Summary for nylon 6/6 rubbing on anodized aluminum Discussion
Nylon 6/6 rubbing on anodized aluminum is discussed as the likely cause of a cramp lock losing grip after being forced past its locking limit. Vincent Jay describes a nylon 6/6 ring that normally locks on an anodized aluminum tube, but after one overtravel event the tube slides easily and even a new ring will not grip the rubbed tube. Interestingly, a new tube still locks well with the rubbed ring, and cleaning the tube with isopropyl alcohol and a clean towel makes the lock work even better than before. Vincent suspects the nylon may be knocking down the anodic oxide and leaving a graphite-like residue. The answer says it seems more likely that nylon particles, not aluminum oxide, are lubricating the tube, but notes that only analytical testing could confirm it. A suggested check is to rinse the tube in IPA, filter the IPA, and analyze the filtrate.
September 11, 2019
Q. I have a cramp lock made of nylon 6/6 that locks an anodized aluminum tube from sliding. When forced beyond the locking limit, the tube will slide. After this happens, the lock will easily slide even with a light load on the tube. However, when the tube cleaned with IPA and a clean towel, the lock works even better than before the issue occurred. I am hoping to nail down the cause of this issue.
1) Cramp lock is a ring made of Nylon 6/6 and locks when the ring tilts.
2) When forced beyond lock limit, the tube will easily slide and the lock will not engage even under a light load.
3) A new locking ring will also easily slide on the “rubbed” tube.
4) A new tube will lock perfectly when used with the “rubbed” lock ring.
5) when “rubbed” tube is cleaned with Isopropyl Alcohol it locks even better than it did before the issue occurred.
My best guess is that the tough nylon knocks down the microscopic ridges of the oxide creating a oxide residue that acts like graphite on the surface. When cleaned off, the surface is even smoother than it was before the knock down, which creates more surface contact for the cramp lock ring. Looking for any thoughts here.
Vincent Jay
– Depoe Bay, Oregon, USA
A. Hi Vincent. It seems more likely to me that what is lubricating the anodized tube is nylon particles rather than aluminum oxide particles. But unless some analytical method is applied it will be hard to tell. Maybe the tube can be rinsed in IPA, then the IPA filtered and the filtrate analyzed?
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
September 2019