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experiments with household goods casting

 Post subject: Re: experiments with white glue casting
PostPosted: Tue Jul 05, 2011 1:24 am 
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nah - next step is silicone sealent. this is just playing around to get comfortable with concepts.


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 Post subject: Re: experiments with white glue casting
PostPosted: Tue Jul 05, 2011 10:03 am 
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Silicone sealant does stick to things, so perhaps try to account for that.

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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Jul 07, 2011 12:06 pm 
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I have changed the name of the thread.

I went rummaging through my toolbox trying to find some woodstain and found the tube of silicone sealant I'd put aside.

The reason I'd put it aside was the nozzle had cracked slightly and the entire tube appeared to have gone solid. In the spirirt of honest scientific enquiry I decided to saw it open to check the set silicon properties.

Quote:
Cave Johnson - I'll be honest here people, we're throwing Science at the wall and seeing what sticks


the top 6cm had set solid, but the rest was still, as Kryt said, sticky.

In tropical humidity I had about 6minutes before it started to go solid. I had to work fast people.
this is why there are no pictures. yet.

First thing, I'd need a mold release agent. I sprayed a ceramic tile with a WD40 rip off, dolloped a blob of the silicone onto it and stuck it in the sun. I covered the cut tube halves with clingwrap and stuck them in the fridge - in theory cooler = slower temp reaction.

I grabbed the first set of bits I could find. Stupidly, this did not involve the munitions truck, the small tank or the racer trukk, all items I will need to replicate in time to come.
Instead it was a big skull, small skull and a bunch of weapons from the 40k space marine scout sprue - shotgun, heavy bolter, bolter. I don't even collect marines (though my squats and sisters of battle might find them handy)
Oh, and a grabba klaw from hotwheels and two panels from the 'shrine of the aqulia' by NSGZ. If it works I can build the shrine and a Capitol Imperialas. If it fails, I still have enough panels for the Capitol or a reduced shrine.

Open top molds here, no fancy two parters:
the big skull I embedded intact in a cut in half plastic jar. I'm hoping I'll be able to pop the lid and easily remove it in a day or two. the others were all laid on plasticine in the bottom of little plastic tubs.

BEFORE DOING ANYTHING WITH SILICONE
1) either prepare your work surface - paper, disposable towels, a disposable tub for excess and placing tools in, gloves ect. Silicon will stick to anything. Don't let it stick to everything.
2) Or get a good divorce lawyer. I'm lucky, my wife is reasonably confident in my ability to clear up and, more importantly, I was working with black silicone on a black table she wants to replace in future.
3) If you are not old enough to pay the bills, it's probably best you don't try this. Better to rope in a gullible adult.
4) It also stinks - acetic acid again. don't leave it to cure in the kitchen.

I stuck the plasticine and tubs in the freezer to stiffen up, and went out to check the WD40 as release agent. Now this was a shiny ceramic tile, there's not many things smoother and the bugger was still stuck to it. I've heard WD40 can inhibit the silicone from setting (drives the water off). Mixed evidence, but the edges of it had dissolved slightly. More to the point, I still had to scrape it off.

Cooking Oil has had bad reviews, and besides, anything that attracts ants is a bad idea around here - I've had one burrowing in the plasticine before!

So, onto the other release agent available, bear in mind the time limit is still ticking. So I brushed all the models, plasticine and tub sides with KY jelly. it does work.

I spooned the silicone sealent in smoothing and pressing the silicone in as much as possible. Used an Obital Sander for the vibrating bed. You will have to hold the mold down to stop it jumping over or falling off. Try not to vibrate your fingers for longer then a minute - Vibration White Finger is a classic construction safety hazard. In one case the sander moved all the silicone up to the side of the tub, leaving a hole in the middle that had to be pressed in again. On the big tray holding the wall panels I put a layer of clingfilm down and pressed it firmly in with my fingers. I then filled the tray above the clingfilm with water to keep some pressure on while it cures. I hope I haven't sealed the atmospheric moisture out too much. We'll see.

on a completely unrelated note.
a. Be careful when opening tins of woodstain on a hot day.
b. the best way to remove woodstain from skin and hair is veg oil, followed by washing that off.
c. hot showers to remove veg oil on hot days are not fun.


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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Jul 07, 2011 2:19 pm 
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Quote:
b. the best way to remove woodstain from skin and hair is veg oil, followed by washing that off.


I just endure being spotty, personally. :P

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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Jul 07, 2011 2:20 pm 
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This has to be one of the most entertaining threads on here for a while.

Keep up the good work!


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 Post subject: Re: experiments with household goods casting
PostPosted: Sun Jul 10, 2011 4:21 am 
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Simulated Knave wrote:
Quote:
b. the best way to remove woodstain from skin and hair is veg oil, followed by washing that off.


I just endure being spotty, personally. :P


A bright red slash of red across face does lend credence to the 'axe murder' theories of the neighbours.

Image

big so you can see the detail. top left Heavy bolter cast perfectly, as did the shotgun and (i think) the bolter. Skull too, but with a large airbubble inside the silicon making the mold a bit easily distorted.

panels came up ok, lots of 'battle damage'. White patch is the ever present white glue - just as a test piece.

Some distortion of mould caused by uneven thickness of silicon resulting in differential shrinking. Vibration did let it flow but only just. I had a nice thin layer behind one of the panels. I think thin layers and longer vibration should reduce the trapped air. KY jelly and clingflim both do not stick to silicone. This is a useful property.

Speaking of experiments - Like plasticine, Silicone caulk is microwave safe, but not fireproof. Just subjected a thin piece to a intense gas flame. It ignited and continued to burn for a few minutes after I removed the heat. Residue was grey powdered ash. Inside silicone unchanged. It's possible on a large scale you'd only loose the outside few mm, with the ash protecting the inside. Not so good for minis.

Also dampens plans with a friend to use silicon molds for slip forming pottery, and then preventing blackening in the wood kiln. Although it might work. I've always wanted a ceramic chess set.

I'm now also considering the use of the Silicone to make some carry trays for my models - specifically the sisters of battle as they're heavy metal and there's not too many of them. will have to build the army case first.

Ps. Can you spot the plaster 'skull on a cog'? Now I've just got to paint the bugger

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jul 15, 2011 12:03 pm 
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Minor update.

Catherdral wall test piece came up poorly - no wall on the mold meant most of it leaked, airbubbles throughout and generally not very good.

Which considering I squeezed some glue on it before going to bed might as well be expected.
It will suffice as a source of nice bits for my 40K SOB rhinos. as they're cardboard, they could use the help.

Intresting property of the white glue panel was it's extreme flexibility. So much so I rolled out a long strip of plasticine, rolled a lego wheel along it and cast a long strip of tank tread. It worked, but be careful of how deep the treads are. 90 degree turns increase the stress in a material dramatically, more then enough to end up with bits of plasticine stuck in your tank treads. Mold release would have been good here.

Since the strip is equally flexible along it's length, it is not suitable for hyper accurate tread link work as your links will bend in the centre too. for epic scale, rubber style or simple chain link types it's a very nice and easy way to do it. One I'll be using a lot in the future.

I also tried to track down some dental resin. I'm not saying it was surreal, but the tape had my Vietnamese teacher laughing till she got a stitch.


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jul 29, 2011 2:30 am 
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A semi minor update.

I cast a whole set of one piece molds based on the micro machine toys my LatD and probably orks will be using.
To try and make things easier on myself, I unscrewed the bottom, removed the wheels and then filled any gaps with plastacine. This was basically to avoid having the silicone grab where it shouldn't but still leave wheel arches for wheels or tracks later.

I was also using transparent silicon. It's very slightly more expensive, but you can see the air bubbles and also manipulate the piece if so required. It's also easier to use in DIY for obvious reasons. As before plasticine was hardened in the freezer and the release agent was ky jelly.

Method was simple. I squeezed a good dob of silicon out into one of the egg cups. I wasn't using the nozzle. Clingfilm over it and squash the air out with my fingers. Repeat for a second layer, squidge (oh these techincal terms!) the model into it and maybe add a bit more silicone if required.
I vibrated them using the sander as before:

Image

Since I'm using thick caulk, this isn't enough to remove airbubbles, but it does seem to help move them off the surface of the model. Hopefully giving a better finish.

Gave it two days to cure. It all went a bit wrong though.

I'd read before of plasticine containing sulphur inhibiting silicone cure. It hadn't happened to me yet so I though I was safe. Clearly the plasticine is an evil double agent, or the transparent silicone has a higher sensitivity to such things. Or it might be something to do with the tempreture being 36 degrees for the two days I left it to cure. Last option is the model was freezing when I put it in, and uncured silicone is sensitive to cold. The plasticine had a consistency of goo, as did the silicone layer around it, most unpleasant.

The silicone cures by exchanging moisture for acetic acid. It's incredibly humid here at the moment. (well, at the actual moment we're bracing for the first tropical storm of the year) but I thought the thickness of the moulds combined with reduced area exposed to air might be problematic. So I poured a little water on them and left them to sit for another two days. Similar to the process for concrete.

Even after that, when I demoulded the models the silicone inside was incredibly soft and easy to damage. I don't think I got a good mold out of the lot sadly. I added more water and left them again to stiffen up. It didn't seem to help.

Last night I decided to try a new experiment. I found a tube of liquid adhesive (No More Nails sort of thing). Cracked it open and squuezed it into the silicon moulds and went to bed. I don't know if this stuff will cure in thick layers, whether it'll be strong enough to use for gaming pieces, and just how damaged the molds are before their first cast. I don't know how it'll react to the water that wa still sitting in the bottom of one of the molds. All I know for sure is that it's grey and stinks.

Image


But here's hoping!


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jul 29, 2011 4:05 am 
Heh heh, KY Jelly.

Edit - no mockery intended, more of a "knowing chuckle".


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jul 29, 2011 4:24 am 
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Hmmm ... interesting ... ;D

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Jul 29, 2011 10:46 am 
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Interesting, on the last bit of bathroom sealant I had, the instructions said "do not allow to come into contact with water until fully cured" or similar.

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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Aug 01, 2011 3:54 am 
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interesting. Might be more to do with water bubbles creating a bad seal then silicone strength?

the 'Vietseal 123' is still soft. Judging from the smell, the fact it's a one ingredient glue caulk and the warning to keep it away from styrene, I'm guessing it's a plastic polymer dissolved in a evaporating solvent.

I'll keep poking holes in the skin of the setting pieces, but it might take a VERY long time for enough solvent to evaporate to allow me to demold the pieces.


Other interesting concepts have been added to the list:

While doing some research on small boat building, I found a guy who was mixing flour into the resin for thicker layers. He said it was a smoother finish then sawdust but much stronger and stable then pure resin. Of course, I'll need to get some resin first.

I've seen similar done with flour and silicone for a faster and more even cure in thick pieces. (the flour is a carrier for water from air vapour). I don't really want silicone pieces though. I've heard of replacing the flour with plaster, the acetic acid decomposes the carbonate, releasing more water. Depends if the silicone can tolerate the alkaline addition.

will have to get some cement at some point too.


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Aug 05, 2011 12:56 pm 
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Some interesting side experiments:

The Vietseal 123 is still soft underneath- I'm going to have scrap that set of moulds. sigh, that's $1.5 of silicone i won't see again.
As it needs the solvent to leave to set, I can't add anything to make the bugger set hard next time.
set it on fire maybe.

speaking of which:

the end goal is plastic injection. Today I decided to experiment on an empty yakult bottle.
Yakult bottles are polysterene, which wikipedia tells us start getting gooey at 95 degrees and melts at 240 deg (C). It doesn't explode into flame until it gets past 345 degrees.

Some of you might have used a water bath for melting chocolate. You can do a similar thing with oil. Remember that boiling oil vapor doesn't just scald, it can catch fire and remove your eyebrows, if not half your kitchen and one ear. Try not to do this.

BUT it's cooler then a gas flame, so can be used to melt plastics safely. for a small value of safely anyway.
I found this out building bamboo trusses - you can deep fry some short PVC pipe, lift it out and crush one end flat. Once cold drill a hole through the flat plate and use them as connection parts for large bamboo stuff.

This time, I wanted to actually melt it to a liquid. The lower the viscosity the easier it should be to get a good cast (and the less pressure needed). So, I put my Yakult bottle into a glass jar, stuck that in a small pan of oil and got the fire going.
Turns out the smoke point of veg oil is about 230 degrees C, so it got pretty gooey but nothing runny.

Testing will continue.

Lesson learned: look the numbers up before the experiment, not afterwards when writing on here.

also don't put a 230 degree glass jar down in the sink if you need to run cold water soon. it will crack at best.
But nothing exploded or set on fire. this is a good thing. espcially as my wife is at the gym and due back in ten min.


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Aug 05, 2011 1:23 pm 
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I don't really have much useful to add but i applaud your ingenuity and experimentation.

madd0ct0r wrote:
I'd read before of plasticine containing sulphur inhibiting silicone cure. It hadn't happened to me yet so I though I was safe. Clearly the plasticine is an evil double agent, or the transparent silicone has a higher sensitivity to such things. Or it might be something to do with the tempreture being 36 degrees for the two days I left it to cure. Last option is the model was freezing when I put it in, and uncured silicone is sensitive to cold. The plasticine had a consistency of goo, as did the silicone layer around it, most unpleasant.


Cover the plasticine so that the silicone does not make contact (use a water bath to melt vaseline petroleum jelly or w/e and brush it on for a very thin layer), the problem is the heavy metal (eg tin in Dibutyltin/DBT cats) in the catalyst bonding with the sulphur.

If the silicone is too viscous to get the bubbles out, do you have anything available to mix through to lower the viscosity? Even a smallish amount of liquid silicone mixed through might have a big effect.

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 Post subject: Re: experiments with household goods casting
PostPosted: Tue Aug 09, 2011 9:17 am 
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I've heard lighter fluid works as a thinner - it does need to evaporate afterwards though, so the silicone caulk suddenly has shrinkage problems.
The obvious thing to try would be a small quantity thinned and painted onto the positive, to give you a good surface for the rest of the caulk to bulk behind.

What else have I tried today?

Kaolin clay. Incredibly fine and pure kaolin is readily available as cat litter. Since the kittens have left home the cat isn't using it and I've a several kilo bag to use up.

Results: no good. Was trying the three weapon moulds as a tester. Made up a slip(really watery clay) and then added more dry granules to the mould to bring the water ratio down (it governs shrinkage). Not enough. The pieces dried very quickly, shrank very quickly and cracked apart into small pieces.
It might be possible with a 6mm tank as that should dry a little slower. In these small amounts the clay has very little strength once dry. I had been planning on 'kilning' them over the gas flame.
Oh well.


Polythene.

The yakult tub was polystyrene. Polythene (shopping bags) have a lower melting temperature. The oil double boiler would work, except you have to heat the shredded bags evenly. There's a good instructable showing the principle: http://www.instructables.com/id/HomemadePlastic/ but I want to be able to paint my toy tanks. Impregnation with oil does not allow this.

There is another, very stupid way. http://www.instructables.com/id/Plastic ... cery-bags/ Naturally I tried it.

So take a plastic bag, twist it up neatly; clamp it in pliers; sit outside above your mould and set the end of the bag on fire. You then sit there, trying to get the burning molten drops of plastic to fall evenly enough in your mould to get a useable cast. The first time I tried this a huge lump of plastic fell off and sat there on the of the mould, burning happily. I squashed it between two ceramic tiles I had handy for fire killing. It actually gave me a recognizable cast. Not a good cast, and where the ash was at the surface it was too brittle for use, but the majority of it was a good hard plastic.

The silicone caulk looked a bit battered, but didn't seem to have acquired any damage from the heat.

The second time was more of a failure. And I set the plastic pot the mould was in on fire.

THIS IS A MONUMENTALLY STUPID WAY TO GO ABOUT IT INVOLVING FIRE, POISONOUS FUMES, HOT MOLTEN PLASTIC AND YOUR FINGERS.

DO NOT TRY THIS.

There's a germ of a good idea here though. And it gets rid of plastic bags which I consider a generally good thing.

Testing will continue.


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