Casting Release Agent?

[klutz_100]

Ahem - silly question time

Can I use silicon oil spray (used for lubricating draw runners, cupboard doors etc etc) as a release agent for a 2-part mould? Or how about WD40?
Will these work or will my 2-part mould bond itself into a one-piece block of silicon rubber with the part encased inside?

I've read about using vaseline but I'm a bit worried that if such a thick, smeary substance gets onto the part I'm casting it then be visible on the final cast so I'm looking for something "thinner".

Are there any other household substances I can use? Washing-up liquid for example? Unfortunately the store where I got my resin and silicon supplies here in Poland doesn't have any proprietary release agent in stock.

Thanks in advance (as usual) for your (as usual) invaluable help.

PS This casting experiment is gonna be "fun" - I can feel it in my bones

[freakray]

Why not just use mold release, it's not THAT expensive and is made for the task.

[klutz_100]

Originally Posted by freakray

Why not just use mold release, it's not THAT expensive and is made for the task.

sorry if I wasn't clear enough in my post.

I would LOVE to use a proprietary mold release but my supplier doesn't have any and I can't find any other supplier - that's why I'm looking for alternatives

[MPWR]

You want to use the mold release to keep the second part of a two part mold from bonding to the first part, or to keep resin from sticking to the silicone? Ordinary tin/platinum catalysed RTV? Polyurathane resin?

Need some specifics, mate. What are you trying to do, with what...?

[klutz_100]

Originally Posted by MPWR

You want to use the mold release to keep the second part of a two part mold from bonding to the first part, or to keep resin from sticking to the silicone? Ordinary tin/platinum catalysed RTV? Polyurathane resin?

Need some specifics, mate. What are you trying to do, with what...?

errrr could you repeat the question please? j/k

I need to cast a copy of a wheel and tyre from my 2CV.

I'm thinking that I'll try 2 approaches both based a 2-piece mould (mold?)
1. cast the tyre and wheel as one whole piece
2. cast the wheel and tyre seprately and mount them afterwards

From reading all I could find, I'm figuring that a 2-piece mould is the way to go. So primarily I need a release agent to stop the 2 halves of the silicon mould binding together.

The silicon I'll be using is a Polish prodcut that is described as a "condensation curing silicone rubber for prodcution of moulds and replicas with medium hardness and good tensile strength" I think this is an RTV silicone?

Sorry, but I'm not too sure about the resin I have. All I know is that it is a 2 part resin with a (seems to me) very short pour time of about 5 minutes!! I think its probably a Polyurathane resin.
I have read somewhere that I should dust the inside of the mould with baby powder before pouring the resin to aid release although they said that the resin and the silicone should seperate OK anyway.

I'm guessing that WD40 would also act well as a mould release between the resin and silicone but not sure if it would prevent the 2 silicone parts binding....

[MPWR]

Will the back of the spare wheel(s) be visible, or mounted flat against bodywork? If it will not be visible, I'd strongly consider doing a flat cast one piece mold of the wheel and tyre. Cut a disk if styrene somewhat smaller diameter than the tyre, set the wheel/tyre on top of it (I like to glue it down with white glue first), build a dam wall around it, and pour the mold. The silicone is flexible so a bit of undercut is fine. Always avoid a two part mold if you can.

The two big potential problems here involve the tyre. Depending on what the kit tyres are made of, they may impede/prevent the curing of the silicone mold where it contacts the tyre. I think Tamiya tends to use some variety of silicone for their tyres- if so, shouldn't be a problem. But it could happen. Also, I don't know what the tread pattern on the 2CV is like- if it's smooth or rather simple, it shold be ok- if it's a deep, complicated pattern (like a Pirelli P Zero or other road tyre), than it's rather unlikely you'll be able to successfully copy the tread. (OK, so not alot of 2CV's were ever put on P Zero's, but hopefully you get the idea.) Grooves like that will catch air whan the mold is poured, and when resin is poured in to the mold. It can be done, but it requires a vacuum chamber to make the mold, and a pressure pot to pour the resin. If the tread pattern doesn't come out on the resin copies, you can always sand them bald.

To avoid the silicone from sticking to itself when pouring two part molds, try a thin film of dish soap.

Got pics of the parts you're trying to copy?

[rsxse240]

what about cooking spray? I have used that in the past when casting model railroad parts. I don't know how it will act with silicone mold though, but it washes up nicely when done.

[rsxse240]

what about cooking spray? I have used that in the past when casting model railroad parts. I don't know how it will act with silicone mold though, but it washes up nicely when done.

[klutz_100]

Originally Posted by MPWR

Will the back of the spare wheel(s) be visible, or mounted flat against bodywork? If it will not be visible, I'd strongly consider doing a flat cast one piece mold of the wheel and tyre. Cut a disk if styrene somewhat smaller diameter than the tyre, set the wheel/tyre on top of it (I like to glue it down with white glue first), build a dam wall around it, and pour the mold. The silicone is flexible so a bit of undercut is fine. Always avoid a two part mold if you can.

The two big potential problems here involve the tyre. Depending on what the kit tyres are made of, they may impede/prevent the curing of the silicone mold where it contacts the tyre. I think Tamiya tends to use some variety of silicone for their tyres- if so, shouldn't be a problem. But it could happen. Also, I don't know what the tread pattern on the 2CV is like- if it's smooth or rather simple, it shold be ok- if it's a deep, complicated pattern (like a Pirelli P Zero or other road tyre), than it's rather unlikely you'll be able to successfully copy the tread. (OK, so not alot of 2CV's were ever put on P Zero's, but hopefully you get the idea.) Grooves like that will catch air whan the mold is poured, and when resin is poured in to the mold. It can be done, but it requires a vacuum chamber to make the mold, and a pressure pot to pour the resin. If the tread pattern doesn't come out on the resin copies, you can always sand them bald.

To avoid the silicone from sticking to itself when pouring two part molds, try a thin film of dish soap.

Got pics of the parts you're trying to copy?

Here's the parts I want to replicate (seperately and together, both sides)



This will be a spare wheel theat will be attached to a roll bar system on the side of tha car. If I weren't so picky, I could argue that the back of the wheel wont be visible but I know that it will, so I want to at least have a try at getting it the way I want it (also, I've already made the fixing system for the spare wheel which is based upon it being just like the main wheels).

Interesting point on the tyre! It DOES look/feel more like a silicone material. Wouldn't that mean that mould release on the master is a MUST in this case? Otherwise the silicone mould will bond to the silicone tyre (I read somewhere that silicone only bonds to silicone)

[the dog]

Well you coudn't have picked a harder thing to start with. Tires are the hardest part to cast as they are 360 degrees of good side. You may just want to mold a little more than half, and pour the tire in 2 parts, then glue them together.

Tamiya tires will mold just fine, no mold release is required on them. But you need to use a "tin" based silicon for the molds.

I use petroleum jelly, mixed with a few drops of motor oil between the first and second part of the mold. Just brush it on, trying to keep it off the part.

No mold release is required for casting the parts in resin until you are into the 10-15th pour. Most good casters use a Parafilm type mold release which is paintable. You do need to clean the parts to remove any loose silicon, not so much the mold release.
Randy

[sausage]

I've used butter and like it. Cheap and good.

[D_LaMz]

Originally Posted by sausage

I've used butter and like it. Cheap and good.

Really? for the molds, not the castings right?

[klutz_100]

Just in case anyone is interested, I thought I'd post the results of my first resin casting. Thanks again for your input and help.

The top-line is that it worked out OK (but only by the skin of my teeth )

For some reason my manufacturer mold release didn't "release" so when I poured the 2nd half of the mold, it locked together.

I managed to cut it apart but the mold ripped in a couple of places. I decided to cast anyway. The results are below - IMO not too bad. Some very minor air bubbles in in a couple of places and the tire needs to be cast again as it broke when I removed it due to a big air bubble.

The good news is that I managed to make a mold in such a way that I don't have a mold lines in the tires!!! and teh tread replication is excellent.

THE MOLD:


DE MOLDING:


FINSHED CAST:


ORIGINAL PARTS:


I made up too much silicone so, just for fun, I whacked off a quick one piece mold of the 2CV's battery:

[the dog]

Looks like you're on the right track, parts came out good. It will take a few tries to get the mold to work right, just part of the learning. You may want to use talc in the mold to help release the little air bubbles (breaks the surface tension).

I use petroleum jelly, mixed with a few drops of motor oil between the first and second part of the mold. Just brush it on, trying to keep it off the part. I've never found a good manufactured product out there.

For some reason my manufacturer mold release didn't "release" so when I poured the 2nd half of the mold, it locked together.

[MPWR]

Looks like they came out great. This was certainly a difficult part to attempt for your first try, so having usable parts is a result to be proud of.