Nylon Absorbtion / Desorbtion (Help!!!!)
Nylon Absorbtion / Desorbtion (Help!!!!)
(OP)
I am having problems with some parts that are Nylon 66 7% glass filled. After a period of time in a relatively low humidity environment, my parts are drying out and becoming very brittle. I am looking for two things:
a) Is there a way to predict how long it will take the parts to beome brittle (1.5mm wall thickness) at a given humidity level?
b) Any suggestions for either treating Nylon 66 7% glass filled or chosing another nylon (or another material) to prevent this problem
Thanks in advance,
Craig
a) Is there a way to predict how long it will take the parts to beome brittle (1.5mm wall thickness) at a given humidity level?
b) Any suggestions for either treating Nylon 66 7% glass filled or chosing another nylon (or another material) to prevent this problem
Thanks in advance,
Craig






RE: Nylon Absorbtion / Desorbtion (Help!!!!)
The rate for desorption depends on the rate the water travels through the nylon. The reaction to the surface is virtually instant, but the diffusion through the nylon is very slow.
The climate would need to be VERY dry if the previously conditioned parts were to lose enough water to become very brittle.
7% glass is probably a fairly poor choice for tough parts. Why is it 7% and what do you mean by brittle, and what is the mode of failure.
Any number of materials might be less brittle, it all depends on why you chose the material in the first place and what other properties are really important to maintain.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
What do you mean by relatively low humidity?
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
Glass filled Nylon was selected for this part before I came on board. I am in the process of changing the material to Xenoy (1760E 11% glass filled) for it's flexural strength, resistance to chemicals and resistance to temperature fluctuations. I am trying to figure out what to do with the existing Nylon parts that I have in stock.
My current Nylon parts have been stored in a temperature controlled warehouse in New England. With the heat on all winter the humidity is low, but certainly no where near 0%. At this point, with minimal force the parts will break and shatter. When we received the parts (3-6 months ago) we did a 100% inspection and found no issues with the parts breaking.
I have a feeling it is a material processing issue on the molders part, but I am hesitant to do a bunch of processing tests (in China) due to the fact that I am changing materials anyway. They claim that they maintained 6-8% humidity in the material as a drying condition.
If I re-hydrate the parts by soaking them in water for ~48 hours they repond well. I am trying to figure out how long they will hold up for.
Thanks for all the input.
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
A real down and dirty test for moisture conditioning is to rattle the parts together. If they clink or tinkle, they are dry, if they have a dull sound, they are conditioned.
For a comparison, leave some parts in an oven at 120 deg C foe 24 hours, and other parts in hot water for 24 hours, then rattle both and listen to the difference.
By keeping the warehouse warm, when outside is very cold, you are effectively creating a dehumidifier, which will dry the mouldings a lot faster than if they were left outside. It is relative humidity that causes the drying, and as you heat the air, you reduce the relative humidity.
Before changing from nylon, I would very carefully consider why it was originally chosen, and whether or not there have been problems in the past.
The 6% to 8% humidity in the material as a drying condition has me a bit perplexed and concerned.
Nylon should be dried to below 0.3% moisture content in the nylon before moulding, and it should be conditioned to about 3% moisture content in the nylon to obtain normal properties in a normal open air environment.
If treated right, nylon is a very tough polymer. That's why it is used a lot in things like chair bases, high quality plastic hammer faces, high quality screwdriver handles, high quality power tool housings, fuel filters, carburetor parts, fuel pump parts, spray gun parts, all sorts of sail boat fittings, car engine parts like inlet manifold, radiator header tank etc. Xenoy would not survive many of these applications, no matter what the guy from GE says.
GE does have a reputation for having very enthusiastic salesmen. To get a balanced view, I would also seek advice from a few of the likes of DuPont, BASF, Ticona, RTP company, DSM and whoever Elf Atochem are now.
An alternative to 7% GF nylon 6.6 might be acetal, or unfilled nylon 6.6 or 25% GF 6, but it depends on what chemicals, what load, what temperatures, what mould shrinkage you now need as the mould is already made for 7% GF nylon 6.6
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
Save a lot of time and naval gazing and cull them out of the system. Suspect parts, unless destroyed have a habit of returning and now, its your call, not the previous guy.
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
- I am designing an electrical connector where two mating pieces flex to snap into the connection so higher flexural yield strength is desirable.
- Due to the way the electrical connection is made, it is also desirable to have a relatively stiff material to keep the contacts in place.
- The parts will be handled often so they need to have some chemical resistance. (perfumes, hairspray, etc.)
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
When we originally received the parts they appeared hydrated and performed well. Am I correct that due to poor processing the parts de-hydrated much faster and to a greater degree than they should have? Is there any way to test the new parts that appear hydrated to see if they are processed correctly?
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
WAG here but if these parts came from a then new supplier and previous to this batch the parts were acceptable I would be rushing back to the old supplier of nylon.
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
The nylon pellets need to be dry for the moulding process, but the mouldings need to be conditioned before high impact or high elongation is applied to the part.
A poor surface finish is the most obvious indicator of the material being wet when moulded. Light weight parts is also an indicator of voids, or insufficient pack during moulding.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Nylon Absorbtion / Desorbtion (Help!!!!)
Mike