I need a mopst efficient way to soften nylon 6/6 without changing any of its properties. These are small dowels with .0.018" deep grooves around them and they are supposed to lock into brass tubing with a mating I.D. shoulder. I'm seriosuly thinking of boiling these dowels to force them into the Brass jackets. anybody have any other ideas? sincerely, John
... but to soften PA66 is a change of its propereties !? Soak those dowels in warm or hot water for some time and use them when they are soft enough for your need. Afterwards you must somehow dry them in order to get their "normal" properties back.
Could you chill the nylon enough to shrink it the required amount? An online value for nylon 6,6 is 80 x10^-6 /C. I don't know your starting diameter, so I don't know how much you would need to chill it to obtain a 0.018" shrinkage. A 1 in diameter would need a 225 C drop to shrink the whole 0.018". A 0.25" rod would need 4 times that temperature drop (not physically possible, and negative temperatures aren't going to help you either.
Of course, this assumes the coefficient above is correct and constant at all tempertures. It also assumes that you need to shrink it the whole 0.018". If you have access to good cooling, you might just want to try it and skip the theoretical prognostications.
John Aspen Research -
"Turning Questions into Answers"
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Hi Rolf. Basically that is what I thought. Don't know how easy it is to deform nylon above Tg. I do know you can actually mold Nomex aramid powder and Kevlar aramid above Tg's but it takes about 1,000 psi. Nylon moisture regain and big drop in Tg can cause resin deformation making the resin unsuitable for some applications like car doors. Our plastic buddies thought they could get away with it with a low moisture regain nylon, but it would not work. In 6/6, I recall the moisture regain be between zero and mayb a 100% humidity of about 5%. Aramids are similar Frank
the Glass Temperature Tg of PA66 is about 60-80 degr.C, depending on your test method, and its Melting Point Tm is ~255 degr.C. Many PA66 automotive applications reach end use temperatures of up to 160 degr.C long term and up to 220 degr.C short term, like air intake manifolds for example! That's why those type of resin need to be optimized for good long term heat ageing performance. One of the issues is, that especially between Tg and Tm, PA66 continues to soften significantly, i.e. looses modulus and strength steadily, until it starts to melt at Tm. Something similar happens as you expose PA66 to water: due to water pickup Tg starts to decrease down to below 0 degr.C, when it absorbs up to over 8% water, when soaked in water and at the same time do both modulus and strength, measured at room temperature, significantly drop.
Just an example: the flexural modulus of unfilled, natural Zytel*101 (PA66) changes with water pick up as follows:
So the original question was how to soften PA66. You can do it with water, but you have to dry out the water afterwards again, in order to regain your nornal, dryer properties at 50% relative humidity again.
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Yes, but the nylon used in air intake manifolds has a heat stabilizer in it.
It sure isn't simple, but you can soften PA66 with warm acetic acid. Formic is even better, but you need to be cautious that you don't dissolve away teh nylon.
My personal opinion is that heating is a useless approach, though the freezing might work is it is a close fit to begin with. To ask a dumb question why don't you trim teh dowel down and glue it? Both epoxies and super gluee work well for plastic to metal bonding.