I would imagien that left over sprues or miscast could be ground up, but in most cases it'd need to be ground up pretty fine (at least for the stuff I cast) If you do larger models like vehicles I think they'd make pretty decent filler. My only concern would be left over mold release and talc from the inital casting. I'm not sure if it'd be worth the trouble to wash the sprues prior to use or not.

I've found that larger models cut the amount of waste resin considerably as the sprue is a smaller volume compaired to the overall volume of the finished piece. WIth a large model I'm sure you coudl cut back waste even further with ground up resin. I'm not sure what you'd use to pulverize, or crush it to a point where it'd be useful.

A standard kitchen blender isn't going to hold up long for that, maybe a meat grinder? Also the dust might be problematic.

[blind pig]

I use my wood lathe and an MDF box which tightly fits the mould and put it on the lowest speed possible. It rotates about once every two seconds.

I use rotothane from barnes, or my usual 4PU with 20% talc to thicken it slightly; never have problems with airbubbles, thought the moulds are fairly simple box-like largish structures (the plasma and las pistol parts).

On the subject of just putting lumps of old resin into new pours, here is a micro Arts Infinity resin base that was at my games club today:

[Lane]

When you rotocast you do not force the resin into the detail. By using a slow set resin and a fairly slow rotation the resin flows into the detail. As the mold is rotated the resin wets the surface then flows away so any bubbles get released. After a few rotations you get a thin film of resin over the entire surface. Then as the resin starts to kick it starts to thicken and stick to the walls more. This allows you to get a thicker wall without bubbles.

[Anvils Hammer]

[mangozac]

[paulson games]

[Anvils Hammer]

Thanks very much for your thoughts guys,

The vehicle project is a while away so Ive got a lot of time to think things through, and when I pull the trigger on it Ill be back here with full details and much feedback wanted!

AH

[mangozac]

No worries - that's what this place is for!

Jon's advice above is very wise, and quite frankly gold to have written out like that