Very low operating temperature required 3

[martincmiller]

Hi all,

I need a rigid polymer which is suitable for injection moulding and has a min. operating temperature of -60C / -76F.

The material needs to have some form of resistance to:

Salt spray
Sulphur
Ammonia
Potash - Pottasium Hydroxide
UV rays

Any suggestions you could provide would be helpful.

Thanks

 

[btrueblood]

PTFE. Actually, most polyethylenes would probably work, though resistance to UV would require additives.

 

[CoryPad]

Btrueblood,

You have applied a loose definition of rigid. Neither of those materials are considered rigid under most circumstances. I imagine one of the polyamide flavors could meet most of that list, of course the high performance ones like PPS and PEEK would too. A little more information about exposure (concentration, time) is necessary to know for sure.

 

[martincmiller]

Thanks for your answers.

The prototypes that I have had made up are of Polymide, PA 66 (Nylon 66), so a similar set of mechanical properties would be preferable.

Tensile Strength: 90 N/mm2 [DIN53455]
Ball Indentation Hardness: 180 [DIN53456]

CoryPad,
I do not have any quantifiable information regarding the concentration of the above, however the parts will be exposed continously, and require resisitance to the list above, apart from UV rays.

 

[CoryPad]

Do the current prototypes (or any other parts) fail in this application? By what mechanism?

 

[martincmiller]

The nylon material used is not suitable for applications down to operating temperatures of -60C.

 

[btrueblood]

Both of those materials are as rigid as other elastomers (to within a close order of magnitude). We have outdoor tankage of polyethylene, it seems pretty rigid to me (have not seen it flowing across the parking lot yet, but it HAS only been 10 years). As martin points out, nylon gets very brittle at those temps. Very few polymers besides the ones I listed have much toughness in extreme cold.

 

[CoryPad]

btrueblood,

Yes, PE and PTFE are as rigid as other elastomers, but why is the material selection restricted to elastomers? The request is for a rigid polymer and PE and PTFE are poor in that regard. While PA may have lower toughness, that requirement was not on the list.

 

[Pud]

LLDPE (with a low MFI) retains reasonable impact down to -70C. UV not good, but UV resistance is a bit of an overstated requirement most times. Plenty of additives to help.
Nylon 12 might be suitable, given it's good chemical resistance.

It would be useful if the op indicated how many he wanted - one off? 1000 off?, 10 million?

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[martincmiller]

Hi Pud,

This is new product, never been made by anyone before so I dont have any real sales figures im afraid but the discussions I have been in have been promising so I would be inlcined to say an initial batch of 10 000.

Iv just had a look at the datasheet for nylon 12 and that looks like it could be suitable to my needs.

Has anyone moulded with this before? Are there any potential pitfalls or points I should be concerned with/research?

Cheers

 

[Pud]

We mould lots of Nylon 12. Unfilled / glass filled / graphite filled - used for pipeline pig parts due to it's chemical resistance. Nice to mould, but a price premium over PA6 or PA66, somewhat offset by it's lower density.
An impact modified grade would take you to an even lower temperature.
Readily available from several manufacturers.
Due to comparatively low water absorption it's dimensionally quite stable. (As far as polymers are!)

H



www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[btrueblood]

"toughness requirement was not on the list"

I guess I just read minds. It's the requirement most people think of when talking about temperatures below about -40C/F, and it is the measureable property that changes most dramatically as temperature drops.

 

[Pud]

it is the measurable property that changes most dramatically as temperature drops.

Quite true, the other being CTE, plastics being magnitudes more than metals! (e.g. Q: "Why does this 6" diameter part not fit?" A: "Because your warehouse where you fit them on your steel parts is currently at -5ºC!")

Another interesting problem: Material for a living hinge at -40ºC?
Answers on a postcard please...

Cheers
H



www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[TomDOT]

I'm thinking that a polyurethane or polyurea is the right track for the -40 living hinge.

 

[btrueblood]

"Material for a living hinge at -40ºC?"

Tough one.

Maybe silicone rubber? Maybe just use a dead hinge (hit them over the head before installing them)?

Instead of a postcard, how about the answer on the back of a $20 bill (or UK equivalent)?

 

[btrueblood]

Tom, I'm not familiar enough with urethanes to know of one that maintains flexibility below about -40F/-40C, and that is a urethane elastomer o-ring material. Fluorosilicone o-rings can retain flexibility down to -75C or thereabouts, but bonding those things to other parts is tricky. I've seen it done using a tongue-in-groove style of joint formed in the part, later infilled in an "overmolding" (overmoulding to Pud) process with silicone. This formed the box cover hinge as well as seal bead for a military device.