Polymer choice for wear pad?
Polymer choice for wear pad?
(OP)
Hello all.
I am looking to implement a polymer insert in a load bearing hook in an effort to address corrosion being worsened by fretting in the interface. The hook is constructed of stainless for stength and corrosion resistance in a submerged marine environment. The passivation layer on the stainless holds up well on non-stressed points, the problem only lies within the hook which interfaces with a glass-filled nylon covered shoulder bolt. I attached a REAL rough 2-second drawing of what the insert may look like just to help with the visualization.
I am hoping a small polymer insert will be a low cost solution by reducing friction and eliminating oxidized metal from the contact surfaces, which promotes the vicious circle of corrosion. The key properties of of the insert would be its ability to withhold the load without cracking (two separate products experience loads of 350lbs and 2500 lbs respectively), not succumb to deforming or cradling the load pin (operation includes freeing the pin by releasing the hook) and be able to stay in place (looking to use a high grade adhesive if possible).
Unfortunately I do not have as much design experience with engineering grade plastics. I have worked with Delrin, but something in my intuition tells me it is too soft and will deform. I have no hard evidence to back this up, but I am aware of much harder polymers which would seem to work better as long cost doesn't get too prohibitive. A quick material property search with Delrin as the baseline (85 Rockwell 'M', Compressive strength 18ksi) yielded many results with hardness level above 110 Hardness and 30ksi Strength. Results included: Ultem (PEI), Celazole (PBI), Torlon (PI), Ketron (PEEK) just to name a very select few that I have at least heard of before. I was hoping this forum could give me some insight to these and similar materials beyond just the hard data sheet numbers. Also I am aware that nylon based composites can be used as self lubricated load bearings and wear pads. However, mechanical properties show them acting closer to Delrin. Could this mean my initial reticence about Delrin was misplaced? My brain would tell me there also may be some adhesion problems if the wrong polymer is used.
I know this a somewhat long post, but I have seen such excellent results, both for myself and others from these forums. Hey, if someone needs some hydrodynamics help down the road, I may be able to return the favor :)
I am looking to implement a polymer insert in a load bearing hook in an effort to address corrosion being worsened by fretting in the interface. The hook is constructed of stainless for stength and corrosion resistance in a submerged marine environment. The passivation layer on the stainless holds up well on non-stressed points, the problem only lies within the hook which interfaces with a glass-filled nylon covered shoulder bolt. I attached a REAL rough 2-second drawing of what the insert may look like just to help with the visualization.
I am hoping a small polymer insert will be a low cost solution by reducing friction and eliminating oxidized metal from the contact surfaces, which promotes the vicious circle of corrosion. The key properties of of the insert would be its ability to withhold the load without cracking (two separate products experience loads of 350lbs and 2500 lbs respectively), not succumb to deforming or cradling the load pin (operation includes freeing the pin by releasing the hook) and be able to stay in place (looking to use a high grade adhesive if possible).
Unfortunately I do not have as much design experience with engineering grade plastics. I have worked with Delrin, but something in my intuition tells me it is too soft and will deform. I have no hard evidence to back this up, but I am aware of much harder polymers which would seem to work better as long cost doesn't get too prohibitive. A quick material property search with Delrin as the baseline (85 Rockwell 'M', Compressive strength 18ksi) yielded many results with hardness level above 110 Hardness and 30ksi Strength. Results included: Ultem (PEI), Celazole (PBI), Torlon (PI), Ketron (PEEK) just to name a very select few that I have at least heard of before. I was hoping this forum could give me some insight to these and similar materials beyond just the hard data sheet numbers. Also I am aware that nylon based composites can be used as self lubricated load bearings and wear pads. However, mechanical properties show them acting closer to Delrin. Could this mean my initial reticence about Delrin was misplaced? My brain would tell me there also may be some adhesion problems if the wrong polymer is used.
I know this a somewhat long post, but I have seen such excellent results, both for myself and others from these forums. Hey, if someone needs some hydrodynamics help down the road, I may be able to return the favor :)





RE: Polymer choice for wear pad?
Ultem would probably be my next choice after acetal. Ask Sabic for more details re abrasion, salt water, UV exposure if applicable, impact and creep resistance.
Regards
Pat
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RE: Polymer choice for wear pad?
Even given that, I'm thinking of brass for your hook insert.
Mike Halloran
Pembroke Pines, FL, USA
RE: Polymer choice for wear pad?
You mention SABIC, and a quick glance at the website seems to indicate they are a large supplier with huge selection of stock sizes. Have you had good experiences working with them in the past?
Mike, thank you for your input also. Your comment sparks me to revisit old design ideas (one of which was square) and take a second look over the calcs, especially for the high load version. I remember one concern was that if there WERE any deformation/corrosion, the hard angled interfaces were much less likely release succesfully. We have had success with the corrosion resistance of brass and Al-brass alloys alone in the past. However, brass and 316 stainless have different galvanic potentials ( http:
Thanks again guys.
--Adam
RE: Polymer choice for wear pad?
Mike Halloran
Pembroke Pines, FL, USA
RE: Polymer choice for wear pad?
One other thought. I can't imagine I need more than a 0.1" thick inert (low load version) to accomplish what I'm looking to do. Perhaps someone could point me towards an appropriate "creep" or "indentation" equation to help document this decision?
RE: Polymer choice for wear pad?
Are these inserts to be moulded or machined from stock?
Rgds
Harry
www.tynevalleyplastics.co.uk
RE: Polymer choice for wear pad?
RE: Polymer choice for wear pad?
Fot that small amount, i would be tempted to use a choice from the following:
Glass reinforced:
PEEK
Torlon (PAI)
Any reinforced Phenolic.
Properties available anywhere.
I would hesitate on using PES (Ultem) as it's an amporphous material and will creep more than crystalline materials.
The idea of a metal insert appeals (MikeHalloran) - maybe this stuff: ht
Cheers
www.tynevalleyplastics.co.uk
RE: Polymer choice for wear pad?
Have you looked at the Nitronic alloys mainly Nitronic 60 or 30 for your complete part?
Nitronic 60 shouldn't have any wear or galling problem in your application.
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RE: Polymer choice for wear pad?
Also you do need to obtain the data yourself from the manufacturers data sheets. I would never trust data I got of a discussion forum as you don't know who you are talking to.
I really do not have time to do your data searches for you. I can give impressions and directions, but not hard data.
A company called Victrex makes PEEK.
Solvay make the largest range of exotic plastics. You should also contact them.
You should remember that nylon permanently in water will absorb about 9% water and swell somewhat and softem dramatically. Glass will reduce the trend but not eliminate it.
Glass filled PET might also be worth a look.
I have no idea of the loads as you quote force but not area or duration or temperature or allowable tolerance or number of impacts or energy of impacts or alternating load or operating cycles.
Regards
Pat
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RE: Polymer choice for wear pad?
Bryan Gebhart
Phoenix Recycling Inc.
www.plasticscrap.us
RE: Polymer choice for wear pad?
I am not sure if you found a solution to this application, but have you considered using a thermoset composite bearing material? I recommend trying "Orkot". It is a fabric reinforced thermoset composite material. It has a a low coefficient of friction(STATIC CO EFFICIENT OF FRICTION 0.05 - 0.10 DRY AT 15N/mm2 / 2180 lb/in), a high load capacity(COMPRESSIVE STRENGTH Normal to Laminate 280 N/mm2 40600 lb/in),( IMPACT STRENGTH 120 kJ/m2 0.079 kJ/in2)... It has good chemical resistance and operates in fresh and salt water without lubrication. It has virtually 0 swell and does not encourage any corrosion. It has minimal thermal softening and is realitivly cheap compared to PEEK.
RE: Polymer choice for wear pad?
Epoxy and phenolic sheet give you plenty of bang for your buck. Epoxy would probably give you the highest compressive strength and the lowest moisture absorbtion, which tends to soften materials. Sheet is manufactured in gauges down to .030" thickness.
RE: Polymer choice for wear pad?