Material to design a box to work at low temperature with internal pres

[Berserk7]

Hello everybody
We are designing a box to contain a formulation of 85% of water and 15 % of one water-soluble synthetic polymer.
One step in our process is freezing this formulation from 20 C to -30C at ambient pressure for 2 hours and then it will be warmed at ambient temperature .
I found these facts about the water:
a) The volume of water increase in 9% from its liquid state to a solid one.
b) The water internal pressure produced when the water change its state from liquid to solid is 55MPa
I tried with a box made from ABS , but the ABS box was broken.
I need your help to select the right polymer for this application.
I are thinking in PC and PMMA , I found some LEXAN and PMMA grades for low temperatures -30C,-40C up to -60C .
The manufacture recommended me use PVC, because its a less expensive option.
Also I afraid because in the materials sheet the mechanical properties were taken at room temperature.
Which other parameter I need to check to cover my requirements?
Is it correct, select the material in base of its flexural strength? Select a polymer with flexural strength bigger than 55 MPa of the internal water pressure?
Finally I read that some glues cracking the PC , I need also glue this box with other parts made from PVC (PVC didn’t exposed at low temperatures)
Do you have any suggestion for the glue?
Thank you in advance for your help and advices.

 

[IRstuff]

Why are you picking hard plastics? Is that a requirement? The harder the material, the more unlikely it is to resist the forces your designing for.

Why not PE or PET, which is what most soda bottles are made from, and can usually tolerate freezing of the drink inside?

TTFN

FAQ731-376

 

[Berserk7]

Hi
Yes we need to use a semi-rigid polymer as requirement.
Do you know is the PVC has good ductility at -30 C?
The recommendation of one manufacture is use PVC.

 

[patprimmer]

PE and PET are both very difficult to glue.

You need a polymer with high elongation at break at the temperatures you will be using.

The water will expand and if the container does not yield it will break.

Manufactures publish data on solvent welding so you can find that yourself.

Manufacturers publish data on elongation at break and sometimes yield so you can find that yourself.

Manufacturers publish data on embrittlement point so you can find that yourself.

They will not have data for change in elongation at below freezing pint

PET carbonated beverage bottles perform so well for several reasons, being:-
1) Shape. They are shaped pretty much like a pressure vessel.
2) Chemical modification. They are co-polymers, not pure PET homo-polymer.
3) They are bi-axially oriented so the micro-structure significantly impacts on physical properties.

For glueable, good elongation and good cold impact, my money is on PC.

From memory PVC can be good to cold impact and has reasonable elongation at room temperature, but its properties are very dependant on the specific make up of the compound.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[Demon3]

Ice cube trays in fridges are made of polyethylene. It stays ductile at lowish temperatures and doesn't break when the water freezes. Why doesn't it break when it has poor strength? I guess it's because the ice can expand upwards instead of all the pressure being directed at the plastic.

So, make sure your box has free space above the water/ice and your requirements should be much easier to meet. The pressure in a full closed vessels is way higher than the pressure in a vessel with an air gap left in the top.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[cloa]

A obvious question is will your mixture of water and synthetic polymer expand by 9%? Surely you need to experiment to find that out.

 

[Berserk7]

Thanks for your help
I will ask to the manufacture more information about the elongation at break and data on embrittlement point for PVC and PC.
The manufacture told me the water pipes in Russia are made in PVC and the external ambient temp is around -50C in winter.

 

[Pud]

You could try a toughened nylon - eg Zytel ST801.

H

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Nylon does not glue all that well.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[IRstuff]

Why do you need to glue anything at all? You've essentially driven the point design already with your OP.

TTFN

FAQ731-376

 

[Demon3]

You can also place rubber blocks in the box to help adsorb the expansion pressure.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[GrumpyPlasticBastard]

Polycarb will crack and craze if you aren't careful about what you expose it to.

PVC is your best bet, I used to run a Brite Dip Line (chromic and nitric acids, cold water rinse, hot water dry. PVC stood up to all of that.

----
BFL Dreamworks
"If we don't have an answer we'll get one"

 

[Berserk7]

Hi again
Thanks for your advices
I would to know if you (GrumpyPlasticBastard ) have experience about PVC behaviour at very low temperature.
Also I would like to know your opinion about the thickness of the box.
We are think about 3 mm to 6 mm for the wall thickness.
6 mm, for me it will very difficult to flex all the walls. In the other hand, 3 mm or less it will be more easy to bend at low temp. (3 mm is ok at room temp)
is this correlation correct?
Thanks

 

[Demon3]

Did you understand my point that the headspace in the box is critical to this? Perhaps as important as the plastic selection because it determines the pressure on the box walls.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Berserk7]

Hi Demon3
You are rigth, It is material selection and design problem.
Can I ask you, where I can found this rubber blocks?
any supply name? , this is my first time as designer.
Thanks

 

[IRstuff]

The objective should not be to design the box to withstand the expansion pressure as that is in the too-hard pile for most materials. The objective should be to let the solution expand into some sort of headspace, as Chris describes it. This then allows you to use a much wider range of materials. Even a plastic baggie can survive that.

TTFN

FAQ731-376

 

[GrumpyPlasticBastard]

The walls on the acid chambers... 3/4 inch thick. 1" thick on the hot water tank... 180 degrees.

My suggestion is to look up a couple of PVC sheet suppliers and start asking specific questions.

----
BFL Dreamworks
"If we don't have an answer we'll get one"

 

[btrueblood]

I'd also look at designing some bellows-like flex features into the walls...