Vacuum chamber vs Pressure Pot for resin curing

Unless you really need the transparent qualities of polyester you are much better off using a polyurethane casting resin. Polyurethane resins have far less shrinkage (usually less than 1%), are easier to use, less stinky, and work better in silicone molds than polyesters. They are more expensive but you get what you pay for.You can still mix marble dust into it if you wish. There are clear polyurethanes as well though they are a little more trouble to work with.

Check out Reynoldsadvancedmaterials.com for their Smooth One resins. There's lots of good information on their site too.
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As Cavx said, a little more information from you, including photos would help us help you. The size of the casting alone can have a huge effect on the results and recomendations. (Larger parts, more exotherm (heat), = higher shrinkage.)

Good luck!
 
DaveG totally agree. I'd rather use epoxy over polyester any day. Polyester stinks and remains tacky for days. I use it ONLY when I have nothing else to use.
Polyurethane is of course the best choice, but it does cost more.
 
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Hi everyone

My mold is open back
I totally agree to you about polyurethane resin it is best choice however here in Istanbul all the good quality resins are dollar or euro based and the companies sell them very very expensive and if I try to buy from the sites you give me the link they could not send here because of the product is in hazardous category
I use polyester resin because it is cheaper
I give you a link below to see my cast
It is back part as you see the resin excess I have to sand it
http://i.hizliresim.com/O0qb9z.jpg

So I pour enough resin to my mold and give it to the pressure pot like 15 minutes under pressure for details to be perfect

Tomorrow I will try with polyurethane resin and share the photos

Thank you all
 
I completely understand about the resin costs. It looks like your parts is fairly large which means it generates a good deal of heat while curing, which causes more shrinkage. With a larger part like that you can reduce the amount of catalyst, which will lengthen the sure time and reduce heat and shrinkage.
 
@DaveG makes a very good point. Typically you mix the CAT in at about 3%(?) for Polyester resin. Been a while since I have used it. If that is the case, try reducing to 2%. Mix really well and degas. Then pour and pressure. Might take a few hours instead of 15mn to cure, but you should get less heat build up and therefore less shrinkage.

@Cirassian what are you paying for polyester resin Vs polyurethane?

The stuff I refer to as "cheap" Polyester is about $40/KG (it comes in 0.5KG cans) where I live and a good polyurethane is about $80/KG. In the middle is epoxy at about $60/KG. I can buy a bulk pack of epoxy for about $200 for 8KG. I'd rather use epoxy over polyester anyday of the week. They both get hot and they both have some shrinkage, but the epoxy is way better to work.
 
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Hi everybody

I prefer polyurethane resin I know it is a good choice however here in Istanbul there is one type of resin which cures like 3 minutes and I have no time left to put it in the pressure chamber
The other ones are like 25 dollars or 30 dollars per kg however polyester resin here is 1,5 dollars per kg
The company gave me the % for polyester is :

2/1000 Cobalt
20/1000 MEK

I will try to reduce the cobalt % to see if something happens about shrinkage
And I will cast polyurethane resin also
Tomorrow I can share photos with the original model all together so that we can see the difference

Here you can see my pressure pot and have an opinion what it looks like
A guy made it for me like 300 dollars


http://i.hizliresim.com/X0vQgk.jpg

Here you can see there are lots of stuff to lock it so I have no enough time before the resin gets cured :) so I should not use the cheap polyurethane here for this reason
 
Damn, that's a serious pressure pot! I've wondered about the feasibility of having one made like that, but I would want a lid that seals with one lever like clamp.
 
Hi everybody

For that pressure chamber I waited for 2 months :))) nobody knows nothing about pressure casting here and the companies importing only to huge prices like this one ! Of course they are better works but I am happy with this and really I get perfect detailed casts
Today I found a polyurethane resin with low cost and I am happy to find it but let's see what happens with it next week I am getting 1 kg sample
This forum is so nice and texting with people like you makes me feel happy with my business

Thank you all
 
robn1 said:
Damn, that's a serious pressure pot! I've wondered about the feasibility of having one made like that, but I would want a lid that seals with one lever like clamp.
Click to expand...
It is a serious bit of kit. I wonder if it is possible to put a low temp heating element in there as well?

One clamp? Umm, I don't know about that. If you did, you'd want a big gauge safety chain incase the clamp fails.
 
I use both, I vacuum out any bubbles and it allows the resin to go to the base of the mold, then I put it in a huge pressure pot and pressure out any bubbles .. works perfect every time


Sent from my iPhone using Tapatalk
 
irishamericanlad said:
I use both, I vacuum out any bubbles and it allows the resin to go to the base of the mold, then I put it in a huge pressure pot and pressure out any bubbles .. works perfect every time


Sent from my iPhone using Tapatalk
Click to expand...

I want/need a pressure pot to create an isobaric environment. Some of the resins I have access too degas really well, but they seem to make bubbles over night. I would suggest that these happen as the temp drops and humidity goes up. Anyway, end result is small visible bubbles that just would not be there if the part was curing under pressure.

Also for the best details, I found that painting the inside of the mold with resin, then degas both the mold and the pot, then back fill the mold just ensures no air trapped at the base. I was making some Star Wars stands for 3 3/4 scale figure and air seemed to get trapped in the foot pegs. Painting and degassing first gave me perfect results each time.
 
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