Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
(OP)
I'm trying to determine what would be a suitable material to make this item which function likes a plastic cotter pin
Part Description: ~0.25"OD x 1" long cylinder (one at each end), connected by a 3/16"OD band
How its Used: Insert one of the plastic cylinder into the hole located on the shaft and then insert the other plastic cylinder into the opposite hole [on shaft, 180° apart] (the connecting band hugs the shaft and there is some tension in the connecting band which helps keep the plastic ends in place)
Part would be used in temperatures: -30°F to +40°F
Product would be exposed to: Water, Grease, Oil
Desired Properties of Material
-Suitable for Injection Molding
-Flexible
-Durable
-Impact Resistant
From my limited research I was leaning towards a Vulcanized EPDM Modified Polypropylene (such as Exxon Mobiles Santoprene) but am not sure it's a good choice
Any insight that can be provided is appreciated
Thanks
Part Description: ~0.25"OD x 1" long cylinder (one at each end), connected by a 3/16"OD band
How its Used: Insert one of the plastic cylinder into the hole located on the shaft and then insert the other plastic cylinder into the opposite hole [on shaft, 180° apart] (the connecting band hugs the shaft and there is some tension in the connecting band which helps keep the plastic ends in place)
Part would be used in temperatures: -30°F to +40°F
Product would be exposed to: Water, Grease, Oil
Desired Properties of Material
-Suitable for Injection Molding
-Flexible
-Durable
-Impact Resistant
From my limited research I was leaning towards a Vulcanized EPDM Modified Polypropylene (such as Exxon Mobiles Santoprene) but am not sure it's a good choice
Any insight that can be provided is appreciated
Thanks
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RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
What tensile/shear stresses will the pin see? Or are you worried about the band (which sounds like an o-ring to me)?
RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
The pin will see very small shear stresses, it's intended to act more as a positioner
I'm more concerned about the band (it's like a half O-Ring, it only goes around one side of the shaft), since its so thin (~3/16" OD) and needs to have some stretch.
I want it to be tough enough so that someone can't easily pull it apart with their hands. The material should have a tensile strength of 550 psi or greater, the material might see impact loads of 1000 psi (impact duration ~ 5 seconds).
Since the intention is to use the part multiple times, it will see some cycles of loading and unloading, particularly in the band. I would like the material to have at least moderate fatigue strength (not start to crack after 20 cycles or less)
Thank you for your comment
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RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
o-ringband. If you notch one end of each pin, then pop the o-ring over the notch, and around the shaft to the other notch, would it not work? A lot less trouble than finding a way to mold the whole thing in one go. I'm willing to watch you try and push a pair of rubber pins into a hole though, if I'm allowed to heckle and eat popcorn.RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
The end user really has their heart set on a one piece construction (only one item to keep track of).
Yes, pushing rubber pins (poisson's ratio = ~0.5) into a tight fitting hole would be problematic. From my understanding the pin to hole isn't a tight fit (pin=~0.25"OD, hole=~0.3125"ID). I would like to use a material with poisson's ratio of 0.3 to 0.4 (the lower the better, I don't want to eliminate too many materials by choosing a very low poisson's ratio requirement).
Any recommendations for a suitable material that could be used for a one piece construction?
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RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
www.lprosperitymold.com
LPmold is a plastic injection mold contract manufacturer with the full capability to work competently with our customers to transform their design into a finished product in the most of competitive prices.
RE: Want Help in Picking a Suitable Material for a Injection Molded Part (~Plastic Cotter Pin)
Do you have a recommended Polypropylene specs/grades? Such as desirable physical parameters (Durometer hardness range, ...)?
What do you think of Vulcanized EPDM Modified Polypropylene (such as Exxon Mobiles Santoprene)?
What are your thoughts on btrueblood's concern that EPDM won't hold up to grease and oil?
Thank you for your time
Kind Regards,
A Fan of EngTips, share the knowledge