Need help in casting resin parts

[dbang1988]

Hi,

I recently bought the silicone and the polyurethane resin to cast.

I want to cast parts of the 120mm figure from Verlinden, so I can work on the copy instead of directly on the original one. The problem I end up to is I make a single side silicone model and try to pour the resin in. But the resin cure so fast that the resin doesn't have time to get all the way to the bottom or the little bubble in the resin could not get to the top fast enough.

Even I have used vacuum chamber to suck the air out, but the curing time of the resin is still too fast. So I called the store where I bought it. He said the problem may be my parts are too small so that is why the resin cannot get into the mold all the way. He recommended me to use injection cast. But based on the material I read, they used single mold and do the same thing but it works. So I am kinda annoying since every time I cast, it becomes a failure.

Hope anyone here can give me some good comment. Thanks

Bang

 

[Anders Heintz]

Get a new resin with a longer potlife. This will allow you more time to deair the resin and get a better casting.

Id recommend a 5-7 minute potlife resin, this will give you plenty of time to mix and pour the resin as well as de air it using your vacuum chamber.

 

[Scott777]

I agree with Anders sounds like the resin you are using would be better used for a spin cast mold. Another thought if you are working in too hot of an area this can also speed up the curing time of the resin. Since you already have the resin try chilling the mold a little, the castings may not turn out to good since chilling the mold also allows moisture to enter into the scenario, wrecks the mold and sometimes affects the cast pieces...but it might get you a couple acceptable castings and since its not working for you now you really don't have anything to lose.

BUT from the standpoint of a manufacturer. It would be appreciated and cheaper for you in the long run to buy a second kit. Also it would help us as manufacturers to stay in business...see recent postings about manufacturers going out of business. I'm a one man business and for the most part if a customer needs some extra parts to a kit I will do my best to get him/her some...just ask.

 

[dbang1988]

Thanks Scott777 and Anders,

I know it would be cheaper if I purchase other kit. But some Verlinden kit in no longer in production, that is why I want to make a copy for myself.

I am planning to make a two side mold or redesign my mold.

Any more comment will be great.

Thanks

 

[Tommi]

Hi
I cast small parts in two piece moulds in a vacuum chamber, I normally use G26 or G27 biresin which will cast the smallest of parts with high precision. The activation time can be from 2 minutes to 4 minutes depending on the ambient temperature of the working environment. It comes in two 1KG tins and is a 50-50% mix. I used this for figure production several years ago and it gave great results. Here is the link to the site that I purchase it from.
http://www.sylmasta.com/acatalog/Online_Catalogue_Polyurethane_Resins_76.html
Hope this helps
Cheers
Tommi

 

[Einion]

But the resin cure so fast that the resin doesn't have time to get all the way to the bottom or the little bubble in the resin could not get to the top fast enough.

How fast are we talking here? There's a wide range in properties among casting resins and setting times vary from literally seconds to much, much longer.

Usually you pick a resin based partly on the curing time; I know when I was looking to buy I had to rule out one or two because they just set far too quickly for the speed I expected to work.

Einion

 

[dbang1988]

How fast are we talking here? There's a wide range in properties among casting resins and setting times vary from literally seconds to much, much longer.

Usually you pick a resin based partly on the curing time; I know when I was looking to buy I had to rule out one or two because they just set far too quickly for the speed I expected to work.

Einion

The resin I use called Insta-Cast, it takes about 3-3.5 minute to cure. The problem is I do not have enough time to suck the air out but the same time let it float through all the way to the small mold.

 

[dbang1988]

Hi
I cast small parts in two piece moulds in a vacuum chamber, I normally use G26 or G27 biresin which will cast the smallest of parts with high precision. The activation time can be from 2 minutes to 4 minutes depending on the ambient temperature of the working environment. It comes in two 1KG tins and is a 50-50% mix. I used this for figure production several years ago and it gave great results. Here is the link to the site that I purchase it from.
http://www.sylmasta.com/acatalog/Online_Catalogue_Polyurethane_Resins_76.html
Hope this helps
Cheers
Tommi

Hi Tommi,

Based on your description of the G26 and G27, it is similar to the one I use. However, I think my problem is how I proceed the casting. I used one side mold which does not seem working. May you give me little hint how you cast them?

Here is how I do it,
1. I mix two parts of the resin together 1:1 by volume within about 30 sec.
2.Then pure it into the mold, since the mold is small so it is hard not to let the air trapped in it as the resin being poured into the mold.
3. then I put the resin with the mold together in the vacuum chamber. However, I see as the air is being sucked out, the resin rises and spill out of the mold. Then I release the air and as the air goes into the chamber, it presses the resin back in the mold, but a lot of resin already spilled. Thus now not enough resin inside the mold. This step take about 2 minutes, and now the resin is about to cure, which cause the little bubble in resin, which is not sucked out completely by the vacuum, trapped in the resin and so my casting failed.

Anything I need to improve here? Such as the time management or other stuffs?

Thanks

 

[Tommi]

HI
The best way for me is to make the mould is in two pieces so that it can be split. When you pour the resin and you still get trapped air you can then split the mould and cut small air fillets on one side of the mould in the affected area running up to the top of the mould, when you then degass the air will be sucked out of these areas through the channels that you have cut and not the main pour hole.

Using a single piece mould makes this difficult to achieve especially if you have big undercuts in the mould that can trap air as the air rises into the undercuts and gets stuck

You also need your design your mould so you have a fairly deep our hole for the a resin to rise back into without affecting the part.
This works well for me using the G26 even in hot weather when the curing time is only 60 seconds and gives perfect results.

I shall be making another mould sometime next week so I will do a SBS and post up the results
Hope this helps
Tommi

 

[WPS]

bang,

I use talcum powder to break the surface tension of the rubber.
most airbubbles are created by this or by negative spacing.
pour some powder in the mold, use air to get rid of the most of the powder.
the residu of the talcum powder is in no way effecting the curing of the resin.
pour the resin (I also use the Biresin)to fill approx half the mould, squeeze the mould, and top off. (or use the vacuum chamber when not able to squeeze the mould)
for casting results see
http://www.planetfigure.com/forums/showthread.php?t=25727

groet Willem

our intelligence is not measured by the answers we have...
...but by the questions which we ask

 

[Anders Heintz]

I would stay away from two piece molds, they are hard to make correctly, hard to line up properly, and you will always have two nasty seamlines on the part.

Most everything can be made in a one pice mold, especially a Verlinden figure as that is what they use. All you have to do is cut the mold so that you can take the piece out, since you have a vacuum chamber, you can deair pretty much any mold as long as you can remove the casting once cured. Since you are using only vacuum, it would be beneficial as well to add a quite large pour block to serve as a resevoir for the resin to come up in so it wont spill too much.

Another thing you can do is to instead of pulling a complete vacuum and loosing all your resin, do it in stages, watch the resin start bubble, let the air back into the chamber, then deair it again and repeat until there is no more air in the resin.

Id suggest to get some Smooth-On Smooth Cast 321, it has a 7 minute pot life, 30 minute demold, and will give you plenty of time to de air and even add more resin into the mold to make up for the lost resin. I can cast 15 kits in 3 molds with one mixing of the 321, including deairing twice and the put them under pressure.

Get some longer potlife resin and I promise you that you will have good results. Don't look at the cure time as it doesnt really matter, look at the pot life, or the 'workability life' of the resin instead so you know how much time you have to work with and stay away from two piece molds!

 

[diamond cutter]

Potlife

I guess that the heat in Texas doesn't help the potlife of your resin|?

 

[Anders Heintz]

No, not much!! Although the building where I do the casting is adobe, so it keeps fairly cool.

I am a bit concerned about this summer though, when the temperature hits 115ºF its hard to say what the resin will do! Id say more then likely I will be installing some airconditioning units!

 

[dbang1988]

I would stay away from two piece molds, they are hard to make correctly, hard to line up properly, and you will always have two nasty seamlines on the part.

Most everything can be made in a one pice mold, especially a Verlinden figure as that is what they use. All you have to do is cut the mold so that you can take the piece out, since you have a vacuum chamber, you can deair pretty much any mold as long as you can remove the casting once cured. Since you are using only vacuum, it would be beneficial as well to add a quite large pour block to serve as a resevoir for the resin to come up in so it wont spill too much.

Another thing you can do is to instead of pulling a complete vacuum and loosing all your resin, do it in stages, watch the resin start bubble, let the air back into the chamber, then deair it again and repeat until there is no more air in the resin.

Id suggest to get some Smooth-On Smooth Cast 321, it has a 7 minute pot life, 30 minute demold, and will give you plenty of time to de air and even add more resin into the mold to make up for the lost resin. I can cast 15 kits in 3 molds with one mixing of the 321, including deairing twice and the put them under pressure.

Get some longer potlife resin and I promise you that you will have good results. Don't look at the cure time as it doesnt really matter, look at the pot life, or the 'workability life' of the resin instead so you know how much time you have to work with and stay away from two piece molds!

I do not add any pour block, since verlinden has its own pour block so I just use some clay to make the parts stay on the surface.

As you mention about the deairing method, since the resin I used only have pot life around 3 minutes, it is kinda tricky to repeat the deair too much.

Do anyone know how Verlinden cast their kits? It is obvious they are using one side mold, but how?

 

[dbang1988]

bang,

I use talcum powder to break the surface tension of the rubber.
most airbubbles are created by this or by negative spacing.
pour some powder in the mold, use air to get rid of the most of the powder.
the residu of the talcum powder is in no way effecting the curing of the resin.
pour the resin (I also use the Biresin)to fill approx half the mould, squeeze the mould, and top off. (or use the vacuum chamber when not able to squeeze the mould)
for casting results see
http://www.planetfigure.com/forums/showthread.php?t=25727

groet Willem

our intelligence is not measured by the answers we have...
...but by the questions which we ask

How exactly you cast? They look perfect. So the powder really work? What is the pot life of your resin?

 

[WPS]

Bang,

the potlife of my Biresin G26 and G27 is appox. 6 minutes.
on these heads I poured the resin and only squeezed the mould to get rid of air.
I didn't use the vacuum chamber.
the resin is thin enough to pour in a small stream.

see pictures:

1. the resin.

2. the pouring.

3. squeeze and top off.

4. a mould.

5. the result of the mould.

6. the pieces used to form a new figure.(still in progress)

P.S. I use paper cups to create the moulds (they are cheap and easy to remove)
good luck with your experiments.. Willem

 

[dbang1988]

Any more help please? Although a lot of comment already, but not much detail about vacuum casting.
That would be great if someone post some picture about vacuum casting.