subsearobot
Mechanical
- Jan 19, 2007
- 217
Hello all!
We have an interesting situation. We have a light- interference fit between an ultem shaft and a polypropylene socket. The interference creates an airtight seal, and retains the polypropylene part.
We carefully measure the force required to insert the ultem into the pp socket. We have noticed that the force roughly doubles or triples when the ultem part is cleaned with ISO alcohol (and allowed to air dry) prior to insertion. We have noticed this effect on multiple high-temp, inert polymers substituted for PEI (Peek, PSU, others). Some polymers (especially fluoropolymers) react less severely in regards to insertion forces & the ISO cleaning. The effect is greater with the ultem surface is roughed (sandblasted) prior to testing.
I'm a mechanism guy, so please forgive my conjecture if it is wildly speculative...
I've done some preliminary testing. Rotational instead of insertion testing- because I could look at a longer distance of interface interactions. (the insertion length is ~.030", and I wanted to see a longer wear case- just curious more than anything)
I think that I notice that when distilled water is wiped over the surface (and dried), it mitigates the increased contact friction due to ISO. this is preliminary, I have not had a chance to measure the forces because of both machine time and this seems crazy. Is this observation crazy, or is it worth machine time to observe?
What is the deal with ISO on supposedly "inert" surfaces? any idea? Can you suggest any references that may help me understand what is happening? and ultimately, how to mitigate?
thanks!!
We have an interesting situation. We have a light- interference fit between an ultem shaft and a polypropylene socket. The interference creates an airtight seal, and retains the polypropylene part.
We carefully measure the force required to insert the ultem into the pp socket. We have noticed that the force roughly doubles or triples when the ultem part is cleaned with ISO alcohol (and allowed to air dry) prior to insertion. We have noticed this effect on multiple high-temp, inert polymers substituted for PEI (Peek, PSU, others). Some polymers (especially fluoropolymers) react less severely in regards to insertion forces & the ISO cleaning. The effect is greater with the ultem surface is roughed (sandblasted) prior to testing.
I'm a mechanism guy, so please forgive my conjecture if it is wildly speculative...
I've done some preliminary testing. Rotational instead of insertion testing- because I could look at a longer distance of interface interactions. (the insertion length is ~.030", and I wanted to see a longer wear case- just curious more than anything)
I think that I notice that when distilled water is wiped over the surface (and dried), it mitigates the increased contact friction due to ISO. this is preliminary, I have not had a chance to measure the forces because of both machine time and this seems crazy. Is this observation crazy, or is it worth machine time to observe?
What is the deal with ISO on supposedly "inert" surfaces? any idea? Can you suggest any references that may help me understand what is happening? and ultimately, how to mitigate?
thanks!!