Folks...
I have a strange problem.
I have a "self-contained hydraulic outer/inner cylinder mechanism". Here is my problem in a nutshell: the inner cylinder [polished steel with seal-rings] is required to extend/retract, AND rotate, relative to the outer aluminum alloy cylinder [Type III anodized ground/polished bore]. We have developed a very noticeable "rusty barn-door staccato-squeal" in some assemblies, ONLY, when rotation occurs [IE: forcing function is apparently the inner-cylinder "turning mechanism"]. Chatter-marks have been appearing in the mechanism bearings and seal races.
The Outer cylinder “bore” should have a MIL-C-8625 Type III [hard] anodize finish that is ground/polished to final dimensions for the inner cylinder piston to “float-on”. This surface is supposed to remain unsealed and be exposed to hydraulic fluid MIL-PRF-87257. There are rubber and plastic high-pressure seals/back-up-rings through-out the cylinder. We, recently, discovered that (2) factors have changed the intended configuration of this component as follows.
A. The polished Type III anodize finish has been "sealed" [inadvertently] during a re-processing [overhaul] operation where exterior Type II/sealed anodize was stripped and re-applied/re-sealed...without masking the unsealed bore.
B. The cylinder is shipped from overhaul with a preservative/hydraulic fluid MIL-PRF-6083... in-lieu-of the MIL-PRF-87257. Some "units" are being "left as-is" without draining the shipping fluid and put directly into service... while other "units" are being drained/flushed of the MIL-PRF-6083... and are refilled with the required fluid [many months after overhaul]. All units that have been drained and refilled with the required fluid have a tendency to squeal… whereas the ones put in-service “as-is” [without draining shipping fluid] are not squealing.
Questions
What would there be a relative frictional coefficient difference between ground/polished/unsealed Type III anodize, and ground/polished/sealed anodize? what if this surface is exposed to a sliding seal/ring combination "dry"; or immersed in MIL-PRF-6083; or immersed in MIL-PRF-8725; or immersed in a cocktail mix of MIL-PRF-6083 (~10%--20%) and MIL-PRF-87257 (remaining)?
What are the possible lubricity and/or chemical effects of MIL-PRF-6083 and MIL-PRF-87257 and/or a “20%/80% combination” on typical rubber seal and plastic rings. note: I’m guessing the rubber T-seal is black nitrile or fluorosilicone rubber and back-up rings are probably graphite filled nylon plastic [seal/ring assy is a proprietary design… can’t get any specs].
Are the rubber and plastic parts [possibly] being "shocked" [swelling, retracting, stiffening, softening or “sticking” with the new fluid and/or fluid mix?? Could a fluid mix increase friction of sliding/rotating parts?
Can a fluid filled hydraulic cylinder with “stiction” [microscopic stick/un-stick movement under high friction loading and slow speeds, in-this-case due to low-speed movement in one axis, IE: Turning]… generate a substantial harmonic frequency capable of “resonating” thru the cylinder Assy and into attaching structure?
Does any of this make sense?
Regards, Wil Taylor
I have a strange problem.
I have a "self-contained hydraulic outer/inner cylinder mechanism". Here is my problem in a nutshell: the inner cylinder [polished steel with seal-rings] is required to extend/retract, AND rotate, relative to the outer aluminum alloy cylinder [Type III anodized ground/polished bore]. We have developed a very noticeable "rusty barn-door staccato-squeal" in some assemblies, ONLY, when rotation occurs [IE: forcing function is apparently the inner-cylinder "turning mechanism"]. Chatter-marks have been appearing in the mechanism bearings and seal races.
The Outer cylinder “bore” should have a MIL-C-8625 Type III [hard] anodize finish that is ground/polished to final dimensions for the inner cylinder piston to “float-on”. This surface is supposed to remain unsealed and be exposed to hydraulic fluid MIL-PRF-87257. There are rubber and plastic high-pressure seals/back-up-rings through-out the cylinder. We, recently, discovered that (2) factors have changed the intended configuration of this component as follows.
A. The polished Type III anodize finish has been "sealed" [inadvertently] during a re-processing [overhaul] operation where exterior Type II/sealed anodize was stripped and re-applied/re-sealed...without masking the unsealed bore.
B. The cylinder is shipped from overhaul with a preservative/hydraulic fluid MIL-PRF-6083... in-lieu-of the MIL-PRF-87257. Some "units" are being "left as-is" without draining the shipping fluid and put directly into service... while other "units" are being drained/flushed of the MIL-PRF-6083... and are refilled with the required fluid [many months after overhaul]. All units that have been drained and refilled with the required fluid have a tendency to squeal… whereas the ones put in-service “as-is” [without draining shipping fluid] are not squealing.
Questions
What would there be a relative frictional coefficient difference between ground/polished/unsealed Type III anodize, and ground/polished/sealed anodize? what if this surface is exposed to a sliding seal/ring combination "dry"; or immersed in MIL-PRF-6083; or immersed in MIL-PRF-8725; or immersed in a cocktail mix of MIL-PRF-6083 (~10%--20%) and MIL-PRF-87257 (remaining)?
What are the possible lubricity and/or chemical effects of MIL-PRF-6083 and MIL-PRF-87257 and/or a “20%/80% combination” on typical rubber seal and plastic rings. note: I’m guessing the rubber T-seal is black nitrile or fluorosilicone rubber and back-up rings are probably graphite filled nylon plastic [seal/ring assy is a proprietary design… can’t get any specs].
Are the rubber and plastic parts [possibly] being "shocked" [swelling, retracting, stiffening, softening or “sticking” with the new fluid and/or fluid mix?? Could a fluid mix increase friction of sliding/rotating parts?
Can a fluid filled hydraulic cylinder with “stiction” [microscopic stick/un-stick movement under high friction loading and slow speeds, in-this-case due to low-speed movement in one axis, IE: Turning]… generate a substantial harmonic frequency capable of “resonating” thru the cylinder Assy and into attaching structure?
Does any of this make sense?
Regards, Wil Taylor
